Multi-scale mechanistic evaluation of reactivity balance in metakaolin-nano-CaCO

This study introduces a multiscale framework for optimizing the metakaolin-nano-CaCO3 (MK–NC) system for enhanced clay stabilization. While previous studies have typically investigated MK or nano-CaCO3 independently and often without a systematic factorial matrix or integrated environmental assessment, the interactive mechanisms governing their coupled performance remain insufficiently clarified. In particular, the absence of full compositional mapping and multi-scale correlation between geotechnical behavior, microstructure, and sustainability metrics has limited mechanistic understanding of synergy domains. Using a comprehensive 4 × 4 factorial design with varying MK (1–10 wt%) and NC (0.1-1.0 wt%) concentrations, we evaluated the effects on plasticity, compaction, unconfined compressive strength (UCS), and consolidation, alongside microstructural and mineralogical analysis via SEM/EDS and XRD. The findings reveal that an optimal MK-NC formulation (about 4 wt% MK + 0.1 wt% NC) significantly improves soil properties, with a 30% reduction in plasticity index, a 2–3% increase in optimum moisture content, and a 250% enhancement in 28-day strength. Consolidation characteristics also improve, indicating a denser, faster-draining microstructure. Furthermore, a cradle-to-gate Life Cycle Assessment (functional unit: 1 kg of material), incorporating the modeled energy requirements for metakaolin calcination and nano-CaCO₃ processing, indicates that the selected C-N1-M40 binder achieves an estimated 68% reduction in Global Warming Potential (GWP) relative to OPC under the defined system boundaries. These results position the MK-NC system as a mechanistically optimized and environmentally promising alternative for high-performance clay stabilization.