Assessment of nano-TiO ₂ and class F fly ash effects on flexural fracture and microstructure of binary blended concrete

Abstract Flexural fracture analysis with an emphasis on microstructural assessment of self-compacting concrete (SCC) containing class F fly ash (FA) and titanium dioxide (TiO ₂ ) nanopowder has been carried out in this paper. For this purpose, Portland cement was replaced by low volumes of FA as 5, 10, and 15 wt% and nanopowder as 1–5 wt%. Flexural and compressive strengths were determined at different ages and empirical relationships were obtained to predict flexural strength based on compressive strength at different ages. Microstructures of different concrete mixtures were also investigated by scanning electron microscopy (SEM). It was found that addition of FA could lead to flexural strength decrease at earlier ages; however, improvement of the flexural strength could be achieved at higher ages. TiO ₂ nanopowder as a partial replacement of cement up to 4 wt% could accelerate C-S-H gel formation as a result of increased crystalline Ca(OH) ₂ amount at the early age of hydration and hence increase flexural strength of concrete specimens. TiO ₂ nanopowder could also improve the microstructure of concrete by shifting the distributed pores to finer and less harmful pores.