United States Department of Transportation
i
Further Validation of ASR Testing and Approach for Formulating ASR-Resistant Concrete Mix: Technical Report
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2018-09-01
[PDF-1.79 MB]
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Edition:March 2015–February 2018
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Abstract:The main objective of this study was to further validate the developed rapid aggregate and concrete test methods and a combined innovative approach for formulating performance-based alkali-silica reaction (ASR)–resistant concrete mixes. An innovative step-by-step approach has been developed to formulate ASR-resistant concrete mixes based on four recommended steps. In Step 1, determination of aggregate ASR composite activation parameter (CAP) and threshold alkalinity (THA) using a rapid aggregate chemical test called the volumetric change measuring device (VCMD) is performed. The lower the CAP, the higher the reactivity. Based on the measured CAP and THA, mix design formulation is conducted in Step 2 by applying mix design controls. In Step 3, verification and adjustment of the mix developed in Step 2 is performed based on the THA and pore solution alkalinity (PSA) relationship—PSA needs to be below THA in order to prevent/minimize ASR. Mix design validation using a recently developed accelerated concrete cylinder test (ACCT) is part of Step 4. Concrete mixes made of aggregates with different levels of alkali-silica reactivity were tested using the above approach. The mixes after Steps 2–3 are actually job concrete mixes. The CAP-based method showed better correlation with ASTM C1293 than ASTM C1260 and was found to be effective for consistently identifying the aggregates belonging to false positive and false negative categories. The VCMD method was found to be effective for identifying alkali loading as a function of aggregate reactivity. A low level of alkali loading (e.g., ≤ 3 lb/cy) is needed for an aggregate with very high reactivity and vice versa. Therefore, the current practice of assigning 3.5 lb/cy for all concrete mixes irrespective of aggregate reactivity and type of application may not provide adequate protection. All four steps are recommended for developing case-specific ASR-resistant mixes with high reliability. If a strong agreement between mixes developed through Steps 1–3 and validated in Step 4 is observed based on extensive testing, then concrete validation testing (part of Step 4) can be considered optional. If the PSA measurement technique is not available, a combined use of the NIST model (estimating PSA contribution from cement portion) and ASTM C311 (determining available alkalis from supplementary cementitious material [SCM] used) was found to be effective to estimate PSA of the cement-SCM combination with acceptable accuracy. For the aggregates whose reactivity prediction based on the current test methods (e.g., C1260 and/or C1293) or field performance is satisfactory, the user can develop mixes based on guidelines in Step 2. However, mix design validation through concrete testing (Step 4) will be very useful and is highly recommended to ensure placement of safe and durable concrete mixes. The combined approach based on rapid and reliable test methods will facilitate formulating (a) case-specific ASR-resistant mixes (tailoring mix design depending on the level of protection needed) using locally available materials to ensure long-lasting durable concrete and save on repair costs, and (b) an effective and safe way to use locally available fly ashes (the ACCT method has the capability to perform fly ash optimization effectively) and meet future challenges when good-quality fly ashes are no longer available.
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