Desempenho de concretos com baixo consumo de ligante

Abstract

The concern of the construction industry with environmental issues has stimulated research aiming at the reduction of cement consumption in concrete. This is because cement industry is responsible for more than 5% of CO2 emissions, which are responsible for the increase in greenhouse effect. Research on that matter already testify the possibility of dosing concrete with lower binder levels, maintaining or even improving its mechanical performance. However, there are still no defined mix design methods for these materials that facilitate application in everyday life. Furthermore, there are few studies on durability assessment of these concretes, mainly as to their performance against the action of chlorides. Within this context, this paper presents a concrete mix design method with lower binder contents and evaluates its mechanical performance and durability. Using the principle of aggregate packing and optimization to control paste volume, concretes were elaborated with cement consumption of approximately 280 kg/m2 and 320 kg/m'. These concretes achieved compressive strength above 60 MPa at 28 days. The results indicate that concrete with lower binder consumption has lower content of voids and pores of smaller diameters, offering very high resistance to the penetration of chlorides. On the other hand, conventional concrete with cement consumption of 350 kg/m2 obtained low resistance to the penetration of these aggressive agents. To evaluate the performance against the action of chlorides in concrete with even lower cement consumption, a unidirectional chloride diffusion test was carried out in dosed and molded concretes in the Microstructure Laboratory of the University of São Paulo. The cement consumption of these concretes varied from 140 kg/moto 280 kg/m'. For lower cement content, due to very high amounts of incorporated filers it was necessary to use a higher water-cement ratio, which may have caused an increase in porosity and loss of performance as the resistance to chloride penetration. Overall, it is found that it is possible to reduce the amount of binder in the concretes and still improve its mechanical and durability performance. In order to achieve this, it is necessary to use new mix design methods that seek the maximum aggregate packaging and the paste optimization.