Experimental investigation on the physical and mechanical properties of metakaolin-based geopolymers: Effects of aging and confining pressure

Geopolymers are more and more investigated as a promising and sustainable green concrete solution for many engineering applications. A thorough characterization of their physical and mechanical properties is crucial for safety and durability analysis of related structures. This paper investigates the physical and mechanical behaviors of metakaolin-based geopolymer at different ages under uniaxial and triaxial compression conditions. The present study first focuses on the setting time, bulk density, porosity, permeability, and pore structure of selected geopolymer specimens. The emphasis is then placed on the characterization of elastic properties, failure strength and patterns of material through uniaxial and triaxial compression tests. The study reveals that with increasing curing age, the bulk density, porosity, pore volume, and permeability decrease, while one obtains an increase of failure strength, Young’s modulus, internal cohesion, and friction angle. Higher confining pressure enhances failure strength and ductility, shifts cracking mode from axial splitting to inclined shearing, and induces irreversible pore structure changes. Permeability and mechanical behavior show nonlinear dependence on confining pressure. These results bring some new insights on the effects of age and confining pressure on the microstructure, mechanical and transport properties of metakaolin-based geopolymers, potentially supporting engineering design and modeling.