Verification of ASR Resistance Property of the Selected Concrete Mix Designs by the Precast Industries in Texas: Technical Report
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2021-09-01
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Alternative Title:Project Title: Verification of ASR Resistance Property of the Selected Concrete Mix Designs by the Precast Industries in Texas [From TRDP box 15]
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Edition:September 2018–August 2019
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Abstract:The Texas A&M Transportation Institute conducted the development and validation of alkali-silica reaction (ASR) testing as well as the approach for formulating ASR-resistant concrete mixtures in Texas Department of Transportation (TxDOT) Projects 0-6656 (ASR Testing: A New Approach to Aggregate Classification and Mix Design Verification) and 0-6656-01 (Further Validation of ASR Testing and Approach for Formulating ASR Resistant Mix). Specifically, development and validation of two innovative ASR test methods and a combined performance-based approach with four recommended steps were performed in these two previous projects. In Step 1 of the performance-based approach, determination of the 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. Formulation of an ASR-resistant mix by applying mix design controls depending on CAP-based reactivity prediction, THA, and some consideration of the severity of ambient conditions is conducted in Step 2. In Step 3, mix design adjustment/verification based on the THA–pore solution alkalinity (PSA) relationship (e.g., PSA needs to be below THA to prevent/minimize ASR) is recommended to perform as an optional control. Concrete mix design validation using a newly developed accelerated concrete cylinder test (ACCT) is part of Step 4. The main objective of this study was to verify the ASR resistance property of the selected concrete mix designs of bridge girders by the precast industries in Texas by applying the above-mentioned combined performance-based approach. It seems that the selected precast mix designs with 20 percent Class F fly ash are sufficient to prevent ASR. Although the ACCT method creates accelerated conditions, dense microstructural development of the precast concrete can affect ASR expansion in the following ways: (a) minimize ASR expansion (especially at the early ages) compared to conventional concrete due to reduced rate of ionic movement (lesser degree of ASR) inside the concrete specimen as well as negligible penetration of soak solutions/ions from the soak solution into the specimen, and (b) enhance ASR due to the relatively higher PSA because of the use of low w/cm. Continuation of ACCT testing for a longer period (more than 75 days) is recommended to ensure a reliable verification. The application of this combined innovative approach to verify and fine tune (if needed) the precast mix designs has the potential to provide favorable life-cycle costs and a tangible measure of how TxDOT is fulfilling its mission to provide a safe and reliable transportation system to the citizens of Texas. However, additional implementation work using this combined approach is recommended to test different job concrete mixes containing different supplementary cementitious materials (e.g., Class C fly ashes, blended ashes, slag, etc.) to validate ASR-resistant concrete mix designs for different applications.
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