Study on the mechanical properties of alluvial silt improved by Alkali–activated basalt powder and slag in Yellow River flood area subgrade construction

This study proposes an eco-efficient soil stabilization approach to resolve subgrade engineering difficulties encountered in Jibin Intercity Railway project, includes structural instability, gradation deficiencies, and low bearing capacity of loess soils, which can also improve the ecological sustainability and minimize cement consumption during construction. Through comprehensive analysis of the gradation properties of silt, unconfined compressive strength, and compaction characteristics, a novel geopolymer binder was developed by synergistically combining waste basalt powder with slag. Employing orthogonal experimental design, the alkali activator components (type, concentration, modulus) and slag proportion were optimized and validated, ultimately formulating a 20% basalt-enhanced cementitious material, and the 7-day unconfined compressive strength of this material is 2.74 MPa, which is 10.96 times that of the Chinese regulatory requirements. Integrated shear strength evaluation and XRD/SEM characterization demonstrated that alkaline-activated basalt-slag composites can produce dual aluminosilicate gels that cohesively bind soil particles, supported by theoretical models clarifying the stabilization mechanisms. This methodology advances sustainable soft subgrade treatment for high-speed rail systems, delivering both technical innovations and actionable protocols for geopolymer implementation in transportation engineering.