Complementary Effects of Coal Fly Ash and Ash-Derived Zeolite on Oil Well Cement for Carbon Capture and Storage

High Resolution Image Download MS PowerPoint Slide This study investigates the effects of coal fly ash (CFA) and CFA-derived zeolite incorporation on the hydration behavior, microstructural evolution, and mechanical performance of oilwell cement pastes under CO 2 -rich conditions relevant to carbon capture and storage (CCS) applications. CFA and CFA-derived zeolite were incorporated into Class G oil well cement, either individually or as hybrid blends, and evaluated before and after exposure to CO 2 -saturated water at 90 °C and 15 MPa for 14 days. The investigated formulations comprised cement pastes with 10 wt % CFA, 10 wt % zeolite, and two combined systems (5Z10CFA and 10Z5CFA), which were compared with a reference paste. Solid-state NMR ( 27 Al and 29 Si), FTIR, TGA, and XRD analyses confirmed the pozzolanic activity of the supplementary cementitious materials through portlandite consumption, increased amorphous phase content, and enhanced C–S–H and C–A–S–H formation. The 29 Si NMR results revealed increased C–S–H polymerization and chain length in blended systems. The 27 Al NMR spectra showed a marked increase in tetrahedrally coordinated Al incorporated into the gel structure. Carbonation resistance was comparable across all systems, while compressive strength was maintained or improved after CO 2 exposure, especially in CFA-containing blends. Among the investigated formulations, the 5Z10CFA blend exhibited the most favorable combination of reactivity, microstructural refinement, and mechanical performance. The results confirmed that the combined use of CFA and CFA-derived zeolite in oil well cement systems is effective incontributing to enhanced durability in CO 2 -rich environments while promoting the circular use of industrial byproducts.