This study investigates the effects of sodium hydroxide activated steel slag on the mechanical properties of loess. The results show that the addition of sodium hydroxide reduced the optimal moisture content, significantly increased the unconfined compressive strength and water stability of loess in the early stages, and effectively improved its shear strength in the later stages. Among these, sodium hydroxide had the most significant impact on the mechanical properties and water stability of the loess after 28 days. This study provides scientific evidence and technical reference for the application of chemically activated steel slag in loess subgrade improvement.

Thailand's highway development project and expansion of the main road are currently being built or planned. The development of stabilizing techniques in soils with various agents has been adopted since the early days due to the insufficient availability of local materials and their unsatisfactory engineering properties. Rice husk ash's (RHA) partial replacement of geopolymers in road-based applications received less attention. This study examines the engineering properties of clay (C) treated by kaolin-rice husk ash geopolymer (K-RHAGP). The ordinary clay is activated by sodium hydroxide solution. The appropriate proportion of kaolin:rice husk ash (K:RHA) of 70:30 stimulated by a sodium hydroxide solution of 8 molars exhibits the highest unconfined compressive strength (qu). Clay is treated by kaolin-rice husk ash geopolymer (K-RHAGP) with various ratios of C:K-RHAGP by weights of 90:10, 80:20, 70:30, 60:40, and 50:50. The results showed that the optimal C:K-RHAGP proportion of treated clay is 70:30, which yielded the highest qu at 7 days under curing temperatures of 70 degrees C and 50 degrees C, resulting in values of 9352 and 4557 kN/m2, respectively. The highest split tensile strength under 70 degrees C and 50 degrees C curing temperatures was 1182 and 576 kN/m2, respectively. The relationship between the modulus of elasticity at 50% strength, E50, and qu is expressed as E50 = 4.531qu. After wet and dry processes, the samples with the C:K-RHAGP ratio of 70:30 exhibit the highest strengths of 2445.89, 1670.55, and 1218.68 kN/m2 for 3, 9, and 12 wet-dry cycles corresponding to the lowest weight loss. The C:K-RHAGP weight loss of 70:30 in cycles 1 to 12 was 1.5 to 7.2%. The authors believe that the proposed K-RHAGP stabilization could be used as an effective replacement for cement-based soil stabilization in road-based construction.