Sustainable alkali-activated concrete with unconventional precursors for ASR mitigation: Mechanisms and alternative predictors using the miniature concrete prism test

Abstract

This study explores the alkali-silica reaction (ASR) mitigation potential of 11 unconventional precursors based alkali-activated concretes (UAACs) developed as sustainable alternatives to portland cement concrete. Using precursors such as calcined low-purity kaolinitic clays, volcanic ashes, coal bottom ash, and fluidized bed combustion ashes, these UAACs aim to reduce environmental impact while enhancing concrete durability. ASR performance of the so-produced UAACs was evaluated through the Miniature Concrete Prism Test (MCPT) across various aggregate reactivities. Most UAACs demonstrated significantly lower ASR expansion than portland cement mixtures, suggesting their viability as ASR-resistant materials. SEM and EDS analyses confirmed that UAACs generate fewer and less viscous ASR gels, with high alumina uptake and negligible levels of calcium enhancing their ASR resilience. Complementary non-invasive assessments on control UAAC specimens, including electrical resistivity, pore solution analysis, and pore structure analysis, were examined for their correlation with MCPT-determined ASR susceptibility. It was observed that mixtures with high inherent pH levels (∼13.34) in the pore solutions showed limited potential for ASR development and progression. Standard electrical resistivity measurements were strongly correlated with reduced ASR expansion in UAACs, with correlation coefficients of −0.85 for bulk resistivity and −0.90 for surface resistivity. Additionally, the native pore structure, particularly the volume of gel pores (<10 nm), appeared to significantly influence the ASR behavior of UAACs, even without exposure to aggressive conditions. These rapid peripheral indicators enable ASR forecasting in UAACs without extensive testing.