Synergistic hydration and carbon mitigation of natural mineral micro-powder cements using tibetan mineral resources

The Tibetan Plateau faces limited cement clinker availability and high carbon emissions. This study systematically evaluated locally abundant natural mineral micro-powders—tuff, volcanic ash, and siliceous shale—on the performance of cement-based materials. The influence of single and binary mineral replacements on mechanical properties, hydration mechanisms, microstructure, and carbon footprint was investigated through compressive strength testing, hydration heat analysis, XRD, TG-DSC, SEM, low-field NMR, and GEMS thermodynamic simulations, with the aim of elucidating synergistic effects across various replacement levels and combinations. Results showed that, for single-mineral systems, tuff and volcanic ash at 15–25% replacement exhibited considerable late-age pozzolanic activity, partially compensating for clinker reduction and retaining approximately 91% of the reference 28-day compressive strength at 25% replacement. Siliceous shale, by contrast, contributed primarily through physical filling, showing lower reactivity and strength retention. In binary blends, tuff-volcanic ash and tuff-siliceous shale combinations showed favorable strength-based interactions, with N7Y3 exhibiting favorable 28-day mechanical performance, a porosity of 8.3%, and an equivalent average pore diameter of 9.4 nm. GEMS simulations predicted that single-mineral systems exhibited an initial increase in C-S-H gel followed by a decline as Ca(OH) 2 was depleted, with straetlingite (C 2 ASH 8 ) and zeolitic phases becoming thermodynamically favored beyond approximately 16.8–23% replacement. Binary systems exhibited enhanced thermodynamic synergy and greater C-S-H formation, whereas replacement levels above 30% tended toward zeolitization. Carbon accounting indicated that N7Y3 cement reduced clinker-related CO 2 emissions by 29.7%, lowered per-cubic-meter concrete emissions by 27.0%, and decreased market-based carbon costs by approximately 4.11CNY /m 3 . These findings provide a scientific basis for the utilization of Tibetan natural mineral resources and the development of low-clinker cement systems for regions with similar resource constraints.