Influence of SiO2, TiO2 and Fe2O3 nanoparticles on the properties of fly ash blended cement mortars

•The influence of SiO2, TiO2 and Fe2O3 nanoparticles on the properties of fly ash blended cement mortars has been investigated.•Small amounts of nanoparticles have limited influence on the workability.•Small amounts of nanoparticles result in higher compressive and tensile strength.•Higher concentrations of nanoparticles have a negative impact on the strength.•Addition of nanoparticles results in a reduction of open porosity of cement paste.•Addition of nanoparticles modifies the micromechanical properties of cement paste. This study explores the effects of different types of nanoparticles, namely nano-SiO2 (NS), nano-TiO2 (NT), and nano-Fe2O3 (NF) on the fresh properties, mechanical properties, and microstructure of cement mortar containing fly ash as a supplementary cementitious material. These nanoparticles existed in powder form and were incorporated into the mortar at the dosages of 1%, 3%, and 5% wt.% of cement. Also, fly ash has been added into in mortars with a constant dosage of 30% wt.% of cement. Compressive and flexural strength tests were performed to evaluate the mechanical properties of the mortar specimens with different nanoparticles at three curing ages, 7, 14, and 28 days. Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) tests were conducted to study the microstructure and the hydration products of the mortars. To elucidate the effects of nanoparticles on the binder phase, additional experiments were performed on accompanying cement pastes: nanoindentation and open porosity measurements. The study shows that, if added in appropriate amounts, all nanoparticles investigated can result in significantly improved mechanical properties compared to the reference materials. However, exceeding of the optimal concentration results in clustering of the nanoparticles and reduces the mechanical properties of the composites, which is accompanied with increasing the porosity. This study provides guidelines for further improvement of concretes with blended cements through use of nanoparticles.