Experimental study on physical sulfate salt attack

Sulfate attack can cause severe damage to concrete structures. The most common mitigation strategy against chemical sulfate attack in concrete is reduction of water to cementitious materials ratio, use of low-C₃A Portland cements, and/or use of supplementary cementitious materials. However, physical salt attack from sodium sulfate exposure may still cause damage to concrete with low water to cementitious materials ratio, and supplementary cementitious materials have been reported to even reduce resistance to physical salt attack. The purpose of the current research is to study the effect of water to cementitious materials ratio and supplementary cementitious materials on the ability of mortar to resist physical salt attack. Mortars, made with water to cementitious materials ratios between 0.35 and 0.50, and with two levels of cement replacement by either fly ash or ground granulated blast-furnace slag, were exposed to physical sulfate attack. Mass loss due to physical sulfate salt attack and its relationship with pore structure and transport properties were studied. The results show a good correlation between the resistance to physical salt attack and the pore threshold radius using mercury intrusion porosimetry, as well as the chloride migration coefficient. For the curing conditions used, ground granulated blast-furnace slag was found to improve the resistance to physical salt attack, while fly ash demonstrated a negative effect.