Avaliação do teor crítico de cloretos em concreto armado em meios com a presença de ácido sulfúrico.

Abstract

The corrosion of reinforcing steel is of great concern in the construction, because the most common cause of deterioration in reinforced concrete. Initially, the embedded steel from corrosion and naturally protected by high alkalinity of the concrete structure. However, this passive state can be broken by destroying the passive film by aggressive ions (chlorides, sulfates). In this paper, we study the behavior of three types of concrete over the water / cement ratio (0.4, 0.5, 0.6) subjected to chemical attack of a solution consisting of only ehlotide (NaCl) and two 1M increased by 0.4% and 2% H2S04 , respectively. To evaluate the critical chloride content in concrete. For the tests we used the electrochemical technique of linear polarization resistance (LPR) to measure the corrosion potential (Ecorr) and corrosion current density (icorr) after their bodies depassivation proof-of-test and were removed from the ruptured for visual evidence of corrosion in the steel and determination of the levels of OH- and CI- total and free, Na + Ca +2, K + and SO4. The leaching method was employed to determine pH. The leaching efficiency was assessed by measuring the pH of the sample despassivada and that obtained by titration. We used the potentiometric titillation to determine the chloride content retained in the concrete. And with the pH and concentration of CI determined the ionic relations [C1-] / [OH-], referring to the contents retained in the concrete in the induction process of corrosion. The concentrations of sulfate were determined by turbidimetric method and the alkali (Na K Ca ~2) by rlame photometry. In this research can be observed that the water / cement ratio and aggressiveness of the solutions were determining factors for the corrosion of steel The concrete of higher water / cement ratio (0.6) subjected to NaCl solution + 2% H2SO4 as the first to despassivarem, had the lowest value of compressive strength and greater retention of chlorides. We obtained an average difference between the results of pH titration and pH meter to about 3% with standard deviation of ± 0.06, a total CI- content (1.07 - 2.5)% by weight of cement and an average ratio of[Cl-]/[OH-](0.1-0.33).