Experimental Investigation on Sustainable Concrete Incorporating Fly Ash, Manufactured Sand and Sisal Fiber

Abstract

This study presents an experimental investigation on sustainable M30-grade concrete incorporating fly ash, manufactured sand (M-Sand) and sisal fiber. The objective is to reduce dependence on ordinary Portland cement and river sand while improving mechanical performance through natural fiber reinforcement. Four mixes were evaluated: a conventional control mix (CM), and three sustainable mixes containing 100% M-Sand, 10-30% fly ash as partial cement replacement and 0.5-1.5% sisal fiber by weight of cementitious material. The available experimental data include compressive strength at 7, 14 and 28 days, and split tensile and flexural strength at 28 days. Mix M1, containing 10% fly ash and 0.5% sisal fiber, achieved the highest 28-day compressive strength of 44.7 MPa, representing a 7.71% improvement over the control mix. Mix M2, containing 20% fly ash and 1.0% sisal fiber, achieved the highest split tensile strength of 4.10 MPa and flexural strength of 6.05 MPa, corresponding to improvements of 17.14% and 16.35%, respectively. The improvement is attributed to the combined contribution of fly ash pozzolanic activity, better particle packing provided by M-Sand, and crack-bridging action of sisal fibers. Higher replacement/fiber content in M3 reduced strength, likely because of lower workability, fiber clustering and delayed hydration. The results indicate that M2 provides the best overall balance between tensile performance, flexural performance and sustainability, whereas M1 gives the maximum compressive strength. The findings support the feasibility of fly ash-M-Sand-sisal fiber concrete as an eco-efficient cementitious composite for structural applications, subject to further durability and microstructural validation.