Fibre hornification improves the long-term properties of hemp fibre-reinforced fly ash-based geopolymer mortar

Abstract

The study investigates the impact of the fibres’ hornification, subjected to 5 wetting/drying cycles, on the physical and mechanical properties of short hemp fibre-reinforced fly ash-based geopolymer mortars at distinct ages (1, 2.5 and 18 months) cured under laboratory conditions and additionally of the mortars underwent the accelerated ageing of 10 wet/dry cycles. The study reveals that fibres’ hornification induced fibrillation and fibres' cleaner surfaces, most likely enhancing fibres' dispersion within the matrix. This phenomenon leads to suppressing the degradation of all tested mortar’s properties. Considering the curing under laboratory condition, in the case of the density, the suppression is more pronounced in the long term. After 18 months, the hornificated fibre-reinforced mortar nearly matches the water absorption capacity of the plain mortar. Furthermore, the fibres’ hornification contributes to the enhancement in compressive- and flexural strengths of the reinforced mortar at the age of 18 months. In the long term, by increasing the pre-peak segment of the force-displacement curves, the fibres’ hornification slightly increases the energy absorption capacity of the raw fibre-reinforced geopolymer mortar. In the case of the mortars’ curing under wet/dry cycles, the hornification proves to slightly (10 %) improve the physical (increase in density, decrease in water absorption) and mechanical properties (increase in compressive- and flexural strength, as well as energy absorption capacity) of the fibre-reinforced mortar. Due to the mortars’ exposure to the dry cycles (happen at 60 °C), the further geopolymerisation speeds up, which results in the denser matrix, increase in its compressive- and flexural strengths, but a general fibre/matrix bond deteriorates and therefore the fibre-reinforced mortars’ energy absorption capacity decreases, when compared to their counterpart tested at the same age but cured under laboratory condition.