Mitigation of ASR Expansion by Biomass/Coal Fly Ash and the Underlying Mechanism by Pore Solution Chemistry

Abstract

This investigation experimentally documents mitigation of alkali-silica-reaction (ASR) expansion through partial replacement of cement and coal-biomass cofired fly ash. ASTM C 277 and 441 guide the experimental techniques. Biomass and Class F fly ash reduce ASR expansion within o.1% at the 6 month with 35% replacement ratio, although biomass fly ash has much higher available Na20equiv (by ASTM C 33). Further analysis of pore solution by high pressure extrusion illustrates that biomass fly ash mixes have similar alkali metal concentrations to Class C mixes, but biomass fly ash is at least equal or much better than Class C in mitigating ASR expansion. This implied that biomass fly ash may absorb alkalis from the pore solution and may form non-expansive products instead of the expansive alkali silica gel.