REFERENCE

NATX INST. OF STAND & TECH V'

NBS

PUBLICATIONS

NBSIR 85-311&

AlllOb 034772

Alkaii-Silica Reaction in Concrete

Leslie J. Strubie

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Gaithersburg, MD 20899

March 1985

Final Report

Prepared for:Science Foundation

-QC"^ “tigton, DC 20550

100

.056 : 85-3116 : 1985 I

national buseau

OF standards

L:na!^i^v

NBSIR 85-3116

ALKALI-SILICA REACTION IN CONCRETE

Leslie J. Struble

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Gaithersburg, MD 20899

March 1985

Final Report

Prepared for: National Science Foundation

Washington, DC 20550

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Alkali-Silica Reaction in Concrete

Leslie Struble

National Bureau of Standards

Gaithersburg, MD 20899

Reaction in concrete between alkalies from the cement

and reactive silica in the aggregate may cause expansion

and cracking, and occasionally may cause significant

weakening of the structure. The mechanisms involved

in this reaction are not well understood, and this

program was undertaken to contribute to a better

understanding of the mechanisms. The objective of

this program is to determine whether there is any

influence of the alkali mineralogy in the cement on the expansion of mortar due to alkali-silica reaction.

The experimental approach consisted of determining

the distribution of alkalies within a group of commercial

Portland cements with a variety of alkali mineralogies,

and measuring expansion of mortar bars prepared using

these cements and various reactive aggregates.

In some cases, differences were observed in both level

and rate of expansion for cements differing in alkali

mineralogy. The differences were substantial with

cements high in alkali and with opal as the reactive

constituent. The results support our hypothesis that

the specific alkali mineralogy of the cement affects

the expansion due to alkali-silica reaction.

1. Introduction

This report describes progress during the last 14 months of

a two-year research program on alkali-silica reaction in concrete.

The first progress report, covering work at Martin Marietta

Laboratories, is included as Appendix A. Reaction in concrete between alkalies from the cement and reactive

silica in the aggregate may cause expansion, cracking, and

occasionally significant weakening of the structure. The mechanisms

that control this reaction are not well understood, and measures

to prevent or control the reaction are largely based on empirical

considerations. The work described in this report was undertaken

in order to improve our understanding of the mechanisms controlling

alkali-si Icia reaction.
The objective of the program was to study whether the alkali

mineralogy in the cement influences the expansion of mortar

due to alkali-silica reaction. In order to meet this objective,

we selected cements with various alkali mineralogies for the

study, and determined their alkali distributions. Mortar bars

were prepared from each cement and a reactive aggregate, and

expansions of the bars due to alkali-silica reaction were measured

over a period of several months.

One study initiated as part of this program is an evaluation

of materials for possible use as a standard reactive aggregate.

ASTM C441 [1]'^ specifies pyrex"^ glass as a standard reactive

aggregate, in order to test the effectiveness of pozzolanic

materials in preventing expansion due to alkali-silica reaction.

However, it appears that this glass will no longer be available

as a lump cullet [2], so experiments have been initiated to

find an alternative material.

2. Experimental Progress

2.1 Materials

The materials used in this study (described in Appendix A) included

eight cements, designated A through G, and four aggregates —

limestone, opal, quartzite, and gneissic granite. An additional

cement (designated I) and several aggregate materials have been

used in the experiments aimed at identifying a standard reactive

aggregate. The aggregates tested as possible standards were

selected for potential reactivity and suitability as a standard.

Thus far, we have tested the opal and quartzite already mentioned,

a rhyolite sand, and three commercial glasses — pyrex glass

(presently specified in C441 [1]), vycor glass, and a porous

silica glass.

2.2 Analysis of Cements for Alkali Distributions

Two techniques were used to analyze cements for their alkali

distributions: qualitative X-ray diffraction (described in

Appendix A), and selective extractions of cement minerals with

chemical analyses of the extracted portions. Two extractions

were used: a water extraction to determine alkalies present

as alkali sulfate, and extraction in solution of salicylic acid in

methanol to determine alkalies combined in the calcium silicate

Numbers in brackets indicate literature references at the end

^f the report.

^Certain trade names and company products are identified in order

to specify adequately the experimental procedure. In no case

does such identification imply recommendation or endorsement

by the National Bureau of Standards, nor does it imply that

the products are necessarily the best available for the purpose.

2
phases (C,S^ and C-S). Alkalies combined in the calcium al-uminate

phases (C^A and C,^) were calculated as the difference between

the alkalies insoluble in the salicylic acid methanol extraction

and the alkalies soluble in the water extraction.

Maintaining selectivity of the extractions required particular

care. Hydration of the cements was a problem, because hydration

would modify the alkali distributions determined using the

extractions. Not unexpectedly, hydration occurred in several

of the cements. Therefore, all extractions were carried out

on freshly ignited samples, to prevent error due to hydration.

During previous experiments (Appendix A), occasional evidence

of C^A dissolution' during a 10 minute water extraction was observed.

This^could be a source of error in determining alkalies present

as alkali sulfate phases. Therefore, the water extractions

were repeated using shorter extraction times in order to prevent,

if possible, dissolution of C^A. Extraction procedures generally

followed Section 17.2 of ASTM'^C114 [3] for determination of

water-soluble alkalies in cement. Samples of ignited cement

were mixed with water (0.4 g with 10 ml) for durations of 5 seconds, 1 minute, or 10 minutes (the duration specified in

ASTM C114 [3]). Samples were vacuum filtered using Whatman

No. 50 paper, and sodium (Na) and potassi'om (K) concentrations

in the liquid portions measured by atomic absorption (AA).

Table 1 lists the concentrat

each cement during these ext

results that the alkalies di

are equivalent to the alkali

extraction. However, in som

during the 10 minute extract

occasional dissolution of C,

the results from the 1 minu-t

minute extraction specified

study to estimate the level

minerals, (K,Na) 230 ^ and K

2 C

ions

rac tions

.

alkalies dissolved from

T-- aooears •om these

ssolved during the 5 second ext

es dissolved during the 1 minut

e cases the alkalies dissolved

ion, which had been shown to al

A, were significantly higher,

e extraction, rather than the 1 in ASTM C114 [3], were used in

of alkali present as alkali sul

^2 ^ ^*^4 ^ 3

’

action

-ow

Th0

0thi

f at

r er ore

,

s

The following abbreviations , common

literature, are used in this report:

A for AI

2 O

2

/ and F for ?e 202 .

in cement and

C for CaO, S

concrete

for Si 02 »

3
Table 1. Alkalies dissolved during water extractions^

(percent of ignited cement)

Cement 5 sec

K 0

1 min 10 min 5 sec Na20

1 min 10 min

A 1.26 1.21 1.26 0.24 0.22 0.39

B 0.54 0.55 0.61 0.07 0.02 0.08

C 0.87 0.96 0.96 0.16 0.13 0.14

D 0.58 0.63 0.65 0.05 0.01 0.06

E 0.14 0.15 0.16 0.04 0.03 0.08

F 0.26 0.30 0.28 0.05 0.00 -0.11

G 0.22 0.20 0.22 0.02 -0.02 0.03

H 0.06 0.08 0.15 0.00 0.06 0.07

I 0.94 0.98 0.97 0.19 0.19 0.18

^Determined by atomic absorption analysis. Negative results

are attributed to analytical error.

Extraction in a solution of maleic acid and methanol was explored

for the determination of alkalies combined in the calcium silicates.

The extraction, whose procedure is described elsewhere [4],

selectively dissolves C,S and C^S. However, during preliminary

experiments it became apparent that methanol was often contaminated

by water, such that water-soluble phases could dissolve during

the extraction. In order to prevent even partial dissolution

of water-soluble phases, the methanol had to be rigorously dried

prior to the extraction. Furthermore, it became apparent that

the solution of maleic acid and freshly dried methanol formed

a gel upon addition of ignited cement, causing the procedure

to be unsuitable for selective extraction. An alternative

extraction, using salicylic acid and methanol, did not form

a gel, and therefore was used for these experiments. A paper

describing the effects of water on the extractions has been

submitted for publication [4].

Because it was not possible to analyze the salicylic acid/methanol

extract directly by AA, alkalies were determined in the extraction

residue, and alkalies dissolved in the extraction calculated

by difference from the total. Both unextracted cements (for

total alkali) and residues from salicylic acid/methanol extractions

4
were analyzed according to ASTM C114 [3], dissolving each sample

in acid and determining by AA the concentrations of Na and K

in solution.

Table 2 lists the distributions of alkalies determined by the

various selective extractions. The extractions demonstrate

quantitatively, as was shown qualitatively by XRD (Appendix

A), that the cements for this program covered a suitable range

of alkali distribution, a principal objective when selecting

the cements. Some cements, particularly A, I, and C, have high

levels of alkali sulfate phases [(K,Na)

2 S 0^ and K

2Ca- ( SO^ ) , ]

.

Other cements, particularly B and H, have nigh levels of alkali

in the calcium aluminate phases (C^A and C^AF). Finally a few

cements, particularly D, have high'^levels of alkali in the calcium

silicate phases (C^S and C

2 S).

Table 2. Alkali distributions'

(percent of ignited cement)

Cement Total Water Soluble SA/M Soluble^ Insoluble*^

(alkali sulfates )( calcium silicates )( calcium aluminates)

Na20 K

2 O Na20 K

2O Na20 CM 0 Na20 K2 O

A 0.36 1.29 0.24 1,26 0.14 0.06 -0.02 -0.03

B 0.24 1.05 0.07 0.54 0.20 0.26 -0.03 0.25

C 0.25 1.00 0.16 0.87 0.19 0.07 -0.10 0.06

D 0.06 1.24 0.05 0.58 0.06 0.56 0.00 0.10

E 0.21 0.43 0.04 0.14 0.17 0.21 0.00 0.08

F 0.10 0.64 0,05 0.26 0.06 0.33 -0.10 0.05

G 0.14 0.50 0.02 0.22 0.07 0.21 0.05 0.07

H 0.32 0.29 0,00 0.06 0.25 0.15 0.07 0.14

I 0.29 0. 98 0,19 0.94 0.12 0.07 -0.02 -0 .03

^Determined by atomic absorption analysis. Negative results

gre attributed to analytical error.

Soluble in a solution of salicylic acid in methanol. Determined

by difference between total alkali and SA/M insoluble alkali.

Determined by difference between SA/M insoluble alkali and

water soluble alkali.

2.3 Mortar Bar Expansions

Mortars, as described in Appendix A, were prepared by mixing

cement, water, and graded aggregate. A limestone was used as

5
the inert aggregate, and each reactive material was substituted

for some portion of the limestone.

The expansion tests involved measuring length changes of mortar

bars while stored over water for a period of several months,

as described in Appendix A. All bars were stored at room temperature

except the bars prepared to explore reactive aggregates for

ASTM C441 [1], which were stored at 37.8°C.

Figure 1 presents the expansion data obtained thus far for Cement

I and the various candidate materials for a standard reactive

aggregate. As this work is in progress, no conclusions have

been made.

Figure 2 presents expansion data for Cement A with various levels

of opal. This figure demonstrates the pessimum proportion,

an important phenomenon in alkali-silica reaction. Pessimum

proportion is a term that describes the occurence of maximum

expansion at an intermediate proportion of reactive aggregate.

For instance, in figure 2 the highest expansion is exhibited

by Cement A with 4% opal, while expansions are substantially

lower both with 8% opal and with 2% opal.

Although a pessimum proportion was observed for most combinations

of cement and aggregate tested, the opal was unique in that

its pessimum proportion was quite low, occuring at approximately

2% or 4% opal for all eight cements tested. Furthermore, each

pessimum curve for opal was quite sharp, i.e., high expansion

occurred over only a narrow range of opal level. Mortar bars

prepared with opal at levels only slightly more or less than

the pessimum level showed little or no expansion. In practical

terms, such sharp pessimum curves require that each pessimum

level be precisely determined if the expansion results are to

be meaningful.

Expansion results for each reactive aggregate shown in figures

3 through 6. In some cases, significant differences were observed

for both level and rate of expansion. In particular, the four

high alkali cements with opal showed substantial differences

in expansion (fig. 3). The four low alkali cements with opal,

on the other hand, showed little difference in expansion (fig.

4). The four high alkali cements with quartzite showed slight

differences in expansion (fig. 5), and the four high alkali

cements with gneissic granite showed little or no difference

in expansion (fig. 6).

The observed differences in expansion may tentatively be explained

in terms of alkali distributions within the cements. In particular,

expansions with opal were highest and most rapid for cements

A and C, which contain the highest levels of alkali sulfate

phases. Expansion with opal was lower and less rapid for cement

B, which contains the highest level of alkali combined in calcium

aluminate phases. Finally, expansion with opal was lowest and

most slow for cement D, which contains the highest level of

6
alkali combined in the calcium silicate phases. Cement D also

showed the lowest and most slow expansion with quartzite (fig.

5) . These results tend to support our starting hypotheses, that

the specific alkali mineralogy of a cement affects the expansion

due to alkali-silica reaction. A full understanding of this

effect, however, requires further experimental work.

3. Conclusions

The following have been concluded from this study;

1) In order to determine the level of alkalies present

as alkali sulfate minerals using a water extraction,

an extraction duration of 1 minute is preferred over

the 10 minute extraction presently specified in ASTM

C114 [3].

2) In order to prevent partial dissolution of water-soluble

phases during the selective extraction of calcium silicates

in a solution of salicylic acid and methanol, it is

necessary to use freshly dried methanol. Maleic acid

may not be used with dried methanol, as the solution

forms a gel when the sarrrole is added.

3) For the eight cements tested, pessimum proportions

of opal occurred between approximately 2% and 4%, and

pessimum curves were very sharp. Such sharp pessimum

curves require that the pessimum levels be precisely

determined in order for the expansion results to be

meaningful

.

4) The specific alkali mineralogy of a cement affects

its expansion due to alkali-silica reaction.

In order to understand more fully how the cement mineralogy

affects alkali-silica expansion, and thus understand more fully

the mechanism of the reaction, further experimental work is

required.

This research will be incorporated by the Principal Investigator

in a dissertation, in partial fullfillment of PhD requirements

at Purdue University. As thesis advisor, Professor Sidney Diamond

has provided much consultation, and his contributions are gratefully

acknowledged

.

7
4. References

1. American Society for Testing and Materials. Standard

test method for effectiveness of mineral admixtures

in preventing excessive expansion of concrete due to

the alkali-aggregate reaction. ASTM C441 in Concrete

and Mineral Aggregates, Vol. 04.02 of Annual Book of

ASTM Standards, 1984.

2. Personal Communication from A. Flood, Corning Glass

Works, to L. Struble, NBS, June 29, 1984.

3. American Society for Testing and Materials. Method

for chemical analysis of hydraulic cement. ASTM C114

in Cement; Lime; Gypsum, Vol. 04.01 of Annual Book

of ASTM STandards, 1984.

4. Struble, L. The effect of water on maleic acid and

salicylic acid extractions. Accepted for publication,

Cem. Conor. Res. 1985.

8
0.9

Figur© 1. Mortar bar expansion for cement I and various aggregates,

each aggregate replacing limestone at approximately its pessimum

level

.

9
EXPANSION

(%)

Figure 2. Mortar bar expansion for cement A and opal, with

opal replacing various levels of limestone.

10
0.4

Figure 3. Mortar bar expansion for the high alkali cements

(A-D) and opal, with opal replacing limestone at approximately

its pessimum level for each cement.

11
Figure 4. Mortar bar expansion for the low alkali cements (E-H)

and opal, with opal replacing limestone at approximately its

pessimum level for each cement.

12
= expansion for the high alkali cements (A D) and quartzite, with quartzite replacing limestone at approximately its pessimum level for eLh ceLnt.

13
EXPANSION

(Z)

Mortar bar expansion for the high alkali cements (A-D) and gneissic granite, each cement with 100% granite.

14
Appendix A

PROGRESS REPORT ON NSF GRANT NO. CEE 8210791,

ALKALI-SILICA REACTION IN CONCRETE

Leslie Struble

Martin Marietta Laboratories

I. INTRODUCTION

This progress report describes the first ten months of a two-year

program on alkali-silica reaction in concrete. Although not required

until the end of the first year of the program, this report is being

prepared two months early because the grantee, Martin Marietta

Laboratories, is presently requesting that the program be transferred with

the Principal Investigator from Martin Marietta Laboratories to the

National Bureau of Standards. It was felt that a progress report should

be prepared early in order to assist the National Science Foundation in

deciding on this request.

II. CRITICAL ISSUES

This is an empirical study, designed to show whether there is an influence of cement alkali mineralogy on the expansion of concrete or mortar containing reactive silica. Such an influence is expected from

mechanistic considerations, and if we find an influence, a follow-up

proposal to NSF is planned to pursue mechanistic studies.

The reaction between alkalies and silica, a major concern in the

production of durable concrete, can lead to expansion, cracking, and even

significant weakening of the concrete structure. Although the reaction

has been studied for many years, the mechanisms that control the reaction

are not yet known. These mechanisms must be understood if the reaction Is

to be adequately controlled or prevented.

15
We expected that alkali mineralogy Influences expansion based on

our proposal that the expansion Is directly controlled by the composition

of the pore solution In the concrete or mortar. This control Is twofold: the pH of the pore solution controls the rate of dissolution of

silica, and the chemical composition of the pore solution controls the

composition of the alkali-silica reaction product, which is best described

as an alkali silica gel. Finally, the potential of the gel to sorb water

and swell is thought to depend directly on its chemical composition —

especially on its relative proportions of alkali and silica.

The cement mineralogy, specifically the alkali mineralogy, is

expected to control the chemical species dissolved in the pore solution.

Including its pH. In the absence of alkalies, the cement pore solution is

saturated with Ca and OH , at a pH of approximately 12.6. However, with

dissolved alkalies, the solution converts to a sodium or potassium

hydroxide solution, with a much higher pH. Therefore, it is the level of

dissolved alkalies from the cement that is the critical factor in both

composition and pH of the pore solution.

The rate of alkali dissolution is expected to depend directly on

the alkali mineralogy — alkalies from the soluble sulfate phases will

dissolve quite rapidly, but alkalies derived from the other clinker phases

are expected to dissolve only as each phase hydrates. The hydration of

these phases proceeds at vastly different rates — C^A undoubtedly

hydrates most rapidly, followed by C^S, and C2S and C^AF hydrate quite

slowly. Therefore, for rapidly reactive silica, we expect cements with

high levels of alkali sulfate or calcium langbeinite to be much more expansive than cements with alkali concentrated in the calcium silicates

or C^AF. In the case of more slowly reactive aggregate, however, it is

possible that cements with high levels of alkali sulfate or calcium

langbeinite will be less expansive than cements with alkali concentrated

in the calcium silicates or C^AF. Our experiments are designed to resolve

these issues.

16
III. EXPERIMENTAL PROGRESS

The proposed technical approach consists of two sets of experiments:

1) Selection and characterization of cements. In order to

determine whether there is an effect of alkali mineralogy, we proposed in the early part of the program to collect cements

with a variety of alkali mineralogies and to determine the

alkali partitioning for each cement.

2) Determination of expansion due to alkali-silica reaction.

Expansions of mortar bars with the selected cements and either

a rapidly reactive or a slowly reactive aggregate are to be

tested throughout most of the program.

A. SELECTION AND CHARACTERIZATION OF CEMENTS

In order to carry out these experiments, we sought commercial

cements with as high a total alkali content as possible (> 0.60%

equivalent Na20 ), and to include sufficient cements such that various

levels of all alkali minerals were included. Table 1 lists the selected

cements, and their alkali contents and mineralogies. The distribution of

mineralogies throughout the selected cements is quite good — cements are Included that contain either high or low levels of each alkali mineral

(alkali sulfate, calcium langelnite, alkali-modified C^A, and alkalimodified C

2 S). In order to achieve this distribution, it was necessary to

select several cements whose total alkali levels were lower than

desired. Lower alkali levels mean that mortar bar expansions will be

significantly lower.

Selective extractions of cement minerals with chemical analyses of

the extracted portion constitute our primary method of determining the

partitioning of alkalies in each cement. Both the total alkalies and the

water soluble alkalies have already been measured (Table 2), In order to

determine the levels of alkali derived from alkali sulfate and calcium

17
langbelnlte. In addition, we plan to carry out extractions In a salicylic acld-methanol solution (to extract calcium silicates) and in

ethylene glycol (to extract alkali sulfate).

XRD analysis of the residues from the water extractions (ASTM Cl 14,

Section 17.2), however, suggest that the alkali solubility do not always measure only alkali sulfate and calcium langbelnlte. In many cases, a significant portion of C^A dissolved during the extraction. Thus, alkali

sulfates and calcium langbelnlte estimated by water extraction may be in

significant error. We will pursue the selective extractions very carefully, continuing to analyze residues by XRD to determine what phases are dissolving. It is hoped that the water extraction can be modified to

provide a better indication of the levels of alkali sulfates and calcium

langbelnlte.

Qualitative XRD analyses have been carried out on all cements —

Including analysis of residues from the salicylic acld-methanol extraction, to facilitate identification of alkali sulfates, calcium

langbelnlte, and alkali-modified C^A, and analysis of residues from an extraction in an aqueous potassium hydroxide-sugar solution, to determine

alkali-modified C

2 S. This qualitative XRD work provided the basis for the

alkali mineralogies listed in Table 1.

Certain of the proposed cement characterizations have not yet been

carried out. The proposed experimental schedule has been modified somewhat, in that the mortar bar tests (described below) were started earlier

in the program, and cement characterizations were delayed until later in

the program. QXRD analyses, SEM-EDS analyses, and further selective

extractions will be carried out during the second year of the program.

B. AGGREGATES

Aggregates were to include one nonreactive aggregate to serve as matrix and control, and two aggregates containing reactive silica, one a rapidly reactive silica and the other a slowly reactive silica. We

selected a limestone as the nonreactive aggregate. Beltane opal as the

rapidly reactive aggregate, and both a quartzite, and a gneissic granite

as slowly reactive aggregates. The Beltane opal is a hydrous silica.

18
known to be highly reactive in mortar, and is used in many laboratories as

a standard reactive rock in studies of alkali-silica reaction. The

quartzite (novaculite) is a high purity, very fine-grained silica. The

gneissic granite is a commercial aggregate from Camak, Georgia, a coarsegrained granite composed primarily of quartz, feldspar, and mica, which

was recommended for this program by A. Buck, U.S. Army Corps of Engineers.

In order to confirm that the aggregates, which were selected based

on petrographic evidence, would have the intended rates of reactivity,

they were tested for potential alkali reactivity according to ASTM C289.

This is a chemical test to determine the extent of reaction in a 1 N NaOH

solution for 24 hours at 80®C. Both the concentration of dissolved

silicon and the reduction in hydroxyl ion concentration are measured. The

test results (Table 3) were as expected: the opal is quite highly

reactive, the novaculite moderately reactive, and the Camak only slightly

reactive. The limestone, while providing no soluble silica, did significantly reduce the alkalinity of the solution.

There is a particular proportion of reactive aggregate — actually,

a particular ratio of reactive silica to total alkali — which causes

maximum expansion of mortar or concrete (called the pessimum proportion). Available evidence suggests that the pessimum for opal will be

approximately 4% (by weight of total aggregate), and the pessimum for

Camak granite will be approximately 80%. Based on the results of the

chemical test (Table 3), the pessimum for novaculite is expected to be

approximately 25%. We are preparing mortars with reactive aggregate

replacing various proportions of limestone, such that these pessimum

proportions are bracketed.

C. MORTAR BAR EXPANSIONS

The following procedures are used for the mortar bar expansion

tests (generally according to ASTM C227): use a graded aggregate, a sandto-cement ratio of 2.25 (by weight), and a single water-to-cement ratio of

0.49 (by weight) — a constant ratio, rather than the variable ratio

specified in ASTM C227; prepare two 10'’xl"xl" bars from each mortar,

-'19 -
demold the bars at an age of 24 hours, and store the bars over water at

room temperature — bars are stored In brass racks in sealed plastic

containers lined with blotter paper, a procedure presently under

consideration by ASTM Subcommittee C09.02.02; periodically measure the

length of each bar using a dial gage.

Expansion measurements are presently in progress for 76 bars.

These Include all the control bars (limestone only), most opal bars (at

4%, 8%, and 12% opal), and a few bars with novaculite or Camak.

Additional tests are planned for some cements with 2% opal, and for most

cements with either novaculite or Camak.

Expansion results for each cement at each level of opal are shown

in Figs. 1-8. Tests with many Cements — A, B, C, D, and G — have been

in progress for more than 1000 hours, and in most cases the expansions

have leveled off. All these cements show high to moderate expansion

(0.27% to 0.04), and a clear pessimum proportion of approximately 4%

opal. The remaining lower alkali Cements — E, F, and H — have been in

progress for less than 600 hours and expansions are much lower (< 0.01%).

These cements do not show a clear pessimum proportion, so we intend to

test them with 2% opal.

In order to compare results for cements with similar alkali levels,

expansions at a single level of 4% opal are shown separately for higher

alkali cements (Fig. 9) and for lower alkali cements (Fig. 10). It is too

early in the tests to draw conclusions regarding the lower alkali cements,

but expansions with opal of the higher alkali cements show clearly that

many cements with similar levels of total alkali have significantly

different expansions. Furthermore, in general the higher expansions with

opal are produced by cements whose alkali is concentrated in more rapidly

soluble forms. For Instance, the highest expansion, 0.27%, was obtained

with Cement A, which has 1.12% equivalent alkali, largely present as potassium sulfate. The next expansion level, 0.15%, was obtained with

Cement C, which contains 0.90% alkali, largely as calcium langbeinlte.

The two cements with much lowe^ expansions of 0.04% have similar alkali

levels. Cement B, alkali with 0.92%, largely concentrated in C

2A, and

Cement D with 0.81%, primarily as potassium sulfate. Thus these first

20
results are generally as we expected, with the exception of Cement D,

whose expansion is much lower than expected.

D.. ALKALI DISSOLUTION

One paper, partially supported by this program, was prepared in

collaboration with Dr. I. Jawed and J. Epp of the Laboratories. Copies of

this paper have already been sent to NSF, in accordance with the contract

reporting requirements. The paper was presented at the Sixth International Conference on Alkalies in Concrete, held in Denmark in June,

1983, the proceedings of which will be published.

The paper describes the dissolution and hydration of C^A - Na20

solid solutions, including direct determinations of the rate of alkali

dissolution from each C^A phase. Through this work, we confirmed that the

alkali goes into solution directly as the C^A phase hydrates.

Furthermore, we found no significant v^tffect of Na20 level on the rate of

hydration of the C^A - Na20 solid solutions. Additional studies of this

nature, to determine the rate of alkali dissolution from other alkali

containing minerals, will undoubtedly be Included in our planned follow-up

proposal

.

IV. CONCLUSIONS

Good experimental progress has been made during the first 10 months

of this program: cements have been selected, their characterizations are

in progress, and a significant portion of the mortar bar tests are already

in progress.

Hydration studies of several C^A - Na20 solid solutions shows that

sodium dissolution occurs directly as the phase hydrates, which supports

our hypothesis that alkali concentration and pH in the pore solution are controlled by cement alkali mineralogy.

Expansion tests are far enough along to conclude that there are, as expected, significant differences in expansion with opal between cements

of different alkali mineralogy. In general, expansions are highest for

cements whose alkali occurs in more rapidly soluble phases.

21
One paper already submitted for publication was partially supported

by this grant. In addition, two presentations are planned in the near

future — one in December at a Federal workshop on concrete durability at

the National Bureau of Standards, and the other in January, 1984, at the

annual meeting of the Transportation Research Board.

22
TABLE 1

Cements

Cement

Total Alkali

(% eg. Na20) ^ Alkali Mineralogy

A

B

C

D

E

F

G

H

1.12

0.92

0.90

0.81

0.53

0.50

0.45

0.44

o largely K

2

S0

^ o some K

2 Ca 2 (SO^)^

o some alkali-modified C

2

A

o some alkali-modified C

2

S

o largely alkali-modified C^A

o some K2

S0

^ o some alkali-modified C

2

S

o predominantly K

2 Ca 2 (SO^)^

o predominantly K

2

S0

^

o largely alkali-modified C

2 S o some K

2 S0

^ o some K

2Ca 2 (SO^)^

o some K

2 S 0

^ o some K

2 Ca 2 o some alkali-modified C

2

S

o some K2Ca 2 o some alkali-modified C^A

o some alkali-modified C

2

S

o largely alkali-modified C^A

1 Eq. Na20 is the sum of the Na20 plus the Na20 - molecular equivalent

of the K

2 O.

2 Determined by XRD.

23
TABLE 2

Cement Alkali Levels

Total Water Soluble^

Cement % Na-,0 % K

2 O % Na^O % K^O

A 0.33 1.20 0.23 1.08

B 0.21 1.08 0.05 0.51

C 0.21 1.05 0.14 0.84

D 0.06 1.14 0.01 0.54

E 0.21 0.48 0.03 0.12

F 0.09 0.63 0.01 0.21

G 0.11 0.51 0.02 0.17

H 0.24 0.30 0.03 0.07

1 Water

there

soluble

is some alkali is derivedcontribution from

largely from alkali

alkali-modified C^A.

sulfates

,

though

24
TABLE 3

Results of Chemical Test for Potential Reactivity

of Aggregates (ASTM C289)^

[Si] [0H“]

Sample moles/liter moles/liter

Blank < 0.006 0.74

Opal 1.154 0.15

Novaculite 0.186 0.82

Camak 0.015 0.82

Limestone < 0.006 0.40

1 Dissolved [Si] and reduction in [OH] due to reaction and dissolution of

aggregate in an aqueous 1 N NaOH solution for 24 hours at 80°C.
EXPANSION

(%)

Mortar bar expansions for Cement A with various levels of opal

(tests in progress).

Figure 1
EXPANSION

(%)

0.04

0.02

0.00

-0.02

A A

Cement E • Cement F

A Cement G

Cement H

0 500 1000 1500 2000

TIME (hr)

2500

Figure 10. Mortar bar expansions for all low alkali cements with opal

(tests In progress).

27
EXPANSION

(%)

Figure 9.

0 500 1000 1500 2000 2500

TIME (hr)

Mortar bar expansions for all high alkali cements with 4% opal

(tests in progress).

28
EXPANSION

(%)

Figure 8. Mortar bar expansions for Cement H with various levels of opal

(tests In progress).

29
EXPANSION

(%)

0.04

Figure 7.

-0.02

500 1000 1500

TIME (hr)

2000 2500

Mortar bar expansions for Cement G with various levels of opal

(tests In progress).

30 -
EXPANSION

(%)

Figure 6. Mortar bar expansions for Cement F with various levels of opal

(tests in progress).

31
Figure Mortar bar expansions for Cement E with various levels of opal

(tests in progress).

32
EXPANSION

(%)

0.08

Figure 4.

-0.04 1 1 1

0 500 1000 1500

TIME (hr)

T 0% Opal • 4% Opal

A 8% Opal

1 2% Opal

I 2000 2500

Mortar bar expansions for Cement D with various levels of opal

(tests in progress).

33
EXPANSION

(%)

Mortar bar expansions for Cement C with various levels of opal

(tests in progress).

Figure 3
NBS-n4A (REV. 2-8C) U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET f See/ nstnictions)

1. PUBLICATION OR

REPORT NO.

NBSIR 85-3116

2. Performing Organ. Report No, 3. Publication Date

March 1985

4. TITLE AND SUBTITLE

ATj<al i-Sil ica Reaction in Concrete

5. AUTHOR(S)

Le?slie Struble

6. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No. CEE 8210791

8. T^pe of Report & Period Covered

Final Progress Reoort

Nov. 1983 - Jan. 1985

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State. ZIP)

National Bureau of Standards and

National Science Foundation

1800 G. Street NW

Washington, DC 20550

10. SUPPLEMENTARY NOTES

I I Document describes a computer program; SF-185, FIPS Software Summary, is attached.

li. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it her^ ^ i Reaction in concrete between alkalies from the cement and reactive silica in the

aggregate may cause expansion and cracking, and occasionally may cause sinnificant

weakening of the structure. The mechanisms that control this reaction are not well

understood, and this orogram was undertaken in order to improve our understandino. The

objective of this program is to determine whether there is any influence of the alkali

mineralogy in the cement on the expansion of mortar due to alkali-silica reaction. The

experimental approach consisted of determining the distribution of alkalies within a nroup of commercial Portland cements with a variety of alkali mineralooies , and

measuring expansion of mortar bars prepared using these cements and various reactive

aggregates. In some cases, differences were observed in both level and rate of expansion for cements differing in alkali mineralogy. The differences were substantial with

cements hiah in alkali and with opal as the reactive constituent. The results support

our hypothesis that the specific alkali mineralooy of the cement affects the expansion

due to alkali-silica reaction.

12. KsEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key ^ordi by temico on*

Alkali; alkali-silica reaction; cement; concrete; selective extraction; soluble

alkal i

13. AVAILABILITY

I "xl Unlimited

I I For Official Distribution. Do Not Release to NTIS

I I Order From Superintendent of Documents, U.S, Government Printing Office, WashmgtO'i. D.C.

20402.

I Order From National Technical Information Service (NTIS), Springfield. VA. 22161

14. NO. OF

PRINTED page:

15. Pfic*