The effects of inert fillers on the alkali-silica reaction expansion induced by the accelerated mortar bar test

Abstract The accelerated mortar bar test (AMBT) is among the most widely used tests for evaluating the susceptibility of aggregates to alkali-silica reaction (ASR), as well as the ability of supplementary cementitious materials (SCMs) in mitigating this expansive reaction. A literature gap was identified regarding the influence of inert fillers, such as limestone and quartz, on the AMBT-induced expansion, which has not yet been thoroughly assessed. This research aims to evaluate the effects of replacing 20% of Portland cement by limestone or quartz and elucidate the physicochemical interactions that govern ASR on AMBT. The results reveal that limestone does not affect ASR expansion, whereas quartz mitigates the reaction. The retrograde solubility behavior of limestone impairs hydration and inhibits the alkali-binding capacity of C–S–H by increasing its Ca/Si ratio. In contrast, quartz undergoes AMBT-induced pozzolanic reaction, which enhances the formation of C–S–H, and increases the concentration of silicon in the pore solution, both of which promote alkali-binding. This study highlights that the commonly assumed dilution effect (i.e., 20% reduction in expansion) cannot be considered a general rule when replacing cement with inert fillers. This key methodological aspect should be factored in when interpreting the influence of prospective SCMs on AMBT-induced ASR expansion.