Effect of high shear-dispersed nano-alumina on concrete strength, durability, and microstructure

This study investigates the effectiveness of high shear dispersion (HSD) as a scalable and energy-efficient technique for incorporating nano-alumina (NA) into conventional M40-grade concrete, addressing a key limitation of nanoparticle agglomeration commonly reported in nano-modified cementitious systems. Nano-alumina was incorporated at dosages of 0.5%, 1.0%, and 1.5% by weight of cement, and its influence on mechanical performance, durability, microstructural refinement, and statistical reliability was systematically evaluated. Results demonstrate that HSD enables uniform NA dispersion in the range of 10–30 nm, leading to pronounced improvements in concrete performance. At 28 days, the compressive, split tensile, and flexural strengths increased by 26.99%, 37.5%, and 48.14%, respectively, for concrete containing 1.5% NA, compared to the control mix. Long-term curing further enhanced performance, with compressive strength reaching 74.04 MPa at 180 days. Durability assessments revealed improved resistance to chemical attack (NaCl, HCl, and H2SO4), freeze–thaw cycles, and elevated temperatures up to 400 °C, attributed to refined pore structure and reduced permeability. Microstructural analysis using SEM–EDX confirmed significant matrix densification, reduction in average void size by approximately 65%, narrowing of the interfacial transition zone, and the formation of secondary calcium–alumina–silicate–hydrate (C–A–S–H) gel. In addition, multivariable regression and Weibull statistical analyses demonstrated enhanced strength predictability and reduced variability with increasing NA dosage. Overall, this study establishes high shear dispersion as a practical and field-compatible alternative to ultrasonication, enabling reliable nano-alumina integration for the development of high-performance and durable concrete systems.