PSI - Issue 70

Vudata Harsha sai et al. / Procedia Structural Integrity 70 (2025) 509–516

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limitations, researchers have explored the incorporation of supplementary cementitious materials (SCMs) such as fly ash, and fiber reinforcements like steel, polypropylene, and natural fibers. Fly ash, a pozzolanic industrial by-product, improves the microstructure of concrete, enhances long-term strength, and contributes to sustainability by partially replacing cement. Simultaneously, fiber reinforcement helps bridge microcracks, improve ductility, and enhance post-cracking behavior. While many studies have investigated these materials independently, the combined effects of fly ash with different types of fibers — especially natural fibers such as coir — remain underexplored. This study aims to evaluate the synergistic effects of hybrid fiber reinforcement (steel, polypropylene, and coir yarn) and varying levels of fly ash replacement on the mechanical and flexural performance of M40 grade concrete. Fly ash is a widely accepted SCM used to reduce the heat of hydration, improve workability, and enhance durability. Mehta and Monteiro (2014) recommend fly ash replacement levels between 15 – 25% for optimal performance, while Neville (2011) reports durability benefits at replacements not exceeding 20% due to reduced permeability. However, excessive replacement may compromise early-age strength due to slower pozzolanic reactions (Johnston, 2001).Fiber reinforcement significantly improves the mechanical properties of concrete. Steel fibers, known for their high tensile strength and crack-bridging capacity, enhance post-crack load-bearing ability and toughness under flexural loads (Banthia & Trottier, 1995). Sivaraja et al. (2010) confirmed that steel fiber reinforced concrete (SFRC) is highly suitable for impact and fatigue resistance. However, increased fiber content may reduce workability, necessitating adjustments to mix proportions. Polypropylene fibers are effective in mitigating early-age shrinkage and enhancing impact resistance. Bentz et al. (2009) and Yin et al. (2015) noted their role in reducing plastic shrinkage and enhancing durability. Although they contribute less to compressive strength, they improve fire resistance and crack control, particularly at dosages of 0.1 – 0.3%. Coir fibers, a biodegradable natural material derived from coconut husks, are a sustainable alternative to synthetic fibers. Studies by Ali et al. (2012) and Mehta & Monteiro (2014) have shown that coir fibers enhance ductility, toughness, and energy absorption. However, their hydrophilic nature leads to weak bonding with cement, which can be improved through alkali surface treatment (Sivaraja et al., 2010). Although several studies have independently examined fly ash and fiber reinforcement, limited research investigates their combined effects in a hybrid system. Recent works suggest that combining fibers with fly ash can enhance flexural performance, shrinkage resistance, and crack control Yin et al. (2015) reported that the use of polypropylene and steel fibers in fly ash-based concrete increased flexural strength by up to 25%. This study addresses this research gap by systematically evaluating the combined effects of fly ash (10%, 20%, 30%) and three types of fibers on the mechanical, flexural, and load-deflection performance of M40 concrete. The outcomes are expected to inform the development of sustainable, high-performance concrete suitable for structural applications. 1.2 Research Justification and Significance Despite the well-documented benefits of fiber-reinforced and fly ash-based concretes individually, there remains a lack of comprehensive studies examining their combined effects — particularly using hybrid fiber systems (steel, polypropylene, and coir) in conjunction with various levels of fly ash in structural-grade concrete. The majority of previous work has focused on single fiber types or limited replacement levels, without evaluating the interactive effects on both mechanical and flexural behaviors across multiple performance criteria. • The significance of this study lies in its integrated approach to sustainability, mechanical enhancement, and durability. By utilizing fly ash, an industrial by-product, as a partial cement replacement, the environmental footprint of concrete is reduced. Simultaneously, the use of coir fiber introduces a renewable, biodegradable reinforcement option, contributing to the principles of circular economy and green construction. • This research provides new insights into how different fiber types interact with optimized fly ash content to enhance compressive strength, split tensile strength, flexural strength, and load-deflection behaviour. The findings are particularly relevant for infrastructure projects requiring crack resistance, ductility, and extended service life under flexural stresses. 1.1 Role of Fly Ash and Hybrid Fiber Reinforcement in Enhancing Concrete Performance