Feasibility of adding calcium hydroxide to FETNS–OPC: working performance, mechanical properties and reaction mechanism

To solve the problem of low early-phase reactivity of ferrous extraction tailings of nickel slag (FETNS), the effects of calcium hydroxide (Ca(OH)₂) as an alkali activator on the working performance, mechanical properties and hydration products of FETNS–ordinary Portland cement (OPC) composite cementitious systems were studied. The addition of calcium hydroxide was found to shorten the initial setting time by about 40% and the final setting time by about 20%. The compressive strength at 3, 7, 28 and 60 days was increased by 51.95%, 45.27%, 8.53% and 8.9%, respectively, with the addition of calcium hydroxide. Microstructural assessment (by scanning electron microscopy, X-ray diffraction, simultaneous thermal analysis, nitrogen adsorption test and low-field nuclear magnetic resonance analysis) showed that the incorporation of calcium hydroxide increased the reaction degree of the FETNS–OPC system, and more calcium silicate hydrate gel and ettringite were generated to fill internal pores, thus improving the compactness of the matrix. In summary, the incorporation of calcium hydroxide stimulated the early-phase reactivity of the composite system, promoted the formation of reaction products and optimised the internal pore structure.