The influence of chemical admixtures on the strength and hydration behavior of lime-based composite cementitious materials

Abstract

This study focused on the modification of a mixture of a lime-based composite cementitious material (LCM) by using chemical admixtures to increase the mechanical performance of the LCM. The different types and amounts of chemical admixtures including NaOH and Na2SO4 were used as activators to prepare the novel modified LCM. The mechanical strength, hydration kinetics, assemblage of hydrates and microstructure of the modified LCM were systemically explored and compared to conventional LCM. The experimental results indicated that Na2SO4 had better effects on the improvement of LCM strength compared to NaOH when used alone as the activator. The composite activator that was composed of Na2SO4 and NaOH showed the optimal effects on the increase of the LCM strength. The composite activator effectively increased the hydration rate of the LCM, and more hydrates were formed during the hydration process of the LCM. Furthermore, the U-phase was formed only in the hydration products of the LCM containing the composite activator. A large amount of U-phase as crystals effectively occupied and filled the space in the LCM paste and led to the formation of a compact microstructure with fewer macro-pores. Thus, the presence of U-phase in the paste increased the strength of the LCM.