Effect of Desulfurization Gypsum on the Properties of Steel Slag-Based Solid Waste Cementitious Materials and the Hydration Mechanism

The accumulation of industrial solid waste poses significant environmental challenges, making the efficient utilization of solid waste for producing cementitious materials a key research focus. In this study, a ternary cementitious material composed of steel slag (SS), ground granulated blast furnace slag (GBFS), and desulfurization gypsum (DG) was synthesized. The effects of DG on the properties of this ternary solid waste-based cementitious system were systematically investigated. The hydration and hardening mechanisms of the SS-GBFS-DG (SGD) ternary system were elucidated through mechanical property testing and microscopic characterization techniques, including XRD, TG-DTG, and FT-IR analyses. The results indicate that when the DG content is 6%, the system exhibits favorable workability, achieving optimal mechanical performance with a 28-day compressive strength of 31.1 MPa and a flexural strength of 8.1 MPa. The hydration process of the SGD system can be categorized into three distinct stages: in the early stage, DG acts as an activator, promoting the reactivity of the SS-GBFS system, while in the later stage, strength development is primarily governed by the formation of C-S-H, C-A-H, and other gel-like phases. A durability assessment of the optimal experimental group (S4) revealed that the SGD ternary system exhibited limited freeze resistance but demonstrated superior carbonation and sulfate resistance. These findings provide theoretical guidance for applying solid waste-based composite cementitious materials as an alternative to ordinary portland cement in yellow soil roadbeds and semirigid bases under saline soil conditions.