Mitigating size and shape effects in geopolymer composites through reinforcement: Implications for strength and standardization

The mechanical performance of geopolymers remains inconsistent due to variations in raw materials, processing techniques, and, critically, specimen dimensions—parameters often governed by standards designed for other materials. This study systematically investigates how specimen size and geometry affect the strength and failure mechanisms of geopolymer composites and how reinforcements can mitigate these effects. Using a unified experimental framework, reinforced and unreinforced potassium-based geopolymers were synthesized and evaluated through compressive, tensile, and flexural testing across multiple geometries and sizes. The incorporation of chamotte particles and basalt fibers (including mini bars and rods) markedly reduced the size effect, improved fracture toughness, and enhanced damage tolerance. Non-destructive methods, such as acoustic emission and dynamic modulus analysis, revealed structural densification and improved stiffness due to reinforcement strategies. A comparative analysis across standards used in ceramics, cement, and polymers underscores the inadequacy of current testing practices and the urgent need for geopolymer-specific protocols. By clarifying the scale-dependent behavior of geopolymers and quantifying the reinforcement effect, this work offers valuable design guidelines for the development of structurally resilient, large-scale geopolymer applications.