Comparative Study of the Properties of Cement Pastes Modified with Nano-Silica and Nano-Alumina

Abstract

This paper presents the effect of adding nanoparticles SiO2 and Al2O3 in the cement with respect to mechanical, physical and structural properties. Nanoparticles were chosen for the development of nanocomposite building materials with high mechanical strength, durability and low permeability. Correspondingly, the cement used is Portland Cement CEMI42.5N. Five compositions have been prepared, a reference sample (OPC) and pastes with different nanoparticles. Nanoparticles of SiO2 and Al2O3 were added in 1.5% and 3% by weight of cement and the produced samples were tested after 7, 28, 90 and 120 days of curing. All the samples, in every hydration period, were tested for compressive strength, while their open porosity was measured and their microstructure was examined by means of infrared spectroscopy. Furthermore, for certain hydration periods, the chemical and elemental composition of the samples was evaluated by means of X-ray diffraction and scanning electron microscopy. The samples were also evaluated for capillary water absorption and shrinkage, while thermal analysis was performed for specific samples. The comprehensive analysis revealed a positive effect, in terms of structural properties, of nanoparticle admixture in cementitious systems. The addition of nanoparticles influence the workability of the composites and contributes to the formation of crystallization nuclei, which in turn enhance the durability of the material. Interestingly, it was found that high concentration of nanoAl2O3 in the admixure, results in high mechanical properties. Highlights: Different analytical techniques were combined in order to holistically test nanomodified cement pastes. nanoalumina is systematically tested as additive in cement pastes.