Initiation Of Chloride-induced Corrosion Research Articles

Influence of Climate Change on the Probability of Chloride-Induced Corrosion Initiation for RC Bridge Decks Made of Geopolymer Concrete

Influence of Climate Change on the Probability of Chloride-Induced Corrosion Initiation for RC Bridge Decks Made of Geopolymer Concrete

Influence of Partial Rust Layer on the Passivation and Chloride-Induced Corrosion of Q235b Steel in the Carbonated Simulated Concrete Pore Solution

A partial pre-rusted wire beam electrode (WBE) was designed to study the influence of the rust layer on rebar corrosion in the carbonated simulated concrete pore solution (SCPS). The results show that the passive film generated on the pre-rusted steel area is more fragile than that formed on the fine polished steel area in carbonaceous media. Nevertheless, the pitting corrosion resulting from the presence of chloride ions still tends to occur on the fine polished steel surface due to the local acidification process being hindered by the rust layer. The rust layer could play a more important role than the passive film in inhibiting the initiation of chloride-induced corrosion on rebar. The expansion path of the corrosion product would be blocked by the rust layer, leading to the pit propagating in the fine polished region. Furthermore, the growth of pitting corrosion is greatly accelerated due to the catalytic cathodic reaction of the rust layer.

Monitoring of steel corrosion and cracking in cement paste exposed to combined sulfate–chloride attack with X-ray microtomography

The degradation process of reinforced cement paste exposed to cyclic wetting and drying with a designated salt solution was monitored through X-ray microtomography (μCT). Three exposure conditions (a 3 wt% NaCl solution, a 5 wt% Na2SO4 solution, or a mixed solution of 3 wt% NaCl and 5 wt% Na2SO4) were studied to investigate the potential synergistic effects between chloride and sulfate ions on the deterioration of reinforced cement-based materials. The time-dependent evolution of steel corrosion and cracking of cement paste cover were tracked and visualized, while the volumes of steel loss, corrosion products and cracks were quantified by image analysis. The results indicated that the presence of sulfate ions significantly delayed the initiation of chloride-induced corrosion, but did not seem to greatly affect the corrosion rate once the corrosion occurred. The existence of chloride ions, in turn, also mitigated the damage of cement paste cause by sulfate attack as evidenced by the reduced volumes of cracks. The conventional volume expansion coefficient of corrosion products can be measured by μCT, but this coefficient may not be applicable for modelling the corrosion-induced cracking process when sulfate ions were present. The use of μCT provides a new angle to directly measure the interfacial displacement in reinforced cement paste, which can be used as a valuable input for modelling non-uniform chloride-induced corrosion in the presence of sulfate ions.

Critical chloride threshold values as a function of cement type and steel surface condition

This paper presents the application of a new test protocol developed for determining chloride threshold values initiating corrosion in reinforced concrete. The experimental set-up was described in previous work and is based on the intrinsic localized aspect of chloride-induced corrosion. The test protocol is also based on the concept of anodic control of corrosion initiation, and therefore independent of the area of passive steel. The test method is applied to mortar and concrete formulations with different binders and steel surface conditions. Chloride-binding isotherms were also determined to allow the transition from total to free chlorides. It is found that the test protocol is rapid and applicable to all formulations. The experimental results provide an understanding of the influence of binder type, w/b ratio and porosity on chloride-induced corrosion initiation. As expected, the steel surface condition is shown to have an important overall effect on corrosion initiation.

The effect of the steel–concrete interface on chloride-induced corrosion initiation in concrete: a critical review by RILEM TC 262-SCI

The steel–concrete interface (SCI) is known to influence corrosion of steel in concrete. However, due to the numerous factors affecting the SCI—including steel properties, concrete properties, execution, and exposure conditions—it remains unclear which factors have the most dominant impact on the susceptibility of reinforced concrete to corrosion. In this literature review, prepared by members of RILEM technical committee 262-SCI, an attempt is made to elucidate the effect of numerous SCI characteristics on chloride-induced corrosion initiation of steel in concrete. We use a method to quantify and normalize the effect of individual SCI characteristics based on different literature results, which allows comparing them in a comprehensive context. It is found that the different SCI characteristics have received highly unbalanced research attention. Parameters such as w/b ratio and cement type have been studied most extensively. Interestingly, however, literature consistently indicates that those parameters have merely a moderate effect on the corrosion susceptibility of steel in concrete. Considerably more pronounced effects were identified for (1) steel properties, including metallurgy, presence of mill scale or rust layers, and surface roughness, and (2) the moisture state. Unfortunately, however, these aspects have received comparatively little research attention. Due to their apparently strong influence, future corrosion studies as well as developments towards predicting corrosion initiation in concrete would benefit from considering those aspects. Particularly the working mechanisms related to the moisture conditions in microscopic and macroscopic voids at the SCI is complex and presents major opportunities for further research in corrosion of steel in concrete.

Reinforced Concrete Bridge Deck Model Considering Delayed Exposure to Chlorides

The paper is focused on the model of the effect of delayed chloride exposure on the chloride induced corrosion initiation on ideal reinforced concrete bridge. The Finite Element-based numerical model is applied. The effect of concrete quality is expressed in the form of time dependent diffusion coefficient in order to evaluate the effect of concrete type as well as the effect of aging. The influence of extended chloride exposure on the corrosion initiation is introduced.

Structural and durability assessment of ECC/concrete dual-layer system for tall wind turbine towers

The increasing consumption of wind energy necessitates the development of taller concrete turbines towers with larger installed rotors. A previous study demonstrated that a dual layer system that incorporates protective layers made from engineered cementitious composites (ECC) improves the durability performance of these towers (Jin and Li, 2019 [1]). However, the introduction of ECC layers could affect the tower design due to its low elastic modulus relative to concrete. This paper first studies the structural impacts of the concrete towers with added ECC layers. An iterative method is employed to examine the requirements of strength, deflection, natural frequency and fatigue. The results show that ECC protective layer produces nonconsequential effects on tall concrete towers with less than 4% increase in tower diameter. After satisfying the aforementioned requirements, a durability analysis is conducted to compare the tower designs with and without ECC layers. The results indicate that the application of ECC layers significantly delays the initiation of chloride-induced corrosion of steel reinforcement and prolongs the service life of concrete wind turbine towers by four times. Therefore, this study allays the concerns that ECC protective layers may compromise the tower’s structural performance and confirms its potential application in tall wind turbine towers for improved durability performance.

Anodic Behavior of Steel in Sulfate-Rich Simulated Grout Pore Solution

Recent observations of severe corrosion of post-tensioned tendons in Florida Bridges were associated with segregated grout containing high sulfate ion concentrations (Lau et al, 2013). Generally, the role of sulfates for steel initiation in alkaline environments have not been well elucidated. In 1970, Gouda identified steel corrosion initiation in saturated calcium hydroxide solutions (pH=12.1) with sulfate concentrations greater than 0.2%; however, steel depassivation was not observed in concrete samples with sodium sulfate concentrations as high as 8%. Dehwah et al. 2002 reported that sulfates did not affect the time to chloride-induced corrosion initiation, but the corrosion rate increased with sulfate content. Research by Carsana and Bertolini in 2011 indicated a strong influence of solution pH on the anodic behavior of steel in sulfate solutions. The objective of the work presented here was to identify the role of early presence of sulfate ions on steel corrosion development. The experiments consisted of anodic polarization tests to determine the anodic behavior of steel samples exposed to alkaine solutions with pH 12.6 or 13.3. Those solutions contained sodium sulfate in the range of 0 to 20,000 ppm. The steel samples were preconditioned for 1 day at either the OCP condition or -1VSCE. The intent to pre-condition the sample at OCP was to initially allow any possible passive film growth to occur. The intent to cathodically pre-condition the steel sample at -1VSCE was to maintain the steel at a low corrosion rate but remaining at active corrosion condition prior to polarization. It this way, it was thought any adverse role of sulfate ions to impede stable passive film formation could be identified. Anodic polarization measurements were made initially from -1 VSCE to +500 mVSCE, with a slow scan rate (0.05 mV/s). Experimental results concluded that anodic polarization tests of steel in pH 13 solution with up to admixed 20,000 ppm sodium sulfate did not indicate strong tendency of sulfates to disrupt passive film formation. However, anodic polarization tests in pH 12.6 and admixed >4,000 ppm sulfate solution indicated instability of passive film resulting in pitting corrosion. It was observed that pH and admixed sulfate concentration will affect the stability of the passive layer. In some cases, as shown in Figure 1, anodic current excursions were indicative of localized depassivation. Indeed, some samples showed indications of pit development. This can be in part explained by the mechanism presented by Gavele (1976) where repassivation of pits can occur in the presence of increased sulfate concentrations within pits but may subsequently diffuse out leading to activation/passivation events. This change of a critical passivation sulfate concentration may result in the observed quick shifts in anodic current. More prominently however, the polarization graphs show transition from passive to active corrosion behavior of steel in solution with the admixed presence of 12,000 to 20,000 ppm sodium sulfate with anodic Tafel slope on the order of ~100 mV/dec. Figure 1

A time-variant model of surface chloride build-up for improved service life predictions

Current service life models for predicting the time to chloride-induced corrosion initiation of steel reinforcement in concrete structures are based on a hypothesized surface chloride concentration, Cs, as a boundary condition. This is either assumed to be constant or varies with time, generally disregarding other factors that influence Cs. For example, Fickian models use a constant Cs and existing time-variant models assume Cs is only a function of time. In this paper, an improved time-variant Cs model is hypothesized using general physical concepts and is then validated by an empirical study. The proposed model, as opposed to the existing time-variant models, not only accounts for the variability of Cs with exposure time but also incorporates the effects of time to exposure and the effects of the concentration of chlorides in the exposure environment. The model assumes that Cs is sigmoidal in shape with an asymptote that is a function of the concentration of chlorides in the environment. The input variables for the proposed model were selected based on best subset sampling analysis on the results of the experimental work to determine the influence of water-to-cement ratio, time to exposure, the concentration of chlorides in the exposure environment, and exposure time on Cs. The accuracy of the proposed model is assessed versus existing time-variant Cs models and the results indicate that the proposed model better predicts the Cs in concrete exposed to chlorides. Moreover, results of service life predictions using the proposed model show that the proposed model yields more accurate results, better protecting owners from financial and engineering risks.

A short-term test method to determine the chloride threshold of steel–cementitious systems with corrosion inhibiting admixtures

Now-a-days, multiple types of corrosion inhibiting admixtures (CIAs) are being used to enhance the chloride threshold (Clth) of steel–cementitious systems. However, due to the application of external potential to drive chlorides, some existing short-term test methods are not suitable to assess the Clth of S–C systems with CIAs containing anions. This paper presents the development of a Modified Accelerated Chloride Threshold (mACT) test to determine the Clth for S–C systems with CIAs. The test specimens consisted of a mortar cylinder with an embedded steel piece and electrodes forming a 3-electrode corrosion cell. The specimens were exposed to chloride solution and the linear polarization resistance tests were conducted every 3.5 days. The corrosion initiation was detected using statistical analysis of the repeated R p measurements. After corrosion initiation, the chloride content in mortar adjacent to the embedded steel piece was determined and defined as Clth. The time required to complete mACT test for an S–C system with CIAs is about 120 days. The Clth of eight specimens each with S–C system containing (i) without inhibitor, (ii) anodic inhibitor [calcium nitrite] and (iii) bipolar inhibitor [both calcium nitrite and amino alcohol] were determined. Both anodic and bipolar CIAs showed enhanced corrosion resistance. Also, the bipolar inhibitor performed better than anodic inhibitor. It was concluded that the use of CIAs could significantly delay the initiation of chloride-induced corrosion. The mACT test can be used to determine the Clth and estimate the service life during the planning and design stages of a project and help select durable materials.

Correlation between chloride-induced corrosion initiation and time to cover cracking in RC Structures

Numerical value of correlation between effective parameters in the strength of a structure is as important as its stochastic properties in determining the safety of the structure. In this article investigation is made about the variation of coefficient of correlation between effective parameters in corrosion initiation time of reinforcement and the time of concrete cover cracking in reinforced concrete (RC) structures. Presence of many parameters and also error in measurement of these parameters results in uncertainty in determination of corrosion initiation and the time to crack initiation. In this paper, assuming diffusion process as chloride ingress mechanism in RC structures and considering random properties of effective parameters in this model, correlation between input parameters and predicted time to corrosion is calculated using the Monte Carlo (MC) random sampling. Results show the linear correlation between corrosion initiation time and effective input parameters increases with increasing uncertainty in the input parameters. Diffusion coefficient, concrete cover, surface chloride concentration and threshold chloride concentration have the highest correlation coefficient respectively. Also the uncertainty in the concrete cover has the greatest impact on the coefficient of correlation of corrosion initiation time and the time of crack initiation due to the corrosion phenomenon

Numerical Simulation of Chloride-Induced Corrosion Initiation in Reinforced Concrete Structures with Cracks

AbstractSteel corrosion is a major problem with concrete structures. For cracked concrete structures exposed to chloride environment, chloride diffusivity through the crack (Dcr) is higher than that through the concrete matrix (Do), and therefore, the corrosion will occur at an earlier time. In this study, finite-element analysis is performed to study the process of chloride diffusion through cracks. For various values of Do, Dcr, and crack width, the chloride-concentration distribution is determined. Based on the simulation results, the empirical equation for an equivalent diffusion coefficient (Deq) will be derived, which can be used directly in the solution of the one-dimensional diffusion equation to calculate the predicted chloride profile, the corrosion-initiation time, and penetration of corrosion front. The study will provide a convenient but accurate approach for predicting the chloride diffusion, including the corrosion initiation, under real-world situations where cracks are present in a concre...

Probabilistic Analysis of Corrosion of Reinforcement in RC Bridges Considering Fuzziness and Randomness

AbstractA general methodology for probabilistic corrosion analysis of reinforcing bar in RC bridges is proposed in this paper. Uncertainties due to limited number of experimental data, incomplete inspection information, as well as the intrinsic randomness of random variables affect the prognostics of corrosion damage. The proposed study includes both fuzziness and randomness to consider different types of uncertainties. First, the chloride-induced corrosion initiation and propagation model are developed for reinforcement in RC bridge. The relationship between the area corrosion rate and the yield strength degradation is proposed on the basis of experimental investigation from accelerated corrosion testing. Following this, the randomness and fuzziness are included using fuzzy random variables to consider the uncertainties of the degradation under corrosive environments. The probabilistic modeling of the mean and the SD of reinforcement yield strength is discussed in detail. Finally, the proposed methodolog...

Initiation of chloride-induced corrosion of steel in concrete: role of the interfacial zone

This paper provides a brief review of research aimed at characterising the steel–concrete interfacial zone (SCIZ) and its influence on the susceptibility of the metal to pitting corrosion when concrete is exposed to environments that cause ingress of chloride ions accompanied by leaching of hydroxyl ions. For reinforced concrete made from Portland cements, exposed to aqueous solutions of sodium chloride, the buffering effect of solid calcium hydroxide (portlandite) at pH ∼12.6 has been shown to restrain the gradual decline in the hydroxyl ion concentration of the concrete pore solution phase at depths corresponding to the embedded steel. When the concrete is produced under laboratory conditions that are carefully controlled to exclude macroscopic defects from the SCIZ and the steel is cleaned before being embedded, this can lead to observed chloride threshold levels being consistently greater than 1% chloride by mass of cement. The buffering action of cement hydration products formed in the SCIZ is believed to be partly responsible for this high tolerance to chloride-induced corrosion because it counters the generation of ‘anodic acidity’ that is a necessary condition for stable growth of pits to occur. Translating this behaviour of laboratory specimens to the performance of full-scale reinforced concrete structures has often proved difficult in the past and there is a need for further research in this area, particularly in relation to the role of non-traditional cements.

Corrosion inhibitors in concrete: Part III. Effect on time to chloride-induced corrosion initiation and subsequent corrosion rates of steel in mortar

The effectiveness of four commercially available corrosion inhibitors for use in cement-based materials was assessed in mortar exposed to chloride solution. Although, in a parallel study of steel in synthetic pore solutions, the inhibitors were observed to be ineffective in increasing the chloride threshold value of reinforcing steel exposed to chlorides, in the present study all inhibitors were found to delay the onset of corrosion, but to differing degrees. Moreover, in agreement with the parallel study, the inhibitors were found to have little detectable effect on the corrosion rate of the embedded steel once active corrosion had been initiated. This study confirmed that calcium nitrite inhibitors delay the onset of corrosion but raises questions regarding the mechanism of inhibition.