Evaluation of Chemical Screening Tool (CST) to Predict Optimum Natural Pozzolans Dosage for ASR Mitigation in Concrete

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Title: Evaluation of Chemical Screening Tool (CST) to Predict Optimum Natural Pozzolans Dosage for ASR Mitigation in Concrete

Author(s): Pravin Saraswatula

Publication: Web Session

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Appears on pages(s):

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Date: 10/23/2022

Abstract:
Our previous study developed a screening tool (ST) to determine the optimum fly ash dosage for ASR mitigation in concrete mixes. The ST uses concrete pore solution alkalinity (PSA) vs. aggregate threshold alkalinity (THA) relationship to establish a criterion, i.e., PSA = THA, to mitigate ASR. A pore solution model called TTI Model-1 was developed as a part of ST development to estimate concrete PSA based on the combined effort of soluble alkali contribution from cement and water-soluble alkali (WSA) from fly ashes. The current research extends our previous study to examine the concrete PSA vs. aggregate THA relationship for 12 Class N pozzolans (ASTM C 618), thereby investigating ST's validity in estimating the optimum dosage of pozzolans for ASR mitigation. Accordingly, quantitative X-ray diffraction measurements in conjunction with water-soluble and available alkali tests were performed to evaluate pozzolans' potential soluble alkali contribution to pore solution and investigate their efficacy in overall PSA reduction. TTI Model-1 estimations show that high alkali contribution to pore solution and investigate their efficacy in overall PSA reduction. TTI Model-1 estimations show that high alkali natural pozzolans can reduce concrete PSA to a greater extent when compared to low-moderate alkali Class F & C ashes at similar cement replacement levels. Furthermore, the ASR evaluation of the pozzolans conducted at ST-predicted replacement levels following the AASHTO TP 142 & ASTM C 1567 tests showed the expansion measurements to be lower than the respective threshold limits. Overall, the results favorably validate the application of ST's scientific and performance-based approach to determine the optimum dosage of natural pozzolans for ASR mitigation with high reliability.




  

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