Effect of alkali activator Ca(OH)2 on the early performance and hydration process of ferrous extraction tailing of nickel slag–ordinary Portland cement cementitious system

Abstract

To enhance the initial reactivity of ferrous extraction tailing of nickel slag, this study investigates the impact of Ca(OH)₂ as an alkali activator on the early mechanical properties, microstructure, hydration products, and hydration kinetics of a composite cementitious system comprising FETNS-ordinary Portland cement with varying FETNS proportions. The findings reveal that the addition of Ca(OH)₂ significantly boosts the 3d and 7d compressive strength of the neat paste by up to 51.95% and 45.27%, respectively. The microstructure of the paste at various ages was examined using scanning electron microscopy to provide insights into its development. The integration of Ca(OH)₂, as evidenced by X-ray diffraction, thermal analysis, and nitrogen adsorption–desorption, enhances early-stage hydration, resulting in increased formation of calcium silicate hydrate and ettringite. These products efficiently seal internal pores and microcracks, bolstering the material’s microstructure. Isothermal calorimetry reveal that adding Ca(OH)₂ markedly accelerates the formation of hydration products and increases heat release during the early stages of the reaction. Finally, the hydration reaction model was developed using Phreeqc, which corroborated the observed trends. The incorporation of Ca(OH)₂ can solve the problem of low early-phase reactivity of FETNS-OPC composite cementitious system, which is conducive to the application of FETNS in building materials.