Assessment of packing, flowability, hydration kinetics, and strength of blended cements with illitic calcined shale

Abstract

The effects of two illitic calcined shales as supplementary cementitious materials (SCMs) on the performance of ordinary Portland cement (OPC)-based pastes and mortars were investigated. The packing density of blended cement pastes and mortars were predicted with compressible packing model (CPM). The water film thickness (WFT) and flowability were calculated and measured. Early hydration was described by calorimetric curves and the hydration microstructure was identified by X-ray diffraction (XRD), differential thermal analysis (DSC/TG), and pore size distribution (MIP). The compressive strength was tested at 2, 7, 28, and 90 days. The results showed that the partial replacement of OPC by illitic calcined shale decreased the packing density and the flowability of cement pastes but this does not occur for standard mortars. For blended cements, the hydration products were similar to that corresponding to OPC, the pozzolanic reaction contributed from 28 days to the densifying of solid structure and it was also noticed the pore size refinement that improved the compressive strength at later age.