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Surface application of multifunctional compound to prevent and control combined chloride and carbonation corrosion in concrete
Abstract
This paper presents the performance of a multifunctional generic compound, 4-Aminobenzoic acid (4ABA) as migratory inhibitor applied on hardened concrete surface to curb corrosion due to combined chloride and carbonated environment. Electrochemical techniques (LPR and EIS), gravimetric analysis were applied to evaluate the corrosion performance and the inhibition mechanism of 4ABA. Chloride and carbonation profiles were developed to investigate the dominant cause of corrosion during the exposure. Visual and microscopic analysis of concrete surface and rebar surface was also done. Compressive strength test was performed to study the effect of corrosion inhibitor on strength property of hardened concrete. Results confirm that 4ABA prolonged the passive state of rebar when used as preventive measure and restrained the on-going corrosion process when employed as repair strategy. Combined exposure by chlorides and CO2 leads to redistribution of chloride ions in concrete matrix. The results also conclude that during the combined exposure, chloride ions initiate the corrosion process and carbonation aggravates this process. Application of 4ABA does not influence the strength properties of concrete. ABA has performed the inhibition by protective layer development and shield formation against the negatively charged corrosive ions. Blended cement concrete system which was observed to be more vulnerable to corrosion was seen to attain similar corrosion resistance as OPC concrete after inhibitor application.
... This non-accumulative trait is particularly advantageous, as it minimizes the risk of undesirable effects associated with surface deposition. Recently, Tiwari et al. (2023) have reported the surface application of three organic corrosion inhibitors, i.e., 4-aminobenzoic acid (4ABA), 2-amino pyridine (2AP) and salicylaldehyde (SA) as MCI for preventing reinforced concrete prisms subjected to cyclic carbonation and chloride corrosive environment. The percolation potential of 2AP and SA was low, causing reduced inhibition efficiency. ...
... A UV testing method was adopted to determine the concentration of the corrosion inhibitor present in the samples [17]. A 4 gm sample from each depth was used to prepare a solution by mixing it with hot water. ...
... In the case of Set 3 specimens, the application of the inhibitor was performed only after confirming that the rebar corrosion had entered the active stage through appropriate testing. The methodology for the CoI application was detailed in the work of Tiwari et al. in 2023, 48 and the application method was adopted from Kaur et al.. 49 In this study, the CoI was applied following the conversion of the 2-AP compound (powder form) into a 1 M solution. Distilled water was used as a solvent to prepare the solution. ...
This paper explores the influence of 2-aminopyridine (2AP) as water-based migratory corrosion inhibitor (M-CoI) on the corrosion resistance of reinforcing steel bars embedded in ordinary Portland cement and pozzolanic Portland cement concrete subjected to combined chloride and carbonation ingress. Two applications of 2AP are considered i.e., preventive (applied before exposure to aggressive environment) and repair (applied after corrosion initiates). Corrosion performance was assessed using electrochemical techniques and gravimetric mass loss method. The study also examines the impact of 2AP application on chloride ion concentration and carbonation depth of both concrete systems. The compressive strength of each concrete system was also measured to study the impact of M-CoI application on strength properties. Surface condition of hardened concrete and extracted rebar was evaluated by optical microscopy. Results conclude that 2AP effectively retards reinforcement corrosion when used as preventive measure by forming a homogeneous inhibitive layer on steel. However, when used as a repair technique, localised and uniform corrosion was perceived. An attempt has been made to identify the cause of non-performance of 2AP as repair measure. It was concluded that reached concentration of 1 mM was not sufficient to reduce ongoing corrosion due to the accumulation of corrosion products. The influence of the inhibitor on chloride profile and carbonation depth was found to be insignificant. It is concluded that chloride ions initiate the corrosion mechanism, while carbonation exacerbates it, particularly in blended cement concrete. Nonetheless, inhibitor application can provide similar resistance in both concrete systems.
Concrete coating technology is a key measure that enhances the durability of concrete structures. This paper systematically studies the performance, applicability, and impact of different types of anti-corrosion coatings on concrete durability, focusing on their resistance to chloride ion penetration, freeze–thaw cycles, carbonation, and sulfate corrosion. The applicability of existing testing methods and standard systems is also evaluated. This study shows that surface-film-forming coatings can create a dense barrier, reducing chloride ion diffusion coefficients by more than 50%, making them suitable for humid and high-chloride environments. Pore-sealing coatings fill capillary pores, improving the concrete’s impermeability and making them ideal for highly corrosive environments. Penetrating hydrophobic coatings form a water-repellent layer, reducing water absorption by over 75%, which is particularly beneficial for coastal and underwater concrete structures. Additionally, composite coating technology is becoming a key approach to addressing multi-environment adaptability challenges. Experimental results have indicated that combining penetrating hydrophobic coatings with surface-film-forming coatings can enhance concrete’s resistance to chloride ion penetration while ensuring weather resistance and wear resistance. However, this study also reveals that there are several challenges in the standardization, engineering application, and long-term performance assessment of coating technology. The lack of globally unified testing standards leads to difficulties in comparing the results obtained from different test methods, affecting the practical application of these coatings in engineering. Moreover, construction quality control and long-term service performance monitoring remain weak points in their use in engineering applications. Some engineering case studies indicate that coating failures are often related to an insufficient coating thickness, improper interface treatment, or lack of maintenance. To further improve the effectiveness and long-term durability of coatings, future research should focus on the following aspects: (1) developing intelligent coating materials with self-healing, high-temperature resistance, and chemical corrosion resistance capabilities; (2) optimizing multilayer composite coating system designs to enhance the synergistic protective capabilities of different coatings; and (3) promoting the creation of global concrete coating testing standards and establishing adaptability testing methods for various environments. This study provides theoretical support for the optimization and standardization of concrete coating technology, contributing to the durability and long-term service safety of infrastructure.
The present study proposes a new technique for retrofitting corroded beam–column joints (BCJs) using high‐strength fiber reinforced concrete (HSFRC) and stirrups replacement. The entire corrosion‐affected concrete was removed and replaced with HSFRC. The corroded reinforcing bars were cleaned and treated to resist the progression of the corrosion mechanism. The severely pitted stirrups were replaced with new stirrups. Four exterior BCJ specimens were tested under seismic loading to determine the effectiveness of the proposed retrofitting scheme. The efficacy of the proposed retrofitting scheme is determined in terms of the hysteresis response, stiffness degradation, cumulative energy dissipation, ductility, and damage index. A significant delay in the fracture of severely pitted reinforcing bars was experienced for the corrosion‐damaged retrofitted specimens compared to the corroded unretrofitted specimen. The cumulative energy dissipation of the corroded unretrofitted and corroded retrofitted specimens was 0.4 and 1.3 times that of the reference specimen, respectively, indicating the effectiveness of the retrofitting strategy, as both specimens had similar corrosion rates. The test results indicated that the proposed retrofitting technique effectively improved the seismic performance of the corrosion‐damaged BCJs.
In this paper an experimental study is presented on the interaction between concrete carbonation and chloride attack. The experiments are carried out on chloride-contaminated cement pastes that have been exposed to a carbon dioxide environment. Free and total chloride contents at different carbonation times are measured in the tested specimens using traditional leaching and acid-soluble methods. Bound chloride contents are calculated from the measured total and free chlorides. The experimental data show that the carbonation of cement paste results in a release of bound chlorides, which is related to not only the decomposition of Friedel's salt, but also the decomposition of calcium-silicate-hydrate (C-S-H) gel. Based on the obtained experimental results, a numerical model is also developed for simulating the carbonation process of the chloride-contaminated cement paste. The model can be used to explain how the bound chlorides are released in a chloride-contaminated cement paste under the influence of carbonation reactions.
Reinforced concrete (RC) has been commonly used as a construction material for decades due to its high compressive strength and moderate tensile strength. However, these two properties of RC are frequently hampered by degradation. The main degradation processes in RC structures are carbonation and the corrosion of rebars. The scientific community is divided regarding the process by which carbonation causes structural damage. Some researchers suggest that carbonation weakens a structure and makes it prone to rebar corrosion, while others suggest that carbonation does not damage structures enough to cause rebar corrosion. This paper is a review of the research work carried out by different researchers on the carbonation and corrosion of RC structures. The process of carbonation and the factors that contribute to this process will be discussed, alongside recommendations for improving structures to decrease the carbonation process. The corrosion of rebars, damage to passive layers, volume expansion due to steel oxidation, and crack growth will also be discussed. Available protection methods for reducing carbonation, such as rebar structure coating, cathodic protection, and modifier implementation, will also be reviewed. The paper concludes by describing the most significant types of damage caused by carbonation, testing protocols, and mitigation against corrosion damage.
The purpose of this study was to solve the chloride corrosion damage problems of the rebar in reinforced concrete structures under the chloride environment. The effects of 1.0% triethanolamine (abbreviated as 1.0% TEA), 1.0% Ca(NO 2 ) 2 , and 0.5% TEA + 0.5% Ca(NO 2 ) 2 (abbreviated as 1.0% composite corrosion inhibitor) on the electrochemical performance and modification mechanism of the mortar specimens were investigated by combining macro experiment and microanalysis. The results showed that the electrode potential of the rebar was effectively improved by incorporating the 1.0% composite corrosion inhibitor. This composite corrosion inhibitor displayed the ability to stabilize the electrode potential of the rebar; it also formed a passive film on the surfaces of the rebar, protected the rebar from chloride attack, and achieved satisfactory electrochemical performance. In addition, it could also effectively improve the strength of the mortar specimens and possessed the strong ability to bind chloride ions, thus signifying that it could promote cement hydration and accelerate the formation of cement to form AFt crystals. Therefore, the results of this investigation confirmed that this composite corrosion inhibitor could be effectively used in practical engineering to prevent the corrosion of reinforced concrete structures.
In this paper, electrochemical impedance spectroscopy was used as non destructive technique (NDT) for studying the carbonation behavior of the concrete sample treated with migratory type of organic corrosion inhibitors. Concrete carbonation was achieved in carbonation chamber by maintaining 5% CO2 by volume, 60-70% relative humidity and 30 ± 2°C temperature for 90 days. The experimental results show that with progressive carbonation, porosity of the concrete reduces and results in denser microstructure. The concrete surface treated with corrosion inhibitor C.I. 1 (amine-ether based) and C.I. 2 (2-aminobenzoic acid) shows the behaviour different form the control sample at the end of exposure conditions. Impedance results indicate that carbonation depth can be predicted by analyzing the high frequency arc of Nyquist plot. Also, both of the tested inhibitors were able to form a passive layer around the rebar surface and their efficiencies improved with time.
Reinforced concrete with lower environmental footprint (lower CO2 emission) can be obtained by reducing the clinker content in the cements. As the carbonation of concrete is faster, corrosion of steel in carbonated concrete during the propagation phase is becoming important both for science and practice. The present literature review summarizes the state of the art, reporting corrosion rate data for a broad range of cement types, w/b ratios and environmental conditions. Correlations between corrosion rate and the main influencing parameters are elaborated and discussed. It confirms that the corrosion rate of steel in carbonated concrete is not under ohmic control. More important are the degree of pore saturation and the effective steel area in contact with water filled pores. It also emerges that the new blended cements have to be systematically studied with respect to the corrosion behavior of steel in carbonated concrete in order to make reliable service life prediction.
In majority of exposure environments for concrete structures, there is a high probability of the cyclic occurence of both chloride ingress and carbonation. This paper reports a detailed investigation on the influence of carbonation on both the ingress and distribution of chlorides in three different types of concretes, by comparing results from exposure to chlorides, chlorides before carbonation and chlorides after carbonation. Concretes studied were of 0.55 water-binder ratio with 100% Portland Cement (PC), 70% PC + 30% pulverized fuel ash (PFA) and 85% PC + 10% PFA + 5% microsilica (MS) as binders. Chloride profiles were compared to assess the effects of all variables studied in this research. The effect of carbonation was quantified by measuring the consumption of hydroxyl ions (OH⁻), air permeability and chloride migration coefficient. The results indicated that carbonation of concrete increases chloride transport, but the precise nature of this is dependent on the combined regime as well as the type of binder. In general, it was found that carbonation of chloride contaminated concretes results in a decrease of their chloride binding capacity, that is it releases the bound Cl⁻ in concretes and pushes chlorides inwards, as has been established previously by other researchers. However, it is established in this research that the combined regimes detrimentally affect the service life of concrete structures, particularly when chloride induced corrosion is a concern.
Organic inhibitors have attracted considerable attention due to their promising application as admixtures in concrete protecting against corrosion of rebars. Over the last decade the use of those inhibitors significantly raised. The inhibition efficiency depends on their physical and chemical properties. This paper gives short overview of the protection of steel in concrete against the ingress of chlorides, oxygen and carbon dioxide in concrete, as species causing the corrosion of rebars. This work involves only organic inhibitors.
A kind of special concrete known for its flowing property and the mixture affixes under its self-weight. Henceforth under congested circumstance it obviates the difficulty of placing concrete moreover reducing the time in setting up large sections meanwhile affording increased strength and commanding durability characteristics than standard concrete. The major consequence facing all around is that durability concern with respect to corrosion of steel. The premature failures in concrete are caused due to this corrosion of steel. To improve a service life of concrete, corrosion inhibitors have been used as effective measures to inhibit corrosion. But there are numerous inhibitors were exists in the market. Only Sodium Nitrite (SN) has proven corrosion inhibiting capabilities simultaneously refine the mechanical properties of concrete. Therefore the presence of sodium nitrate in the self compacting concrete as the corrosion inhibiting admixture, the strength and corrosion resisting properties were studied by the dosage added 0%, 1%, 2%, 3%, 4% and 5%, by the weight of cement. Mix design for M25 grade of concrete according to BIS method (IS 10262:2009). Cement is replaced with consistent percentage of fly ash (40%). Then the standard concrete mix proportions were modified into SCC properties as per EFNARC specifications and different trail mixes were done. The investigation on the properties of self compacting concrete in spite of the effect of corrosion inhibiting admixture is done on the trial basis. The effect of Corrosion inhibiting admixture (a sodium nitrate based inhibitor) along with the properties of fresh concrete and the hardened concrete are determined. From the results it is proven that the self compacting concrete increases the strength of the concrete with accretion of inhibitor (sodium nitrite). Ultimately it was concluded that the compressive strength of cubes at 3% of sodium nitrite was increased strength by 8.8% in comparison with standard self compacting concrete (SN0) mix.
Electrochemical techniques, including electrochemical impedance spectroscopy (EIS), are among the most common techniques used for the evaluation and study of corrosion in reinforced concrete. Electrochemical impedance spectroscopy (EIS) is a powerful technique for characterizing a wide variety of electrochemical systems and for determining the contribution of electrode or electrolytic processes in these systems. The analysis of EIS results from samples of concrete is highly complex due to overlapping arcs from simultaneous phenomena and noise associated with the heterogeneity of the samples. Thus, this paper proposes a new method of analysis based on the characteristic relaxation angular frequency, w, of each phenomenon and the association of typical capacitances and frequencies.
This study presents an analysis of a 30 000 strong data matrix derived from 227 studies originating from 35 countries since 1968. Similar to the fly ash effect, the carbonation of concrete increases with the incorporation of ground granulated blast-furnace slag (GGBS), but the rate increases as GGBS content is increased. This effect is greater for concrete designed on an equal water/cement (w/c) basis to the corresponding Portland cement (PC) concrete than on an equal strength basis. The Eurocode 2 specification for XC3 carbonation exposure in terms of the characteristic cube strength of concrete (or its w/c ratio) may need to be increased (or decreased) with the addition of GGBS. Other influencing factors, including GGBS fineness, total cement content and curing, were also investigated. In some cases, the carbonation of in-service GGBS concrete has been estimated to exceed the specified cover before 50 years of service life. Measures to minimise the carbonation of GGBS concrete are proposed. Fully carbonated reinforced GGBS concrete is assessed to show a higher corrosion rate. In relation to PC concrete, the carbonation of GGBS concrete is essentially similar when exposed to 3–5% carbon dioxide accelerated or indoor natural exposure, and the conversion factor of 1 week accelerated carbonation equal to 0·6 year is established.
Corrosion of reinforced concrete (RC) structures has been one of the major causes of structural failure. Early detection of the corrosion process could help limit the location and the extent of necessary repairs or replacement, as well as reduce the cost associated with rehabilitation work. Non-destructive testing (NDT) methods have been found to be useful for in-situ evaluation of steel corrosion in RC, where the effect of steel corrosion and the integrity of the concrete structure can be assessed effectively. A complementary study of NDT methods for the investigation of corrosion is presented here. In this paper, acoustic emission (AE) effectively detects the corrosion of concrete structures at an early stage. The capability of the AE technique to detect corrosion occurring in real-time makes it a strong candidate for serving as an efficient NDT method, giving it an advantage over other NDT methods.
The objective of this paper is to investigate the behaviour of amino
alcohol corrosion inhibitors when they are used in reinforced cement mortars
either as admixtures in the cement paste or as coating applications on the
surface of the rebars.
The reinforced cement mortars were exposed to both partial and full immersion
in 3.5 wt% NaCl solution. Electrochemical measurements such as half-cell potential and linear
polarization technique, as well as weight loss of the embedded rebars were
performed in order to obtain information on the corrosion behaviour of the
reinforcing steel in cement mortar. Results demonstrate that the amino alcohol
corrosion inhibitors offer protection against rebar corrosion in cement
mortars.
The purpose of this article is to investigate the carbonation mechanism of CH and C-S-H within type-I cement-based materials in terms of kinetics, microstructure changes and water released from hydrates during carbonation. Carbonation tests were performed under accelerated conditions (10% CO2, 25 °C and 65 ± 5% RH). Carbonation profiles were assessed by destructive and non-destructive methods such as phenolphthalein spray test, thermogravimetric analysis, and mercury intrusion porosimetry (destructive), as well as gamma-ray attenuation (non-destructive). Carbonation penetration was carried out at different ages from 1 to 16 weeks of CO2 exposure on cement pastes of 0.45 and 0.6 w/c, as well as on mortar specimens (w/c = 0.50 and s/c = 2). Combining experimental results allowed us to improve the understanding of C-S-H and CH carbonation mechanism. The variation of molar volume of C-S-H during carbonation was identified and a quantification of the amount of water released during CH and C-S-H carbonation was performed.
The purpose of this study is to achieve a better understanding of the inhibition mechanism of molybdate as a potential corrosion inhibitor for reinforcing steel embedded in chloride-contaminated mortars. After adding sodium molybdate, mortars with and without admixed chlorides were exposed to chloride solution for evaluating the inhibition behavior of molybdate using electrochemical measurements and microstructural characterization techniques. In addition, the influence of molybdate on mechanical properties, pore structures and hydration products of mortars was also investigated. Although molybdate could yield a negative impact on mortar properties in terms of reduced strength and electrical resistance due to the increased porosity, the improved corrosion resistance was highlighted for steel in mortars containing molybdate. Based on the interactions between steel corrosion products and mill scale at the steel-mortar interface, the possible inhibition mechanisms of molybdate in chloride-contaminated mortars were proposed.
Chloride ingress is considered as the primary reason causing corrosion of steel inside reinforced concrete (RC). Carbonation can also result in significant corrosion of RC structures in locations where CO2 concentration is high due to atmospheric condition or environmental hazards. Consequently, RC structure could experience considerable degradation if carbonation occurs in conjunction with chloride induced corrosion. However, from the available literature, inconsistent outcome has been found regarding the effect of amount of supplementary cementing materials (SCMs) such as fly ash and slag on concrete’s carbonation. In this study, an attempt has been made to establish interaction zones from the contrasting results observed between carbonation and chloride penetrability of concrete with respect to fly ash or slag addition. The findings of the study were based on results obtained from Rapid Chloride Permeability Test (RCPT) and carbonation tests of 108 mixes with a range of water to binder (w/b) ratios, binder contents, aggregate gradations and fly ash/slag percentages. An apparent optimum proportion of 20% replacement of cement by fly ash or slag has been proposed considering combined action of chloride ingress and carbonation. Moreover, tentative service life has been estimated using fib model with the observed carbonation depth data. In addition, replacing cement with the optimized amount of fly ash or slag will reduce cost and provide a sustainable solution to concrete construction.
The existence of vitamins nicotinic acid (B3), pyridoxine (B6) and ascorbic acid (C) affects cement hydration when utilized as a new corrosion inhibitor. The mechanism of the effect of vitamin molecules on ordinary Portland cement hydration is still unclear at the atomic level. In this work, the microstructures of hydration products are found to be changed by vitamin inhibitors, which is the main reason for their impact on cement workability and mechanical performances. The pre-induction period was delayed in various degrees by vitamin inhibitors. The paste with vitamin C shows no induction and acceleration period in the tests. DFT calculations show that vitamin molecules dissociated in the adsorption process. The dissociated H atom occupied the ionic O site of the C3S (tricalcium silicate) surface, preventing the dissociation of water. This phenomenon may be one reason for the hydration postponement of cement with vitamin type inhibitors at the atomic level. The charge density difference and the independent gradient model analysis also confirmed the chemical and physical interactions between vitamin molecules and the C3S surface. The findings in this research may broaden the applicability of these new environment-friendly corrosion inhibitors.
Steel corrosion caused by chloride penetration is an important problem in construction practices threatening the long-term durability of reinforced concrete structures. In this study, the effects of blast-furnace slag on the passivation and corrosion processes of carbon steel embedded in cement pastes were investigated by electrochemical measurements, and equivalent circuit models were proposed for analysis of the passivation and corrosion processes. The spatial chloride distributions in the cement paste after corrosion initiation were determined distinguishing between amounts of total, free and bound chloride. The values of the open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) measurements indicated that the carbon steel embedded in cement pastes was passivated due to the presence of an alkaline pore solution. However, the formation of passive layers on the surface of carbon steel in the slag-blended cement paste was weakened by the more negative OCP value due to a lower pH value and higher sulphide concentration in the pore solution. Upon initiation of corrosion during the electrical acceleration test, the OCP value dropped to a significantly more negative value whereas the Warburg impedance in the equivalent circuit model sharply decreased. Moreover, the addition of slag decreased the threshold chloride concentration at the steel surface to initiate steel corrosion. On the other hand, the enhanced resistance against chloride penetration and the higher chloride binding capacity resulted in an overall increase of the corrosion resistance of carbon steel in slag-blended cement paste.
Incorporation of corrosion inhibitor into the cement-slag composite pastes can effectively improve the resistance to seawater erosion. However, corrosion inhibitor inevitably affects the microstructures and transport properties of cement-slag composite pastes, which poses a great challenge for the engineering application prospects of the composite pastes modified by corrosion inhibitor. In this paper, a smart organic polymer with hydrophilic and hydrophobic components is designed as corrosion inhibitors, and a combination of experiments and molecular dynamics (MD) simulations is employed to investigate the effect of this smart polymer-based corrosion inhibitor on cement-slag composite pastes under seawater erosion. Experiments show that this smart polymer-based corrosion inhibitor has profound effect on the hydration properties, pore structures and ions resistance of cement-slag composite pastes, with an optimum content of approximately 6%. MD simulations reveal the nano-mechanism by which this smart polymer-based corrosion inhibitor hinders water and ion transport in the calcium aluminate-silicate hydrate (CASH) nanopores. Analysis suggests that strong electrostatic interactions, originating from the CaCASH-Oinhibitor pairs and the H-bond networks, are the primary sources of the corrosion inhibitor-CASH bonding mechanism. Besides, the migration rates of water and ions are reduced as the large cluster structures formed among the corrosion inhibitor molecules, water molecules and erosive ions.
Chloride-induced corrosion of steel reinforcement is the most important cause of premature failure of reinforced concrete structures. Corrosion inhibitors have proven to be an effective method to reduce corrosion rate in terms of application and cost-effectiveness. Various types of inhibitors are present such as organo-functional silanes, Amino-alcohol and Surfactant & amine salts-based inhibitors. The inhibitor efficiency of six major commercial migratory corrosion inhibitors, for reinforced concrete available in UK, was investigated using electrochemical study and permeability measurements to determine the most efficient inhibitor to protect steel in concrete with high chloride environment. It is showed that these compounds are effective inhibitors for reinforced concrete structures. Out of the tested inhibitors, organo-functional based inhibitors showed the best inhibitor efficiency and barrier properties.
Supplementary cementitious materials are known to refine the pore structure of concrete and accelerate the carbonation progress. The combination of the two processes can have both beneficial and disadvantageous effects on corrosion, especially when chlorides are also involved. In this study the corrosion properties of multiple blended cements were evaluated in carbonated and non‑carbonated states, with chlorides introduced through cyclic ponding. The examination involved monitoring the propagation phase, determining the microstructural properties of cements, and assessing the final corrosion damage. The results showed that the steel in the blended cements initially had a relatively high corrosion activity, which later decreased compared to the OPC. This stabilisation was presumably due to the beneficial changes to the pore structure. Carbonation had a significant impact on the corrosion, with carbonated mortars revealing shallower damage over a larger surface area. This effect was more pronounced for blended cements that exhibited greater susceptibility to carbonation.
Highlights: Inhibition efficiency of compounds was tested in carbonated pore solution contaminated with chloride. Inhibition mechanism was determined by using electrochemical and surface analysis tests. Percolation ability in hardened concrete was also studied by using TLC and UV spectroscopy. Abstract: In the present study, corrosion inhibition effect of generic compounds in simulated carbonated pore solution contaminated by chloride ions (Cl-) was investigated. The performance of two generic compounds, namely Triethylphosphate (TEP) and Salicyaldehyde (SA) at varying concentrations was investigated by electrochemical measurement technique (potentiodynamic polarization curves), optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and Fourier transform infrared spectroscopy (FTIR). The test results in simulated pore solution show that both TEP and SA reduced the corrosion rate irrespective to the tested concentration levels. It is found that efficiency of TEP increases from 65.36% to 83.18% with increase in concentration from 0.05 M to 0.2 M; while efficiency of SA was as high as 96.4% even at 0.05 M concentration. Surface analysis data confirms that corrosion product on specimen immersed in contaminated environment contains FeOOH, Fe 2 O 3 and Fe 3 O 4 , while presence of phosphate group in TEP able reduce the formation of corrosion product. SEM and EDS data shows the formation of protective layer on specimen immersed in SA admixed solution that contains higher C and O content. The spectra band obtain by FTIR confirms the adsorption of SA through the interaction of CHO and phenolate ion with metal surface. The mechanism of inhibition revolves around the type of heteroatom present within the molecular structure. While TEP retarded the corrosion of rebar by advancing the iron oxide film growth and healing the defects present in the protective film; SA formed an adsorptive black layer over the exposed surface by chelation process. Out of the two compounds, the inhibition efficiency of SA was as high as 99%. The best performing compound was further applied on the concrete surface to check its migration ability through the cover concrete. The percolation ability was determined by using thin layer chromatography (TLC) and ultraviolet-visible spectroscopy (UV-Vis). The tests conducted on the powdered samples collected from various depths at different time intervals confirmed the percolation potential of the generic compound. Overall, it can be concluded that SA has the potential to act as migratory inhibitor to retard rebar corrosion in the dual corrosive environment of chlorides and carbonation.
In the present study,the performance of two generic compounds, namely 2-Aminopyridine (AP) and 4-Aminobenzoic acid (ABA) at varying concentrations in carbonated pore solution contaminated by chlorides was investigated by using electrochemical measurement technique (potentiodynamic polarization curves) and surface analysis technique (optical microscope, SEM, EDX, XRD and FTIR). The migration ability of the two compounds in concrete was also investigated by using thin layer chromatography (TLC) and ultraviolet-visible spectroscopy (UV-Vis).The test results in simulated pore solution showed that both AP and ABA lowered the rate of corrosion irrespective of the tested concentration levels. Surface analysis data shows that corrosion product on specimen immersed in contaminated environment contains FeOOH, Fe2O3 and Fe3O4. From the electrochemical data, it was confirmed that AP behave like mixed kind of inhibitor and blocks both the anodic and cathodic reactions on the surface of steel rebar; which is supported by surface analysis data showingthe presence of Fe (88.07%) on the surface of specimen. ABA protected the steel rebar by forming a protective layer containing higher C and O content. The spectra band of the bar in ABA mixed solution obtained by FTIR confirmed the presence of protective film in the form of chelate ring formed by –COO⁻ on the specimen surface. The mechanism of inhibition revolves around the presence of heteroatoms within the molecular structure.While AP retarded the corrosion of rebar by forming a thin adsorption layer and restricted the corrosion mechanism, ABA formed an adsorptive black layer over the exposed surface by chelation process.Selected compounds were further applied on the concrete surface to check its migration ability through the cover concrete. Overall, it can be concluded that both the compounds have the potential to act as migratory inhibitor to retard rebar corrosion in the dual corrosive environment of chlorides and carbonation.
In order to understand the role of untreated sugarcane bagasse ash (UtSCBA) in chloride binding of ternary concretes prepared with fly ash, an experimental program was carried out. Concrete specimens containing only Portland cement, Portland cement + fly ash and Portland cement + fly ash + UtSCBA were manufactured. After curing these specimens were exposed to a chloride solution for 3000 days. After exposure, a microstructural characterization using scanning electron microscopy and X-Ray diffraction was conducted. The compressive strength, electrical resistivity of the concretes and percentage of voids, were also obtained, while information on chloride binding was obtained from the difference between the amount of total and free chlorides. Diffractograms showed that chlorides chemically reacted with the Afm and Aft phases of all concretes to form Friedel's salt. In summary, ternary concretes containing UtSCBA showed the highest chloride-binding capacity.
Reinforcing steel is used extensively in buildings to provide strength and integrity to the concrete structure. This material is, however, highly susceptible to corrosion in chloride-contaminated environments, which increases the risk of structural instability and failure. This work characterises the mechanisms and efficiency of corrosion protection offered by sodium nitrate, casein, and two amino acids (11–aminoundecanoic acid, and p–aminobenzoic acid) in simulated concrete pore solutions with different contents of chloride ions. The performance of each inhibitor in the critical chloride concentration (Ccirt) was investigated using electrochemical techniques. Open circuit potential and linear polarisation were used to identify the Ccrit in synthetic pore solutions. Potentiodynamic polarisation and electrochemical impedance spectroscopy were performed to evaluate the corrosion activities and the passivation mechanism of inhibitors in Ccrit. Results indicate that reinforcing steel can be protected through an appropriate selection of corrosion inhibitors. Among of the inhibitors studied here, casein demonstrated the highest corrosion inhibition efficiency with minimum current density of 9.19×10⁻⁸ μA/cm² and inhibitor efficiency of more than 80%. Casein provides passivity to the reinforcing steel in the presence of the Ccirt in the pore solution.
Steel corrosion is the main cause of deterioration of reinforced concrete (RC) structures. We provide an up-to-date review on corrosion mechanisms and recent advances in electrical methods for corrosion monitoring. When assessing corrosion mechanism, the inherent heterogeneity of RC structures and the significant effect of environmental factors remain major issues in data interpretations. The steel surface condition and local inhomogeneities at the steel–concrete interface appear to have an important effect on corrosion initiation. Considering uniform corrosion in atmospherically exposed RC structures, the two main influencing factors of the corrosion process are the water content and the pore structure at the steel–concrete interface. However, irrespective of the depassivation mechanism, i.e. carbonation or chloride-induced corrosion, non-uniform corrosion is expected to be the main process for RC structures due to local variations in environmental exposure or the presence of interconnected rebars with different properties. Future studies may then be focused on their effect on macrocell corrosion to gain further insights in the corrosion mechanisms of RC structures.
Concerning corrosion monitoring using electrical methods, the half-cell potential technique with potential mapping is accurate for locating areas with a high corrosion risk. Recent developments in the measurement of concrete resistivity have shown that the use of electrical resistivity tomography allows to consider appropriately the inherent heterogeneity of concrete and provides more insights on transport phenomena (e.g. water and salts ingress) in the material. Nevertheless, during the corrosion propagation stage, the polarization resistance remains the most important parameter to be determined as it provides quantitative information of the corrosion rate. If conventional three-electrode configuration methods can supply an accurate determination in the case of uniform corrosion, they often fail in the case of macrocell corrosion in field experiments. Recent advances have shown that a four-electrode configuration without any connection to the rebar can rather be used for the non-destructive testing and evaluation of corrosion. If studies are still required to quantify the corrosion rate, this method appears sensitive to localized corrosion and thus more suitable to field investigations. Finally, the coupling of numerical simulations with complementary electrical and other non-destructive testing methods is essential for consolidating the results to provide a better diagnosis of the service life of RC structures.
The microstructural changes of paste, mortar and concrete based on Portland and fly ash containing Portland composite cements caused by carbonation have been studied. The objective was to find out why fly ash containing mortars carbonate with double rate of the neat Portland cement mortars. The reason is partly because they contain less calcium containing species prone to carbonation, but mainly because of their different hydrate assemblage: 1) Less calcium hydroxide that gives a volume increase upon carbonation. 2) More C-S-H with lower Ca/Si that might give an overall shrinkage upon carbonation. 3) More AFt and AFm phases that yield a substantial volume decrease per mole upon carbonation since their crystal water goes back to liquid form. The third microstructure difference is thought to be the dominating reason for coarser pores in the carbonated zone of CEM II/B-V compared to CEM I resulting in a faster carbonation rate.
An experimental study is carried out in this paper to evaluate the corrosion performance of mild steel reinforcing bars (MS), high strength steel reinforcing bars (HS), epoxy-coated steel reinforcing bars (EC), and high-chromium steel reinforcing bars (HC) under harsh environmental conditions. Reinforcing bars (rebar) of 16 mm diameter and 310 mm length were embedded in cylindrical concrete samples of 60 mm diameter and 350 mm length, and subjected to a Southern Exposure test for sixteen months. The open circuit potential (OCP) was monitored during the exposure period until corrosion initiation.
The linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS), and Tafel plot techniques were employed to assess the corrosion rates on the rebar surfaces. The macrocell corrosion current was monitored by connecting the corroding rebar with an external stainless steel bar of the same size. The polarization resistance of the HC was found to be 1.5 times higher than that of the MS. The EIS technique showed that EC, even with damaged epoxy coating, has the highest resistance to chloride
attack. The macrocell current of HC rebar was 48% less than that of MS during the active corrosion state. The LPR, EIS and Tafel plots analysis provided the current densities, which were close to each other; indicating the validity of these techniques to study the problem at hand. The corrosion rates from electrochemical methods were compared against the ones calculated by gravimetric methods. The quantitative results from this research may be used in service life prediction of concrete structures with different types of rebar. Extensive analysis of the results indicates that the corrosion resistance of the
evaluated steels was in the following decreasing order: EC, HC, MS, and HS.
Inhibitor is one of the most accepted method to reduce, prolong the initiation of steel corrosion and increase the threshold value of Cl⁻ and CO3²⁻ ions. In present study, we have mixed sodium salt of phosphate and benzoate along with benzo triazole in water to prepare the inhibitor. Open circuit potential (OCP) results show that 5 v/v% inhibitor was exhibited most positive (nobler) potential than others at its prolonged exposure in simulated concrete pore (SCP) + 3.5 wt% NaCl solution. The OCP of 3 and 5% inhibitor containing solution proved that these concentrations are away from under corrosion region of steel rebar even after 192 h of exposure in SCP + 3.5 wt% NaCl solution. Electrochemical impedance spectroscopy (EIS) results show that the charge transfers resistance (Rct) to be highest for 5% inhibitor and gradually decreased once the concentration was reduced with exposure periods. Potentiodynamic studies reveal that inhibitor shows passive properties due to adsorption of inhibitor molecules on steel surface and enhance the corrosion resistance properties. The efficiency was calculated using Rct and corrosion current density (Icorr) process and found that 3 and 5% inhibitor exhibit around 89 and 96%, respectively after 1 h of exposure in SCP + 3.5 wt% NaCl solution.
The present study concerns the resistance of silica fume (SF) concrete against chloride-induced corrosion, when SF concrete is built in a chloride-bearing environment. Chloride transport and critical chloride threshold level were experimentally obtained, which were subsequently used for the Fick's 2nd law to calculate the corrosion-free life. As a result, it was found that SF concrete had lower chloride transport in terms of the apparent diffusion coefficient, due to a refinement of the pore structure, resulting from a further formation of C-S-H gel in the cement matrix. Simultaneously, the surface chloride for SF concrete had a slightly lower range, arising from the lower capacity to bind chlorides. However, SF mortar imposed the increased corrosion risk. The chloride threshold for SF mortar accounted for 0.45% by weight of binder, while OPC produced 0.96%. Despite the increased corrosiveness in SF concrete, SF concrete produced the longer corrosion-free life, compared to OPC. From the sensitivity analysis, a reduction of the parametric values on chloride transport in SF concrete could significantly increase the corrosion-free life. For example, the apparent diffusion coefficient for SF concrete was about 74% reduced compared to OPC concrete, and thus the time to corrosion was 270% increased.
This paper summarizes the grand societal, economic, technological, and educational challenges related to corrosion of steel in concrete, and presents the state-of-the-art of the most relevant issues in the field. The enormous financial impact of infrastructure corrosion seems to be inadequately balanced by educational and research activities. This presents a unique opportunity in many countries for maintaining or improving their competitiveness, given the major technological challenges can be solved. The main technological challenges are (1) the ever-increasing need to cost-effectively maintain existing, ageing reinforced concrete structures, and (2) designing durable, thus sustainable new structures. The first challenge arises mainly in industrialized countries, where there is a need to abandon conservative, experience-based decision taking and instead move to innovative, knowledge-based strategies. The second challenge regards mainly emerging countries expanding their infrastructures and where thus a major beneficial environmental impact can still be made by providing long-lasting solutions. This means to be able to reliably predict the long-term corrosion performance of reinforced concrete structures in their actual environments, particularly for modern materials and in the absence of long-term experience. During the second half of the last century, civil engineers, materials scientists, and chemists have in many countries made considerable attempts towards understanding corrosion of steel in concrete, but many of the approaches got bogged down in empiricism. From reviewing the state-of-the-art one can conclude that transport modeling in concrete is relatively well-advanced, at least in comparison with understanding corrosion initiation and corrosion propagation, where many questions are still open. This presents a number of opportunities in scientific research and technological development that are discussed in this paper.
Supplementary cementitious materials (SCMs) like fly ash (FA) and blast furnace slag (BFS) are normally used to replace parts of Ordinary Portland cement (OPC) to reduce the cost and CO2 emission. During the carbonation, a relatively high amount of C-S-H with low Ca/Si ratio will be carbonated in cement paste blended with SCMs. Therefore, it’s very important to figure out the influences of the carbonation of C-S-H on the pore structure of SCMs blended cement paste.
In this paper, Mercury Intrusion Porosimetry (MIP) are used to determine the pore volume and size distribution of capillary pores. Results reveal that carbonation of most of the species of C-S-H results in increased porosity of cement paste. Total and effective capillary porosity of pastes blended with high amount of BFS increase after carbonation. This will bring adverse effects on the durability of blended cement concrete exposed to the carbonation.
Early carbonation curing of concretes was developed for accelerating the strength gain and promoting carbon dioxide utilization in concrete. However, the effect of early carbonation curing on chloride penetration was not clear. It was reported that weathering carbonation of concrete could increase chloride penetration. The purpose of this paper is to examine if early carbonation curing would also accelerate the chloride penetration and the weathering carbonation depth in concrete during service. Both carbonation cured and hydration cured concretes with and without fly ash were exposed to two severe cyclic conditions: (1) chloride immersion/air drying cycles and (2) chloride immersion/accelerated weathering carbonation cycles. It was found through one-year cyclic tests that total chloride content was actually reduced by more than 50% in concrete subjected to carbonation curing comparing to hydration reference. Reduction in free chloride (water-soluble) in carbonation cured concrete reached more than 60%. It was also found that carbonation cured concrete was not more vulnerable to weathering carbonation. This was attributed to the carbonate-rich surface protective layer which was less permeable, less absorptive, and with comparable pH value, enabling the carbonation cured concretes higher resistance to chloride penetration.
Chloride induced corrosion of steel in concrete is a major threat to the construction industry leading to the premature failure of concrete structures. Electrochemical injection of corrosion inhibitor (EICI) into concrete is a promising technique for existing concrete structures, which can serve as a rehabilitative measure to retard or reduce rebar corrosion. An attempt has been made to evaluate the effectiveness of a hybrid inhibitor formulation injected into chloride contaminated concrete. The optimised current density of 0.5 A/m² was found to be a minimum requirement with maximum efficiency. During EICI, the amount of free chloride removed from cover concrete was also tested. The mechanism of inhibitive action was established through FTIR, SEM, EDAX and MIP studies.
In this paper, the rarely studied aryl aminoalcohols, namely comp. a-c were synthesized and then their corrosion inhibitions for carbon steel in 0.3 M NaCl saturated Ca(OH)(2) solutions were investigated using electrochemical techniques. The potentiodynamic polarization and electrochemical impedance spectroscopy tests showed comp. a and c had higher corrosion inhibition efficiencies than the most commonly used aminoalcohol type inhibitor N, N-dimethylaminoethanol (DMEA), but comp. b seemed no suppression of corrosion process. Based on the obtained results and previous work, we made a brief discussion on the inhibitive effectiveness related to the N-substituents of tested organic compounds. Besides, comp. a with the highest inhibition efficiency was further investigated, and it could act as an anodic inhibitor by a comprehensive interaction with the carbon steel surface according to the Langmuir adsorption isotherm. The surface morphology of the carbon steel observed by scanning electron microscope showed a less amount of corrosion pits formed under inhibited conditions.
Based on systematic analysis, evaluation and synthesis of a 30 000 strong data matrix generated from 213 studies from 33 countries published since 1968, this paper details the extent of research that has been undertaken and discusses the effect of fly ash (FA) on the carbonation and carbonation-induced corrosion of concrete. It is shown that FA as a cement component, such as those adopted in BS EN 197-1:2011, increases the carbonation rate of concrete, both when concrete is designed in terms of equal water/cement ratio or strength, though with the latter to a lesser extent. This increase in carbonation has also been confirmed for in-service concrete. The net effect of FA content on the carbonation of concrete is dependent upon the combination of mix design, curing and exposure related parameters. FA in concrete is also shown to increase the corrosion of reinforcement, which can only be overcome by increasing the cover to reinforcement, concrete strength, or a combination of the two, beyond those specified in standards such Eurocode 2, BS EN 206-1:2013 and BS 8500. Contrary to the commonly held view, this study shows that the relative rate of carbonation of FA concrete with reference to corresponding Portland cement concrete remains similar under accelerated and natural carbon dioxide exposures.
In this paper, electrochemical impedance spectroscopy (EIS) was adopted as a nondestructive testing method for studying the carbonation behavior of the cementitious materials. A newly proposed electrochemical model was used to explain the carbonation related phenomenon. Results of the micromorphology observation were obtained to evaluate the reliability and the accuracy of the model. The experimental results demonstrate that the porous structure of the cement changes and porosity of the cement reduces during the carbonation process. With the increase of the water/cement ratio, the internal porosity increases, resulting in even more remarkable carbonation. The carbonation can be quantitatively analyzed by the parameters fitted from the electrochemical model based on EIS. It was found that the fitted parameter has direct function related to carbonation time and carbonation depth. As a result, it is possible to predict carbonation depth quantitatively.
Cement is a huge carbon dioxide producer. Supplementary cementitious materials can help reduce this outcome. However, carbonation of these blended cements remains an active subject of research. Accelerated carbonation tests (10% CO2, 25 °C and 62% RH) are performed on fly ash blended cement pastes. Experiments are performed at varying ages of carbonation (1 to 16 weeks) to measure the evolution of the carbonation depth over time and to quantify key parameters: thermogravimetric analysis (TGA), mercury intrusion porosimetry (MIP) and gamma ray attenuation method (GRAM). The total porosity decreases with a rearrangement of the microstructure due to carbonation and the creation of big capillary pores for the paste with the highest contents of fly ash (60 vol.%). The C-S-H molar volume evolution during fly ash-blended cement carbonation is calculated using a method combining MIP, TGA and GRAM formerly successfully applied to OPC paste in a paper published in the same journal.
The present research aims at studying two corrosion inhibitors, that is sodium 2-amino-benzoate (2AMB) and sodium glycero-phosphate (GPH), in a synthetic solution simulating the composition of the pore solution in a carbonated concrete, containing chlorides. Tests have been performed to verify if the simultaneous use of the two substances is compatible and if their addition can efficiently hinder the corrosion attack in the presence of both chlorides and carbonation. The synthetic solution has been prepared by bubbling carbon dioxide through a saturated (and filtered) solution of Ca(OH)2, containing 0.1 M NaCl, in order to reach pH 7. Polarization curve recording and EIS technique have shown that, after an induction period of about 24 h, the highest inhibiting efficiencies are obtained by mixtures of the two additives at the concentration of 0.05 M, which still produce high inhibiting efficiencies (87%) at the end of 120 h immersion. At the end of this exposure period, also more diluted symmetric mixtures (0.025 and 0.01 M) exhibit comparable efficiencies. The analysis of EIS spectra gives interesting information concerning the inhibiting mechanism of the studied mixture.
Steel reinforced concrete is one of the most durable and cost effective construction materials, but it can suffer in high chloride environments from corrosion due to chloride induced breakdown of the normal passive layer protecting the steel. One way of protecting embedded steel reinforcement from chloride induced corrosion is by the addition of corrosion inhibiting admixtures. The most widely used corrosion inhibiting admixture is calcium nitrite, due to its excellent inhibitor properties and its benign effect on concrete properties.One advantage to calcium nitrite is that its protection mechanism is well defined. In this paper data are presented that show the levels of chloride to which given levels of calcium nitrite will protect. Furthermore, it will be shown that once corrosion initiates, the rates are lower with calcium nitrite present. Finally, it is demonstrated how these results can be used by the design engineer in an integrated durability model to produce reinforced concrete structures with durabilities in excess of 50–100 years.
An improved hydration model of slag-blended cements, taking into account new insights, is used to estimate and quantify the hydration products of slag-blended cements. Individual chloride binding isotherms are used to correlate these amounts of hydration products with the amount of bound chlorides. A number of parameters are directly or indirectly taken into account when estimating the chloride binding ability of a slag-blended cement paste: cement composition, slag content, water/binder ratio, curing age, and free chloride concentration. The model allows the study of the breakdown of bound chlorides by hydration products and their source – either the OPC or the slag.
This paper presents a systematic study of the features seen in typical Nyquist plots (-imaginary vs. real impedance) for cement-paste/steel systems and discusses the assignment of each feature to its appropriate origin, e.g., bulk, contact, interface, product layer, etc. Assignments are made based upon as many considerations as possible—dc measurements, sample geometry, capacitance, local chemical modifications, alternative electroding schemes, etc. In addition to three distinct arcs from lowest (mHz) frequency to highest (MHz) frequency (due to product layer, interfacial reaction, and bulk, respectively), a fourth arc is sometimes observed between the bulk and interface arcs. When this occurs in paste-only systems, this arc is attributable to imperfect electrodes due to drying/shrinkage. In composite systems, e.g., cement with conductive chopped fibers added, this arc is clearly a “bulk” feature and an important indicator of microstructural inhomogeniety.
Concrete performance is traditionally based on assessing the effect of a single degradation mechanism. In the field, however, concrete is simultaneously affected by degradation mechanisms, possibly with a synergetic effect on deterioration. This paper presents the results of a Finnish research project assessing coupled deterioration mechanisms including frost attack, carbonation and chloride penetration.
Research was composed of an extensive laboratory testing regime, in parallel to the exposure of several concrete specimens at field stations. Testing took into account the effects of ageing and repeated exposure cycles to different conditions. More than 60 concrete mixtures were evaluated with varying binder types and air contents. Testing results together with local weather data serve as a basis for modelling and development of service life assessment tools.
The results show the synergetic effect on concrete deterioration of coupled deterioration and quantitatively support that a holistic approach should be adopted for predicting deterioration.