Optimization of the whole-waste binder containing molten iron desulfurization slag from Kambara Reactor for concrete production

Abstract

Kambara Reactor desulfurization slag (KRDS) is an alkaline solid waste, which is not properly utilized. The potential applications of KRDS in ground granulated blast-furnace slag (GGBS)-based cementitious materials and cement-free concrete were investigated in this study. An orthogonal test was conducted through range analysis and a multivariate nonlinear regression model to examine the effect of three factors: the GGBS content, KRDS/flue gas desulfurization gypsum (FGDG) ratio, and water/binder (W/B) ratio on the compressive strength of mortar. Next, a cement-free concrete was prepared with different strength grades using the cementitious material at the optimal ratios of raw materials. X-ray diffraction (XRD), thermogravimetry-differential scanning calorimetry (TG-DSC), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDS) analysis were carried out to reveal the hydration mechanism of the binder. The factors affecting the strength of the mortar are in this order: GGBS > KRDS/FGDG > W/B. The increase in KRDS enhances the early strength of the binder, but shows an adverse effect on its late strength. The optimum contents of GGBS, KRDS, and FGDG in the binder are 55%, 33.7% and 11.3%, respectively, with a W/B of 0.3. High levels of GGBS lead to an inhibitory effect of KRDS/FGDG on the compressive strength of the concrete. In order to improve the utilization rate and strength of KRDS, the level of GGBS should not exceed 55%. The main hydration products of the binder are needle-like ettringite (AFt) and spherical C-(A)-S-H gels. KRDS dissolution provides a strong alkaline environment, which promotes the disintegration of the Si(Al)–O tetrahedron of GGBS and the formation of the hydration products. C30–C40 concrete exhibit a small 1-h slump loss and good fluidity, making them more suitable for ready mix pumped concrete, whereas C50 and C60 concrete with a large slump loss are more suitable for high-strength precast members. This study has a theoretical and practical significance for a comprehensive utilization of multi-solid waste, energy saving, and carbon-emission reduction.