Effect of direct electric curing on the mechanical properties, hydration process, and environmental benefits of cement-steel slag composite

Abstract

Steel slag (SS) is a solid waste produced from the steelmaking process. The weak early hydration activity of steel slag limits its application in cementitious materials. This study attempts to improve the early-age performance of cement-SS composite by direct electric curing (DEC) to broaden the application of SS in cementitious materials. Specifically, The study involves continuous monitoring of performance changes of the specimens over time, with a particular focus on early-age characteristics. The change in strength and capillary water absorption of the hardened paste are evaluated. The pore size distribution and content are investigated by BET, and the effects of DEC on the hydration process of cement-SS composite are determined by XRD, TG, and BSE. The results demonstrate that DEC effectively improves the early-age strength of specimens. The 1d strength of the specimens increased by more than 50% at 50% steel slag dosage. Additionally, DEC effectively reduces the pore size. DEC does not change the type of hydration products of the paste but effectively accelerates the hydration process of the cement-SS composite. This accelerated reaction leads to a notable increase in calcium hydroxide and bound water content at an early age, consequently improving the degree of hydration reaction in steel slag. SEM-BSE analysis revealed changes in the atomic composition of the C-S-H gel near the SS, accompanied by blurred boundaries in the morphology of SS particles. Moreover, this study analyzes the economic and environmental benefits of using cement-steel slag composite with DEC. Considering the strength factor, the cost required to obtain a unit strength by DEC is only 55.88%-71.28% of that required with standard curing method. Simultaneously, carbon emission is reduced by 28.79%-44.16%. Thus, DEC is a sustainable and practical method for promoting the utilization of steel slag in cementitious materials, offering both economic and environmental benefits.