Performance deterioration of fly ash/slag-based geopolymer composites subjected to coupled cyclic preloading and sulfuric acid attack

Abstract

Coupled effects of cyclic preloading and sulfuric acid attacks on the performance deterioration of fly ash/ground granulated blast furnace slag (GGBFS) geopolymer mortar (GPM) were investigated in this study. Ordinary Portland cement mortar (OPM) was also prepared as the control for comparison. The testing parameters include visual appearance, mass change, compressive strength, degradation depth, microstructure and leaching behavior after exposure to sulfuric acid solutions. Before the exposure to sulfuric acid solutions, compressive strength of GPM was increased with the addition of GGBFS, but more strength reduction was caused by cyclic preloading compared to the OPM. On the other hand, after the exposure to different sulfuric acid attacks, GPM with higher content of GGBFS experienced server deterioration after preloading. Cyclic preloading probably caused microcracks or damages in mortars, thus increasing the probability of sulfuric acid deterioration. Although GPM exhibited more strength reduction due to preloading than the OPM, after 18-month exposure to sulfuric acid attacks, GPM with preloading still performed better than the corresponding OPM. Similarly, the corresponding GPM exhibited a lower mass loss and degradation depth compared to the OPM under the same conditions. This implies that the higher content of CaO in GGBFS and OPC increase the formations of ettringite and gypsum, which lead to more expansion and severer cracks and damages. Compared with the calcium silicate hydrate (C-S-H) gels in OPM, there are higher Al/Si ratios but lower Ca/Si ratios of cross-linked aluminosilicate polymer gels in GPM. Therefore, GPM exhibited less severe deterioration even with exposure to sulfuric acid attacks though.