Effect of nano-SiO2 on the hydration products of C3S in Portland cement

Abstract

Nano-Silica (NS) modification is a way to enhance the performance of the cement stone. However, the mechanism of NS-modified cement is not clear at low (80 °C) and high (140 °C) temperatures. Therefore, this study focused on tricalcium silicate (C3S) and the porosity, types and polymerization degree of hydration products with different NS contents with C3S at 80 and 140 °C were analyzed using 1H NMR, XRD, SEM, TGA, XPS, and FTIR methods. According to the following results, temperature and initial Ca/Si are the key factors affecting the hydration products of the silicate phase: NS-induced decalcification led to an increase in C-S-H polymerization degree and chain length, but an excessive amount of NS increased the porosity of the hydration product. NS reacted with Ca(OH)2(CH) and high Ca/Si hydration products, resulting in the formation of structurally dense hydration products with low Ca/Si. However, excessive NS rendered the hydration product unstable and caused high Ca/Si at 80 °C, while it deteriorated Xonotlite with excellent performance at 140 °C, thus affecting the polymerization degree and strength of products.