Evaluating the use of nano-SiO2/Al2O3 to mitigate damage in cement mortar exposed to magnesium chloride solution under different conditions

Abstract

In this study, nano-SiO2 (NS) and nano-Al2O3 (NA) were introduced alone and together to modify the MgCl2 attack resistance of cement mortar in the conditions of low air pressure (60 kPa) and low humidity (60% RH), from the aspects of appearance damage, pore structure, product composition and morphology, and compressive strength. The results showed that low pressure environment accelerated the occurrence of damage, exhibiting intact surface and internal expansion and cracking in the evaporation zone of semi-immersed mortar. The MgCl2-induced erosion products mainly include Mg(OH)2, M–S–H, Ca2Al(OH)6Cl·2H2O and Mg2(OH)3Cl·4H2O. The introduction of NS/NA reduced the adsorption height of the solution on the surface of the mortar and alleviated the degree of damage to the mortar exposed to air. Meanwhile, the nano-modification decreased the number of harmful pores above 50 nm and consumed erodible Ca(OH)2 in samples, reducing the generation of erosion products. Finally, the compressive strength of nano-modified mortar under MgCl2 attack coupled with low air pressure environments was enhanced based on the nucleation effect and chemical activity of NS and NA. Among them, the system containing NS performed better.