Evaluation of the effect of nanosilica and recycled fine aggregate in Portland cement rendering mortars

ABSTRACT This paper evaluated the incorporation of nanosilica (NS) in rendering mortars produced with recycled fine aggregate (RFA). Initially, a study was carried out on cementitious pastes, replacing Portland cement with NS at levels of 0%, 0.4%, 0.6%, 0.8%, and 1.0%. The samples were submitted to scattering, rheology, calorimetry, x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and compressive strength analysis at 28 days. The results demonstrated that the pastes with 0.4% NS and 0.6% NS presented an increase in strength of 55% and 58%, respectively, due to a greater formation of calcium silicate hydrate (C-S-H), when compared with the reference paste. From that, the RFA samples were produced, replacing Portland cement with 0% NS, 0.4% NS, and 0.6% NS. At 28 days, mechanical performance, microstructure, and durability were evaluated by means of flexural strength and compression, scanning electron microscopy (SEM), dynamic elasticity module, and water absorption by capillarity. From the results, it was concluded that the RFA samples with 0.4% NS resulted in the optimal nanosilica content, increasing compressive strength values and reducing the sorptivity, in relation to the other mixtures. The SEM images suggest that NS reacted with portlandite formed of the cement hydration, improving the microstructural development of the samples.