TECHBRIEF

Research, Development, and 

Technology

Turner-Fairbank Highway 

Research Center

6300 Georgetown Pike

McLean, VA 22101-2296

www.fhwa.dot.gov/research

Alkali-Silica Reaction 

Mechanisms and Detection: 

An Advanced Understanding

Publication No. FHWA-HRT-14-079

FHWA Contacts: Paul Virmani, HRDI-60, (202) 493-3052, 

paul.virmani@dot.gov; Fred Faridazar, HRDI-20, (202) 493-3076, 

fred.faridazar@dot.gov.

This document is a technical summary of the Federal 

Highway Administration project that is fully documented in a 

separate, forthcoming technical report under the same title, 

Alkali-Silica Reaction Mechanisms and Detection: An Advanced 

Understanding (FHWA-HRT-14-078).

Introduction

The deterioration caused by alkali-silica reaction (ASR) was 

first described 70 years ago in the pioneering paper by Stanton 

and has since been extensively researched.(1) The traditional 

attempts to mitigate ASR in concrete structures focused on 

preventing and/or reducing the amount of gel formed by modifying the chemical environment. Limiting the alkali content of 

concrete, using supplementary cementitious materials, or using 

chemical admixtures all have been found to be effective and 

have been extensively used for that purpose. However, the complexity of chemical and mechanical mechanisms of ASR made 

it difficult to develop reliable quality control test methods and 

performance prediction models. Therefore, increased understanding of the fundamental mechanisms of ASR may lead to 

the development of additional (and possibly better) options for 

ASR control and for reactivity characterization of susceptible 

aggregates.

The main purpose of this research was to investigate the fundamental mechanisms involved in the ASR process and to 

advance approaches to detect the damage caused by ASR. A 

more indepth understanding of the mechanisms underlying 

ASR, combined with the methods to detect ASR damage developed in the course of this study, is expected to help establish 

more reliable methods of mitigating ASR and increasing the 

design life of newly constructed concrete structures.
2

Fundamental Mechanisms

Experiments and Modeling of Chemical 

Sequence of ASR Processes

To advance the understanding of the fundamental mechanisms of ASR and more comprehensively evaluate the rate of chemical reactions, a series of model reactant experiments 

were conducted using selected silica minerals 

(α-cristobalite and chalcedony). This TechBrief 

presents the results obtained from testing of 

α-cristobalite. This mineral was selected to represent the siliceous component of the ASR-prone 

aggregate because it is known for its reactivity. In 

addition, it only contains negligible amounts of 

nonevaporable water and thus easily facilitates 

quantification of the amount of silica dissolved 

during the model reactant experiments. During 

testing, the cristobalite was exposed to an aqueous mixture of calcium hydroxide (Ca(OH)2) and 

three different types of alkali hydroxide solutions 

(0.7 M of potassium hydroxide (KOH), 0.7 M of 

sodium hydroxide (NaOH), and 0.35 M of KOH 

+ 0.35 M of NaOH) roughly representing the 

pore solution of reactive concrete. Each test was 

conducted at three different temperatures (38, 

55, and 80 °C). The quantitative data generated 

during these experiments—including the degree 

of chemical changes in the composition of solution, the mass changes of Ca(OH)2, and the mass 

changes of reactive silica minerals—allowed for 

establishment of the sequence of chemical steps 

involved in ASR.

Specifically, this study identified a distinct 

sequence of chemical steps associated with the 

ASR process. These steps are marked as I to IV 

in figure 1: (I) the formation of calcium silica 

hydrate (C-S-H), (II) the formation of high alkali 

and low calcium silica hydrate (C-(Na/K)-S-H), 

(III) the increase in concentration of silica ions in 

the solution, and (IV) the formation of ASR gels 

((Na/K)-S-H). Based on this sequence, it appears 

that the overall ASR process starts with the dissolution of silica, which, once in solution, rapidly 

reacts with the available Ca2+ ions to produce 

C-S-H. During this period (step I in figure 1), the 

concentrations of alkali ions and the values of pH 

remain more or less constant, but the amounts 

of remaining reactive silica and the Ca(OH)2 significantly decrease. 

Once the Ca(OH)2 in the reacting system is 

exhausted, the process of removing dissolved 

silica from the solution also ceases (or significantly decreases), leading to an increase in the 

concentration of Si4+ ions. These dissolved Si4+

ions can further react with previously formed 

C-S-H, generating polymerized (amorphous) 

C-(Na/K)-S-H with a reduced (compared with 

typical C-S-H gel) value of Ca/Si molar ratio 

(step II in figure 1). After the formation of this 

amorphous and polymerized C-(Na/K)-S-H gel, 

the rate of change in the concentration of alkalis decreases, but the concentration of Si4+ ions 

keeps increasing up to a certain (maximum) 

point (step III in figure 1). Following this action, a 

decrease in the concentrations of Si4+ and alkali 

ions can be observed. It is believed that the point 

when the concentrations of the Si4+ ions and 

alkali ions start to decrease coincides with onset 

of ASR (step IV in figure 1). 

Figure 1. Sequence of steps in the ASR process obtained 

from the reacting system (mixture of α-cristobalite, 

CA(OH)2, and KOH solution at 55 °C).

Lines represent modeling results, whereas individual points 

represent experimental data.

 = cristobalite.

∆ = Ca(OH)2.

o = concentration of K+ ions.

◊ = concentration of Si4+ ions.
3

The results of this model reactant experiments 

were used to develop a thermodynamic model 

for the ASR process. The model accounts for 

such parameters as chemical equilibrium 

between Ca(OH)2, reactive silica (α-cristobatlie), 

alkali ions, other various secondary species, and 

solid products. When developing the thermodynamic model, it was assumed that the ASR 

process simulated in the model reactant method 

is the surface-controlled (rather than transportcontrolled) reaction between the solution and 

the exposed surface of reactive silica. The model 

considers formation of three major products: 

C-S-H, C-(Na/K)-S-H, and (Na/K)-S-H.

The results produced by this model are shown 

as lines in figure 1. The proposed model produced results that are in good agreement with 

the experimental results (represented by the 

points). In addition, this model can reproduce 

the distinct features of experimental results, 

such as the consumption of cristobalite and 

Ca(OH)2, changes in the concentration of alkali 

ions, the timing of the increase in silica ions 

concentration, and the change in pH values. 

This model also confirms the existence of, and 

offers indication of possible mechanism for, 

the threshold value of alkali concentration in 

concrete. By using the experimental results to 

provide the thermodynamic properties of reactive silica minerals, this model can be used to 

evaluate the kinetics of ASR, including the evolution of changes in concentrations of various 

species in the pore solution and the formation of 

reaction products.

Role of Aggregates

To better understand the role of aggregate in the 

basic mechanism of ASR, a variety of aggregate 

sources were examined. The selected aggregates 

represented a range of reactivity, mineralogy, 

Table 1. Master table of aggregate sources and their properties.

Source Aggregate Potentially 

Reactive 

Mineralogy

Percent Expansion1

Location

Source 

Name Size Rock Type

ASTM 

C1293

MCPT 56-

day

ASTM 

C1260

Ontario, 

Canada

ON1 CA Limestone (Q) Siliceous 

inclusions

0.181 0.149 0.35

North Carolina NC1 CA Argillite (Q) Microcrystalline 

quartz

0.192 0.149 0.53

South Dakota SD1 CA Quartzite (Q) Chert, strained 

quartz

0.109 0.095 0.22

Massachusetts MA3 CA Lithic 

greywacke (Q)

Matrix with 

high silica 

igneous 

minerals

N/A 0.096 0.41

New Mexico NM1 CA Igneous gravel Glassy volcanic 0.251 0.185 0.90

El Paso, TX TX1 FA Volcanic sand Glassy volcanic 0.59 0.44 0.64

Illinois IL3 FA Glacial sand Chert, 

weathered chert

N/A 0.121 0.41

Nebraska 1 NE2 FA and CA Glacial gravel 

and sand

Chert 0.09 0.091 0.23

Nebraska 2 NE4 FA and CA Glacial gravel 

and sand

Chert and 

jasper

0.15 0.115 0.46

Pittsburgh, PA PA3 FA Glacial sand Chert N/A 0.111 0.25

1

The percent expansion results were obtained via personal communication with Dr. Prasada Rangaraju and were generated 

during work completed by Clemson University.

ASTM = American Society for Testing and Materials; MCPT = miniature concrete prism test.

CA = coarse aggregate; FA = fine aggregate.

N/A = not applicable; Q = quarried aggregate.
4

and rock types from a wide geographic distribution (see table 1). The reactive mineralogy and 

other pertinent components of each source were 

identified. These same aggregate sources were 

then examined in the reacted state in a concrete system, and the ASR induced changes were 

identified. 

The amount and type of reactive silica identified 

in each source varied but in general included 

microcrystalline quartz, strained quartz, chert, 

cristobalite, and various silica-rich volcanic 

rocks, including rhyolite, andesite, and dacite. 

The miniature concrete prism test (MCPT) 

specimens made from each source identified in 

table 1 exhibited deleterious expansion (based 

on a 0.04-percent expansion limit after 56 days 

of testing). Besides expansion, other evidence 

of reaction included spalling of the concrete 

surface; gel deposits; reaction rims around 

aggregate particles; cracks through, around, and 

radiating out from the aggregates; altered paste 

at the interfacial transition zone, and chemical 

alterations of the aggregate. All MCPT concrete 

specimens showed some evidence of ASR, but 

not all prisms showed all aforementioned features. The only variable in the concrete systems 

examined was the aggregate, suggesting that 

not only is the aggregate’s role to supply reactive silica, but that its other characteristics also 

influence how the concrete behaves and how it 

exhibits evidence of ASR reaction.

Influence of ASR on the Chemistry of Pore 

Solution

The kinetics of changes in the chemistry of the 

solution in systems undergoing ASR can provide useful information regarding the extent of 

ASR over time and may offer some indication of 

potential expansion. In this research, the chemistry of pore solutions obtained from mortars 

prepared with both reactive aggregate (TX1 

sand) and the nonreactive aggregate (Ottawa 

sand) were examined. Because of the space 

limitation, this report only presents the results 

of mortars prepared with reactive aggregate and

cured in a moist environment at three different 

temperatures (23, 38, and 55 °C). The threshold 

alkali concentration for the ASR process was 

obtained from the mortar samples exposed at 

55 °C, and this value (0.22 mol/L) was used to 

investigate the kinetic laws that best explain the 

observed changes in alkali concentration in the 

pore solution undergoing ASR. 

The nature of the linear plot shown in figure 2 

indicates that the alkali ion concentrations in 

pore solution can best be expressed as the first 

order reaction, as shown in figure 3.

[Na+ + K+ - 0.22]t is the concentration of available alkali ions present in the solution of 

the system undergoing ASR (mol·L-1) at a 

certain time (t), and kexp is the experimental rate constant (s-1). The values of kexp at 

three different test temperatures were determined from the slope of the linear regression line shown in figure 2. Figure 4 shows 

that the experimental data is fairly well 

represented by the proposed rate equation

(figure 3). This kinetic analysis, which has 

R2 values over 0.905, strongly suggests that 

the proposed rate equation (the first order 

reaction) for the changes in concentration 

of alkali ions as a function of time provided 

very reasonable predictions of the actual concentrations. Because reduction of the alkali 

concentration was not observed in the control 

mortars made with nonreactive aggregate, the 

reduction of alkali concentration in pore solution was the direct result of ASR. Therefore, 

these results also indicate that the rate of ASR 

in cementitious systems can be correlated (via 

the first order reaction) with the concentration 

of the alkali ions in the pore solution.

Influence of Lithium Ions in ASR Systems

The use of lithium-based chemical admixtures 

for the purposes of ASR mitigation has been 

extensively studied for more than 60 years. 

These studies resulted in several proposed 

mechanisms by which Li+ ions may potentially control ASR. However, none of these 
5

mechanisms fully explains the role of lithium in 

controlling ASR. In this context, several experiments were conducted during this study in an 

effort to understand the role of lithium ions in 

ASR systems. 

Loss of Li+ Ions From Pore Solution During Early 

Hydration Period

Pore solutions obtained from numerous mixtures (cement slurries and mortars) were 

analyzed to develop better understanding of the 

interaction between lithium ions and other ions 

present in the pore solution. 

The cement slurry experiments were designed 

to investigate the effect of timing of the addition of lithium nitrate (LiNO3) on the concentration of lithium ions in pore solution during 

the early hydration period. It has been shown 

that at early age the loss of Li+ ions from pore 

solution is the result of their incorporation in 

the developing hydration products and not the 

results of sorption by the existing hydrates. In 

addition, pore solutions obtained from various 

mixtures of mortar samples (containing nonreactive aggregate) were analyzed to quantify the 

effects of water-to-cement ratio, LiNO3 dosage, 

and length of curing time on the loss of lithium 

ions during the early stages of hydration. The 

results indicated that about half (50~60 percent) 

of the originally added Li+ ions will be removed 

from the pore solution after about two days of 

hydration, regardless of the initial amount of 

admixture added. Furthermore, the percentage 

of Li+ lost remained constant in mixtures prepared at the same w/c. However, that percentage 

will decrease with the increase in the w/c value.

Modeling of the Loss of Li+ Ions From Pore 

Solution

The data generated during the experiments presented in the previous section were examined 

thoroughly to develop a model to predict the 

extent of Li+ ion loss from the pore solution. 

Based on this model, the rate of loss of Li+ ions 

per kilogram of cement can be represented by 

the equation shown in figure 5. 

Figure 3. First order reaction for changes in alkali 

concentra

Figure 2. The plots of In[Na+ + Na+ - 0.22] versus time 

for reactive mortar (TX1 sand) with a water-to-cement 

ratio (w/c) of 0.55 (R0.55) mixtures reacting at different 

temperatures (23, 38, and 55 °C).

Figure 4. Change in alkali concentration [Na+ + K+] over 

time.
6

Where:

t is the time since the start of hydration (hours).

k is the rate constant (unitless).

r(t) is the rate of loss of Li+ ions per kilogram of 

cement (mol·kg-1·hr-1).

[Li]0 is the initial concentration of Li+ ions in the 

mix water (mol·kg-1).

αu is the ultimate degree of hydration.

τ is the hydration time parameter (representing 

the time delay from mixing until setting).

β is the hydration shape parameter (representing 

the slope of the S-shaped curve of the degree of 

hydration).

It should be noted that all variables needed in 

figure 5 (except for the rate constant k) can be 

determined from the initial mix design of the 

cementitious system and properties of cement. 

The value of the rate constant (k) was determined during the model calibration process. The 

resulting value of k was 0.499. That value of k

was, in turn, used as an input into the equation 

shown in figure 5. 

Figure 6 shows the scatter plot of the experimentally determined versus predicted adjusted concentrations of lithium ions in the pore solution. 

This plot contains experimental data obtained 

from both, the mixtures used in the current 

study (mortars containing nonreactive aggregate) and literature.(2,3) Collectively, these data 

represent systems with five different cements, 

four different w/c (0.42, 0.47, 0.49 and 0.55), and 

15 different [Li]0 values (corresponding to eight 

different ratios of [Li]/[Na+K]). Individual points 

are located quite close to the equity line (R2 = 

0.98), indicating that the proposed model accurately predicts the experimental results.

This model can also predict the beneficial effect 

of the delayed release of LiNO3 in paste or mortar 

systems. The concept of delayed release of LiNO3

into the cementitious system might be explored 

further to develop a new lithium-ion delivery 

method that can minimize the early-age losses 

of the LiNO3 admixture. In conclusion, the presented model appears to provide a useful tool 

for investigating the effects of various factors on 

the Li+ ions concentration without the need for 

time-consuming experiments.

Study of the Role of Lithium Ions in Controlling 

ASR

This part of the study focused on the investigation of the effect of Li+ ions on the chemical 

reactions involved in the ASR process. The experimental results show that the addition of the Li+

ions to the reactive system prevents the very 

Note: o represents data from mortar samples with 

nonreactive aggregate, while ∆ and  represent data from 

pastes.

Figure 6. Scatter plot of adjusted versus predicted 

adjusted concentrations (based on figure 5) of Li+ ions in 

various pore solutions.

Figure 5. Rate loss of Li+ ions per gram of cement.
7

first step of the ASR process (i.e., the dissolution 

of silica) and thus hinders the subsequent steps. 

Results from the model reactor experiments provided evidence for the mechanism by which the 

Li+ ions can prevent the dissolution of silica during the early reaction period. This mechanism 

can be summarized as follows. The ASR process 

starts with the hydroxyl ions (OH-) attacking the 

siloxane groups on the surface of reactive silica 

and breaking them down to form silanol groups. 

In turn, these silanol groups rapidly react with 

Li+ and Ca2+ ions present in the pore solution and 

form reaction products composed of silica, calcium, and lithium. These reaction products serve 

as the physical barrier that surrounds the surface 

of the reactive aggregate and prevents further 

attacks of reactive silica by hydroxyl ions.

The study of the effects of Li+ ions on the 

chemistry of the pore solution obtained from 

actual cementitious systems (mortar made with 

reactive aggregates) confirmed the results 

obtained from the model reactor experiment. 

The presence of Li+ ions in the pore solution 

resulted in significant reduction of the amount 

of alkali ions being removed. On the other hand, 

the concentrations of Li+ ions in the pore solution of mortars made with reactive aggregates 

also significantly decreased with time. This 

reduction in concentration of Li+ ions might be 

the result of the formation of the Si-Li reaction 

products on the surface of the reactive aggregate. These products appear to prevent further 

attack of silica by hydroxyl ions. As a result, the 

rate of consumption of K+ and Na+ ions by ASR 

was significantly reduced (or even completely 

halted), thus leading to establishment of the 

more or less constant levels of alkali ions in the 

pore solution with time.

Role of Deicers on ASR

Deicers play a significant role in further intensifying existing distress mechanisms (including 

ASR already active in concrete), especially if concrete was not produced using quality materials 

and sound construction practices. The effects of

deicers on paste and mortars with or without 

reactive aggregate were explored using expansion tests and microscopic analysis. 

Mortar Bar Expansion Tests (Modified American 

Society for Testing and Materials (ASTM) C1260)

The ASTM C1260 standard mortar bar test was 

modified by replacing the 1 N NaOH solution with 

various deicers. The concentrations of these deicers were as follows: potassium acetate (KAc)—

50 weight percent; NaCl—23 weight percent; 

magnesium chloride (MgCl2)—25 weight percent; 

and calcium chloride (CaCl2)—28 weight percent. 

The expansion data collected in the course of this 

study clearly demonstrate that mortars incorporating reactive aggregates undergo significantly higher expansion in the presence of KAc 

and NaCl deicers when compared with those 

containing nonreactive aggregates. The MgCl2

and CaCl2 deicers do not seem to contribute to 

ASR gel formation, and the observed expansions 

should therefore be attributed to the changes in 

the cement matrix itself. 

Scanning Electron Microscopy With Energy 

Dispersive X-ray Spectroscopy (SEM-EDX) 

Investigation of Spratt, Jobe, and Ottawa Mortar 

Bars Exposed to KAc Deicer

The SEM-EDX examinations were performed 

on specimens prepared from mortar bars 

subjected to a modified ASTM C1260 test procedure in which the standard soak solution, 

1 N NaOH, was replaced with various deicers. In addition, the test was performed at 

temperatures different than the standard 

ASTM C1260 temperature of 80 °C (e.g., 38 or 

23 °C). These investigations confirmed that when 

incorporated in the cement matrix, the reactive 

aggregates do undergo active deterioration by 

ASR in the presence of the KAc deicer, as shown 

in figure 7. Deposits of a calcium-bearing potassium sulfate phase (secondary reaction product) 

were observed in cracks around the aggregate 

particles, along cracks in the matrix, and in some 

voids.
8

SEM-EDX Investigation of Concrete Exposed to 

NaCl, MgCl2, and CaCl2 Deicers Under Wetting 

and Drying (W/D) and Freezing and Thawing 

(F/T) Conditions

The interactions of concrete specimens containing nonreactive aggregate with three different 

deicers were investigated by exposing them to 

solutions of NaCl (23 weight percent), MgCl2

(25 weight percent), and CaCl2 (28 weight percent). To evaluate the influence of deicers on 

ASR under conditions resembling field exposure, a series of experiments were performed 

in which concrete specimens were exposed to 

deicers while being subjected to either wetting 

(at 4 °C) and drying (at 23 °C) or freezing (at 

-20 °C) and thawing (at 23 °C) cycles. 

Deposits of MgCl2 and brucite (Mg(OH)2) were 

found in both matrix and air voids close to the 

edges of specimens exposed to MgCl2 deicer 

under both W/D and F/T conditions (figure 8). 

Hexagonal plates of portlandite were observed 

in the air voids under W/D conditions, and cracks 

could be easily found in the specimen exposed 

to CaCl2 deicer under F/T conditions. Friedel’s salt 

(Ca2Al(OH)6(Cl, OH) · 2 H2O) was observed close 

to the edges of specimens exposed to NaCl, 

MgCl2, and CaCl2 deicers under both W/D and F/T 

conditions, indicating the reaction of penetrating 

chlorides with the components of the matrix.

Advanced Approaches to Detect 

the Damange Caused By ASR

Two approaches (passive acoustic emission 

monitoring and X-ray and neutron imaging) 

have been evaluated as potential tools that can 

be used to detect the damage (cracking) caused 

by ASR. Passive acoustic emission monitoring 

has the potential to be used to determine the 

reactivity of the aggregate faster than current 

length change measurements. In addition, X-ray 

and neutron imaging are discussed as potential 

methods to detect cracking as well as to assess 

the impacts of cracks on transport properties of 

the matrix.

Passive Acoustic Emission Monitoring

Acoustic emission was investigated as an 

experimental technique that may be used to 

detect cracking due to ASR faster than current 

length change measurements. Figure 9 shows 

the length change of mortars made with reactive and non-reactive aggregates, and figure 10 

shows the acoustic emission activity. A greater 

acoustic activity was observed in samples with 

reactive aggregate (TX1) as compared with

samples with nonreactive aggregates (Ottawa). 

Figure 8. Deposit of MgCl2 and Mg(OH)2 in concrete 

exposed to MgCl2 deicer after 275 W/D cycles.

Figure 7. SEM-EDX micrograph of Spratt mortar with 

extensive cracking within aggregate and through matrix.
9

Figure 9. Length change of ASTM mortar bars in 1 N NaOH solution during testing period.

Figure 10. Cumulative acoustic emission energy for large mortar samples immersed in 1 N NaOH solution during testing 

period.
10

Acoustic activity was detected more easily at an 

earlier testing time, making the use of acoustic 

emission a potentially good approach for quantifying the onset of ASR cracking. Much more 

substantial reaction and cracking (resulting in 

longer testing times) is needed to assess the 

potential for ASR. The acoustic waves generated 

by cracking appear to show a frequency shift 

that correlates with a shift in cracking from the 

aggregate (onset of damage) to cracking in the 

matrix (at later ages).

X-ray and Neutron Imaging

X-ray and neutron radiography were used to 

investigate unsaturated fluid transport in cementbased materials (figure 11 and figure 12). Beer’s 

Law was used to quantify fluid absorption, and 

the influence of solution properties (viscosity 

and surface tension) was captured both experimentally and numerically.(4) X-ray tomography 

shows promise; however, it does not appear to 

be able to capture the earliest cracking using the 

sample sizes tested in this work because of limits 

on resolution.

Implementation of Research Study 

Findings

The results and findings of this research suggest 

several potential approaches to determine the 

reactivity of aggregate, mitigate ASR, and detect 

the damage induced by ASR. These approaches 

include the following: 1) the advanced quick 

chemical test (AQCT), 2) use of the model to 

predict the minimum dosage of LiNO3, 3) use 

of acoustic emission, and 4) X-ray and neutron 

imaging to detect damage caused by ASR.

AQCT

The proposed AQCT was developed using the 

thermodynamic modeling approach presented 

in the previous section. The methodology of the 

aggregate reactivity classification used in the 

AQCT is essentially the same as that used in 

the ASTM C289, the Standard Test Method for 

Potential Alkali-Silica Reactivity of Aggregates, 

also called the quick chemical test. However, the 

one distinct difference between those two methodologies is that the AQCT method replaces the 

laboratory testing required in the ASTM C289 

Figure 12. X-ray tomography of samples after 116 days 

of exposure to NaOH illustrating cracking due to ASR.

Figure 11. X-ray tomography of samples—initial imaging.
11

method with thermodynamic simulation, which 

utilizes the data on mineralogical composition of 

the aggregate as input value for the model.

The results obtained from the thermodynamic 

simulation are compared with the empirically 

derived criteria, which evaluate the reactivity of 

aggregates. Therefore, this approach is referred 

to as “semi-fundamental method to evaluate the 

reactivity of aggregates.” AQCT can predict the 

reactivity of aggregates quite accurately. If further study was conducted to collect the required 

kinetic parameters for various types of silica 

minerals, then this test method can be modified or improved to increase the accuracy. In 

addition, because the AQCT method was developed based on the fundamental aspect of ASR—

dissolution of silica and chemical steps involved 

in the ASR process—it represents a good 

example of how the fundamental study of ASR 

can lead to practical engineering solution.

Prediction of Minimum Dosage of LiNO3

A developed model to predict the concentration 

of Li+ ions in pore solution was implemented 

to determine the minimum [Li]/[Na+K] ratios 

required for various mixture designs from the 

value of minimum [Li]/[Na+K] obtained from just 

one particular design. The proposed method has 

potential for reducing number of trials needed 

to determine the minimum amount of LiNO3

required for each of a different concrete mixture 

designs. Once the minimum dosage of LiNO3 is 

determined for one concrete mixture design, the 

proposed method allows estimation of the minimum lithium-to-alkali molar ratio for a range of 

different mixture designs using the same reactive aggregate.

Implementation of Acoustic Emission

Acoustic emission is an experimental technique that is capable of determining the reactivity of the aggregate faster than current length 

change measurements. In samples containing 

reactive aggregates, substantially greater acoustic emission activity was observed than in samples with nonreactive aggregates. Samples with 

active ASR showed acoustic activity long before 

sufficient expansion occurred, suggesting the 

potential for using acoustic emission as an early 

detection technique and that the testing was 

more effective in larger samples, which would 

better facilitate concrete mixtures. The frequency 

of the acoustic wave shifts over time appears 

to correlate with a shift in cracking from the 

aggregate (onset of damage) to the cementitious 

matrix.

Implementation of X-ray and Neutron Imaging

X-ray and neutron imaging (radiography and 

tomography) are powerful tools for detecting 

cracking as well as the impact of cracks on fluid 

transport. While not immediately ready for use in 

quality control or acceptance testing, the use of 

X-ray or neutron imaging shows promise in aiding in the interpretation of experimental results 

or in the development of models that include 

the influence of cracking on the increased rate 

of ASR damage development. An approach was 

developed using Beer’s Law to determine the 

moisture content; this is more promising for neutron imaging because of the higher sensitivity of 

the technique. While tomography technique is 

promising, its use for ASR damage detection is 

limited because of the restrictions on sample size 

and resolution. These restrictions make it difficult 

to detect the onset of damage. However, damage 

at later ages can be seen and used to supplement 

other measurements.

References

1. Stanton, T.E., “Expansion of concrete through 

reaction between cement and aggregate,” 

Proceedings of the American Society of Civil 

Engineers, 66, 1940, pp. 1,781–1,811.

2. Bérubé, M.A., C. Tremblay, B. Fournier, M.D. 

Thomas, and D.B. Stokes, “Influence of 
12

OCTOBER 2014 FHWA-HRT-14-079

HRDI-60/10-14(600)

Researcher—This study was performed by School of Civil Engineering, Purdue University, West 

Lafayette, Indiana, 47907, Contract No. DTFH61-08-R-00010.

Distribution—This TechBrief is being distributed according to a standard distribution. Direct distribution is being made to the Divisions and Resource Center.

Availability—The publication associated with this TechBrief is Alkali-Silica Reaction Mecahnisms and 

Detection: An Advanced Understanding (FHWA-HRT-14-078). It is available in print and online at http://

www.fhwa.dot.gov/research. 

Key Words—Alkali-silica reaction, thermodynamic model, reactive aggregates, lithium nitrate, deicers, 

passive acoustic emission, x-ray and neutron imaging.

Notice—This document is disseminated under the sponsorship of the U.S. Department of 

Transportation in the interest of information exchange. The U.S. Government assumes no liability for 

the use of the information contained in this document. The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers’ names appear in this report only because they 

are considered essential to the objective of the document.

Quality Assurance Statement—The Federal Highway Administration (FHWA) provides high-quality 

information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and 

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lithium-based products proposed for counteracting ASR on the chemistry of pore solution and ccement hydrates,” Cement Concrete 

Research, 34(9), 2004, pp. 1,645–1,660.

3. Diamond, S., “Unique response of LiNO3 as 

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