Effect of sodium sulfate on the hydration and mechanical properties of lime-slag based eco-friendly binders

Alkali-activated materials (AAMs) shows great potential to be a candidate of ordinary Portland cement (OPC) when considering the relative lower carbon emission of AAMs. In the present work, the authors investigated the influence of sodium sulfate (Na2SO4) content on the properties of lime (CaO) activated slag to overcome the slow strength evolution of CaO activated slag binders. Setting time, compressive strength, hydration products and microstructure were systemically studied. The research work has brought about a discovery that the properties of CaO activated slag was influenced significantly in the presence of Na2SO4. Adding 1% Na2SO4 enhanced the compressive strength of the binders at all curing ages with the pore structure refinement. The authors attributed the beneficial effects to the accelerated reaction of slag and the additional ettringite (AFt) formation, which was confirmed by the XRD, FTIR and TGA analysis. While increasing the Na2SO4 content, although the early compressive strength was enhanced, decreased the compressive strength at the later curing periods. (C) 2020 Elsevier Ltd. All rights reserved.