Abstract
In this study, the fracture response of ternary geopolymer concrete (GC) comprising fly ash, slag, and silica fume reinforced with jute and sisal fibers was systematically examined under modes I, III, and mixed-mode loading regimes. Fiber lengths of 20, 40, and 60 mm at 0.5% by volume were incorporated to evaluate their influence on the fracture behavior. Employing the edge-notched disc bend configuration, this study quantified the effects of fiber type on the stress intensity factors, fracture toughness, effective fracture parameters, and mode mixity. The primary objective of this study is to clarify the mechanisms by which natural fibers influence crack initiation, propagation, and mode interaction in geopolymer concrete, thereby addressing existing deficiencies in the understanding of out-of-plane shear fracture and mixed-mode fracture behavior. The results revealed that the natural fibers significantly enhanced the GC fracture resistance, with optimum performance at a fiber length of 40 mm. Sisal fibers increased the mode I fracture toughness from 0.86 to 1.07 MPa·m0.5 (23.43%), whereas the mixed-mode and mode III toughness improved by 24.13% and 12.40%, respectively. However, the 60 mm fibers reduced these gains. Microstructural investigations revealed superior fiber-matrix interfacial bonding and enhanced gel formation in the sisal-reinforced composites. The findings demonstrate the potential of natural fiber-reinforced geopolymer composites for developing sustainable and crack-resistant construction materials