Preparation and characterization of foamed concrete with Ti-extracted residues and red gypsum

The recycling of Ti-extracted residues (TRs) and red gypsum (RG), which are the industrial wastes from titanium dioxide manufacturing industry, will avoid the increasing impact on the environment due to their difficulty for disposal. In this paper, the ternary blended binder mainly consisting of ordinary Portland cement (OPC), TRs and RG for the preparation of foamed concrete (FC) was formulated in the laboratory. The hydration kinetics of blended cement, mechanical characteristics and microstructure of FC were investigated. The results indicated that quick lime and sulfoaluminate cement (SAC) evidently reduced the setting time of the complex binder, but mechanical activation for TRs could not substantially shorten those of blended binder. In the case of FC, the optimum technological parameters were proposed as follows: OPC: TRs: RG = 10:45:45 (by mass, the same below), quick lime 2%, SAC 4%, Na2SO4 0.4%, water reducer 0.2%, foam 4.6% and W/B 0.60. The maximum compressive strength and specific strength of FC with density of 437 kg/m3 reached up to 2.14 MPa and 4.91 kN·m/kg, respectively. Microstructure analysis revealed that the interconnected assemblages in FC are floccular and petal-like hydrated gels, need-like ettringite and unreactive plate-like gypsum.