1,721,148 research outputs found
The mechanism controlling corrosion of steel in carbonated cementitious materials in wetting and drying exposure
No full textExperiments were performed to study the mechanism of corrosion of steel in carbonated concrete in cyclic wetting/drying exposure. It was found that the corrosion rate increased during wetting, followed by a decrease during drying. The increase and decrease of the corrosion rate can be explained by changes in electrochemically active steel area as a function of the moisture state of the mortar and its porosity. The corrosion rate achieved in the wet phase stabilizes during the first few wetting and drying cycles. The mechanism of the electrochemical process is discussed on the basis of theoretical considerations. It is concluded that the corrosion kinetics are under activation control. The availability of oxygen does not seem to be a limiting parameter for the corrosion process in cyclic wetting/drying exposure
Innovative sample design for corrosion rate measurements in carbonated blended concrete
No full textLowering the clinker content of concrete using SCMs can contribute significantly to reduce the energy consumption for cement production and the CO2 emissions of building materials. Substitution of clinker up to 65% is now possible according to European and Swiss standards. Uncertainty about durability, especially carbonation induced corrosion, is the main factor limiting the practical use of these blended cements. For service life prediction of concrete structures with new, blended cements corrosion rate data are urgently needed because the so called “corrosion propagation stage” might be a significant part of the total service life. Such data so far can be obtained only with very time consuming tests due to the sample size of standard concrete samples and the slow carbonation process. In this paper an innovative experimental setup is presented that overcomes these limitations. The setup consists in miniaturised thin samples with a size of 80 x 80 x 6 mm, thus with an effective carbonation depth of only 3 mm. With this new sample design the corrosion rate of steel in carbonated samples can be studied at any relative humidity. Our preliminary results show that these samples allow any kind of electrochemical measurements can be performed – thus the study of corrosion and related influencing parameters, in homogenous carbonated conditions, is possible within a short time scale
Analysis of corrosion with electrochemical techniques applied to geothermal power plants in Switzerland
No full textA systematic data collection on chloride-induced steel corrosion in concrete to improve service life modelling and towards understanding corrosion initiation
Full text linkWhile the critical chloride content for corrosion initiation in concrete, Ccrit, is a vital parameter for (probabilistic) service life modelling, little information is available on its statistical distribution. To close this gap, we present a comprehensive data collection of Ccrit measured on samples retrieved from various engineering structures. Additional detailed information about the structures (steel type, concrete properties, age, etc.) is systematically documented. This provides guidance to engineers performing service life modelling to select the statistical distribution of Ccrit as model input. Finally, the systematic documentation will allow identifying the dominant parameters influencing chloride-induced corrosion initiation in concrete
Critical Analysis of Experiments on Reinforcing Bar Corrosion in Cracked Concrete
No full textCracks in concrete are expected to accelerate the degradation of
reinforced concrete—mainly reinforcement corrosion. Previous
literature studies have shown that the initiation time can decrease
due to cracks, whereas the accelerating effect on corrosion propagation
has no clear experimental evidence. This paper critically
assesses how different common experimental setups may influence
the test results. It is found that, particularly, the exposure duration
and condition, the water-binder ratio (w/b), and the crack width
have an impact on the outcome of the experimental study about
corrosion rates in cracked concrete. Hence, these parameters
should be carefully considered when designing experiments to
study the influence of cracks. Recommendations for future research
work are given
Chloride-induced reinforcement corrosion in cracked concrete: the influence of time of wetness on corrosion propagation
No full textLiterature data on the influence of concrete cracks on corrosion propagation of reinforcing steel are contradictory. This might be due to very different exposure and test conditions but also to a lack of time-resolved data in cyclic wetting–drying exposure. Here, the influence of the environmental conditions on the corrosion rates in cracked concrete is studied experimentally. The results show that the corrosion rate in cracked concrete depends on the duration of wetting and drying phases and the relative humidity (RH) during the drying phase. The lower the ambient RH in the drying phase, the faster the cracks dry, which depresses the corrosion rate in the periods between the wetting events. A model is proposed to estimate corrosion rates in cracked concrete cyclic wetting/drying exposure
PH-monitoring in mortar with thermally-oxidized iridium electrodes
Full text linkThe pH of the concrete pore solution plays a vital role in protecting the reinforcing steel from corrosion. Here, we present results from embeddable pH sensors that permit the continuous, in-situ monitoring of the pH in the concrete pore solution. These are potentiometric sensors, based on thermally-oxidized iridium/iridium oxide (IrOx) electrodes. We propose an iterative calculation algorithm taking into account diffusion potentials arising from pH changes, thus permitting the reliable, non-destructive determination of the pore solution pH over time. This calculation algorithm forms an essential part of the method using IrOx electrodes. Mortar samples were exposed to accelerated carbonation and the pH was monitored at different depths over time. Comparative tests were also performed using thymolphthalein pH-indicator. The results from the pH sensors give insight in the carbonation process, and can, in contrast to thermodynamic modelling and titration experiments, give insight in kinetic processes such as transport and phases transformations. Additionally, it was found that the front at which the pH is decreased from initially 13-14 down to 12.5 can be significantly ahead of the common carbonation front corresponding to pH 9-10. This has major implications for laboratory testing and engineering practice
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