Reinforcement of weathered aggregates on the Qinghai–Tibet Plateau: Cross-scale coupling of microstructural evolution and macroscopic performance

Weathered aggregates widely distributed on the Qinghai–Tibet Plateau (QTP) suffer from high initial porosity (32–52%), elemental leaching, and insufficient mechanical resistance, severely restricting their direct use in cold-region transportation infrastructure where durable local materials are urgently required. This study establishes a cross-scale evaluation framework that quantitatively links microstructural evolution to macroscopic mechanical enhancements under targeted reinforcement. Seven aggregate lithologies were modified using epoxy resin, silane coupling agent, and nano-SiO₂ sol, and evaluated through both macroscopic indices (apparent density, water absorption, aggregate crushing value, Los Angeles abrasion value) and microscopic analyses (SEM–ImageJ porosity quantification and SEM–EDS elemental mapping). Results demonstrate significant performance improvement after treatment: epoxy resin consistently reduced porosity to 8–20% and decreased ACV/LAAV by 2–4 percentage points; silane provided up to 29% porosity reduction; and nano-SiO₂ exhibited strong lithology dependence, with CF and AS achieving minimal porosity (3–4%) while SD responded weakly. Grey relational analysis with entropy weighting further identified optimal lithology–modifier compatibilities, including AS–epoxy (Γ = 0.872) and SD–nano-SiO₂ (Γ = 0.806). By revealing how pore refinement and elemental stabilization drive macroscopic performance gains, this study elucidates lithology-specific reinforcement mechanisms and proposes a compatibility-oriented material selection workflow, supporting sustainable utilization of marginal aggregates in high-altitude cold-region infrastructure.