Effects of silanes and silane derivatives on cement hydration and mechanical properties of mortars

Abstract

An experimental research was conducted with the objectives to study the effects silanes (amino, vinyl, and epoxy-based) and their derivatives (silane oligomers and silane nanoparticles) on cement hydration and mechanical properties of mortars. Silanes and silane derivatives are used as coupling agents to combine different compositions in mortars and to chemically react with calcium silicate hydrates to introduce organic component into CSH structure. The use of silanes retarded the cement hydration. However, silane derivatives were found to effectively mitigate the retardation. Liquid-state 29Si nuclear magnetic resonance (NMR) spectroscopy indicated that silanes and silane derivatives have different hydrolysis and condensation products in the solutions of cement pastes. Further analysis of silicon concentration in the solution indicated that the hydrolysis and condensation products of silane oligomer is opt to be in the solution, instead of adsorption onto the surface of cement hydration products, to retard the cement hydration.Ordinary mortars with the silanes and silane derivatives showed general enhancement in flexural strength and some improvement in compressive strength after curing for 7days and 28days. Due to good strength properties, negligible hydration retardation, and simple preparation method, epoxy-based silane oligomer was selected for further study in high-strength mortar. Results indicated that the compressive strength, splitting tensile strength, and elastic modulus of the high-strength mortar were increased by 20%, 38%, and 13%, respectively, compared with the control mortar.