ALKALI-AGGREGATE REACTIVITY (AAR) 

FACTS BOOK 

1. Report No. 

FHWA-HIF-13-019 

2. Government Accession No. 3. Recipient’s Catalog No. 

4. Title and Subtitle 

Alkali-Aggregate Reactivity (AAR) Facts Book 

5. Report Date 

March 2013 

6. Performing Organization Code 

7. Author(s) 

Thomas, M.D.A., Fournier, B., Folliard, K.J. 

8. Performing Organization Report No. 

9. Performing Organization Name and Address 

The Transtec Group, Inc. 

6111 Balcones Drive 

Austin, TX 78731 

10. Work Unit No. 

11. Contract or Grant No. 

DTFH61-06-D-00035 

12. Sponsoring Agency Name and Address 

Office of Pavement Technology 

Federal Highway Administration 

1200 New Jersey Avenue, DE 

Washington, DC 20590 

13. Type of Report and Period Covered 

Final Report March 2013 

14. Sponsoring Agency Code 

15. Supplementary Notes 

Contracting Officer’s Representative (COR): Gina Ahlstrom, HIAP-10 

16. Abstract 

This document provides detailed information on alkali-aggregate reactivity (AAR). It primarily discusses alkali-silica reaction (ASR), covering the chemistry, symptoms, test methods, prevention, specifications, diagnosis and prognosis, and mitigation. Alkali-carbonate reaction 

(ACR) is also addressed. 

17. Key Words 

Alkali-silica reactivity, alkali-aggregate reaction, reactive 

aggregates, ASR, concrete durability, symptoms, identification, prevention, mitigation, lithium 

18. Distribution Statement 

No restrictions. This document is available to the public through the National Technical Information Service, Springfield, VA 22161. 

9. Security Classif. (of this 

report) 

20. Security Classif. (of this 

page) 

21. No of Pages 

211 

22. Price 

 

 

 

 

 

 

 

 

 

 

 

 

SI* (MODERN METRIC) CONVERSION FACTORS 

APPROXIMATE CONVERSIONS TO SI UNITS 

Symbol When You Know Multiply By To Find Symbol 

in

ft

yd 

mi 

in2 

ft2 

yd2 

ac 

mi2 

fl oz 

gal 

ft3 

yd3 

oz 

lb 

T 

o

F

fc 

fl 

lbf 

lbf/in2 

LENGTH 

 inches 25.4 millimeters 

feet 0.305 meters 

yards 0.914 meters 

miles 1.61 kilometers 

AREA 

square inches 645.2 square millimeters 

square feet 0.093 square meters 

square yard 0.836 square meters 

acres 0.405 hectares 

square miles 2.59 square kilometers 

VOLUME 

fluid ounces 29.57 milliliters 

gallons 3.785 liters 

cubic feet 0.028 cubic meters 

cubic yards 0.765 cubic meters 

NOTE: volumes greater than 1000 L shall be shown in m3 

MASS ounces 28.35 grams 

pounds 0.454 kilograms 

short tons (2000 lb) 0.907 megagrams (or "metric ton") 

TEMPERATURE (exact degrees) 

 Fahrenheit 5 (F-32)/9 Celsius 

or (F-32)/1.8 

ILLUMINATION 

foot-candles 10.76 lux 

foot-Lamberts 3.426 candela/m2 

FORCE and PRESSURE or STRESS 

poundforce 4.45 newtons 

poundforce per square inch 6.89 kilopascals 

mm 

m 

m 

km 

mm2 

m2 

m2 

ha 

km2 

mL 

L 

m3 

m3 

g 

kg 

Mg (or "t") 

o

C 

lx 

cd/m2 

N 

kPa 

APPROXIMATE CONVERSIONS FROM SI UNITS 

Symbol When You Know Multiply By To Find Symbol 

mm 

m 

m 

km

mm2 

m2 

m2 

ha

km2 

mL

L

m3 

m3 

g 

kg 

Mg (or "t") 

o

C 

lx 

cd/m2 

N 

kPa 

LENGTH 

millimeters 0.039 inches 

meters 3.28 feet 

meters 1.09 yards 

 kilometers 0.621 miles 

AREA 

square millimeters 0.0016 square inches 

square meters 10.764 square feet 

square meters 1.195 square yards 

 hectares 2.47 acres 

square kilometers 0.386 square miles 

VOLUME 

 milliliters 0.034 fluid ounces 

liters 0.264 gallons 

cubic meters 35.314 cubic feet 

cubic meters 1.307 cubic yards 

MASS 

grams 0.035 ounces 

kilograms 2.202 pounds 

megagrams (or "metric ton") 1.103 short tons (2000 lb) 

TEMPERATURE (exact degrees) 

Celsius 1.8C+32 Fahrenheit 

ILLUMINATION 

lux 0.0929 foot-candles 

candela/m2 0.2919 foot-Lamberts 

FORCE and PRESSURE or STRESS 

newtons 0.225 poundforce 

kilopascals 0.145 poundforce per square inch 

in 

ft 

yd 

mi 

in2 

ft2 

yd2 

ac 

mi2 

fl oz 

gal 

ft3 

yd3 

oz 

lb 

T 

o

F 

fc 

fl 

lbf 

lbf/in2 

*SI is the symbol for theInternational System of Units. Appropriate rounding should be made to comply with Section 4 of ASTM E380. 

(Revised March 2003) 

Table of Contents 

1 – Introduction .............................................................................................................................1
 

1.1 DEFINITIONS.....................................................................................................................1
 

1.2 HISTORY OF AAR.............................................................................................................2
 

1.3 AAR TODAY .......................................................................................................................4
 

REFERENCES ..........................................................................................................................8
 

2 – Fundamentals of Alkali-Silica Reaction................................................................................9
 

2.1 INTRODUCTION ...............................................................................................................9
 

2.2 CHEMISTRY OF THE REACTION ..............................................................................10
 

2.3 MECHANISM OF EXPANSION ....................................................................................13
 

2.4 REACTIVE SILICA .........................................................................................................15
 

2.4.1 Types of Reactive Silica ...............................................................................................15
 

2.4.2 Effect of Aggregate Size ...............................................................................................18
 

2.4.3 Pessimum Effect ........................................................................................................... 20
 

2.5 SOURCES OF ALKALI ...................................................................................................22
 

2.5.1 Pore Solution Composition ...........................................................................................22
 

2.5.2 Threshold Alkali Contents ............................................................................................25
 

2.5.3 Alkali Recycling ........................................................................................................... 27
 

2.6 ROLE OF MOISTURE.....................................................................................................29
 

REFERENCES ........................................................................................................................31
 

3 – Symptoms of Alkali-Silica Reaction (ASR).........................................................................35
 

3.1 INTRODUCTION .............................................................................................................35
 

3.2 CRACKING .......................................................................................................................35
 

3.3 EXPANSION CAUSING MOVEMENTS AND DEFORMATIONS...........................40
 

3.4 POP-OUTS .........................................................................................................................43
 

3.5 SURFACE DEPOSITS (GEL EXUDATION VS. EFFLORESCENCE).....................45
 

REFERENCES ........................................................................................................................46
 

4 – Test Methods..........................................................................................................................47
 

4.1 INTRODUCTION .............................................................................................................47
 

4.2 ASR TEST METHODS FOR EVALUATING AGGREGATE REACTIVTY ...........47
 

4.2.1 ASTM C 295: Standard Guide for Petrographic Examination of Aggregates for Concrete........................................................................................................................................ 48
 

4.2.2 ASTM C 289: Standard Test Method for Potential Alkali-Silica Reactivity of Aggregates (Chemical Method) .......................................................................................................50
 
4.2.3 ASTM C 227: Standard Test Method for Potential Alkali Reactivity of CementAggregate Combinations (Mortar-Bar Method) .................................................................... 51
 

4.2.4 AASHTO T 303 (ASTM C 1260): Standard Test Method for Potential Alkali Reactivity of Aggregates (Mortar-Bar Method) ................................................................................ 51
 

4.2.5 ASTM C 1293: Standard Test Method for Concrete Aggregates by Determination of 

Length Change of Concrete Due to Alkali-Silica Reaction ................................................... 54
 

4.3 ASR TEST METHODS FOR EVALUATING PREVENTIVE MEASURES ............ 58
 

4.3.1 ASTM C 441: Standard Test Method for Effectiveness of Mineral Admixtures or 

Ground Blast-Furnace Slag in Preventing Excessive Expansion of Concrete Due to the Alkali-Silica Reaction................................................................................................................ 59
 

4.3.2 ASTM C 1567: Standard Test Method for Determining the Potential Alkali-Silica Reactivity of Combinations of Cementitious Materials and Aggregate (Accelerated Mortar-Bar 

Method).................................................................................................................................. 61
 

4.3.3 ASTM C 1293: Standard Test Method for Concrete Aggregates by Determination of 

Length Change of Concrete Due to Alkali-Silica Reaction ................................................... 63
 

4.3.4 Other ASR Test Methods.............................................................................................. 64
 

4.4 ACR TEST METHODS FOR EVALUATING AGGREGATE REACTIVITY......... 66
 

4.5 SUMMARY........................................................................................................................ 69
 

REFERENCES ........................................................................................................................ 70
 

5 – Prevention of Alkali-Silica Reaction.................................................................................... 75
 

5.1 INTRODUCTION ............................................................................................................. 75
 

5.2 PREVENTIVE MEASURES – OPTIONS...................................................................... 75
 

5.3 USE OF NON-REACTIVE AGGREGATES ................................................................. 76
 

5.4 LIMITING THE ALKALI CONTENT OF THE CONCRETE................................... 76
 

5.5 USE OF SUPPLEMENTARY CEMENTING MATERIALS ...................................... 81
 

5.5.1 Effect of SCM on the Availability of Alkalis ............................................................... 83
 

5.5.2 Effect of SCM on the Expansion of Concrete .............................................................. 91
 

5.5.3 Summary on Effect of SCM on ASR ......................................................................... 101
 

5.6 USE OF LITHIUM ......................................................................................................... 102
 

REFERENCES ...................................................................................................................... 104
 

6 – Alkali-Aggregate Reactions: Specifications...................................................................... 111
 

6.1 INTRODUCTION ........................................................................................................... 111
 

6.2 EXISTING SPECIFICATIONS IN USA ...................................................................... 111
 

6.2.1 ASTM ......................................................................................................................... 111
 

6.2.2 ACI ............................................................................................................................. 113
 

6.2.3 State Specifications ..................................................................................................... 114
 

6.3 AASHTO PP65-11........................................................................................................... 114
 

6.3.1 Evaluating Aggregate Reactivity ................................................................................ 114
 
6.3.2 Selecting Preventive Measures ................................................................................... 117
 

REFERENCES ...................................................................................................................... 127
 

7 – Diagnosis and Prognosis of Alkali-Silica Reaction in Concrete Structures................... 131
 

7.1 INTRODUCTION ........................................................................................................... 131
 

7.2 MANAGEMENT PROGRAM FOR ASR-AFFECTED STRUCTURES ................. 131
 

7.2.1 ASR Investigation Program Step 1 - Diagnosis ......................................................... 132
 

7.2.2 ASR Investigation Program Step 2 - Prognosis .......................................................... 153
 

7.3 CONCLUSION................................................................................................................ 169
 

REFERENCES ...................................................................................................................... 171
 

8 – Mitigation Methods for ASR-Affected Structures........................................................... 177
 

8.1 INTRODUCTION ........................................................................................................... 177
 

8.2 OVERVIEW OF MITIGATION METHODS.............................................................. 177
 

8.3 REDUCING INTERNAL RELATIVE HUMIDITY ................................................... 179
 

8.4 APPLICATION OF LITHIUM COMPOUNDS .......................................................... 187
 

8.5 APPLICATION OF EXTERNAL RESTRAINT......................................................... 192
 

8.6 STRESS RELIEF ............................................................................................................ 193
 

8.7 SUMMARY...................................................................................................................... 194
 

REFERENCES ...................................................................................................................... 195
 

9 – Alkali-Carbonate Reaction................................................................................................. 197
 

9.1 INTRODUCTION ........................................................................................................... 197
 

9.2 CHARACTERISTICS OF ALKALI-CARBONATE REACTIVE ROCKS............. 198
 

9.3 CHEMISTRY OF ALKALI-CARBONATE REACTION.......................................... 200
 

9.4 MECHANISMS OF EXPANSION DUE TO ACR ...................................................... 201
 

9.5 FACTORS CONTRIBUTING TO EXPANSION DUE TO ALKALI-CARBONATE 

REACTION............................................................................................................................ 202
 

9.6 DIFFERENCES BETWEEN ACR AND ASR ............................................................. 203
 

9.7 PREVENTION OF EXPANSION DUE TO ALKALI-CARBONATE REACTION204 

9.8 SUMMARY OF ALKALI-CARBONATE REACTION ............................................. 206
 

REFERENCES ...................................................................................................................... 208 

 

 

AAR Facts Book Chapter 1 – Introduction 

1 – Introduction 

1.1 DEFINITIONS 

Alkali-aggregate reaction (AAR) is a reaction in concrete between the alkali hydroxides, which 

originate mainly from the portland cement, and certain types of aggregate. Two types of AAR 

are currently recognized; these are alkali-silica reaction (ASR) and alkali-carbonate reaction 

(ACR). As the names imply, these types of reaction differ in that they involve reactions with 

either siliceous or carbonate phases in the aggregates. The following definitions can be found 

on the website of the American Concrete Institute (ACI)1: 

Alkali-aggregate Chemical reaction in either concrete or mortar between hydroxyl 

reaction, AAR ions (OH-

) of the alkalies (sodium and potassium) from hydraulic 

cement (or other sources), and certain constituents of some 

aggregates; under certain conditions deleterious expansion of 

concrete or mortar may result. 

Alkali-carbonate Chemical reaction in either concrete or mortar between hydroxyl 

reaction, ACR ions (OH-) of the alkalies (sodium and potassium) from hydraulic 

cement (or other sources) and certain carbonate rocks, 

particularly calcitic dolostone and dolomitic limestones, present 

in some aggregates. The reaction is usually accompanied by 

dedolomitization and expansion of the affected aggregate 

particles, leading to abnormal expansion and cracking of concrete 

in service. 

Alkali-silica Chemical reaction in either concrete or mortar between hydroxyl 

reaction, ASR ions (OH-

) of the alkalies (sodium and potassium) from hydraulic 

cement (or other sources), and certain siliceous rocks and 

minerals, such as opal, chert, microcrystalline quartz, and acidic 

volcanic glass, present in some aggregates. This reaction and the 

development of the alkali-silica gel reaction product can, under 

certain circumstances, lead to abnormal expansion and cracking 

of the concrete. 

1 www.concrete.org 

1 
AAR Facts Book Chapter 1 – Introduction 

ASR is far more widespread than ACR and is the main focus of this text. However, it should be 

noted that some test methods used to detect alkali-silica reactive aggregates may fail to detect 

alkali-carbonate reactive aggregates. In addition, measures used to prevent damaging ASR are 

generally ineffective in preventing ACR expansion and, consequently, alkali-carbonate reactive 

rocks should not be used in the production of concrete. 

1.2 HISTORY OF AAR 

Problems due to ASR were first identified in the State of California in the 1930s (see Figure 

1.1) and reported by Thomas Stanton of the California State Division of Highways in 1940 

(Stanton 1940). Stanton’s studies demonstrated that the expansion of mortar bars was 

influenced by the alkali content of the cement, the type and amount of the reactive silica in the 

aggregate, the availability of moisture, and temperature. He further showed that expansion was 

negligible when the alkali content of the cement was below 0.60% Na2Oe and that expansion 

could be reduced by pozzolans, thus setting the groundwork for preventive measures. 

Subsequent to Stanton’s discovery, ASR was diagnosed as the cause of abnormal cracking in a 

number of dams operated by the U.S. Bureau of Reclamation, such as the Parker Dam in 

Arizona (Meissner 1941), and in the 1940s a number of agencies initiated studies on ASR in the 

USA (Army Corps of Engineers, Bureau of Public Roads, Portland Cement Association) and 

other countries (Denmark and Australia). ASR is now recognized as a major cause of concrete 

deterioration in the USA, incidences having occurred in most, if not all, of the contiguous 

states, and numerous countries worldwide. 

2 
AAR Facts Book Chapter 1 – Introduction 

Figure 1.1. Thomas Stanton of the California State Division of Highways and a Bridge Parapet 

Wall that is Showing Signs of Damage due to Alkali-Silica Reaction 

Alkali carbonate reaction (ACR) was first discovered by Swenson (1957a) as the cause of 

concrete deterioration in Canada at about the same time that ASR was first documented in the 

same country (Swenson 1957b). ACR was subsequently implicated in cases of degradation of 

concrete structures in the USA (Hadley 1961) and alleged cases of ACR have now occurred in 

Virginia, West Virginia, Kentucky, Missouri, Tennessee, Iowa, Illinois, Indiana, and New 

York, as well as England, Bahrain, Iraq, and China (Ozol 2006). However, unlike ASR, 

problems with ACR are still restricted to a few isolated locations worldwide. Consequently, 

there has been comparatively little research conducted on this topic. 

A series of international conferences on alkali-aggregate reaction (ICAAR) in concrete began in 

1974 (see Table 1.1). The first conference was held in Køge, Denmark in 1974 with 23 

delegates presenting 13 papers and representing just 5 countries (Denmark, Germany, Iceland, 

U.K., USA). Interest in AAR grew rapidly from this time and in 1992 over 300 delegates 

representing 29 countries attended the 9th ICAAR in London, U.K., and 150 papers were 

3 
 

 

 

AAR Facts Book Chapter 1 – Introduction 

published in the proceedings. Interest has remained at this level since that time with the most 

recent conference being held in Austin, Texas, USA, in 2012 (131 papers from 27 countries). 

Table 1.1. International Conferences on Alkali-Aggregate Reaction in Concrete 

# Year Host 

1 1974 Køge, Denmark 

2 1975 Reykjavik, Iceland 

3 1976 London, U.K. 

4 1978 West Lafayette, USA 

5 1981 Cape Town, S. Africa 

6 1983 Copenhagen, Denmark 

7 1986 Ottawa, Canada 

# Year Host 

8 1989 Kyoto, Japan 

9 1992 London, U.K. 

10 1996 Melbourne, Australia 

11 2000 Quebec City, Canada 

12 2004 Beijing, China 

13 2008 Trondheim, Norway 

14 2012 Austin, U.S.A. 

Alkali-silica reaction is now widely recognized as one of the more prevalent deterioration 

mechanisms affecting concrete worldwide2. 

1.3 AAR TODAY 

Seventy years after ASR was first documented, much is now known about the chemistry of the 

reaction, the factors that contribute to the reaction and expansion, methods for testing 

aggregates, and strategies for preventing expansion. Proper application of the knowledge 

available today to new concrete construction should result in a very low risk of damage due to 

ASR occurring in the normal service life of the structure. A number of specifications or 

practices have been developed in recent years to assist the practitioner in the selection of 

materials and preventive measures for ensuring durable construction (with regards to AAR). 

This text reviews one such practice, AASHTO PP65, in detail (see chapter 6). 

It is well established that the ASR results from a reaction between the alkali hydroxides 

provided (mainly) by the portland cement and certain types of reactive silica minerals present in 

some aggregates, and that limiting the availability of one (or both) of these is an effective 

2

 A comprehensive review of the history of alkali-aggregate reaction from 1940 to 1996 is given by Idorn (1997). 

4 
AAR Facts Book Chapter 1 – Introduction 

means of preventing deleterious expansion due to ASR. Thus, selecting “non-deleteriouslyreactive” aggregates or using “low-alkali cement” have become common practices for 

preventing ASR, although it is now considered that controlling the alkali content of the concrete 

is more appropriate than merely limiting the alkali content of the cement. 

The potential for using pozzolans to control damaging ASR was demonstrated by Stanton 

(1940) in his landmark paper that first revealed the phenomenon of alkali-silica reaction to the 

concrete community. The use of pozzolans for this purpose was first put into practice in the 

same decade when calcined clay was used to prevent ASR in the Davis Dam (Gilliland and 

Moran 1949), which was constructed between 1942 and 1950, the reaction having been 

implicated as the cause of cracking in the Parker Dam (Meissner 1941), which was completed 

shortly before construction began on the Davis Dam and is located 88 miles (141 km) upstream 

on the Colorado River. Ten years after Stanton’s (1940) discovery of ASR the potential for 

using fly ash and slag for controlling expansion was first documented, and it is now widely 

accepted that supplementary cementing materials are an effective means for controlling ASR 

expansion provided they are used at a sufficient level of replacement (see chapter 5). The longterm field performance of fly ash in the role of ASR prevention was recently documented 

(Thomas et al. 2012) in the form of the excellent condition of the 50-year-old Nant-y-Moch 

Dam in Wales (Figure 1.2) and the 40-year-old Lower Notch Dam in Canada, both structures 

being built with the combination of fly ash and highly reactive aggregates. 

5 
AAR Facts Book Chapter 1 – Introduction 

Figure 1.2. The Nant-y-Moch Dam in 2011 – No Symptoms of ASR after 50 Years – 

Constructed with Reactive Aggregate and 25% Fly Ash 

Test methods for correctly identifying reactive aggregates and evaluating the efficacy of 

preventive measures have constantly evolved since Stanton’s (1940) mortar-bar test, which was 

a precursor to the standard ASTM C 227 method. At the current time practitioners face the 

dilemma of selecting between tests that are reliable but have (often unacceptably) a long test 

duration or rapid tests that often have a poor correlation with field performance. The search is 

still on for rapid and reliable test methods. Testing methods for ASR and ACR are discussed in 

chapter 4. 

There are few options available for mitigating ongoing AAR in existing structures. In other 

words, once concrete has alkali-aggregate reaction, it is very difficult to stop the reaction. In 

some cases, it may be possible reduce the availability of moisture and slow the reaction down. 

In other cases, methods have been developed to either physically confine the expansion or 

create space to allow for expansion and relieve stresses. Chapters 7 and 8 in this text discuss 

6 
AAR Facts Book Chapter 1 – Introduction 

methodologies for evaluating existing concrete structures to (a) determine the extent of ASR 

and its impact on the concrete, (b) predict the future growth of the concrete due to ASR, and (c) 

select appropriate strategies for mitigating the effects of ASR. 

There is comparatively little information on ACR, and consensus has yet to be reached on the 

exact mechanisms of expansion. Although it is agreed that alkali-carbonate reactive dolomitic 

limestones have a characteristic texture and composition and undergo a chemical reaction 

resulting in dedolomitization (dolomite → brucite + calcite), there is disagreement as to 

whether the accompanying expansion results from this reaction or from reaction of 

cryptocrystalline silica in the limestone (i.e., ACR expansion may be due to ASR). There does 

appear to be consensus that, regardless of the true mechanism of expansion, there are features 

of the alkali-carbonate reaction that set it apart from ASR with aggregates that are undisputedly 

alkali-silica reaction. These features include (a) the relatively short timeframe before damage is 

observed, (b) reaction (and expansion) at very low alkali levels, (c) the general ineffectiveness 

of pozzolans and slag in controlling expansion, and (d) the inability of certain tests to identify 

the reactive aggregates. ACR is discussed in chapter 9 and a case is made for treating these 

reactive rocks as a separate category of AAR, irrespective of whether expansion is due to ACR 

or ASR. 

7 
AAR Facts Book Chapter 1 – Introduction 

REFERENCES 

AASHTO. 2011. “Standard Practice for Determining the Reactivity of Concrete Aggregates 

and Selecting Appropriate Measures for Preventing Deleterious Expansion in New Concrete 

Construction.” PP65-11, American Association of State and Highway Transportation Officials, 

Washington, DC, 24 p. 

ASTM. 2010. “Standard Test Method for Potential Alkali Reactivity of Cement-Aggregate 

Combinations (Mortar-Bar Method).” ASTM C 227, ASTM International, West Conshohocken, 

PA, 6 p. 

Gilliland, J.L. and Moran, W.T. 1949. “Siliceous admixture specified for Davis Dam concrete.” 

Engineering News Record, February, 62-64. 

Hadley, D.W. 1961. “Alkali reactivity of carbonate rocks; expansion and dedolomitization.” 

Proceedings of the Highway Research Board, 40, 462-474. 

Idorn, G. 1997. “Concrete progress: from antiquity to the third millennium.” Thomas Telford, 

London, 359p. 

Meissner, H.S. 1941. “Cracking in concrete due to expansive reaction between aggregate and 

high-alkali cement as evidenced in Parker Dam.” Proceedings of the American Concrete 

Institute, 57, 549-568. 

Stanton, T.E. 1940. “Expansion of concrete through reaction between cement and aggregate.” 

Proceedings of the American Society of Civil Engineers, 66(10): 1781-1811. 

Swenson, E.G. 1957a. “A reactive aggregate undetected by ASTM tests.” Proceedings of 

American Society for Testing and Materials, 57, 48-51. 

Swenson, E.G. 1957b. “Cement aggregate reaction in concrete of a Canadian bridge.” ASTM 

Proceedings, 57 1043–1056. 

Thomas, M.D.A., Hooton, R.D., Rogers, C. and Fournier, B. 2012. “50 years and still going 

strong: fly ash puts paid to ASR.” Concrete International, January, 35-40. 

8 
AAR Facts Book Chapter 2 – Fundamentals of ASR 

2 – Fundamentals of Alkali-Silica Reaction 

2.1 INTRODUCTION 

As described in the introduction, alkali-silica reaction is a reaction between the alkali 

hydroxides in the pore solution of concrete (or mortar) and certain types of silica minerals 

present in some aggregates. The reaction product, an alkali-silica gel with varying amounts of 

calcium, is hygroscopic having a tendency to absorb water and swell. Under certain conditions 

the reaction causes expansion of the concrete and may eventually lead to cracking. A schematic 

showing the sequence of events is shown in Figure 2.1. 

It is clear from this brief description of ASR that there are three requirements for damaging 

reaction to occur; these are: 

• A sufficient quantity of reactive silica (within aggregates) 

• A sufficient concentration of alkali (primarily from portland cement) 

• Sufficient moisture 

Elimination of any one of these requirements will prevent the occurrence of damaging alkalisilica reaction; this is discussed further in the sections dealing with prevention and mitigation of 

ASR. 

This chapter describes the chemistry of the reaction and the mechanisms of expansion, and 

discusses the role of various contributing factors including the composition and nature of the 

reactive aggregate, sources of alkali, and the impact of the exposure conditions. 

Alkali-carbonate reaction (ACR) is discussed in chapter 9. 

9 
AAR Facts Book Chapter 2 – Fundamentals of ASR 

Figure 2.1. Alkali-Silica Reaction Sequence 

2.2 CHEMISTRY OF THE REACTION 

Despite the term, alkali-silica reaction is initiated by a reaction between the hydroxyl ions in the 

pore solution and certain types of silica in the aggregate. Silica (SiO2) is composed primarily of 

siloxane groups (≡Si-O-Si≡) but even crystalline silica is disordered at the surface and the 

10 
 

 

 

AAR Facts Book Chapter 2 – Fundamentals of ASR 

surface oxygens are hydroxylated (even in pure water) forming silanol groups (≡Si-OH); see 

Figure 2.2. In the presence of a high concentration of hydroxyl ions (OH-

) silica tends towards 

dissolution first by neutralization of the silanol groups and then by attack on the siloxane 

groups; the reactions may be represented as follows3: 

≡Si-OH + OH- → Si-O- + H2O Eqn. 2.1 

≡Si-O-Si≡ + 2OH- → 2Si-O- + H2O Eqn. 2.2 

Figure 2.2. The Structure of Silica 

The structure breaks down progressively as the siloxane bridges are broken (see Figure 2.3). 

The negatively charged Si-O- ions attract positively charged species such as sodium (Na+

) and 

potassium (K+

), which are abundant in concrete pore solution. The initial result is an alkalisilicate solution or gel depending on the moisture content. However, in the presence of calcium, 

the silica precipitates from solution as an alkali-silicate gel (CaO-Na2O/K2O-SiO2-H2O), 

primarily composed of sodium, potassium, and silica, with small amounts of calcium. The 

hydroxyl ion concentration (and the pH) decreases as silica dissolves. In a system composed 

solely of alkali hydroxide and silica, the silica will continue to dissolve until the concentration 

in solution reaches the silica-pH equilibrium curve (see Figure 2.4). The data show that final 

3

 The reactions may as also be written as follows (modified from Dent Glasser and Kataoka 1981a): 

Si-OH + OH-

 + Na+ → Si-O-Na + H2O Eqn. 2.1a 

Si-O-Si + 2OH- + 2Na+ → 2(Si-O-Na) + H2O Eqn. 2.2a 

11 
AAR Facts Book Chapter 2 – Fundamentals of ASR 

silica concentration depends on the initial SiO2/Na2O ratio as will be discussed later in the 

section on “pessimum behavior”. The situation is more complex in concrete, probably due to 

the presence of abundant calcium, which reduces silica concentrations in solution and provides 

an additional source of hydroxyl ions. Consequently, equilibrium conditions are reached slowly 

in concrete (and mortar). 

Figure 2.3. Mechanism of Dissolution of Silica due to Attack by Hydroxyl Ions. Dotted Line 

Represents the Interface between Silica and Water (Iler 1979; Urhan 1987) 

Figure 2.4. Equilibrium Solubility Curve (SiO2-pH) and Change in Composition for Different 

Solutions of SiO2-NaOH (from Dent Glasser and Kataoka 1981b) 

The chemical composition and morphology of the reaction product (gel) vary widely as shown 

by Moranville-Regourd (1989), and other researchers have shown that the physical properties of 

12 
AAR Facts Book	 Chapter 2 – Fundamentals of ASR 

gels, in terms of the capacity for unconfined swelling or for exerting forces when confined, also 

vary considerably. 

2.3 MECHANISM OF EXPANSION 

Figure 2.5 shows a petrographic thin section of ASR-affected concrete viewed under a 

microscope with transmitted light. The image shows a flint sand particle (at left) embedded in 

cement paste. The flint particle has reacted, expanded, and cracked, and the crack extends out 

into the surrounding cement paste. The crack within the aggregate and in the paste is partially 

filled with a reaction product, alkali-silica gel. 

Figure 2.5. Photograph of a Thin Section of Concrete Undergoing ASR (field of view ~ 5 mm) 

Despite general acceptance of the chemical reactions involved, a number of different 

mechanisms of expansion have been proposed as follows: 

• Hansen (1944) suggested that the cement paste surrounding reactive grains acts as a 

semi-permeable membrane through which water (or pore solution) may pass but not the 

larger complex silicate ions. The water is drawn into the reacting grain where its 

chemical potential is lowest. An osmotic pressure cell is formed and increasing 

hydrostatic pressure is exerted on the cement paste, inevitably leading to cracking of the 

surrounding mortar. 

• McGowan and Vivian (1952) disputed the classical osmotic theory on the basis that 

cracking of the surrounding cement paste “membrane” due to ASR would relieve 

hydraulic pressure and prevent further expansion. They proposed an alternative 

13 
AAR Facts Book	 Chapter 2 – Fundamentals of ASR 

mechanism based on the physical absorption of water by the alkali silica-gel and 

subsequent swelling of the gel. 

• Powers and Steinour (1955a, 1955b) proposed a compromise, suggesting that both 

osmotic and imbibition pressures may be generated depending on whether the alkalisilicate complex is fluid or solid. In their hypothesis, the reaction product itself may act 

as a semi-permeable membrane depending on its composition. 

Regardless of the mechanism, the fundamental cause of swelling is thermodynamically the 

same, i.e., the entry of water into a region where the effect of a solute or of adsorption reduces 

its free energy. 

A number of experimental studies have concluded that significant expansion only occurs when 

an adequate supply of calcium is available as calcium hydroxide [Ca(OH)2]. In systems with 

abundant alkali hydroxides and reactive silica, but no calcium hydroxide, silica dissolves and 

remains in solution. Although the precise role calcium plays in gel expansion remains unclear, a 

series of mechanisms have been proposed, as listed below (ACI 201): 

• Calcium promotes “alkali recycling” by replacing alkalis in the reaction product thereby 

regenerating alkalis for further reaction (Thomas 2001; Hansen 1944). Alkali recycling 

is discussed further in section 2.5.3 of this chapter. 

• Ca(OH) - - 2 provides a reservoir of OH ions to maintain a high level of OH in solution 

(Wang and Gillott 1991). 

• High calcium concentrations in the pore solution prevent the diffusion of silica away 

from reacting aggregate particles (Chatterji 1979; Chatterji and Clausson-Kass 1984). 

• If calcium is not available, reactive silica dissolves in alkali hydroxide solution without 

causing damage (Thomas 1998; Diamond 1989). 

• The formation of calcium-rich gels is necessary to cause expansion either directly or 

indirectly through the formation of a semi-permeable membrane around reactive 

aggregate particles (Thomas 1998; Thomas et al. 1991; Bleszynski and Thomas 1998). 

• Pozzolans are effective in controlling the expansion of concretes (and mortars) 

immersed in alkaline salt (including alkali hydroxide) solutions (Chatterji et al. 1987; 

Kawamura et al. 1988; Alasali and Malhotra 1991; Bleszynski and Thomas 1998) and 

this is attributed to the consumption of Ca(OH)2 by the pozzolanic reaction which 

reduces the availability of calcium for the alkali-silica reaction. Bleszynski and Thomas 

(1998) showed considerable evidence of reaction in concrete containing 40% fly ash and 

a reactive flint sand after 4 years immersion in 1 NaOH at 80°C, but no expansion. 

Alkali-silica gel was observed to be migrating into and saturating the cement paste 

surrounding reactive flint particles with no signs of damage (see Figure 2.4). They 

14 
AAR Facts Book	 Chapter 2 – Fundamentals of ASR 

attributed this to the very low viscosity of the reaction product formed in the absence of 

calcium. By contrast, other workers (Tang et al. 1983; Wang and Gillott 1991) showed 

that the addition of CaO can induce expansion on concretes containing fly ash or silica 

fume. 

• Expansion of mortars or concretes containing reactive aggregate can be prevented by 

removal of the Ca(OH)2 prior to immersion of the sample in alkaline solutions. Chatterji 

(1979) removed the Ca(OH)2 from concrete by leaching, and Thomas (2000) carbonated 

the Ca(OH)2 by exposing mortar bars to an enriched-CO2 environment. 

Although the precise role(s) of Ca(OH)2 is equivocal, it is evident that calcium must be 

available for damaging reaction to occur. Thus reducing the availability of calcium – for 

example, by consuming Ca(OH)2 through pozzolanic reactions – should result in a reduction in 

the expansion due to ASR. 

Dependence on Ca(OH)2 for the promotion of damaging AAR is not a recent phenomenon. 

Conrow (1952) suggested that the expansion of concretes containing a siliceous sand-gravel 

may be related to the quantity of Ca(OH)2 produced by the cement and that the beneficial effect 

of pozzolan is related to its ability to react with Ca(OH)2. In a discussion of this paper, Mather 

stated an observation that concrete that has undergone ASR is characterized by “... materially 

reduced quantities of crystalline calcium hydroxide” and suggested that Ca(OH)2 may be 

consumed by ASR and that “... the mere consumption of calcium hydroxide by reaction with a 

pozzolan is sufficient to explain the beneficial effects of pozzolans in preventing abnormal 

expansion.” 

2.4 REACTIVE SILICA 

2.4.1 Types of Reactive Silica 

Table 2.1 provides a list of deleteriously reactive rocks, minerals, and synthetic substances. 

15 
AAR Facts Book Chapter 2 – Fundamentals of ASR 

Table 2.1. Deleteriously Reactive Rocks, Minerals and Synthetic Substances 

(from ACI Committee 201, 1991) 

Reactive substance (mineral) Chemical composition Physical character 

Opal SiO2·nH2O Amorphous 

Chalcedony SiO2 Microcrystalline to 

cryptocrystalline; commonly 

fibrous 

Certain forms of quartz SiO2 Microcrystalline to 

cryptocrystalline; crystalline, 

but intensely fractured, 

strained, and/or inclusionfilled 

Cristobalite SiO2 Crystalline 

Tridymite SiO2 Crystalline 

Rhyolitic,dacitic, latitic, or Siliceous with lesser Glass or cryptocrystalline 

andesite glass or proportions of Al2O3, Fe2O3, material as the matrix of 

cryptocrystalline alkaline earths and alkalis volcanic rocks or fragments in 

devitrification products tuffs 

Synthetic siliceous glass Siliceous, with lesser Glass 

proportions of alkalis, Al2O3, 

and/or other substances 

The most important deleteriously alkali-reactive rocks (that is, rocks containing excessive 

amounts of one or more of the substances listed above) are as follows: 

Opaline cherts Rhyolites and tuffs Opaline concretions 

Chalcedonic cherts Dacites and tuffs Fractured, strained, and 

limestone-filled quartz and 

Quartzose cherts Andesites and tuffs quartzites 

Siliceous limestones Siliceous shales 

Siliceous dolomites Phylites 

NOTE: A rock may be classified as, for example “siliceous limestone,” and be innocuous if its 

siliceous constituents are other than those indicated above. 

16 
AAR Facts Book Chapter 2 – Fundamentals of ASR 

Silica, SiO2, is a component of many rocks; however, not all forms of silica react significantly 

with the pore solution of concrete and, thus, not all siliceous aggregates produce damaging 

ASR. For example, the mineral quartz is stable whereas the mineral opal is highly reactive, 

although both are silica minerals with similar chemical composition, being primarily composed 

of SiO2. Figure 2.6 shows the differences in the solubility of the silica and the crystalline 

structure of these two minerals. Opal has a highly disordered (amorphous) structure which 

renders it unstable at high pH and, as such, aggregates containing significant quantities of the 

mineral opal may be expected to react and result in expansion when used in concrete, provided 

there is sufficient alkali present. On the other hand, quartz will not react deleteriously regardless 

of the alkali content of the concrete4. 

Figure 2.6. Solubility and Structure of Opal and Quartz 

The following silica minerals are considered to be alkali-silica reactive: opal, tridymite, 

cristobalite, volcanic glass, chert, cryptocrystalline (or microcrystalline) quartz, and strained 

quartz. These minerals may be found in the following rock types: shale, sandstone, silicified 

carbonate rocks, chert, flint, quartzite, quartz-arenite, gneiss, argillite, granite, greywacke, 

4

 The potential for reaction exists even with well-crystallized silica (e.g. quartz), but the reaction is slow and may 

be considered to be negligible with regards to the design life of a concrete structure. However, temperature 

dramatically increases the rate of reaction and, in hydrothermal conditions, finely ground quartz is extremely 

reactive. 

17 
AAR Facts Book Chapter 2 – Fundamentals of ASR 

siltstone, arenite, arkose, and hornfels. However, this does not mean that all sources of such 

rocks will produce deleterious reaction when used in concrete. For example, granitic aggregate 

is widely used in concrete and only certain sources produce damaging ASR. The reactivity of a 

rock depends on the type and quantity of reactive minerals present, if any. 

Although, the presence of reactive minerals can usually be detected by an experienced 

petrographer, appropriate performance testing of specific aggregate sources is recommended to 

confirm alkali-silica reactivity. Test methods are discussed in chapter 4. 

Poorly crystalline or amorphous silica minerals such as opal, cristobalite, volcanic and artificial 

glasses react rapidly and may cause damaging reaction in a few years when present in amounts 

as little as 1%. Varieties of quartz such as cryptocrystalline, microcrystalline, or strained quartz 

react more slowly, take longer to produce damage, and are generally required to be present in 

greater quantities than poorly crystalline and amorphous forms of silica. However, it is difficult 

to classify aggregate reactivity based solely on mineralogy as aggregates may contain various 

types of reactive minerals in different quantities, and the extent to which reactive minerals 

cause damage in concrete depends on other factors such as particle size. 

2.4.2 Effect of Aggregate Size 

Stanton (1940) showed in his formative work on ASR that the particle size of the reactive 

aggregate could have a profound effect on the magnitude of expansion of mortar. Figure 2.7(a) 

shows the expansion of mortar bars containing a reactive siliceous magnesian limestone 

partitioned into various size ranges. As expected, the expansion at a given age was greater for 

mortars produced with the 180-600 micron fraction than for the larger fractions (0.6-2 mm and 

2-6.7 mm), especially at earlier ages, and this is attributed to the greater surface area and 

increased accessibility of the reactive silica. What was surprising was that the mortar bars 

produced with reactive aggregate passing 180 micron did not exhibit any deleterious reaction. 

Stanton (1940) hypothesized that the absence of expansion when the aggregate is in a finelydivided form is due either to (a) the reaction being “dissipated throughout the mass in such a 

way as to cause no high expansive forces” or (b) the reaction being essentially complete before 

the mortar sets. Other workers have since shown similar data although the particle size to which 

the reactive aggregate has to be reduced to prevent expansion has not been established 

unequivocally. For example, Vivian (1951) using the same reactive aggregate as Stanton (1940) 

showed that expansion was delayed but not prevented for aggregate passing the 70-μm but 

retained 50-μm sieve, whereas no expansion was observed for aggregate passing the 50-μm 

sieve. Vivian (1951) also showed similar trends in behavior with opal as the reactive aggregate. 

18 
AAR Facts Book Chapter 2 – Fundamentals of ASR 

Figure 2.7. Effect of Aggregate Size (a) and Proportion (b) on 

Expansion due to ASR (Stanton 1940) 

Numerous laboratory studies have shown that the expansion of mortar or concrete containing 

highly-reactive recycled glass as an aggregate can be eliminated provided the glass is crushed to 

a certain fineness (Carpenter and Cramer 1999; Shayan and Xu 2004; Jin et al. 2000). In fact 

glass crushed to high fineness may be effective in preventing damaging alkali-silica reaction 

when larger particles of the same glass are used as (reactive) aggregates (Shayan and Xu 2004), 

although such an approach may not be effective if the alkali content of the glass is high. Jin et 

al. (2000) suggested that the pessimum size, that is the size fraction that causes the greatest 

expansion when tested in mortar, reduces as the reactivity of the glass increases. 

The strategy of using ground reactive aggregate as a preventive measure for ASR has been 

employed in Iceland where up to 9% ground rhyolite has been interground with portland 

cement clinker to produce a blended cement for controlling expansion with reactive rhyolitic 

aggregates (Asgeirsson and Gudmundsson 1979). The use of finely-divided, alkali-silica 

reactive materials (e.g., pozzolans) to control ASR is discussed in detail in chapter 5. 

It should be noted that there is some evidence that reactive silica may cause damaging reaction 

even when it is finer than 30 μm. Diamond and Thaulow (1974) observed expansion of mortar 

bars containing a high-alkali cement and reactive opal in the size range 20–30 μm (the fraction 

was separated by sedimentation). However, to the authors’ knowledge, this is the only reported 

case of damaging ASR with reactive silica particles in this size range (e.g., < 30 μm) and such 

behavior has not been confirmed by subsequent studies. 

19 
AAR Facts Book Chapter 2 – Fundamentals of ASR 

2.4.3 Pessimum Effect 

Another phenomenon observed by Stanton (1940) in his landmark paper was that expansion did 

not necessarily increase with an increase in the reactive aggregate content. Figure 2.7(b) shows 

the expansion of mortar bars stored over water as a function of the proportion of reactive 

aggregate, in this case a siliceous magnesian limestone, in the mix. The maximum expansion 

occurred when 20% of the aggregate was comprised of the reactive sand, and the expansion 

decreases with greater amounts of reactive aggregate such that mixes containing 60% or more 

of reactive sand showed no significant expansion. This phenomenon is known as the pessimum 

effect, and such behavior is associated with some, but not all, highly reactive aggregates such as 

Beltane opal (an aggregate used in many earlier research studies on ASR). 

Figure 2.8(a) shows pessimum behavior for six aggregates (five different types) containing 

opaline material, and Figure 2.8(b) shows the four regions of behavior described by Hobbs 

(1988), explained in Table 2.2. 

Figure 2.8. (a) Pessimum Behavior for Five Aggregates Containing Opaline Material 

and (b) Four Regions of Pessimum Behavior (from Hobbs 1988) 

20 
AAR Facts Book Chapter 2 – Fundamentals of ASR 

Table 2.2. Regions of Pessimum Behavior 

Region Effect Explanation 

A Reaction but no cracking Insufficient gel forms to cause damage. 

B Reaction, cracking – 

excess of alkalis 

Expansion continues until all the reactive silica is depleted. 

Composition of gel is probably independent of the alkali/ 

reactive silica ratio. 

C Reaction, cracking – 

excess of reactive silica 

Expansion continues until the alkali level is insufficient to 

sustain ASR. 

Alkali/silica ratio and swelling capacity of gel decreases 

with increasing silica content. 

D Reaction but no cracking Reactive silica content very high and reaction so rapid that 

the gel forms before concrete has hardened sufficiently and 

there is no damage. Copious quantities of gel can be 

observed. 

Hobbs’ theory is based on two assumptions. Firstly, it is assumed that, as the reactive-silica-toalkali ratio (SiO2/Na2Oe) in the system increases beyond the pessimum, the reaction product 

(gel) formed has a lower alkali-to-silica ratio (Na2Oe/SiO2) which reduces its affinity for water 

uptake and thus reduces its swelling capacity. Secondly, it is assumed that when the reactive 

silica content is very high, gel forms rapidly before the concrete has gained sufficient rigidity to 

suffer damage. The rapid gel formation consumes the alkalis and insufficient reaction occurs 

after the concrete has hardened to result in damage. 

Dent Glasser and Kataoka (1981b) showed that quantity of silica dissolved depends on the ratio 

of silica to alkali (SiO2/Na2Oe). As discussed previously, in a system of reactive silica and 

alkali hydroxides, the concentration of silica in solution increases until the equilibrium 

solubility curve (SiO2-pH) is reached as shown in Figure 2.3. If the silica content is low, the 

silica concentration increases until all of the silica is dissolved, and the solubility curve is not 

reached. If the silica content is very high, the concentration increases until the solubility curve 

is reached but then the excess silica in the mix removes hydroxyl ions (OH-) from solution and 

reduces the pH. This leads to a reduction of the quantity of silica in solution. Consequently, 

there is an optimum silica to alkali ratio (SiO2/Na2Oe) where the maximum silica concentration 

is reached, and this occurs when the content of silica is such that it all dissolves when the 

solubility curve is reached. This is the pessimum reactive silica content with regards to 

expansion of mortar or concrete. 

It is somewhat surprising that the pessimum effect is still observed when aggregates are tested 

using the accelerated mortar bar test (e.g., Shayan et al. 1988). In this test mortar bars are 

21 
AAR Facts Book Chapter 2 – Fundamentals of ASR 

immersed in 1 M NaOH at 80°C (176°F). Despite this, expansion may not be observed with 

some aggregates in the test if the amount of reactive silica is above the pessimum level. It is 

difficult to explain such behavior on the basis of there being an excess of silica (that is, SiO2/ 

Na2Oe too high) since there is an inexhaustible supply of alkali. 

2.5 SOURCES OF ALKALI 

While portland cement is considered the main contributor of alkalis, under certain conditions 

other materials may provide additional alkalis that are available to the reaction. The source of 

alkalis can be from any of the following: 

• Portland cement 

• Supplementary cementing materials (e.g., fly ash, slag, silica fume, natural pozzolans) 

• Aggregates 

• Chemical admixtures 

• External sources (e.g., seawater and deicing salts) 

• Wash water (if used) 

The quantity of alkalis in portland cement is typically expressed in terms of equivalent sodium 

(written either Na2Oe or Na2Oeq) which may be calculated using the following formula: 

Na2Oe = Na2O + 0.658 x K2O Eqn. 2.3 

where: Na2O and K2O are the mass percentages of sodium oxide and potassium oxide in the 

portland cement as reported on the cement mill test report. The percentage of alkalis in portland 

cement is in the range of 0.2 to 1.3% Na2Oe for most North American sources, but may be as 

high as 1.65% Na2Oe or more worldwide. 

2.5.1 Pore Solution Composition 

Although the percentage of alkalis in portland cement is relatively low in comparison to other 

oxides, the alkalis are highly soluble and dominate the pore solution of the concrete. Figure 2.9 

shows the composition of the pore solution extracted from portland cement pastes and mortars 

at various ages. During the first few hours the pore solution is mainly composed of alkali 

sulfates (Na+

, K+, and SO4

2-), but beyond this time the formation of solid sulfate phases 

(calcium mono-sulfo-aluminate and ettringite) results in a reduction of the SO4

2- concentration 

in solution, and hydroxyl ions (OH-) come into solution to maintain balance with the positively 

charged alkali cations. Beyond the first day, the pore solution is composed almost entirely of 

22 
AAR Facts Book Chapter 2 – Fundamentals of ASR 

Na+, K+, and OH-. The pore solution is saturated with calcium (Ca2+) but the concentration is 

very low, 0.6 to 2.5 mmol/L according to measurements made by Struble (1987), at the high pH 

resulting from the high concentration of alkali hydroxides. 

Figure 2.9. Pore Solution Composition in Portland Cement Pastes and Mortars (Diamond 1983) 

Figure 2.10 shows that the alkali concentration of the pore solution is strongly influenced by the 

alkali content of the portland cement, the concentration being approximately 0.7 mol/L per 1% 

Na2Oe in the cement. Note in Figure 2.10 that the OH- concentration ranges from about 0.15 M 

for the lowest alkali cement to about 1.00 M for the highest; this represents a pH range from 

13.2 to 14.0 (calculated from the hydroxyl ion concentration assuming an activity coefficient of 

unity). The data in Figure 2.10 are for paste samples produced at a water-to-cement ratio of 

approximately w/c = 0.50. 

23 
 

 

1.0 

0.8 

0.6 

0.4 

0.2 

0.0 

Cement Alkalis (% Na2Oe) 

OH Concentration (mol/L) . 

y = 0.7231x - 0.0011 

R2 = 0.9148 

Diamond & Penko, 1988 

Nixon & Page, 1987 

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
 

AAR Facts Book Chapter 2 – Fundamentals of ASR 

Figure 2.10. Relationship between the Alkalinity of the Pore Solution and the Alkali Content of 

the Portland Cement (Diamond and Penko 1992; Nixon and Page 1987) 

A more general formula has been developed by consideration of the data in Figure 2.10 together 

with other published data; the expression is (Helmuth et al. 1993): 

[OH-] = 0.339Na2Oe%/(w/c) + 0.022 ± 0.06 mol/L Eqn. 2.4 

If reactive aggregate is present in the system the concentration of hydroxyl and alkali ions will 

decrease due to the alkali-silica reaction. Figure 2.11(a) shows the effect of reactive Beltane 

opal on the pore solution alkalinity of mortars (Diamond et al. 1981). After a brief induction 

period, alkalis are rapidly consumed by reaction with the opal until a steady-state is reached 

after approximately 1 month at 20°C; the hydroxide concentration is approximately 0.28M OHat this time. Tests at 40°C showed a rapid acceleration of the reaction, which is essentially 

complete in mortar containing Beltane opal after only 3 days (Diamond et al. 1981). 

24 
AAR Facts Book Chapter 2 – Fundamentals of ASR 

Figure 2.11. Effect of Reactive Aggregate on Pore Solution Composition in (a) Mortars 

(Diamond et al. 1981) and (b) Concrete (Thomas 1996) 

Results from similar studies on concretes containing reactive flint sand (U.K.) are shown in 

Figure 2.11(b) (Thomas 1996). The pore solution of the control concrete showed some 

reduction in alkalinity with time, suggesting that there may be some interaction between the 

alkali hydroxides and the "inert" aggregate. However, this reduction is minimal compared to 

that observed in the concrete containing flint sand. The rate of consumption of alkalis due to the 

presence of flint was considerably slower compared with Beltane opal; steady-state conditions 

do not appear to be attained until after 1 year has elapsed. However, the hydroxyl ion 

concentration at this time (approximately 0.27M OH-

) is remarkably similar to the steady-state 

concentration observed with opal (approximately 0.28M OH-

). Diamond (1983) has postulated 

that the threshold alkali concentration required to sustain alkali-silica reaction is likely to be 

0.25M OH- or higher. 

2.5.2 Threshold Alkali Contents 

Based on Stanton’s early work (1940), it was proposed for many years that expansion resulting 

from the alkali-silica reaction is unlikely to occur when the alkali content of the cement is 

below 0.6% Na2Oe. Many specifications allow the use of potentially-reactive aggregates 

provided that the cement alkali content does not exceed 0.6% Na2Oe. However, it is now 

recognized that limiting the alkali content of portland cement is not, by itself, an effective way 

of preventing ASR-induced damage because this approach does not control the total alkali 

content of the concrete mixture. 

25 
AAR Facts Book Chapter 2 – Fundamentals of ASR 

Limiting the maximum alkali content of concrete is the preferred approach when specifying 

alkali levels. The alkali content of portland cement concrete is calculated by multiplying the 

cement content by the alkali content of the cement. Figure 2.12 illustrates the effects of the 

concrete alkali content on the expansion of concrete prisms stored over water at 38°C (100°F) 

for one year. Concrete mixtures were produced with a reactive siliceous limestone and varying 

cement contents (275 to 450 kg/m3

, 458 to 750 pcy) using cements with a wide range of alkali 

contents (0.67 to 1.40% Na2Oe). From the data it is evident that the expansion of concrete with 

a given reactive aggregate is dependent on the alkali content of the concrete. Figure 2.12 

indicates that deleterious expansion of the concrete prisms containing this reactive aggregate 

may be prevented if the alkali content of the concrete is kept below 3.0 kg/m3 (5.0 lb/yd3) 

Na2Oe. It should be noted that expansion has been found to occur in the field at lower alkali 

contents than that found necessary to cause expansion in concrete specimens stored over water 

in the laboratory. The reason for this is that a portion of the alkalis may be lost through leaching 

under the conditions of the concrete prism test (Thomas et al 2006). For example, the aggregate 

for which expansion data are presented in Figure 2.12 caused expansion and cracking of fieldexposed concrete blocks (approximately 0.6 x 0.6 x 2.0 m, 2 x 2 x 6 ft.) with an alkali content 

of just 1.9 kg/m3

 (3.2 lb/yd3) Na2Oe (MacDonald et al. 2012). 

Figure 2.12. Effect of Concrete Alkali Content on Expansion 

The alkali content of concrete may increase during service due to (i) alkali migration caused by 

moisture movements or electrical currents, (ii) penetration of alkalis from external sources (e.g., 

deicing salts), or (iii) long-term release of alkali from aggregates. These factors should be taken 

into consideration when setting alkali limits for concrete containing reactive aggregates. 

26 
AAR Facts Book Chapter 2 – Fundamentals of ASR 

2.5.3 Alkali Recycling 

As discussed in previous sections of this chapter, alkali-silica reaction results in a reduction of 

the concentration of alkali ions (Na+

 and K+) and hydroxyl ions (OH-) in the concrete pore 

solution due to the formation of an alkali-silica gel (CaO-Na2O/K2O-SiO2-H2O) containing 

small amounts of calcium. There is evidence that a portion of the alkalis in the gel exchange for 

calcium with time, and alkalis are released back into the pore solution presumably fueling 

further reaction with the aggregate providing reactive silica is still available. This phenomenon 

was first proposed in Hansen in 1944 (Hansen 1944). Knudsen and Thaulow (1976) showed, 

using electron probe microanalysis of concrete, that gel formed within or close to aggregates 

was low in calcium and high in alkali, but that as the distance from the aggregate increased the 

calcium content of the gel increased, presumably due to close association with the calcium-rich 

cement paste. 

Urhan (1987), summarizing observations from a number of studies, proposed that there is a 

progressive passage from low viscosity alkali-silica gel to C-S-H and that this is accompanied 

by a change in the physical and mechanical properties of the gel. Figure 2.13 illustrates changes 

in composition, physical and mechanical properties, and structure of the reaction product. Gel 

with a low calcium content may have a high swelling capacity, but the viscosity is very low. On 

the other hand, gel high in calcium is more rigid, but does not swell. Although not explicitly 

stated by Urhan (1987), at some point the composition of the gel is such that the gel has 

sufficient swelling capacity and viscosity to cause damage to the surrounding cement paste. 

Figure 2.13. Changes in the Nature and Properties of the Alkali-Silica Reaction Product 

(Urhan 1987) 

27 
AAR Facts Book Chapter 2 – Fundamentals of ASR 

Thomas (2001) compared the composition of alkali-silica gels found in 7-year-old laboratory 

concrete and a 55-year-old concrete dam with the composition of calcium-silicate hydrate (C-SH) in the concrete from the dam; the data expressed as alkali/silica and calcium/silica atomic 

ratios are presented in Figure 2.14. The composition covers a wide range, but it appears that 

there is a reasonable relationship between the alkali and calcium contents; i.e., as the calcium 

content decreases the potassium content decreases. This supports the concept of a cation 

exchange with the calcium replacing the alkali in the initially alkali-rich reaction product. This 

exchange occurs as the gel migrates away from the aggregate particle and comes into contact 

with the calcium-rich cement paste. The data in the figure indicate that the process continues 

slowly as the concrete ages and that the composition of the reaction product may ultimately 

approach something similar to C-S-H. This "final product" appears to retain very little alkali 

indicating that almost all of the alkali that originally participated in the reaction process may 

eventually be recycled to participate in further reaction. 

Figure 2.14. Composition of Alkali-Silica Gels in Concrete 

In the same paper, Thomas (2001) compared the evolution of the pore solution extracted from 

concrete cubes containing a reactive flint aggregate with the expansion of concrete prisms from 

the same mixture. The data in Figure 2.15 show that the pore solution alkalinity drops steadily 

to an age of 12 weeks, after which it appears to remain stable with a hydroxyl ion concentration 

between 0.26 and 0.27 Mol/liter, whereas the expansion of the concrete continues long beyond 

the point at which the alkali concentration in the pore solution reaches a steady concentration. 

28 
AAR Facts Book Chapter 2 – Fundamentals of ASR 

This can be explained by alkali recycling, the alkalis being released from the gel being 

consumed by reaction, resulting in long-term expansion. Thomas (2001) suggested that alkali 

recycling might partially explain why in many large concrete dams the expansion continues for 

decades and does not appear to reach a maximum value as is the case for laboratory specimens 

(stored over water) where the expansion-time relationship is typically represented by an Sshaped curve reaching a maximum after a few years or less. In large structures, alkali recycling 

may continue to fuel ASR (until all the reactive silica is consumed), whereas in laboratory 

specimens leaching of the alkalis eventually reduces the alkali concentration to a level below 

that necessary to sustain ASR. 

Figure 2.15. Evolution of the Pore Solution and Expansion in Concrete 

Containing Reactive Flint Sand (Thomas 2001) 

2.6 ROLE OF MOISTURE 

Sufficient moisture is required to both sustain the chemical reaction and to provide for the 

expansion of the gel. It is generally considered that the chemical reaction will cease if the 

internal relative humidity inside the concrete falls below 80% (Figure 2.16). Local differences 

in moisture availability within the same structure can result in very different levels of ASR 

damage occurring within that structure. Specifically, portions of the structure exposed to a 

constant or steady source of moisture (e.g., as a result of poor drainage or poor detailing) can 

29 
AAR Facts Book Chapter 2 – Fundamentals of ASR 

exhibit significant ASR-induced damage, while other portions of the structure that remain 

essentially dry may show little or no damage. 

Figure 2.16. Effect of Relative Humidity on Expansion of Concrete Prisms (Pedneault 1996) 

30 
AAR Facts Book Chapter 2 – Fundamentals of ASR 

REFERENCES 

ACI Committee 201. 1991. “Proposed revisions of: Guide to Durable Concrete.” ACI Materials 

Journal, 88(5): 544-582. 

Alasali, M.M. and Malhotra, V.M. 1991. "Role of concrete incorporating high volumes of fly 

ash in controlling expansion due to alkali aggregate reactions." ACI Materials Journal, 88(2): 

159-163. Discussion in Vol. 89, 1992, 110-111. 

Asgeirsson, H. and Gudmundsson, G. 1979. “Pozzolanic activity of silica dust.” Cement and 

Concrete Research, 9: 249-252. 

Bleszynski, R.F. and Thomas, M.D.A. 1998. “Microstructural Studies of Alkali-Silica Reaction 

in Fly Ash Concrete Immersed in Alkaline Solutions.” Advanced Cement Based Materials, 7: 

66-78. 

Carpenter, A.J. and Cramer, S.M. 1999. “Mitigation of ASR in pavement patch concrete that 

incorporates highly reactive fine aggregate.” Transportation Research Record 1668, Paper No. 

99-1087: 60– 67. 

Chatterji, S. 1979. “The Role of Ca(OH)2 in the Breakdown of Portland Cement Concrete due 

to Alkali-Silica Reaction.” Cement and Concrete Research, 9(2): 185-188. 

Chatterji, S. and Clausson-Kass, N.F. 1984. “Prevention of Alkali-Silica Expansion by Using 

Slag-Portland Cement.” Cement and Concrete Research, 14(6): 816-818. 

Chatterji, S., Thaulow, N. and Jensen, A.D. 1987. “Studies of alkali-silica reaction. Part 4. 

Effect of different alkali salt solutions on expansion.” Cement and Concrete Research, 17: 777­

783. 

Conrow, A.D. 1952. "Studies of abnormal expansion of portland cement concrete." Proceedings 

of the American Society for Testing and Materials, 52: 1205-1227. 

Dent Glasser, L.S. and Kataoka, N. 1981a. “The chemistry of alkali-aggregate reactions.” 

Proceedings of the 5th International Conference on Alkali-Aggregate Reaction, Cape Town, 

S252/23. 

Dent Glasser, L.S. and Kataoka, N. 1981b. “The chemistry of alkali-aggregate reactions.” 

Cement and Concrete Research, 11: 1-9. 

Diamond, S. 1983. "Alkali reactions in concrete - Pore solution effects." Proceedings of the 6th 

International Conference on Alkalis in Concrete, (Eds. G.M. Idorn and Steen Rostam), Danish 

Concrete Association, Copenhagen, 155-166. 

31 
AAR Facts Book Chapter 2 – Fundamentals of ASR 

Diamond, S. 1989. “ASR - Another Look at Mechanisms.” Proceedings of the 8th International 

Conference on Alkali-Aggregate Reaction, (Eds. K. Okada, S. Nishibayashi, and M. 

Kawamura), Kyoto, Japan, 83–94. 

Diamond, S. and Penko, M. 1992. “Alkali silica reaction processes: the conversion of cement 

alkalis to alkali hydroxide.” Durability of Concrete – G.M. Idorn International Symposium, (Ed. 

Jens Holm), ACI SP-131, American Concrete Institute, Detroit, 153-168. 

Diamond, S., Barneyback, R.S. and Struble, L.J. 1981. "On the Physics and Chemistry of Alkali 

Silica Reactions." Proceedings of the 5th International Conference on Alkali-Aggregate 

Reaction in Concrete, Cape Town, NBRI of the Council for Scientific and Industrial Research, 

Pretoria, S.A., S252/22. 

Fournier, B. and Berube, M.A. 2000. “Alkali-aggregate reaction in concrete: a review of basic 

concepts and engineering implications.” Canadian Journal of Civil Engineering, 27: 167-191. 

Glasser, L.S. and Kataoka, N. 1981. "The chemistry of alkali-aggregate reactions." Proceedings 

of the 5th International Conference on Alkali-Aggregate Reaction, Cape Town, S252/23. 

Hadley, D.W. 1961. “Alkali reactivity of carbonate rocks; expansion and dedolomitization.” 

Proceedings of the Highway Research Board, 40: 462-474. 

Hansen, W.C. 1944. “Studies relating to the mechanism by which the alkali-aggregate reaction 

proceeds in concrete.” Journal of the American Concrete Institute, 15(3): 213-227. 

Helmuth, R., Stark, D., Diamond, S. and Moranville-Regourd, M. 1993. “Alkali-Silica 

Reactivity: An Overview of Research.” SHRP-C-342, Strategic Highway Research Program, 

National Research Council, Washington, D.C., 105 p. 

Hobbs, D.W. 1988. Alkali-Silica Reaction in Concrete. Thomas Telford, London, 183 p. 

Iler, R.K. 1979. The Chemistry of Silica. Wiley-Interscience, New York, 886 p. 

Jin, W., Meyer, C. and Baxter, S. 2000. “'Glascrete'—Concrete with Glass Aggregate.” ACI 

Materials Journal, 97(2): 208-213. 

Kawamura, M., Kayyali, O.A. and Haque, M.N. 1988. “Effects of a fly ash on pore solution 

composition in calcium and sodium chloride-bearing mortars.” Cement and Concrete Research, 

18: 763-773. 

Knudsen, T. and Thaulow, N. 1979. “Quantitative microanalyses of alkali-silica gel in 

concrete.” Cement and Concrete Research, 5: 443-454. 

32 
AAR Facts Book Chapter 2 – Fundamentals of ASR 

MacDonald, C.A., Rogers, C. and Hooton, R.D. 2012. “The relationship between laboratory 

and field expansion – observations at the Kingston outdoor exposure site for ASR after twenty 

years.” Proceedings of the 14th International Conference on Alkali-Aggregate Reaction in 

Concrete, Austin, TX, USA, May. 

McGowan, J.K. and Vivian, H.E. 1952. “Studies in cement-aggregate reaction: correlation 

between crack development and expansion of mortars.” Australian Journal of Applied Science, 

3: 228-232. 

Moranville-Regourd, M. 1989. "Products of Reaction and Petrographic Examination.” 

Proceedings of the 8th International Conference on Alkali-Aggregate Reaction, (Eds. K. Okada, 

S. Nishibayashi and M. Kawamura), Kyoto, The Soc. of Mat. Science, Japan, 445-456. 

Newlon, H.H., Jr. and Sherwood, W.C. 1964. “Methods for Reducing Expansion of Concrete 

Caused by Alkali-Carbonate Rock Reactions.” Highway Research Record No. 45, Highway 

Research Board, Washington, D.C., 134-150. 

Nixon, P.J. and Page, C.L. 1987. "Pore solution chemistry and alkali aggregate reaction." 

Concrete Durability, Katherine and Bryant Mather International Conference, (Ed. J.M. 

Scanlon), ACI SP-100, Vol. 2, American Concrete Institute, Detroit, 1833-1862. 

Pedneault, A. 1996. “Development of testing and analytical procedures for the evaluation of the 

residual potential of reaction, expansion, and deterioration of concrete affected by ASR.” M.Sc. 

Memoir, Laval University, Québec City, Canada, 133 p. 

Powers, T.C. and Steinour, H.H. 1955a. “An investigation of some published researches on 

alkali-aggregate reaction. I. The chemical reactions and mechanism of expansion.” Journal of 

the American Concrete Institute, 26(6): 497-516. 

Powers, T.C. and Steinour, H.H. 1955b. “An interpretation of some published researches on the 

alkali-aggregate reaction. Part 2: A hypothesis concerning safe and unsafe reactions with 

reactive silica in concrete.” Journal of the American Concrete Institute, 26(8): 785-811. 

Shayan, A. and Xu, A. 2004. “Value-added utilisation of waste glass in concrete.” Cement and 

Concrete Research, 34: 81–89. 

Stanton, T.E. 1940. “Expansion of concrete through reaction between cement and aggregate.” 

Proceedings of the American Society of Civil Engineers, 66(10): 1781-1811. 

Swenson, E.G. 1957. “A reactive aggregate undetected by ASTM tests.” American Society for 

Testing and Materials, 57: 48-51. 

33 
AAR Facts Book Chapter 2 – Fundamentals of ASR 

Swenson, E.G. and Gillott, J.E. 1964. “Alkali-carbonate rock reaction.” Highway Research 

Record, 45: 21-40. 

Tang, M., Ye, Y.F., Yuan, M.Q. and Zheng, S.H. 1983. "The preventive effect of mineral 

admixtures on alkali-silica reaction and its mechanism." Cement and Concrete Research, 13: 

171-176. 

Tang, M., Liu, Z. and Han, S. 1987. “Mechanism of alkali-carbonate reaction.” Proceedings of 

the 7th International Conference on Concrete Alkali-Aggregate Reactions, (Ed. P.E. GrattanBellew), Noyes Publications, New Jersey, 275-279. 

Thomas, M.D.A. 1998. “The Role of Calcium in Alkali-Silica Reaction.” Materials Science of 

Concrete - The Sidney Diamond Symposium, (Eds. M. Cohen, S. Mindess and J.P. Skalny), 

American Ceramic Society, Westerville, OH, 325-331. 

Thomas, M.D.A. 2001. “The role of calcium hydroxide in alkali recycling in concrete.” 

Materials Science of Concrete Special Volume on Calcium Hydroxide in Concrete, (Ed. J. 

Skalny, J. Gebauer and I. Odler), American Ceramic Society, Westerville, OH, 269-280. 

Thomas, M.D.A., Nixon, P.J. and Pettifer, K. 1991. “The effect of pfa on alkali-silica reaction.” 

Second CANMET/ACI Conference on the Durability of Concrete, (Ed. VM Malhotra), ACI SP126, II, American Concrete Institute, Detroit, 919-940. 

Thomas, M.D.A., Fournier, B., Folliard, K., Ideker, J. and Shehata, M. 2006. “Test methods for 

evaluating preventive measures for controlling expansion due to alkali-silica reaction in 

concrete.” Cement and Concrete Research, 36(10): 1842-1856. 

Urhan, S. 1987. “Alkali silica and pozzolanic reactions in concrete. Part 1: Interpretation of 

published results and an hypothesis concerning the mechanism.” Cement and Concrete 

Research, 17: 141-152. 

Wang, H. and Gillott, J.E. 1991. “Mechanism of Alkali-Silica Reaction and the Significance of 

Calcium Hydroxide.” Cement and Concrete Research, 21(4): 647-654. 

34 
AAR Facts Book Chapter 3 – Symptoms of ASR 

3 – Symptoms of Alkali-Silica Reaction (ASR) 

3.1 INTRODUCTION 

As mentioned before, three conditions are necessary to initiate and sustain AAR in concrete: (1) 

reactive mineral forms must be present in the aggregate materials, (2) the concentration of 

alkali hydroxides ([Na+

,K+-OH-]) in the concrete pore fluid must be high, and (3) sufficient 

moisture must be present. Concrete elements affected by AAR respond quite differently from 

one another, reflecting wide variations in the above conditions. 

Common visual symptoms of ASR consist of: 

• Cracking 

• Expansion causing deformation, relative movement, and displacement 

• Localized crushing of concrete 

• Extrusion of joint (sealant) material 

• Surface pop-outs 

• Surface discoloration and gel exudations 

A brief description and photographs of these symptoms are given hereafter. Additional 

photographs could be found in Thomas et al. (2011). 

3.2 CRACKING 

The pattern of cracking due to ASR is influenced by factors such as the shape or geometry of 

the concrete member, the environmental conditions, the presence and arrangement of 

reinforcement, and the load or stress fields (restraint) applied to the concrete. The classic 

symptom of ASR is map cracking (also called pattern cracking), which takes the form of 

randomly-oriented cracks on the surface of concrete elements that are relatively free 

(unrestrained) to move in all directions (Figures 3.1A & 3.1B). However, drying shrinkage, 

freezing/thawing cycles, and sulfate attack can also result in a pattern of cracks showing a 

random orientation. 

35 
 

A B 

C D 

E 

AAR Facts Book Chapter 3 – Symptoms of ASR 

Figure 3.1. A. Map-cracking in the wing wall of a 30-year-old bridge structure affected by ASR 

(CSA 2000). B. Severe map-cracking and associated gel staining around cracks in a median 

highway barrier affected by ASR. C. Well-defined crack pattern associated with the development 

of ASR in highway pavement; the orientation of predominant cracks is longitudinal, while map- or 

pattern-cracking is also identified. D. Preferred alignment of cracks in an ASR-affected concrete 

column. E. Longitudinal cracking in a precast, reinforced concrete beam affected by ASR. 

36 
AAR Facts Book Chapter 3 – Symptoms of ASR 

Steel reinforcement or other restraint arising from applied compressive stress may reduce ASR 

expansion in concrete. However, surface cracking due to AAR is often not significantly reduced 

by the use of internal or external restraint. When expansion is restrained in one or more 

directions, more expansion occurs in the direction of least confinement, and the cracks become 

oriented in the same direction as the confining stresses. For example, with concrete pavements, 

the expansion being restrained in the longitudinal direction, a greater amount of expansion 

occurs in the transverse direction and cracks develop preferentially in the longitudinal direction 

(Figure 3.1C); in the case of reinforced concrete columns, cracks tend to be aligned vertically 

due to the restraint imposed by the primary reinforcement and the dead load (Figure 3.1D); for 

prestressed bridge girders, the cracks will usually be aligned horizontally due to the 

confinement imposed by the prestressing tendons parallel to the beam axis (Figure 3.1E). 

In many cases, discoloration occurs around the cracks, often due to gel exudation in the vicinity 

of the cracks (Figure 3.1B). 

Cracking is usually most severe in areas of structures where the concrete has a renewable 

supply of moisture, such as close to the waterline in piers, from the ground behind retaining 

walls, beneath pavements slabs, elements/parts of structures exposed to rain, or by wick action 

in piers or columns (Figure 3.2). Concrete members undergoing ASR and experiencing cyclic 

exposure to sun, rain, and wind, or portions of concrete piles in tidal zones often show more 

severe surface cracking resulting from induced tension cracking in the “less expansive” (due to 

alkali leaching/dilution processes, variable humidity conditions, etc.) surface layer under the 

expansive thrust of the inner concrete core (Stark and Depuy 1987, ACI 1998) (Figure 3.3). 

37 
 

 

A B 

C D 

E 

AAR Facts Book Chapter 3 – Symptoms of ASR 

Figure 3.2. A&B. Map-cracking in wing walls (exposed elements) of bridge structures affected by 

ASR. C. Cracking in the column and the exposed portion of a beam affected by ASR. D&E. 

Cracking in the exposed portion (above ground) of the wing wall of a bridge structure affected by 

ASR; the wing wall has been excavated before being demolished. The lower ground portion 

shows limited cracking; discoloration occurs around the cracks above ground (E). 

38 
 

 

A 

B
 

3-D Humid Exp 

Water 

Table 

Surface layer shows less reactivity 

• Drier 

• Alkali leaching 

• Carbonation 

Saturated 

3-D 

Exp 

Saturated 

Humid 

Water 

Table 

AAR Facts Book Chapter 3 – Symptoms of ASR 

Figure 3.3. Concrete member undergoing ASR and experiencing cyclic exposure to sun, rain 

and wind show more severe surface cracking resulting from induced tension cracking in the 

“less expansive” (due to alkali leaching/dilution processes, variable humidity conditions, etc.) 

surface layer under the expansive thrust of the inner concrete core. 

39 
AAR Facts Book	 Chapter 3 – Symptoms of ASR 

3.3 EXPANSION CAUSING MOVEMENTS AND DEFORMATIONS 

The extent of ASR often varies between or within the various members/parts of an affected 

concrete structure, thus causing distresses such as: 

• relative movement of adjacent concrete members or structural units (Figure 3.4); 

• deflection, closure of joints with associated squeezing/extrusion of sealing materials, 

and, ultimately, spalling of concrete at joints (Figure 3.5). 

40 
 

 

A B 

C E 

D 

AAR Facts Book Chapter 3 – Symptoms of ASR 

Figure 3.4. A. Relative movement of abutting sections of parapet wall in a bridge structure affected by 

ASR (Stark 1991). B-D. Expansion of concrete pavement due to ASR (overlaid with asphalt), which 

pushes against the adjacent building foundation causing shearing of concrete columns. E. Concrete 

sidewalk made with alkali-carbonate reactive limestone aggregate. Originally, the sidewalk and the curb 

were adjacent to each other; however, the expansion of the sidewalk created a gap that had to be filled 

with asphalt. 

41 
 

A B 

C D 

Figure 3.5. A. Expansion of bridge girder leading to loss of clearance between the girder and 

embankment and eventually crushing of the girder end with localized spalling. B&C. Expansion 

causing spalling at joints in concrete pavement sections incorporating highly-reactive 

aggregates. D. Expansion with associated severe spalling in abutting jersey barrier sections 

affected by ASR. 

AAR Facts Book Chapter 3 – Symptoms of ASR 

It is important to remember that deformations in concrete structures may be caused by a range 

of different mechanisms, such as loading, thermal or moisture movements, differential 

shrinkage, gravity and foundation effects, hydraulic pressure, creep, impact, and vibrations 

(BCA 1992). 

42 
AAR Facts Book Chapter 3 – Symptoms of ASR 

3.4 POP-OUTS 

The expansion of individual unsound or frost-susceptible aggregate particles [such as 

laminated, schistose and argillaceous, clayey or porous particles or certain varieties (porous) of 

chert, ironstones] at or near the concrete surface due to frost action is likely to be the main 

factor for the development of pop-outs in northern countries (Figure 3.6A). Pop-outs can also 

be caused by a poor bond between the cement paste and dusty coarse aggregate particles. Alkali 

-silica reactive aggregates undergoing expansion near the concrete surface may also induce the 

detachment of a portion of the skin of concrete leaving the reactive aggregate in the bottom 

(Figure 3.6B). 

43 
 

A B 

C D 

E 

 

AAR Facts Book Chapter 3 – Symptoms of ASR 

Figure 3.6. A. Pop-out created by the expansion of a frost-susceptible porous coarse aggregate 

particle (leached chert). B. ASR-induced pop-out in a concrete pavement incorporating highlyreactive aggregates; also noted pattern cracking. C. Efflorescence and exudations of alkali-silica 

gel at the surface of the concrete foundation of 25-year-old highway bridge affected by ASR. D. 

Efflorescence and exudations of alkali-silica gel at the surface of a small concrete monument 

affected by ASR. E. Surface discoloration and exudation associated with cracks. 

44 
AAR Facts Book Chapter 3 – Symptoms of ASR 

3.5 SURFACE DEPOSITS (GEL EXUDATION VS. EFFLORESCENCE) 

Although surface gel exudation is a common and characteristic feature of ASR, the presence of 

surface deposits is not necessarily indicative of ASR as other mechanisms (such as frost action 

or the movement of water through cracked concrete members) can also cause surface deposits 

called efflorescence (without the presence of ASR gel) (Figures 3.5C-E). 

45 
AAR Facts Book Chapter 3 – Symptoms of ASR 

REFERENCES 

ACI Committee 221. 1998. “Report on Alkali-Aggregate Reactivity.” ACI 221.1R-98, 

American Concrete Institute, Farmington Hills, MI, 30 p. 

British Cement Association (BCA). 1992. “The Diagnosis of Alkali-Silica Reaction – Report of 

a Working Party.” Wexham Springs, Slough, U.K., SL3 6PL, 44 p. 

CSA. 2000. “Guide to the Evaluation and Management of Concrete Structures Affected by 

Alkali-Aggregate Reaction.” CSA A864-00, Canadian Standards Association, Mississauga, 

Ontario, Canada. 

Institution of Structural Engineers (ISE). 1992. “Structural Effects of Alkali-Silica Reaction – 

Technical Guidance Appraisal of Existing Structures.” Institution of Structural Engineers, 

London, 45 p. 

Stark, D. 1991. “Handbook for the Identification of Alkali-Silica Reactivity in Highway 

Structures.” SHRP-C/FR-91-101, TRB National Research Council, 49 p. 

Stark, D. and Depuy, G. 1987. “Alkali-Silica Reaction in Five Dams in Southwestern United 

States.” Proceedings of the Katherine and Bryant Mather International Conference on Concrete 

Durability, Atlanta, Georgia, USA, ACI SP-100, April, 1759-1786. 

Thomas, M.D.A., Fournier, B., Folliard, K.J. and Resendez, Y.A. 2011. “Alkali-Silica 

Reactivity Field Identification Handbook.” Office of Pavement Technology, Federal Highway 

Administration, 72 p. 

46 
AAR Facts Book Chapter 4 – Test Methods 

4 – Test Methods 

4.1 INTRODUCTION 

Ever since Stanton (1940) reported his discovery of alkali-aggregate reaction (AAR) in 

California, there has been keen interest in laboratory tests to (1) predict whether a given 

aggregate will cause expansion and cracking in concrete and (2) to evaluate preventive 

measures to allow for safe use of those aggregates found to be potentially reactive. This chapter 

describes the various test methods currently being used to assess the reactivity of aggregates 

(with regard to alkali-silica reaction (ASR) and alkali-carbonate reaction (ACR)). 

In addition to describing and recommending appropriate test methods for evaluating aggregate 

reactivity, this chapter also provides recommendations for tests aimed at evaluating measures 

for preventing ASR, such as supplementary cementing materials (SCMs) and lithium nitrate. 

Only limited information is provided on ACR, with the primary focus on test methods aimed at 

identifying aggregates susceptible to ACR so that they can be avoided for use in concrete as 

there are no available preventive measures for such aggregates. In addition to test methods 

aimed at assessing aggregate reactivity and preventive measures, this chapter also includes 

discussion on alkali release from aggregates and SCMs. There are no standardized tests that 

adequately address this important issue of alkali release, but for completeness, relevant 

information and recent trends are presented that should provide some useful insight to readers. 

4.2 ASR TEST METHODS FOR EVALUATING AGGREGATE REACTIVTY 

Stanton (1940) was not only the first to discover ASR in field structures, but he was also the 

first researcher to develop a test method to assess aggregate reactivity, and he used this 

technique to also evaluate the use of pozzolans to control ASR-induced expansion. The method 

developed by Stanton, which is essentially the same as the current ASTM C 227 test method, is 

still in use today by some researchers and practitioners, but a wide variety of test methods have 

been developed and implemented since the time of Stanton’s pivotal research on ASR. Some of 

these test methods have been successful, some have proven to be complete failures, and others 

fall somewhere in the middle. Through research and development, as well as trial and error, test 

methods have evolved over the years, and there has been a general convergence in terms of the 

tests that are generally used. This chapter describes the various test methods that are currently 

being used, discusses the positive and negative attributes of each test, and provides 

recommendations on what current standard tests are most appropriate for testing aggregate 

reactivity and preventive measures. 

47 
AAR Facts Book Chapter 4 – Test Methods 

Table 4.1 lists the most common standard test methods that have been or are currently being 

used to assess aggregate reactivity, including relevant comments related to the positive and/or 

negative attributes of each test. Discussion on each of these methods follows, with particular 

emphasis placed on the Accelerated Mortar Bar Test (AMBT) and Concrete Prism Test (CPT) 

as these two are the most commonly used ASR test methods and are integrated into AASHTO 

PP65-11, Standard Practice for Determining the Reactivity of Concrete Aggregates and 

Selecting Appropriate Measures for Preventing Deleterious Expansion in New Concrete 

Construction, which is a newly-developed standard practice developed under FHWA Project 

DTFH61-06-D-00035. 

4.2.1 ASTM C 295: Standard Guide for Petrographic Examination of Aggregates for Concrete 

A detailed petrographic examination, following ASTM C 295, provides useful information 

regarding the potential reactivity (with respect to both ASR and ACR) of a given fine or coarse 

aggregate. Within ASTM C 295 various techniques are employed that allow for the 

identification and quantification (through point count) of minerals that have been known to lead 

to expansion and cracking in concrete containing such aggregates. The specific minerals that 

are identified and quantified in ASTM C 295 are: 

• Opal 

• Chalcedony 

• Cristobalite 

• Tridymite 

• Highly Strained Quartz 

• Microcrystalline Quartz 

• Volcanic Glass 

• Synthetic siliceous Glass. 

The minerals listed above are found in a range of aggregate types, as per ASTM C 295, 

including: 

• Chert 

• Gneiss 

• Gneissic Granite 

• Graywacke 

• Phyllites 

• Schist 

• Vein Quartz 

• Sandstone 

• Quartzite 

48 
 

 

 

AAR Facts Book Chapter 4 – Test Methods 

Table 4.1. Test Methods for Evaluating Aggregate Reactivity 

Test Method Comments 

ASTM C 295: Standard Guide for Petrographic • Useful evaluation to identify many (but not all) potentially reactive 

Examination of Aggregates for Concrete components in aggregates. 

• Reliability of examination depends on experience and skill of 

individual petrographer. 

• Results should not be used exclusively to accept or reject aggregate 

source – findings best used in conjunction with other laboratory 

tests (e.g., AASHTO T 303 and/or ASTM C 1293). 

ASTM C 289: Standard Test Method for Potential 

Alkali-Silica Reactivity of Aggregates (Chemical 

Method) 

• Aggregate test in which crushed aggregate is immersed in 1M 

NaOH solution for 24 hours – solution is then analyzed for amount 

of dissolved silica and alkalinity. 

• Poor reliability. 

• Problems with test include: 

- Other phases present in aggregate may affect dissolution of silica 

(Bérubé and Fournier 1992). 

- Test is overly severe, leading aggregates with good field 

performance to fail the test. 

- Some reactive phases may be lost during pretest processing. 

ASTM C 227: Standard Test Method for Potential • Mortar bar test (aggregate/cement = 2.25), intended to study cement 

Alkali Reactivity of Cement-Aggregate -aggregate combinations. 

Combinations (Mortar-Bar Method) • Specimens stored in high-humidity containers at 38°C. 

• Several reported problems with test, including excessive leaching of 

alkalis from specimens. 

AASHTO T 303 (ASTM C 1260): Standard Test 

Method for Potential Alkali Reactivity of Aggregates 

(Mortar-Bar Method) 

• Mortar bar test, originally designed to assess aggregate reactivity. 

• Bars are soaked in 1N NaOH solution for 14 days. 

• Accelerated test suitable as screening test, but because of severity 

of test, it should not be used, by itself, to reject a given aggregate. If 

aggregate is tested using both AASHTO T 303 and ASTM C 1293, 

the results of ASTM C 1293 should govern. 

ASTM C 1293: Standard Test Method for Concrete 

Aggregates by Determination of Length Change of 

Concrete Due to Alkali-Silica Reaction 

• Concrete prism test, generally regarded as best indicator of field 

performance, is conducted at high humidity (close to 100%) at 38° 

C. 

• Uses high-alkali cement (raised to 1.25% Na20e), with a cement 

content of 420 kg/m3 

. 

• Developed as aggregate test (using non-reactive fine aggregate to 

test reactivity of coarse aggregate, and vice-versa). 

• Test requires one year for completion – this long duration limits its 

use by many agencies and owners. 

• Cannot be used to determine the alkali threshold for a given 

aggregate due to leaching of alkalis from the prisms during the 

course of the test. 

The identification and quantification of reactive phases within aggregates are accomplished 

following ASTM C 295 through the use of optical methods (using reflective and transmitted 

light) and may be aided with the complementary use of x-ray diffraction (XRD) and scanning 

49 
AAR Facts Book Chapter 4 – Test Methods 

electron microscopy (SEM). Most of the minerals that cause ASR can be identified and 

quantified, but some finely divided forms of quartz are not visible using a petrographic 

microscope. For example, some siliceous limestones contain less than 5 percent undetectable 

(using petrographic microscope) finely divided quartz particles, which can cause ASR-induced 

expansion in concrete (Fournier and Bérubé 1991). As such, caution should be taken in 

classifying a given aggregate as being non-reactive based solely on petrographic evaluation – 

information from other laboratory tests and/or field performance can be combined with such 

petrographic data/information to more accurately determine whether an aggregate may cause 

deleterious expansion in field structures. 

4.2.2 ASTM C 289: Standard Test Method for Potential Alkali-Silica Reactivity of Aggregates 

(Chemical Method) 

ASTM C 289, often referred to as the “Quick Chemical Test,” is a test that involves crushing an 

aggregate (passing the 300 μm sieve and retained on the 150 μm sieve), soaking it in 1 N NaOH 

solution for 24 hours at 80°C and measuring the amount of silica that goes into solution and the 

alkalinity at the completion of the test. The results of the test, specifically the amount of silica 

that went into solution and the reduction in the alkalinity of the soak solution, are plotted on a 

graph, contained in the Appendix to ASTM C 289. Based on how the data (amount of silica 

dissolved and reduction in alkalinity) plots within this graph, the aggregate is classified as 

innocuous, potentially deleterious, or deleterious. 

Although ASTM C 289 is still used by some researchers and practitioners, experience has 

shown that it is generally not an accurate predictor of aggregate reactivity, with many 

aggregates showing discrepancies between the classification (innocuous, potentially deleterious, 

or deleterious) obtained from ASTM C 289 and the performance of such aggregates in the 

concrete prism test (ASTM C 1293) or in actual field structures (Hooton 1990; Grattan-Bellew 

1989). The extreme severity of this test, specifically the high temperature and high alkalinity 

soak solution in which the aggregates are placed, coupled with the high surface area of the 

sample as a result of crushing, will cause some aggregates to be identified as reactive, even 

though such aggregates perform satisfactorily in ASTM C 1293 and in field structures (Bérubé 

and Fournier 1993). On the other hand, some reactive aggregates may lose most or all of their 

reactive phases during crushing and sieving and would thus be found to be innocuous per 

ASTM C 289, even though concrete containing such aggregates would exhibit significant 

expansion and cracking in the laboratory and field (Bérubé and Fournier 1992). Because of the 

above issues, ASTM C 289 is not recommended as a test method for evaluating aggregate 

reactivity, even though the test is still being used by some agencies and owners. 

50 
AAR Facts Book Chapter 4 – Test Methods 

4.2.3 ASTM C 227: Standard Test Method for Potential Alkali Reactivity of Cement-Aggregate 

Combinations (Mortar-Bar Method) 

ASTM C 227 is essentially the method Stanton (1940) developed of storing mortar bars (25 mm 

x 25 mm x 285 mm) over water at 38°C to provide for a high-temperature, high-humidity 

atmosphere within a sealed container. Because of the small cross section of the mortar bars used 

in this test, coarse aggregates must be processed by crushing, sieving, and washing in order to 

produce particles small enough to be used in the mortar bars. The aggregate to cement ratio is 

specified to be 2.25 (by mass), and there is no specific requirement for the cement to be used in 

the test. The ASTM standard specification for concrete aggregates (ASTM C 33) classifies an 

aggregate as being reactive when a given aggregate expands by more than 0.05% at 3 months or 

0.10% at 6 months. 

There are several technical problems associated with this test method, some of which spurred 

the development of more accurate methods for evaluating aggregate reactivity. The most 

significant issue with this test is that due to the small specimen cross section, appreciable 

amounts of the alkalis within the mortar bars leach out and end up residing in the water in the 

bottom of the container or being absorbed by the wicking material that lines the side of the 

container (Swenson 1957). Slowly-reactive aggregates are particularly sensitive to the leaching 

issue as the alkalis may leach from the bars before the aggregates ever have the opportunity to 

react and expand. Some slowly-reactive aggregates that have been observed to pass this test but 

that will fail more accurate tests and/or that will exhibit expansion and cracking in field 

structures include greywackes, argillites, quartzites, and some gneisses (Grattan-Bellew 1978; 

Stark 1980). Another issue with this test is that only fine aggregates can be tested so coarse 

aggregates have to be crushed, graded, and washed, which may alter the textural nature of the 

aggregates or remove some reactive phases. 

Given the technical issues associated with this test, specifically that a wide range of known, 

reactive aggregates will pass this test, it is not recommended as a test method for evaluating 

aggregate reactivity. 

4.2.4 AASHTO T 303 (ASTM C 1260): Standard Test Method for Potential Alkali Reactivity 

of Aggregates (Mortar-Bar Method) 

AASHTO T 303 (ASTM C 1260) is based on the method developed by Oberholster and Davies 

(1986) at the National Building Research Institute in South Africa. The test, often referred to as 

the accelerated mortar bar test (AMBT), has been adopted by various countries and agencies, 

including the United States (ASTM and AASHTO) and Canada. The test entails casting mortar 

bars containing the subject aggregate (either coarse or fine), which is processed to a standard 

gradation. The mortar bars are then removed from their molds after 24 hours and placed in 

51 
 

 

AAR Facts Book Chapter 4 – Test Methods 

water at room temperature. The temperature of the water is then raised to 80°C in an oven, and 

the mortar bars are stored in this condition for the next 24 hours. Upon removing the bars from 

the water, they are measured for initial length and then submersed in a 1N NaOH solution at 

80°C, where they are then stored for 14 days. Length change measurements are made 

periodically during this storage period. The total expansion at the end of the 14-day soaking 

period typically is used in specifications, although the expansion limits specified by different 

agencies vary. For example, the expansion criteria established by ASTM and CSA are as 

follows: 

ASTM C 1260 expansion criteria: CSA A23.2-25A expansion criteria: 

< 0.10% is considered innocuous > 0.15% (0.10% for limestones) is considered reactive 

0.10 to 0.20% is considered potentially reactive < 0.15% (0.10% for limestones) is considered non-reactive 

> 0.20% is considered reactive 

In ASTM C 1260, these expansion limits are proposed in an appendix to the standard test 

method and are not a mandatory part of the standard, whereas in CSA, the limits form part of a 

standard practice for assessing reactivity and evaluating the effectiveness of preventive 

measures (CSA A23.2-27A). AASHTO PP65-11 specifies a 0.10 percent expansion limit at 14 

days; aggregates with expansions below this are considered non-reactive. However, AASHTO 

PP65-11 cautions that AASHTO T 303 is not as accurate as the concrete prism test (ASTM C 

1293) for evaluating aggregate reactivity and that users who rely upon AASHTO T 303 are 

assuming some degree of risk in doing so. 

AASHTO T 303 is recognized as a very severe test method because of the extreme test 

conditions, specifically the use of a highly alkaline storage solution and high temperature. 

Because of this inherent severity, the test has been shown to identify some aggregates as being 

reactive, sometimes with expansions as high as 0.25 percent at 14 days, even though they have 

performed well in concrete prism testing (ASTM C 1293) and in field applications (Bérubé and 

Fournier 1992). In fact, recent, unpublished work performed by the authors of this Facts Book 

included the evaluation of an aggregate from Oahu that when tested according to AASHTO T 

303 expanded greater than 0.40 percent at 14 days but easily passed ASTM C 1293. Because 

AASHTO T 303 has been shown to fail a significant number of aggregates, especially natural 

sands and gravels, an aggregate should not be rejected based solely on the test results. 

More recently, a number of coarse aggregates have been found to pass AASHTO T 303 but fail 

ASTM C 1293 and expand and crack in outdoor exposure blocks (Folliard et al. 2006). Arrieta 

(2012) reported that the primary reason the aggregates tested by Folliard et al. (2006) passed the 

AASHTO T 303 test but failed ASTM C 1293 was related to the pessimum effect. Specifically, 

the primary reactive mineral was found petrographically to be chert, which is an aggregate 

known to exhibit a pessimum effect. The concept of the pessimum effect is shown graphically 

in Figure 4.1 (adapted from Poole (1992) by Arrieta (2012)). According to Poole (1992), the 

52 
 

 

 

 

AAR Facts Book Chapter 4 – Test Methods 

pessimum behavior proposes that ASR will cease when either the alkalis in the pore solution or 

the reactive constituents within the aggregate particles are depleted. If the content of the 

reactive mineral (chert, in this case) is too low compared to the availability of alkalis, very little 

gel will form and hence expansion will be limited. On the contrary, if there is an overabundance 

of reactive minerals compared to the availability of alkalis, the alkalis will become depleted and 

only a small amount of gel with form, with minimal expansion observed. When an optimum 

ratio of reactive silica to available alkalis is achieved (50 percent for the illustration in Figure 

4.1, and about 10-12 percent for most cherts), expansion will be at a maximum. 

0.3 

0.25 

0.2 

0.15 

0.1 

0.05 

0 

Amount of reactive aggregate present (%) 

Figure 4.1. Graphical Representation of the 'Pessimum' Behavior Concept 

(adapted from Poole (1992) by Arrieta (2012)) 

For the aggregates studied by Folliard et al. (2006) and evaluated in more detail by Arrieta 

(2012), AASHTO T 303 was modified by replacing the pessimum aggregate with varying 

amounts of non-reactive sand. Figure 4.2 shows the typical response for an aggregate from 

Central Texas. Based on petrographic evaluations, it was found that the chert content in this 

pessimum aggregate was approximately 75% of the as-received coarse aggregate. Figure 4.2 

takes the chert content into account, along with the level of replacement by the non-reactive 

aggregate, to plot the approximate chert content on the x-axis versus the expansion observed 

after 14 or 28 days storage in 1 N NaOH solution at 80°C. As shown in this figure, the 

pessimum proportion was found to be approximately 10 percent chert, which is consistent with 

past studies (Nixon et al. 1989; Hudec 1990). These results are encouraging in that they show 

that AASHTO T 303 can be used to not only identify pessimum aggregates but also to 

determine the actual pessimum proportion. Also, the results help to explain why these coarse 

aggregates failed the concrete prism test. The coarse aggregate content used in ASTM C 1293 is 

70 percent of the overall aggregate content. Assuming that 75 percent of the coarse aggregate is 

comprised of flint, the total amount of flint in the mixtures was about 52 percent, whereas in the 

unmodified AASHTO T 303 test, the coarse aggregate content was 100 percent, hence resulting 

in a chert content of 75 percent. Referring to Figure 4.2, the higher the chert content (beyond 

the pessimum proportion of about 10 percent), the lower the expansion. Only when the chert Measured expansion (%) 

0 10 20 30 40 50 60 70 80 90 100 

53 
AAR Facts Book Chapter 4 – Test Methods 

content was reduced by replacing the reactive sand with a non-reactive sand did expansion 

exceed the 0.10 percent expansion limit typically specified for AASHTO T 303. 

 

ASTM C 1260 expansion (%) 

0.450 

0.400 

0.350 

0.300 

0.250 

Expansion limit 

0.200 14 days 

0.150 28 days 

0.100 

0.050 

0.000 

0 10 20 30 40 50 60 70 80 

Chert present in the mixture (%) 

igure 4.2. Pessimum Graph for Coarse Aggregate from Central Texas, Expressed as Chert 

Percent, when using AASHTO T 303 Testing Regime (Arrieta 2012) 

F

In summary, AASHTO T 303 is a rapid test that in some cases yields results that agree with the 

results from ASTM C 1293 tests or field experience. However, as described herein, there are a 

wide range of aggregates that will give erroneous and misleading results in AASHTO T 303, 

when compared to the more accurate and realistic concrete prism test. As such, when both 

AASHTO T 303 and ASTM C 1293 data are available for a given aggregate, the ASTM C 1293 

data should be relied upon for assessing aggregate reactivity. 

4.2.5 ASTM C 1293: Standard Test Method for Concrete Aggregates by Determination of 

Length Change of Concrete Due to Alkali-Silica Reaction 

ASTM C 1293, commonly referred to as the concrete prism test, is generally considered the 

most accurate and effective test in predicting the field performance of aggregates. In this test, 

concrete is cast with a cement content of 420 kg/m3. The cement is required to have an 

equivalent alkali content between 0.8% and 1.0%, and additional alkalis (NaOH) then are added 

to the mixing water to obtain a total alkali content of 1.25% (by mass of cement), which equates 

to a total alkali content in the concrete mixture of 5.25 kg/m3. Concrete prisms are cast, cured 

for 24 hours at 23°C, and then stored over water at 38°C. Expansion measurements are taken at 

regular intervals, and when testing plain concrete (without SCMs or chemical admixtures), the 

test typically is run for one year (or as described later in this chapter, the test is conducted for 

two years when evaluating supplementary cementing materials or lithium-based admixtures). 

54 
AAR Facts Book Chapter 4 – Test Methods 

In recent years, more countries and agencies have adopted the concrete prism test as a standard 

method. An expansion limit of 0.04% (at the end of the one- or two-year test) typically is 

specified, as this value has been reported to correlate well with cracking of test prisms. This 

expansion limit (0.04%) is referenced in the appendix to ASTM C 1293 and in AASHTO PP65. 

Although ASTM C 1293 is generally regarded as the most accurate test for assessing aggregate 

reactivity, it is not without its limitations or drawbacks. Thomas et al. (2006) reported that 

approximately 35 percent of the internal alkalis within concrete prisms may leach out during the 

course of a one-year test, with as much as 20 percent of the alkalis leaching out in the first 90 

days, as shown in Figure 4.3. In this figure, the concentration of alkalis in the water at the 

bottom of the bucket (above which the prisms are stored) is shown as a function of time for a 

selected mixture following ASTM C 1293. Taking into account the volume of water at the 

bottom of the bucket and ignoring that some of the alkalis may be absorbed into the wicking 

material on the side of the bucket, Thomas et al. (2006) calculated the total amount of alkalis 

that leached from the prisms, arriving at the values shown above (20 percent after 90 days and 

35 percent after one year). As such, higher alkali contents are needed to cause expansion in the 

CPT than what is actually needed in field concrete or exposure blocks, which also limits the use 

of the CPT to estimate the alkali threshold for a given aggregate, as discussed in more detail 

next. 

80 

60 

40 

20 

0 

Alkali Concentration (mMol/Litre) 

K 

Na 

0 3 6 912

Age (months) 

Figure 4.3. Concentration of Alkalis Measured in the Water at the Bottom of an ASTM C 1293 

Container as a Function of Time (after Thomas et al. 2006) 

The effects of alkali leaching from concrete prisms tested during the course of an ASTM C 

1293 test were clearly illustrated in a study by Folliard et al. (2006), in which a series of three 

concrete mixtures with varying alkali loadings were cast using a highly-reactive sand from El 

Paso, Texas. Prisms from these mixtures were then tested using ASTM C 1293, and exposure 

55 
 

 

 

 

AAR Facts Book Chapter 4 – Test Methods 

blocks were cast and stored outdoors in Austin, Texas. Table 4.2 summarizes the CPT data at 

one year and the exposure block data after approximately 3.5 years of outdoor exposure. Of 

most significance is the mixture containing the low-alkali cement (Na20e=0.52 percent), whose 

prisms easily passed the 0.04 percent expansion criteria after the one-year ASTM C 1293 test 

but whose exposure blocks expanded and cracked significantly. The reason for this discrepancy 

is the leaching from the concrete prisms which dropped the concrete below its alkali threshold, 

thereby suppressing expansion. The larger exposure blocks were less susceptible to leaching 

and hence exhibited significant expansion and cracking. 

Based on these results, and results from other researchers, it is not recommended that one use 

ASTM C 1293 to determine the alkali threshold for a given aggregate or aggregate-binder 

combination.

 Table 4.2. Comparison of Expansions in ASTM C 1293 Compared to Outdoor Exposure 

Blocks, Highlighting Importance of Leaching in Concrete Prism Test (Folliard et al. 2006) 

Cement 

Alkalinity 

ASTM C 1293 – 

Expansion at one year 

Outdoor Exposure Blocks – Expansion 

after approximately 3.5 years 

0.52 0.01 0.88 

0.95 0.33 1.10 

1.25 0.59 1.07 

Another drawback to ASTM C 1293 is that the test duration (one year for aggregates, two years 

for preventive measures) is often deemed to be too long, especially in the United States. As 

such, very few agencies specify this test and very few practitioners run the test. The excessive 

duration is due to the fact that the storage conditions (storing real concrete prisms above water 

at 38°C) are nowhere near extreme as the AMBT, and the source of alkalis is finite and internal. 

Researchers have attempted to accelerate the test by increasing the storage temperature to 60°C, 

in hopes of generating relevant data in a few months instead of 1-2 years. However, as reported 

recently by Ideker et al. (2010), this accelerated version of the CPT yields significantly less 

expansion than the standard CPT for the following reasons: 

• Additional leaching of alkalis at 60°C, compared to 38°C 

• Additional prism drying observed at 60°C, compared to 38°C 

• Changes in pore solution at 60°C (Ettringite begins to dissolve, contributing sulfates to 

the pore solution at the expense of hydroxyl ions, thus lowering pore solution pH.) 

• The “non-reactive” sand used in conjunction with the subject coarse aggregate has 

major effect on expansions at 60 °C. 

56 
 

 

AAR Facts Book Chapter 4 – Test Methods 

Figure 4.4 shows the relationship between expansion after one year using the standard CPT at 

38°C and the expansion after 13 weeks using the accelerated CPT at 60°C (Ideker et al. 2010) 

for a range of aggregates (note all mixtures are plain concrete). A test duration of 13 weeks is 

based on previous research by the same authors where it was observed that most aggregates 

have exhibited most of their expansion by this point (see Figure 4.5). In addition, other 

researchers have proposed that expansions at 13 weeks in the accelerated CPT correlate best 

with one-year expansions in the standard CPT when testing plain concrete (without SCMs or 

lithium-based admixtures). 

Figure 4.4. Relationship between Expansion after One Year Using the Standard CPT (38°C) 

and the Expansion after 13 Weeks Using the Accelerated CPT (60°C) (Ideker et al. 2010) 

57 
AAR Facts Book Chapter 4 – Test Methods 

Figure 4.5. Expansion of Concrete Prisms Containing Spratt Limestone and Stored 

above Water at 38°C vs. 60°C (Folliard et al. 2006) 

Referring to Figure 4.4, it is quite evident that most of the data points are well below the line of 

equity, which represents expansion values that are identical for both test methods/durations. As 

such, the general trend is that expansion values obtained at 60°C are significantly lower than 

those at 38°C for the aforementioned reasons. For some of the aggregates tested by Ideker et al. 

(2010), the results of testing at the two different temperatures yielded similar classifications 

when using a 0.04 percent expansion limit, meaning that some aggregates “passed” both tests or 

“failed” both tests. From a specification point of view, this may be acceptable in that both 

versions of the CPT would conclude that the aggregate is either reactive or non-reactive (and 

such requiring preventive measures). However, there were also aggregates that yielded 

conflicting results when they were tested at the two different temperatures, with the 

classification being “fail” at 38°C and “pass” at 60°C. 

Because the two versions of the CPT can produce conflicting conclusions with regard to a 0.04 

percent expansion criteria, caution should be taken when considering the accelerated CPT, by 

itself or in parallel to the standard CPT, for a given application or project. 

4.3 ASR TEST METHODS FOR EVALUATING PREVENTIVE MEASURES 

When considering the use of reactive aggregates, it is essential that test methods exist that can 

determine the safe level or dosage of a given product to prevent or substantially reduce ASR58 
 

 

 

AAR Facts Book Chapter 4 – Test Methods 

induced expansion and cracking. This section will discuss and critique the most commonly used 

test methods that aim to achieve this goal. 

Table 4.3 details the most common test methods used to evaluate preventive measures, such as 

SCMs and lithium-based admixtures. Specific details are listed in the table for each test, but 

additional focus of this section is on ASTM C 1567, which is a modified version of AASHTO T 

303, and ASTM C 1293 as these two methods are the most commonly used test methods and 

the ones that are integrated into AASHTO PP65-11. 

Table 4.3. Test Methods for Evaluating Preventive Measures 

Test Method Comments 

ASTM C 441: Standard Test Method for • Mortar bar test, intended to assess effectiveness of SCMs in 

Effectiveness of Mineral Admixtures or Ground reducing ASR expansion. 

Blast-Furnace Slag in Preventing Excessive • Test uses high-alkali cement and PyrexTM glass. 

Expansion of Concrete Due to the Alkali-Silica • Test not very reliable because of the use of Pyrex glass, which is 

Reaction sensitive to test conditions and contains alkalis that may be released 

during the test. Test does not correlate well with data from concrete 

mixtures containing natural aggregates (Bérubé and Duchesne 

ASTM C 1567: Standard Test Method for • Mortar bar test, originally designed to assess aggregate reactivity. 

Determining the Potential Alkali-Silica Reactivity of • Bars are soaked in 1N NaOH solution for 14 days. 

Combinations of Cementitious Materials and • Should only be used for aggregates for which a reasonable 

Aggregate (Accelerated Mortar-Bar Method) correlation between AASHTO T 303 (ASTM C 1260) and ASTM C 

1293 has been established (see AASHTO PP65-11 for details). 

• ASTM C 1567 can be modified as per AASHTO PP65-11 to 

evaluate lithium nitrate-based admixtures, although ASTM C 1293 

is deemed to be a more effective test method for determining 

ASTM C 1293: Standard Test Method for Concrete 

Aggregates by Determination of Length Change of 

Concrete Due to Alkali-Silica Reaction 

• Modified version of concrete prism test, allows for testing SCMs, 

blended cements, and lithium admixtures. 

• Test duration is two years, with expansion limit of 0.04 percent. 

4.3.1 ASTM C 441: Standard Test Method for Effectiveness of Mineral Admixtures or Ground 

Blast-Furnace Slag in Preventing Excessive Expansion of Concrete Due to the Alkali-Silica 

Reaction 

This test method was developed by U.S. Bureau of Reclamation in the 1940s to evaluate SCMs 

(known as siliceous admixtures or pozzolans at the time) for the construction of the Davis Dam 

and other large projects (Gilliland and Moran 1949). The test is essentially the same as ASTM 

C 227, where small specimens (25x25 mm in cross section) are stored above water at 38°C, 

with one major difference – Pyrex (borosilicate) glass is used as a “model” reactive aggregate. 

The objective of the test is to have somewhat of an internal standard, Pyrex glass, that can be 

used to evaluate the relative efficacy of SCMs in reducing expansion. Specifically, the 

59 
 

 

AAR Facts Book Chapter 4 – Test Methods 

expansion after 14 days of storage above water at 38°C of mortar bars containing a high-alkali 

cement (0.95 to 1.05% Na2Oe) and either 25% fly ash or 50% slag cement is compared to the 

expansion of control mortar bars (portland cement only). The percentage reduction in expansion 

is then calculated. Although the test specifies the use of either 25% fly ash or 50% slag cement, 

other SCMs and dosages may also be used. Various ASTM specifications allow for the use of 

ASTM C 441 to assess the efficacy of SCMs in controlling ASR-induced expansion, as 

summarized in Table 4.4. 

Table 4.4. ASTM Materials Specifications and Expansion Limits for ASTM C 441 

Specification Limit 

ASTM C 618: Fly Ash and Natural 

Pozzolans 

14-day expansion of cement/fly ash blend ≤ expansion of control mix 

with low-alkali cement (≤ 0.60% Na2Oe) 

ASTM C 989: Ground Granulated Blast 

-Furnace Slag 

If job cement and proportions of cement and slag are known: 14-day 

expansion ≤ 0.020% 

Otherwise: 14-day expansion of cement/slag blend ≤ 25% of the 

expansion of control mix with the high-alkali cement only (i.e., slag 

should reduce expansion by at least 75% compared with the control) 

ASTM C 1240: Silica Fume 14-day expansion of blend of 90% cement and 10% silica fume ≤ 20% 

of the expansion of control mix with the high-alkali cement only (i.e., 

10% silica fume should reduce expansion by at least 80% compared 

with the control) 

ASTM C 595: Blended Hydraulic 

Cement 

14-day expansion of blended cement ≤ 0.020% 

and 

56-day expansion of blended cement ≤ 0.060% 

ASTM C 1157: Hydraulic Cement 

(Option R) 

14-day expansion of hydraulic cement ≤ 0.020% 

and 

56-day expansion of hydraulic cement ≤ 0.060% 

Although ASTM C 441 is referenced by all of the materials specifications shown in Table 4.4, 

this test method has numerous technical issues and has fallen out of favor with most agencies 

and owners. The test inherently suffers from the same major flaw described earlier for ASTM C 

227, specifically leaching of alkalis from the mortar bars. But in addition to this, the use of 

Pyrex glass adds other complexities and problems that have led to high variability in test 

results. Although Pyrex glass was selected with the intention of it being a “model” or 

“standard” reactive aggregate, several issues with the glass have limited the widespread use of 

ASTM C 441 to evaluate SCMs, in favor of ASTM C 1567 (described next) and ASTM C 

1293. Pyrex glass varies in its composition and particle size from source to source. Further, 

Pyrex glass, itself, contains relatively high alkali contents, which are released during the course 

of the test, and different sources of Pyrex glass will vary in alkali content. Hobbs (1989) 

showed that the amount of SCMs needed to reduce expansion triggered by Pyrex glass does not 

60 
 

 

may be used to evaluate 

preventive measures. 

1.0 –

If AMBT vs CPT data fall 

within this range, the AMBT 0.8 – 

0.6 – 

0.4 – 

0.2 – 

0 – 

Expansion in AMBT at 14 Days (%) 

0 0.1 0.2 0.3 0.4 0.5 0.6 

AAR Facts Book Chapter 4 – Test Methods 

correlate well with the SCM content needed to suppress expansion from natural aggregates used 

in concrete construction. Because of the technical issues with ASTM C 441, the high level of 

variability of test results, and the lack of correlation between Pyrex glass and natural 

aggregates, this test is not recommended as a means of evaluating SCMs for use in controlling 

ASR in concrete. 

4.3.2 ASTM C 1567: Standard Test Method for Determining the Potential Alkali-Silica 

Reactivity of Combinations of Cementitious Materials and Aggregate (Accelerated Mortar-Bar 

Method) 

ASTM C 1567 is essentially identical to AASHTO T 303, with the one exception that it is 

aimed at evaluating the use of SCMs. The test utilizes the same test specimens and storage 

conditions as AASHTO T 303 and is, as such, subject to the same issues and pitfalls as the 

standard version of the AMBT. First and foremost, if the aggregate to be evaluated does not 

produce accurate results when tested under AASHTO T 303, due to false negatives or false 

positives, it should be quite evident that the AMBT is not a suitable test for evaluating the 

specific aggregate in combination with SCMs to determine the dosage needed to control 

expansion. This is recognized in AASHTO PP65-11, as shown in Figure 4.6, where it is 

recommended that a reasonable correlation between AASHTO T 303 and ASTM C 1293 must 

first be developed for a given aggregate of interest; only upon obtaining such agreement 

between test methods can ASTM C 1567 then be used to evaluate preventive measures, such as 

SCMs, blended cements, and lithium admixtures. 

Expansion in CPT at 1 Year (%) 

Figure 4.6. Comparison of AMBT and CPT Data for the Purpose of Determining Whether 

the AMBT is Suitable for Evaluating Preventive Measures with a Specific Aggregate 

(after AASHTO PP65-11) 

61 
 

 

 

 

 

 

60 

50 

40 

30 

20 

10 

0 

'Safe Level' in Concrete Test (%)

S - Slag 

F - Fly Ash

 CI - Fly Ash 

CH - Fly Ash

 N - Pozzolan 

0 10 20 30 40 50 60 

'Safe Level' in Mortar Bar Test (%) 

AAR Facts Book Chapter 4 – Test Methods 

Once it has been determined that ASTM C 1567 is an appropriate test method for evaluating a 

given aggregate, past work has shown that there is generally a good agreement between ASTM 

C 1567 (using a 0.10 percent expansion limit at 14 days) and ASTM C 1293 (using a 0.04 

percent expansion limit at two years) when testing various SCMs (Thomas and Innis 1998), as 

shown in Figure 4.7. This figure illustrates that similar SCM dosages are needed in each of 

these tests to reduce the expansions below the aforementioned limits. 

Figure 4.7. Comparison of SCM Dosage Needed to Reduce Expansions below Test Limits for 

ASTM C 1567 and ASTM C 1293 (after Thomas and Innis 1998) 

When considering using lithium nitrate as an admixture in concrete, AASHTO PP65-11 

recommends ASTM C 1293 as the most suitable and accurate test for determining the requisite 

dosage to control expansion below an expansion limit of 0.04 percent at two years. The AMBT, 

in its current form, is not suited for testing lithium compounds as any lithium present in the 

mortar bars would be overwhelmed by the sodium hydroxide in the soak solution. AASHTO 

PP65-11 provides guidance, based on Tremblay et al. (2008), for how to test lithium 

compounds in a modified version of the AMBT. This approach recognizes that certain 

aggregates cannot be tested using the AMBT in conjunction with lithium nitrate as erroneous 

results are generated that do not correlate with actual performance in concrete prisms or 

exposure blocks. As such, the procedure recommended in AASHTO PP65-11 identifies such 

aggregates and requires that these aggregates only be tested using ASTM C 1293. Aggregates 

that are suitable for being tested in combination with lithium nitrate in the modified AMBT are 

also identified, and a testing regime is then specified that will arrive at an estimated dosage of 

lithium to control expansion, based on an extensive database that is correlated with CPT results. 

A broad overview of the approach specified in AASHTO PP65-11 is shown in Figure 4.8; 

readers are directed to Tremblay et al. (2008) for a more detailed description of this 

methodology for evaluating lithium nitrate in the modified AMBT (or in the CPT if it is deemed 

not possible to use the modified AMBT for a given aggregate). 

62 
 

 

AAR Facts Book Chapter 4 – Test Methods 

Figure 4.8. Approach to Using the Modified Accelerated Mortar Bar Test to Determine the 

Dosage of Lithium Nitrate (expressed as [Li]/ [Na+K]) to Adequately Suppress Expansion 

in Concrete (Tremblay et al. 2008) 

4.3.3 ASTM C 1293: Standard Test Method for Concrete Aggregates by Determination of 

Length Change of Concrete Due to Alkali-Silica Reaction 

The concrete prism test was initially developed for evaluating aggregate reactivity, but the most 

recent version, ASTM C 1293, has been modified to allow for testing SCMs as means of 

preventing or reducing deleterious expansion. The procedures and testing regimes are identical 

to those previously described for evaluating aggregate reactivity (see section 4.2.5), except for 

two significant modifications: (1) test duration is two years, and (2) SCMs may be used as 

replacement for portland cement (replacement by mass). 

In addition, when testing SCMs that significantly increase water demand, such as silica fume, 

ASTM C 1293 allows for the use of high-range water reducers (HRWR) meeting ASTM C 494. 

The dosage of HRWR may be adjusted to ensure adequate workability and sample preparation 

while still achieving the target w/cm of 0.42-0.45. Conversely, if SCMs are used that 

substantially reduce water demand, such as high-volume fly ash mixtures, a viscositymodifying admixture (VMA) may be used to minimize segregation and bleeding, while still 

achieving the target w/cm of 0.42 to 0.45. 

63 
AAR Facts Book Chapter 4 – Test Methods 

Testing SCMs using ASTM C 1293 carries with it the same inherent shortcomings encountered 

when testing aggregates in the concrete prism test. It is not possible to accurately assess the 

effects of cement alkalis (and to some extent alkalis from SCMs) due to leaching of alkalis from 

the prisms over a two-year period. Concerns raised over the long-term nature of ASTM C 1293 

when evaluating aggregates, which takes one year, are elevated when testing SCMs, as two 

years are required. This extended, two-year testing period is necessary to evaluate preventive 

measures, such as SCMs and lithium-based admixtures. 

However, because two years are need to test preventive measures using ASTM C 1293, it has 

led most agencies and owners in the United States to rely on ASTM C 1567 (accelerated mortar 

bar test) for evaluating and selecting preventive measures. As mentioned in the previous 

section, ASTM C 1567 is a suitable test for evaluating preventive measures, provided that the 

aggregate yields comparable results when tested using AASHTO T 303 and ASTM C 1293 (see 

Figure 4.6). For the aggregates meeting this criteria, AASHTO PP65-11 recommends the use of 

an expansion limit for ASTM C 1567 of 0.10 percent after 14 days as this correlates best with 

0.04 percent expansion after two years testing the same SCM(s) following ASTM C 1293 

(Thomas et al. 2007). 

Some agencies have specified a 28-day expansion criteria when evaluating SCM/aggregate 

combinations, but increasing from a 14- to 28-day expansion limit in ASTM C 1567 results in 

SCM levels significantly higher (that is, by 1.5 times on average) than that required to prevent 

damage in concrete, based on concrete prism tests and/or performance of outdoor exposure 

blocks (Thomas et al. 2007). The perception that much higher levels of SCM are required to 

control ASR may present a barrier to using such materials when potentially reactive aggregates 

are used due to concerns related to slow setting and strength gain, and even deicer salt scaling 

resistance. 

4.3.4 Other ASR Test Methods 

There are several other ASR test methods that have been developed and used, besides the ones 

previously described in this chapter, since the discovery of ASR in the late 1930s. Some of 

these methods are described briefly herein for completeness, including accelerated tests aimed 

at evaluating aggregate reactivity and tests related to alkali-release from aggregates and SCMs. 

Although the latter tests, those focusing on the release of alkalis from aggregates and/or SCMs, 

are not direct tests for ASR (e.g., expansion tests), they are discussed here because of the 

importance of alkali release in field structures. Although no standardized methods exist for 

accurately predicting the release of alkalis from aggregates and/or SCMs, some relevant studies 

and published literature are cited that should provide useful information on this important topic. 

64 
AAR Facts Book Chapter 4 – Test Methods 

Over the years, there has been interest in and research related to ultra-accelerated ASR test 

methods, where ASR is accelerated through the use of an autoclave, which can subject mortar 

specimens to high temperatures and pressures. Fournier et al. (1991) and Nishibayashi et al. 

(1996) conducted extensive work on autoclaved mortar tests – these tests generated results 

within a couple days (typically less than 24 hours) through the use of extremely high alkali 

loadings (2.0 to 3.5% Na2Oe by mass of cement), high autoclave pressures (up to 1.03 MPa), 

and high temperatures (up to 130°C). Fournier et al. (1991) and Giannini (2012) reported that 

the autoclaved test was as good as or better than the accelerated mortar bar test (AASHTO T 

303) at identifying reactive aggregates. There has only been limited work done on testing 

concrete prisms in an autoclave test (Nishibayashi et al. 1996). Overall the interest in autoclave 

testing lies in the rapid results, accomplished through high alkalinity, high temperature, and 

high pressure. This test is very aggressive and unrealistic compared to field exposure, and its 

only benefit would be that it generates results, for good or bad, in about a day instead of two 

weeks, as in AASHTO T 303. 

The Concrete Microbar Test (formerly the Chinese Accelerated Mortar Bar Method), was 

introduced by Xu and co-workers to capture reactivity of alkali-carbonate rocks (Xu et al. 1998; 

2000), but has since been used to identify aggregates susceptible to ASR (Lu et al. 2008; East 

2007). This mortar test uses larger specimens (40 mm x 40 mm cross section) and thus allows 

for testing larger aggregate particles, preserving the textural and mineralogical characteristics of 

the original coarse aggregate. This test is also advantageous for aggregates in which reactive 

phases are removed due to crushing and processing required in other accelerated mortar tests, 

such as AASHTO T 303 and ASTM C 227. 

Past laboratory and field evaluations have demonstrated that some aggregates may release 

significant amounts of alkalis into the pore solution of concrete, thus increasing the likelihood 

of ASR-induced expansion and cracking (Stark 1980; Thomas et al. 1992; Bérubé et al. 2002). 

There are no standardized tests for estimating the alkali release from aggregates. There is a 

general agreement that the total alkali content of an aggregate, as measured through bulk 

chemical analysis, is not indicative of the available alkalis that will be released from aggregates 

into the pore solution in concrete. Recent work by Bérubé et al. (2002) has shown promise in 

better estimating the alkali release from a given aggregate by measuring the release of 

potassium from the aggregate immersed in sodium hydroxide and measuring the release of 

sodium from the same aggregate immersed in potassium hydroxide. This technique maintains 

the type of alkaline environment in which the aggregate will reside and selectively promotes the 

release of the two critical alkalis present in aggregates that may have an adverse effect on ASR. 

The release of alkalis from SCMs, in general, and fly ash, in particular, into the pore solution of 

concrete has been the focus of considerable research over the years. ASTM C 311 (Standard 

Test Methods for Sampling and Testing Fly Ash or Natural Pozzolans for Use in Portland65 
AAR Facts Book Chapter 4 – Test Methods 

Cement Concrete) is a standard test that measures the total alkali content, as well as the 

“available” alkali content of fly ash. However, research has shown that ASTM C 311 does not 

accurately measure the available alkalis from within fly ash, mainly because the aqueous 

solution in which the fly ash is immersed (pH = 7) is vastly different from the highly-alkaline 

pore solution found in mature concrete, with pH values typically in excess of 13.2. To attempt 

to generate data that is more relevant to actual alkali release from fly ash to concrete pore 

solution, a method was developed by Shehata and Thomas (2006) in which mature paste 

specimens, containing subject fly ash, are immersed in various alkaline solutions that are 

intended to better mimic the pore solution in concrete (e.g., 0.25 OH- mol/L) undergoing ASR. 

The leaching of alkalis from the fly ash paste specimens is measured at the end of a 90-day 

immersion period, thereby directly measuring the alkali contribution from the fly ash to the host 

solution. Although the test developed by Shehata and Thomas (2006) is not a standardized test, 

it does show promise in being able to better estimate the release of alkalis from fly ash to 

concrete pore solution under realistic conditions. 

4.4 ACR TEST METHODS FOR EVALUATING AGGREGATE REACTIVITY 

ACR, described in chapter 9, is a unique form of AAR that is highly expansive and damaging to 

concrete structures. It is also a reaction for which there are no known preventive measures. 

Measures that are effective in controlling ASR, such as the use of low-alkali cement, SCMs, 

and lithium compounds, are ineffective in suppressing ACR-induced expansion. As such, the 

only safe strategy for dealing with ACR is to identify susceptible aggregates and disallow their 

use in concrete. This section briefly describes how practitioners and researchers can identify 

ACR-susceptible aggregates. 

AASHTO PP65-11 provides guidance, based primarily on Canadian experience, on how to 

evaluate aggregates that are potentially susceptible to ACR-induced expansion and cracking. 

The test methods recommended for evaluating aggregates potentially susceptible to ACR are 

presented in Table 4.5. 

66 
 

 

 

AAR Facts Book Chapter 4 – Test Methods 

Table 4.5. Test Methods for Evaluating Alkali-Carbonate Reactivity of Aggregates 

Test Method Comments 

ASTM C 295: Standard Guide for Petrographic 

Examination of Aggregates for Concrete 

• Useful evaluation to identify many (but not all) potentially reactive 

components in aggregates. 

• Reliability of examination depends on experience and skill of 

individual petrographer. 

• Petrographer focuses specifically on calcareous dolomites or 

dolomitic limestones with clayey insoluble residues, some dolomites 

essentially free of clay, and some very fine-grained limestones free 

of clay and with minor insoluble residue (mostly quartz). 

CSA A23.2-26A: Determination of Potential AlkaliCarbonate Reactivity of Quarried Carbonate Rocks 

by Chemical Composition 

• Measures the CaO, MgO, and Al2O3 content of quarried carbonate 

rocks. 

• Chemical composition plotted (see Figure 4.10) and classified as 

nonexpansive or potentially expansive. Guidance, including 

additional testing ̧ such as ASTM C 1105, is provided based on 

classification. 

ASTM C 1293: Standard Test Method for Concrete • Test method developed originally for evaluating aggregates 

Aggregates by Determination of Length Change of susceptible to ASR. 

Concrete Due to Alkali-Silica Reaction • Test method will also trigger ACR if such susceptible aggregates are 

present in mixture – petrography is required to confirm ACR is the 

cause of part or all of the measured expansion. 

ASTM C 1105: Standard Test Method for Length 

Change of Concrete Due to Alkali-Carbonate Rock 

Reaction 

• Similar test to ASTM C 1293, except lower cement alkali content is 

used. ASR will not occur at lower alkali loading, and as such, any 

observed expansion is assumed to be caused by ACR. 

• Expansion limits are 0.025 percent at 6 months or 0.030 percent at 1 

year. Aggregates exceeding limit(s) are considered to be alkalicarbonate reactive and shall not be used in concrete. 

A petrographic evaluation (ASTM C 295) is recommended when assessing the potential for an 

aggregate being susceptible to ACR. Aggregates prone to ACR are typically calcareous 

dolomites or dolomitic limestones with clayey insoluble residues. Figure 4.9 shows a unique 

petrographic feature of ACR – rhombs of dolomite floating in a fine-grained matrix of clay 

minerals, calcite and silica. 

67 
 

 

 

 

 

 

 

 

CaO/MgO Ratio 

200 

100 

50 

20 

10 

5 

2 

1 

Rock Cylinder ExpansionTest (ASTM C 586) 

<0.1% expansion at 4 weeks 

<0.1% at 4 weeks but >0.2% at 16 weeks 

>0.1% expansion at 4 weeks 

Concrete Prism ExpansionTest (CSA A23.2-14A) 

<0.025% expansion at 1 year 

in 1.25% Na2O equivalent cement 

<0.025% expansion at 1 year 

in 1.25% Na2

O equivalent cement 

Aggreg

consi

ates 

dered

 nonexpansive 

Aggregat

consid

es 

ered 

pot

 e

entially

xpansive 

Aggregates considered nonexpansive 

0 1 2 3 4 5 6 7 8 9 10 

Al2O3 in percent 

AAR Facts Book Chapter 4 – Test Methods 

Figure 4.9. A Unique Petrographic Feature Typical of ACR Susceptible Aggregates: Rhombs of 

Dolomite Floating in a Fine-grained Matrix of Clay Minerals, Calcite and Silica 

(photo courtesy of C. Rogers) 

If the aggregate being assessed is a quarried carbonate rock, the potential for alkali-carbonate 

reaction may be assessed on the basis of its chemical composition using the test method CSA 

A23.2-26A. This test involves the determination of the lime (CaO), magnesia (MgO), and 

alumina (Al2O3) content of the rock, and determining where the composition of the rock falls on 

a plot of CaO/MgO ratio versus the Al2O3 content, as shown in Figure 4.10. 

Figure 4.10. Using Chemical Composition as a Basis for Determining Potential AlkaliCarbonate Reactivity of Quarried Carbonates (from CSA A23.2-26A) 

68 
AAR Facts Book Chapter 4 – Test Methods 

If the composition falls in one of the two ranges identified as “aggregates considered nonexpansive” in Figure 4.10, the aggregate is not potentially alkali-carbonate reactive. However, 

the aggregate should be tested to determine the potential for alkali-silica reaction using the 

methods described in section 4.2. 

If the composition falls in the range of “aggregates considered to be potentially expansive” in 

Figure 4.10, the aggregate is potentially alkali-carbonate reactive and must be evaluated further. 

There are two options for further testing. One option is to test the aggregate in the concrete 

prism test, ASTM C 1293, to simultaneously determine the potential for alkali-carbonate and 

alkali-silica reactivity. After the test, the prisms are examined by petrography to determine the 

role played by the alkali-carbonate reaction. The second option is to test using the specific 

concrete prism test developed for ACR-susceptible aggregates, ASTM C 1105, which employs 

a reduced alkali loading to determine the potential for alkali-carbonate reaction only. If 

expansion of the specific aggregate-cement combination is equal to or greater than 0.025 

percent at 6 months or 0.030 percent at 1 year, the aggregate shall be considered to be alkalicarbonate reactive and shall not be used in concrete. If the specific aggregate-cement 

combination passes the above expansion criteria, it is considered not to be alkali-carbonate 

reactive but should still be evaluated for potential ASR reactivity (see section 4.2). 

4.5 SUMMARY 

This chapter briefly described the various test methods that have been or are currently being 

used to evaluate aggregate reactivity (with regard to ASR and ACR) and to evaluate preventive 

measures against ASR, such as the use of SCMs or lithium-based admixtures. The test methods 

recommended in this chapter are consistent with those integrated into AASHTO PP 65-11, the 

first nationwide recommended practice aimed at preventing ASR in new concrete construction. 

It is worth noting that the expansion limits and performance criteria recommended in this 

chapter are based extensively on the performance of large exposure blocks stored at outdoor 

exposure sites in the United States and Canada. As new data emerges from these sites and as 

blocks that had not previously expanded start to expand and crack, the expansion limits and 

performance criteria will evolve. It is hoped that future evolutions will increase the accuracy of 

AAR test methods and will also spur the development of improved test methods that better 

predict field performance. 

69 
AAR Facts Book Chapter 4 – Test Methods 

REFERENCES 

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AASHTO. 2008. “Standard Method of Test for Accelerated Detection of Potentially 

Deleterious Expansion of Mortar Bars Due to Alkali-Silica Reaction.” AASHTO T 303, 

American Association of State and Highway Transportation Officials, Washington, DC, 6 p. 

Arrieta, G. 2012. Experimental studies of the behavior of ‘pessimum’ aggregates in different 

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ASTM. 2013. “Standard Specification for Concrete Aggregate.” ASTM C 33, ASTM 

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ASTM. 2010. “Standard Test Method for Potential Alkali Reactivity of Cement-Aggregate 

Combinations (Mortar-Bar Method).” ASTM C 227, ASTM International, West Conshohocken, 

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ASTM. 2007. “Standard Test Method for Potential Alkali-Silica Reactivity of Aggregates 

(Chemical Method).” ASTM C 289, ASTM International, West Conshohocken, PA, 7 p. 

ASTM. 2012. “Standard Guide for Petrographic Examination of Aggregates for Concrete.” 

ASTM C 295, ASTM International, West Conshohocken, PA, 9 p. 

ASTM. 2013. “Standard Test Methods for Sampling and Testing Fly Ash or Natural Pozzolans 

for Use in Portland-Cement Concrete.” ASTM C 311, ASTM International, West 

Conshohocken, PA, 10 p. 

ASTM. 2011. “Standard Test Method for Effectiveness of Pozzolans or Ground Blast-Furnace 

Slag in Preventing Excessive Expansion of Concrete Due to the Alkali-Silica Reaction.” ASTM 

C 441, ASTM International, West Conshohocken, PA, 3 p. 

ASTM. 2012. “Standard Specification for Blended Hydraulic Cements.” ASTM C 595, ASTM 

International, West Conshohocken, PA, 13 p. 

ASTM. 2012. “Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan 

for Use in Concrete.” ASTM C 618, ASTM International, West Conshohocken, PA, 5 p. 

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AAR Facts Book Chapter 4 – Test Methods 

ASTM. 2012. “Standard Specification for Slag Cement for Use in Concrete and Mortars.” 

ASTM C 989, ASTM International, West Conshohocken, PA, 8 p. 

ASTM. 2008. “Standard Test Method for Length Change of Concrete Due to Alkali-Carbonate 

Rock Reaction.” ASTM C 1105, ASTM International, West Conshohocken, PA, 4 p. 

ASTM. 2011. “Standard Performance Specification for Hydraulic Cement.” ASTM C 1157, 

ASTM International, West Conshohocken, PA, 5 p. 

ASTM. 2012. “Standard Specification for Silica Fume Used in Cementitious Mixtures.” ASTM 

C 1240, ASTM International, West Conshohocken, PA, 7 p. 

ASTM. 2007. “Standard Test Method for Potential Alkali Reactivity of Aggregates (Mortar-Bar 

Method).” ASTM C 1260, ASTM International, West Conshohocken, PA, 5 p. 

ASTM. 2008. “Standard Test Method for Determination of Length Change of Concrete Due to 

Alkali-Silica Reaction.” ASTM C 1293, ASTM International, West Conshohocken, PA, 7 p. 

ASTM. 2013. “Standard Test Method for Determining the Potential Alkali-Silica Reactivity of 

Combinations of Cementitious Materials and Aggregate (Accelerated Mortar Bar Method.” 

ASTM C 1567, ASTM International, West Conshohocken, PA, 6 p. 

Berube, M-A., Duchesne, J., Doriona, J. and Rivest, M. 2002. “Laboratory assessment of alkali 

contribution by aggregates to concrete and application to concrete structures affected by alkali– 

silica reactivity.” Cement and Concrete Research, 32: 1215–1227. 

Bérubé, M.A. and Duchesne, J. 1992. “Evaluation of Testing Methods Used for Assessing the 

Effectiveness of Mineral Admixtures in Suppressing Expansion Due to Alkali-Aggregate 

Reaction.” Proceedings of the Fourth International Conference on Fly Ash, Silica Fume, Slag, 

and Natural Pozzolans in Concrete, (Ed. V.M. Malhotra), ACI SP132, Vol. 1, American 

Concrete Institute, Detroit, MI, 549–575. 

Bérubé, M.A. and Fournier, B. 1992. “Accelerated Test Methods for Alkali-Aggregate 

Reactivity.” Advances in Concrete Technology, (Ed. V.M. Malhotra), CANMET/EMR, Ottawa, 

Canada, 583–627. 

Bérubé, M.-A. and Fournier, B. 1993. “Testing for Alkali-Aggregate Reactivity in Concrete.” 

Memoria del Seminario Internacional sobre Tecnologia del Concreto, (Ed. R. Rivera Villareal), 

Universidad Autonoma de Nuevo Leon, Nuevo Leon, Mexico, October, 54-78. 

CSA. 2009. "Test Method for Detection of Alkali-Silica Reactive Aggregate by Accelerated 

Expansion of Mortar Bars.” CSA A23.2-25A. A23.2-09 - Test methods and standard practices 

for concrete, Canadian Standards Association, Mississauga, Ontario, Canada. 

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AAR Facts Book Chapter 4 – Test Methods 

CSA. 2009. "Determination of Potential Alkali-Carbonate Reactivity of Quarried Carbonate 

Rocks by Chemical Composition." CSA A23.2-26A. A23.2-09 - Test methods and standard 

practices for concrete, Canadian Standards Association, Mississauga, Ontario, Canada. 

CSA. 2009. "Standard Practice to Identify Degree of Alkali-Reactivity of Aggregates and to 

Identify Measures to Avoid Deleterious Expansion in Concrete.” CSA A23.2-27A. A23.2-09 - 

Test methods and standard practices for concrete, Canadian Standards Association, 

Mississauga, Ontario, Canada. 

East, B.L. 2007. “Laboratory and Field Investigations on the Use of Lithium Nitrate to Prevent 

or Mitigate Alkali-Silica Reaction.” M.S. Thesis, The University of Texas at Austin, Austin, 

TX, USA, 400 p. 

Folliard, K.J., Barborak, R., Drimalas, T., Du, L., Garber, S., Ideker, J., Ley, T., Williams, S., 

Juenger, M., Thomas, M.D.A. and Fournier, B. 2006. “Preventing ASR/DEF in New Concrete: 

Final Report.” The University of Texas at Austin, Center for Transportation Research (CTR), 

CTR 4085-5. 

Fournier, B., Berube, M. and Bergeron, G. 1991. “A Rapid Autoclave Mortar Bar Method to 

Determine the Potential Alkali-Silica Reactivity of St. Lawrence Lowlands Carbonate 

Aggregates (Quebec, Canada).” Cement, Concrete, and Aggregates, 13(1): 58-71. 

Fournier, B. and Bérubé, M.A. 1991. “Application of the NBRI Accelerated Mortar Bar Test to 

Siliceous Carbonate Aggregates Produced in the St. Lawrence Lowlands (Québec, Canada) — 

Part II: Proposed Limits, Rates of Expansion, and Microstructure of Reaction Products.” 

Cement and Concrete Research, 21:1069–1082. 

Giannini, E. 2012. Unpublished data. 

Gilliland, J.L. and Moran, W.T. 1949. "Siliceous admixture for the Davis Dam." Engineering 

News Record, 3 February, 62. 

Grattan-Bellew, P.E. 1978. “Study of Expansivity of a suite of quartzites, argillites and quartz 

arenites.” Proceedings of the 4th International Conference on the Effect of Alkalies in Cement 

and Concrete, Purdue University, Indiana, 113-140. 

Grattan-Bellew, P.E. 1989. “Test Methods and Criteria for Evaluating the Potential Reactivity 

of Aggregates.” Proceedings of the 8th International Conference on Alkali-Aggregate Reaction 

in Concrete, 279–294. 

Hobbs, D.W. 1989. “Effect of Mineral and Chemical Admixtures on Alkali-Aggregate 

Reaction.” Proceedings of the 8th International Conference on Alkali-Aggregate Reaction, 

(Eds. K. Okada, S. Nishibayashi, and M. Kawamura), E&FN Spon, 173-186. 

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Hooton, R.D. 1990. “Case Studies of Ontario Hydro’s Experience with Standard Tests for 

Alkali-Aggregate Reactivity.” Canadian Developments in Testing Concrete Aggregates for 

Alkali-Aggregate Reactivity, Ontario Ministry of Transportation Engineering Materials Report 

92: 181–189. 

Hudec, P.P. 1990. “Rapid test for predicting alkali reactivity: promises and problems.” 

Canadian developments in testing concrete aggregates for alkali-aggregate reactivity, 

University of Windsor Geology Department, Ontario, 111-117. 

Lu, D., Fournier, B., Grattan-Bellew, P., Xu, Z. and Tang, M. 2008. "Development of a 

Universal Accelerated Test for Alkali-silica and Alkali-carbonate Reactivity of Concrete 

Aggregates." Materials and Structures, 41(2): 235-246. 

Nishibayashi, S., Kuroda, T. and Inoue, S. 1996. Expansion Characteristics of AAR in Concrete 

by Autoclave Method. (Ed. A. Shayan), Melbourne, Australia, 370-376. 

Nixon, P.J., Page, C.L., Hardcastle, J., Canham, I. and Pettifer, K. 1989. “Chemical studies of 

alkali silica reaction in concrete with different flint contents.” 8th International Conference on 

Alkali-Aggregate Reaction, Kyoto, Japan. 

Oberholster, R.E. and Davies, G. 1986. “An Accelerated Method for Testing the Potential 

Reactivity of Siliceous Aggregates.” Cement and Concrete Research, 16: 181–189. 

Poole, A.B. 1992. “Introduction to alkali-aggregate reaction in concrete.” The alkali-silica 

rection in concrete, (Ed. R.N. Swamy), New York: Van Nostrand Reinhold, 1-28. 

Shehata, M.H. and Thomas, M.D.A. 2006. "Alkali Release Characteristics of Blended 

Cements." Cement and Concrete Research, 36: 1166–1175. 

Stanton, T.E. 1940. “Expansion of concrete through reaction between cement and aggregate.” 

Proceedings of the American Society of Civil Engineers, 66(10): 1781-1811. 

Stark, D. 1980. “Alkali-silica reactions: some reconsiderations.” Cement, Concrete and 

Aggregates, 2(2): 92-94. 

Swenson, E.G. 1957. “A reactive aggregate undetected by ASTM test.” ASTM Bulletin No. 

226: 48–50. 

Thomas, M.D.A., Blackwell, B.Q. and Pettifer, K. 1992. “Suppression of Damage from AlkaliSilica Reaction by Fly Ash in Concrete Dams.” Proceedings of the 9th International Conference 

on Alkali-Aggregate Reaction in Concrete, Vol. 2, The Concrete Society, Slough, UK, 1059­

1066. 

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AAR Facts Book Chapter 4 – Test Methods 

Thomas, M.D.A. and Innis, F.A. 1998. “Effect of Slag on Expansion Due to Alkali-Aggregate 

Reaction in Concrete.” ACI Materials Journal 95 (December): 716–24. 

Thomas, M.D.A., Fournier, B., Folliard, K., Ideker, J. and Shehata, M. 2006. “Test methods for 

evaluating preventive measures for controlling expansion due to alkali-silica reaction in 

concrete.” Cement and Concrete Research, 36(10): 1842-1856. 

Thomas, M. D. A., Fournier, B., Folliard, K.J., Shehata, M.H., Ideker, J.H. and Rogers, C. 

2007. “Performance Limits for Evaluating Supplementary Cementing Materials Using 

Accelerated Mortar Bar Test.” ACI Materials Journal, 104(2): 115-122. 

Thomas, M.D.A., Fournier, B. and Folliard, K.J. 2008. “Report on determining the reactivity of 

concrete aggregates and selecting appropriate measures for preventing deleterious expansion in 

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Research Council, Washington, D.C., A34. 

Tremblay, C., Bérubé, M.A., Fournier, B., Thomas, M.D.A., Folliard, K.J. and Nkinamubanzi, 

P.C. 2008. “Use of the Accelerated Mortar Bar Test to Evaluate the Effectiveness of LiNO3 

Against Alkali-Silica Reaction -- Part 2: Comparison with Results from the Concrete Prism 

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September 2008, 21 p. 

Xu, Z., Shen, Y., Lu, D., Deng, M., Lan, X., Hu, R. and Tang, M. 1998. "Investigation on A 

New Test Method for Determining the Alkali Silica Reactivity of Aggregates." Journal of 

Nanjing University of Chemical Technology, 20(2): 1-7. 

Xu, Z., Lan, X., Deng, M. and Tang, M. 2000. “A New Accelerated Method for Determining 

the Potential Alkali-Carbonate Reactivity.” Proceedings of the 11th International Conference on 

Alkali-Aggregate Reactivity, (Eds. M.A. Bérubé, B. Fournier, and B. Durand), CRIB, SainteFoy Québec, Canada, June, 129-138. 

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AAR Facts Book Chapter 5 – Prevention of ASR 

5 – Prevention of Alkali-Silica Reaction 

5.1 INTRODUCTION 

This chapter discusses various strategies for preventing alkali-silica reaction (ASR) in concrete, 

including avoiding reactive aggregates, controlling the alkali content of the concrete, using 

supplementary cementing materials, and the use of lithium-based compounds. The chapter does 

not discuss methods for preventing alkali-carbonate reaction (ACR). Strategies for controlling 

ASR are not generally effective for preventing ACR and, consequently, alkali-carbonate 

reactive rocks must not be used in concrete. Alkali-carbonate reaction is discussed in chapter 9. 

5.2 PREVENTIVE MEASURES – OPTIONS 

In chapter 2 it was shown that there are three basic requirements for damaging ASR to occur in 

concrete; these are: 

• A sufficient quantity of reactive silica (within aggregates) 

• A sufficient concentration of alkali (primarily from portland cement) 

• Sufficient moisture 

Elimination of any one of these requirements will prevent the occurrence of damaging alkalisilica reaction. Exclusion of water from civil engineering structures is not practical in most 

cases and so, from a consideration of the fundamental aspects of ASR discussed in chapter 2, 

the most obvious options for preventing expansion due to ASR are the following: 

1. Avoid the use of reactive aggregates 

2. Minimize the amount of alkalis from the portland cement 

Two other options are as follows: 

3. Use supplementary cementing materials (SCM) 

4. Use lithium-based compounds 

In fact, the use of SCM is a form of Option 2 as these materials consume a portion of the alkalis 

contributed by the portland cement and reduce their availability for reaction with the aggregate. 

Lithium compounds work in a different manner by changing the nature of the reaction product. 

Both of these mechanisms are discussed later in the chapter. 

75 
 

 

AAR Facts Book	 Chapter 5 – Prevention of ASR 

5.3 USE OF NON-REACTIVE AGGREGATES 

Using non-reactive, or more correctly, non-deleteriously-reactive, aggregates is certainly a 

viable method of preventing ASR-induced damage if such aggregates are available. Competent 

and thorough testing is required to ensure that aggregate sources are non-reactive. This can be 

achieved through a combination of petrographic examination, expansion testing of mortar 

(ASTM C 1260) or concrete (ASTM C 1293), and field performance. Such testing should be 

performed on a regular basis to ensure that the composition (and reactivity) does not change 

within a pit or a quarry. If the aggregate sources can be confirmed to be truly non-reactive, no 

further precaution is required to prevent ASR. 

There are a number of reasons why the option of using non-reactive aggregates is not always 

feasible; these include: 

• Non-reactive aggregates are not available locally and the cost of shipping non-reactive 

materials from other locations is prohibitive 

• Reactive aggregates that are otherwise wholly suitable for concrete are readily and 

abundantly available at lower cost and reduced environmental impact compared with 

non-reactive materials 

• Lack of confidence in test results (or testing laboratories) or test results are ambiguous 

(e.g., different test methods do not agree) 

• All of the locally-available materials fail the very aggressive accelerated test (regardless 

of true reactivity) 

In such cases, it is necessary to adopt one of the other options for preventing damaging ASR. 

Furthermore, some instances warrant extra caution even when using aggregates believed to be 

non-reactive; examples include the design of critical structures (e.g., prestigious structures or 

those with an extended design life) and the construction of structural elements exposed to a very 

aggressive environment (e.g., structures exposed to seawater or deicing salts, which may 

provide an external source of alkalis). 

5.4 LIMITING THE ALKALI CONTENT OF THE CONCRETE 

Stanton's (1940) formative work on ASR indicated that expansive reaction is unlikely to occur 

when the alkali content of the cement is below 0.60% Na2Oe. However, later research indicated 

that damaging ASR could occur both in the laboratory and in the field (e.g., Woolf 1952; Stark 

1980; Blaikie et al. 1996) when low-alkali cements are used. Despite this, the 0.60% value has 

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AAR Facts Book Chapter 5 – Prevention of ASR 

become the accepted maximum limit for cement to be used with reactive aggregates in the 

United States, and appears in ASTM C 150 Standard Specification for Portland cement as an 

optional limit when concrete contains deleteriously reactive aggregate. Appendix X1 of ASTM 

C 33 Standard Specification for Concrete Aggregates includes “low-alkali cement” (meeting the 

ASTM C 150 limit of 0.60% Na2Oe) as a measure “known to prevent excessive expansion.” 

Limiting the alkali level of the cement takes no account of the cement content of the concrete 

which, together with the cement alkali content, governs the total alkali content of concrete, and 

is considered to be a more accurate index of the risk of expansion when a reactive aggregate is 

used in concrete. Figure 2.12 (in chapter 2) shows the relationship between alkali content and 

expansion for concretes produced with a range of cement contents and cements of varying 

alkali content (Lingård et al. 2012). The figure was produced using previously unpublished data 

from the Building Research Establishment (Blackwell, private communication). The 

relationship clearly shows that it is the product of cement content and cement alkali level (i.e., 

the alkali content of the concrete) that controls the alkali content rather than the cement alkali 

level alone. 

Figure 5.1 shows expansion of concrete prisms plotted against the alkali content of the concrete 

for three different reactive aggregates (selected to demonstrate the range of behavior observed). 

It can be seen that the threshold alkali content required to initiate damaging expansion in the 

concrete prism test varies considerably between aggregates, with values ranging from 

approximately 3.0 kg/m3

 (5 lb/yd3) Na2Oe to more than 5.0 kg/m3 (8.3 lb/yd3) Na2Oe for the 

aggregates shown in Figure 5.1. 

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AAR Facts Book Chapter 5 – Prevention of ASR 

Figure 5.1. Effect of Alkali Content on Expansion of Concrete Prisms (Stored over Water at 

38oC, 100oF) with Different Aggregates (data from Thomas et al. 1996 and Figure 2.12) 

A number of specifications have employed a maximum concrete alkali content as an option to 

control expansion in concrete containing reactive aggregates. Nixon and Sims (1992) reported 

that maximum permissible alkali contents between 2.5 and 4.5 kg/m3

 (4.2 to 7.5 lb/yd3) Na2Oe 

have been specified by various countries and agencies, with the allowable alkali content 

sometimes varying depending on aggregate reactivity. 

Unfortunately, traditional concrete prism tests tend to underestimate the threshold alkali content 

for aggregates as a result of alkali being leached from the concrete during exposure. This 

phenomenon has been discussed in literature (Thomas et al. 2006; Lindgård et al. 2012) and a 

further example is shown in Figure 5.2. The figure shows the expansion of concrete blocks 

(0.38 x 0.38 x 0.71 m, 15 x 15 x 28 in.) containing reactive (Jobe) sand and various levels of 

alkali, and stored on an outdoor exposure site at the University of Texas in Austin, compared 

with the expansion of concrete prisms from the same mix stored over water (ASTM C 1293). It 

is evident that the concrete prism test will yield a higher threshold alkali content than may be 

observed for larger elements stored under field conditions. 

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AAR Facts Book Chapter 5 – Prevention of ASR 

Figure 5.2. Effect of Alkali Content on the Expansion of Blocks Stored Outdoors and Prisms 

Stored over Water (unpublished data from the University of Texas at Austin) 

In 2000, CSA A23.2-27A introduced a “sliding-scale” for the alkali limit used as a preventive 

measure, the value varying from 1.8 to 3.0 kg/m3 (3 to 5 lb/yd3) Na2Oe as follows: 

Table 5.1. Alkali Limits Specified in CSA A23.2-27A 

Level of prevention 

required 

Alkali limit (Na2Oe) 

kg/m3 lb/yd3 

Mild (W) 3.0 5.0 

Moderate (X) 2.4 4.0 

Strong (Y) 1.8 3.0 

Exceptional (Z) 1.8 + SCM 3.0 + SCM 

As the data available from laboratory tests at the time was considered unreliable for the purpose 

of establishing threshold alkali values, the maximum alkali content limits were based on 

published data from structures and field experience. Thomas (1996a) had previously reported 

damaging ASR in concrete dams in the U.K. and Canada where the estimated alkali content was 

in the range of 2.0 to 2.4 kg/m3

 (3.3 to 4.0 lb/yd3) Na2Oe. Rogers et al. (2000) reported results 

from a study of 8-year-old concrete blocks (0.6 x 0.6 x 2 m, 2 x 2 x 6.6 ft) stored on an 

exposure site in Ontario, Canada. Specimens produced with high-alkali cement showed very 

significant expansion and cracking after 8 years. Specimens with low-alkali cement (0.46% 

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AAR Facts Book Chapter 5 – Prevention of ASR 

Na2Oe) and a calculated alkali content of 1.91 kg/m3 (3.18 lb/yd3) Na2Oe showed significantly 

less expansion; however, the expansion did exceed 0.04% at 8 years and small cracks were 

evident. Subsequent investigations (Hooton et al. 2006; MacDonald et al. 2012) of these blocks 

at later ages (14 and 20 years) confirmed the presence of significant ASR-induced damage in 

the blocks produced with low-alkali cement and measured expansion of approximately 0.08% at 

20 years (see Figure 5.3). Based on the information available, a maximum alkali limit of 1.8 kg/ 

m3 (3.0 lb/yd3) Na2Oe was selected for Prevention Level Y (e.g., concrete with highly reactive 

aggregate, exposed to moisture with a service life up to 75 years), and it was decided to require 

the same limit plus incorporate minimum levels of supplementary cementing material (SCM) 

for Level Z. This was supported by anecdotal evidence available to the committee preparing the 

guidelines, there being no known case of ASR in concrete structures with lower alkali contents. 

In the absence of any other data, the same alkali limits were adopted in AASHTO PP65-11; this 

is discussed further in chapter 6. 

Figure 5.3. Expansion of Concrete Prisms in the Laboratory and Concrete Blocks and Slabs on 

the Kingston Exposure Site (data from MacDonald et al. 2012) 

Aggregates that are used in concrete with an alkali content below the threshold for expansion 

may cause damaging expansion if the alkali content of the concrete increases at some locations 

during the service life of the structure. This may occur through alkali concentration caused by 

drying gradients, alkali release from aggregates, or the ingress of alkalis from external sources, 

such as deicing salts or seawater (Nixon et al. 1987). Stark (1978) reported increases in soluble 

alkali from 1.1 to 3.6 kg/m3

 Na2Oe close to the surface of some highway structures. Migration 

of alkalis due to moisture, temperature, and electrical gradients has also been demonstrated by 

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AAR Facts Book Chapter 5 – Prevention of ASR 

laboratory studies. 

Alkali migration can occur very early in the life of concrete and has been implicated as the 

cause of popouts at the surface of slabs (Cong et al. 2004; Landgren and Hadley 2002). Alkalis 

may be carried upwards with the bleed water in freshly placed concrete, and this migration may 

be exacerbated during and after setting by the evaporation of water from the surface of the slab 

especially during hot, dry weather. The concentration of alkalis at the surface leads to ASR in 

the near surface of the concrete where the formation of gel and expansion of aggregates can 

lead to the fracture of a small conical-shaped mortar fragment (popout) overlying the reacting 

aggregate. Oftentimes the damage is restricted to the surface of the concrete where the alkalis 

are concentrated as there is insufficient alkali in the bulk concrete to cause damage. Some 

studies have reported surface concentrations that are as much as six times the alkali 

concentration in the bulk concrete (Nixon et al. 1979). This phenomenon can occur even when 

low-alkali cement or pozzolans are used (Cong et al. 2004). 

A number of workers have demonstrated that many aggregates contain alkalis that may be 

leached out into the concrete pore solution, thereby increasing the risk of alkali-aggregate 

reaction. Stark and Bhatty (1986) reported that, in extreme circumstances, some aggregates 

release alkalis equivalent to 10% of the portland cement content. A comprehensive review on 

alkali release from aggregates, including methods for determining the “releasable or available 

alkali” in aggregates, has been presented by Berube et al. (2002). 

Supplementary cementing materials (SCM), such as fly ash, silica fume, slag, and natural 

pozzolans may also contain significant quantities of alkali. However, these alkalis generally do 

not need to be included in the calculation of the concrete alkali content as SCMs tend to reduce 

the alkalis that are available for reaction with the aggregate; this is discussed in the next section. 

5.5 USE OF SUPPLEMENTARY CEMENTING MATERIALS 

One of the most efficient means of controlling ASR in concrete containing reactive aggregates 

is the appropriate use of supplementary cementing materials (SCM). Such materials include 

pozzolans (e.g., fly ash, silica fume, calcined clay, or shale) and ground-granulated blast 

furnace slag. The potential use of pozzolans to control ASR dates back as far as the discovery 

of ASR, having been reported in the first major publication on the phenomenon (Stanton 1940). 

In this paper, Stanton not only demonstrated that damaging reaction would only occur if there 

was a sufficient quantity of alkalis in the portland cement and reactive silica in the aggregate, 

but also that expansion was reduced when a pozzolanic cement was used. Ten years later, 

Stanton (1950) further demonstrated that partially replacing portland cement with a sufficient 

quantity of pozzolan (pumicite or calcined shale) eliminated deleterious expansion whereas 

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AAR Facts Book	 Chapter 5 – Prevention of ASR 

replacement with similar quantities of ground quartz (Ottawa) sand did not, indicating that the 

beneficial action of the pozzolan extended beyond merely diluting the cement alkalis. In the 

early 1950s, various studies (Cox et al. 1950; Barona 1951; Buck et al. 1953) showed that other 

supplementary cementing materials (SCM), namely fly ash and slag, were also effective in 

reducing expansion. 

Since these early studies there have been literally hundreds of studies and technical papers 

dealing with the effects of SCM on ASR, and it is now generally recognized that the use of a 

sufficient quantity of a suitable SCM is one of the more efficient preventive measures for 

controlling expansion when a deleteriously reactive aggregate is used in concrete (Thomas et al. 

2008). Thomas (2011) reviewed selected published works dealing with (i) the mechanisms by 

which SCM controls ASR, (ii) the effect of SCM composition on its efficacy in this role, and 

(iii) test methods for determining the amount of SCM required to minimize the risk of 

damaging expansion to an acceptable level. 

Thomas (2011) showed that almost any SCM can be used to control ASR provided it is used at 

a sufficient level of replacement. The amount required varies widely depending on, among 

other things, the following: 

• The nature of the SCM (especially mineralogical and chemical composition); more 

SCM is required as its silica content decreases or as its alkali and calcium content 

increase, 

• The nature of the reactive aggregate; generally, the more reactive the aggregate, the 

higher the level of SCM required, 

• The availability of alkali within the concrete (i.e., from the portland cement and other 

sources); the amount of SCM required increases with the amount of available alkali, and 

• The exposure conditions of the concrete; concrete exposed to external sources of alkali 

may require higher levels of SCM. 

Figure 5.4 shows the (conceptual) relationship between the (long-term) expansion of concrete 

and the level of replacement for different SCMs. Generally, as the level of replacement 

increases with a particular SCM, the expansion decreases and eventually reaches an acceptable 

level at which no damage occurs. SCMs that are very high in reactive silica, such as silica fume 

and metakaolin, tend to be very efficient in controlling expansion and are only required at 

relatively low levels of replacement (e.g., 10 to 15%). On the other hand, SCMs with lesser 

amounts of silica, such as Class C fly ash and slag, need to be used at higher levels of 

replacement (e.g., ≥ 40%). Some SCMs (e.g., some Class C fly ashes) may produce a pessimum 

effect by increasing the amount of expansion (compared to concrete without SCM) if they are 

used at low levels of replacement, but decreasing expansion at higher levels of replacement. 

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AAR Facts Book Chapter 5 – Prevention of ASR 

Level of replacement required to

control ASR expansion increases as: 

• SiO2 of SCM decreases 

• CaO of SCM increases 

• Alkali content of SCM 

• Alkali available in the concrete 

increases 

• Reactivity of aggregate increases 

Figure 5.4. Expansion versus SCM Content - Conceptual Relationship (Thomas 2011) 

It is generally considered that the principal mechanism by which SCMs control ASR expansion 

is by reaction with and consumption of the alkalis in the concrete pore solution which reduces 

the alkali available for reaction with the aggregates. However, the use of SCMs also results in a 

reduction in the availability of calcium (due to the dilution of and consumption of calcium 

hydroxide) and in a refinement in the pore structure, which leads to reduced ionic and moisture 

diffusivity; these effects may also be beneficial in terms of minimizing the risk and extent of 

ASR (Thomas 2011). 

This section begins with a discussion on the effect of SCMs on the composition of the pore 

solution and the availability of alkalis, and then provides examples on the impact of SCMs on 

the expansion of concrete. The role of SCM composition, cement alkalis, and aggregate 

reactivity on the expansion of concrete containing SCMs is also discussed. 

5.5.1 Effect of SCM on the Availability of Alkalis 

Although all SCMs contain some level of alkali and some may contain significantly more alkali 

than the portland cement that they partially replace, the main mechanism by which SCMs 

reduce expansion due to ASR is by reducing the alkalis that are available to the concrete pore 

solution. Once the alkalis in the binder phase (portland cement + SCM) of concrete are 

“released” by hydration they may be present in one of three ways: dissolved within the pore 

solution, bound by the hydration products, or incorporated in alkali-silica gel. In the absence of 

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AAR Facts Book Chapter 5 – Prevention of ASR 

reactive aggregate, alkalis will not be consumed by ASR, and the partition of the alkalis 

between the pore solution and the hydrates is largely a function of the composition of the 

binder. 

Numerous workers have shown that SCMs have a significant impact on the concentration of 

alkalis in the pore solution (see Thomas 2011). Studies on the effect of fly ash and slag on the 

pore solution of pastes have been reviewed by Thomas (1996b), and studies involving silica 

fume have been reviewed by Thomas and Bleszynski (2001). These studies show that the 

incorporation of most SCMs leads to a reduction in the concentration of alkali hydroxides in the 

pore solution of pastes, mortar, and concretes, the amount of reduction increasing with higher 

SCM replacement levels. Figure 5.5 shows the evolution of the hydroxyl ion concentration of 

the pore solution extracted from sealed paste samples with w/cm = 0.50, and Figure 5.6 shows 

the OH- concentration at 2 years as a function of the level of SCM (Shehata et al. 1999; 

Ramlochan et al. 2000; Bleszynski 2002; Shehata and Thomas 2002). Silica fume is the most 

efficacious SCM in this role, at least initially, followed by metakaolin, low-calcium fly ash, and 

slag. High-calcium or high-alkali fly ashes are less effective and have to be used at relatively 

high levels of replacement to produce a significant reduction in the pore solution alkalinity. It is 

interesting to note that in the case of the paste with 10% silica fume the OH- concentration 

drops rapidly over the first 28 days but then starts to increase slowly with time beyond 3 

months; similar behavior was observed in pastes containing 5% silica fume (Shehata and 

Thomas 2002). This behavior is not observed for pastes containing any of the other SCMs. As 

shown in Figure 5.5, the long-term increase in the OH-

 concentration seems to be prevented in 

pastes containing 5% silica fume by the addition of either slag (25%) or fly ash (15%). It is 

conjectured that the presence of alumina in the SCM possibly contributes in some way to 

prevent the long-term release of alkalis back in to the pore solution. Hong and Glasser (2002) 

showed that introducing alumina into C-S-H, to form C-A-S-H, markedly increases its alkalibinding capacity, and they suggest that this partially explains the beneficial effects of aluminous 

SCM with regards to reducing pore solution alkalinity and the potential for ASR. 

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AAR Facts Book Chapter 5 – Prevention of ASR 

Figure 5.5. Evolution of the Pore Solution in Pastes Containing SCM (Shehata et al. 1999; 

Ramlochan and Thomas 2000; Bleszynski 2002; Shehata and Thomas 2002) 

Figure 5.6. Effect of Type and Amount of SCM on Pore Solution Composition (Shehata et al. 

1999; Ramlochan et al. 2000; Bleszynski 2002; Shehata and Thomas 2002) 

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AAR Facts Book	 Chapter 5 – Prevention of ASR 

Figure 5.7 shows an empirical relationship between the OH- concentration of the pore solution 

extracted from 2-year-old sealed pastes with w/cm = 0.50 (Thomas and Shehata 2004; Thomas 

and Folliard 2007) and a “chemical index” derived from the chemical composition of the 

binder. 

Figure 5.7. Relationship Between Pore Solution Composition and the Chemical 

Composition of the Binder (Thomas 2011) 

A total of 79 different binders were tested including the following: 

• 100% portland cement at a range of different alkali contents (0.36 to 1.09% Na2Oe), 

• Binary mixes with 25 to 70% fly ash using 18 different fly ashes with a range of 

chemical compositions (1.1 to 30.0% CaO, 1.4 to 9.7% Na2Oe), 

• Binary mixes with 25 to 50% slag, 5 to 10% silica fume and 10 to 20% metakaolin; each 

SCM came from a single source, and 

• Ternary mixes containing silica fume blended with either slag or fly ash; both lowcalcium and high-calcium fly ash were used. 

The relationship was derived empirically to find the “chemical index” that was most reliably 

correlated to the OH-

 concentration based on a least-square fit. The best-fit index was found to 

be the product of the equivalent alkalis and calcium divided by the square of the silica content 

of the binder (Na2Oe x CaO)/(SiO2)

2

. Although this is an empirical relationship it makes sense 

intuitively because the alkalinity of the pore solution can be expected to be a function of the 

alkalis in the binder and the ability of the hydrates to bind alkalis, which has been shown to be a 

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AAR Facts Book Chapter 5 – Prevention of ASR 

function of the calcium-to-silica ratio of the binder (see discussion below). The alumina content 

of the binder was not found to be statistically significant based on the empirical analysis 

conducted using this dataset, despite the apparent benefit of alumina discussed above. 

Analyzing the composition of the pore solution extracted from a paste sample only provides one 

point on the equilibrium curve between bound and free alkalis. If the alkali content of the pore 

solution in concrete decreases, due perhaps to leaching or reaction with reactive silica in the 

aggregate, a portion of the bound alkalis may be released to regain equilibrium. It is important 

to establish what portion of the alkalis in a binder are “available” to a solution at a pH that is 

just able to sustain the alkali-silica reaction, as it is these alkalis that are available to fuel the 

reaction. Shehata and Thomas (2006) studied the alkali release characteristics of pastes 

produced with high-alkali cement and combinations of silica fume and various fly ashes. Paste 

samples, 1 to 3 years of age, were immersed in solutions of alkali hydroxide at initial molar 

concentrations of 0, 0.10, 0.25, and 0.40 and the change in concentration was observed to 

determine how much alkali was leached from the binder. Figure 5.8 shows a selection of the 

data produced in this study. When mature paste samples were immersed in distilled water (pH = 

7.0) almost all of the alkalis present in the binder (80 to 90%) were released regardless of 

composition. As the alkali concentration of the leaching solution increased, the amount of alkali 

released from the binder decreased and was strongly dependent on the composition of the 

binder. Pastes containing 100% portland cement, 5% silica fume, or 25% high-CaO fly ash still 

released a significant portion of the alkalis present in the binder (50 to 80%) even in the 

solution of the highest initial alkali concentration (0.40M). Much less alkali (~ 20%) was 

released from pastes containing 25% low-CaO fly ash or ternary blends containing silica fume 

with either low-CaO or high-CaO fly ash. A correlation of the data (Shehata and Thomas 2006) 

available for 24 different binders showed that the amount of alkali released to a solution with an 

initial alkali hydroxide concentration of 0.25M (assumed to be the concentration necessary to 

sustain alkali-silica reaction) was related to the chemical composition of the binder as 

represented by the parameter (Na2Oe x CaO)/(SiO2). 

87 
 

Figure 5.8. Available Alkalis in Pastes with SCM Stored in Solutions of Varying Reactivity 

(Shehata and Thomas 2006) 

AAR Facts Book Chapter 5 – Prevention of ASR 

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AAR Facts Book Chapter 5 – Prevention of ASR 

The ability of SCMs to reduce the pore solution alkalinity is linked to their effect on the 

composition and alkali-binding capacity of the hydrates (especially C-S-H). Bhatty and 

Greening (1978) found that C-S-H with a low Ca/Si ratio was able to retain more alkali (Na + 

K) compared to hydrates of higher lime to silica ratios. The addition of fly ash reduces the Ca/ 

Si ratio of the C-S-H hydrates, and there is a concomitant increase in the alkali content. 

Rayment (1982) observed significant differences in the C-S-H composition of portland cement 

and fly ash pastes after just 8 days curing at 20oC. However, Uchikawa et al. (1989) found little 

difference in pastes after 91 days at 20oC but substantial changes due to the incorporation of fly 

ash after 60 days at 40oC, indicating the role of the pozzolanic reaction in the CSH composition. 

Thomas et al. (1991), reporting results for 7-year-old concretes containing reactive flint sand, 

showed that the alkali binding capacity of C-S-H hydrates in concretes was increased 

significantly by the addition of fly ash. Uchikawa et al. (1989) showed that slag has a similar 

effect to low-calcium fly ash on hydrate composition. Glasser & Marr (1985) explain the 

differences in alkali absorption on the basis of the surface charge on the C-S-H, which is 

dependent on the Ca/Si ratio. At high ratios, the charge is positive and the C-S-H tends to repel 

cations. As the Ca/Si ratio decreases the positive charge reduces, becoming negative at low Ca/ 

Si ratios, e.g., less than 1.3 (Glasser 1992). Negatively charged C-S-H has an increased capacity 

to sorb cations, especially alkalis. Hong and Glasser (1999) confirmed the importance of the 

Ca/Si ratio on the alkali-binding capacity of synthesized single-phase C-S-H but subsequently 

showed that the binding capacity could be greatly increased by introducing alumina into the CS-H to form C-A-S-H (Hong and Glasser 2002). 

Many of the studies on the alkali-binding of C-S-H have involved microanalysis (e.g., using 

scanning electron microscopy equipped with energy dispersive x-ray analysis) of the innerproduct C-S-H forming around remnant alite and belite grains. However, outer-product C-S-H 

also forms by reaction between Ca(OH)2 and pozzolans, but this phase is more difficult to 

identify and analyze separately than the inner-product C-S-H. The pozzolanic reaction is 

actually very similar to the alkali-silica reaction. The reactive silica in the pozzolan reacts first 

with the alkali-hydroxides in the pore solution, and alkali-silica gel containing small amounts of 

calcium is formed. Over time, calcium exchanges for alkali in the gel, and C-S-H forms with a 

relatively low Ca/Si ratio compared to that formed in portland cement paste. The only 

substantial differences between this pozzolanic reaction and the alkali-silica reaction is the 

timescale over which the reactions occur and the absence of any detectable expansion due to the 

pozzolanic reaction. The lack of expansion can perhaps be explained by the fact that pozzolans 

are very-finely divided materials and the alkali-silica gel that forms and is subsequently 

converted to C-S-H is distributed throughout the cement paste, whereas the presence of reactive 

aggregate particles leads to the accumulation of larger deposits of alkali-silica gel in discrete 

locations that can become sites of expansion. The importance of the size and distribution of the 

reactive silica can be demonstrated in two ways. Firstly, it has been known since the formative 

work of Stanton (1940) that if a reactive aggregate is ground to sufficient fineness (sub-180 

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AAR Facts Book Chapter 5 – Prevention of ASR 

microns in Stanton’s studies) expansion is eliminated. Figure 5.9 shows data from Thomas 

(2011) relating to the effect of ground Vycor glass (sub-100 micron) on the expansion of mortar 

bars containing sand-sized Vycor glass as a reactive aggregate. The sand-sized Vycor glass 

behaves as a reactive aggregate causing expansion of the mortar with portland cement as the 

only binder. However, the same material, when ground, behaves like a pozzolan when it is used 

to replace 20% of the portland cement and prevents expansion. Secondly, if finely-divided 

pozzolans agglomerate and form sand-sized particles, these particles will behave like reactive 

aggregates and may result in expansion and cracking. This effect has been observed with 

agglomerated silica fume both in the field and in the laboratory. Figure 5.10 (from Maas et al. 

2007) shows a back-scattered electron image of a mortar bar containing agglomerated silica 

fume after storage in 1M NaOH solution at 80oC for 14 days (Maas et al. 2007). The mortar, 

which contained non-reactive sand, expanded during test, and the expansion was attributed to 

the reaction of the agglomerated silica fume. 

Figure 5.9. Role of Particle Size on the Behavior of Vycor Glass (Thomas 2011) 

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AAR Facts Book Chapter 5 – Prevention of ASR 

Figure 5.10. Agglomerated Silica Fume Particle Behaving as a Reactive Aggregate and 

Source of ASR Expansion (Maas et al. 2007) 

5.5.2 Effect of SCM on the Expansion of Concrete 

Stanton proposed a test method for evaluating the potential for cement-aggregate combinations 

to expand due to ASR in his first major paper on the subject (Stanton 1940). This involved the 

manufacture of small mortar bars and storing them over water in sealed containers. Subsequent 

modifications included elevating the temperature to 38oC (100oF), and the test was eventually 

standardized to become ASTM C 227. Pozzolans were often evaluated using a modified version 

of this test with either the job aggregate or a standard reactive aggregate, Pyrex glass; the test 

with Pyrex became standardized as ASTM C 441. ASTM C 227 is no longer widely used as it 

fails to detect many slowly-reacting aggregates because the small sample size and test 

conditions promote the leaching of alkalis from the bars; such a drawback is also a problem for 

evaluating SCMs (Thomas et al. 2006). ASTM C 441 is a much more rapid test (typically 14 to 

56 days) because of the high reactivity of the Pyrex glass, and leaching is less significant during 

the test. However, this test fails to account for the nature of the reactive aggregate which is 

known to impact the amount of SCM required, and tends to overestimate the amount of SCM 

required to control expansion with natural aggregates (Thomas et al. 2006). However, the use of 

Pyrex glass does allow a comparative evaluation of pozzolans, and a number of investigators 

have used the test to observe the reduced efficacy of high-calcium ash compared with lowcalcium ash (Dunstan 1981; Buck and Mather 1987; Klieger and Gebler 1987; Smith 1988; 

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AAR Facts Book Chapter 5 – Prevention of ASR 

Carrasquillo and Snow 1987). Dunstan's (1981) work was the most comprehensive with regards 

to fly ash composition. He reported results from Pyrex mortar bar tests for 17 ashes of varying 

chemistry and showed a reliable correlation between the calcium content of the ash and the 

expansion of mortar bars at 14 days. 

The test methods most commonly used today to evaluate the efficacy of SCM in controlling 

ASR expansion are the concrete prism test (ASTM C 1293) and the accelerated mortar bar test 

(ASTM C 1567). The accelerated test is by far the most widely used test, however, it is only 

intended as a screening test and should not be relied upon for phenomenological studies. The 

test involves the immersion of small mortar bars in 1 M NaOH solution at 80oC, and this tends 

to mask the importance of the alkalis in the system under test. Since SCMs control ASR 

expansion mainly by reducing the availability of alkalis, providing an inexhaustible supply of 

alkalis is not desirable as eventually the beneficial effects of the SCM will be swamped by the 

ingress of alkalis from the storage solution. Furthermore, the very high temperature used in this 

test is not representative of the conditions that concrete encounters in the field. The review 

presented here focuses on expansion tests involving concrete exposed either to field conditions 

or to accelerated conditions (up to 38oC) in the laboratory (e.g., ASTM C 1293 concrete prism 

tests and similar tests). Data from ultra-accelerated tests, such as the accelerated mortar bar test 

(ASTM C 1567), are not included. 

5.5.2.1 Effect of SCM Composition on Expansion 

As discussed above and illustrated in Figure 5.4, almost any SCM can be used to control 

expansion due to alkali-silica reaction provided it is used in sufficient quantity. The amount of 

SCM required is, of course, dependent on the composition of the SCM, but also on the 

reactivity of the aggregate, the quantity of alkalis supplied by the portland cement (and other 

sources), and whether the concrete will be exposed to alkalis (e.g., seawater, deicing chemicals) 

during service. On one extreme, a highly efficient pozzolan with a high level of reactive silica 

and negligible alkali content may be expected to eliminate damaging expansion with a 

moderately reactive aggregate when used with a moderate-alkali cement at replacement levels 

of about 10%; this scenario is represented by the left-hand curve in Figure 5.4. On the other 

extreme, as represented by the right-hand curve in Figure 5.4, an SCM with a higher alkali and 

lower silica content might need to be used at a replacement level of 50 to 60% or more with a 

highly reactive aggregate and high-alkali cement. 

Figure 5.11 shows the expansion of concretes at 2 years as a function of the type and amount of 

SCM used; the tests were performed in a single laboratory using a reactive aggregate from a 

single source (siliceous limestone from the Spratt quarry in Ontario, Canada) and were, 

generally, performed in accordance with ASTM C 1293. Silica fume and metakaolin are the 

most efficient with regards to reducing the expansion at 2 years, followed by low-calcium fly 

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AAR Facts Book Chapter 5 – Prevention of ASR 

ash. Slag, high-calcium fly ash, and high-alkali fly ash were less efficient and had to be used at 

significantly higher replacement levels to control expansion to below 0.040% at 2 years. 

Generally, the effect of the different SCMs on the expansion of concrete prisms was consistent 

with their effect on pore solution alkalinity. 

Figure 5.11. Effect of SCMs on Two-Year Expansion of Concrete Containing Siliceous 

Limestone (Shehata and Thomas 2002; Ramlochan et al. 2000; Thomas and Innis 1998) 

Figure 5.12 (modified from Shehata and Thomas 2000) shows the 2-year expansion of concrete 

containing 25% fly ash and a siliceous limestone (Spratt) aggregate; fly ashes from 29 different 

sources are shown in this figure. Fly ashes with low to moderate alkali (≤ 4% Na2Oe) and 

calcium contents (≤ 20% CaO) are generally effective in controlling expansion below 0.040% 

at 2 years. As the calcium content increases above 20% CaO there is a marked increase in 

expansion with increasing calcium content. Fly ashes with high alkali contents (> 5% Na2Oe) 

are not effective in controlling expansion when used at a replacement level of 25% regardless of 

the calcium content of the fly ash. High-calcium fly ashes may be effective in controlling ASR 

expansion when used at increased levels of replacement. Figure 5.13 shows the expansion of 

concrete prisms at 2 years plotted as a function of the level of fly ash replacement for Class F 

fly ashes with less than 10% CaO and Class C fly ashes with more than 20% CaO. Whereas 20 

to 25% low-CaO Class F fly ash was sufficient to control expansion, replacement levels of 50% 

or more were required with the high-CaO Class C fly ashes. 

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AAR Facts Book Chapter 5 – Prevention of ASR 

Figure 5.12. Effect of the Calcium Content of Fly Ash on the Two-Year Expansion of Concrete 

Containing Siliceous Limestone (Shehata and Thomas 2002; Thomas 2011) 

Figure 5.13. Effect of Fly Ash Replacement Level on Expansion of Concrete 

(Shehata and Thomas 2000) 

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AAR Facts Book Chapter 5 – Prevention of ASR 

Ternary blends of portland cement with two SCMs are also effective in controlling ASR 

expansion. Figure 5.14 shows the expansion of concrete containing 5% silica fume in 

combination with fly ashes with different calcium contents. Combinations of 5% silica fume 

with either 10 to 15% low-CaO fly ash or 20 to 30% high-CaO fly ash are effective in 

controlling expansion (≤ 0.040% at 2 years). Similarly Figure 5.15 shows that combinations of 

moderate amounts of silica fume (2 to 6%) are effective with moderate amounts of slag (15 to 

35%). 

Figure 5.14. Expansion of Concrete with Blends of Silica Fume and Fly Ash 

(Shehata and Thomas 2002) 

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AAR Facts Book Chapter 5 – Prevention of ASR 

Figure 5.15. Expansion of Concrete with Blends of Silica Fume and Slag 

(Bleszynski 2002; Bleszynski et al. 2002) 

Figure 5.16 shows an empirical relationship between the expansion of concrete at 2 years and a 

“chemical index” derived from the chemical composition of the cementing materials to produce 

132 different concrete mixes which were tested in accordance with ASTM C 1293 (Thomas and 

Shehata 2004). The cementing materials used to produce these concretes were the same as those 

used for the pore solution study discussed above. The reactive coarse aggregate was siliceous 

limestone (Spratt). The best fit between expansion and chemical composition was found to be 

with the following index: [(Na2Oe)0.33 x CaO]/(SiO2)

2

. This relationship is not intended as a 

method for predicting expansion based on the chemical composition of the binder phase, but 

merely to examine what constituents of the binder tend to most influence ASR expansion. The 

relationship is likely quite different if a different reactive aggregate or, even, a different test 

method is used. However, the relationship does indicate that expansion is likely to increase as 

the alkali and calcium content of the binder increase or as the silica content decreases, and this 

is somewhat intuitive. It is interesting that the alkali content of the binder appears to play a less 

important role in determining expansion compared with the pore solution composition, but this 

is likely an artifact of the test conditions as significant leaching of alkalis occurs during the 

concrete prism test, and this may reduce the apparent importance of the initial alkali content. 

This effect can be observed when looking at the expansion data for the concrete mixes produced 

with low-alkali cement. The expansion is lower than that expected based on the chemical 

composition. However, it is known that the concrete prism test will likely underestimate the 

96 
AAR Facts Book Chapter 5 – Prevention of ASR 

expansion with low-alkali cement because of leaching (Thomas et al. 2006). As with the 

relationship with pore solution, the alumina content of the binder does not appear to 

significantly affect the expansion of concrete. The role of alumina, however, is not yet well 

understood, and further study is needed to determine its impact. 

Figure 5.16. Effect of Binder Composition on the Expansion of Concrete 

Containing Siliceous Limestone 

5.5.2.2 Effect of Cement Alkalis 

One of the drawbacks of the concrete prism test is that significant alkali leaching occurs during 

the test, which means it cannot generally be used to determine the threshold alkali content 

required to initiate expansion with a specific aggregate or to determine how the minimum 

amount of SCM required varies as the alkali content of the cement changes (Thomas et al. 

2006). Larger samples exposed under natural conditions should be relatively immune from the 

effects of alkali leaching, however, much longer testing periods are required. 

Figure 5.17 shows the expansion of 300-mm concrete cubes containing a reactive hornfels 

aggregate and stored outdoors at the National Building Research Institute (NBRI) in South 

Africa (Oberholster and Davies 1987; Oberholster 1989). Two series of mixes were cast with 

cementitious contents of approximately 350 and 450 kg/m3

. Within each series 5% or 10% of 

the portland cement by mass was replaced with an equal volume of silica fume, resulting in 

silica fume levels of 3.5% and 7.0% by mass. The “active” alkali content was maintained at a 

constant level within a given series by addition of alkali hydroxide (using the same Na2O to 

97 
AAR Facts Book Chapter 5 – Prevention of ASR 

K2O ratio as the cement). The “active alkalis” included the available cement alkalis (using 

ASTM C 311) plus the alkali hydroxide, but excluded alkalis in the silica fume. The use of 

3.5% or 7% silica fume delayed the onset of expansion and time to cracking in all cases. 

However, only the mixture at the lower cement content with 7% silica fume failed to expand 

after just over 7 years field exposure. These data clearly show the effect of alkali content on the 

efficacy of silica fume in controlling expansion. A replacement level of 7% silica fume appears 

to have been sufficient to provide long-term prevention of expansion when the “active alkalis” 

of the mix were just less than 4 kg/m3

 Na2Oe but not at the higher alkali content of 5 kg/m3 

Na2Oe. 

Figure 5.17. Effect of Cement Alkalis and Expansion of Concrete Containing Silica Fume 

(Oberholster 1989) 

Figure 5.18 shows data from Fournier and co-workers (2004) for concrete blocks stored 

outdoors in Ottawa, Canada. The blocks contain a reactive greywacke coarse aggregate 

(Springhill Quarry in New Brunswick) and 420 kg/m3

 of cementing material. High-alkali 

portland cement with 0.90% Na2Oe was used to manufacture the blocks and in some cases the 

alkali content of the portland cement component of the concrete was boosted to 1.25% Na2Oe 

by the addition of NaOH to the mix water as per ASTM C 1293. The data in Figure 5.18 show 

that although the differences in expansion between boosted and unboosted blocks is not large, 

increased amounts of SCM are clearly needed to control expansion to acceptable levels when 

the alkali content of the mixture is increased. 

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AAR Facts Book Chapter 5 – Prevention of ASR 

Figure 5.18. Effect of Cement Alkalis on Expansion of Concrete Containing Fly Ash 

or Silica Fume (Fournier et al. 2004) 

5.5.2.3 Effect of Aggregate Reactivity 

Figure 5.19 shows 2-year expansion data for concrete prism tests containing various reactive 

aggregates and different amounts of slag (Thomas and Innis 1998) or metakaolin (Ramlochan et 

al. 2000). It can be seen that the amount of slag required to limit expansion below 0.040% at 2 

years varies between 35% and 50% depending on the aggregate type. Figure 5.20 shows similar 

data for blocks exposed on an outdoor exposure site in Ottawa (Fournier et al. 2004); the blocks 

contain high-alkali cement (boosted to 1.25% Na2Oe), either low-CaO Class F fly ash or silica 

fume, and aggregates of varying reactivity. For three of the reactive aggregates, which produced 

expansion levels between 0.097% and 0.219% when tested with 100% portland cement, a fly 

ash replacement level of 20% or a silica fume replacement level of 7.5% was sufficient to 

reduce expansion below 0.040%. For the aggregates that produced an expansion of 0.338% 

when tested with 100% portland cement, neither 30% fly ash nor 10% silica fume was quite 

sufficient to reduce the expansion below 0.040%, although expansions were much reduced 

(0.051% and 0.046% with 30% fly ash and 10% silica fume, respectively). For the aggregate 

that produced the largest expansion when tested with portland cement (0.386%), significant 

expansion (0.148%) still occurred with 30% fly ash. In this figure, it would appear that the 

amount of fly ash required increases as the reactivity (as determined by the expansion when 

tested with portland cement alone) of the aggregate increases. 

99 
 

0.30 

Expansion at 2 Years (%) 0.25 

0.20 

0.15 

0.10 

0.05 

0.00 

0 20 40 60

Spratt 

Sudbury 

Potsdam 

Granite 

Spratt 

Sudbury 

Slag 

Metakaolin 

 

 

0.40 

Expansion at latest measurement (%) 0.30 

0.20 

0.10 

0.00 

0 10 20 30

NM - FA Con - FA 

Su - FA Su - SF 

Al - FA Al - SF 

Sl - FA Sl - SF 

Silica Fume (SF) or Fly Ash (FA) Replacement Level (%) 

Figure 5.20. Effect of Aggregate Type on the Amount of Silica Fume (SF) or Fly Ash (FA) 

Required to Control ASR Expansion (Fournier et al. 2004). NM, Con, Su, Al and Sl are 

different aggregates. FA and SF are fly ash and silica fume, respectively. 

AAR Facts Book Chapter 5 – Prevention of ASR 

Metakaolin or Slag Replacement Level (%) 

Figure 5.19. Effect of Aggregate Type on the Amount of Metakaolin or Slag Required to 

Control ASR Expansion (Thomas and Innis 1996; Ramlochan et al. 2000) 

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AAR Facts Book	 Chapter 5 – Prevention of ASR 

5.5.3 Summary on Effect of SCM on ASR 

Supplementary cementing materials are an effective means for controlling expansion due to 

alkali-silica reaction and most, if not all, SCMs can be used in this role provided they are used 

at a high enough level of replacement. The level of SCM required generally increases with the 

following parameters: 

• The alkali available from the portland cement increases (If significant alkalis are available 

from the aggregates – e.g., feldspars, greywackes – or from external sources, this will likely 

also increase the level of SCM required.) 

• The alkali from the SCM increases 

• The CaO/SiO2 of the SCM increases 

• The reactivity of the aggregate increases 

The amount of SCM required to prevent damaging ASR expansion generally falls in the ranges 

below (modified from Thomas and Folliard 2007): 

Table 5.2. Required Levels of SCM 

Type of SCM Level required (%) 

Low-calcium fly ash (< 8% CaO) 20 to 30 

Moderate-calcium fly ash (8 - 20% CaO) 25 to 35 

High-calcium fly ash (> 20% CaO) 40 to 60 

Silica fume 8 to 15 

Slag 35 to 65 

Metakaolin (calcined kaolin clay) 10 to 20 

However, the level of SCM required may exceed these values under exceptional conditions 

(e.g., extremely reactive aggregate, high alkali availability in concrete – including alkali 

contribution from aggregates, concrete exposed to high concentrations of alkali in service, 

critical structure with extended service life). 

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AAR Facts Book Chapter 5 – Prevention of ASR 

5.6 USE OF LITHIUM 

The ability of lithium to control deleterious expansion due to alkali-silica reaction (ASR) in 

mortar and concrete was first demonstrated by McCoy and Caldwell (1951). They showed that, 

out of more than 100 chemical compounds tested, various salts of lithium (e.g., LiCl, Li2CO3, 

LiF, Li2SiO3, LiNO3, and Li2SO4) were the most promising and could virtually eliminate the 

expansion of mortar containing Pyrex glass provided they were used at sufficient levels of 

replacement. Since then, there have been numerous studies which corroborate this earlier 

discovery (Feng et al. 2005). 

It is somewhat paradoxical that lithium compounds are effective suppressants of ASR as lithium 

is an alkali metal like sodium and potassium. The precise mechanism by which lithium controls 

ASR is not known, although many theories have been put forward (Feng et al. 2005). The 

simplest and most commonly used explanation is that lithium salts will react with reactive silica 

in a similar way to sodium and potassium salts, but the reaction product is an insoluble lithiumsilicate with little propensity to imbibe water and swell. The lithium silicate forms around 

reactive aggregate particles and protects the underlying reactive silica from “attack” by alkali 

hydroxides. 

The initial work of McCoy and Caldwell (1951) showed that the amount of lithium required to 

control expansion was a function of the availability of other alkalis (Na + K) in the system, and 

they concluded that the expansion of mortar bars containing reactive Pyrex glass could be 

effectively suppressed provided that the lithium-to-sodium-plus-potassium molar ratio was 

greater than 0.74, i.e., [Li]/[Na+K] > 0.74. Since then numerous workers have demonstrated a 

similar relationship between the amount of lithium required and the amount of alkali available, 

but the minimum value of [Li]/[Na+K] has been shown to vary depending on a number of 

issues such as the form of lithium, nature of reactive aggregate, and, perhaps, the method of test 

used (Feng et al. 2005). 

Although most lithium compounds have a beneficial effect, lithium nitrate (LiNO3) is 

considered to be the most efficient form for suppressing ASR (Stokes et al. 1997). Lithium 

nitrate solution is commercially available from a number of companies in North America, being 

marketed as an “ASR-suppressing admixture.” Currently the product is sold as a 30% solution 

of LiNO3. To achieve a lithium-to-sodium-plus-potassium molar ratio of [Li]/[Na+K] = 0.74 

using a 30% solution of LiNO3 requires a dose of 4.6 gallons of LiNO3 solution per 1 kg of 

Na2Oe (0.55 gallons of solution per 1 lb Na2Oe). This has been referred to as the “standard 

dose” of lithium nitrate solution. 

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AAR Facts Book Chapter 5 – Prevention of ASR 

Recent research (Tremblay et al. 2007) has highlighted the influence of aggregate type on the 

amount of lithium required to suppress expansion due to ASR. Figure 5.21 shows the 2-year 

expansion of concrete prisms with 12 different reactive aggregates and 1 non-reactive aggregate 

(NF), and various levels of lithium (standard dose is [Li]/[Na+K] = 0.74). For 6 of the 12 

aggregates 75% to 100% of the standard dose was sufficient to control expansion (≤ 0.040% at 

2 years). For 3 of the aggregates 125% to 150% of the standard dose was required; however, for 

the remaining 3 aggregates expansion could not be controlled even at 150% of the standard 

dose. 

Figure 5.21. Effect of Lithium Dose on the Expansion of Concrete with Different Reactive 

Aggregates (from Tremblay et al. 2007) 

As the effectiveness of lithium appears to be extremely aggregate dependent, it is not possible 

to prescribe a single dose for controlling ASR, and the minimum dose must be determined by 

testing lithium with the specific reactive aggregate being considered for use. At this point in 

time there is no consensus regarding the appropriateness of accelerated tests for determining the 

correct lithium dose, and it is recommended that the concrete prism test is used for this purpose. 

103 
AAR Facts Book Chapter 5 – Prevention of ASR 

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Ash, Silica Fume, Slag and Natural Pozzolans in Concrete, Supplementary Papers, Las Vegas, 

591-607. 

Thomas, M.D.A., Nixon, P.J. and Pettifer, K. 1991. "The effect of pulverized fuel ash with a 

high total alkali content on alkali silica reaction in concrete containing natural U.K. aggregate." 

Proceedings of the 2nd CANMET/ACI International Conference on Durability of Concrete, 

(Ed. V.M. Malhotra), Vol. 2, American Concrete Institute, Detroit, 919-940. 

Tremblay, C., Berube, M-A., Fournier, B., Thomas, M.D.A. and Folliard, K.F. 2007. 

“Effectiveness of lithium-based products in concrete made with Canadian reactive aggregates.” 

ACI Materials Journal, 104(2): 195-205. 

109 
AAR Facts Book Chapter 5 – Prevention of ASR 

Uchikawa, H., Uchida, S. and Hanehara, S. 1989. "Relationship between structure and 

penetrability of Na ion in hardened blended cement paste mortar and concrete." Proceedings of 

the 8th International Conference on Alkali-Aggregate Reaction, (Ed. K.Okada, S. Nishibayashi 

and M. Kawamura), Kyoto, 121-128. 

Woolf, D.O. 1952. “Reaction of aggregate with low-alkali cement.” Public Roads, August, 50­

56. 

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AAR Facts Book	 Chapter 6 – AAR Specifications 

6 – Alkali-Aggregate Reactions: Specifications 

6.1 INTRODUCTION 

This chapter discusses specifications for alkali-aggregate reaction focusing on AASHTO PP65­

11 “Standard Practice for Determining the Reactivity of Concrete Aggregates and Selecting 

Appropriate Measures for Preventing Deleterious Expansion in New Concrete Construction.” 

Requirements within ASTM and ACI are also discussed. 

Essentially there are two approaches to specifying preventive measures for controlling alkaliaggregate reaction. In the prescriptive approach, reactive aggregates are permitted provided 

they are used with prescribed amounts of ameliorative materials such as a minimum level of fly 

ash or slag (for example). In a performance-based approach, a certain combination of materials 

(reactive aggregates and preventive measures) are permitted provided they are tested and shown 

to meet certain performance requirements such as meeting the expansion limits of mortar-bar or 

concrete-prism expansion tests. AASHTO PP65-11 has both prescriptive and performance 

options. 

6.2 EXISTING SPECIFICATIONS IN USA 

6.2.1 ASTM 

ASTM C 33 Standard Specification for Concrete Aggregates states that “concrete aggregates 

for use in concrete ... shall not contain any materials that are deleteriously reactive with the 

alkalies in the cement in an amount sufficient to cause excessive expansion of mortar or 

concrete” unless one of the following three conditions is met: 

• the aggregate is “used with a cement containing less than 0.60% alkalies calculated as 

sodium oxide equivalent (Na2Oe = Na2O + 0.658 x K2O),” 

• there is a satisfactory service record evaluation, or 

• the aggregate is used “with the addition of a material that has been shown to prevent 

harmful expansion due to the alkali-aggregate reaction.” 

Within the ASTM concrete standards there are number of laboratory test methods that can be 

used to determine the potential for aggregates to be deleteriously reactive or the effectiveness of 

different preventive measures against ASR; these are: 

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AAR Facts Book	 Chapter 6 – AAR Specifications 

• C 295 Petrographic Examination of Aggregates 

• C 227 Standard Test Method for Potential Alkali Reactivity of Cement-Aggregate 

Combinations (Mortar-Bar Method) 

• C 289 Standard Test Method for Potential Alkali-Silica Reactivity of Aggregates 

(Chemical Method) 

• C 441 Standard Test Method for Effectiveness of Pozzolans or Ground Blast-Furnace 

Slag in Preventing Excessive Expansion of Concrete Due to the Alkali-Silica Reaction 

• C 1105 Standard Test Method for Length Change of Concrete Due to Alkali-Carbonate 

Rock Reaction 

• C 1260 Standard Test Method for Potential Alkali Reactivity of Aggregates (Mortar-Bar 

Method) 

• C 1293 Standard Test Method for Determination of Length Change of Concrete Due to 

Alkali-Silica Reaction 

• C 1567 Standard Test Method for Determining the Potential Alkali-Silica Reactivity of 

Combinations of Cementitious Materials and Aggregate (Accelerated Mortar-Bar 

Method. 

Appendix X1 of ASTM C 33 provides some limited guidance on interpretation of the results 

from these tests and measures for mitigating alkali-silica reaction5. If the aggregate produces 

little or no expansion in C 1260 or C 1293, or has a satisfactory service history (with similar 

cementitious materials) no mitigation is necessary. On the other hand, if the aggregates are 

considered to be deleteriously alkali-silica reactive Appendix X1 (section 4.3) recommends one 

of the following preventive measures: 

• Use of ASTM C 150 portland cement meeting the low-alkali option (≤ 0.60% Na2Oe) 

• Use of ASTM C 595 blended cement meeting the optional mortar-bar-expansion 

requirement 

• Use of hydraulic cement meeting the ASTM C 1157 performance specification 

including Option R - Low Reactivity with Alkali-Reactive Aggregates. 

• Use of pozzolans or slag meeting the optional requirements of the relevant material 

specifications (C 618 for fly ash and natural pozzolans, C 1240 for silica fume, and C 

989 for slag) for preventing excessive expansion due to ASR. 

5

 ASTM C 33 Appendix X1 also provides guidance on mitigation of alkali-carbonate reaction. The guidance is 

limited to “avoiding reactive carbonate rocks; selective quarrying; diluting reactive rock to less than 20 % of the 

aggregate in the concrete; use of smaller maximum size; and the use of very low alkali cement.” 

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AAR Facts Book Chapter 6 – AAR Specifications 

The optional requirements for blended cements, C 1157 cements, pozzolans, and slag all make 

use of C 441 (Pyrex) mortar-bar method for demonstrating the effectiveness in controlling 

expansion due to ASR. However, each material specification has different performance 

requirements and these may be summarized as follows: 

ASTM Specification Expansion Limit of Mortars with Pyrex Glass 

C 595 Blended cements Maximum expansion of 0.020% at 14 days and 0.060% 

at 56 days 

C 1157 Hydraulic cements 

(performance-based specification) 

Maximum expansion of 0.020% at 14 days 

C 618 Fly ash and natural pozzolans Expansion of fly ash mortars not greater than expansion 

of control mortars with low-alkali cement (≤ 0.60% 

Na2Oe) at 14 days 

C 989 Slag Expansion of the job cement plus slag should not expand 

by more than 0.02% at 14 days or, if the job cement is 

not known, the slag should reduce the 14-day expansion 

of a mixture with high-alkali cement by at least 75% 

when compared with a mix with high-alkali cement on 

its own. 

C 1240 Silica fume Blend of high-alkali cement plus silica fume must reduce 

expansion by at least 80% compared with high-alkali 

cement alone 

A joint C09/C01 Task Group recently recognized that numerous ASTM specifications provide 

requirements and guidance for avoiding deleterious ASR expansion for individual concrete 

materials (e.g., cementitious materials, aggregates, and SCMs) while, together, these 

specifications do not provide coherent guidance for preventing deleterious expansion in 

concrete; also, the specifications utilize standard test methods that are in many cases considered 

to be unreliable (Struble 2010). The Task Group thus recommended that clear and consistent 

guidance/specification for the prevention of ASR be developed that addresses performance at 

the concrete level and includes requirements for aggregates. A joint ASTM technical 

subcommittee, C01/C09-50, was then formed to develop new global requirements for the Risk 

Management of Alkali-Aggregate Reactions. This new subcommittee started its activities in 

2010. 

6.2.2 ACI 

ACI 301 Specifications for Structural Concrete (ACI 301-10) states that potentially reactive 

aggregates may be used either with low-alkali cement (≤ 0.60% Na2Oe) or supplementary 

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AAR Facts Book Chapter 6 – AAR Specifications 

cementing materials “in an amount shown to be effective in preventing harmful expansion due 

to alkali-aggregate reaction in accordance with ASTM C441” and defers to ASTM C 33. 

ACI 318 Building Code Requirements for Structural Concrete (ACI 318-08) requires 

aggregates to meet the requirements of ASTM C 33 but makes no reference to alkali-aggregate 

reactions (ASR or ACR) or the use of deleteriously-reactive aggregates in concrete. 

Guidance for preventing damage due to AAR is provided in ACI 201 Guide to Durable 

Concrete (ACI 201.2R-08) and ACI 221 Report on Alkali-Aggregate Reactivity (ACI 221.1R98). 

6.2.3 State Specifications 

Many state transportation agencies have developed specifications for minimizing the risk of 

deleterious alkali-aggregate reactions in concrete. These are too numerous to discuss here but 

examples of these specifications are available for review at the following link: 

http://www.fhwa.dot.gov/pavement/concrete/asr/reference.cfm?main_category=Specifications. 

6.3 AASHTO PP65-11 

A version of AASHTO PP65-11 Standard Practice for Determining the Reactivity of Concrete 

Aggregates and Selecting Appropriate Measures for Preventing Deleterious Expansion in New 

Concrete Construction was first published in 2010. As the title suggests, these guidelines can be 

broken down into two steps as follows: 

• Evaluating aggregate reactivity (for alkali-silica and alkali-carbonate reactive aggregates) 

• Selecting preventive measures (for alkali-silica reactive aggregates only) 

The practice is based on the 2004 version of the practice developed in Canada: CSA A23.2-27A 

Standard practice to identify degree of alkali-reactivity of aggregates and to identify measures 

to avoid deleterious expansion in concrete. Further information on the development of this 

approach can be found in Report No. FHWA-HIF-09-001 (Thomas et al. 2008). The rationale 

for preventive measures recommended in the “prescriptive approach” is also documented in a 

report by the Federal Highway Administration (Thomas et al. 2012). 

6.3.1 Evaluating Aggregate Reactivity 

Aggregate reactivity is evaluated by considering one or more of the following options: (i) field 

performance history, (ii) petrographic assessment, (iii) chemical composition (for quarried 

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AAR Facts Book	 Chapter 6 – AAR Specifications 

carbonates), (iv) data from accelerated mortar bar tests (AASHTO T 303), and (v) data from 

concrete prism tests (ASTM C 1293). A flow chart showing the sequence of testing is presented 

in Figure 6.1. Aggregates may be classified as non-deleteriously-reactive and can be used 

without preventive measures provided they meet one of the following conditions: 

• There is an established history of satisfactory field performance (minimum 15 years) 

with the aggregate used in the same exposure conditions with similar cementitious 

materials. 

• Petrographic examination of the aggregate by a skilled and experienced petrographer 

indicates that potentially deleterious minerals are not present in sufficient concentration 

to cause deleterious reaction and expansion. 

• Expansion of mortar bars (AASHTO T 303; ASTM C 1260) is not greater than 0.10% 

after 14 days immersion in 1 M NaOH at 176oF (80oC). 

• Expansion of concrete prisms (ASTM C 1293) is not greater than 0.040% at 1 year. 

Although AASHTO PP65-11 allows aggregates to be accepted solely based on field history 

and/or petrography it strongly recommends expansion testing using either the accelerated 

mortar bar test or, preferably, the concrete prism test. If, after testing, the aggregate is identified 

to be alkali-silica reactive, AASHTO PP65-11 requires that it is either rejected for use or used 

together with appropriate preventive measures. 

Prior to expansion testing, quarried carbonates must be subjected to chemical analysis to 

determine whether there is a risk of alkali-carbonate reaction (ACR). The composition of the 

aggregate is plotted on a graph of CaO/MgO vs. Al2O3 (see Figure 6.2) and if the results of the 

analysis indicate a potential for ACR the aggregate must be tested by the concrete prism test as 

the accelerated mortar bar test is not capable of detecting alkali-carbonate reactive aggregate. 

Two options are allowed for the concrete prism test. One is to follow ASTM 1105 using a total 

alkali of no more than 1.8 kg/m3 (3 lb/yd3) Na2Oe. If the expansion of the concrete prisms is 

equal to or greater than 0.025 % at 6 months or 0.030 % at 1 year, the aggregate shall be 

considered to be alkali-carbonate reactive and shall not be used in concrete. If the expansion of 

the concrete is below these limits, it is not considered to the alkali-carbonate reactive and can be 

evaluated in the same manner as non-carbonate rocks for alkali-silica reaction. The second 

option is to follow ASTM C 1293 (5.25 kg/m3

, 8.75 lb/yd3 Na2Oe). If the expansion of concrete 

prisms exceeds 0.040% at one year, the aggregate is deemed to be reactive and the concrete 

prism must be subjected to a petrographic examination to determine if ACR has contributed to 

the expansion. If ACR is considered to have contributed to the expansion the aggregate must be 

rejected for use in concrete; however, if there is no sign of ACR, the aggregate is deemed to be 

alkali-silica reaction and can be used in concrete with appropriate preventive measures. If the 

aggregate does not produce expansion in excess of 0.040% at 1 year in the concrete prism test it 

115 
 

 

 

AAR Facts Book Chapter 6 – AAR Specifications 

is considered to be non-deleteriously reactive and may be used in concrete without preventive 

measures. 

†The type of reaction only needs to be determined after the concrete prism test if the aggregate being tested is a 

quarried carbonate that has been identified as being potentially alkali-carbonate reactive by chemical composition 

in accordance with test method CSA A23.2-26A. 

The solid lines show the preferred approach. However, some agencies may want to reduce the amount of testing 

and accept a higher level of risk and this can be achieved by following the direction of the hashed lines. 

Figure 6.1. Sequence of Testing in AASHTO PP65-11 for Evaluating Aggregate Reactivity 

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AAR Facts Book Chapter 6 – AAR Specifications 

Figure 6.2. Potential for Alkali-Carbonate Reactivity of Quarried Carbonates based on 

Chemical Composition (from CSA A23.2-26A) 

6.3.2 Selecting Preventive Measures 

PP65-11 provides two approaches for selecting preventive measures, these being: (i) a 

performance approach based on laboratory testing, and (ii) a prescriptive approach based on a 

consideration of the reactivity of the aggregate, type and size of structure, exposure conditions, 

and the composition of cementitious materials being used. The two test methods used for the 

performance-based approach are the accelerated mortar bar test for evaluating combinations of 

cementing materials and aggregates (ASTM C 1567) and the concrete prism test (ASTM C 

1293), with preference given to the latter test. The rationale behind the use of these two tests 

and the preference for the concrete prism test is presented in FHWA-HIF-09-001 (Thomas et al. 

2008) and in Thomas et al. (2006). 

The options for preventive measures included in the prescriptive approach of PP65 are to (i) 

control the alkali content of the concrete to a maximum allowable level, (ii) use a minimum 

level of supplementary cementing material (SCM) or combination of SCMs, or (iii) use a 

combination of these two options (that is controlling the alkali content of the concrete and using 

SCM). The precise level of alkali permitted or SCM required depends on a number of factors 

including the aggregate reactivity, type and size of structure, exposure conditions, and even the 

composition of the cement and SCM being used. 

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AAR Facts Book	 Chapter 6 – AAR Specifications 

A brief summary of the prescriptive and performance options are described here. 

6.3.2.1 Prescriptive Approach for Selecting Preventive Measures 

The prescriptive approach of AASHTO PP65 can be summarized in the following steps: 

Step 1. Determine aggregate reactivity class: The aggregate is tested in either the 

accelerated mortar bar test (AMBT), AASHTO T 303, or, preferably, the concrete 

prism test (CPT), ASTM C 1293. The criteria in Table 6.1 are used to classify the 

aggregate reactivity, which can range from “R0 – non-reactive” to “R3 – very 

highly reactive.” 

Step 2. Determine level of ASR risk: Based on the aggregate-reactivity class determined 

in Step 1 (Table 6.1) and the size and exposure conditions of the concrete under 

construction, the level of ASR risk is determined using the criteria in Table 6.2. 

The risk may range from Level 1 (lowest or negligible risk) to Level 6 (highest 

risk). 

Step 3. Determine level of prevention: Based on the level of ASR risk determined in Step 

2 (Table 6.2) and the classification of the structure6, the level of prevention 

required is determined using Table 6.3. The level of prevention required may 

range from Level V (no measures necessary) to Level ZZ (extreme preventive 

measures necessary). 

Step 4. Identification of preventive measures: Based on the level of prevention required 

that was determined in Step 3 (Table 6.3), a number of options are presented as 

acceptable measures for preventing ASR; these are: 

Option 1 – limiting the alkali content of the concrete (Table 6.5) 

Option 2 – using supplementary cementing materials, SCM7

 (Table 6.6 and Table 

6.7) 

Option 3 – limiting the alkali content of the concrete and using SCM (Table 6.8) 

The prescriptive approach does not allow the option for using lithium compounds as a 

preventive measure. Research has shown that the efficacy of lithium compounds in controlling 

expansion due to ASR is highly influenced by the nature of the reactive aggregate (Tremblay et 

al. 2007). Currently, it is not possible to prescribe the required lithium dose based on aggregate 

reactivity or mineralogy and, consequently, lithium compounds must be tested using the 

prescriptive approach to determine the minimum dose required with a specific aggregate. 

6 Table 6.4 is intended to provide guidance in selecting the Class of Structure. 

7

 For Option 2, the minimum amount of SCM determined from Table 6.6 may be adjusted based on the alkali level 

of the portland cement using Table 6.7. 

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AAR Facts Book Chapter 6 – AAR Specifications 

Table 6.1. Classification of Aggregate Reactivity 

AggregateReactivity Class Description of Aggregate Reactivity One-Year Expansion 

in CPT (%) 

14-Day Expansion in 

AMBT (%) 

R0 Non-reactive ≤ 0.04 ≤ 0.10 

R1 Moderately reactive > 0.04, ≤ 0.12 > 0.10, ≤ 0.30 

R2 Highly reactive > 0.12, ≤ 0.24 > 0.30, ≤ 0.45 

R3 Very highly reactive > 0.24 > 0.45 

Table 6.2. Determining the Level of ASR Risk 

Aggregate-Reactivity Class 

Size and exposure conditions R0 R1 R2 R3 

Non-massive1

 concrete in a dry2 

environment Level 1 Level 1 Level 2 Level 3 

Massive1 elements in a dry2 

environment Level 1 Level 2 Level 3 Level 4 

All concrete exposed to humid air, 

buried or immersed Level 1 Level 3 Level 4 Level 5 

All concrete exposed to alkalis in 

service3 Level 1 Level 4 Level 5 Level 6 

1 A massive element has a least dimension > 3 ft (0.9 m). 

2 A dry environment corresponds to an average ambient relative humidity lower than 

60%, normally only found in buildings. 

3 Examples of structures exposed to alkalis (sodium and potassium) in service include 

marine structures exposed to seawater and highway structures exposed to deicing salts 

(e.g., NaCl) or anti-icing salts (e.g., potassium acetate, potassium formate, sodium 

acetate, sodium formate, etc.). 

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AAR Facts Book	 Chapter 6 – AAR Specifications 

Table 6.3. Determining the Level of Prevention 

Classification of Structure (Table 6.4) 

Level of ASR 

Risk (Table 4) S1 S2 S3 S4 

Risk Level 1 V V V V 

Risk Level 2 V V W X 

Risk Level 3 V W X Y 

Risk Level 4 W X Y Z 

Risk Level 5 X Y Z ZZ 

Risk Level 6 Y Z ZZ †† 

†† It is not permitted to construct a Class S4 structure (see Table 6.4) when the 

risk of ASR is Level 6. Measures must be taken to reduce the level of risk in 

these circumstances. 

The level of prevention V, W, X, Y, Z and ZZ are used in Tables 6.5 to 6.8. 

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AAR Facts Book	 Chapter 6 – AAR Specifications 

Table 6.4. Structures Classified on the Basis of the Severity of the Consequences Should ASR1
 

Occur (Modified for Highway Structures from RILEM TC 191-ARP) 

Class Consequences of Acceptability of Examples2 

S1 

Safety, economic, or 

environmental 

consequences small 

or negligible 

Some deterioration 

from ASR may be 

tolerated 

 Non-load-bearing elements inside 

buildings 

 Temporary structures (e.g. < 5 years) 

S2 

Some safety, 

economic, or 

environmental 

consequences if 

major deterioration 

Moderate risk of 

ASR is acceptable 

 Sidewalks, curbs and gutters 

 Service-life < 40 years 

S3 

Significant safety, 

economic, or 

environmental 

consequences if 

minor damage 

Minor risk of ASR 

acceptable 

 Pavements 

 Culverts 

 Highway barriers 

 Rural, low-volume bridges 

 Large numbers of precast elements 

where economic costs of replacement 

are severe 

 Service life normally 40 to 75 years 

S4 

Serious safety, 

economic, or 

environmental 

consequences if 

minor damage 

ASR cannot be 

tolerated 

 Major bridges 

 Tunnels 

 Critical elements that are very 

difficult to inspect or repair 

 Service life normally > 75 years 

1 This table does not consider the consequences of damage due to ACR. This practice does not permit the use of 

alkali-carbonate reactive aggregates. 

2 The types of structures listed under each Class are meant to serve as examples. Some owners may decide to use 

their own classification system. For example, sidewalks or curbs and gutters may be placed in the Class S3. 

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AAR Facts Book Chapter 6 – AAR Specifications 

Table 6.5. Maximum Alkali Contents in Portland Cement Concrete to Provide Various 

Levels of Prevention 

Prevention Level Maximum Alkali Content of Concrete (Na2Oe) 

lb/yd3 kg/m3 

V No limit 

W 5.0 3.0 

X 4.0 2.4 

Y 3.0 1.8 

Z1 

Table 6.8 

ZZ1 

1 SCMs must be used in prevention levels Z and ZZ. 

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AAR Facts Book	 Chapter 6 – AAR Specifications 

Table 6.6. Minimum Levels of SCM to Provide Various Levels of Prevention 

Type of SCM1 

Alkali level 

of SCM 

Minimum Replacement Level3 

(% by mass of cementitious material) 

(% Na2Oe) Level W Level X Level Y Level Z Level ZZ 

Fly ash ≤ 3.0 15 20 25 35 

Table 6.7 

(CaO ≤ 18%) > 3.0, ≤ 4.5 20 25 30 40 

Slag ≤ 1.0 25 35 50 65 

Silica Fume2 

(SiO2 ≥ 85%) ≤ 1.0 

1.2 x LBA 

or 

2.0 x KGA 

1.5 x LBA 

or 

2.5 x KGA 

1.8 x LBA 

or 

3.0 x KGA 

2.4 x LBA 

or 

4.0 x KGA 

1 The SCM may be added directly to the concrete mixer or it may be a component of a blended cement. SCMs 

should meet the requirements of AASHTO M 295, M 302, or M 307. Blended cements should meet the 

requirements of AASHTO M 240 or ASTM C 1157. 

2 The minimum level of silica fume (as a percentage of cementitious material) is calculated on the basis of the 

alkali (Na2Oe) content of the concrete contributed by the portland cement and expressed in either units of lb/yd3 

(LBA in Table 6.6) or kg/m3

 (KGA in Table 6.6). LBA is calculated by multiplying the cement content of the 

concrete in lb/yd3 by the alkali content of the cement divided by 100. For example, for a concrete containing 500 

lb/yd3

 of cement with an alkali content of 0.81% Na2Oe, the value of LBA = 500 x 0.81/100 = 4.05 lb/yd3. For 

this concrete, the minimum replacement level of silica fume for Level Y is 1.8 x 4.05 = 8.1%. KGA is calculated 

by multiplying the cement content of the concrete in kg/m3

 by the alkali content of the cement divided by 100. 

For example, for a concrete containing 300 kg/m3

 of cement with an alkali content of 0.91% Na2Oe, the value of 

KGA = 300 x 0.91/100 = 2.73 kg/m3

. For this concrete, the minimum replacement level of silica fume for Level 

X is 2.5 x 2.73 = 6.8%. Regardless of the calculated value, the minimum level of silica fume shall not be less 

than 7% when it is the only method of prevention. 

3 The use of high levels of SCM in concrete may increase the risk of problems due to deicer salt scaling if the 

concrete is not properly proportioned, finished, and cured. 

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AAR Facts Book	 Chapter 6 – AAR Specifications 

Table 6.7. Adjusting the Minimum Level of SCM Based on the Alkali Content 

in the Portland Cement 

Cement Alkalis 

(% Na2Oe) 

Level of SCM 

≤ 0.70 

Reduce the minimum amount of SCM given in 

Table 6.6 by one prevention level1 

> 0.70, ≤ 1.00 Use the minimum levels of SCM given in Table 6.6 

> 1.00, ≤1.25 Increase the minimum amount of SCM given in 

Table 6.6 by one prevention level 

> 1.25 No guidance is given 

1 The replacement levels should not be below those given in Table 6.6 for prevention level W, regardless of the 

alkali content of the portland cement. 

Table 6.8. Using SCM and Limiting the Alkali Content of the Concrete to Provide 

Exceptional Levels of Prevention 

Prevention 

Level 

SCM as Sole Prevention Limiting Concrete Alkali Content Plus SCM 

Minimum SCM Level Maximum Alkali 

Content, lb/yd3

 (kg/m3) Minimum SCM Level 

Z SCM level shown for 

Level Z in Table 6.6 3.0 (1.8) SCM level shown for Level Y in Table 6.6 

ZZ Not permitted 3.0 (1.8) SCM level shown for 

Level Z in Table 6.6 

6.3.2.2 Performance Approach for Selecting Preventive Measures 

AASHTO PP65-11 recommends that the concrete prism test (ASTM C 1293) is used to 

evaluate the efficacy of supplementary cementing materials or lithium-based compounds for 

controlling alkali-silica reaction. Preferably tests should be conducted at a range of SCM levels 

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AAR Facts Book Chapter 6 – AAR Specifications 

or lithium doses to determine the “safe” level. The preventive measure is considered to be 

effective provided the expansion of concrete prisms is not greater than 0.040% after 2 years. 

If there is insufficient time to conduct concrete tests, ASTM C 1567 (modified accelerated 

mortar bar test for evaluating combinations of reactive aggregate and SCM) may be used to 

evaluate SCMs. The SCM is deemed to be effective in controlling ASR expansion with the 

aggregate under test provided the expansion of mortar bars is not greater than 0.10% after 14 

days immersion in 1 M NaOH at 176oF (80oC). 

AASHTO PP65-11 recommends that, before using ASTM C 1567 to determine the amount of 

SCM (or lithium required), the aggregate is tested in both the concrete prism test and the 

accelerated mortar bar test (ASTM C 1260) to ensure that the latter test gives a reliable 

prediction of the aggregate reactivity. The expansions from the two tests are plotted on the 

graph shown in Figure 6.3 to determine the validity of using the accelerated test. 

Figure 6.3. Comparison of Accelerated Mortar Bar Test (AMBT) and Concrete Prism Test 

(CPT) Data for the Purpose of Determining Whether the AMBT is Suitable for Evaluating 

Preventive Measures with a Specific Aggregate 

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AAR Facts Book	 Chapter 6 – AAR Specifications 

AASHTO PP65-11 also includes a modified version of the accelerated mortar bar test for 

evaluating lithium-based compounds based on the approach proposed by Tremblay et al (2008). 

The approach is summarized as follows: 

• Test the aggregate using the standard accelerated mortar bar test (AASHTO T 303, 

ASTM C 1260). Extend the duration of the test such that the mortar bars are exposed to 

sodium hydroxide for a period of 28 days. Let E1 = expansion of bars without lithium 

nitrate at 28 days. 

• Test the aggregate in a modified version of the accelerated mortar bar test. In this test 

add sufficient lithium nitrate to the mortar bar mixture and the soak solution to achieve 

lithium-to-alkali molar ratios of [Li]/[Na+K] = 0.74 in the mortar and [Li]/[Na+K] = 

0.148 in the soak solution (see Appendix A2 on calculation of lithium nitrate additions). 

Conduct the rest of the test in accordance with AASHTO T 303, extending the period in 

sodium hydroxide to 28 days. Let E2 = expansion of bars with lithium nitrate at 28 days. 

Note: To achieve [Li]/[Na+K] = 0.74 in the mortar add 4.6 liters of 30%-LiNO3 

solution for every 1 kg of alkali (as Na2Oe) in the mix (70.4 fl.oz. of 30%-LiNO3 solution 

for every 1 lb of alkali). 

There are few data available for calibrating this test method, and it is strongly recommended 

that the concrete prism test be used to evaluate lithium-aggregate combinations. 

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AAR Facts Book Chapter 6 – AAR Specifications 

REFERENCES 

AASHTO. 2012. “Standard Specification for Blended Hydraulic Cement.” AASHTO M 240, 

American Association of State and Highway Transportation Officials, Washington, DC, 23 p. 

AASHTO. 2011. “Standard Specification for Coal Fly Ash and Raw or Calcined Natural 

Pozzolan for Use in Concrete.” AASHTO M 295, American Association of State and Highway 

Transportation Officials, Washington, DC, 4 p. 

AASHTO. 2012. “Standard Specification for Ground Granulated Blast-Furnace Slag for Use in 

Concrete and Mortars.” ASHTO M 302, American Association of State and Highway 

Transportation Officials, Washington, DC, 9 p. 

AASHTO. 2005. “Standard Specification for Silica Fume Used in Cementitious Mixtures.” 

ASHTO M 307, American Association of State and Highway Transportation Officials, 

Washington, DC, 13 p. 

AASHTO. 2011. “Standard Practice for Determining the Reactivity of Concrete Aggregates and 

Selecting Appropriate Measures for Preventing Deleterious Expansion in New Concrete 

Construction.” PP65-11, American Association of State and Highway Transportation Officials, 

Washington, DC, 24 p. 

AASHTO. 2008. “Standard Method of Test for Accelerated Detection of Potentially 

Deleterious Expansion of Mortar Bars Due to Alkali-Silica Reaction.” AASHTO T 303, 

American Association of State and Highway Transportation Officials, Washington, DC, 6 p. 

ACI Committee 201. 2008. “Guide to Durable Concrete.” ACI 201.2R-08, American Concrete 

Institute, Farmington Hills, MI, 49 p. 

ACI Committee 221. 1998. “Report on Alkali-Aggregate Reactivity.” ACI 221.1R-98, 

American Concrete Institute, Farmington Hills, MI, 30 p. 

ACI Committee 301. 2010. “Specifications for Structural Concrete.” ACI 301-10, American 

Concrete Institute, Farmington Hills, MI, 77 p. 

ACI Committee 308. 2008. “Building Code Requirements for Structural Concrete.” ACI 318­

08, American Concrete Institute, Farmington Hills, MI, 473 p. 

ASTM. 2013. “Standard Specification for Concrete Aggregate.” ASTM C 33, ASTM 

International, West Conshohocken, PA, 11 p. 

127 
AAR Facts Book Chapter 6 – AAR Specifications 

ASTM. 2012. “Standard Specification for Portland Cement.” ASTM C 150, ASTM 

International, West Conshohocken, PA, 9 p. 

ASTM. 2010. “Standard Test Method for Potential Alkali Reactivity of Cement-Aggregate 

Combinations (Mortar-Bar Method).” ASTM C 227, ASTM International, West Conshohocken, 

PA, 6 p. 

ASTM. 2007. “Standard Test Method for Potential Alkali-Silica Reactivity of Aggregates 

(Chemical Method).” ASTM C 289, ASTM International, West Conshohocken, PA, 7 p. 

ASTM. 2012. “Standard Guide for Petrographic Examination of Aggregates for Concrete.” 

ASTM C 295, ASTM International, West Conshohocken, PA, 9 p. 

ASTM. 2011. “Standard Test Method for Effectiveness of Pozzolans or Ground Blast-Furnace 

Slag in Preventing Excessive Expansion of Concrete Due to the Alkali-Silica Reaction.” ASTM 

C 441, ASTM International, West Conshohocken, PA, 3 p. 

ASTM. 2012. “Standard Specification for Blended Hydraulic Cements.” ASTM C 595, ASTM 

International, West Conshohocken, PA, 13 p. 

ASTM. 2012. “Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan 

for Use in Concrete.” ASTM C 618, ASTM International, West Conshohocken, PA, 5 p. 

ASTM. 2012. “Standard Specification for Slag Cement for Use in Concrete and Mortars.” 

ASTM C 989, ASTM International, West Conshohocken, PA, 8 p. 

ASTM. 2008. “Standard Test Method for Length Change of Concrete Due to Alkali-Carbonate 

Rock Reaction.” ASTM C 1105, ASTM International, West Conshohocken, PA, 4 p. 

ASTM. 2011. “Standard Performance Specification for Hydraulic Cement.” ASTM C 1157, 

ASTM International, West Conshohocken, PA, 5 p. 

ASTM. 2012. “Standard Specification for Silica Fume Used in Cementitious Mixtures.” ASTM 

C 1240, ASTM International, West Conshohocken, PA, 7 p. 

ASTM. 2007. “Standard Test Method for Potential Alkali Reactivity of Aggregates (Mortar-Bar 

Method).” ASTM C 1260, ASTM International, West Conshohocken, PA, 5 p. 

ASTM. 2008. “Standard Test Method for Determination of Length Change of Concrete Due to 

Alkali-Silica Reaction.” ASTM C 1293, ASTM International, West Conshohocken, PA, 7 p. 

128 
AAR Facts Book Chapter 6 – AAR Specifications 

ASTM. 2013. “Standard Test Method for Determining the Potential Alkali-Silica Reactivity of 

Combinations of Cementitious Materials and Aggregate (Accelerated Mortar Bar Method.” 

ASTM C 1567, ASTM International, West Conshohocken, PA, 6 p. 

CSA. 2009. "Determination of Potential Alkali-Carbonate Reactivity of Quarried Carbonate 

Rocks by Chemical Composition." CSA A23.2-26A. A23.2-09 - Test methods and standard 

practices for concrete, Canadian Standards Association, Mississauga, Ontario, Canada. 

CSA. 2009. "Standard Practice to Identify Degree of Alkali-Reactivity of Aggregates and to 

Identify Measures to Avoid Deleterious Expansion in Concrete.” CSA A23.2-27A. A23.2-09 - 

Test methods and standard practices for concrete, Canadian Standards Association, 

Mississauga, Ontario, Canada. 

Struble, L. 2010. “Opening remarks.” Workshop on specifications on alkali-aggregate reaction. 

Sponsored by ASTM Committees C09 on Concrete and Concrete Aggregates and C01 on 

Cement, 6 June, St. Louis, MO, USA. (Available on ASTM website.) 

Thomas, M.D.A., Fournier, B., Folliard, K., Ideker, J. and Shehata, M. 2006. “Test methods for 

evaluating preventive measures for controlling expansion due to alkali-silica reaction in 

concrete.” Cement and Concrete Research, 36(10): 1842-1856. 

Thomas, M.D.A., Fournier, B. and Folliard, K.J. 2008. “Report on determining the reactivity of 

concrete aggregates and selecting appropriate measures for preventing deleterious expansion in 

new concrete construction.” Federal Highway Administration, FHWA-HIF-09-001, National 

Research Council, Washington, D.C., 20 p. 

Thomas, M.D.A., Fournier, B. and Folliard, K.J. 2012. “Selecting Measures to Prevent 

Deleterious Alkali-Silica Reaction in Concrete: Rationale for the AASHTO PP65 Prescriptive 

Approach.” Federal Highway Administration, FHWA-HIF-13-002, National Research Council, 

Washington, D.C., 47 p. 

Tremblay, C., Bérubé, M-A., Fournier, B., Thomas, M.D.A. and Folliard, K.F. 2007. 

“Effectiveness of lithium-based products in concrete made with Canadian reactive aggregates.” 

ACI Materials Journal, 104(2): 195-205. 

Tremblay, C., Berube, M-A., Fournier, B., Thomas, M.D.A. and Folliard, K.J. 2008. “Use of 

the Accelerated Mortar Test to Evaluate the Effectiveness of LiNO3 against Alkali-Silica 

Reaction. Part 2: Comparison With Results from the Concrete Prism Test.” Journal of ASTM 

International, 5(8). 

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AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

7 – Diagnosis and Prognosis of Alkali-Silica Reaction in Concrete Structures 

7.1 INTRODUCTION 

Alkali-silica reaction (ASR) is one of the many factors that might be fully/partly responsible for 

the deterioration and premature loss in serviceability of concrete infrastructure. Comparative 

field and laboratory investigations can be carried out to confirm that AAR is the main cause or a 

significant contributor to the deterioration observed, thus aiming at selecting appropriate 

remedial actions. Such investigations will likely include one or several of the following steps: 

• the field inspection of the structure(s) under study to identify the presence/distribution 

and severity of the defects affecting the various structural elements (especially those 

features diagnostic of AAR), as well as the exposure conditions to which the above 

components of the structure are subjected; 

• the in-situ monitoring of deterioration (especially signs of expansion/deformation, extent 

and progress of cracking, spalling, etc.); and 

• a range of laboratory tests (including petrographic characterization, chemical, physical, 

and mechanical tests) on samples collected from one or several components of the 

affected concrete structure (especially those showing features of deterioration typically 

associated with or diagnostic of AAR). 

7.2 MANAGEMENT PROGRAM FOR ASR-AFFECTED STRUCTURES 

A global approach was recently proposed by FHWA for the diagnosis and prognosis of ASR in 

transportation structures (Fournier et al. 2010); the main features of the above protocol are 

illustrated in Figure 7.1. This step-by-step approach aims at evaluating the cause of concrete 

distress (diagnosis) and the progress or potential for future expansion/damage (prognosis), 

both elements providing information for the selection of appropriate mitigation measures in 

ASR-affected structures. The extent to which each of the various methods proposed in the 

above approach will need to be implemented in a particular case will depend upon different 

factors, including the nature/extent of the problem, the criticality of the structure, the potential 

impact on the safety of users, etc. 

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AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

Figure 7.1. Global Approach for the Diagnosis and Prognosis of ASR in Concrete Structures 

(modified from Fournier et al. 2010) 

7.2.1 ASR Investigation Program Step 1 - Diagnosis 

7.2.1.1 Condition Survey 

Signs of premature deterioration in concrete transportation structures that could be related to 

ASR can generally be detected during routine site inspections of concrete structures (condition 

survey). For example, FHWA recently proposed Alkali-Silica Reactivity Surveying and 

Tracking Guidelines (Thomas et al. 2012a) that are intended to assist engineers and inspectors 

in tracking and surveying ASR-induced features of deterioration in bridges, pavements, and 

tunnels. 

In the case of bridge structures, basic inspection data can first be collected for the various 

elements/components of the structure, for example in accordance with the new AASHTO Guide 

Manual for Bridge Element Inspection (AASHTO 2011). The concept is to identify defects that 

are specific/unique enough so the manifestation of distress may be attributed to ASR. The 

presence and extent of ASR-related defects are then noted and quantified in accordance with the 

four condition states described in Table 7.1. The Alkali-Silica Reactivity Field Identification 

Handbook (Thomas et al. 2011, updated from Stark (1991)) provides detailed coverage on the 

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AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

causes and effects of ASR and a wide range of photographs illustrating common features of 

ASR, as well as examples of condition states (or severity ratings) for a range of transportation 

structures. Such features include map cracking, aligned cracking, gel exudation, and relative 

dislocation/ misalignment of adjacent sections. Table 7.2 summarizes the proposed ASR-related 

defects, defect descriptions, and criteria/threshold for bridge element types using a similar 

approach as in the AASHTO guide manual (2011). More detailed descriptions of the above 

defects are provided in Table 7.3; examples of defects with different condition states are given 

in Figure 7.2. In addition, environmental conditions, especially temperature, relative humidity, 

exposure to sun and winds, and precipitation, can be tracked and coupled with other inspection 

findings to attempt linking the specific climatic conditions to the progress of ASR. For instance, 

concrete that is subjected directly to moisture and exposed to sun (i.e., wetting-drying cycles) is 

likely to exhibit more severe symptoms of ASR (e.g., cracking) than concrete that is less 

exposed to moisture in the same structure of even the same element (see chapter 3). 

Table 7.1. Standard Condition States for Defects in Bridge Elements (after AASHTO 2011) 

Condition State # Condition State 

1 Good 

2 Fair 

3 Poor 

4* Severe 

* Condition state 4 (severe) is typically reserved for conditions 

that warrant safety concerns and that are beyond the range of 

defects described in condition states 1 through 3. 

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Table 7.2. Recommended Defects and Condition States for Bridge Elements Potentially 

Affected by ASR (Thomas et al. 2012a) 

Defect 

Condition 

State 1 

Condition 

State 2 

Condition 

State 3 Condition State 4 

Map 

Cracking 

None to 

hairline 

Narrow size or 

density, or both 

Medium size or density, or 

both 

The condition is beyond the 

limit state of Condition State 3, 

warrants a structural review to 

determine the strength or 

serviceability of the element or 

bridge, or both 

Aligned 

Cracking 

None to 

hairline 

Narrow size or 

density, or both 

Medium size or density, or 

both 

Gel 

Exudation None Moderate Severe (with gel staining) 

Relative 

Dislocation/ 

Misalignment 

None Tolerable 

Approaching or exceeding 

limits (including causing 

local crushing) 

Table 7.3. Recommended Defects and Condition States for Bridge Elements Potentially 

Affected by ASR (Thomas et al. 2012a) 

Defect Hairline-Minor Narrow-Moderate Medium-Severe 

Map Cracking 

Crack width < 0.0625” 

(1.6 mm) 

% Map Cracking < 5% 

Crack width: 0.0625” (1.6 mm) 

– 0.1250” (3.2 mm) 

% Map Cracking: 5 to 25% 

Crack width > 0.1250” (3.2 mm) 

% Map Cracking > 25% 

Aligned 

Cracking 

Crack width < 0.0625” 

(1.6 mm) 

Crack width: 0.0625” (1.6 mm) 

– 0.1250” (3.2 mm) 

Crack width: > 0.1250” (3.2 

mm) 

Gel Exudation None 

Gel visible on surface (< 20% 

of concrete surface, with no 

build-up of gel) 

Gel build-up on surface (> 20% 

of concrete surface), typically at 

or near cracks; gel staining 

visible (especially once structure 

dries after a rain event) 

Relative 

Dislocation/ 

Misalignment 

None 

Tolerable (movement is visible 

but no loss of clearance, 

exudation of sealants at joints, 

or local crushing) 

Movement is visual, with loss of 

clearance, exudation of sealants 

at joints, or local crushing 

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AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

A B 

C D 

E F 

Figure 7.2. ASR-related defects in bridge elements and severity assessment. A. Map cracking 

on bridge abutment (condition state 2). B. Map cracking on bridge abutment (condition state 3). 

C. Map cracking in bridge deck (condition state 1). D. Aligned (longitudinal) cracking in 

bridge deck (condition state 2). E. Aligned (longitudinal) cracking in post-tensioned concrete 

bridge girder (condition state 2). F. Aligned (longitudinal) cracking in reinforced concrete beam 

(condition state 3). 

135 
 

G H 

I J 

K 

AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

Figure 7.2 (cont’d). ASR-related defects in bridge elements and severity assessment. G. Map cracking 

on a parapet wall (condition state 3); moderate gel exudations are also present, which give the 

impression of permanent dampness. H. Map cracking in massive column foundation block of a bridge 

structure (condition state 3). I. Aligned (vertical/longitudinal) cracking in reinforced concrete column 

(condition state 2). J. Severe (condition state 3) aligned (longitudinal) cracking connected by moderate 

map cracking in a reinforced concrete column. K. Aligned (longitudinal) cracking in the top chord of a 

reinforced concrete arch bridge (condition state 3 to 4). 

136 
 

 

L M 

N O 

AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

Figure 7.2 (cont’d). ASR-related defects in bridge elements and severity assessment. L. Closure 

of joint between adjacent parapet wall sections causing the buildup of concentrated stresses 

which led to crushing of the concrete. M. Severe relative dislocation/misalignment, leading to 

loss of clearance and localized spalling (photo from SHRP C-315 1991). N. Aligned 

(longitudinal) cracking with associated white exudations (mainly calcium carbonate with lesser 

amounts of potassium indicating both lime and alkali leaching from the concrete) on the 

underside of the arch shown in Figure 7.2K. O. Moderate aligned cracking and exudations in 

the exposed portions of abutment and wing wall of a bridge structure (condition state 2). 

A similar approach can be adopted for pavements. The distresses most commonly associated 

with ASR in pavements include map cracking, joint deficiencies/deterioration, and, in some 

cases, popouts. The latter are generated by reactive aggregate particles causing expansion close 

to the surface of the pavement (or other concrete elements), thus inducing the detachment of a 

conical portion of the surface leaving the reactive aggregate in the bottom (Figure 7.3J). 

Popouts can also be caused by the expansion of frost-susceptible aggregate particles (such as 

laminated, schistose and argillaceous, clayey or porous particles or certain varieties of chert, 

137 
 

 

 

 

 

 

 

AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

ironstones), as well as by a poor bond between the cement paste and dusty coarse aggregate 

particles. 

Table 7.4. Recommended Distress and Condition States for Pavements Potentially 

Distress 

Condition 

State 1 

Condition 

State 2 

Condition 

State 3 

Condition 

State 4 

Map Cracking None to 

hairline 

Narrow size or 

density, or 

both 

Medium size or 

density, or both The condition is beyond the 

limit state of Condition State 3, 

warrants a structural review to 

determine the strength or 

serviceability of the pavement, 

or both. 

Joint Sealant Failure None Moderate Severe 

Joint Deterioration None Moderate Severe 

Popouts None Moderate Severe 

Affected by ASR (Thomas et al. 2012a) 

Table 7.5. Recommended Distress and Distress Description for Pavements Potentially 

Affected by ASR (Thomas et al. 2012a) 

Defect Hairline-Minor Narrow-Moderate Medium-Severe 

Map Cracking 

Crack width < 0.0625” (1.6 mm) 

% Map Cracking < 5% 

Crack width: 0.0625” (1.6 

mm) – 0.1250” (3.2 mm) 

% Map Cracking: 5 to 25% 

Crack width > 0.1250” 

(3.2 mm) 

% Map Cracking > 25% 

Joint Sealant 

Failure 

Joint sealant failure in less than 

10% of joints. 

Joint sealant failure in 10 to 

50% of joints. 

Joint sealant failure in 

greater than 50% of joint 

Joint 

Deterioration 

None or only minor cracking 

near corners/joints 

Wide, open cracks exist and 

mass loss has occurred in 

joint region (less than 5% 

of joints). No patching 

applied. 

Wide, open cracks and mass 

loss has occurred in joint 

region (greater than 5% of 

joints). Patching has been 

applied. 

Popouts 

None Popouts isolated and few 

[< 1 popout per 10 ft] 

Popouts prevalent 

[> 1 popout per 10 ft] 

* Popout data generally not collected and not included in LTPP. Estimates are in [] 

138 
 

 

A B 

C E 

Expansion Expansion 

D 

AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

Figure 7.3. ASR-related defects in pavements and severity assessment. A. Minor cracking in a concrete 

pavement (condition state 1). B. Cracking at the corner of paving slabs (condition state 2). C. Map 

cracking of concrete pavement; cracking is much more evident after rainy periods (condition state 2). 

D. Longitudinal cracking connected by map cracking in severely damaged concrete pavement 

(condition state 3) (photo from SHRP C-315 1991). E. Enlargement (red rectangle) of a section of the 

pavement in figure D showing the aligned (longitudinal) cracking in pavement with connecting map 

cracking. 

139 
 

 

F G 

H I 

J 

AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

Figure 7.3 (cont’d). ASR-related defects in pavements and severity assessment. F. Expansion (with 

related map cracking) in pavement slabs causing the extrusion of joint sealant material. G. Spall 

occurring at a joint in a concrete pavement; as ASR advances the cracked concrete at the vicinity of the 

joint may be further distressed by the action of freezing and thawing, and vehicular loading. Eventually 

spalling starts to occur at the joint. H. Joint Sealant Failure in Concrete Pavement (condition state 3). I. 

Joint deterioration in concrete pavement (condition state 3). J. Popout involving a porous (leached) 

chert particle (with complements of C.A. Rogers). 

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AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

It is important to mention that if the condition survey points out issues that can impair the 

integrity of the structure or public safety (related or not to ASR), immediate action should be 

taken in consultation with experts in the respective fields. 

Conclusions from the Condition Survey 

Signs of premature deterioration in concrete pavement and bridge structures that could be 

related to ASR can generally be detected during routine site inspections that are performed 

regularly by trained personnel (e.g., inspectors from State Highway Authorities) (Figure 7.1). 

Visual symptoms of deterioration are noted and compared to those commonly observed on 

structures affected by ASR (Figures 7.2 and 7.3). 

It is often difficult to determine only from field observations whether ASR is the only/main 

factor responsible for the observed distresses since some of the visual signs of deterioration 

generally associated with ASR may have been caused by other processes such as internal 

sulphate attack, or plastic or drying shrinkage. Table 7.6 classifies the occurrence of the features 

obtained from the condition survey as indicative of low, medium, and high potential of ASR 

contribution in the deterioration observed. The assessment of the exposure conditions should 

also contribute to support the observations of the symptoms of distress listed in Table 7.6, as 

follows: 

• Low potential for ASR: Element in dry and sheltered environment. 

• Medium potential for ASR: Element exposed outdoors but sheltered from constant wetting. 

• High potential for ASR: Parts of components frequently exposed to moisture–e.g., rain, 

groundwater, or water due to natural function of the structure (e.g., hydraulic dam or 

bridge). 

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AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

Table 7.6. Classification System for the Condition Survey (modified from CSA A864-00) 

Feature Probability for ASR 

Low Medium High 

Expansion 

and/or 

displacement 

of elements 

None Some evidence (e.g., closure of joints 

in pavements, jersey barriers, spalls, 

misalignments between structural 

members) 

Fair to extensive signs of volume increase 

leading to spalling at joints, displacement 

and/or misalignment of structural members 

Cracking and 

crack pattern 

None Some cracking pattern typical of ASR 

(e.g., map cracking or cracks aligned 

with major reinforcement or stress) 

Extensive map cracking or cracking aligned 

with major stress or reinforcement 

Surface 

discoloration 

None Slight surface discoloration associated 

with some cracks 

Many cracks with dark discoloration and 

adjacent zone of light colored concrete 

Exudations None White exudations around some cracks; 

possibility of colorless, jelly-like 

exudations 

Colorless, jelly-like exudations readily 

identifiable as ASR gel associated with 

several cracks 

If the probability of ASR is low or no visual signs suggestive of ASR are noted during the 

routine inspection program, further work can be postponed until the next inspection. However, 

when the visual signs of deterioration observed on the structure(s) examined are such that AAR 

is a possibility, sampling of the structure under evaluation is recommended to confirm the first 

diagnostic obtained from the visual survey. 

7.2.1.2 Documentation 

Any documents (i.e., testing reports of materials, construction and/or inspection reports) related 

to the structure examined should be gathered as they may provide valuable information in the 

appraisal process. This activity could also be carried out either in preparation for the condition 

survey or following it, i.e., for structures where some signs of deterioration potentially 

indicative of ASR have been noticed. Useful information could include the following (CSA 

2000): 

• Type and location of the structure and, hence, its likely exposure conditions due to the 

nature of operation(s) and geography. 

• Age of the structure and details and dates of any modifications or repairs. ASR may take 

from 3 to even more than 25 years to develop significantly in concrete structures 

depending on factors such as the nature (reactivity level) of the aggregates used, the 

moisture and temperature conditions, and the concrete alkali content. 

• Plans, drawings, and “original” specifications. 

• Details of concrete mixes used, particularly mix proportions, source of cement and 

aggregates, and details of any analyses or tests carried out on concrete materials. The 

availability of samples of these materials should also be checked; some agencies store 

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AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

samples of cements and aggregates used in major projects. 

• Previous inspection/testing reports, especially dates when deterioration was first 

observed. 

• Information from the inspection of other local structures that may have been constructed 

with similar materials, especially if these structures are exhibiting signs of deterioration 

typical of ASR. 

Details regarding the concrete materials, especially the composition and proportion of the 

cement and the type of aggregate used, are most useful when assessing the likelihood of ASR. It 

is recognized that information of this nature is often not available or lacks specific details in the 

case of many structures; however, it is important to collect whatever data are available. 

7.2.1.3 Sampling of Structural Components 

At this stage of the program, sampling is carried out on component(s) of the structures showing 

typical defects suggestive of ASR, which most often correspond to structural components 

exposed to a constant or renewable supply of moisture, with/without cycles of wetting and 

drying (e.g., Figure 7.4A-7.4C). This is essentially done to determine whether or not the 

concrete contains petrographic evidence of ASR. For comparison purposes, it will also be 

useful/appropriate to collect cores from structures/components that are less deteriorated than the 

structure in question, not deteriorated, or not exposed to the severe environmental elements. 

143 
 

 

A B 

C 

D 

Figure 7.4. A-C. Sampling of concrete structures/elements affected by ASR for laboratory 

investigations (e.g., petrographic examination, mechanical testing). D. Cores are properly 

identified and wrapped in plastic film/bag to avoid moisture loss. 

AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

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AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

The samples collected should be labeled carefully, photographed, and, immediately after their 

preliminary examination (for obvious signs of degradation....), wrapped in a plastic film and 

sealed in a plastic bag to prevent alkali-silica gel and surfaces to carbonate, become 

contaminated, or dry out during subsequent transport and storage (Figure 7.4D). More details 

regarding sampling (i.e., type and sample size) and preliminary treatment/analysis of samples 

can be found in Fournier et al. (2010). 

7.2.1.4 Diagnosis – Petrographic Examination 

Petrographic examination is a powerful technique in the diagnosis of the cause of concrete 

deterioration. ASTM C 856 outlines procedures for the petrographic examination of samples of 

hardened concrete. Interesting information regarding petrographic features of ASR-affected 

concrete can be found in several publications, including BCA (1992), St. John et al. (1998), 

CSA (2000), Walker et al. (2006) and Fournier et al. (2010). 

Macroscopic Features of ASR 

Macroscopic signs of concrete deterioration due to ASR (but sometimes not exclusively) can be 

detected by examining the cores immediately after the extraction or in the laboratory in an as 

received condition. Such features can consist of (Figure 7.5): macrocracks in the outer portion 

(or "skin") of the concrete member turning into microcracking in the "internal" part of the 

concrete member, gel staining surrounding surface cracks, dark reaction rims at the periphery of 

reacted aggregate particles, cracks within reactive aggregate particles sometimes extending into 

the cement paste (with/without reaction products gels), alkali-silica gel in air voids of the 

cement paste, and deposits of reaction products on the cracked surfaces of cores. 

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A B
 

C D E
 

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AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

Figure 7.5. Macroscopic observations on cores (as received condition). A. Cores extracted from a 

concrete pavement affected by ASR and showing macrocracks penetrating from the upper and lower 

parts of the pavement. B. Gel staining surrounding cracks and gel exudations at the surface of a core 

extracted from a sidewalk section affected by ASR. C. Fine cracking pattern showing up after re-wetting 

of the core. D. Dark rim surrounding reactive aggregate particles. E. Macrocracks in reactive coarse 

aggregate particles. F. Deposits of alkali-silica gel in a void on core surface. G. Deposits of alkali-silica 

reaction products on the broken surface of a core extracted from a highway bridge structures affected by 

ASR. 146 
AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

Microscopic Features of ASR 

Petrographic features of ASR can be detected on various types of specimens prepared from the 

drilled cores (e.g., polished sections or slices, broken (fresh) surfaces, and thin sections). 

Although not necessarily exclusive to ASR, these features generally consist of the following: 

• Microcracking in aggregates and/or cement paste 

• Reaction product “gel” 

• Reaction rims 

• Loss of the cement paste-aggregate bond 

Microcracking - BCA (1992) and St. John et al. (1998) compared “idealized” cracking patterns 

in concrete specimens affected by various deleterious mechanisms (Figure 7.6). In the case of 

concrete affected by ASR when the reactive fraction is part either of the fine aggregate (Figure 

7.6E) or coarse aggregate (7.6F) fraction, a network of microcracks develops in the inner part of 

the concrete, with only a few “macrocracks” being observed in its outer (surficial) portion. The 

microcracks are found connecting the aggregate particles; when the reactive material is found in 

the coarse aggregate particles, cracks typically run through the particles (Figure 7.6F). 

In the early stages of the reaction, microcracks are generally limited to the reacting aggregate 

particles and the cement paste-aggregate interface. With the progress of expansion, 

microcracks, more or less filled with alkali-silica gel, will extend from the aggregate particles 

into the cement paste (Figures 7.7A-C); depending on the extent of expansion, the cracks will 

cover considerable distances through the paste where they are often filled with secondary 

reaction products (Figures 7.7A, 7.7D, 7.7E). In badly deteriorated concrete specimens, cracks, 

even filled with gel, may run through non-reactive aggregate particles. Consequently, great care 

should be taken to correctly identify the sites (or the aggregate particles) that have generated the 

expansive forces. 

147 
 

A B 

C D 

E F 

AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

Figure 7.6. Typical cracking patterns in concrete affected by different deleterious mechanisms (from 

BCA 1992). A. Internal crack pattern which can be induced by drying shrinkage. B. Internal crack 

pattern which can be caused by internal sulfate attack for delayed ettringite formation (DEF), or 

from sulfates derived from the aggregates. C. Internal crack pattern which can be induced by 

shrinkage of the coarse aggregate. D. Internal crack pattern which can be induced by frost attack. 

E. Internal crack pattern which can be caused by ASR: reactive silica in the sand fraction. F. 

Internal crack pattern which can be caused by ASR: reactive silica in the coarse aggregate. 

148 
 

 

 

 

 

 

 

 

A 

2,5 cm 

B (distance between the vertical lines = 1 cm) C (distance between the vertical lines = 1 cm) 

D (distance between the vertical lines = 1 cm) E (distance between the vertical lines = 1 cm) 

Figure 7.7. Petrographic features of ASR observed on polished concrete sections. Cracks with reaction 

products in coarse (A, C, E) and fine (C) aggregate particles. Cracks running from one aggregate particle 

to another through the cement paste (A-C). Reaction rims around reactive coarse aggregate particles (E, 

B). Reaction products (ASR gel) in cracks (B, D) and voids (A, B, E) of the cement paste. 

AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

149 
 

 

 

 

 

 

 

F G 

H I 

2 mm 0.5 mm 

J K 

10 mm 5 mm 

AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

Figure 7.7 (cont’d). Petrographic features of ASR. F&G. Polished concrete sections treated with uranyl 

acetate solution to enhance the presence of alkali-silica gel (F. natural light; G. under UV illumination 

showing the gel in greenish-yellow staining color filling cracks in the cement paste in the vicinity of 

reactive aggregate particles). H&I. Thin sections micrograph showing reaction products (ASR gel) in 

cracks of coarse aggregate particles and of the cement paste (H), as well as in an adjacent air void of the 

cement paste (I). J&K. Micrographs of concrete sample under the stereomicroscope showing alkali-silica 

reaction products on broken surfaces of reactive coarse aggregate particles and in voids (J), or covering 

cracked surfaces of the cement paste (K). 

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AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

Reaction product “gel” - ASR generates secondary reaction products containing silica, alkalis 

and calcium as typical constituents. The so-called “alkali-silica gel” will be found filling cracks 

within the aggregate particles (Figures 7.7B-7.7E), lining or filling voids (Figures 

7.7B,7.7H,7.7J) and fractured surfaces of the cement paste and the aggregate particles (Figures 

7.7J,7.7K). These deposits will cover more or less important surfaces depending on many 

factors, such as the extent of the reaction-expansion processes that have occurred, the 

availability of water, etc. However, the abundance of gel deposits is not necessarily indicative 

of the magnitude of any resultant expansion and cracking (BCA 1992); cracking due to ASR 

has been observed in many concrete structures while very little gel was found in concrete 

specimens taken from the affected members. 

The confirmation of the presence and the nature of reaction products is not easy. This is often 

done under the scanning electron microscope equipped with an energy dispersive X-Ray 

analyzer (Fournier et al. 2010). Staining techniques have also been proposed to facilitate 

identification of the reaction product gel in concrete affected by ASR (Natesaiyer et al. 1991; 

Stark 1991; Guthrie and Carey 1997). Natesaiyer et al. (1991) proposed a method that consists 

of applying an uranyl acetate solution on polished or fresh broken surfaces of concrete 

specimens to be examined followed by a visual observation of the section under a UV light. 

Stark (1991) indicated that “by applying the uranyl acetate solution to a surface containing the 

gel, the uranyl ion substitutes for alkali in the gel, thereby imparting a characteristic yellowishgreen glow when viewed in the dark using short wavelength ultraviolet light ASR gel fluoresces 

much brighter than cement paste due to the greater concentration of alkali and, subsequently, 

uranyl ion in the gel” (Figures 7.7F-7.7G). This technique, which has also been applied to field 

structures (Stark 1991; AASHTO 1993; ASTM C 856-02), should be used with great care 

following appropriate health and safety procedures because of the potentially hazardous nature 

of the product. Also, technically speaking, the results of the test should be interpreted with great 

care since some aggregates fluoresce naturally, which can incorrectly suggest the presence of 

alkali-silica gel through macroscopic or microscopic examinations. Guthrie and Carey (1997) 

proposed a method that consists in treating fresh concrete surfaces to successive applications of 

Sodium Cobaltinitrite and Rhodamine B. Upon treatment, regions affected by ASR stain either 

yellow or pink. According to Guthrie and Carey (1997), yellow staining would be associated 

with massive ASR-related precipitate with gel-like morphology as well as granular precipitate 

consisting of crystals that have grown from the gel. Yellow stained regions would correspond to 

alkali-bearing siliceous reaction products resulting from ASR. 

Reaction rims - Dark reaction rims are observed at the internal periphery of a number of alkali 

-silica reactive aggregates in deteriorated concrete specimens; these are particularly evident on 

polished sections or slabs of affected concrete cores (Figures 7.7B,7.7E). However, these rims 

must not be mixed up with dark rims that are often found in the outer (but also internal) portion 

of "weathered" gravel particles. When concrete cores are fractured for examining “fresh” 

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AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

broken surfaces, cracks that have formed within the aggregate particles and the cement paste, 

due to the ASR processes, will form zones of weakness where the core will preferentially break. 

The fractured surfaces thus created (which in many cases correspond to “ASR cracking 

surfaces”) often show a dark rim surrounding internal deposits of whitish color (Figure 7.7J). 

Such a feature does not correspond to a "reaction rim" per se; it actually corresponds to a 

typical arrangement of reaction products deposited on the cracking surface, i.e., 1) a dark rim 

covering the immediate internal periphery of the particle, and 2) white deposits going through 

the central portion of the particle showing a powdery aspect. 

Loss of the cement paste-aggregate bond - The interfacial region between the cement paste 

and the aggregate particles certainly represents, because of its nature and the arrangement of 

hydrates that form herein, a preferential zone of weakness where cracks will initiate and run. 

Loss of the cement paste-aggregate bond has been reported as a petrographic consequence but 

is not necessarily indicative of AAR. 

Conclusions from the Petrographic Examination 

Table 7.7 classifies the occurrence of the features obtained from the petrographic examination 

as indicative of low, medium, and high probability of ASR. When petrographic evidence of 

ASR is confirmed, a decision on further steps to be taken is based on factors such as the 

severity of the damage and the "criticality" of the structure (Fournier et al. 2010) (Figure 7.1). 

In some cases, it may be decided that additional “technical” investigations are not required and 

some remedial actions could/should already be implemented. Examples of such cases are 

further discussed in Fournier et al. (2010). Also, in some cases, the extent of the damage is such 

that no immediate action is needed; the structure will then be re-examined as part of the routine 

condition survey (Figure 7.1). However, in the case of “critical” structures (e.g., large size/ 

major highway bridges and pavements, hydraulic dams) or when the extent of deterioration is 

significant, a detailed laboratory and/or in-situ investigation program may be desirable/ 

necessary to determine the potential for the progress of ASR in the structure (prognosis). 

152 
 

 

AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

Table 7.7. Classification System for Petrographic Examination (Fournier et al. 2010) 

Probability of ASR Nature and Extent of Features 

Low 

No potentially reactive rock types (from petrographic examination of thin sections): 

• no alkali-silica gel present (or only in a very few air voids), no (or very few) 

reaction rims, no (or very few) sites of expansive reaction, very limited cracking 

within the aggregate particles that extends, or not, into the cement paste; 

• presence of other indicative features rarely found. 

Medium 

Presence of some features generally consistent with AAR: 

• damp patches on core surfaces; 

• presence of potentially reactive rock types; 

• cracking/microcracking within a fair number of aggregate particles; some of the 

cracks may extend into the cement paste; 

• alkali-silica gel observed in cracks within a fair number of aggregate particles 

and/or cracks within the cement paste and/or air voids; 

• darkening of cement paste around reactive aggregate particles, cracks or voids; 

• reaction rims around the internal periphery of a fair number of reactive particles. 

High 

Presence of extensive signs of ASR (as described in the previous section but observed 

in larger frequency), for instance: 

• evidence of site of expansion reaction, i.e., where evidence or reaction and 

emanation of swelling pressure can be positively identified; and/or 

• presence of gel in cracks and voids associated with several reactive particles and 

readily visible to the unaided eye or under low magnification. 

7.2.2 ASR Investigation Program Step 2 - Prognosis 

This part of the study aims at generating additional technical information, leading to a more 

complete assessment of the degree of damage due to ASR in the concrete structure and the 

selection of most appropriate remedial measures (Figure 7.1). The selection of the activities will 

depend on the criticality of the structure, the amount of time/funding available to generate the 

data, and the degree of precision expected. 

7.2.2.1 In-Situ Investigations 

An in-situ investigation program, which could include monitoring of expansion, deformation, 

availability of moisture (to account for seasonal temperature changes), and non-destructive 

testing, can provide “prognostic” information for ASR-affected structural members when 

carried out at regular intervals over several years. The in-situ investigation program can include 

one or several of the activities described hereafter. Details on the procedures/methods can be 

found in Fournier et al. (2010). 

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AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

Surface Cracking 

The extent of surface cracking on severely exposed/cracked sections of concrete elements is 

somewhat related to the overall amount of expansion reached by the affected member. The 

Cracking Index (CI) method consists of the measurement and summation of crack widths along 

a set of lines drawn perpendicularly on the surface of the concrete element investigated (LCPC 

1997, 1999) (Figure 7.8). 

154 
 

 

 

 

 

 

 

 

 

 

 

A B 

B

O

C

A

C D 

E 

Interval (10 cm) 

1 2 3 4 5 Base 

Length 

(m) 

# 

cracks 

Crack opening (mm) 

6 7 8 9 10 Total 

sum 

Avg. 

/crack 

Avg. 

/m 

C.I. 

mm/m 

Vertical

direction

OA 0.1, 0.1 0.2 -­ -­ 0.6 0.5 6 1.8 0.3 3.6 

3.2 0.4 -­ -­ 0.4 -­

BC 0.1 0.4 -­ 0.1 0.1 0.5 7 1.4 0.2 2.8 

-­ 0.3 0.2 0.2 -­

Horizontal

direction

OB 

-­ -­ 0.3, 0.5 0.4 0.3 

0.5 7 2.8 0.4 5.6 

4.6 0.4 0.3 -­ -­ 0.6 

AC 

0.5 0.2 -­ -­ 0.3 

0.5 8 1.6 0.2 3.6 0.05 0.05 0.1, 0.2 -­ 0.2 

Figure 7.8. Measurements of the Cracking Index on ASR-affected pavement (A) and jersey barrier (B). 

The cracks can be examined with a magnifying lens (C). Using a transparent crack card to measure their 

width along the measurement lines (D). An example of the data generated in the Cracking Index method 

is given in (E); the values of C.I. are given separately for the vertical and horizontal measurements. 

AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

The method gives a quantitative assessment of the extent of cracking in structural members, 

either punctually (when obtained at a specific time) or as a progressive process when 

performing the measurements on a regular basis at the exact same location (rate of expansion – 

prognosis). 

155 
 

 

   

   

   

Jan 2012

May 2012

Aug 2012

A B 

0,130 4,00 

CIMay 2011

CIMay 2012

CIAug 2012

Cracking Index (mm/m) 

0,110 3,50 

3,00 

2,50 

2,00 

1,50 

1,00 

0,50 

Expansion (%) 0,090 

0,070 

0,050 

0,030 

0,010 

1 2 3 4 

Figure 7.9. Measurements of Expansion and Cracking Index on Concrete Housing Foundations 

Suffering from Deleterious Aggregate Reactions (Francoeur et al. 2012) 

-0,010 0,00 

Blocks 

1 2 3 4 

Blocks 

AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

For example, Francoeur et al. (2012) used the CI method to study the progress of expansion and 

cracking in metric size concrete blocks exposed outdoors and suffering from deleterious 

aggregates reactions (oxidation of sulphide-bearing aggregates). The authors found a good 

correlation between the expansion of the concrete blocks and the progress of the surface 

cracking measured through the CI Method (Figure 7.9). 

Expansion and Deformation Measurements 

Measurements of expansion/deformation can be performed using different means (e.g., demec 

points, metallic references drilled into the surface of selected structural members, 

extensometers, invar wires/rods or optical systems (leveling)) (Fournier et al. 2010; LCPC 2003, 

2009; Thomas et al. 2012b) (Figure 7.10). Fiber-optic and vibrating wire systems can also be 

used, deformation measurements being performed and the data transmitted automatically to 

central servers for further treatment. On a larger scale, instruments such as inclinometers and 

inverted pendulums can be installed in strategic parts of the structure to evaluate the relative 

156 
AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

movement, deflections, clearances at joints, etc. (e.g., Thompson et al. 1995; Danay et al. 1993; 

Gaudreault 2000). 

157 
 

 

A B C 

D E 

F G 

Figure 7.10. In-situ measurements of expansion and deformation in ASR-affected concrete 

elements. A-E. Length-change measurements in a concrete highway barrier wall, reinforced 

concrete columns and a concrete pavement affected by ASR. F-G. Invar-bar extensometer used 

for the in-situ monitoring of deformation/movement associated with ASR (Gaudreault 2000). 

AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

158 
 

 

 

C D 

Figure 7.11. In-situ measurements of humidity in concrete. A. Wooden-stick method. B-C. 

Portable humidity probes. D. Automatic in-situ monitoring of temperature, humidity and 

expansion (vibrating wire) in a bridge deck affected by ASR (Siemes and Gulikers 2000). 

AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

Temperature and Humidity Measurements 

The relative humidity is one of the essential conditions to maintain ASR in a concrete structure; 

it can be measured over time with depth or laterally in different concrete elements using various 

techniques (e.g., wooden stick, portable or permanent probes) (Thomas et al. 2012b; Jensen 

2004) (Figure 7.11). The monitoring of relative humidity provided very useful information for 

the understanding of the beneficial effect of silane treatments on median barriers affected by 

ASR (Bérubé et al. 2002a). 

A B 

Non-Destructive Testing 

Periodic measurements, such as pulse velocity, impact echo, acoustic methods, etc. can be made 

on specific members of the affected structure (at the surface or in the bottom of drilling holes) 

to determine the evolution/extent of internal cracking or deterioration (Thomas et al. 2012b; 

Moradi-Marani et al. 2011; Tajari et al. 2011; Sargolzahi et al. 2010) (Figure 7.12). 

159 
 

 

 

A B 

Figure 7.12. Non-destructive testing of ASR-affected concrete structures. A. Impact-echo. 

B. Non-linear acoustic technique. 

AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

7.2.2.2 Advanced Laboratory Investigations 

A series of tests can be performed on core samples extracted from structural members showing 

different degrees of deterioration and/or of exposure conditions. The data will provide 

information for further evaluating the current concrete condition, the expansion reached to date, 

the current rate of expansion, and the potential for future expansion of the concrete. 

Quantitative Petrography 

The Damage Rating Index (DRI), a semi-quantitative petrographic technique, evaluates the 

condition of concrete by counting, under the stereomicroscope (~16x magnification), the 

number of typical petrographic features of ASR in a grid system drawn at the surface of 

polished concrete sections (Grattan-Bellew 1992) (Figure 7.13). The DRI represents the 

normalized value (to 100 mm2) of the presence of these features after the count of their 

abundance over the surface examined has been multiplied by weighing factors representing 

their relative importance in the overall deterioration process (Grattan-Bellew and Mitchell 

2006) (Table 7.8). The method gives a quantitative assessment of the extent of internal damage 

in structural concrete members, exposed or not to moisture, either punctually (i.e., at a specific 

time - diagnosis) or as a progressive process when performing the measurements on a regular 

basis on cores extracted at the same location (prognosis). 

160 
 

 

A B 

1cm

1cm 

Figure 7.13. Examination of the polished concrete section under the stereomicroscope for the 

determination of the Damage Rating Index. Petrographic features of deterioration (Table 7.8; 

Figure 7.7) are counted in a one cm x one cm grid system drawn at the surface of the polished 

concrete section. 

 

 

AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

Table 7.8. Petrographic Features and Weighing Factors for the DRI 

(Grattan-Bellew and Mitchell 2006) 

Petrographic feature Abbreviation Weighing factor 

Coarse aggregate with cracks CrCA x 0.75 

Open crack in coarse aggregate OCrCA x 4.0 

Coarse aggregate with cracks and reaction products Cr + RPCA x 2.0 

Coarse aggregate debonded CAD x 3.0 

Reaction rims around aggregate RR x 0.5 

Cement paste with cracks CrCP x 2.0 

Cement paste with cracks and reaction products Cr + RPCP x 4.0 

Air voids lined or filled with reaction products RPAV x 0.50 

Thomas et al. (2012) found a strong correlation between the extent of ASR (obtained from the 

DRI) and the exposure conditions of structural bridge members (Figure 7.14). Rivard et al. 

(2000) used the method to estimate the amount of expansion reached by concrete specimens 

cored from a large concrete dam affected by ASR. 

161 
 

 

 

 

 

A B 

Sites 1,2,3 

C D 

Site 3 

Site 1 

MS 3 

MS 2 

MS 1 

0 100 200 300 400 500 600 700 

CrCA OCrCA 

Cr+RPCA CrCP 

Cr+RPCP CAD 

RR RPAV 

528 

195 

133 

Damage Rating Index 

E (distance between the vertical lines = 1 cm) F (distance between the vertical lines = 1 cm) 

AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

Figure 7.14. A. Highway bridge affected by ASR in Bangor, Maine. Coring sites in the 

abutment (not exposed (site 1 - B) and the wing wall (exposed (site 3 - C)). D. DRI results for 

cores obtained from sites 1 to 3; the higher the DRI, the higher the degree of ASR damage in 

the concrete. E. Polished section from site 1 showing very limited signs of deterioration. F. 

Polished section from site 3 showing extensive cracking filled with alkali-silica gel in aggregate 

particles and the cement paste. 

162 
AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

Mechanical Testing 

Several authors have shown that tensile strength is a much better indicator of the progression of 

ASR than compressive strength (Blight et al. 1981; Swamy and Al-Asali 1986; Clayton 1989; 

ISE 1992; Siemes and Visser 2000; Smaoui et al. 2006) which is generally affected only at 

much higher expansion levels (Figures 7.15 and 7.16). Direct tensile strength (traction tests) is 

also more sensitive to ASR than splitting tensile (Brazilian) strength (Clayton 1989; ISE 1992; 

Siemes and Visser 2000; Smaoui et al. 2006). The use of the tensile-to-compressive strength 

ratio was suggested as a good indication of internal damage due to AAR (Nixon and 

Bollinghaus 1985). The tensile-to-compressive strength ratio of sound concrete typically varies 

from 0.07 to 0.11. In investigations dealing with AAR, it was suggested that a ratio less than 

0.06 was indicative of internal deterioration due to ASR. Since the ultimate compressive 

strength of concrete supplied in the field is generally greater than the designed 28-day strength, 

a reduction in compressive strength due to AAR is unlikely to be critical in current practice, and 

failure through loss in compressive strength is also unlikely (ISE 92; Swamy 1995). 

Figure 7.15. Residual mechanical properties for concrete affected by ASR, as percentage of 

values obtained at the same age from unaffected concrete; the expansions of the companion test 

prisms are also given (Pleau et al. 1989) 

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AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

Figure 7.16. Lower Bound of Residual Mechanical Properties for ASR-Affected Concrete 

Specimens, Expressed as a Percentage of Values Obtained for Unaffected Concrete at 28 Days 

(ISE 1992) 

A number of tests have shown that losses in elastic modulus and flexural strength could lead to 

substantial reductions in flexural rigidity and structural stiffness of affected members. Hobbs 

(1986) and Smaoui et al. (2006) noted that the modulus of elasticity is more affected than the 

compressive and indirect tensile strengths, both of which having been quite similarly affected 

by ASR. The rate of reduction in modulus of elasticity can vary according to the type of 

reactive aggregate (Smaoui et al. 2006); important reduction in the modulus of elasticity can 

occur even at a low level of AAR expansion – actually even when compressive strength of the 

affected concrete is still increasing (Pleau et al. 1989) (Figure 7.15). According to Clark (1990), 

there would be no significant reduction in modulus of elasticity for expansions less than 0.05%. 

Losses in modulus of elasticity and flexural strength between 20 and 60% were reported for 

expansions ranging from 0.1 to 0.3% (ISE 1992), and could even reach 80% for the former at 

very high expansion levels. For the two reactive aggregates tested in their study, Smaoui et al. 

(2006) found relatively similar reductions in the modulus of elasticity measured in compression 

and in traction. Swamy and Al-Asali (1986, 1988) observed that the dynamic modulus of 

elasticity is affected at an early age, even before reaching the 0.1% expansion level. 

The Stiffness Damage Test (SDT), which consists in subjecting concrete cores to 5 cycles of 

uniaxial loading/unloading up to a maximum of 5.5 MPa (Chrisp et al. 1989) or 10 MPa 

(Smaoui et al. 2004) (Figure 7.17A), can be used for assessing the ASR expansion attained to 

date through (1) the energy dissipated during the first cycle (hysteresis loop), and (2) the 

accumulated plastic strain after the 5 load/unload cycles (Figure 7.17B). Recent research 

164 
 

 

AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

indicates that more accurate results are obtained when the SDT is carried out at a percentage of 

the design (28-day) strength (40%) instead of a fixed load (Sanchez et al. 2012). Calibration 

curves correlating the above output parameters and expansion obtained on laboratory specimens 

can be used for estimating the amount of expansion reached to date by the field concrete 

(Smaoui et al. 2004) (Figure 7.17C). 

A B 

 

 

 

Hysteresis loop 

(1st cycle) 

Total strain 

(5 cycles) 

Strain (mm/m) 

C 

0.0 

0.2 

0.4 

0.6 

0.8 

1.0 

1.2 

Potsdam 

R2=1 

Quebec 

R2=0.98 NM 

R2=0.99 

Texas 

R2=0.92 

Limeridge

R2=0.83 

Dissipated energy (joules x 10-3/m3) 

0.000	 0.080 0.160 0.240 0.320 0.400 

Expansion (%) 

Figure 7.17. Mechanical testing of concrete cores using the Stiffness Damage Test (SDT). A. 

Cores subjected to 5 loading/unloading cycles up to 10 MPa. B. The best output parameters 

correspond to the energy dissipated during the first cycle (hysteresis loop) and the accumulated 

plastic strain after the 5 cycles. C. Calibration curves for different reactive aggregates (Smaoui 

et al. 2004). 

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AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

Similar to the DRI, the SDT can provide a quantitative assessment of the extent of internal 

damage in structural concrete members, exposed or not to moisture, either punctually (i.e., at a 

specific time - diagnosis) (e.g., Figure 7.18) or as a progressive process when performing the 

measurements on a regular basis on cores extracted at the same location (prognosis). 

A – Core from Site 1 B – Core from Site 3 

60,00 60,00

50,00 50,00

Load (KN)40,00

30,00

20,00

Load (KN)40,00

30,00

20,00

10,00 10,00

0,00

0 200 400 600 800 1000

Strain (microstrain)

C D 

0,00

0 200 400 600

Strain (microstrain)

800 1000

Dissipated Energy (J/m3

)

3000 

A First Cycle hysteresis 

Modulus of elasticity (GPa) 35 

2500 B 30 Modulus of elasticity 

C 

2000 Average

1500 

1000 

500 

0 

A 25 

20 

B
 

C
 

Average 15 

10 

5 

0 

Site 1 Site 3 Site 1 Site 2 

Core samples Core samples 

Figure 7.18. Results of Stiffness Damage Testing on cores extracted from the highway bridge 

structure illustrated in Figure 7.14. A. SDT result for a core extracted from site 1 (abutment not 

exposed). B. SDT result for a core extracted from site 3 (wing wall exposed). C. Comparison of 

SDT results, for instance the first cycle hysteresis, for cores extracted from sites 1 (under bridge 

deck - less deteriorated) and 3 (exposed to moisture – more deteriorated). Higher dissipated 

energy values are obtained for ASR-affected concrete cores (site 3). D. Comparison of SDT 

results, for instance the average values of the modulus of elasticity for the 2nd and 3rd cycles, 

for cores extracted from sites 1 (under bridge deck - less deteriorated) and 3 (exposed to 

moisture – more deteriorated). Lower modulus of elasticity values are obtained from ASRaffected concrete cores (site 3). 

Expansion Tests on Cores

The most commonly used method involves the testing of concrete cores maintained at 38°C and 

95% R.H. They are expected to provide an ‟estimate” of the potential for further expansion of 

166 
AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

ASR-affected concrete over a relatively short period of time, e.g., six months to one year 

(Fournier et al. 2010; Fecteau et al. 2012; Bérubé et al. 2002b; CSA 2000) (Figure 7.19). After 

an initial “conditioning” period during which the concrete core will reach a volumetric 

equilibrium with respect to its new condition (i.e., unrestrained, high temperature and humidity, 

additional expansion of preexisting ASR gel due to unrestrained and very humid test 

conditions), expansion is measured and tentatively related to a potential for further expansion 

due to ASR. However, difficulties are often encountered in the interpretation of the test results 

(Bérubé et al. 2002b), mainly because of: (1) unknown true correlation between “free 

expansion” of cores and the actual expansion in reinforced concrete members; (2) uncertain 

correlation of ASR expansion with respect to temperature, which is normally lower in the field; 

(3) extreme humidity in the expansion tests; and (4) the possibility that the tested concrete may 

be abnormally cracked and porous with respect to the overall field concrete member under 

study. A further complication arises from the leaching of alkalis from relatively small 

specimens stored at 100% relative humidity; this can lead to an underestimation of the residual 

potential for ASR. Immersion tests on cores in 1N NaOH solution at 38°C are generally 

considered to indicate the absolute degree of reactivity of the aggregates present in the concrete 

under study (Bérubé et al. 2002b). 

167 
 

A C
 

B 

AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

Figure 7.19. Residual expansion testing carried out on core samples (38oC, R.H. > 95%). A. 

Expansion measurement of the core. B. Mass measurements are also carried out in parallel to 

the expansion measurements to determine the moisture uptake capacity of the core. C. Example 

of comparative mass and residual expansion measurements for cores. This allows 

differentiating the hydric reequilibration of the concrete at the beginning of the test (due to 

moisture uptake only) and the residual expansion potential due to ASR. 

Alkali Content of Concrete 

The measurement of the ‟available/residual” alkali content in concrete can yield interesting 

information in assessing whether the concrete tested contains sufficient alkalis to sustain this 

reaction (prognosis). The ‟available/ residual” alkali content in concrete can be obtained by hot 

168 
AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

-water extraction or, when possible, using pore solution extraction devices (Fournier et al. 

2010; Bérubé and Tremblay 2004). Over time, significant alkalis can be released from 

aggregates and contribute to an increase in the concrete alkali content (Bérubé et al. 2002c). 

Since the alkali content can be subject to considerable variation within a single concrete 

element, or between different concrete components of the same structure, separate 

determinations should be made on a number of samples taken from different components at 

different depths, and representing concrete showing varying severity of deterioration and 

subjected to different exposure conditions (rain, sun, buried or underwater portions of the 

structures, etc.). 

7.2.2.3 Collective Assessment of In-situ and Laboratory Investigations 

Fournier et al. (2010) provides a scheme for the analysis of the results obtained from the in-situ 

and laboratory investigations for prognostic evaluation of ASR. In summary, the authors 

suggest that in the case of reinforced concrete members (e.g., bridges), the potential for further 

expansion due to ASR will be expressed by the number of years before the reinforcing steel 

yield (in the direction of lower or lack of restraint) could occur, which requires data on the ASR 

expansion attained to date and the current expansion rate. In the case of concrete pavements, 

the potential for further expansion due to ASR will be expressed by the number of years before 

the joints could close, which requires information on the current expansion rate and widths of 

joints. The urgency of applying remedial actions will then be partly based on criteria related to 

the delay before steel yielding in reinforced concrete members (expansion criteria of > 0.20% is 

proposed), or the delay before the closure of expansion joints occur in the case of concrete 

pavements. It is recommended that further action be taken when the delay before steel yielding 

or joint closure is estimated to be less than 5 years, for example by starting an in-situ 

monitoring program of expansion, with measurements at least on a yearly basis, and/or by 

performing a structural assessment of the member/structure; it would be appropriate to confirm 

an assessment that has been based essentially on expansion tests on cores rather than on in-situ 

monitoring. 

7.3 CONCLUSION 

Unexpected or premature concrete deterioration due to alkali-silica reactivity (ASR) is a 

widespread problem worldwide. Routine site inspections performed on a regular basis may 

permit identification of the problem; however, ASR in concrete cannot generally be diagnosed 

without detailed laboratory and site investigations. Such investigations would include 

determination of the distribution and severity of the various defects affecting the concrete 

structure, as well as laboratory testing (petrography) of samples collected from the affected 

concrete structures. For critical structures such as large dams and fair to large size highway 

169 
AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

bridges, detailed investigations including a more extensive sampling program might be 

necessary to quantify the current condition of the concrete, and to evaluate the potential for 

future deterioration (prognosis). Such investigations can involve a detailed sampling program 

for further testing in the laboratory and in-situ monitoring of the progress of expansion/ 

deterioration. The results of the above processes of investigation will then be analyzed to 

propose appropriate management actions to be taken for each of the particular applications. 

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AAR Facts Book Chapter 7 – Diagnosis and Prognosis 

REFERENCES 

AASHTO. 1993. “Standard Method of Test for Rapid Identification of Alkali-Silica Reaction 

Products in Concrete.” AASHTO T 299, American Association of State and Highway 

Transportation Officials, Washington, DC. 

AASHTO. 2011. AASHTO guide manual for bridge element inspection, 1st Edition, American 

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Book of ASTM Standards, Section Four, Vol. 04.02 Concrete and Aggregates, ASTM C856-02, 

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Bérubé, M.A. and Tremblay, C. 2004. “Chemistry of pore solution expressed under high 

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Bérubé, M.A., Chouinard, D., Pigeon, M., Frenette, J., Rivest, M. and Vézina, D. 2002a. 

“Effectiveness of Sealers in Counteracting Alkali-Silica Reaction in Highway Median Barriers 

Exposed to Wetting and Drying, Freezing and Thawing, and Deicing Salts.” Canadian Journal 

of Civil Engineering, 29(2): 329-337. 

Bérubé, M.A., Frenette, J. and Rivest, M. 2002b. “Laboratory Assessment of the Potential Rate 

of ASR Expansion of Field Concrete.” Cement, Concrete and Aggregates, 24(1): 28-36. 

Blight, G.E., McIver, J.R., Schutte, W.K. and Rimmer, R. 1981. “The Effects of AlkaliAggregate Reaction on Reinforced Concrete Structures Made with Witwatersrand Quartzite 

Aggregate.” Proceedings of the 5th International Conference on Alkali-Aggregate Reaction in 

Concrete, S252/15, Cape Town, South Africa. 

Bérubé, M.A., Duchesne, J., Dorion, J.F. and Rivest, M. 2002c. “Laboratory Assessment of 

Alkali Contribution by Aggregates to Concrete and Application to Concrete Structures Affected 

by Alkali-Silica Reactivity.” Cement and Concrete Research, 32: 1215-1227. 

British Cement Association (BCA). 1992. The Diagnosis of Alkali-Silica Reaction – Report of 

a Working Party. Wexham Springs, Slough, U.K., 44 p. 

CSA. 2000. Guide to the Evaluation and Management of Concrete Structures Affected by 

Alkali-Aggregate Reaction. CSA A864-00, Canadian Standards Association, Mississauga, 

Ontario, Canada. 

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Chrisp, T.M., Wood, J.G.M., Norris, P. 1989. “Towards Quantification of Microstructural 

Damage in AAR Deteriorated Concrete.” International Conference on Recent Developments 

on the Fracture of Concrete and Rocks, Elsevier Applied Science, London, U.K., 419-427. 

Clark, L.A. 1990. “Structural Aspects of Alkali-Silica Reaction.” Structural Engineering 

Review, 2(2), June. 

Clayton, N. 1989. “Structural Performance of ASR Affected Concrete.” Proceedings of the 8th 

International Conference on Alkali-Aggregate Reaction in Concrete, (Eds. K. Okada, S. 

Nishibayashi and M. Kawamura), Kyoto, Japan, 671-676. 

Danay, A., Adeghe, L. and Hindy, A. 1993. “Diagnosis of the Cause of the Progressive 

Concrete Deformations at Saunders Dam.” Concrete International, 25-33. 

Fecteau, P.L., Fournier, B. and Duchesne, J. 2012. “Residual expansion testing : new aspects 

on cores extracted from exposure blocks submitted to environmental conditions.” 14th 

International Conference on AAR in Concrete, 20-25 May, Austin, TX, electronic. 

Fournier, B., Bérubé, M.A., Folliard, K.J. and Thomas, M.D.A. 2010. Report on the diagnosis, 

prognosis and mitigation of alkali-silica reaction (ASR) in transportation structures. FHWAHIF-09-004, Federal Highway Administration. 

Francoeur, J., Fournier, B. and Duchesne, J. 2012. Étude de la détérioration du béton en 

présence de granulats incorporant des sulfures de fer. ACI Quebec and Eastern Ontario Chapter 

Annual Seminar on Progress in Concrete Technology, November, Boucherville, Québec. 

Gaudreault, M. 2000. “The St. Lawrence Seaway (Quebec, Canada): A Case Study in the 

Management of Structures Affected by Alkali-Aggregate Reaction.” Proceedings of the 11th 

International Conference on Alkali-Aggregate Reaction in Concrete, (Eds. M.A. Bérubé, B. 

Fournier and B. Durand), Quebec City, Canada, 1293-1302. 

Grattan-Bellew, P.E. 1992. “Comparison of Laboratory and Field Evaluation of Alkali-Silica 

Reaction in Large Dams.” First International Conference on Concrete AAR in Hydroelectric 

Plants and Dams, September-October, Fredericton, NB, Canada, 23 p. 

Grattan-Bellew, P.E. and Mitchell, L.D. 2006. “Quantitative petrographic analysis of concrete – 

The Damage Rating Index (DRI) method, a review.” Marc-André Bérubé symposium on AAR 

in concrete, CANMET/ACI Advances in concrete technology, Montréal, Canada, 321-334. 

Guthrie, G.G., Jr. and Carey, J.W. 1997. “A Simple Environmentally Friendly, and Chemically 

Specific Method for the Identification and Evaluation of the Alkali-Silica Reaction.” Cement 

and Concrete Research, 27(9): 1407-1417. 

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Hobbs, D.W. 1986. “Alkali-Silica Reaction in Concrete.” The Structural Engineer, 64A(12): 

381-383. 

Institution of Structural Engineers (ISE). 1992. Structural Effects of Alkali-Silica Reaction – 

Technical Guidance Appraisal of Existing Structures. Institution of Structural Engineers, 

London, 45 p. 

Jensen, V. 2004. “Measurements of cracks, relative humidity and effects of surface treatments 

on concrete structures damaged by alkali-silica reaction.” 12th International conference on 

AAR in Concrete, Beijing, China, October, Int. Academic Publishers, Beijing World Publishing 

Corp., 1245-1253. 

Laboratoire Central des Ponts et Chaussées (LCPC). 1997. Détermination de l’indice de 

fissuration d’un parement de béton. Méthode no. 47, Ministère de l’équipement, des transports 

et du logement, Paris. 

Laboratoire Central des Ponts et Chaussées (LCPC). 1999. Manuel d’identification des 

réactions de dégradation interne du béton dans les ouvrages d’art. Ministère de l’équipement, 

des transports et du logement, Paris. 

Laboratoire Central des Ponts et Chaussées (LCPC). 2003. Aide à la gestion des ouvrages 

atteints de réactions de gonflement interne. Ministère de l’équipement, des transports et du 

logement, Paris. 

Laboratoire Central des Ponts et Chaussées (LCPC). 2009. Méthodes de suivi dimensionnel et 

de suivi de la fissuration des structures. Ministère de l’équipement, des transports et du 

logement, Paris. 

Moradi-Marani, F., Kodjo, S.A., Rivard, P. and Lamarche, C.P. 2011. “Application of the 

mechanical perturbation produced by traffic as a new approach of nonlinear acoustic technique 

for detecting microcracks in concrete : a laboratory simulation.” Conference on Review of 

progress in quantitative nondestructive evaluation (QNDE), Burlington, USA, 17-22 July. 

Natesaiyer, K., Stark, D. and Hover, K.C. 1991. “Gel Fluorescence Reveals Reaction Product 

Traces.” Concrete International, January, 25-28. 

Nixon, P.J. and Bollinghaus, R. 1985. “The effect of Alkali-Aggregate Reaction on the Tensile 

and Compressive Strength of Concrete.” Durability of Building Materials, 2: 243-248. 

Pleau, R., Bérubé, M. A., Pigeon, M., Fournier, B. and Raphaël, S. 1989. “Mechanical Behavior 

of Concrete Affected by AAR.” 8th International Conference on AAR in Concrete. Kyoto, 

Japan, 721-726. 

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Rivard, P., Fournier, B. and Ballivy, G. 2000. “Quantitative Petrographic Technique for 

Concrete Damage Due to ASR: Experimental and Application.” Cement, Concrete and 

Aggregates, 22(1): 63-72. 

St-John, D.A., Poole, A.W. and Sims, I. 1998. Concrete Petrography: A handbook of 

investigative techniques. Arnold, London, 474 p. 

Sanchez, L., Fournier, B. and Jolin, M. 2012. “Study of the parameters of the stiffness damage 

test for assessing concrete damage due to alkali-silica reaction.” Proceedings of the 14th 

International Conference on AAR in Concrete, Austin,Texas, 20-25 May, electronic. 

Sargolzahi, M., Kodjo, S.A., Rivard, P. and Rhazi, J. 2010. “Effectiveness of nondestructive 

testing for the evaluation of ASR in concrete.” Construction & Building Materials, 24(8): 1398­

1403. 

Siemes, T. and Gulikers, J. 2000. “Monitoring of Reinforced Concrete Structures Affected by 

Alkali-Silica Reaction.” Proceedings of the 11th International Conference on Alkali-Aggregate 

Reaction in Concrete (Eds. M.A. Bérubé, B. Fournier and B. Durand), Quebec City, Canada, 

1205-1214. 

Siemes, T. and Visser, J. 2000. “Low Tensile Strength in Older Concrete Structures with Alkali 

-Silica Reaction.” Proceedings of the 11th International Conference on Alkali-Aggregate 

Reaction in Concrete (Eds. M.A. Bérubé, B. Fournier and B. Durand), Quebec City, Canada, 

1029-1038. 

Sims, I. and Nixon, P.J. 2010. Outline guide to the use of RILEM methods in assessments of 

alkali-reactivity potential. RILEM Recommended Test method AAR-0. RILEM committee 

documentation, September. 

Smaoui, N., Bissonnette, B., Bérubé, M.A., Fournier, B. and Durand, B. 2006. “Mechanical 

Properties of ASR-Affected Concrete Containing Fine or Coarse Reactive Aggregates.” Journal 

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Smaoui, N., Bérubé, M.A., Fournier, B., Bissonnette, B. and Durand, B. 2004. “Evaluation of 

the Expansion Attained to Date by ASR-Affected Concrete – Part I: Experimental Study.” 

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Swamy, R.N. and Al-Asali, M.M. 1988. “Engineering Properties of Concrete Affected by 

Alkali-Silica Reaction.” ACI Materials Journal, 85: 367-374. 

Swamy, R.N. 1995. “Effects of Alkali-Aggregate reactivity on Material Stability and Structural 

Integrity.” Proceedings of the CANMET/ACI International Workshop on Alkali-Aggregate 

Reactions in Concrete, Dartmouth, Nova Scotia, 1-4 October, 293-309. 

Tajari, M., Shekarchi, M. and Sadri, A. 2011. “Use of Impact-echo Technique for Detection of 

Distributed Damage in Concrete due to ASR.” Material Evaluation, 69(7): 881-890. 

Thomas, M.D.A., Fournier, B., Folliard, K.J. and Resendez, B. 2011. Alkali-Silica Reactivity 

Field Identification Handbook, FHWA-HIF-12-022, FHWA, 80 p. 

Thomas, M.D.A., Fournier, B., Folliard, K.J. and Resendez, B. 2012a. Alkali-Silica Reactivity 

Surveying and Tracking Guidelines, July, 32 p. 

Thomas, M.D.A., Folliard, K.J., Fournier, B., Drimalas, T. and Rivard, P. 2012b. “Study of 

remedial actions on highway structures affected by ASR.” 14th International Conference on 

AAR in Concrete, Austin, Texas, 20-25 May, electronic. 

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Program – Mactaquac Generating Station, NB.” Proceedings of the CANMET/ACI 

International Workshop on Alkali-Aggregate Reactions in Concrete, Dartmouth, Nova Scotia, 1 

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Villeneuve, V., Fournier, B. and Duchesne, J. 2012. “Determination of the damage in concrete 

affected by ASR – the Damage rating Index (DRI).” 14th International Conference on AAR in 

Concrete, Austin, Texas, 20-25 May, electronic. 

Walker, H.N., Lane, D.S. and Stutzman, P.E. 2006. Petrographic Methods of Examining 

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Highway Administration. 

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AAR Facts Book Chapter 8 – Mitigation Methods 

8 – Mitigation Methods for ASR-Affected Structures 

8.1 INTRODUCTION 

This chapter describes various mitigation measures that are available for ASR-affected 

structures, identifies options that have been used the most, discusses those whose effectiveness 

has been proven in the laboratory and field, and describes those that remain experimental in 

nature due to lack of data/information proving their merit in real-world applications. 

The main objective of this chapter is to provide guidance on means of extending the service life 

of ASR-affected structures. The term “mitigation” is used in lieu of “repair” because the 

methods described herein are generally not able to, nor are they intended to, repair or restore the 

original properties or integrity to the ASR-affected structure. Rather, the intention is to reduce 

future expansion of the structure or to lessen the detrimental impact of future expansion. 

The majority of the work to date on treating existing structures has focused on ASR-affected 

structures, as opposed to ACR-affected structures, and there are by far many more ASRaffected structures worldwide. As such, the focus of this portion of this protocol is aimed at 

ASR-affected structures. However, some of the mitigation measures, particularly those aimed at 

drying the concrete, would be helpful whether it is ASR or ACR that is impacting the structure. 

 

8.2 OVERVIEW OF MITIGATION METHODS 

Figure 8.1 summarizes the various mitigation options that have been applied to field structures 

affected by ASR. This section will briefly discuss each of the options shown in Figure 8.1 and 

will then focus on those that have the greatest potential for effectively treating ASR-affected 

structures. For each of these options, the merits will be discussed, as well as inherent 

shortcomings, both in terms of general applicability to field structures and specific application 

to certain structures. 

• Improved drainage 

• Application of coatings/sealers 

• Application of cladding 

• Crack filling 

• Application of lithium compounds 

• Application of restraint (FRP, etc.) 

• Saw cutting/slot cutting 

Figure 8.1. Mitigation Methods for ASR-Affected Concrete Structures 

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AAR Facts Book Chapter 8 – Mitigation Methods 

The first four methods highlighted in Figure 8.1 are all aimed at reducing the relative humidity 

in concrete, and for convenience, these methods will be discussed together in section 8.3. 

Section 8.4 will describe various methods of applying lithium-based compounds to ASRaffected structures. Lastly, methods aimed at restraining ASR-induced expansion and relieving 

ASR-induced stress are briefly discussed in sections 8.5 and 8.6, respectively. 

The Federal Highway Administration (FHWA) established the ASR Development and 

Deployment Program (under FHWA Contract DTFH61-06-D-00035) in 2006 to provide 

technical assistance to States and practitioners to address ASR issues. As part of these efforts, 

field trials were initiated that included the implementation of various mitigation measures in 

highway infrastructure, including bridges, barrier walls, and pavements. Figure 8.1 provides an 

overview of the FHWA-funded field trials, including information on the various mitigation 

measures (Ahlstrom 2012). Discussion on several of these field trials is included in this chapter, 

but it should be kept in mind that the key findings from these studies may not be known for 

several years, and certainly beyond the conclusion of the FHWA project in 2013. 

Table 8.1. FHWA-Funded Field Trials (adapted from Ahlstrom 2012) 

State Structure Mitigation Technique 

Alabama Historic bridge 

arch 

Silane sealer 

Arkansas Pavement Silane sealer 

Delaware Pavement Topical application of lithium nitrate 

Delaware Pavement Monitoring an asphalt overlay of pavement with 

lithium nitrate 

Hawaii Aggregates Testing aggregates and development of field 

exposure site 

Massachusetts Median barrier Silane sealers; topical application of lithium nitrate 

Massachusetts Aggregates Testing aggregates and development of field 

exposure site 

Maine Bridge abutments 

and piers 

FRP wrap; silane sealer; electrochemical application 

of lithium nitrate 

Texas Bridge Columns Electrochemical application of lithium nitrate; 

vacuum impregnation of lithium; silane sealers 

Texas Precast Bridge 

Girders 

Aggregate testing and investigation of specific 

mixture designs 

Vermont Bridge barrier 

walls 

Silane sealers 

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AAR Facts Book Chapter 8 – Mitigation Methods 

8.3 REDUCING INTERNAL RELATIVE HUMIDITY 

The availability of moisture is critical for ASR to cause significant expansion and cracking. In 

the laboratory, Pedneault (1996) showed that below a relative humidity (RH) of 80 percent, 

ASR-induced expansion is significantly reduced or suppressed, as shown in Figure 8.2. The 

data in Figure 8.2 are for concrete prisms composed of various reactive aggregates and stored at 

different relative humidities. Although the effects of moisture on expansion did vary from 

aggregate to aggregate, reducing the relative humidity to 80 percent greatly reduced the 

observed expansions after two years of testing for all aggregates in the study. 

Figure 8.2. Influence of Relative Humidity on Expansion due to ASR (after Pedneault 1998) 

The effects of moisture availability on ASR are also quite evident in the field. It is quite 

common for part of a structure that is directly exposed to water (e.g., rain water) to exhibit signs 

of ASR-induced expansion and cracking while part of the same structure that is protected from 

direct contact with water will show very little symptoms of ASR. Figure 8.3 illustrates the 

importance of moisture availability on ASR-induced cracking – the bent cap, from a bridge in 

Houston, Texas, only exhibits visual cracking on the exterior faces that are subject to direct 

rainfall. The portions of the bent cap well below the bridge deck, and thus protected from direct 

rainfall, show only negligible signs of distress. This is typically the case with precast bridge 

girders – only the exterior girders tend to show signs of ASR-induced expansion and cracking, 

whereas interior girders that are shielded from rain often show negligible symptoms of ASR. 

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AAR Facts Book Chapter 8 – Mitigation Methods 

Figure 8.3. Photograph of bridge in Houston, Texas, illustrating effects of moisture availability 

on ASR-induced expansion and cracking. Only the exposed face of the bent cap (left side of 

photo) shows visual cracking, whereas the portions of the bent cap protected by the bridge deck 

show very little cracking. 

Figure 8.4 shows a photograph of a bridge structure included as part of the FHWA ASR 

Development and Deployment Program. Prior to applying various sealers/coatings to the 

bridge, cores were extracted from Location A (under the bridge deck, sheltered from rain) and 

Location B (exposed directly to precipitation). Petrographic evaluations of the cores showed 

that the concrete mixture proportions were identical, meaning the same concrete was used in 

each location of the bridge. Using the Damage Rating Index (DRI), a quantitative petrographic 

technique described in chapter 7, it was found that the DRI of a core extracted from Location A 

was 528, whereas the DRI of a core extracted from Location B was only 133 (note – the higher 

the DRI, the greater the extent of ASR). Thus, the effects of exposure conditions on ASR are 

evident both to the naked eye, as shown in Figure 8.3, and under a petrographer’s microscope, 

as evidenced by the elevated DRI values for cores extracted from portions of the bridge directly 

exposed to precipitation in Figure 8.4. 

A great deal can be learned from the examples shown in Figures 8.3 and 8.4, where there is a 

clear link between moisture availability and ASR-induced expansion and cracking. Examples of 

this type are ubiquitous in highway infrastructure, where the influence of moisture availability 

on ASR is evident not only in bridges, but also in pavements, where joints tend to deteriorate 

first due to the increased availability of water at or near joints. These observations can be 

synthesized and applied to mitigation measures for ASR-affected concrete – whenever possible, 

one should try to limit the availability of moisture. This can involve improving drainage for a 

given structure, for example, by diverting drainage from a bridge deck away from an ASRaffected column or cap. Likewise, improving the drainage conditions for an ASR-affected 

pavement, when possible, can help to reduce future expansion and cracking. 

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AAR Facts Book Chapter 8 – Mitigation Methods 

Figure 8.4. Photograph of bridge in Bangor, Maine. Location A is sheltered by the bridge deck, 

whereas Location B is exposed directly to precipitation. Sampling of concrete cores from each 

location showed strong correlation between moisture availability and ASR-induced expansion 

and cracking. 

It is not always a feasible option to simply improve drainage for a given ASR-affected 

structure, and other, more advanced or aggressive measures may be warranted. For example, the 

application of exterior cladding that prevents the ingress of additional moisture may be 

beneficial, but it should be noted that the moisture already present within the concrete may be 

sufficient for ASR to remain active, and this fact must be considered when contemplating a 

cladding as a mitigation measure. The use of ventilated cladding slowed down the progression 

of ASR in a race course grandstand by minimizing access to external moisture while still 

allowing the concrete to dry out (Hobbs 1989). 

For instances where it is not possible to adequately dry concrete out through improved drainage 

or where it is not feasible (technically or economically) to apply ventilated cladding, the use of 

coatings or sealers to reduce the internal relative humidity should be considered. A coating or 

penetrating sealer that will trigger this reduction in internal relative humidity must provide the 

following characteristics (after CSA 2000): 

1. be resistant to water absorption; 

2. penetrate to a measurable depth; 

3. resist deterioration from ultraviolet (UV) radiation; 

4. possess long-term stability in an alkaline environment; 

5. be of long-term stability in an alkaline environment; and 

6. allow vapor transmission 

There are a range of products, some proprietary in nature, that satisfy the above characteristics, 

but silicone-based products have been used most commonly as mitigation measures for not 

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only ASR, but also to help reduce the ingress of water (to enhance frost resistance) and 

external chlorides (to reduce the rate of corrosion of reinforcing steel). Silicones exhibit several 

characteristics that make them well-suited for such applications, including (after Mayer 1998): 

• strong repellence to liquid water, 

• chemical inertness in most cases, 

• stability in a wide range of temperatures, and 

• excellent insulative properties. 

Members of the silicone family that have been used the most for such applications are silanes, 

siloxanes, and silicone resins, with silanes being the most commonly used, as well as the most 

commonly evaluated with regard to ASR. Because of the relevance of silanes to ASR research 

and implementation, discussion follows on the mechanisms by which silanes are able to reduce 

the internal relative humidity. 

When silanes are applied to the concrete surface, a chemical reaction known as crosslinking or 

polycondensation occurs within the concrete substrate or at the surface to form a silicone resin 

network, which is responsible for water repellency, permeability to water vapor, and durability 

(Mayer 1998). Silanes achieve their unique properties by chemically bonding a water-repellent 

hydrocarbon molecule to the substrate, as illustrated in Figure 8.5. As a result, the critical 

surface tension of the concrete substrate is reduced, and if the surface tension of the substrate 

falls below that for water, it will be water repellent (McGettigan 1992). 

Figure 8.5. Mechanism by which Silanes React with Concrete (adapted from Dow Corning 

2005) 

There are a variety of silane products available, varying primarily based on the concentration of 

silane in the specific formulation (ranging from 20 percent to close to 100 percent) and based 

on the type of carrier with which the silane is combined (either water-based or solvent-based). 

More stringent restrictions regarding VOC emissions have resulted in more water-based silanes 

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AAR Facts Book Chapter 8 – Mitigation Methods 

or solvent-based silanes with higher silane contents (and thus lower solvent content and reduced 

VOCs). 

Silanes are almost always applied topically (see Figure 8.6), at a coverage rate typically in the 

range of 2.4 – 4.8 m2/L (or 100 – 200 ft2/gal). The depth of penetration will vary from product 

to product and based on environmental conditions. Lute (2008) reported depths of penetration 

of silanes into concrete mixtures typically used in highway applications to be in the range of 2 

to 6 mm. This depth of penetration is sufficient to form a functional barrier, preventing water 

from entering but allowing moisture vapor to escape. 

Figure 8.6. Photograph Showing Topical Application of 40%-Silane Solution (solvent-based) to 

ASR-Affected Highway Barrier in Massachusetts (part of FHWA Project DTFH61-02-C00097) 

There have been several studies that have confirmed the benefits of applying silanes to field 

structures to reduce future ASR-induced expansion. The research by Bérubé et al. (2002) was 

particularly encouraging as it showed that applying silane to highway barriers heavily damaged 

by ASR resulted in a dramatic reduction in cracking (Figure 8.7), as well as future expansion 

(Figure 8.8). 

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Control Silane-treated 

Figure 8.7. Reduction in Cracking of Highway Barriers in Canada, after Application of Silane 

(Bérubé et al. 2002) 

AAR Facts Book Chapter 8 – Mitigation Methods 

Figure 8.8. Reduction in Expansion of Highway Barriers in Canada, after Application of Silane 

(Bérubé et al. 2002) 

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AAR Facts Book Chapter 8 – Mitigation Methods 

Badly cracked concrete piers supporting the Hanshin Expressway in Japan were repaired at an 

age of 7 years by first filling the cracks with an epoxy resin injected under pressure and then 

either coating with an epoxy resin or impregnating with silane followed by a cosmetic coating 

of a polymer cement paste (Kojima et al. 1992), as shown in Figure 8.9. Of all the treatments 

shown in Figure 8.9, the columns treated with silane performed the best, and those columns 

treated with non-breathable coatings, such as epoxy and acrylic, performed the worst as 

moisture vapor was not allowed to escape the concrete. 

Figure 8.9. Reduction in Expansion of Bridge Columns (Hanshin Expressway, Kobe, Japan) 

Triggered by Use of Silane Coating (Kojima et al. 1992) 

Several FHWA-funded field trials over the past few years (under FHWA Project DTFH61-06-D 

-00035) have included the topical application of silane-based products, as detailed in Table 8.1. 

Silanes were topically applied to highway barriers, pavements, and bridges. Most of the ASRaffected elements treated by silane-based products were treated quite recently (2010-2012), and 

as such, it is too premature to make conclusions regarding the efficacy of the various coatings 

and sealers in reducing the relative humidity inside concrete and reducing future ASR-induced 

expansion. 

Fortunately, highway barriers treated under a previous FHWA project (DTFH61-02-C-00097) 

focusing on implementation of lithium technologies have been included in the latest FHWA 

project (DTFH61-06-D-00035), and as such, the barriers were included in the ongoing 

monitoring efforts and have been monitored for a total of about five years. Figure 8.10 shows 

the significant reduction in cracking of highway barriers in Massachusetts, approximately three 

years after the topical application of various silane-based products. Figure 8.11 shows the 

expansion data for the barriers, confirming that all of the silane products studied reduced 

expansion, compared to the control. In fact, the barriers that were most affected by silane 

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AAR Facts Book Chapter 8 – Mitigation Methods 

applications underwent shrinkage, which is consistent with the work done in Canada on 

highway barriers (see Figures 8.7 and 8.8). 

Silane 

Control 

Figure 8.10. Reduction in Cracking of Highway Barriers in Massachusetts, 

after Application of Silane (FHWA Project DTFH61-06-D-00035) 

Figure 8.11. Effects of Silane Treatment on the Expansion of Highway Barriers in 

Leominster, MA (note Silanes A and B are water-based. Silane C is solvent-based) 

Based on the experience with highway barriers, silanes can be quite effective in reducing 

internal relative humidity, expansion, and cracking. However, this is somewhat of an ideal 

situation for applying silanes – the barriers are relatively thin and are treated on both sides, 

thereby allowing for the relative humidity to be reduced from both sides of the wall. There are 

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certainly other applications where silanes or products that work in a similar manner may not be 

effective. For pavements, slabs on grade, wingwalls, or other applications where moisture is 

available from below (or beneath), silanes will likely not be as effective (or effective at all) as 

their benefits are only realized from the treated surface. To quantify the effects of treating such 

elements with silane, FHWA-funded field trials have in recent years included the treatment of 

wingwalls in Maine and Rhode Island and pavements in Arkansas; it is too early to determine 

what benefits, if any, will be derived from such treatments. 

Lastly, it should be noted that the application of silanes will not be effective in concrete with 

large crack widths. For these larger cracks, flexible caulking or similar products should be used 

to seal the larger cracks. In a FHWA field trial in Wetumpka, Alabama, flexible caulking was 

applied to selected cracks in a bridge that were deemed to be too wide to be effectively treated 

by silanes. There have been other recent developments, including the use of “high-build” paints 

or elastomeric coatings that may show promise in bridging larger cracks and avoiding the need 

for caulking of individual cracks. The need to seal larger cracks becomes critical when 

reinforced concrete is exposed to external chlorides or in regions exposed to cycles of freezing 

and thawing. These elastomeric coatings have recently been applied to bridge structures in 

Maine and Vermont and highway barriers in Massachusetts as part of ongoing FHWA field 

trials; again, it is too premature to make any conclusions about the efficacy of such applications, 

but monitoring is ongoing. 

8.4 APPLICATION OF LITHIUM COMPOUNDS 

There have been several laboratory-based publications related to using lithium compounds to 

treat concrete already suffering from ASR-induced expansion. Research by Stark et al. (1993), 

Stokes et al. (2000), and Barborak et al. (2004) have shown that lithium compounds can reduce 

future expansion of small, ASR-affected concrete specimens in accelerated laboratory tests. 

Figure 8.12 shows that immersing concrete prisms in lithium nitrate reduced the future 

expansion of these prisms when subjected to storage conditions similar to ASTM C 1293 

(Stokes et al. 2000). Although one cycle of lithium application slightly reduced expansion, 

multiple cyclical applications of lithium nitrate significantly reduced long-term expansion. It 

should also be noted that prisms that were treated by multiple cycles of immersion in water, as 

opposed to lithium nitrate, exhibited reduced expansion as well, presumably due to the leaching 

of alkalis from the prisms to the water during the immersion period. 

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AAR Facts Book Chapter 8 – Mitigation Methods 

Figure 8.12. Effects of Submerging Concrete Prisms in Lithium Nitrate (or water) on 

Expansion of Prisms in ASTM C 1293 Environment (after Stokes et al. 2000) 

Although the mechanisms by which immersing concrete or mortar specimens in lithium 

compounds may reduce future expansion are not fully understood, it is generally believed that it 

changes the nature and behavior of the gel from expansive to essentially non-expansive. 

Because of the positive results in laboratory-based work and driven by the need for viable 

mitigation measures for ASR-affected structures and pavements, there has been considerable 

interest in treating ASR-affected field structures, especially in recent years under FHWAfunded research. A detailed review of past field trials using lithium compounds can be found in 

Folliard et al. (2006), and several field trials are still being monitored under current FHWA 

projects. The most common method of applying lithium compounds in field trials has been via 

topical application, primarily for pavements (Figure 8.13), highway barriers (Figure 8.14A), 

and bridge decks. There have also been a handful of field trials where lithium was applied either 

by vacuum (Figure 8.14B) or through electrochemical means, both aimed at increasing the 

depth of penetration of lithium. 

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AAR Facts Book Chapter 8 – Mitigation Methods 

Figure 8.13. Photograph Showing Topical Application of 30%-LiNO3 Solution to 

Concrete Pavement in Idaho 

A B 

Figure 8.14. Photographs Showing Topical Application (A) and Vacuum Application (B) of 

30%-LiNO3 Solution to Highway Barrier in Massachusetts 

Although lithium compounds have been found to be effective in laboratory-based research, 

which has focused on treating small specimens affected by ASR, there is, unfortunately, very 

little, if any, documentation that lithium is effective in reducing ASR-induced expansion in 

actual structures in the field. Part of this is due to the general lack of monitoring of field trials in 

which lithium compounds have been applied to structures (or pavements). Recognizing the need 

to obtain such critical data, field trials were initiated under FHWA funding (under FHWA 

Project DTFH61-02-C-00097) in Idaho, Massachusetts, and Texas. The primary focus of these 

studies was primarily on the topical application of lithium nitrate, but the applications of lithium 

nitrate by vaccum and by electrochemical methods were also evaluated. 

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AAR Facts Book Chapter 8 – Mitigation Methods 

Table 8.2 summarizes the lithium penetration data for field trials in three states (after Folliard 

2008). When evaluating lithium profile data, it is important to view it in context of how much 

lithium is needed to control expansion. Consider the following example: Assuming a plain 

concrete mixture contains 3 kg/m3

 Na2Oe, a “standard dose” of 30% lithium nitrate solution (4.6 

L of solution per 1 kg of Na2Oe) would amount to 13.8 L/m3 of lithium nitrate solution. This 

dosage of LiNO3 solution contains 504 g of Li, and assuming that half of this lithium gets bound 

in early hydration products (as well documented in literature), approximately 250 g of lithium 

per m3 will remain in the concrete to combat ASR. If one assumes a concrete density of 2350 

kg/m3 the concentration of lithium ions in pore solution would be approximately 100 ppm, and 

this concentration would be enough to control expansion when used as an admixture. However, 

it should be noted that the “standard dose” of 30% lithium nitrate solution (4.6 L of solution per 

1 kg of Na2Oe) has been reported to be sufficient for controlling expansion in about half of the 

aggregates recently tested in North America (Tremblay et al. 2008). Some aggregates, 

especially greywackes, still expand considerably at over twice the “standard dose.” For the 

purpose of this discussion, it is assumed that the aggregate in the concrete being treated 

responds favorably to lithium (4.6 L of solution per 1 kg of Na2Oe) and that 100 ppm would be 

required in pore solution for suppression of excessive expansion. 

Table 8.2. Summary of Lithium Penetration Data for Highway Applications of Lithium Nitrate 

Following the above discussion and assuming a requisite lithium threshold of 100 ppm, the data 

in Table 8.2 was not very positive with regard to topical or vacuum applications of lithium 

nitrate. In fact, depths of penetration for topical applications in an Idaho pavement were found 

to be only a few millimeters, with dosages of lithium necessary to suppress expansion measured 

only down to the first 2 to 3 mm, even after three treatments in heavily cracked pavements. 

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AAR Facts Book Chapter 8 – Mitigation Methods 

These penetration results are consistent with laboratory evaluations performed under the same 

project, and when taken as a whole, it appears that due to an inherent lack of penetration, the 

topical application of lithium compounds shows little, if any, promise of mitigating ASR in 

structures and pavements. 

Figure 8.15 shows that none of the topical lithium applications reduced expansion in the 

highway barriers treated in Leominster, MA, unless the lithium treatment was followed up with 

a subsequent application of 40% silane. Given that multiple treatments of lithium nitrate did not 

reduce expansions, it is logical to conclude that the reduction in expansion can be attributed 

solely to the benefits of silane in reducing the internal relative humidity of the concrete. Similar 

results were obtained for the barriers in which a vacuum was applied to try to drive lithium 

nitrate in further. Reductions in expansion were only observed when the vacuum treatment was 

followed up with an application of 40% silane. 

Figure 8.15. Effects of Topical Lithium Nitrate Application on Expansion. Note that only the 

barriers treated with silane reduced long-term expansion. 

Because of the documented lack of penetration in field and laboratory trials in which lithium 

compounds have been applied topically, recent focus has shifted towards more aggressive 

means of driving lithium into ASR-affected concrete, specifically through vacuum 

impregnation and electrochemical methods. Unfortunately, in research performed under FHWA 

Project DTFH61-02-C-00097, vacuum impregnation was not found to be effective in the 

laboratory or in field structures in Texas and Massachusetts. For example, for ASR-affected 

bridge columns in which lithium nitrate was applied via vacuum, the depths of lithium 

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AAR Facts Book Chapter 8 – Mitigation Methods 

penetration were found only to be present in the outer 9 to 12 mm, drawing into question 

whether such an elaborative and expensive vacuuming technique is justified. Substantially 

higher depths of penetration were observed in the same study when lithium nitrate was 

electrochemically driven into bridge columns, with dosages sufficient to reduce ASR measured 

all the way down to the reinforcing steel (50 mm from outer surface). Information on the 

specific details of the electrochemical method used for this bridge structure can be found in East 

(2007). However, one major concern with this technique is that the electrochemical process, 

itself, tends to drive alkalis already present in the concrete towards the rebar, which may be a 

significant obstacle to this technology. It appears that as a whole, this technique is quite 

powerful in driving external lithium into the concrete, but the rearrangement of internal alkalis 

and accumulation of sodium and potassium (which in turns leads to an augmented pH near the 

rebar) is a serious concern that deserves further attention. More work is in progress to evaluate 

this treatment technique and to quantify the benefits (and downsides) of this approach. 

Despite the general lack of penetration observed in laboratory and field structures in which 

lithium was applied topically or by vacuum, it is hoped that data will be generated from other 

field trials, thereby increasing the state of knowledge and expanding the database of depth of 

penetration data. Lastly, the success in driving lithium all the way to the reinforcing steel is 

encouraging, but the adverse effects of pushing sodium and potassium to the vicinity around the 

steel deserve further attention. Given that lithium compounds have clearly been shown to be 

effective in reducing future expansion in ASR-affected concrete in the laboratory, and given 

that the options for treating the cause of ASR in the field are limited, it is hoped that additional 

lithium-based field trials will be conducted and monitored, thereby helping to quantify the 

effects, if any, of lithium application on remaining service life. 

8.5 APPLICATION OF EXTERNAL RESTRAINT 

Numerous studies and field trials have shown that physical restraint or confinement (e.g., 

encapsulation of the affected member by a surrounding non-reactive concrete, applied stress or 

reinforcement) can significantly reduce deleterious expansion due to ASR in the direction of 

restraint (Fournier et al. 2004). Because of the unique nature of this mitigation approach and the 

fact that the structural response is impacted, it is imperative that a structural engineer play the 

leading role in specifically designing the methodology for a given ASR-affected structure. 

Post tensioning in one or two dimensions, or by encasement in conventional reinforced 

concrete, is currently used as a means to restore the integrity of the structure; however, it should 

generally be restricted to relatively small masses of structural concrete because of the huge 

forces that may result from the expansive process due to ASR (Rotter 1995; CSA 2000). Posttensioned tendons or cables are considered to be an effective solution for thin arch dams 

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AAR Facts Book Chapter 8 – Mitigation Methods 

(Singhal and Nuss 1991) or structural members of bridge/highway structures; however, they 

may be less attractive for large concrete structures because of the necessity of periodic 

destressing (Rotter 1995). Methods to restrain expansion and movement in mass concrete 

foundations such as tower bases have also included rock anchors and/or encapsulation (Bérubé 

et al. 1989). 

Strengthening by introducing reinforcement with straps, steel plates, and tensioning through 

bolts was also found to be effective in providing containment for selected ASR-affected 

concrete members (Wood and Angus 1995). Wrapping ASR-affected reinforced concrete 

columns with composite materials (FRP) has also been applied in field structures (Figure 8.16) 

and more recently in Vermont as part of ongoing FHWA field trials (under FHWA Project 

DTFH61-06-D-00035). 

Figure 8.16. Photograph Showing Topical Bridge Column Wrapped with FRP (Carse 1996) 

8.6 STRESS RELIEF 

For certain applications, such as a pavement suffering from ASR-induced expansion, a viable 

option to extend the service life is to remove sections of concrete near the joints by saw cutting. 

Removing these sections is helpful in eliminating joint-related failures and minimizing ride 

quality issues. The sections that have been removed can be replaced by sound concrete, with 

careful attention paid to restoring the intended joint details (opening, dowel bars, etc.). This 

approach has been done on a much larger scale for concrete dams, where large slots have been 

cut to accommodate future expansion. It should be noted that this approach (saw cutting/joint 

cutting) only relieves stresses but does nothing to address the root cause of the expansion. It is 

common for this method to be performed repeatedly as expansion continues and negates the 

benefits achieved from the previous concrete removal. 

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AAR Facts Book Chapter 8 – Mitigation Methods 

8.7 SUMMARY 

This section described a variety of methods that have been applied to field structures suffering 

from ASR-affected expansion and cracking. Some methods, such as the application of silanes, 

have shown significant promise, especially when applied to elements such as small columns 

and highway barriers, whereas other methods, such as the topical application of compounds, 

have shown little or no promise in reducing ASR-induced expansion and cracking. It is hoped 

that ongoing FHWA field trials (under FHWA Project DTFH61-06-D-00035) will better 

quantify the potential benefits of these and other preventive measures and will help to 

contribute to improved management of ASR-affected structures in the future. 

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AAR Facts Book Chapter 8 – Mitigation Methods 

REFERENCES 

Ahlstrom, G. 2012. “The United States Federal Highway Administration’s Alkali-Silica 

Reactivity Development and Deployment Program.” Proceedings of the 14th International 

Conference on Alkali-Aggregate Reactivity (ICAAR), Austin, TX, USA, 20-25 May. 

ASTM. 2008. “Standard Test Method for Determination of Length Change of Concrete Due to 

Alkali-Silica Reaction.” ASTM C 1293, ASTM International, West Conshohocken, PA, 7 p. 

Barborak, R., Folliard, K.J. and Thomas, M.D.A. 2004. “Using Lithium Compounds to Treat 

Hardened Concrete Suffering from ASR: Preliminary Laboratory Results.” Proceedings of the 

12th International Conference on Alkali-Aggregate Reactivity (ICAAR), Beijing, China, 483­

489. 

Bérubé, M.A., Fournier, B. and Frenette, J. 1989. “Détérioration de fondation de pylônes 

d'ancrage de lignes de transport d'électricité par des réactions alcalis-granulats, performance 

mécanique et réparation du béton.” Canadian Journal of Civil Engineering, 16(6): 945-959. 

Bérubé, M.A., Chouinard, D., Pigeon, M., Frenette, J., Rivest, M. and Vézina, D. 2002. 

“Effectiveness of Sealers in Counteracting Alkali-Silica Reaction in Highway Median Barriers 

Exposed to Wetting and Drying, Freezing and Thawing, and Deicing Salts.” Canadian Journal 

of Civil Engineering, 29(2): 329-337. 

Canadian Standards Association (CSA). 2000. Guide to the Evaluation and Management of 

Concrete Structures Affected by Alkali-Aggregate Reactions. CSA A864-00, 2000b, Ontario, 

Canada. 

Carse, A. 1996. “The Asset Management of Alkali-Silica Rection in a Long Bridge Structure.” 

Proceedings of the 11th International Conference on Alkali-Aggregate Reaction in Concrete 

(Eds. M.A. Bérubé, B. Fournier and B. Durand), Quebec City, Canada, 1025-1032. 

Dow Corning. 2005. "A Guide to Silane Solutions." Dow Corning Corporation, http:// 

www.dowcorning.com/content/publishedlit/SILANE-GUIDE.pdf, (July 24, 2008). 

East, B. 2007. Laboratory and Field Investigations on the use of Lithium Nitrate to Prevent or 

Mitigate Alkali-Silica Reaction. M.S. Thesis, The University of Texas at Austin. 

Folliard, K.J., Thomas, M.D.A., Ideker, J.H., East, B.L. and Fournier, B. 2008. “Case Studies of 

ASR-Affected Structures with Lithium Nitrate.” Proceedings of the 13th International 

Conference on Alkali-Aggregate Reaction (Eds. M.A.T.M. Broekmans and B.J. Wigum), 

Trondheim, Norway, 90-99. 

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Hobbs, D.W. 1988. Alkali-Silica Reaction in Concrete. Thomas Telford, London, 183 p. 

Hobbs, D.W. 1989. “Countering alkali-silica reaction in concrete – Experience in the United 

Kingdom.” Concrete Construction, C890948, The Aberdeen Group. 

Lute, R. 2008. Evaluation of Coatings and Sealers for Mitigation of Alkali-Silica Reaction and/ 

or Delayed Ettringite Formation. M.S. Thesis, The University of Texas at Austin. 

Mayer, H. 1998. "The Chemistry and Properties of Silicone Resins." Pigment & Resin 

Technology, 26(6): 364-373. 

McGettigan, E. 1992. "Silicon-Based Weatherproofing Materials." Concrete International, 

14(6): 52-56. 

Pedneault, A. 1996. “Development of Testing and Analytical Procedures for the Evaluation of 

the Residual Potential of Reaction, Expansion, and Deterioration of Concrete Affected by 

ASR.” M.Sc. Memoir, Laval University, Québec City, Canada, 133 p. 

Rotter, H.M. 1995. “Alkali-Aggregate Reaction: from Basic Principles to Structural Behaviour 

– A literature Review.” Rapport No. EPM/GSC 1995-11, École Polytechnique de Montréal, 

Montréal, PQ, 166 p. 

Singhal, A.C. and Nuss, K.L. 1991. “Cable Anchoring of Deteriorated Arch Dam.” Journal of 

Performance of Constructed Facilities, 5(1): 19-37. 

Stark, D., Morgan, B., Okamoto, P. and Diamond, S. 1993. Eliminating or Minimizing AlkaliSilica Reactivity, SHRP-C-343, National Research Council, Washington, D.C. 

Stokes, D.B., Thomas, M.D.A. and Shashiprakash, S.G. 2000. “Development of a LithiumBased Material for Decreasing ASR-Induced Expansion in Hardened Concrete.” Proceedings of 

the 11th International Conference on Alkali-Aggregate Reaction in Concrete (Eds. M.A. Bérubé 

et al.), CRIB, Quebec City, Canada, 1079–1087. 

Wood, J.G.M. and Angus, E.C. 1995. “Montrose Bridge: Inspection, Assessment and Remedial 

Work to a 65 Year Old Bridge with AAR.” Structural Faults and Repair – 95, 6 p. 

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AAR Facts Book Chapter 9 – Alkali-Carbonate Reaction 

9 – Alkali-Carbonate Reaction 

9.1 INTRODUCTION 

As discussed in the introduction, alkali-carbonate reaction (ACR) is a reaction between alkali 

hydroxides (NaOH and KOH) in the pore solution and certain carbonate rocks, particularly 

calcitic dolostone and dolomitic limestones, present in some aggregates. The reaction is usually 

accompanied by dedolomitization and expansion of the affected aggregate particles, leading to 

abnormal expansion and cracking of concrete in service. 

Cases of ACR-induced damage in concrete are much less widespread than cases of ASR and, 

consequently, the carbonate reaction has attracted significantly less attention by researchers. 

The precise mechanisms of expansion are equivocal, and it has been conjectured that ACR may 

be a form of ASR involving reactive silica (e.g., cryptocrystalline quartz) present in the 

dolomitic limestone; however, this theory has not been universally accepted. 

There are some distinct features of ACR that differentiate it from ASR including, obviously, the 

nature and composition of the rock, the timeframe of the reaction, the influence of aggregate 

size, the inability of some standard tests to identify reactive aggregates, the threshold alkali 

content required to generate expansion, and the impact of preventive measures such as 

pozzolans, slag, and lithium-based compounds. Generally measures that have been found to be 

effective in preventing expansion due to ASR do not work with alkali-carbonate rocks and it is 

generally recommended that such rocks are avoided for use in concrete. 

This chapter presents an overview of alkali-carbonate reaction (ACR) including a discussion of 

the chemistry of the reaction, the mechanisms of expansion, contributing factors, and 

differences between ACR and ASR. Field symptoms in ACR-affected concrete structures are 

similar to those observed in structures affected by ASR, and these are discussed in chapter 3. 

Chapter 4 discusses test methods for both types of alkali-aggregate reaction. Recently 

developed AASHTO PP65, for identifying reactive aggregates, includes procedures for 

detecting and, subsequently, avoiding alkali-carbonate reactive rocks. This practice is presented 

in chapter 6. 

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AAR Facts Book Chapter 9 – Alkali-Carbonate Reaction 

9.2 CHARACTERISTICS OF ALKALI-CARBONATE REACTIVE ROCKS 

Alkali-carbonate reactive rocks can generally be described as argillaceous dolomitic limestones 

and tend to have a characteristic texture and structure comprising dolomite [CaMg(CO3)2] 

rhombohedra (typically 10 to 50 μm) dispersed or “floating” in a fine-grained matrix of fine 

calcite, clay, and, usually, silica. Figure 9.1 shows the microstructure of typical reactive rock. 

Typically the carbonate-mineral composition of the rock consists of substantial amounts of 

calcite (CaCO3) and dolomite, and the (HCl-acid) insoluble residue comprises of a significant 

amount of clay (ACI 221 2000; Ozol 2006). A modification of this typical texture has been 

observed in “late expanding” alkali-carbonate rocks which may have interlocking dolomite 

rhombs in a coarser-grained matrix. 

Figure 9.1. Photograph of Petrographic Thin Section Showing Dolomite Rhombs 

(clear equilateral parallelograms) “Floating” in a Matrix of Fine-Grained 

Calcite, Clay and Silica (dark background) 

The bulk composition of some early and late expanders is shown in Table 9.1. Rogers (1986) 

compared the composition of expansive and non-expansive limestones in Ontario and observed 

that the expansive rocks fell within a fairly distinct region when plotted on a graph of 

CaO:MgO ratio versus either the alumina (Al2O3) or (HCl-acid) insoluble residue (see Figure 

9.2). This observation forms the basis of the chemical screening test (CSA A23.2-26A) for 

potential alkali-carbonate reactivity which has been adopted by the Canadian Specification 

(CSA A23.2-27A) and the AASHTO PP65 Standard Practice (see chapter 6). 

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AAR Facts Book Chapter 9 – Alkali-Carbonate Reaction 

Table 9.1. Composition of Alkali-Carbonate Reactive Rocks 

(adapted from Walker 1978; ACI 221 2000; Ozol 2006) 

Acid-insoluble residue (%) Dolomite (% total 

carbonate) 

Kingston, Ontario, Early Expanders 

(Swenson, 1957; Swenson and Gillott, 

1960; Dolar-Mantuani, 1964) 

5 to 15 Approx. 50 

Iowa, Illinois & Indiana Early Expanders 

(Hadley, 1961, 1964) 

10 to 20 40 to 60 

Virginia Early Expanders 

(Newlon and Sherwood, 1962; Sherwood 

and Newlon, 1964) 

13 to 29 46 to 73 

Gull River, Ontario, Late Expanders 

(Dolar-Mantuani, 1964) 

21 to 49 75 to 87 

Virginia Late Expanders 

(Newlon, Ozol, and Sherwood, 1972) 

33 

> 90 

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AAR Facts Book Chapter 9 – Alkali-Carbonate Reaction 

Figure 9.2. Using Chemical Composition as a Basis for Determining Potential Alkali-Carbonate 

Reactivity of Quarried Carbonates (from CSA A23.2-26A) 

Observation of the characteristic texture and composition is considered to be a reliable 

indication of potential alkali-carbonate reactivity (Ozol 2006), and rocks that display the 

characteristic texture or composition should be tested further to evaluate their reactivity in 

concrete. 

9.3 CHEMISTRY OF ALKALI-CARBONATE REACTION 

Dolomitic limestones with the characteristic microscopic texture described in the previous 

section will react in an alkaline environment and undergo a process termed dedolomitization8

, 

which can be written as follows: 

CaMg(CO3)2 + 2ROH → CaCO3 + Mg(OH)2 + R2CO3 Eqn 9.1 

dolomite + alkali hydroxide → calcite + brucite + alkali carbonate 

8

 ACI 221.1R-98 states “...there appear to be no known exceptions to the observation that all limestones that possess the characteristic texture and composition will react, or dedolomitize, in an alkaline environment. Also, all 

limestones that dedolomitize in an alkaline environment possess the characteristic texture and composition. 

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AAR Facts Book	 Chapter 9 – Alkali-Carbonate Reaction 

where R represents K or Na. In some cases the magnesium may further react to form 

magnesium silicate. 

The alkali carbonate produced in the dedolomitization reaction may react with calcium 

hydroxide in the cement paste as follows: 

R2CO3 + Ca(OH)2 → CaCO3 + 2ROH Eqn. 9.2 

thereby “regenerating” alkalis for further reaction. This reaction may result in “carbonation 

halos” forming around reacted aggregate particles. 

9.4 MECHANISMS OF EXPANSION DUE TO ACR 

The dedolomitization reaction shown in Equation 9.1 is accompanied by a reduction in solid 

volume. In other words the molar volume of CaCO3 plus Mg(OH)2 is less than the molar 

volume CaCO3·MgCO3 and, since Na2CO3 is expected to pass in to solution, no volume 

expansion is expected (Gillott 1964). Hence, dedolomitization does not provide a simple 

mechanical explanation for expansion. Several theories have been proposed to explain the 

expansion mechanism, and these include: 

• Swelling of clay matrix (Swenson and Gillott 1964; Gillott 1964; Gillott and Swenson 

1969). Dedolomitization of the reactive material exposes previously “trapped” clay 

minerals (illite and chlorite) to alkali solution. The previously unhydrated clay minerals 

are in an “active” state. Exchange sites on the surfaces of the clay, which may be vacant 

or occupied by Ca2+ or Mg2+ ions, absorb Na+ (and K+) ions from solution (cation 

exchange) and a double layer develops accompanied by water uptake, which leads to 

swelling of the clay minerals and, consequently, an increase in the solid volume of the 

aggregate. The expansion essentially results from the wetting (and cation exchange) of 

previously unhydrated clay minerals that was made possible by the dedolomitization 

reaction which opened access channels for the moisture. 

• Growth and rearrangement of the products of dedolomitization (i.e., brucite and calcite) 

through a topochemical reaction (Tang et al. 1987). Clay is not embedded in dolomite 

rhombs but forms a network between the fine calcite grains surrounding the rhombs. 

The clay network provides channels for alkali hydroxides in the pore solution to 

“attack” the dololomite rhombs resulting in dedolomitization. After reaction, brucite is 

observed to form around the outside of the original rhomb in rings approximately 2 μm 

thick, the original structure of the rhomb being maintained by a framework of calcite 

which largely remains in place after the migration of the magnesium. The original 

rhomb with the peripheral brucite layer requires more space resulting in the generation 

of expansive forces. A schematic illustrating the phenomenon is presented in Figure 9.3. 

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AAR Facts Book	 Chapter 9 – Alkali-Carbonate Reaction 

• Alkali-silica reaction of cryptocrystalline quartz in matrix surrounding the dolomite 

rhombs (Katayama 1992; 2010). Alkali-silica gel has been observed in mortars and 

concretes containing alkali-carbonate reactive aggregates, and it has been postulated that 

reaction of cryptocrystalline quartz contained within the carbonate is responsible for the 

expansion of the mortar and concrete, and that the accompanying dedolomitization is 

“harmless”. 

Figure 9.3. Schematic Showing Topochemical Formation of Brucite (and Calcite) Ring 

around Dolomite Rhomb (modified from Tang et al. 1987) 

Although the clay-swelling mechanism appears to have lost support, there is still debate among 

researchers whether the expansion is due to the dedolomitization reaction or the alkali-silica 

reaction. 

9.5 FACTORS CONTRIBUTING TO EXPANSION DUE TO ALKALI-CARBONATE 

REACTION 

Regardless of the mechanism(s) causing expansion there are a number of contributing factors 

that increase the expansion of concrete containing reactive argillaceous dolomitic limestones. 

The petrological features of the rock that appear to maximize reactivity/expansion are (Ozol 

2006): 

• 5 to 25% clay or insoluble residue, 

• Ratio of calcite:dolomite of approximately 1:1, 

• Increase in dolomite content up to point at which interlocking of the dolomite rhombs 

becomes a restraining factor, and 

• Small size of the discrete floating rhombs. 

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AAR Facts Book	 Chapter 9 – Alkali-Carbonate Reaction 

Other factors that increase expansion are (Ozol 2006): 

• Increasing coarse aggregate size, 

• Moisture availability, 

• Increased alkali content of concrete (or pH of solution), 

• Increased proportion of reactive stone in the coarse aggregate, and 

• Lower concrete strength. 

Clearly if the expansion truly does result from alkali-silica reaction the quantity and form of the 

reactive silica will be a major determining factor. Grattan-Bellew et al. (2010) have 

demonstrated that there is a correlation between the amount of quartz in the insoluble residue 

and expansion of concrete prisms produced with three different reactive limestones. 

9.6 DIFFERENCES BETWEEN ACR AND ASR 

As discussed above, the debate between the cause(s) of expansion in concrete containing 

reactive argillaceous dolomitic limestones is ongoing and, at the time of writing, there appears 

to be no overall consensus. However, regardless of whether ACR or ASR produces the 

expansion, there are some features of reactive aggregates that undergo the dedolomitization 

reaction that set them apart from aggregates that are unequivocally alkali-silica reaction; these 

are summarized as follows: 

• Expansion in the laboratory or damage in the field occurs in a much shorter timeframe 

with ACR. 

• Expansion increases with an increase in the size of the reactive aggregate particles. 

• Many tests used for the detection of alkali-silica reaction are not capable of detecting 

ACR rocks; these include the mortar bar test (ASTM C 227), the accelerated mortar bar 

test (ASTM C 1260), and the quick-chemical test (ASTM C 289). 

• Expansion occurs in concrete with alkali contents below the threshold level generally 

considered necessary for ASR. 

• The use of pozzolans and slag at levels normally sufficient for controlling ASR is not 

effective with ACR rocks, even when combined with low-alkali cement. 

• Lithium-based compounds are not effective in controlling expansion with ACR rocks. 

Indeed, concrete microbars with ACR aggregate and immersed in LiOH solution have 

been observed to expand, albeit at 150oC (Tang et al. 2000). 

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• Little (or no) gel is observed after expansion has occurred. Even when alkali-silica gel 

has been observed it is often difficult to reconcile the high amount of expansion with the 

meagre content of gel. 

Proponents of the ASR mechanism have provided partial explanation for some of the apparent 

anomalies between the behaviour of these rocks and that of established alkali-silica reactive 

rocks (Katayama 2010; Grattan-Bellew et al. 2010). However, it is clear that rocks that cause 

expansion and undergo dedolomitization need to be treated as a separate category with regards 

to AAR, whatever the predominant expansion mechanism (ACR or ASR). 

9.7 PREVENTION OF EXPANSION DUE TO ALKALI-CARBONATE REACTION 

Regardless of the true mechanism of expansion, it is extremely difficult to control expansion of 

alkali-carbonate reactive aggregates that have the characteristic composition and texture 

described in section 9.2 and undergo the dedolomitization reaction described in section 9.3. 

Consequently, it is strongly recommended that such aggregates are not used in the production of 

concrete. 

The reactive material may be avoided by selective quarrying or, alternatively, the reactive phase 

can either be diluted until the reactive material represents less than 20% of the coarse aggregate 

(or 15% of the total aggregate if both fine and coarse aggregate contain reactive material), or 

crushed to a smaller particle size until deleterious expansion is eliminated. However, avoidance 

of the reactive material appears to be the most prudent solution in the authors’ opinion. 

It has been suggested that expansion can be reduced to an acceptable level using very low alkali 

cement, e.g. no greater than 0.40% Na2Oe (Newlon et al. 1964). However, expansion has been 

observed with cements with alkali contents only marginally above this level such as 0.43% 

Na2Oe (Deng Min and Tang Mingshu 1993). Williams and Rogers (1991) observed cracking in 

sidewalk slabs after just 24 months of field exposure in Kingston, Ontario, Canada, even though 

the alkali content of the concrete was just 1.74 kg/m3

 (2.9 lb/yd3) Na2Oe. A section of sidewalk, 

curb, and gutter in the same vicinity also exhibited cracking, and it is believed (Williams and 

Rogers 1991) that the alkali content of the cement was just 0.31% Na2Oe. Figure 9.4 (from 

Shehata et al. 2009) shows the effect of cement alkalis on the expansion of concrete prisms 

produced with an argillaceous dolomitic limestone (Pittsburg aggregate) compared with a 

siliceous limestone (Spratt aggregate). The results provide a good illustration of the different 

behavior of ACR versus ASR reactive limestones. 

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Figure 9.4. Effect of Cement Alkali Content on Expansion of Concrete Prisms with 

Argillaceous Dolomitic Limestone versus Siliceous (Spratt) Limestone (Shehata et al. 2009) 

Swenson and Gillott (1964) reported that a variety of pozzolans found to be effective with the 

alkali-silica reaction when used at replacement levels of 25% were not effective in mitigating 

ACR. Subsequent research has reinforced this finding. Ground granulated blast-furnace slag 

used at replacements of 25 and 50% with high alkali cement of 1.04% Na2Oe was also not 

effective in controlling expansion of laboratory-exposed concrete prisms and field-exposed 

concrete slabs produced with the Pittsburg Quarry dolomitic limestone from Kingston, Ontario 

(Rogers and Hooton 1992). Thomas and Innis (1998) tested the same aggregate with slag in 

concrete prisms (CSA A23.2-14A; ASTM C 1293) and found that neither 65% slag combined 

with high-alkali cement (1.25% Na2Oe) nor 50% slag combined with low-alkali cement (0.50% 

Na2Oe) was sufficient to control expansion; the data are shown in Figure 9.5. The data in Figure 

9.5 serve again to accentuate the different behavior of ACR aggregate (Pittsburg) and ASR 

aggregate (Spratt). Tang et al. (1994) have shown that very high levels of fly ash (70%) or slag 

(90%) may be effective in controlling expansion when combined with low-alkali cement 

(0.43% Na2Oe). Perry and Gillott (1985) showed that 20% silica fume was not effective in 

suppressing the expansion due to ACR. 

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AAR Facts Book Chapter 9 – Alkali-Carbonate Reaction 

Figure 9.5. Effect of Slag Content and Cement Alkalis on Expansion of Concrete with 

Argillaceous Dolomitic Limestone versus Siliceous (Spratt) Limestone (Thomas and Innis 

1998) 

Testing has also shown that incorporating lithium-compounds (e.g., LiCl, LiOH, and Li2CO3) in 

concrete was not effective in controlling ACR expansion (Swenson and Gillott 1964; Wang et 

al. 1994). Such compounds have been shown to be effective with many (but not all) alkali-silica 

reactive aggregates, including siliceous limestones (Feng et al. 2010). 

9.8 SUMMARY OF ALKALI-CARBONATE REACTION 

The alkali-carbonate reaction was first documented in 1957 (Swenson 1957). Since this time, 

damage due to ACR has been observed in a limited number of states in the USA and a few 

other countries. ACR is much less widespread than ASR. Rocks that are alkali-carbonate 

reactive have a characteristic composition and microscopic texture, and expansion of concrete 

containing these rocks appears to be accompanied by dedolomitization of the rock. It is not 

been established unequivocally whether expansion results directly from the dedolomitization 

reaction or whether other mechanisms create the expansive forces. One school of thought is that 

reactive silica is present in these rock types and that the expansion is due to alkali-silica 

reaction. Regardless of whether the expansion is due to ACR or ASR, reactive rocks that have 

the characteristic composition and texture and that undergo dedolomitization clearly behave 

differently compared with reactive aggregates that are universally accepted as being alkali-silica 

reactive. From a practical standpoint the main differences are that these rocks cause expansion 

of concrete at very low alkali contents and even when relatively high replacement levels of 

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AAR Facts Book Chapter 9 – Alkali-Carbonate Reaction 

pozzolans or slag are used. As such, it is very important that appropriate test procedures are 

adopted to identify these rock types and that they are excluded from use for the production of 

concrete. 

207 
 

 

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