Effects of Carbonation on Corrosion Rate of Reinforcing Steel in Different Concrete and Repair Materials

Reinforced concrete with different concrete mix proportions, i.e. binder types or w/b ratio, would provide different quality to protect the reinforcing steel from corrosion. When carbonation occurred, corrosion of steel embedded in concrete can be initiated. This paper reports effects of carbonation on electrochemical properties of steel embedded in concrete with different mix proportions as w/b ratio of 0.4 and 0.6, fly ash added up to 30% by weight of binder, and also in six repair materials. All samples was exposed to accelerated carbonation (4% CO2, 50 ± 5% relative humidity (RH), and 40 0C temperature) and laboratory environment (0.04% CO2, 75 ± 5% RH, and 28 0C). The electrical resistivity was monitored by using four-point Wenner probe. The Linear polarization resistance (LPR) was used to characterize the corrosion rate of embedded steel at different exposure time. The carbonation depth of specimens was also tested by using the phenolphthalein indicator. The void contents of repair material specimens were also determined. The results showed that the electrical resistivity of concretes and repair materials increased along with an increase of carbonation depth. However, in case of fly ash concrete, the electrical resistivity decreased at longer exposure period in accelerated carbonation due to decomposition of C-S-H by carbonation. It was also found that the corrosion rate of steel embedded in concrete and repair materials increased as an increase of carbonation depth, even the carbonation depth was less than the covering depth. Steel embedded in ordinary Portland cement (OPC) concrete or low w/b concrete shows lower corrosion rate due to higher pH of concrete. The guideline for evaluation of corrosion initiation and severity due to carbonation is also proposed

Effect of Chloride and Corrosion of Reinforcing Steel on Thermal Behavior of Concrete and Its Modeling

Chloride induced corrosion of reinforcing steel is a significant problem. Non-destructive technique to inspect the corrosion of reinforcing steel is required. Thermograph is one of the Non-Destructive Testing methods which may be useful for detecting corroded bar in reinforced concrete. This study aims to investigate the thermal behavior of concrete influenced by chloride and corrosion of reinforcing steel at different corrosion levels. The results of thermal behavior of chloride and corrosion product contaminated concrete are useful for determining the detectability of corrosion by thermograph. Different mix proportions of concrete and also level of corrosion were studied. The results of temperature profiles obtained from experimental work proved that when there is presence of dense rust confined at the interfacial zone between concrete and steel, thermal behavior of concrete around steel bar changed. The results revealed that when applying heat source on the top surface of the specimen, there was a slight change of temperature on top of corroded bar while there was more signification change of temperature below the corroded bar. This is because the dense rust with low porosity is a better heat conductor when compared to concrete, transferring the heat faster to the part below the rusted bar

Effects of Concrete Mix Proportion and Chloride Content on Electrochemical Properties of Reinforcing Steel in Concrete

Corrosion of steel in concrete has been considered as a major cause reducing the lifespan of reinforced concrete (RC) structures. Evaluation of corrosion rate is crucial to determine service life and maintenance plaining for RC structures. Electrochemical properties of corrosion of embedded steel in concrete, including the Tafel slope, corrosion potential and corrosion current density, are significant parameters predicting corrosion rate. The objective of this paper was to quantitatively evaluate electrochemical properties of steel in different compositions of concrete. Varied parameters include the water to binder ratio of concrete, type of binder and chloride content. The electrochemical properties were evaluated at three periods of exposure. Experimental results reveal that the electrochemical properties of reinforcing steel depend on water to binder ratio, type of binder and chloride content. An increase in chloride content significantly decreases the corrosion potential and increases the corrosion rate of steel. The anodic equilibrium potential is lower with an increase in chloride content. The varied concrete mix proportion significantly influence the cathodic polarization. This is due to the effects of concrete porosity on oxygen concentration, which is influenced by the concrete mix proportions. The results can be used to predict corrosion rate of steel in various concrete mix proportion for determining service life and repairing of RC structures

CORROSION OF REINFORCING STEEL IN GGBS CONCRETE DUE TO CYCLIC EXPOSURE OF CHLORIDE AND CARBONATION

ABSTRACT: Better chloride resistance; however, worse carbonation resistance of GGBS concrete compared to that of OPC concrete are well known. Also there is a possibility that RC structure is exposed to both chloride and carbonation. So objective of this research is to study corrosion of steel in GGBS concrete under cyclic exposure to carbonation and chloride. GGBS concretes were mixed with different replacement ratios. Specimens, individually or cyclically exposed to chloride and carbon dioxide, were measured corrosion by half-cell potential. Results show that corrosion was accelerated by NaCl-CO 2 cycle but retarded by water-CO 2 cycle