Análise da frente de carbonatação natural em concretos à base de cimentos Portland CP IV-32 RS e CP V-ARI RS

Abstract

The carbonation is considered one of the main pathologies in concrete, which can cause issues like the consumption of CSH and mainly the corrosion of the steel reinforcement bars. The carbonation is a phenomenon that occurs naturally in concrete structures from a physical-chemical process between the carbon dioxide (CO2) of the atmosphere and the compounds of the cement paste. It causes the reduction of alkalinity in the surface layer and formation of calcium carbonate (CaCO3) inside the pores. The carbonation occurs from the outside to the inside, forming a layer with reduced pH denominated carbonation front, which upon reaching the depth of the steel reinforcement causes destabilization of the passivating film around the steel, causing the beginning of the corrosion. Research on the behavior of this natural phenomenon and considering the real variables to which the structures are submitted are scarce. In this context, the present research show an analysis of factors that directly influence the front of carbonation, such as cement type, water/cement ratio, porosity and shrinkage in concrete in a natural environment. The cement types used were Portland cement CPIV-32 RS and CPV-ARI RS, and water/cement ratios used were 0,5 and 0,65. The concretes made intended to perform the tests of resistance to axial compression, water absorption, carbonation, hydraulic retraction, and cement pastes were used for morphological and microstructural analysis. The tests were performed at 28 days, 3, 6 and 9 months with concretes and pastes conditioned to a natural environment partially sheltered from rain in the parking lot of UTFPR - Pato Branco. At the end of the analysis, the results showed that the water/cement ratio was the main responsible for the advance of the carbonation front, since it increases the pore network in the cement matrix, since the results were not significant when changed the type of cement. Concretes with higher water/cement ratios showed larger mass and shrinkage variations, and cement-based concretes with higher content of incorporated additives (CPIV-0,5) presented lower values of mass variation and retraction. Comparing the results of natural carbonation depth with the accelerated test, it was found that it would take 364 days for the natural test to reach the depth found within 30 days of the accelerated test, which was 6,01 mm.