Evaluating Natural Pozzolans and Marginal Coal Ashes for ASR Mitigation: Insights from AASHTO T380 and Electrical Resistivity

Abstract This study evaluated the effectiveness of 11 supplementary cementitious materials (SCM) in mitigating alkali-silica reaction (ASR) in concrete using the miniature concrete prism test (MCPT). Seven reactive aggregates were used in combination with SCMs at several dosages to produce and test 64 concrete mixtures. All SCMs, even those with high alkalis, reduced ASR expansion; however, their effectiveness varied significantly. While the SCM’s pozzolanic reactivity (measured using the R 3 test) is an important parameter, it did not consistently explain SCM’s performance against ASR during MCPT. In contrast, since MCPT relies on diffusion of ions from the alkali bath into concrete specimens, the ability of an SCM to increase the electrical resistivity of concrete (i.e., reduce ion diffusivity) was strongly correlated with the measured ASR expansions. Regression analysis demonstrated that the 56 day MCPT expansion of concrete containing SCM is strongly correlated with a 10 day electrical resistivity of the concrete specimen and the MCPT expansion of the aggregate in a control mixture without SCM (which indicates the aggregate reactivity tier). These findings suggest that electrical resistivity may serve as an early indicator of MCPT expansion and may help reduce the time needed to assess adequate SCM dosages for ASR mitigation.