Investigating the influence of fibre type and content on the toughness and ductility of geopolymer mortar with acoustic emission technology

Abstract

The in-depth investigation on the toughness and ductility strengthening mechanism by fibres is essential to efficiently design geopolymer composites with high toughness and ductility. This paper investigates the influence of fibre type (steel and PP fibre) and fibre content (0 %, 0.5 %, 1.0 %, and 1.5 %) on the flexural performance of geopolymer mortar (GPM) with acoustic emission (AE) technology. The results reveal that GPM specimens with steel fibre exhibit higher ultimate flexural strength compared to those with PP fibre. Additionally, both flexural toughness and ductility of GPM specimens exhibit an increasing trend with fibre content. A novel finding is that steel fibre displays a greater sensitivity to external load than PP fibre, which explains the distinctive load-deflection characteristics observed in GPMs with steel and PP fibre. Furthermore, steel fibre is found to be more advantageous in improving flexural strength and toughness, while PP fibre exhibits a more favourable effect on enhancing ductility. The AE results confirm that the bond strength between matrix and steel fibre is higher than that between PP fibre and matrix. Moreover, the inclusion of PP and steel fibre increase the proportion of shear cracks caused by fibre-matrix debonding and fibre pullout. These increasing shear cracks are responsible for tortuous flexural paths in fibre-reinforced GPMs. Significantly, the flexural toughness of GPMs with fibres are found to exhibit a positive correlation with the proportion of shear cracks. These findings can contribute to the optimization of GPM design for various applications where enhanced toughness and ductility are required.