The synergistic effect of nano-silica and calcium carbide residue on the mechanical properties and freeze-thaw durability of loess

Loess deposits with low strength and high collapsibility may cause significant engineering challenges, including severe erosion and geotechnical instability. Therefore, stabilization of such loess soils before application in civil engineering projects is of great importance. Traditional stabilizers pose significant environmental concerns, including natural resource depletion and greenhouse gas emissions. To overcome these challenges, this study investigated the effect of nano-silica (NS) alone and combined with calcium carbide residue (CCR) on loess soil's mechanical properties and microscopic mechanisms. Different NS concentrations (0.4 %, 0.7 %, 1 %, and 1.3 %) were added to loess samples, with optimal strength achieved at 1 % based on unconfined compressive strength (UCS) tests. After incorporating CCR with various contents (3 %, 6 %, 9 %, and 12 %) into the optimized NS-treated loess, the samples were cured for 7 and 28 days and then subjected to 1, 4, and 10 freeze-thaw (F-T) cycles. Evaluations included compaction, UCS, ultrasonic pulse velocity, double consolidation, Brunauer-Emmett-Teller analysis, Fourier-transform infrared spectroscopy, scanning electron microscopy, and X-ray diffraction. CCR enhanced strength through pozzolanic and hydration reactions, forming stabilizing gels that significantly improved UCS and F-T resistance. The optimal blend (1 % NS + 6 % CCR) exhibited an 18-fold UCS increase and only 12 % strength loss after 10 F-T cycles compared to the untreated soil. This combination reduced the collapse potential from over 90 % ( severe ) to minimal levels. Consequently, NS and CCR, as eco-friendly materials, enhance the mechanical properties of loess and effectively mitigate related geotechnical problems.