Influences of Water Glass and Sodium Methyl Silicate Combined Treatment on Recycled Coarse Aggregate and Concrete Made with It

The increasing generation of construction and demolition waste (CDW) and the overexploitation of natural aggregates (NA) have necessitated sustainable solutions for recycled aggregate concrete (RAC). This study proposes an innovative inorganic–organic combined modification method using water glass (WG) and sodium methyl silicate (SMS) to enhance the performance of recycled coarse aggregate (RCA) and RAC. A comprehensive experimental program was conducted, including crushing value tests, capillary water absorption, compressive and splitting tensile strength analysis, nanoindentation and Fourier transform infrared spectroscopy (FTIR). The results demonstrated that the combined treatment of 40% WG and 10% SMS significantly improved the RCA properties, reducing water absorption by up to 46.47% and increasing the compressive strength of the RAC by 34.8%. Through mechanistic analysis, it was found that after treatment with SMS solution, a hydrophobic film formed on the surface of the RCA, thereby preventing the transmission of moisture. The interface transition zone between the RCA and the new cement mortar was enhanced, consequently improving the mechanical properties of the RAC. This study contributes to improving the properties of recycled aggregate and recycled aggregate concrete, and to the understanding of the mechanism of combined modification.