Transport property, mechanical behavior, and failure process of carbon fiber-reinforced metakaolin-based rock-like materials under triaxial compression conditions

Fiber-reinforcement is possibly seen as an effective solution to improve the performance of geopolymers. This new study provides an extensive experimental work on a typical carbon fiber-reinforced metakaolin-based geopolymer composites. Both mechanical and transport properties are investigated in relation with multi-scale analysis of microstructure. The focus is to analyze the effects of fiber reinforcement and confining pressure. Based on workability and mechanical performance, an optimal carbon-fiber (CF) volume fraction of 0.5% is first identified, resulting in an increase of 44.30%, 29.56%, and 52.60% respectively in flexural, compressive, and tensile strength. Microstructural observations, combined with porosity and permeability analyses, demonstrate that the CF network refines the pore structure and suppresses crack initiation and propagation. Transport property under hydrostatic compression is further evaluated, revealing stress path-dependent permeability evolution. X-ray micro-computed tomography and scanning electron microscopy analyses allow for the observation of progressive failure processes in triaxial compression tests, underscoring coupled effects of confining pressure and fiber reinforcement. Due to the interaction between CF and confining pressure, there is a transition of failure model from brittle splitting to ductile shearing. Mohr–Coulomb strength envelope fitting yields a cohesion of 12.85 MPa and internal friction angle of 49.23°, exceeding typical values for most conventional cementitious and geopolymer materials. These findings provide valuable experimental background for design and analysis of engineering structures with fiber-reinforced geopolymers.