Effect of nanomaterials on the mechanical properties and microstructure of cement mortar under low air pressure curing

Abstract

Initial curing is very important for the mechanical properties and durability of cement-based materials. Buildings located in high altitude areas have been exposed to low air pressure and low humidity for a long time, which makes the water inside the buildings move to the outside continuously, thus affecting the service life of the buildings. In this study, nano-SiO2 and nano-Al2O3 are introduced into cement to study the mechanical properties and microstructure of cement mortar under low relative humidity (60% RH) and low air pressure (50 kPa, 60 kPa, 70 kPa). Compressive strength, flexural strength, mass change, pore structure and hydration products are studied. The results show that the hydration degree and strength of the cement specimens cured in low air pressure and low humidity environments decrease. The mass loss and porosity increase, and the number of harmful pores (50~200 nm) increase. However, the existence of nanomaterials can compact microstructure, cut off connected capillary channels, so as to reduce water evaporation, increase the degree of cement hydration, and finally improve the flexural and compressive strength.