Effect of Polypropylene Fibre Dosage on Portland Cement Concrete: Early-Age Compressive Strength, Workability, and Practical Dosage Guidance

The present study was conducted to systematically investigate the effect of adding Polypropylene (PP) fibre at various dosages (0–1.0 kg/m3) on the compressive strength and workability of Blended Portland Cement concrete. All mix variables were kept constant except for fibre content (w/c = 0.45), thereby allowing the dosage effect to be isolated. Standard-sized 150 × 150 × 150 mm cubes were prepared and tested for slump (ASTM C143), fresh density and early-age compressive strength BS 1881-116:1983 at 7 days and 14 days. Slump decreased monotonically from 200 mm to 160 mm as the dosage increased and remained within the EN 206 S4 (High) workability class throughout. Fresh density was essentially unaffected. The early-age compressive strength increased continuously for both test ages, reaching 51.7 MPa at 1.0 kg/m3 at 14 days. One-way analysis of variance confirmed a statistically significant dosage effect at both ages (7-day p < 0.001; 14-day p = 0.003). Based on the strength-workability trade-off, it was found that a pragmatic recommended dosage range is 0.6–0.8 kg/m3, which gives an appreciable strength improvement with a moderate decrease in workability without the need for the addition of extra admixtures. These results offer early age mix design guidance for practitioners and engineers in a wide range of construction applications and can be used to calculate a potential circular economy impact for the mix design: a 100 m3 pour at 0.8 kg/m3 could potentially divert 80 kg of PP waste from landfill or incineration if recycled PP fibres were used instead of the virgin fibres used in the study.