Green concrete with ground granulated blast-furnace slag activated by desulfurization gypsum and electric arc furnace reducing slag

This paper studies the mechanical properties and hydration of green concrete which is made from ground granulated blast-furnace slag (GGBS), desulfurization gypsum (DG) and electric arc furnace reducing slag (EAFRS) as cementitious materials. The green concrete with a water to cementitious materials ratio of 0.32 yields a compressive strength over 50 MPa at 28 days. The hydration mechanisms of GGBS-DG-EAFRS systems are studied using isothermal calorimetry (IC), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (SEM-EDX). Although gypsum alone is able to slowly activate GGBS, the addition of EAFRS significantly accelerates the activation of GGBS. Compared to the portland cement paste, the ternary GGBS-DG-EAFRS pastes exhibit similar hydration heat evolution patterns but significantly lower hydration heat. The results from TGA and XRD show negligible amounts of Ca(OH)2 and Mg(OH)2, which is beneficial in the soundness of the green concrete. The results of XRD and SEM-EDX confirm that the main hydration products in the ternary GGBS-DG-EAFRS systems are ettringite, hydrotalcite and amorphous-S-H with a low Ca/Si ratio (1.15-1.73) and a high Al/Ca ratio (0.02-0.42), which is favorable in obtaining good mechanical properties in the green concrete. The green GGBS-DG-EAFRS concrete sheds light on recycling industrial solid wastes, lowering the material cost and improving the sustainability in concrete industries. (C) 2020 Elsevier Ltd. All rights reserved.