Applicability of Portland cement standards to granite-based one-part geopolymers: A rock mechanical perspective

• Granite-based one-part geopolymer evaluated under downhole triaxial conditions • Bulk and axial bulk moduli showed temperature-independent thermal stability • Young’s modulus and Poisson’s ratio were dependent on loading rate, not temperature • Peak and yield strengths mainly governed by confining pressure • API TR 10TR7 applicable to OPG with adaptations for rate- and temperature effects Geopolymers are emerging as sustainable alternatives to conventional Portland cement for wellbore sealing applications. However, the applicability of established rock mechanical testing standards, originally developed for cement-based materials, to these chemically distinct systems remains uncertain. This study examines the mechanical performance of a granite-based one-part geopolymer (OPG) under triaxial conditions representative of subsurface environments, using protocols adapted from API TR 10TR7. Tests were conducted on two specimens per condition, across confining pressures of 8-26 MPa, temperatures of 30, 60, and 90°C, and deviatoric loading rates of 0.5-12 MPa/min. Results from two triaxial setups (Triax1 and Triax2) were compared, with consistency checks included to avoid misinterpretation. Bulk and axial bulk moduli were found to be largely temperature-independent, confirming the thermal stability of the OPG system during hydrostatic loading. In contrast, Young’s modulus and Poisson’s ratio increased with loading rate, indicating strain rate-dependent stiffness, while showing limited sensitivity to temperature. Peak and yield strengths were primarily governed by confinement, with only minor influence from temperature or loading rate. These findings suggest that while API TR 10TR7 protocols are broadly applicable to granite-based OPG, modifications may be needed to capture rate- and temperature-sensitive elastic behavior. The granite-based OPG demonstrated robust and stable mechanical performance, supporting its suitability as a sealing material for well integrity under demanding downhole conditions. Additionally, this study provides the first systematic evaluation of the applicability and limitations of API TR 10TR7 for granite-based OPG, establishing a benchmark framework for adapting cement testing standards to alternative binder systems.