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Non-clinkered Calcium Carbonate Based Cementitious Composites for Enhanced Geothermal Systems (EGS)
Tatiana PYATINA, Michelle DEVOE, Sizhan LIU, Jianming BAI
[, USA]
Reliable cementing solutions are critical for high-temperature geothermal wells, yet current technologies rely on clinkered Ordinary Portland Cement (OPC) or costly Calcium Aluminate Cement (CAC) systems with limited economic and environmental sustainability. This work presents a distinct, non-clinkered alternative that reconstitutes calcium-silicate binding chemistries relevant to geothermal well cementing from low-cost mineral precursors. A calcium carbonate-silica-olivine system activated under hydrothermal conditions was systematically designed and evaluated to elucidate the roles of precursor composition, activator chemistry, and phase evolution on mechanical performance at 300 °C. Unconfined compressive strength and water-fillable porosity were measured as functions of activator concentration, curing time, and mineral replacement. Sodium metasilicate was found to control early activation kinetics through competitive dissolution of calcium carbonate, olivine and silicate phases, resulting in non-monotonic relationships between strength and porosity. Silica flour acted as a latent silicate source, sustaining binder formation at later ages, while partial replacement of calcium carbonate with olivine provided a rigid structural backbone and a delayed magnesium source, increasing compressive strength to above 2000 psi. Addition of sodium bicarbonate further enhanced sodium availability and phase stability, producing compressive strengths exceeding 3000 psi within 21 days of curing. Crystalline phase analysis revealed that activator selection governs reaction pathways and phase assemblages, with sodium bicarbonate acting as a strong phase-directing agent that accelerates kinetics and shifts calcium-sodium silicate formation from transitional lalondeite to the more stable pectolite phase. Mechanical performance was shown to depend primarily on phase assemblage, crystallinity, and interfacial bonding rather than total porosity alone. The results demonstrate that economically viable, non-clinkered mineral systems can be chemically designed to achieve mechanical performance consistent with geothermal cementing requirements while following fundamentally different pathways from previously explored high-temperature cement alternatives.
Topic: Enhanced Geothermal Systems