The ambient and elevated temperature performance of hemp fibre reinforced alkali-activated cement foam: Effects of fibre dosage and alkali treatment

Abstract

Hemp fibre is gaining attention as a sustainable alternative to synthetic fibres in cementitious composites. This study investigates the effects of dosage and alkali treatment of hemp fibre (HF) on the strength, shrinkage, and fire resistance of alkali-activated cement foam (AACF). Raw untreated and NaOH-treated HFs were added at 0.3%, 0.7%, and 1% of the volume of precursor slurry. The findings reveal that alkali-treated HF increases the compressive strength, which increased with dosage up to 0.7% and then dropped slightly at 1%. Whereas raw HF lowered compressive strength except for 0.7%. Flexural strength was enhanced by both treated and untreated fibre, which increased with the dosage up to 0.7% and then dropped slightly at 1%. The flexural strength enhancement (up to 260%) was higher than compressive strength (up to 54%) at all dosages. Moreover, alkali-treated HF exhibited higher strength compared to raw HF (54% vs 32% under compression and 260% vs 220% under flexure). Residual compressive strength after exposure was measured as an indicator of fire resistance. It followed a similar variation with fibre dosage to their ambient compressive strength when exposed to 100°C and 200°C, where the optimum dosage of 0.7% had up to 65% higher strength for treated fibre and 16% higher strength for raw fibre. However, HF did not improve the residual strength for higher temperatures (400°C and 800°C). In contrast, they caused a higher proportion of strength loss by up to 83–91% of the original strength compared to 67–84% in the control.