A Rapid Test to Determine Alkali-Silica Reactivity of Aggregates Using Autoclaved Concrete Prisms.pdf

Research & Development Information

PCA R&D Serial No. 3235

A Rapid Test to Determine Alkali-Silica Reactivity of Aggregates Using Autoclaved Concrete Prisms

by Eric R. Giannini and Kevin J. Folliard

© Portland Cement Association 2013 All rights reserved

KEYWORDS Concrete, ASR, aggregates, test methods, autoclave

ABSTRACT Prevention of alkali-silica reaction (ASR) in new structures relies on accurately identifying reactive aggregates so that mitigation measures can be taken in the concrete mixture design. Rapid test methods to identify potentially reactive aggregates, such as the accelerated mortar bar test (ASTM C1260), tend to correlate poorly to the performance of concrete in the field. The concrete prism test (ASTM C1293) is considered the most reliable accelerated test method, but takes one year to complete.

This report details a new rapid test using autoclaved concrete prisms. Concrete prisms similar to those used in ASTM C1293 are subjected to a 0.20 MPa saturated steam environment for 24 hours using a commercially-available autoclave. The test takes a total of four days from mixing of the concrete to the final expansion measurement. An expansion limit of 0.08% has been proposed to distinguish non-reactive and potentially reactive aggregates.

The first phase of testing included two non-reactive and three benchmark reactive aggregates from the southwestern United States. The second phase of the project consisted of six additional aggregates of varying reactivity and mineralogy from across North America, some of which are incorrectly classified by ASTM C1260 or ASTM C1293.

REFERENCE Giannini, Eric R., and Folliard, Kevin J., A Rapid Test to Determine Alkali-Silica Reactivity of Aggregates Using Autoclaved Concrete Prisms, SN3235, Portland Cement Association, Skokie, Illinois, USA, 2013, 21 pages.

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TABLE OF CONTENTS Page Keywords ......................................................................................................................................... i Abstract ............................................................................................................................................ i Reference ......................................................................................................................................... i Table of Contents ............................................................................................................................ ii Introduction ..................................................................................................................................... 1 Research Signficance ...................................................................................................................... 4 Experimental Program .................................................................................................................... 4 Materials and Mixture Proportions ............................................................................................. 4 Test Procedure ............................................................................................................................ 7 Results and Discussion ................................................................................................................. 10 Phase I Tests ............................................................................................................................. 10 Phase II Tests ............................................................................................................................ 14 Conclusions and Future Work ...................................................................................................... 16 Acknowledgements ....................................................................................................................... 18 References ..................................................................................................................................... 19

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A Rapid Test to Determine Alkali-Silica Reactivity of Aggregates Using Autoclaved Concrete Prisms by Eric R. Giannini* and Kevin J. Folliard **

INTRODUCTION Alkali-silica reaction (ASR) is a major durability issue affecting many concrete structures worldwide. ASR is triggered by alkalis in concrete, mainly from portland cement but from other internal and external sources as well, which result in high OH- concentration within the pore solution. The OH- ions first attack certain siliceous phases in aggregate particles, and the alkalis then form an expansive gel, resulting in concrete expansion and cracking (Hobbs 1988). Expansive ASR can be prevented in new concrete if appropriate mitigation measures are taken, such as the use of supplementary cementing materials (SCMs); however, this requires accurate identification of potentially reactive aggregates. While some aggregates have wellestablished histories of participating in expansive ASR in the field, new sources of unknown reactivity must be tested prior to use. The Concrete Prism Test (CPT), also referred to as ASTM C1293 (2008), is considered to be the most reliable accelerated test method, but takes one year to complete (two years if mitigation measures such as SCMs are being tested). The duration of the CPT has inhibited widespread use of this test to qualify aggregates, and efforts to reduce the duration to three months by increasing the test temperature from 38°C to 60°C have had mixed results. The accelerated mortar bar test (AMBT), or ASTM C1260 (2007) is a widely-used ultraaccelerated test which takes 16 days to complete (30 if mitigation measures are tested). Mortar bars are stored in a 1N NaOH solution; the test essentially provides an unlimited amount of *

Assistant Professor, Department of Civil, Construction, and Environmental Engineering, The University of Alabama, Box 870205, Tuscaloosa, AL, 35487-0205, USA, (205) 348-0785. ** Professor, The University of Texas at Austin, Department of Civil, Architectural and Environmental Engineering, 301 E. Dean Keeton Street, Stop C1747, Austin, TX, 78712-1068, USA, (512) 471-1944.

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alkalis. This has proven to be too severe for some aggregates that are known to be innocuous based on field performance, but exceed the expansion limits in ASTM C1260 (Bérubé and Fournier 1992). Still other aggregates that are known to be deleteriously reactive are incorrectly classified as innocuous in this test. Aggregates which display pessimum behavior will also be incorrectly identified as innocuous, if they are not tested with some fraction replaced by a nonreactive sand (Shayan 1992). Grattan-Bellew (1997) provides an excellent review of ultra-accelerated test methods that were in use prior to 1997, and set forth several criteria for a satisfactory ultra-accelerated test to determine whether an aggregate is, or is not, potentially reactive. These are paraphrased below: 1. The duration should be no more than a few weeks, preferable a few days. 2. The test should be simple and not require “excessively expensive” apparatus. 3. Test results and field experience should be in agreement. 4. The test should correctly identify the reactivity of more than 90% of aggregates. 5. Reaction products should be similar to those found in field concrete and the CPT. 6. The expansion limit should be greater than 0.05%. 7. The coefficient of variation (C.V.) should be less than 10% for a single operator and 12% for inter-laboratory tests. Among the ultra-accelerated test methods reviewed by Grattan-Bellew were several tests involving autoclaved prismatic mortar and concrete specimens. The common features of the autoclaved mortar bar tests included a total duration from mixing to final measurement of less than one week, and the use of significantly elevated alkali loadings (2.0 to 3.5% Na2Oe by mass of cement). Of particular note were tests developed by Fournier, et al. (1991) at Laval University and CANMET, and by Nishibayashi, et al. (1996) in Japan. The Laval/CANMET test was evaluated using 40 different aggregates from the St. Lawrence Lowlands in the Canadian provinces of Quebec and Ontario. Mortar bars with mixture proportions and dimensions similar to those specified by ASTM C227 were used, but the alkali content was increased by adding NaOH to the mixing water. Alkali contents ranging from 1.0 to 3.5% Na2Oe were investigated, along with autoclaving durations ranging from 4 to 8 h, autoclave pressures from 0.10 to 1.03 MPa, and w/c ranging from 0.45 to 0.60. The final procedure (shown in Figure 1) involved raising the alkali content of the mortar bars to 3.5% Na2Oe and autoclaving for 5 h at 130°C (0.17 MPa gauge pressure). Expansion measurements

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were taken before and after autoclaving (after the bars had been cooled to ambient temperatures). The authors also noted that the influence of the alkali content of the cement was minimized if high-alkali cement (in this case, >0.80% Na2Oe) was used. Despite promising results, this test method was not a subject of further study.

Figure 1. Laval/CANMET autoclaved mortar bar test procedure (Fournier, et al. 1991).

The test developed by Nishibayashi,et al. (1996), is the only known test method that involved autoclaved concrete, rather than mortar, specimens. The researchers developing this test also had prior experience with autoclaved mortar bar specimens (Nishibayashi, et al. 1987). For their concrete prism test, they investigated alkali contents ranging from 1.0 to 4.0% Na2Oe, autoclaving durations ranging from 1 to 8 h, and autoclaving pressures ranging from 0.10 to 0.30 MPa. The final proposed test method involved autoclaving concrete made with an alkali content of 3.0% Na2Oe for 4 h at a gauge pressure of 0.20 MPa. Unfortunately, only two aggregates were investigated in the development of this test, so it is difficult to assess how broadly applicable the method may be. Yet, the work performed by these researchers provides a starting point for the research described in this report.

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RESEARCH SIGNIFICANCE This report details the development of a rapid autoclaved concrete prism test to determine the susceptibility of an aggregate to expansive ASR. The test can be completed in four days; a significant improvement over the CPT and the AMBT. This research builds primarily on earlier work at Laval University and CANMET (Fournier, et al. 1991) and Japan (Nishibayashi, et al. 1996). It marks a significant improvement over the Laval/CANMET work by using concrete, rather than mortar specimens, and investigates a wider range of aggregates than were used in the development of the Japanese test.

EXPERIMENTAL PROGRAM The project was divided into two phases and eleven aggregates of varying reactivity were tested. In Phase I, two non-reactive and three benchmark highly-reactive aggregates were tested; these aggregates had all been tested extensively in ASTM C1260, ASTM C1293, and in outdoor exposure and/or field performance. Several test durations and alkali contents were evaluated in this phase to optimize the test parameters. The optimized procedure was repeated on four to five batches of specimens for each reactive aggregate to evaluate the variability of the test procedure and establish a proposed failure criterion. In Phase II, six additional aggregates of varying reactivity were tested. With the exception of a fine aggregate believed to be non-reactive, these aggregates had established histories in ASTM C1260, ASTM C1293, and in outdoor exposure/field performance. Phase II tests were used to evaluate the applicability of the test to a wider range of reactivity levels and mineralogies. Because of limited material availability, only one batch of specimens per aggregate was tested.

Materials and Mixture Proportions The mixture proportions generally follow that specified for ASTM C1293, although the total alkali content of the mixture is greatly increased. Table 1 provides a description of the origin and mineralogy of the aggregates and cement used in the test program, as well as the assigned designation that will be used to reference them in the remained of this report. Aggregates F1 and C1 were the standard non-reactive fine and coarse aggregates in use at the authors’ laboratory in

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Austin, Texas, while F4 was a candidate to replace F1 in future testing. The performance of F1 and C1 have been verified through many published (Folliard, et al. 2006) and unpublished tests, using a combination of ASTM C1260, ASTM C1293 and years of outdoor exposure testing. F4 and C1 are produced from the same quarry in San Antonio, Texas, thus F4 was also expected to be a non-reactive fine aggregate. The remaining eight aggregates were known reactive aggregates, with field and laboratory test performance documented in numerous sources (Stark, et al. 1993; Johnston, et al. 2000; Lane 2000; Touma, et al. 2001; Folliard, et al. 2006, Transtec 2009; Tremblay, et al. 2012; Giannini 2012; Fournier 2012). Table 1. List of Materials Used in Testing

Designation F1 F2 F3 F4 C1 C2 C3 C4 C5 C6 C7 CEM 1

Origin San Antonio, Texas El Paso, Texas Robstown, Texas San Antonio, Texas San Antonio, Texas Bernalillo, New Mexico Ottawa, Ontario North East , Maryland Dell Rapids, South Dakota North Garden, Virginia Taunton, Massachusetts Evansville, Pennsylvania

Mineralogy Manufactured sand; limestone Natural sand; quartz, feldspars, volcanics, chert Natural sand; quartz, chert Manufactured sand; limestone Crushed limestone Mixed gravel; rhyolite, other volcanics Crushed siliceous limestone Crushed granitic gneiss Crushed quartzite Crushed granite Crushed greywacke Type I/II portland cement, 0.90% Na2Oeq

Table 2 lists the aggregates and their performance in ASTM C1260 and C1293, based on the results of both published (Folliard, et al. 2006; Ideker, et al. 2012) and unpublished (Fournier 2012) tests. Expansion limits for classifying an aggregate as non-reactive in these tests are generally recognized to be 0.10% at 14 days and 0.04% at one year, respectively (ASTM C1260 2007; ASTM C1260 2008). Expansions between 0.10% and 0.20% in ASTM C1260 are considered to be inconclusive, while expansions greater than 0.20% are considered indicative of deleteriously reactive aggregates. Two reactive aggregates used in Phase II of this study fall in the 0.10 to 0.20% expansion range in ASTM C1260 (C4 and C5), but are correctly identified as reactive by ASTM C1293. A third aggregate (C6), is incorrectly identified as innocuous in

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ASTM C1260, and only marginally meets the classification for a reactive aggregate in ASTM C1293. Table 2. ASTM C1260 and ASTM C1293 Performance of Aggregates Used in this Study

Expansion (%) Aggregate ASTM C1260 ASTM C1293 F1 0.05 0.014 F2 0.66 0.509 F3 0.29 0.201 F4 0.01 0.014 C1 0.04 0.014 C2 0.90 0.168 C3 0.39 0.201 C4 0.11 0.060 C5 0.14 0.149 C6 0.05 0.047 C7 0.47 0.277

Tables 3 and 4 show the mixture proportions for Phase I and Phase II testing, respectively. Sodium hydroxide was added to the mixing water as a 50% (by weight) aqueous solution, in order to boost the equivalent total alkali loading of the mixture to the desired level. Table 3. Phase I Mixture Proportions

Component Coarse Aggregate (SSD) (kg/m3) Fine Aggregate (SSD) (kg/m3) Cement (kg/m3) NaOH added Total Na2Oeq, (kg/m3) w/cm Water (kg/m3)

C1

Phase I Mixtures C1 C1

C2

F1

1107 F2

F3

1161 F1

600

626

621

561

CEM 1 420 5.96 (2.0%); 8.68 (2.5%); 11.39 (3.0%) 8.40 (2.0%); 10.50 (2.5%); 12.6 (3.0%) 0.42 176

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Table 4. Phase II Mixture Proportions.

Component Coarse Aggregate (SSD) (kg/m3) Fine Aggregate (SSD) (kg/m3) Cement (kg/m3) NaOH added Total Na2Oeq, (kg/m3)

Phase II Mixtures C4 C5

C1

C3

1091 F4

1111 F1

1090 F1

639

635

709

C6

C7

1061 F1

1127 F1

1064 F1

674

674

694

CEM 1 420 11.39 12.6

w/cm Water (kg/m3)

0.42 176

Test Procedure In Phase I, several alkali loadings (2.0, 2.5 and 3.0% Na2Oe,by mass of cement) were investigated, as well as autoclaving durations of 4, 6 and 24 h. In this report, the autoclave duration refers to the time at peak temperature and pressure. The actual time in the autoclave includes heating/pressurization and cooling/depressurization periods; this increased the total time the specimens were in the autoclave by approximately 2 h. Autoclaving durations between 6 and 24 h were not investigated, as 6 h was deemed to be the maximum for a single-day procedure (from initial to final expansion measurements). In Phase II, the procedure was finalized to use an alkali loading of 3.0% and autoclave duration of 24 h, based on the results of the Phase I tests, discussed in the next section. The proposed test procedure is as follows: 1. Day one: Mix concrete, cast specimens and moist cure in molds for 24 h, according to ASTM C192 (2007). 2. Day two: Demold specimens at 24 h and moist cure for an additional 24 h. 3. Day three: Take initial length change measurements, place specimens in autoclave. Autoclave for 4, 6 or 24 h at 133°C (0.20 MPa gauge pressure). 4. Day three/four: Remove specimens from autoclave, cool to ambient temperature (23°C) over approximately 1 h, and take final length change measurements. Except for the elevated alkali content, specimens were otherwise identical to the 75 x 75 x 286 mm concrete prisms specified by ASTM C1293. Stainless steel gauge studs in each end

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facilitated axial length-change measurements over a gauge length of 254 mm. Three specimens were cast from each batch of concrete. The autoclave was a commercially available medical sterilizer capable of holding six prisms at once; two aggregates can therefore be simultaneously tested if two batches of concrete are mixed in rapid succession (< 1 h). A stainless steel basket supplied with the autoclave was subdivided using stainless steel wire to position the specimens with at least 6 mm spacing between them, as shown in Figure 2. The basket was also positioned above the base stand in the autoclave so that the weight of the specimens would not be bearing directly on the gauge studs during the autoclaving process.

Figure 2. Concrete prisms and specimen basket in the autoclave.

Prior to the end of the autoclaving cycle, a large stockpot was filled halfway with hot water (~60°C) and placed on a hot plate to heat the water to approximately 70 to 75°C by the time the specimens were removed from the autoclave. The stock pot was then placed in a large sink, and a second stainless steel basket placed in the hot water to hold the specimens. The specimens were removed after the autoclave had completely depressurized and cooled to a

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temperature of 90°C, and they were then placed in the stock pot. Hot water remaining in the autoclave chamber was drained off and added to the stock pot; this was sufficient to cover the specimens completely. Cold water was fed into the stock pot to gradually cool the specimens to ambient temperature, as shown in Figure 3, prior to final expansion measurements.

Figure 3. Specimens cooling to ambient temperature under running cold water.

Length change was measured and calculated according to ASTM C157 (2008) and ASTM C490 (2011). The initial measurement was taken immediately prior to placing the specimens in the autoclave, at an age of 48 h (± 0.5 h). The second and final measurement was taken after cooling to 23°C (± 2°C), and the length change calculated to the nearest 0.001% for each specimen. Data were then averaged for all three specimens.

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Because of the high temperature used in the autoclaving process, the authors recognized the importance of ruling out delayed ettringite formation (DEF) as a contributing cause of expansion in this test. DEF can occur if curing temperatures exceed 70°C, due to the destruction of ettringite above this temperature and subsequent formation of ettringite at later ages after cooling below 70°C (Taylor, et al. 2001). However, expansion requires an extended period of moist storage and typically takes several weeks to months to appear (Taylor, et al. 2001); separate tests involving aggregates F2 and C2 cured at showed expansions of less than 0.01% at an age of seven days for storage in both moist air and in saturated limewater (Giannini 2012). Thus, although Nishibayashi, et al. (1996) measured both the expansion immediately after the autoclaving process and residual expansion of specimens placed in storage at 40°C and 100% RH after autoclaving. Because residual expansions could be partly caused by DEF, they were not measured in this study. The selection of the autoclave temperature and pressure was influenced strongly by the work of Nishibayashi, et al. (1996) and Fournier, et al. (1991), and the capabilities of commercially available equipment. Only a small number of commercially available autoclaves, pressure chambers, or pressure cookers were found to be both capable of holding three concrete prisms and safely containing pressurized steam at pressures of 0.20 MPa or higher, while at the same time costing less than $10,000 (USD). The autoclave purchased for this study had a maximum operating temperature of 135°C (0.21 MPa).

RESULTS AND DISCUSSION Phase I Tests Phase I of the project involved first testing combinations of five well-studied aggregates in order to select the optimal alkali content and autoclaving duration for the test procedure. All tests were performed with at aFigure 4 shows the results of test on a nonreactive mixture containing aggregates F1 and C1 and a reactive mixture containing aggregates F2 (reactive) and C1 (nonreactive). Each datum represents the average expansion of specimens tested for each combination of alkali content and autoclaving duration. In this figure it is clear that there is only minimal expansion for both mixtures at an alkali content of 2.0% and duration of 4 h. Because F2 is known to be a very highly reactive aggregate, for a test procedure to be considered viable, it must produce a large amount of

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expansion. For this reason, an alkali content of 2.0% was eliminated from further testing. For alkali contents of 2.5% and 3.0%, expansion of specimens containing the F2 aggregate exhibited a nearly linear relationship to the autoclaving duration, while those with the non-reactive F1 and C1 aggregates all exhibited approximately 0.05% expansion or less. In fact, for the non-reactive mixture with 3.0% alkalis, there was little increase in expansion as a result of increasing the autoclaving duration from 6 to 24 h. Expansions of the F2 specimens autoclaved for 24 h were consistent with typical expansions obtained in ASTM C1293 for this aggregate. F2

0.06%

0.6%

0.05%

0.5%

0.04% 0.03% 3.0%

0.02%

2.5%

0.01%

2.0%

0.00% 0

Expansion

Expansion

F1+C1

0.4% 0.3% 3.0%

0.2%

2.5%

0.1%

2.0%

0.0%

4 8 12 16 20 24 Autoclave Duration (Hrs)

0

4 8 12 16 20 24 Autoclave Duration (Hrs)

Figure 4. Autoclave expansions for various alkali contents and durations for non-reactive mixture (left) and mixture with F2 aggregate (right).

Based on the results shown in Figure 4, alkali contents of 2.5% and 3.0% and autoclaving durations of 4, 6 and 24 h were retained as potential test parameters and applied to the moderately to highly reactive F3 and C2 aggregates. Figure 5 shows the results of tests for these reactive mixtures. The C2 specimens experienced similar trends as the F2 specimens shown in Figure 4, with increasing expansion linked to higher alkali content and longer autoclave durations. Expansions were most similar to those obtained in ASTM C1293 when the autoclaving duration was 24 h. Specimens made with the F3 aggregate, however, exhibited very little reactivity at 2.5% alkalis, and a significant increase can be seen as the alkali content was increased to 3.0%. Based on these results, the optimal test parameters were determined to be an alkali content of 3.0% and 24 h autoclaving duration at a temperature and pressure of 133°C and 0.20 MPa. An expansion limit of 0.08% was proposed based on the Phase I tests to distinguish between reactive and non-reactive aggregates.

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F3

C2

0.30%

0.20%

0.20% 3.0%

0.15%

2.5%

0.10%

Expansion

Expansion

0.25%

0.05%

0.15% 0.10% 3.0% 0.05% 2.5%

0.00%

0.00% 0

4 8 12 16 20 24 Autoclave Duration (Hrs)

0

4 8 12 16 20 24 Autoclave Duration (Hrs)

Figure 5. Autoclave expansions for various alkali contents and durations for mixtures containing F3 (left) and C2 (right) aggregates.

After determining the optimal test parameters, multiple sets of specimens containing the reactive aggregates were fabricated and tested to determine the repeatability of the test method. A total of five batches of three prisms were tested for the F2 aggregate, and four batches each for the F3 and C2 aggregates. The coefficients of variation ranged from 2.4% for the F2 specimens to 10.0% for the F3 specimens. The nonreactive mixture of F1 and C1 was not tested again, to preserve supplies of these aggregates for Phase II testing. However, the variation in expansion within each set of three specimens for the nonreactive mixture for all combinations of alkalis and autoclave duration ranged from 0.000% to 0.008%; the average C.V. was 4.8%. Figures 6 and 7 compare the expansion of the Phase I aggregates in the autoclaved concrete prism test to their performance in ASTM C1293 and ASTM C1260, respectively. Each datum represents the average of a set of three autoclaved prisms for 3.0% alkalis and 24 h autoclave duration. The ASTM C1293 and ASTM C1260 results represent typical results for these aggregates as reported in Table 2. Expansion limits for all three tests are plotted as dashed lines.

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Reactive 0.4%

F1+C1

Non-reactive

Autoclave Expansion (24 Hrs @ 0.2 MPa)

0.6%

F2 F3 C2

0.2%

Non-reactive 0.0% 0.0%

0.2% 0.4% ASTM C1293 Expansion

0.6%

Figure 6. Autoclave expansions (3.0% alkalis, 24 h, 0.20 MPa) vs. ASTM C1293 expansions for Phase I aggregates.

All the aggregates in Phase I are correctly identified as potentially reactive or nonreactive by both ASTM C1260 and ASTM C1293, and the expansions of the autoclaved concrete prisms compare favorably to these tests. This is particularly true when compared to ASTM C1293; the expansion of aggregate C2 in ASTM C1260 is extraordinarily high compared to ASTM C1293 and its known field performance. Autoclaved prisms containing C2 expanded more similarly to prisms tested according to ASTM C1293. There also appears to be some inherent expansivity in the autoclaved concrete prism test, even for known non-reactive aggregates. The cause of this is not known, but it does justify a higher proposed expansion limit of 0.08%.

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0.8% Reactive 0.6%

F1+C1

Non-reactive

Autoclave Expansion (24 Hrs @ 0.2 MPa)

1.0%

F2 F3

0.4%

C2

0.2%

Non-reactive 0.0% 0.0%

0.2%

0.4% 0.6% ASTM C1260 Expansion

0.8%

1.0%

Figure 7. Autoclave expansions (3.0% alkalis, 24 h, 0.20 MPa) vs. ASTM C1260 expansions for Phase I aggregates.

Phase II Tests Figures 8 and 9 compare the expansion of the Phase II aggregates in the autoclaved concrete prism test to their performance in ASTM C1293 and ASTM C1260, respectively. Each datum represents the average of a set of three autoclaved prisms for 3.0% alkalis and 24 h autoclave duration. The ASTM C1293 and ASTM C1260 results represent typical results for these aggregates as reported in Table 2. Expansion limits for all three tests are plotted as dashed lines. Based upon an expansion limit of 0.08%, the autoclave concrete prism test correctly classified all of the Phase II aggregates. Although the specimens containing aggregates C3, C5 and C7 expanded less (in some cases significantly so) than in previous ASTM C1293 tests, they are still clearly above the 0.08% expansion limit. Specimens containing aggregates C4 and C6 exhibited greater expansion than in ASTM C1293; this is particularly significant for C6, which is only marginally classified as reactive in ASTM C1293 despite a clear record of deleterious field performance.

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Reactive 0.16% C3 0.12%

Non-reactive

Autoclave Expansion (24 Hrs @ 0.2 MPa)

0.20%

C4 C5 C6

0.08%

C7 F4+C1

0.04% Non-reactive 0.00% 0.00%

0.08%

0.16% 0.24% ASTM C1293 Expansion

0.32%

Figure 8. Autoclave expansions (3.0% alkalis, 24 h, 0.20 MPa) vs. ASTM C1293 expansions for Phase II aggregates.

In comparison to ASTM C1260, the results of the autoclaved concrete prism test are clearly superior for the Phase II aggregates. ASTM C1260 incorrectly classifies aggregate C6 as non-reactive, and is inconclusive regarding C4 and C5; all three are classified correctly as reactive in the autoclaved concrete prism test when an expansion limit of 0.08% is used. The nonreactive aggregate combination used in Phase II (C1 and F4) exhibits similar behavior as the combination of C1 and F1 in Phase I; the average expansion was 0.059%. This exceeds the expansions in both ASTM C1293 and ASTM C1260 and may be, as suggested above, a result of some inherent expansivity of the specimens under the proposed test conditions. The cause of this expansion requires further investigation in order to determine if it is related to the specific materials used in this study, or if non-reactive aggregates can be universally expected to expand similarly.

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0.40% C3

Reactive

C4 0.30%

0.20%

Non-reactive

Autoclave Expansion (24 Hrs @ 0.2 MPa)

0.50%

C5 C6 C7 F4+C1

0.10% Non-reactive 0.00% 0.0%

0.1%

0.2% 0.3% ASTM C1260 Expansion

0.4%

0.5%

Figure 9. Autoclave expansions (3.0% alkalis, 24 h, 0.20 MPa) vs. ASTM C1260 expansions for Phase II aggregates.

Although the data set is not large enough for a more comprehensive statistical analysis, the specimens in Phase II did exhibit very low variability within each set of three specimens. The variability within each set can be measured in terms of a rough C.V. (half of the range of expansions divided by the average expansion); this ranged from 1.6% (C7) to 8.6% (C4) and was in every case less than the maximum C.V. of 10% recommended by Grattan-Bellew (1997) for a single operator.

CONCLUSIONS AND FUTURE WORK The autoclaved concrete prism test proposed in this report compares favorably with both ASTM C1293 and ASTM C1260 with regards to its ability to rapidly classify the potential alkali-silica reactivity of the eleven aggregates tested. In particular, this test method was superior to ASTM C1260, both in speed and accuracy. An expansion limit of 0.08% is proposed based on the results obtained in this study.

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Of the seven criteria set forth by Grattan-Bellew (1997) for a viable ultra-rapid test method, all but one was satisfied. The remaining criteria, that the reaction products be similar to those produced in the CPT (ASTM C1293) and field concrete, remains unanswered. 25 mmthick slices were cut from one specimen each for each aggregate following the conclusion of the test and sent to Laval University for petrographic analysis; this has not been completed at the time of this writing. The autoclaved concrete prism test has been shown to be a viable candidate for an ultrarapid test for potential alkali-silica reactivity, and worthy of future study. This method appears to be best suited as a screening test for aggregates and potentially for combinations of aggregates. However, the test is not likely to be suited to testing mitigation measures because of the high alkali content required to produce expansion in just 24 h. Future research and development involving this method should be focused in several areas: •

Effect of cement alkalis on expansion. ASTM C1293 requires a cement alkali content of 0.8 to 1.0% (Na2Oe). This may not be necessary in the autoclaved prism test because the vast majority of alkalis will come from NaOH even for very-high-alkali cements.

•

Determining the cause of the expansion of the non-reactive mixtures tested in this study. This may include testing mortar bars containing Ottawa sand, cement paste bars, and can be coupled with the testing of various cements described above

•

Testing an expanded range of aggregates, with particular attention to slow/late expanding aggregates and those exhibiting pessimum behavior in ASTM C1260.

•

Inter-laboratory studies to determine the variability of results to be expected across multiple laboratories and operators.

•

Petrographic examination of the reaction products.

•

Potential for testing “job mixes” or combinations of aggregates that do not necessarily include a standard non-reactive aggregate.

•

Potential variations in the test method to allow evaluation of mitigation options.

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ACKNOWLEDGEMENTS The research reported in this paper (PCA R&D Serial No. 3235) was conducted at The University of Texas at Austin with the generous sponsorship of the Portland Cement Association Education Foundation (PCA Project Index No. F10-02), through the Educational Foundation Fellowship program. The contents of this report reflect the views of the authors, who are responsible for the facts and accuracy of the data presented. The contents do not necessarily reflect the views of the Portland Cement Association.

The authors would like to thank Benoît Fournier at Université Laval for his advice, Mike Rung and Jessica Little for their assistance in setting up the autoclave used in this study, and Max Layne for his assistance with test preparations.

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REFERENCES ASTM C1260-07. "Standard Test Method for Potential Alkali Reactivity of Aggregates (Mortar Bar Method)." West Conshohocken, PA, USA: ASTM International, 2007.

ASTM C1293-08b. "Standard Test Method for Determination of Length Change of Concrete Due to Alkali-Silica Reaction." West Conshohocken, PA, USA: ASTM International, 2008.

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Grattan-Bellew, P.E. "A Critical Review of Ultra-accelerated Tests for Alkali-Silica Reactivity." Cement and Concrete Composites 19 (1997): 403-414.

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Stark, D., B. Morgan, and P. Okamoto. Eliminating or Minimizing Alkali-Silica Reactivity. SHRP-C-343, Washington, DC: Strategic Highway Research Program, National Research Council, 1993, 266.

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Tremblay, S., B. Fournier, M. Thomas, T. Drimalas, and K. Folliard. "The Lomas Boulevard Road Test Site, Albuquerque (New Mexico) - A Case Study on the Use of Preventative Measures Against ASR in New Concrete." Edited by T. Drimalas, J. H. Ideker and B. Fournier. Proceedings of the 14th International Conference on Alkali-Aggregate Reactions in Concrete. Austin, Texas, USA, 2012. 10.

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