Modification effect of anhydrous gypsum on steel slag-cement soil under short age: Unconfined compressive strength, dynamic triaxial characteristics, micro mechanism

• The addition of anhydrous gypsum increases the compressive strength of steel slag-cement soil. • The addition of anhydrous gypsum and steel slag can replace 3 % of the cement. • The addition of anhydrous gypsum improves the dynamic properties of steel slag-cement soil. • The prediction model can well predict the relationship between cumulative plastic strain and cycle number. • The addition of anhydrous gypsum can optimize the internal structure of the slag cement soil sample. This study investigates the use of anhydrous gypsum to improve the early-age performance of steel slag–cement soil (GSCS) while reducing cement consumption. Unconfined compressive strength (UCS) tests and dynamic triaxial tests were conducted at 1, 3, and 7 days of curing. Results show that UCS increases with gypsum content, reaching 1116 kPa at an optimal dosage of 0.6 %. At this level, 0.6 % anhydrous gypsum combined with 5 % steel slag can replace 3 % of cement, reducing CO₂ emissions by 225–338 kg per unit volume. Compared to GSCS-0, GSCS-0.6 shows up to 55 % lower cumulative plastic axial strain and 25 % lower damping ratio at 7 days. The dynamic elastic modulus also increases significantly. A simplified model was proposed to predict cumulative plastic strain under cyclic loading, with errors below 5 %. SEM and XRD analyses confirm that gypsum promotes AFt formation, enhances hydration, and improves microstructural compactness. This study provides a sustainable approach for improving the mechanical and dynamic performance of cementitious materials and promoting the resource utilization of industrial by-products in geotechnical applications.