Amirkabir University of Technology AUT Journal of Civil Engineering 2588-2899 10 3 2026 07 01 Effect of nano magnesium oxide and microsilica on the mechanical behavior of fiber reinforced concrete 211 226 6076 10.22060/ajce.2026.24740.5946 EN Mojtaba Etemadi Department of Civil Engineering, Mahdishahr Branch, Islamic Azad University, Mahdishahr, Iran Hamid Beiraghi Department of Civil Engineering, Mahdishahr Branch, Islamic Azad University, Mahdishahr, Iran Journal Article 2025 09 14 This study investigates the synergistic influence of nano magnesium oxide (nMgO), microsilica (silica fume), and polypropylene (PP) fibers on both fresh and hardened properties of concrete, aiming to propose an optimized hybrid mixture for structural applications. The novelty lies in the integrated, multi-scale approach—combining nano (nMgO), micro (microsilica) and macro (PP fibers) constituents—and a systematic experimental program covering 16 mix variants. Specimens were prepared with nMgO dosages of 0–2% and PP fibers of 0–1.4% by cement weight, while microsilica was kept at 4% replacement of cement. Mechanical tests (compressive, splitting tensile, flexural) were performed at 7, 28 and 90 days; water absorption was measured at 28 days. All reported values are the mean of replicates (n=3) and statistical dispersion is reported alongside mean values (raw data available upon request). The optimum performance was observed for the mix containing 0.5% nMgO and 0.8% PP fibers, which produced improvements up to 18% in compressive strength, 22% in splitting tensile strength and 20% in flexural strength relative to the control mix, while reducing water absorption from 4.3% to 3.1%. Mechanistic interpretation attributes these gains to combined pore-filling and nucleation effects of nMgO, pozzolanic reaction of microsilica improving C–S–H content, and fiber-bridging improving post-crack behavior. Limitations and reproducibility (replicates, statistical reporting) are discussed. https://ajce.aut.ac.ir/article_6076_beb22abb9ec56c0cf7ec7d811dd91a56.pdf