Chloride-induced Reinforcement Corrosion Research Articles

Synthesis of CaFeAl layered double hydroxides 2D nanosheets and the adsorption behaviour of chloride in simulated marine concrete

Chloride-induced reinforcement corrosion in marine concrete structures adversely impacts its durability, which leads to the decrease of the actual service life of concrete. Three kinds of layered double hydroxides (LDHs), CaFe–NO3 LDHs (LDHs-CF), CaAl–NO3 LDHs (LDHs-CA) and CaFeAl–NO3 LDHs (LDHs-CFA), were synthesized to bind chloride. The results showed that all of the synthetized LDHs could effectively adsorb chloride from simulated concrete pore solutions (SCPSs) and artificial seawater (ASW) through the surface adsorption and ion exchange. The maximum chloride adsorption capacity of the LDHs-CFA was 3.18 mmol g−1. The adsorption process could be described by the Langmuir isotherm and pseudo-second-order kinetic models. For the chloride desorption experiments, the chloride desorption rate of the LDHs-CF (29.20%) and LDHs-CFA (39.31%) were lower than that of the LDHs-CA (47.45%), because the presence of Fe3+ in LDHs suppressed the concentration of dissolved metals, and a crystal transformation occurred to form 3CaO·Fe2O3·0.5CaSO4·0.5CaCl2·10H2O, exhibiting excellent stability for LDHs-CF and LDHs-CFA. In conclusion, LDHs show excellent chloride binding behaviour, which makes it promising to achieve the goal of high efficiency and stability of chloride binding for marine concrete by LDHs.

Chloride-induced reinforcement corrosion in cracked concrete: the influence of time of wetness on corrosion propagation

ABSTRACT Literature 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.

A novel green reinforcement corrosion inhibitor extracted from waste Platanus acerifolia leaves

In this study, an environmentally friendly corrosion inhibitor was prepared from waste Platanus acerifolia leaves (PAL) for reducing the chloride-induced reinforcement corrosion. Four extraction methods were employed in the preparation work. The inhibiting performances of the four types of PAL extracts and two benchmark inhibitors were studied by various electrochemical measures. After that, the optimal group was obtained (extract #4, prepared by an ultrasonic-assisted alkali-pretreated ethyl extraction method) and analyzed with ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) to determine its main chemical constituents. The inhibition/adsorption mechanism was analyzed via X-ray photoelectron spectroscopy (XPS) as well as the quantum mechanics and molecular dynamics simulations. According to the results of electrochemical experiments, the PAL extract is an excellent mixed type inhibitor that restrains both the cathodic and anodic reactions. UPLC-MS results provided the existence evidence of more than ten kinds of flavonoids or oligopeptides in the PAL extract. XPS and simulation results indicated that these flavonoids/oligopeptides exerted their inhibition effect by generating a nitrogen-carbon film on the steel substrate via the donor–acceptor interactions of reactive sites.

Using X-ray microtomography to study the initiation of chloride-induced reinforcement corrosion in cracked concrete

Corrosion is the main cause of premature degradation of reinforced concrete structures. In particular, the mechanisms of chloride-induced corrosion in cracked structures are not fully elucidated. The aim of this study is to investigate by X-ray tomographic imaging the initiation and propagation of chloride-induced corrosion in cracked concrete. On reinforced prismatic cracked specimens exposed to seawater spray-drying cycles, the approach consists in characterizing in a non-destructive way the crack geometry, corroded steel volume and corrosion products migrating in the cementitious matrix and crack, as a function of time. Sub-volume scans and difference images allow a study of the first stage of chloride-induced corrosion in cracked concrete with respect to the number of spraying cycles, geometry and crack opening. The volume of steel consumed measured by 3D imaging is validated against destructive measurements, and it is shown that insights about the phenomenology of pitting (depth, displacement of corrosion products, densification, crack clogging…) can be obtained.

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.

Experimental and numerical investigation of chloride-induced reinforcement corrosion and mortar cover cracking

To investigate the time-varying progress of chloride-induced reinforcement corrosion and cover cracking, the authors embedded mortar specimens with side-located rebars and corner-located rebars. These specimens were exposed to a chloride contaminated environment to accelerate the corrosion process. This study focuses on the chloride ions penetration, corrosion products accumulation and surface crack propagation, and proves that the circumferential corrosion profile of steel bars is time-dependent. Considering the interaction between corrosion propagation and crack growth, a numerical model was developed by combining chloride diffusion law and electrochemical theory. The comparison between the predicted and measured evolution of rust layer distribution and surface crack width indicates that the modified model can simulate the process of chloride-induced rebar corrosion and mortar cover cracking reasonably. Finally, the simulation of mortar cover cracking induced by different corrosion profiles demonstrate that earlier cracking of mortar cover and faster development of surface cracks can be observed under the time-varying non-uniform corrosion condition. In addition, wedge-shaped cracks are more prone to occur as cover thickness decreases, and the delaying effect on the surface cracking time is more noticeable with the increase of interface transition zone (ITZ) thickness when using the authors’ time-dependent non-uniform corrosion model.

Corrosion-induced shear performance degradation of reinforced concrete beams

Chloride-induced corrosion of reinforcement has been recognized as one of the most predominant causes of structural degradation. In this paper, experimental and numerical investigation was conducted to study the degraded shear performance of reinforced concrete beam. The corrosion of reinforcements, crack patterns, and structural behaviors of corroded specimens with various corrosion levels accelerated by the impressed current method were analyzed. The test results indicated that the corrosion-induced crack patterns have a close relationship with the level of reinforcement corrosion. Moreover, an obvious degradation of shear performance of corroded RC beams in terms of initial stiffness, cracking loads, ultimate bearing capacity, post-peak behavior, and energy dissipation capacity was observed, which became more pronounced as the corrosion level increased. When a severe corrosion level (ηa ≥ 12%) was encountered, the failure mode could even be changed from the shear-compression failure into a much more brittle diagonal splitting failure. In parallel, to numerically simulate the propagation of the main diagonal crack faithfully, the extended finite element method (XFEM) specified with an exponential softening traction-separation relationship was adopted. Moreover, to investigate the effect of corrosion-induced bond degradation, a user-defined element (UEL) was also developed to represent the interfacial bond response. The reasonable agreement between the numerical simulation and experimental results proved the feasibility of the proposed approach.

Proračun prodora klorida u beton

Na armiranobetonskim konstrukcijama izloženim agresivnom okolišu često nastaju oštećenja uslijed korozije armature izazvane kloridnim ionima. Oštećenja nastaju u obliku pukotina i odlamanja zaštitnog sloja betona uslijed bubrenja produkata korozije, što nepovoljno utječe na nosivost i trajnost konstrukcije. Povrh toga, površina poprečnog presjeka armature smanjuje se istovremeno s procesom degradacije betona. No, oštećenja se javljaju neposredno nakon depasivacije čelika uslijed kritične koncentracije kloridnih iona u blizini armature. Vrijeme koje je potrebno da kritična koncentracija kloridnih iona prodre do armature naziva se faza inicijacije, a osnovni cilj ovog rada je procjena njezinog trajanja. Trajanje faze inicijacije moguće je predvidjeti ukoliko se u obzir uzmu transportni procesi koji se odvijaju kroz zaštitni sloj betona. Najvažniji fizikalni procesi vezani uz fazu inicijacije su transport kapilarne vode, kloridnih iona te topline. Stoga je u okviru ovog rada razvijen 2D numerički model pomoću metode konačnih razlika, koji simulira navedene transportne procese. Primjena modela pokazana je na numeričkom primjeru u kojem je kvadratni poprečni presjek armiranobetonskog stupa izložen agresivnim morskim uvjetima. Proračun je proveden kako bi se istražio utjecaj širine pukotina na trajanje faze inicijacije. Numerički rezultati pokazuju da raspucalost zaštitnog sloja betona značajno smanjuje trajanje faze inicijacije, a samim time i uporabni vijek konstrukcija.

Semi-empirical prediction model of chloride-induced corrosion rate in uncracked reinforced concrete exposed to a marine environment

Chloride-induced corrosion of reinforcement in uncracked concrete was simulated by a test method combining an artificial-natural diffusion test (ANDT) and an accelerated chloride migration test (ACMT). The electrochemical kinetics of the corrosion process were evaluated by linear polarization resistance (LPR), weak polarization technology (WPT) and Tafel test, which indicates that the corrosion process is mainly under anodic control. Based on the hypothesis of anodic diffusion control, a semi-empirical prediction model for the corrosion rate in reinforced concrete has been proposed. This model reflects the effects of concrete resistivity, chloride content, chloride diffusion coefficient and concrete cover thickness on the corrosion rate. It also provides a non-destructive method to evaluate the corrosion rate of steel bars in uncracked concrete, which makes it convenient and available to the engineering community.

Evaluation and comparison of traditional methods and Electron Probe Micro Analysis (EPMA) to determine the chloride ingress perpendicular to cracks in self-healing concrete

The appearance of cracks in reinforced concrete structures accelerates the penetration of aggressive substances such as chloride ions into the concrete matrix. This leads to durability problems due to the accelerated onset of chloride induced reinforcement corrosion. Chloride ions penetrate the concrete matrix along the crack tip and also along the crack walls in a direction perpendicular to the crack. This research focused on the application of autonomous crack healing by encapsulated polyurethane as a method to reduce (perpendicular-to-crack) chloride ingress. Three investigation methods were applied: profiling by grinding followed by potentiometric titration, visualization of the chloride penetration front using AgNO3 and Electron Probe Micro Analysis (EPMA).The proposed healing mechanism proved to be efficient to reduce the chloride concentrations in the direct vicinity of the crack and to cause a reduction of the perpendicular-to-crack chloride penetration. Furthermore, the results found by the different evaluation methods were comparable to each other. In this sense, the data obtained by EPMA contained most of the information that was obtained by the AgNO3 spray method and the chloride profiling together. This proves that EPMA is a powerful technique for analyzing the chloride penetration in concrete and a valuable tool to determine the crack healing efficiency of self-healing concrete.

Parallel Finite Element Model for Multispecies Transport in Nonsaturated Concrete Structures.

The chloride-induced corrosion of steel reinforcement embedded in concrete is undoubtedly one of the most important durability problems of reinforced concrete structures. The chloride ions as well as other ionic species (Na+, Ca2+, K+, OH−) come from various deicing salts and they are transported from the environment into concrete. To investigate the transport mechanism of the multispecies, complex scientific methods and accurate mathematical models are needed. The purpose of this study is to develop a more robust mathematical model and better computational technique to characterize the coupled effect of ionic transport mechanisms as well as the influence of interaction of ionic species. The new mathematical model was developed based on the Nernst–Planck equation and null current condition to solve the ionic-induced electrostatic potential, and the model was implemented by a parallel finite element algorithm. The verification of mathematical model was done by comparing the model prediction with experimental results for ionic transport in saturated concrete. The comparisons showed good results. The model prediction of the multispecies transport in partially saturated concrete demonstrated that the ionic species dissolved in pore solution could be carried by the moisture movement and pressure gradient. Therefore, the multispecies transport model based on the parallel finite element method is effective, accurate, and can be used for solving the partial differential equations for ionic species transport in concrete.

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.

Chloride Induced Reinforcement Corrosion in Mortars Containing Coal Bottom Ash and Coal Fly Ash.

Coal bottom ash is normally used as aggregate in mortars and concretes. When it is ground, its characteristics are modified. Therefore, the assessment of its long-term durability must be realized in depth. In this sense, an accelerated chloride ingress test has been performed on reinforced mortars made of Portland cement with different amounts of coal bottom ash (CBA) and/or coal fly ash (CFA). Corrosion potential and corrosion rate were continuously monitored. Cement replacement with bottom and fly ash had beneficial long-term effects regarding chloride penetration resistance. Concerning corrosion performance, by far the most dominant influencing parameter was the ash content. Chloride diffusion coefficient in natural test conditions decreased from 23 × 10−12 m2/s in cements without coal ashes to 4.5 × 10−12 m2/s in cements with 35% by weight of coal ashes. Moreover, the time to steel corrosion initiation went from 102 h to about 500 h, respectively. Therefore, this work presents experimental evidence that confirms the positive effect of both types of coal ashes (CBA and CFA) with regard to the concrete steel corrosion.

Prediction model of chloride diffusion in concrete considering the coupling effects of coarse aggregate and steel reinforcement exposed to marine tidal environment

Abstract Chloride-induced corrosion of steel reinforcement is one of the significant factors for the durability of the reinforced concrete structures exposed to marine environments. Reinforced concrete is a multiphase composite material composed of mortar, coarse aggregate, and rebar. The coarse aggregate and rebar can both affect the chloride diffusion characteristics of concrete. Nevertheless, the current researches related to the effects of the aforementioned two impact factors on chloride diffusion in concrete either considered the coarse aggregate only, or taken into account the steel bar separately. The coupling effects of coarse aggregate and steel reinforcement on chloride transport in concrete required to be further explored and discussed. In this paper, an in-door physical experiment for chloride diffusion in plain and reinforced concrete specimens exposed to marine tidal environment was carried out. The specimens were cast using different volume fractions of coarse aggregate and diameters of steel reinforcement. The chloride concentrations for experimental specimens were measured at various exposure times, and these measurements were adopted to further investigate the common influences of coarse aggregate volume fraction and blocking effect of rebar on chloride diffusion in concrete. Using the impact factors of coarse aggregate volume fraction f(v), the direct and indirect blocking effect coefficients of rebar α(v), βr(Φ/c) to improve the analytical solution of Fick’s second law, a prediction model of chloride diffusion in concrete considering the coupling effects of coarse aggregate and steel reinforcement was proposed. The accuracy of this proposed prediction model was validated by comparing the chloride concentrations evaluated by the prediction model with the experimental measurements. The findings are expected to be useful in realistically predicting the durability of reinforced concrete structures.

Investigation of the Cl− migration behavior of cement materials blended with fly ash or/and slag via the electrochemical impedance spectroscopy method

Abstract The chloride-induced corrosion of reinforcement in concrete is a serious problem. In this study, the chloride ion migration in cement materials blended with fly ash or/and slag is studied by the electrochemical impedance spectroscopy (EIS) method. A novel equivalent circuit model Rs(Q1(Rct1W1))(Q2(Rct2W2)) is established to analyze the chloride ion migration. The results indicate that increasing the amount of fly ash or/and slag enhances the resistance to chloride ion migration. The chloride ion migration depth can be qualified by an equation that is a function of the parameter (Rct1) of the circuit model. With this function, the chloride ion migration depth in cement materials replaced with fly ash or/and slag can be predicted by EIS method.

Experimental and numerical study of accelerated corrosion of steel reinforcement in concrete: Transport of corrosion products

Chloride-induced corrosion of steel reinforcement in concrete is one of the major causes for deterioration of reinforced concrete (RC) structures. Currently, there are only a limited number of coupled 3D chemo-hygro-thermo-mechanical models capable to realistically simulate corrosion process in cracked concrete. Especially moisture behavior coupled with transport of corrosion products in cracked concrete and its effect on the corrosion induced damage has not been addressed so far. In the present paper experiments performed on concrete cylinders under accelerated conditions are presented and discussed. The experiments are simulated using recently developed chemo-hygro-thermo-mechanical model. Based on the experimental results the model is verified and calibrated with respect to the parameters that are responsible for transport of rust through pores and cracks of concrete.

Predicting residual service life of concrete infrastructure: a considerably controversial subject

There is an increasing demand from asset owners for service life prediction of existing reinforced concrete structures. This requires assessment of the current condition and modelling to allow for a prediction. This paper critically discusses a number of subjects relevant for service life prediction with respect to durability related to chloride-induced reinforcement corrosion. The subjects include the physical meaning and variability of the end-of-service-life criterion, the validity of the deterioration models, the availability, variability and reality level of input values for some model parameters, as well as some practical issues concerning site investigations. The findings are exemplified by calculation examples using both a deterministic as well as a full probabilistic approach. It is anticipated that in the future a full probabilistic approach will be adopted which makes service life predictions more prone to manipulation of input values, as literature provides a wide spectrum of values to choose from. Although a probabilistic approach seems very impressive to most asset owners it usually disguises the lack of knowledge, responsibility and liability of the consultant involved. It is concluded that asset owners will be easy prey for consultants to play a lucrative numbers game eventually providing a desirable and realistic outcome, mostly already known beforehand.

Influence of carbonation on the resistance of concrete structures to chloride penetration and corrosion

Chloride-induced corrosion of steel rebar embedded in concrete is one of the major concerns influencing the durability of reinforced concrete structures. It is widely recognized that the carbonation in concrete affects the chloride diffusivity and accelerates the chloride-induced reinforcement corrosion. However, only very limited studies have dealt with this issue in the literature. The presence of service load related cracks also affects the reinforcement corrosion. This study aims to investigate the potential impact of concrete carbonation on the chloride penetration resistance, and degree of corrosion, in RC structures subjected to service related microcracks.The experimental programme involves casting of concrete prisms (100 x 100 x 500 mm) with different water-cement ratios (w/c) of 0.4, 0.5 and 0.6 and with four different crack widths (0, 0.05-0.15 mm, 0.15-0.25 mm and 0.25-0.35 mm). These samples were exposed initially to accelerated carbon dioxide (CO2) environment and then exposed to the accelerated chloride environment. Carbonation depth, chloride penetration, and the degree of corrosion (using half-cell) were experimentally measured. The results indicated that (i): The depth of carbonation increases with the increase in crack width and w/c ratio, (ii) chloride penetration depth in concrete structures increases significantly due to the influence of carbonation and (iii) half-cell corrosion potential increases significantly when carbonated concrete samples are exposed to the chloride environment relative to the uncarbonated concrete samples.

Effect of mineral additions incorporated in concrete on thermodynamic and kinetic parameters of chloride-induced reinforcement corrosion

In this article, the beneficial effects of pozzolanic mineral additions incorporated in concrete under the attack of chlorides are evaluated. Three different mineral additions incorporated in binary combinations with Portland cement (silica fume, metakaolin and fly ash) were studied. By monitoring and analyzing thermodynamic and kinetic parameters, the corrosion performances of reinforced test specimens were evaluated over an extended period of chloride attack (44 weekly cycles of wetting in a solution of NaCl and air drying, equivalent to 308 days of attack). The electrochemical techniques (Ecorr, Rp and EIS)1Electrical resistivity (ER), corrosion potential (Ecorr), polarization resistance (Rp), electrochemical impedance spectroscopy (EIS), corrosion rate (icorr), control concrete (C), concrete with silica fume (SF), concrete with fly ash (FA), concrete with metakaolin (MK).1, added to the electrical resistivity technique (ER), are allowed to evaluate the protection capacity of the concretes under study, in relation to this strong attack on the reinforcement. They also allowed the production of subsidies capable of generating scientific discussion about the mechanisms of protection, imparted to concrete by mineral additions, in this specific aggressive medium rich in chlorides. The results showed that the used mineral additions produced significant increases in the resistivity of concretes, which is probably due to physical changes in the pore structure of cement paste, besides the improvement of paste-aggregate interface and the changes in the conductivity of pore solution. This higher resistivity certainly delayed the transport of chlorides and their attack on the reinforcement, seen by small changes in the values of Ecorr, Rp and icorr in concretes with pozzolans. The EIS results showed that there was little change in the impedance values at the steel-concrete interface in these systems with mineral additions, in spite of the strong and prolonged attack.

Chloride induced reinforcement corrosion behavior in self-healing concrete with encapsulated polyurethane

Cracks in reinforced concrete structures accelerate the ingress of chlorides and therefore cause a higher risk for corrosion. In this research, autonomous healing of cracks by encapsulated polyurethane was investigated as a possible method to reduce reinforcement corrosion. Reinforced concrete beams were exposed weekly to a chloride solution and electrochemical parameters were measured to determine the influence of the self-healing mechanism on the corrosion process. The rebars were visually examined afterwards.For the cracked beams an active state of corrosion was detected within an exposure period of 10 weeks and clear pitting corrosion was observed on the rebars. Autonomous crack healing with low viscosity polyurethane could significantly reduce the corrosion in the propagation stage. For these specimens no visual damage to the rebars was detected. In conclusion, the application of self-healing concrete with a low viscosity polyurethane is able to enhance the durability of reinforced concrete structures in marine environments.