Mitigation effect of accelerators on the lead–zinc tailing induced retardation in autoclaved concrete

Abstract

• Na 2 CO 3 significantly shortens the induction period of lead–zinc tailing cement pastes. • Na 2 CO 3 promotes the alkali activation of SiO 2 in tailing under autoclave curing. • No apparent coating of zinc containing compounds can be seen on C 3 S surface. • Accelerators inhibit the retardation by promoting the dissolution of cement particles. Reutilization of lead–zinc tailing in autoclaved concrete greatly reduces the land pollution by the wastes and CO 2 emission by the cement production. Given the retardation of lead and zinc on the cement hydration, three kinds of accelerators, Na 2 CO 3 , Li 2 CO 3 and triethanolamine (TEA) were employed. In this paper, the effect of accelerators on the autoclaved lead–zinc tailing blended cement mortars was investigated from aspects of compressive strength, hydration heat, phase assemblages and leachability of cement mortar. Results show that when the dosage of lead–zinc tailing exceeds 20 %, the demolding strength and the autoclaved strength of cement mortar decrease with increasing tailing dosage. Compared with Li 2 CO 3 and TEA, Na 2 CO 3 shows a more effective accelerating impact on the cement hydration. Incorporating 0.5 % Na 2 CO 3 can shorten the induction period of the lead–zinc tailing cement pastes by 20 h. Additionally, the SiO 2 in lead–zinc tailing can react with cement under autoclave curing, and the reaction is obviously promoted by the incorporation of Na 2 CO 3 . It lies in that Na 2 CO 3 and Li 2 CO 3 inhibit the retardation of lead–zinc tailing by promoting the dissolution of cement and nucleation of hydrates.