Durability assessment of a granite-based one-part geopolymer system exposed to CO2-water conditions: Implications for CO2 geosequestration

Abstract

Geopolymers (GPs), derived from natural rock and other wastes, are viable alternatives to Ordinary Portland Cement (OPC) for various applications, including Carbon Capture and Storge (CCS), where high resistance to CO₂-exposure is required. This study investigates the performance of a specialized one-part GP system tailored for CO₂ geosequestration under simulated downhole conditions. Cured GP specimens were subjected to an imposed flow of CO₂-saturated water in coreflooding experiments, while reference samples were kept in water in an autoclave. These experiments were conducted at 30 MPa confining pressure and 80 °C for periods of three or six months. After exposure, the performance of the GP samples was assessed through uniaxial compressive strength (UCS) experiments, Brazilian tensile strength assessments, indentation tests, and density measurements. This was further supplemented with a range of analytical techniques to evaluate changes in the GPs' microstructure, chemical bonding, and mineralogical and chemical composition. The obtained results indicate that after three months of CO₂ exposure, there was a decline in mechanical performance, as evidenced by reductions in UCS and tensile strength. However, following an additional three-month exposure, while UCS remained constant, tensile strength exhibited an increase. Conversely, indentation tests demonstrated an enhancement in mechanical performance at both three and six months of CO₂ exposure, particularly notable near the inlet. Changes in Young's modulus after six months of exposure to CO₂-saturated also revealed a return to ductility levels comparable to the reference sample, while a slight increase in Poisson's ratio may indicate a reduced risk of mechanical failure. Additionally, findings from Scanning Electron Microscopy (SEM) combined with Energy-Dispersive X-ray Spectroscopy (EDS), along with X-ray diffraction (XRD) analysis, demonstrated how increased crystallinity due to carbonate precipitation within the evolving carbonated zone contributed to improved system durability. Fourier-transform infrared (FTIR) analysis showed that carbonation also resulted in increased silica network connectivity. Chemical analysis of effluent samples provided further insight into how a complex interplay between silicate dissolution, alkali leaching, and carbonate mineral formation contributed to the significant resistance of the GP system to bi-carbonation and degradation. These results advance understanding of the GP system studied in CO₂-rich environments and offer new insights into the impacts of carbonation on cementitious materials.