Stabilization of soft soils with Al³⁺, Fe³⁺, and Si⁴⁺ modified cementitious materials: Comparison, simulation, and...

Soft clay soils posed engineering risks due to low shear strength, high compressibility, and water sensitivity. Although low-carbon solid waste cement has been extensively implemented for soil stabilization, fundamental principles underlying cement design remained poorly understood. In this study, four solid waste-modified cement formulations were developed to investigate stabilization mechanisms at ionic scales. Compressive strength reached 15 MPa under Al³⁺-modified cement treatment. Pore sizes were confined to 4-5 nm, with no large voids observed. Reduced porosity was confirmed. FTIR analyses confirmed FeO and AlO bond formation. RDF and MSD simulations revealed that Fe³⁺ and Al³⁺ reduced zeta potential values on soil surfaces and decreased diffuse double-layer thickness, accelerating flocculation. SEM-EDS measurements demonstrated that elevated aluminum concentrations promoted uniform hydration and gel-phase formation, while high silicon content inhibited ettringite crystallization. Fe³⁺ and Al³⁺ modified systems exhibited interaction energies as low as -22,000 kJ/mol, indicative of robust structural stability. Optimal stabilization was achieved with moderate-to-high Al³⁺ and Fe³⁺ content, confirming their critical role in mitigating clay deficiencies.