The volume stability of cement-based materials under different extreme environments in the plateau: Experimental evolution

With the advancement of the western development strategy in China, concrete materials and structures in the plateau would be subjected to extreme environments, which highlights the issue of volume stability for cement-based materials. In this study, four conditions (i.e., low air pres-sure, ultraviolet radiation, extreme dryness, and large temperature difference) were selected to investigate the volume stability of cement mortar under extreme environments on the plateau. The experimental results show that, compared with the standard drying shrinkage condition, all the selected environments aggravate water evaporation and drying shrinkage of cement mortar. Such effects were the most significant under the condition of extreme dryness, which was fol-lowed by ultraviolet radiation, large temperature difference, and low air pressure. Besides, a series of microscopic experiments were carried out to investigate the influence of various plateau environments on the microstructure of cement mortar. It was observed that various environments have different effects on the hydration degree, C-S-H gel polymerization degree, mesoporosity (<50 nm) and carbonization degree of cement mortar. Moreover, a fitting formula was proposed for the drying shrinkage by introducing an environmental impact coefficient (Aef), and mean-while, the relationship between mass loss and dry shrinkage of mortar for different environmental conditions is also established by employing an environmental efficiency coefficient (Cef).