Effect of low-calcium fly ash on the resistance of cement mortar to sulfate attack in the form of acid rain

In this paper, the influence of a low-calcium fly ash on the strengths of mortars attacked by acid rain is examined. The method used is the accelerated dry/wet cycle tests, in which the mortar specimens are exposed to the simulated acid rain solutions with 1.1 of pH, involving the ions Of SO42-, Mg2+, Ca2+, H+, for 1 day, and dried at air with room temperature for 1 day. Through the measurement of the strength of the specimens treated by the cycle tests, it was found that the strengths of the mortars with the fly ash were worse than that of the control mortars. The roughing and spilling of surface of the specimens was observed. Also, the analysis of XRD shows that the phase deposited on the surface of mortars is gypsum instead of ettringite. Thus, it is considered that the mechanism of the acid rain attack on mortar is mainly the surface dissolution of cement paste. Therefore, it is concluded that the replacement of fly ash is likely unfavorable to improve the resistance of Portland cement mortars to acid rain attack of low pH.