Study on the Composition of Calcium Alumina Silicate Hydrate (Cash) in Lime-Activated Low Carbon Cementitious Materials: The Influence of Alkaline Additives

Abstract

The composition of CASH in lime-activated low carbon cementitious materials (LCM) was investigated in this study, and the influence of alkaline additives on the composition of CASH in LCM was analyzed, particularly for the hydration rim of slag. Compared to LCM-control mixture, alkali additives effectively improved the hydration of GGBFS and significantly increased the thickness of the hydration rim as the inner hydration product.The enlargement of the hydration rim zone led to a lower Ca/(Si+Al) ratio of the hydrated gel mainly due to the interference of Al from intermixing phases in the rim. For LCM with alkaline additives, the hydration rim of slag contained C(N)ASH, ettringite, U-phase, and a minor amount of amorphous or poorly crystalline hydrotalcite-like phase, and the hydrated gel in paste was mainly composed of C(N)ASH due to the uptake of Na+ ions in CASH.

Keywords: lime, hydration rim, alkaline additives, CASH, Slag