Innovative Development of Low Carbon Cementitious Materials Based on Magnesium Smelting Slag by the Response Surface Method: Chemical Activation, Hydration Characteristics and Application

The swift expansion of the worldwide magnesium industry has resulted in substantial accumulation of magnesium slag (MS) as a byproduct of the magnesium metal smelting process, presenting a growing environmental hazard. To effectively address the issue of MS resource usage, the synergistic activation impact among MS, fly ash (FA), and desulfurized gypsum (DG) was examined utilizing response surface methodology (RSM). This study calculated the appropriate ratio of cementitious materials and investigated the hydration characteristics of magnesium-slag-based low-carbon cementitious materials (MSLCM). The findings indicate that the optimal 28-day compressive strength of the MS–FA binary cementitious material is attained with 60% MS content, resulting in a strength of 19.40 MPa. Response surface analysis indicates that the incorporation of DG improves the 28-day compressive strength of the MS–FA–DG ternary cementitious material. The 7-day compressive strength enhancement is facilitated by MS, but the 7-day and 28-day strengths of the cementitious material are augmented with a higher FA content. The response surface model employed to forecast compressive strength is precise, with the projected 28-day compressive strength for the ideal ratio (MS:FA:DG = 49.54:34.90:15.56) being 31.40 MPa, closely aligning with the experimental measurement of 31.31 MPa. The principal hydration products of MSLCM consist of C–S–H gel, ettringite (AFt), and calcite. The mechanical strength is principally derived from the intricate honeycomb gel structure created by the interconnection of C–S–H gel and ettringite. The dissolution of DG increases the concentrations of Ca²⁺ and SO₄^2– in the system, while Ca(OH)₂ formed during MS hydration accelerates the dissolution of SiO₄^4– and AlO^2–. SiO₄^4– reacts with Ca²⁺ to form C–S–H gel, and AlO^2– combines with SO₄^2– and Ca²⁺ to form the AFt phase. The road base stabilization material, prepared using aeolian sand (AS) solidified with MSLCM, meets the performance requirements of expressways and first-class highways under heavy traffic conditions.