Improving the physical and mechanical properties and alkali resistance of fireclay-based castables by modifying their structure with SiO2 sol

In this study, we analysed the possibilities of improving the physical and mechanical properties and alkali resistance of fireclay-based conventional (CC) and medium cement castables (MCC) containing milled quartz sand by modifying its structure with SiO2 sol impregnation. Refractory fireclay-based castables impregnated with SiO2 sol under vacuum demonstrated increased density, ultrasonic pulse velocity, modulus of elasticity, and compressive strength compared to the non-impregnated samples. The samples impregnated with SiO2 sol also had a lower open porosity and denser microstructure of the binder. X-ray diffraction (XRD) analysis showed that similar minerals were formed both in the impregnated samples and in the control samples, but the impregnated samples had higher amounts of mullite and cristobalite. Alkali resistance tests showed that a distinct glassy barrier formed on the surfaces of castables with milled quartz sand, but the impregnated samples had a denser and thinner barrier, thus reducing further penetration of potassium into deeper layers of the samples. The impregnated samples of all concrete compositions withstood 20 cycles of alkali attack at elevated temperatures without any obvious signs of disintegration. © 2022 Elsevier Ltd and Techna Group S.r.l.