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In Brazil, the air-entrained concrete has been extensively used as structural walls of popular housing units. Some of these units built recently in urban areas were inspected. Upon inspection, a significant variation of the potential corrosion measurement was obtained and reddish stains on the surface of the reinforcement, were also observed indicating active state of corrosion. Not always the concrete was fully carbonated and there wasn´t chloride contaminations. In order to understand the occurrence of premature corrosion of the inspected reinforcement, a complementary study was conducted at the laboratory to characterize air-entrained concretes and evaluate the behavior of steel bars immersed in solutions that simulate the water in the pores of these concrete and compare them to the pore solution of an ordinary Portland concrete.
The steel bars were evaluated under three conditions: blasted, corroded and galvanized. The behavior of the bars was monitored by visual examination and by electrochemical measurements. Finally, the corrosion rate was calculated. Tests on concrete specimens were also conducted to validate the results. The characterization tests showed an inferior quality of the air-entrained concretes, having both high concentrations of pores, many of them fully interconnected. This justified the high deep carbonation observed in a short period of time and a variable electrical resistivity detected in the field. The pore solution immersion tests showed the higher corrosion susceptibility of metallic reinforcement in air-entrained concretes. In the studied air-entrained concretes, the corrosion occurred preferentially under the sealant applied on the bar extremities. In one of them, corrosion was also observed on the free surface of the blasted bars. The corrosion was also observed in the air-entrained concrete specimens, confirming the tests solution results.
No Brasil, o concreto com ar incorporado tem sido intensamente utilizado como parede estrutural de unidades habitacionais. Algumas dessas unidades construídas recentemente (inferior a três anos) em regiões urbanas, do norte, sul e sudeste do país, foram inspecionadas. Na inspeção, foram detectadas manchas avermelhadas na superfície das armaduras, indicando um estado ativo de corrosão do aço-carbono. Diante desse fato, foi conduzido um estudo experimental objetivando avaliar o comportamento de barras imersas em soluções que simulam a água presente nos poros do concreto com ar incorporado e do concreto convencional. As barras foram avaliadas em três condições: aço jateado, aço já em processo de corrosão e aço zincado. Em algumas barras foram fixados anéis de material não metálico para estudo da corrosão em frestas. O comportamento das barras foi acompanhado por exame visual e por medidas eletroquímicas. Ao final, a taxa de corrosão foi calculada.
As soluções foram obtidas pela mistura de água destilada e do material resultante da moagem de co