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Title: Development of a Rapid Screening Tool to Estimate Fly Ash Dosage for Mitigating ASR in Concrete

Author(s): Saraswatula

Publication: Web Session

Volume: ws_S22_Saraswatula.pdf

Issue:

Appears on pages(s):

Keywords:

DOI:

Date: 3/28/2022

Abstract:
The current performance-based approaches to determine optimum fly ash (FA) dosage to suppress/mitigate alkali silica reaction (ASR) in concrete require testing for a wide range of replacement levels, which is time-consuming and impractical. In addition, ASR tests such as ASTM C1293 & C1567 are not sensitive in detecting FA soluble alkali's effect on ASR expansion due to alkali boosting test conditions. Therefore, a screening tool (ST) was developed to determine optimum fly ash dosage to mitigate ASR in concrete mixes in the present work. The ST determines concrete pore solution alkalinity (PSA) at different fly ash replacement levels considering the combined effect of soluble alkali contribution from cement & water-soluble alkali (WSA) from fly ashes. The WSA from fly ashes was measured following the modified ASTM C114 procedure. The optimum fly ash dosage for ASR mitigation is determined based on concrete PSA vs. aggregate threshold alkalinity (THA) relationship, i.e., PSA = THA to suppress ASR. Based on the evaluation of several fly ashes covering both conventional & unconventional ashes in the current study, the ST predictions of optimum FA dosage demonstrated a mean absolute error (MAE) (= ± 6-9%) compared to the ASR tests and other prediction models. The ST also demonstrated fly ash dosage predictions with high reliability & accuracy (= 87%) for the unconventional ashes (e.g., blended, reclaimed & natural pozzolans). Overall, the ST developed in the current research provides a scientific, rapid (3-5 days), and reliable approach to determine optimum fly ash dosage for ASR mitigation.