Deterioration mechanism of cementitious materials under acid rain attack

摘要

Cementitious material specimens were immersed in a simulated acid rain solution for different time periods to allow deterioration to occur and then the specimen strengths were measured and the mineralogical compositions and microstructures were analyzed using X-ray diffraction (XRD), Fourier Transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) diffraction. The simulated acid rain solution was prepared by mixing pure chemical reagents such as H_2SO_4, HN0_3, MgSO_4, and (NH_4)_2SO_4. The experimental results show that the deterioration of cementitious material specimens under acid rain attack was mainly caused by the coupling of H~+ and SO_4. In addition, simulated acid rain attack led to the gradual decomposition of cement hydration products such as Ca(OH)_2, calcium silicate (C-S-H) gel, xCaOAl_2O_3yH_2O (C_xAH_y) and ettringite followed by conversion to a white mushy mixture consisting of SiO_2nH_2O gel, Al_2O_3nH_2O gel and CaSO_4-2H_2O but no AFt crystal, leading to the further deterioration of cementitious material specimens. The deterioration began from the exterior to the interior and continuously accumulated until the specimens were fully degraded.