Characterization and optimization of eco-friendly cementitious materials based on titanium gypsum, fly ash, and calcium carbide residue

Abstract

• Cementitious materials was prepared by FA, TG, CCR based on RSM under ambient curing. • The influences of FA, TG, CCR or their interaction on different ages was analyzed. • The transformation behavior of Fe 3+ in FTC system was observed. • The hydration mechanism, environmental performance of FTC materials was investigated. Titanium gypsum (TG), fly ash (FA) and calcium carbide residue (CCR) are harmful industrial by-products that need to be addressed. In this study, TG, FA and CCR were selected to prepare the eco-friendly FA-TG-CCR (FTC) cementitious materials. Respond surface methodology (RSM) was undertaken to optimize and understand the influence of design factors of m(TG/FA), m(CCR/FA) and W/B on compressive strength, and the mechanical properties, microstructure, hydration mechanism and environmental performance of FTC cementitious materials were investigated. The morphology and structure were characterized by X-ray diffraction (XRD), thermogravimetry- differential scanning calorimetry (TG-DSC) and Scanning electron microscopy energy dispersive X-ray (SEM-EDX), the concentration of hazardous elements was determined via inductively coupled plasma optical emission spectrometer (ICP-OES). The results show that the optimal mixture with RSM methodology (m(TG/FA) = 30.80 %, m(CCR/FA) = 27.85 %, W/B = 0.62) reached 18.93 MPa at 28 days of curing, which confirmed via experimental verification. The FTC cementitious materials are mainly consist with C-(A)-S-H, ettringite; the existence of Fe 3+ was disadvantageous to early age strength, however partial Fe 3+ participated in the formation of Fe-ettringite as the curing time increased, which is beneficial to later age strength. The leaching results indicate that the FTC materials can effectively consolidate the heavy metal ions in raw materials, and the leaching concentration of ions all meet the Chinese Standard for Pollution Control on the Landfill Site of Municipal Solid Waste. Therefore, the synergistic of FTC material offers a novel approach to the efficient utilization of original TG and other industrial by-product wastes.