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Abstract

Partial replacement of cement with supplementary cementitious materials (SCMs) remains one of the most effective strategies for reducing concrete's greenhouse gas emissions through clinker factor reduction. However, conventional SCM sources are increasingly constrained: coal fly ash supplies are declining, natural pozzolan deposits are geographically limited, and blast-furnace slag is fully utilized. This dissertation presents in-flight vitrification as a novel technique to transform abundant, otherwise unreactive silicate rocks into SCMs. Three archetype feedstocks representing globally abundant rock types (granite, shale, and basalt) were milled and thermally activated by in-flight vitrification, producing glassy microspheroidal powders. Comprehensive characterization including automated SEM-EDS, XRD, XRF, and standardized reactivity tests demonstrated that vitrification increased pozzolanic reactivity approximately five-fold compared to unvitrified controls. All vitrified SCMs exceeded ASTM C618 requirements, achieving >100% strength activity index at 28 days, with R³ heat release consistent with commercial siliceous pozzolan. Notably, vitrification successfully activated illitic shale that resisted activation by conventional calcination, expanding the palette of possible feedstocks that can be activated. Concrete testing with 20% cement replacement matched or exceeded 100% Portland cement control strength after 28 days. The microspheroidal morphology reduced water demand compared to controls, a practical advantage over other SCM manufacturing techniques. Automated SEM-EDS revealed that vitrified particles are primarily discrete mineral-derived glasses rather than homogenized compositions, which may guide future reactivity modeling. Particle circularity emerged as a proxy for glass content in vitrified SCM, with strong correlation (R=-0.89) between higher circularity particles having lower crystallinity. Theoretical estimates suggest process energy requirements could be 1.23-2.30 GJ/tonne when scaled and optimized, comparable to flash calcination and with minimal yield loss (<4%) versus (40% for) clinker production. Field demonstrations totaling 300 cubic yards of concrete validated vitrified granite SCM in commercial applications, achieving performance equivalent to high-quality fly ash. The abundance of suitable silicate feedstocks worldwide includes quarry overburden and aggregates already mined almost everywhere concrete is sold. Therefore, in-flight vitrification, needing mainly just rock and heat energy as inputs, could democratize future production of low-CO₂ SCM by converting the most common silicate rocks into microspheroidal pozzolans.