Efeito da redução do teor de cimento no desempenho de matrizes e compósitos cimentícios

Abstract

The main purpose of this research is to investigate the effect of partial replacement of cement by fine particles materials – limestone and nanosilica – on the performance of cementitious matrices and composites. The concern in reducing the use of cement is due to the great environmental impact of its production: the use of high amount of natural resources and carbon dioxide emissions that contributes to the increase of global warming. The limestone is an inert material known by its positive effect of the filling voids and nanosilica that besides this physical effect has a pozzolanic activity. It reacts with the hydrated products of cement to produce compounds more resistant than the original. For the evaluate the effects of cement reduction, mortars were made with 5%; 25%; 45% and 65% of limestone and with the 2% of nanossilica in replacement of weight cement. The use of nanossilica was evaluated alone and in combination with 25% of limestone – both content were in replacement of weight cement. The agglomeration effect was reduced by the adding 0.02% of polycarboxylate-based dispersing admixture in relation to total weight of solids. The water content was determined by Powers’ model. Mortars were evaluated by bulk density, air content by gravimetric method and flow table test in the fresh state. Porosity and compressive strength test were developed in hardened state. The mechanical performance of granite-mortar interface was evaluated by bond strength at 28 days. The results showed that the replacement of cement by limestone fines has more impact to compressive strength of mortar than bond strength of mortar-granite interface. However, the use of this may be advantageous in both cases, if the mechanical performance required to the application in mortar or in a rendering systems is verified. The use of nanosilica did not contribute significantly to the mechanical performance, probably it occurred due to the age of the mortars evaluated.