Initiation Of Reinforcement Corrosion Research Articles

6-Methoxyquinoline immobilized nylon sensor for monitoring chloride concentration in reinforced concrete

An excess in the threshold concentration of chloride in concrete leads to the initiation of reinforcement corrosion, which in turn results in a reduction in the load-bearing capacity of reinforced concrete (RC) structures. Accordingly, the chloride concentration of RC is periodically investigated via a destructive method, but this process is time-consuming, labor-intensive, and costly. In order to overcome the limitations, this study sought to develop an optical chloride sensor that can be used in structural health monitoring. To this end, nylon was functionalized using formaldehyde and epichlorohydrine, after which 6-methoxy quinoline was covalently immobilized to manufacture a sensor. The developed sensor was found to be capable of measuring chloride concentrations (0–5,000 mM) and exhibited rapid responsiveness and reversibility. In addition, the developed sensor also showed a stable response even when exposed to the pH 13.4 environment for three months, and it could detect changes in chloride concentration even inside the mortar.

Effect of coarse calcareous aggregates on corrosion of steel reinforcement in marine concretes

Finely ground limestone, perhaps as part cement replacement, has been shown to reduce concrete permeability and enhance strength. Whether this holds also for coarse limestone aggregates is of both practical and environmental interest, particularly the effect on corrosion of steel reinforcement. This is confirmed herein with exposure tests over 14 years for a range of concretes exposed to a high chloride environment. Importantly, these concretes also showed delayed initiation of reinforcement corrosion and lower long-term corrosion losses compared with similar concretes made with coarse igneous or siliceous aggregates. The observations are attributed to enhanced bonding between cement-hydration products and the limestone aggregate surfaces. These findings are important both for reducing environmental impacts and greenhouse gasses and for extending the durability of reinforced concrete structures.

Review and analysis of RC bridge half-joints strengthening techniques

In the past, the extensive use of the Gerber scheme in the construction of existing bridges has been justified by the advantages in terms of reduced stresses of the statically determined scheme and rapid execution. On the other hand, the presence of junction elements at the ends of the beams has over time led to a series of issues, especially related to their durability. In fact, the half-joints’ geometric configuration leads to the accumulation of degradation due to platform water seepage, resulting in the initiation of reinforcement corrosion, especially in the presence of chlorides derived from de-icing salts used in the winter season. Furthermore, these elements have been designed for lower loads than those specified in current regulations, and therefore, they may be in critical conditions where the strength reduction, due to existing degradation, can lead to failure. For these reasons, local repairs and/or strengthening interventions are necessary to ensure adequate levels of safety. Within this study, the topic of reinforcing half-joints is addressed, first by describing the currently available intervention techniques in the literature, and then by deepening an intervention technique based on the use of external post-tensioned bars, applied to a case study bridge through nonlinear numerical simulations. These analyses allow quantifying the performance improvements of this technique under both service conditions and ultimate loads, considering various parameters, including the pre-stress value applied to the external tendons and different scenarios of chloride-induced corrosion.

Two-stage deterioration model updating of RC structures in marine environment using long-term field inspection data

For the deterioration of reinforcement concrete (RC) structures in marine environment at various stages, models on chloride penetration, crack initiation and crack propagation have been proposed and studied in literature. However, to be applied to real existing structures, these models, usually associated with significant uncertainties, have to be calibrated and modified with long-term in-situ inspection data. Toward this goal, this paper develops a two-stage updating framework to incorporate measured data into existing models to achieve a more realistic modeling of deterioration process. To improve the computation efficiency, the framework can be integrated with simple rejection sampling and other advanced sampling techniques such as the modified sequential adaptive importance sampling (SAIS). A real case study of high-pile wharf structure in Guangzhou Port is carried out to demonstrate the updating effect of the proposed framework. The observed data of chloride content profile and steel bar corrosion depths from one field inspection are used to construct the likelihood functions in the two updating stages. Comparison between the results of the first and second updating stages is made, and the sensitivities of different parameters to the data are analyzed, subsequently the year of reinforcement corrosion initiation and the evolution of corrosion depth are inferred using these results. At last, the data from an early inspection are also incorporated to investigate the impact of two inspections on updating effects.

Concrete Alkali–Aggregate-Reactivity-Induced Steel Reinforcement Corrosion

The alkali–aggregate reactivity (AAR) of concrete, long known for mass concrete, can also induce corrosion of steel in reinforced concrete structures. Several examples are given for which the origin of observed reinforcement corrosion and loss of concrete cover originally was attributed to chloride-induced or to carbonation-induced reinforcement corrosion. Critical reviews of these cases, using available information, suggest that, more likely, the observed crack patterns and concrete deterioration are the result of long-term AAR-induced concrete matrix expansion and loss of concrete strength and that these effects occurred prior to the eventual initiation of reinforcement corrosion. This proposition is supported by finite element and other stress analyses of various concrete–steel ensembles. They show that concrete expansion produces tensile stresses localised at and near exterior concrete surfaces or relative to the reinforcement. The locations of high-stress and -strain zones so produced correlate with field observations of long-term concrete cracking and delamination. The present interpretations highlight that AAR may be a significant contributor to initiation and subsequent long-term development of reinforcement corrosion in structurally reinforced concretes.

Engineering vulnerability evaluation of building structures in coastal areas considering the effects of corrosion

Chloride-induced corrosion is an important factor that affects the durability of building structures in coastal areas; it causes serious deterioration of reinforced concrete (RC) structures and leads to structural failure. However, chloride-induced corrosion is a slow process which spans the whole service life of building structures, and many factors can affect their service life, such as location, structural design, and drug management. This paper aims to predict the service life of building structures in terms of chloride-induced corrosion and through the concept of engineering vulnerability. It first investigates the model of corrosion initiation of reinforcement, along with the consequent concrete cover cracking. Second, according to the characteristics of building structure and corrosion, it determines an evaluation index system of engineering vulnerability and establishes an evaluation method of engineering vulnerability, considering that corrosion is based on the AHP method and fuzzy comprehensive evaluation. Finally, using a case study of a pharmaceutical factory structure in a coastal city, this study verifies the feasibility of the assessment method considering corrosion effects.

Carbonation, Neutralization, and Reinforcement Corrosion for Concrete in Long-Term Atmospheric Exposures

This paper presents observations of carbonation and alkali loss for well-compacted reinforced concrete columns from the exterior and interior of a 60-y-old in-land building. Calcium carbonate formation was detected only in the outermost 10 mm to 15 mm. However, alkali loss and concrete pH reduction extended much further inward but reinforcement corrosion was not observed. Theoretical thermodynamic conditions dictate that corrosion initiation of reinforcement can result only from the long-term dissolution and loss by leaching of calcium hydroxide from the concrete matrix. These appear rate-limited by the barrier effect of carbonated concrete. These interpretations provide a new model for “carbonation” initiation of reinforcement corrosion. The results also show the potential for concretes to absorb atmospheric carbon dioxide (greenhouse gases) for an extended time without significant risk of reinforcement corrosion.

Study of Effect of Reference Time of Chloride Diffusion Coefficient in Numerical Modelling of Durability of Concrete

The results of numerical calculations on the resistance of the reinforced concrete bridge deck to chlorides are compared with a different approach to the diffusion coefficient of the input parameter, and presented. The aim is to point out the necessity of a correct model adjustment in the case of using diffusion parameters obtained differently at different measurement times. The diffusion parameter, as a typical concrete material constant, was derived from electrical resistivity measurements and using the least-squares method from a direct chloride test. Due to the different times of obtaining the concrete parameters, a control calculation was performed, which showed that the numerical model for calculating the initiation of reinforcement corrosion in chloride-exposed reinforced concrete requires the application of not only a suitable diffusion parameter but also an adequate reference time. The article points out the need to use an adequate reference time introduced in the numerical calculation of the durability of reinforced concrete with respect to aggressive substances. The results show that the most appropriate reference time value is derived from the average measurement time related to the lifetime of the concrete.

Corrosion-Fatigue Life Prediction of the U-Shaped Beam in Urban Rail Transit under a Chloride Attack Environment.

The coupled effect of the chloride attack environment and train load seriously affects the safety and durability of urban rail transit viaducts and dramatically reduces their service life. In this research, a corrosion-fatigue life prediction model of the prestressed concrete (PC) beam under the coupled effect of the chloride attack environment and train load was developed. This proposed model was illustrated by a 30 m-span PC U-shaped beam in an urban rail transit viaduct. The competitive relationship between concrete fatigue cracking time, non-prestressed reinforcement corrosion initiation time, and concrete corrosion-induced cracking time was discussed. The effects of train frequency, the chloride attack environment grade, and the environmental temperature and relative humidity were investigated on corrosion-fatigue life. Results indicate that train frequency, the chloride attack environment grade, and the environmental temperature can reduce the corrosion-fatigue life of a U-shaped beam by up to 30.0%, 50.7%, and 21.5%, respectively. A coupled chloride attack environment and train frequency can reduce the corrosion-fatigue life by up to 61.2%. Distinct from the environmental temperature, the change of relative humidity has little effect on the corrosion-fatigue life of the U-shaped beam.

Effect of Sunlight/Ultraviolet Exposure on the Corrosion of Fusion-Bonded Epoxy (FBE) Coated Steel Rebars in Concrete

Currently, highway/railway bridges are designed for the service life of more than 100 y. In such reinforced concrete structures, fusion-bonded epoxy (FBE) coated steel rebars are being used in anticipation of delayed initiation of reinforcement corrosion. However, the FBE steel rebars get exposed to sunlight/ultraviolet rays during prolonged storage and delayed/staged construction. This paper presents microanalytical and electrochemical data (Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersion x-ray diffraction, and electrochemical impedance spectroscopy) and shows the adverse effects of sunlight/UV exposure on the corrosion resistance of FBE-coated steel reinforcement in concrete construction. Based on tests on steel-mortar specimens, the mechanisms of UV-induced chemical changes, shrinkage, and cracking of FBE coating, and the resulting steel corrosion mechanisms are proposed. Also, the adverse effects of sunlight/UV exposure on chloride threshold and reduction in the service life of FBE-coated steel in cementitious systems are presented. The paper recommends to minimize the exposure of FBE-coated steel rebars to sunlight/UV rays to less than one month.

Long-Term Durability of Marine Reinforced Concrete Structures

The sustainability of reinforced concrete is critical, particularly for structures exposed to marine environments. Chlorides are implicated in causing or accelerating reinforcement corrosion and potentially earlier expensive repairs, yet there are many older reinforced concrete structures in good condition for many decades despite very high chloride levels at the reinforcement. The reasons for this are reviewed briefly, together with recent experimental work that better defines the role of chlorides. One is initiation of reinforcement corrosion but only through localized pitting at air-voids in concrete at the interface with the steel reinforcement. These tend to be small or negligible for high quality well-compacted concretes. The other role for chlorides has been shown, in experimental work, to accelerate the long-term loss of concrete alkali material. On the other hand, a review of practical experience shows that what has been termed chloride-induced reinforcement corrosion often is not that at all, but is the end-product of factors that impair the protective nature of the concrete. As reviewed herein, these include poor compaction, physical damage to concrete cover, concrete shrinkage, and alkali-aggregate reactions. The various observations presented are important for the proper understanding, analysis, and design of durable reinforced concrete structures exposed to chloride-rich environments.

Probability distribution and influence factors on corrosion initiation of reinforcing steel induced by chloride

Chloride-induced corrosion of steel in reinforced concrete structures is one of the major causes of their deterioration over time. Chlorides from de-icing salts or marine breeze penetrate through the concrete cover and break down the natural protective oxide layer formed around the reinforcements by the strong alkalinity of pore solution. As a matter of fact, the free chloride in concrete could not transport through reinforcing steel and accumulated at front point of reinforcing steel rapidly which made reinforcement corrosion initiation earlier. Therefore, the current studies on corrosion initiation might be hazardous without considering the obstruction action of reinforcing steel. In this paper, the Fick’s second law was used to describe the free chloride concentration evolution in concrete and obstruction action of reinforcing steel was considered. The influences of the variability on boundary chloride concentration, thickness of concrete cover, and chloride diffusion coefficient on cumulative distribution of corrosion initiation of reinforcing steel were studied thoroughly. The obstruction of reinforcing steel gave much influence on corrosion initiation, especially for thinner concrete cover, higher concrete strength, and higher environmental temperature.

Randomness of bidirectional chloride corrosion of sluice gate and time to corrosion initiation of reinforcement in a strong tidal environment

Six concrete core samples in the sluice gate exposed to a strong tidal environment have been drilled. Firstly, the chloride concentration with 1 mm interval was measured and the bidirectional chloride diffusion coefficient was fitted by Fick's second law. Besides, based on the probabilistic method, the randomness of each parameter which influences the time to corrosion initiation of reinforcement (including depth of concrete cover, peak values of chloride concentration, convection depth, chloride diffusion coefficient and critical chloride concentration) has been determined. And then, the Monte Carlo simulation method was used to analyze the probability of the time to corrosion initiation. Finally, sensitivity analysis was adopted to identify the main influence factor of service life prediction. Results indicated that the chloride diffusivity at positive side of gate is stronger than that at back surface. The time to corrosion initiation of reinforcement follows a normal distribution and the predicted mean value is consistent well with the actual measured value, confirming that in the strong tidal environment, the critical chloride content of 0.16%–0.18% by weight of concrete can be substituted into the service life prediction model. Besides, the depth of concrete cover is identified as the uppermost parameter which influences the time to corrosion initiation, followed by critical chloride concentration, peak value of chloride concentration and convection depth.

Influence of temperature and relative humidity variations on non-uniform corrosion of reinforced concrete

Response of reinforced concrete structures under chloride induced non-uniform corrosion considering the effect of varying temperature and relative humidity (T-RH) in the environment was studied. Chloride concentration around the reinforcing bars was determined under varying T-RH conditions. The obtained chloride concentrations were then used to model the formation of macro-cell and micro-cell around the reinforcing bars under the same varying environment. The study was applied to two cases; Case 1- to understand the effect of considering T-RH variations on corrosion initiation and corrosion propagation, Case 2: to study in detail the effect of considering real climatic variations on corrosion initiation and corrosion propagation phases. Considering T-RH variations in the environment have a considerable effect on initiation of corrosion, corrosion rate and steel section loss. This effect can further be extended to service life models incorporating concrete damage under different varying environment. Also, use of different temporal schemes i.e., average daily, weekly and monthly values for real exposure data, affects prediction of reinforcement corrosion initiation and propagation.

Randomness of critical chloride concentration of reinforcement corrosion in reinforced concrete flexural members in a tidal environment

In this paper, the free chloride concentrations at different depths and the corrosion rates of tensile reinforcements in tensile concrete zone of reinforced concrete (RC) beams under flexural loads in a simulated and natural tidal environment are tested. By considering the influence of time-dependent reinforcement corrosion, the time to corrosion initiation and critical chloride concentration (Ccr) in tensile concrete zone of RC beams under different exposure conditions can be obtained. The probability distribution forms of Ccr of tensile reinforcement corrosion initiation subjected to different exposure environments and flexural load levels have been compared by using the Kolmogorov-Smirnov (KS) hypothesis test method. Results indicate that the values of Ccr from the field exposure tests are lower than those obtained from the artificial simulation experiments. In a natural tidal environment, the chloride transport in concrete shows a stronger randomness, and the effect of flexural loads on the probability distribution forms of Ccr are also more significant. Moreover, under the flexural loads, Ccr in the simulated and natural tidal environment obeys a Gumbel distribution with mean value of 0.382% by weight of concrete and a Normal distribution with mean value of 0.328% by weight of concrete, respectively. However, without flexural loads, the values of Ccr in the simulated and natural tidal environment are found to follow a Gumbel distribution with mean value of 0.572% by weight of concrete and a Log-normal distribution with mean value of 0.356% by weight of concrete, respectively.

The effect of hydrophobic (silane) treatment on concrete durability characteristics

Hydrophobic (silane) impregnation represents a cost-effective way to increase the durability of concrete structures in cases where insufficient design cover quality and depth have been achieved. The water repellent product lines the internal capillary pore structure and provides a water-repellent concrete surface. Thus, the risk of reinforcement corrosion initiation and subsequent deterioration can be reduced as the ingress of water-dissolved aggressive species (chlorides) is minimised or prevented. The purpose of this study was to investigate the effect of silane impregnation on durability indicators, including penetrability tests and chloride ingress (bulk diffusion). The results indicate that silane impregnation reduces capillary absorption and conductivity of chloride ions. Similarly, chloride ingress in the treated concrete mixes was suppressed.

Chloride-Induced Corrosion of Steel in Concrete: An Overview on Chloride Diffusion and Prediction of Corrosion Initiation Time

Initiation of corrosion of steel in reinforced concrete (RC) structures subjected to chloride exposures mainly depends on coefficient of chloride diffusion, Dc, of concrete. Therefore, Dc is one of the key parameters needed for prediction of initiation of reinforcement corrosion. Fick’s second law of diffusion has been used for long time to derive the models for chloride diffusion in concrete. However, such models do not include the effects of various significant factors such as chloride binding by the cement, multidirectional ingress of chloride, and variation of Dc with time due to change in the microstructure of concrete during early period of cement hydration. In this paper, a review is presented on the development of chloride diffusion models by incorporating the effects of the key factors into basic Fick’s second law of diffusion. Determination of corrosion initiation time using chloride diffusion models is also explained. The information presented in this paper would be useful for accurate prediction of corrosion initiation time of RC structures subjected to chloride exposure, considering the effects of chloride binding, effect of time and space on Dc, and interaction effect of multidirectional chloride ingress.

The effect of carbonate and sulfate ions on chloride threshold level of reinforcement corrosion in mortar with/without fly ash

The aim of the study is to evaluate the effect of carbonate and sulfate ions on chloride threshold level of reinforcement corrosion in mortar with/without fly ash. The initiation of active corrosion for the reinforcement was detected by half-cell potential and electrochemical impedance spectra methods. The free chloride or total chloride by mass of binder was used to express the chloride threshold level. The results indicate that the presence of carbonate ions in the chloride solution shortened the time to initiation of reinforcement corrosion and decreased chloride threshold level in both the Portland cement mortar and fly ash mortar specimens. And compared with the single chloride solution, the concomitant presence of chloride ions and sulfate ions decreased the chloride threshold level, but did not influence the time to initiation of chloride-induced reinforcement corrosion. Besides, although the presence of fly ash decreased the chloride threshold level, it delayed the time to initiation of reinforcement corrosion.

Durability assessment of concrete bridge deck considering waterproof membrane and epoxy-coated reinforcement

Summary The effect of waterproof membrane and steel reinforcement protection on the concrete bridge deck is modeled. The attention is paid to the durability prediction related to steel reinforcement corrosion initiation based on the chloride penetration. Thus 2-D finite element chloride ingress model is applied. The transient finite element model serves to solve Fick's second diffusion law using the computer tool compatible with the Matlab environment. The model focuses on the transport of chloride ions through a reinforced concrete bridge deck with and without the effect of waterproof membrane and on an estimate of the concentration of chlorides at the reinforcement level or in places with damage to the epoxide coating of the reinforcement. The model allows the incorporation of damage to the waterproof insulation under the asphalt coating. The time to chloride induced onset of corrosion is predicted and results are compared. The effect of water proof membrane reinforcement protection strategy typical for Central Europe and epoxy-coating protection widely used in North-Western United States is evaluated.

The effect of industrial coating type acrylic and epoxy resins on the durability of concrete subjected to accelerated carbonation

The effect of industrial coating type acrylic and epoxy resin on the durability of concrete subjected to accelerated carbonation. Concrete carbonation is an important factor that affects reinforced concrete durability. One of the major consequences of this phenomenon is the initiation of reinforcement corrosion; reinforcement loses their protections initially protected by the basic environment nature of concrete. The migration of CO2 takes place in the concrete through the gas phase when the concrete is not completely saturated and through the liquid phase in the form of carbonate ions. The main objective of this work is to minimize the carbonation depth in concrete elements in order to increase the service life of reinforced concrete structures by applying two types of coatings on the concrete surface: acrylic coating in aqueous phase and a epoxy resin coating produced by the Algerian industry. For this reason, we are interested in formulating binary and ternary concrete compositions to prepare prismatic test specimens of 7 cm × 7 cm × 28 cm. For each composition, two types of coatings, acrylic and epoxy resin were applied; other test specimens have been made to follow the evolution of the mass during the test using enclosure accelerated carbonation. The results show clearly the beneficial contribution of the epoxy resin coating in decreasing the carbonation depth compared with the acrylic coating. In addition, the binary composition of the concrete presented a good advantage on carbonation durability.