Hydration properties of ground granulated blast-furnace slag (GGBS) under different hydration environments

Abstract

The hydration properties of various cementitious materials containing Ground Granulated Blast-furnace Slag (GGBS), two alkali-activated slag cements (AAS-1 and AAS-2), in which sodium silicate and sodium hydroxide act as alkaline activators respectively, supersulfated cement (SSC) and slag Portland cement(PSC), are compared with ordinary Portland cement (OPC) to investigate the effect of activating environment on the hydration properties in this study by determining the compressive strength of the pastes, the hydration heat of binders within 96 hours, and the hydration products at age of 28 and 90 days. The results show that C-S-H gels are the main hydrated products for all cementitious systems containing GGBS. Ca(OH)2 is the hydration products of OPC and PSC paste. However, ettringite and gypsum crystals instead of Ca(OH)2 are detected in SSC paste. Additionally, tobermorite, a crystalline C-S-H, and calcite are hydrated products in AAS-1. Tobermorite, cowlesite and calcite are hydrated products of AAS-2 as well. Based on strength results, AAS-1 paste exhibits the highest compressive strength followed by OPC, PSC, SSC in order at all testing ages and AAS-2 give the lowest compressive strength except for the early age at 3 days, which is higher than SSC but still lower than PSC. From hydration heat analysis, alkalinity in the reaction solution is a vital factor influencing the initial hydration rate and the initial hydration rate from higher to lower is AAS-2, AAS-1, OPC, PSC and SSC. Although AAS possesses a faster reaction rate in the initial hours, cumulative hydration heat of AAS is comparably lower than that of OPC, but higher than those of PSC and SSC in turn, which indicates that the hydration heat of clinkers is much higher than that of slag.