Feasibility study of adding alkali activator Ca(OH)2 into ferrous extraction tailing of nickel slag-ordinary Portland cement composite cementitious system: working performance, mechanical properties, and reaction mechanism

To solve the problem of low early-phase reactivity of ferrous extraction tailing of nickel slag (FETNS), the effects of Ca(OH)2 as an alkali activator on the working performance, mechanical properties, and hydration products of FETNS-ordinary Portland cement (OPC) composite cementitious system were studied. The results show that the addition of Ca(OH)2 shortens the initial setting time of the composite cementitious system by about 40% and the final setting time by about 20%. The compressive strength at 3d, 7d, 28d and 60d is increased by 51.95%, 45.27%, 8.53% and 8.9%, respectively. The microstructure inside the pastes is characterized by scanning electron microscopy (SEM). X-ray diffraction (XRD), simultaneous thermal analysis (TG-DTG), nitrogen adsorption test (N2-Sorption isotherm), and low-field nuclear magnetic resonance (LF-NMR) analysis show that the incorporation of Ca(OH)2 increases the reaction degree of the composite cementitious system, and more C-S-H gel and ettringite (AFt) are generated to fill the internal pores, which improve the compactness of the structure. The incorporation of Ca(OH)2 can stimulate the early-phase reactivity of the composite cementitious system, promote the formation of reaction products, and optimize the internal pore structure.