Development of ultrafine and highly reactive SCMs via combined CO₂ and mechanical activation of steel slag

Abstract

Using steel slag (SS) as supplementary cementitious material (SCMs) represents a promising strategy for resource utilization. However, challenges such as poor grindability and low reactivity hinder its direct application. This study addressed these limitations by employing combined CO₂ and mechanical activation (CMA) to produce ultrafine, highly reactive SCMs. Results indicated that SS treated with this method exhibited ultrafine characteristics, featuring nano-scale grains. This enhancement was attributed to carbonation-induced structural disintegration, where micro-cracks compromised the material's integrity, increasing its friability and grindability. Moreover, CO₂ mineralization yielded products with reduced hardness and improved grindability. On the other hand, the resulting SCMs demonstrated enhanced reactivity, increasing the compressive strength of cement composites by approximately 14 % and 27 % at 1 day and 28 days, respectively. This improvement was linked to the ultrafine structure and the formation of metastable calcium carbonate, silica gels, and FeOOH gels. Additionally, the process of utilizing SS to produce SCMs in this study could offset emissions associated with energy consumption, thereby achieving a carbon-negative outcome.