Microstructural insight into the deterioration mechanism of the mortar subject to the combined action of external sulfate attack and cyclic wetting–drying

• Published in: Construction & building materials Vol. 317; p. 125484
• Main Authors: Yang, Rongwei, Zhang, Mingliang, Li, Zhipeng, He, Fubo
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 24.01.2022
• Subjects: Cyclic wetting–drying; Deterioration mechanism; External sulfate attack; Microstructure; Mortar; Cyclic wetting–drying; Deterioration mechanism; Mortar; Microstructure; External sulfate attack
• ISSN: 0950-0618; 1879-0526
• DOI: 10.1016/j.conbuildmat.2021.125484

Combined action of external sulfate attack (ESA) and cyclic wetting–drying (CWD) results in the severe durability issue of cement-based materials. A comprehensive microstructural investigation of deterioration mechanism of mortar exposed to ESA and CWD is scarce until now. By means of multiple techniques, the phase evolution, microstructural evolution, pore structure variation and thus the deterioration mechanism of mortars with different water-to-cement ratios (0.3 and 0.5) exposed to ESA and CWD, are investigated in this study. It is found that the amount of portlandite declines fast at the first two wetting–drying cycles and decrease gently in the following cycles, the loss of OH− into external sulfate solution plays a dominant role over uptake of Na+ from external sulfate solution during combined action of ESA and CWD; the evolution of pore size distributions of mortars with different water-to-cement ratios exhibit distinct patterns; decalcification of CSH leads to the shrinkage of CSH and collapse of interlayer space and gel pore, responsible for the decreasing amount of interlayer/gel pore at the first 10 wetting–drying cycles and the increase of the amount of interlayer/gel pore at the following 8 cycles; only a few gypsum and thenardite/mirabilite are detected, ettringite is the principal cause of deterioration of mortar subject to ESA and CWD. •A microstructural study on the mortar subject to CWD and ESA is carried out in this study.•The amount of interlayer/gel pore space decreases with CWD at the initial 10 cycles.•AFt is the primary cause for the degradation of the mortar subject to ESA and CWD.