Experimental investigation on mechanical and durability characteristics of metakaolin-based fibre reinforced concrete

This study investigates the combined effects of metakaolin (MK) and steel fibres (SF) on the mechanical and durability properties of M30-grade concrete. An experimental programme was designed comprising six concrete mixes with varying MK replacement levels (5%, 10%, 15%, 20%, and 25%) and a constant 1% SF dosage. The experimental results showed that the mix containing 15% MK and 1% SF produced the highest compressive strength at both 7 days (37.06 MPa) and 28 days (58.13 MPa), with increases of 59.7% and 69.9% compared to the conventional M30 mix. Significant improvements were also observed in split tensile and flexural strengths, with increases of 106.1% and 129% at 7 days, and 98.2% and 129% at 28 days, respectively. Durability tests showed a 29.9% reduction in water absorption, a 28.7% decrease in chloride permeability, and a 156.1% increase in electrical resistivity for the optimal mix compared to the control. The UPV results rated the 15% MK + 1% SF mix as ‘Excellent’, with a pulse velocity of 4.781 km/sec. This research highlights that a 15% MK replacement level, combined with 1% SF, offers the best balance of strength and durability, making it a promising approach for enhancing the performance of concrete in construction applications.