Mechanical properties and pore structure multifractal characterization of low-cost engineered cementitious composites

Engineered Cementitious Composites (ECC) with high ductility and crack control face challenges in large-scale applications due to reliance on expensive quartz sand and polyvinyl alcohol (PVA) fibers. This study presents a sustainable ECC system using manufactured sand (MS), hybrid polypropylene (PPF) and basalt (BF) fibers. Experimental investigations evaluated the effects of aggregate type, particle size, water-to-binder ratio (W/B), sand-to-binder ratio (S/B), and hybrid fiber ratios on ECC's flowability, mechanical properties, and pore structure. Advanced characterization techniques, including scanning electron microscopy (SEM), low-field nuclear magnetic resonance (LF NMR), and multifractal detrended fluctuation analysis (MF-DFA), were employed to elucidate pore distribution patterns and their correlations with macroscopic performance. Results demonstrated that MS-ECC mixtures exhibited superior flowability. The compressive and flexural strengths of MS-ECC surpassed those of NS-based counterparts. Optimal performance was observed in specimens with 1.0 % PPF and 1.0 % BF, demonstrating enhanced flexural-to-compressive strength ratios. The low-cost ECC with hybrid fibers can achieve a tensile strength of 3.7 MPa and a tensile strain of 2.0 %. MS-ECC displayed superior uniformity in harmful pore distribution compared to NS-ECC. Lower fineness modulus, W/B, and S/B result in reduced multifractal strength of harmful pores and more uniform pore distribution. The synergistic combination of MS fineness modulus= 1.4, W/B= 0.3, S/B= 0.5, and 1.0 % PPF+ 1.0 % BF emerged as the optimal formulation balancing performance. Economic analysis confirmed the cost-effectiveness of low-cost ECC compared to conventional options, offering a viable solution for broader engineering applications.