Effects of silica sol on hydration properties, impedance response, microstructure and strength of calcium aluminate cement

Abstract

Hydration phenomena of a commercial white calcium aluminate cement (CAC; Al2O3 – 69–72 %) at 20 ◦C was modified by adding silica nanoparticles addition in varying amounts and additives in the context of using CACs in the aspiration to achieve climate neutrality and the goal of net zero. The hydration process of CAC modified with silica sol (SS) was tracked by heat flow calorimetry, XRD, SEM, MIP and TR-EIS experiments supplemented by mechanical strength determination at different curing ages. The findings demonstrate the potential to modify the traditional early (24 h) hydration pathway of CAC-based systems by both SS and additives, leading to an accelerated process, in terms of the second exothermic peak of paste, and improved mechanical strength, even though no crystalline hydrates were formed. The results indicate that the evolution of the impedance between mixing and 24 h is closely related to the effect of the SS content and additives on the densification and microstructure properties. CAC-based mortar containing 5 wt% SS and additives exhibited the highest compressive strength, suggesting that early strength development may be attributed to silica nanoparticles acting as a filler or formation of a low-impedance rigid gel or low-impedance amorphous solids. It is also evident that SS promotes the formation of CAH10 rather than C2AH8. All binder systems remain strength increase when exposed to 28-days curing conditions.