Air pore structure, strength and frost resistance of air-entrained mortar with different dosage of nano-SiO2 hydrosol

Abstract

The use of nano-SiO2 in concrete has attracted intense attention recently due to its notable improvement in mechanical properties as well as consumption of industrial by-product to enhance the life cycle sustainability. However, the effect of nano-SiO2 on the air pore structure and properties of air entrained cement-based materials is almost not involved in former studies. In this paper, the influence of nano-SiO2 hydrosol (NSH) on the air pore structure, strength and frost resistance of air-entrained mortar was reported. Two typical air entrained agents (AEAs) were utilized to prepare air-entrained mortar with the targeted air content of fresh mortar at the same level. The effects of the addition of NSH on air pore structure, hydration heat release and frost resistance of air-entrained mortar were investigated. Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Spectroscopy (EDS) were used to analyze the mechanism of NSH on entrained air bubbles and pores. Results suggest that the incorporation of NSH can affect entrained air bubble behavior, influence the pore size distribution and densify the hydration products of the air pore wall, thereby effecting the mechanical properties and frost resistance of air-entrained mortar. SEM and EDS data proved differences in chemical composition of air bubble shell entrained by two types of AEAs. The differences resulted in diverse degree of NSH affected air-entrained mortar performance. Due to the effect of early accelerated heat release of cement on the stability bubbles and excessive mortar consistency on the retention of coarse air bubble, it is not recommended to add too much NSH in order to optimize the air pore structure and frost resistance of air-entrained mortar. This study deepens our understanding into the fundamental mechanism of NSH in air-entrained mortar, which also prompts its application to create a sustainable built environment.