Effects of Air-Cooled Blast Furnace Slag Aggregate on Pore Solution Chemistry of Cementitious Systems

Abstract

Air-cooled blast furnace slag (ACBFS) can be used to replace naturally mined aggregates to minimize the environmental and economic costs associated with construction. This paper compares pore solution chemistry of mortars prepared using ACBFS aggregate with pore solution chemistry of control mortars (i.e., mortars containing siliceous sand). The objective of the study was to evaluate the effects of the chemistry of ACBFS particles on the composition of the pore solution and how this chemistry may influence the process of hydration in cementitious systems incorporating ACBFS aggregate. The chemical composition of pore solutions was determined using the inductively coupled plasma optical emission spectroscopy (ICP-OES) technique. During the initial hydration period (<5 h), the concentration of sulfur in the pore solution of mortars was not affected by the presence of ACBFS aggregate. However, after 7 days of hydration, the concentration of sulfur in mortars containing ACBFS aggregate was 3.4–5.6 times higher than that observed in corresponding control mortars. Thermogravimetric analysis of mortars revealed that those containing the ACBFS aggregate underwent a lower degree of hydration compared to control mortars. For mortars with and without ACBFS aggregate, partial replacement of Type I ordinary portland cement (OPC) with fly ash reduced the concentration of sulfur in pore solutions after 7 days of hydration when compared with corresponding mortars prepared using only Type I OPC or a blend of Type I OPC and slag cement.