New insights of MgCl2 attack to cement mortar in the condition of low air pressure

Abstract

Almost all the studies about the deterioration of cement-based materials by chloride salts are conducted in the condition of curing and exposing the samples in the normal air pressure. In this study, Portland cement paste and mortar were firstly cured in the environment with low air pressure (60 kPa) and then transferred to the immersion in the10 wt.% MgCl2 solutions under the same air pressure up to 6 months. Experimental results revealed a new corrosion mechanism during the MgCl2-induced deterioration of semi-immersed mortar, i.e., the formation Mg2(OH)3Cl·4H2O with fireworks-like shaped (surface) and dandelion-like shaped (inside), leading to a nearly intact surface and cracked interior with peeling onion shape. Besides, the generation of Mg10(OH)18Cl2·5H2O with higher alkalinity in the full-immersed cement paste resulted from the presence of Mg(OH)2 layer on the surface. Two types of white sediments found on the surface of paste and mortar are respectively composed of Mg(OH)2 and M − SH detected by XRD, SEM/EDS, and TG-HDSC. Finally, the accumulation of MgCl2-induced corrosion products resulted in significantly deteriorations in pore structure as well as compromised compressive strength.