Influence of Sand and Fiber Type on the Fiber-Bridging Properties of Metakaolin-Based Engineered Geopolymer Composites

Abstract

This study investigates the physical, mechanical, matrix, and fiber-bridging properties of metakaolin-based engineered geopolymer composites (EGCs) using conventional river sand (RS), or microsilica sand (MS) and polyvinyl alcohol fiber, or ultrahigh molecular weight polyethylene (UHMWPE) fiber. The research evaluated the effects of aggregate type, fiber type, and fiber length (i.e., 10 or 12 mm UHMWPE fiber). Results from compressive strength and single crack tensile tests indicated that the effects of aggregate type, fiber type, and fiber length were statistically similar. All EGC materials manufactured outperformed regular concrete’s compressive strength (30 MPa) by approximately 31%–58% while having densities about 21%–24% lower than that of regular concrete (2.3 g/cm³). The three-point bending test on the notched geopolymer mortars showed that RS specimens exhibited a lower crack tip matrix toughness (J_tip) value than MS, favoring multiple cracking behavior. All EGC specimens displayed promising pseudo-strain-hardening (PSH) behavior, with PSH strength and energy indices exceeding 1.3 and 2.7, respectively. RS-based composites displayed a more robust PSH behavior compared to those with MS. Notably, the study determined that the tensile strain capacity was more influenced by the PSH energy index than by the strength index, with a coefficient of determination of 0.77 supporting this correlation. The standout composite, incorporating RS and 0.8 vol.% 12 mm UHMWPE fiber, achieved exceptional tensile strain capacities of up to 8%. This performance level is comparable to Grade 60 steel reinforcement, highlighting the potential of EGCs as a sustainable and high-strength alternative for civil infrastructure projects.