Estudo do desempenho dos aditivos redutores de permeabilidade no concreto

Abstract

Ensuring the impermeability of concrete should be the first line of the defense system against any deteriorating physicochemical process. In this context, the use of Permeability-Reducing Admixtures represents an alternative to guarantee greater durability for reinforced concrete structures. Permeability-Reducing Admixtures (PRA) can be classified into two categories: Permeability-Reducing Admixture for Hydrostatic conditions (PRAH) and non-hydrostatic conditions (PRAN). This research aims to study the influence of the two types of admixtures (PRAH and PRAN) on the mechanical and durability properties of concrete. Therefore, samples of five different traits, one reference mix composition (no PRA additions), two mix composition with different PRAH admixtures and two other mix composition with different PRAN admixtures were molded and tested. Tests of compressive strenght, total immersion absorption, capillary water absorption, pressurized water penetration, volumetric electrical resistivity and resistance of concrete to chloride ion penetration were performed. As for mechanical properties, the results shows that PRA admixtures do not change the compressive strength of concrete. With regards to durability tests, the results of the total immersion absorption test indicate that PRA admixtures do not cause any changes in absorption values, making the test inconclusive about the performance of the admixtures. For low water pressure penetration situations, such as the capillary water absorption test, the PRAN admixture excelled in reducing water absorption over the reference mix composition, while for high water pressure incidence situations, such as the penetration of water under pressure test, PRAH admixtures had a more significant absorption reduction. Regarding the tests of penetrability of chloride ions and volumetric electrical resistivity, there was no trend related to the type of admixture, the results were different between products, but the correlation between the tests showed that a more resistive concrete is less permissive for the passage of chloride ions (and other ions in general). Finally, a comparison was made between the results obtained in the research and the minimum permeability limits allowed by the concrete of the eastern subway line of Fortaleza. Based on the capillarity and immersion absorption limits, all the mix compositions would be in agreement. However, based on the limits of water penetration under pressure, none of the mix compositions would be within the established limits.