Chloride Threshold Value Research Articles

Macrocell Effect on Chloride Threshold Value and Corrosion Rate of Steel Bar in Simulated Concrete Pore Solution

Macrocell Effect on Chloride Threshold Value and Corrosion Rate of Steel Bar in Simulated Concrete Pore Solution

Chloride absorption capacity of calcium silicate hydrate (C-S-H) and its effect on steel corrosion in simulated concrete pore solution

The effect of calcium silicate hydrate (C-S-H) on chloride (Cl−) binding and steel corrosion in simulated concrete pore solution (SCPS) was evaluated. The results showed that Cl− absorbed by C-S-H conformed to Freundlich isotherm for 0.1–1.0 M of Cl−. When C-S-H reached equilibrium in saturated Ca(OH)2 solution, its degree of polymerization increased. The high pH is unfavorable for the absorption of Cl− by C-S-H, but favorable for the passivation of steel. The synthetic C-S-H powder contains NO3 −, which prolongs the passivation time of steel, but the presence of silicate is favorable for the formation of a passivation film with good corrosion resistance. The addition of C-S-H promoted the chloride threshold value of steel corrosion and delayed the corrosion development process.

Determination of the Chloride Threshold of Cr-Based Steel Rebars in a Synthetic Concrete Pore Solution Based on Electrochemical Methods

Steel rebars are widely applied in reinforced concrete structures due to their contribution to significant improvements in mechanical properties. However, exposure to corrosive environments, such as solution-containing chloride, may induce an accelerated corrosion and jeopardize the sustainability and durability of reinforced concrete. The current work evaluated the chloride thresholds (in both wt% and [Cl−]/[OH−]) of steel rebar with different chromium contents (0 wt%, 4 wt%, and 23 wt%) in synthetic concrete pore solution based on AC and DC electrochemical measurements, and chemical and structural characterizations. The study found that the chloride threshold (CT) values varied slightly based on the different measurement methods and the values were compared with values obtained from the literature. The values are 0.01 wt% to 0.1 wt% (3.76), 0.1 wt% to 1 wt% (>23.8), and 2.9 wt% to 3.5 wt% (>23.8) for 615, 4% Cr, and SS23, respectively, where the values in parentheses are [Cl−]/[OH−]. Therefore, it is demonstrated that multiple measurements are necessary to determine a reliable CT value. Corrosion mechanisms giving rise to CT are included to illustrate the processes involved in establishing CT.

Chloride binding of monosulfate hydrate (AFm) and its effect on steel corrosion in simulated concrete pore solution

The impact of monosulfate hydrate (AFm) on chloride (Cl−) binding and steel corrosion in simulated concrete pore solutions (SCPSs) was evaluated. In the SCPS with AFm added, a high concentration of Cl− promoted the Cl− binding amount per unit AFm without producing Kuzel's salt. The Cl− binding capacity of AFm could be improved by appropriately changing the amount of AFm with a constant Cl− concentration. The addition of AFm to the SCPS shortened the passivation time and created a more stable passivation film of the steel. The SO42− produced by the AFm binding with Cl− preferentially reacted with AFm to form AFt, and it affected the stability of the Friedel's salt to release Cl−. The addition of AFm raised the chloride threshold value (CTV) for steel corrosion. However, after reaching the CTV, the corrosion rate of steels increased dramatically, due to the release of the bound Cl−.

Mechanistic study of macrocell effect on corrosion initiation and propagation of reinforcement in submarine immersed tunnel

Submarine immersed tunnel (SIT) is generally in a specific corrosive environment with inner marine atmosphere and outer high-pressure seawater. In this work, a setup was designed to simulate the specific structure and corrosive environment of the SIT, and the mechanism of the macrocell corrosion of reinforcement in SIT was investigated. The chloride threshold value (CTV) and the corrosion rate of macrocell corrosion were obtained and mainly discussed. The results indicated that the anodic corrosion process could be accelerated by increasing SC/A and reducing the thickness of the concrete layer (d) at the cathode. The corrosion initiation was promoted drastically, and the corrosion current density was increased. A remarkable decrease of CTV was discovered in the condition of higher SC/A and reducing d (mainly to improve oxygen acquisition) coexistent. The time to onset of corrosion could be reduced by up to 33%, and the CTV was decreased from 0.749% to 0.562% (by weight). The corrosion will occur earlier, and the damage to the structure will be more severe where the macrocell effect exists in the reinforced concrete structure.

Effect of chloride concentration on the properties of passive film formed on Q235 steel in simulated concrete pore solutions

PurposeThis paper aims to study the effect of chloride concentration on the properties of passive film formed on Q235 steel in simulated concrete pore solutions.Design/methodology/approachMott–Schottky analysis and electrochemical impedance spectroscopy were used to study the passive film of Q235 steel in simulated concrete pore solution. X-ray photoelectron spectroscopy was used to analyze the composition of passive film on Q235 steel.FindingsWhen the chloride concentration is below the chloride threshold value, open circuit potential (OCP) and Rct gradually increases and donor concentration (ND) remains unchanged with the increasing immersion time. When the chloride concentration exceeds chloride threshold value, OCP and Rct decreases after a temporary increase and ND increases. The linear region of the Mott–Schottky curve lost its linearity. The electrochemical process control step is changed from charge transfer control to oxygen diffusion control. As the chloride concentration increases, the FeO content in the passive film increases and the Fe2O3 content decreases. Chloride can destroy the outer layer of passive film and introduce impurities.Originality/valueThe effects of chloride and immersion time on the change process of passive films on Q235 steel in simulated concrete pore solution were studied using electrochemical methods. The mechanism of chloride destroying passive film was analyzed.

Semiconducting Behaviour and Corrosion Resistance of Passive Film on Corrosion-Resistant Steel Rebars.

Chloride-induced corrosion of steel rebars is one of the major causes of the premature failures of reinforced concrete structures served in different environments. This paper investigates the semiconducting behaviour and corrosion resistance of the passive film formed on the corrosion-resistant rebars exposed to simulated concrete pore solutions with different pH values and chloride concentrations. The electronic properties of the passive film were studied using potentiodynamic measurements and capacitance measurements (Mott-Schottky analysis). The results indicate that, firstly, the passive film of corrosion-resistant steel rebar shows n-type semiconducting behaviour with shallow and deep donor states in the band gap during passivation, and the deep donor energy level of corrosion-resistant steel rebar passive film is not sensitive to the decreasing pH value; secondly, under the same conditions, the passive film of corrosion-resistant rebars has a larger negative flat-band potential and thicker space charge layer than hot-ribbed rebars; thirdly, n-type semi-conductivity at a higher potential disappears once the chloride concentration at the rebar surface attains the chloride threshold value; and finally, a reverse charge layer forms on the surface of CR rebar at 0.50 V potential.

Assessing the critical chloride threshold of conventional reinforcement embedded in alternate cementitious systems

Alternate cementitious materials (ACMs), such as calcium aluminate cements (CAC) and calcium sulfoaluminate cements (CSA), contain lower embodied energy and carbon footprints when compared to traditional ordinary portland cement (OPC) systems. However, the sustainability of these ACM systems can be nullified by a lack of durability and/or resiliency. To develop an understanding of the durability and long-term performance of the ACMs, standardized test methods are required to assess their corrosion resistance. OCcrit, a new test method that was developed at Oregon State University, is a fast and reliable method to study the corrosion performance of cementitious systems. This method, however, has only been evaluated using OPC systems. In the first part of this study, testing was performed to potentially extend the applicability of this new test method to CAC and CSA systems, thereby increasing its robustness and value. In the second part of the study, the updated OCcrit method was used to assess the critical chloride threshold of steel reinforcement embedded in CAC and CSA systems. Results indicate that CSA specimens exhibit lower critical chloride threshold values than OPC and CAC specimens and the critical chloride threshold of the CAC seems to be dependent on the water-cementitious materials ratio.

Cleaner construction of durable green rooftop in residential buildings with municipal water supply

Rooftop vegetation is a popular choice among architects and builders at present because of its aesthetical appeal and environmental benefits. It has consistently been regarded as a sustainable and eco-friendly approach to the construction of buildings. Recently, people have adopted rooftop vegetation in their homes, and it has become popular. Large scale roof gardens in commercial buildings are safe due to proper design and protection techniques by experts. Due to economic constraints, rooftop vegetation in normal residential buildings cannot follow stringent regulations and expensive protection techniques. However, it is to be kept in mind that any rooftop vegetation endeavour, if not properly designed and maintained, might result in severe durability problems in roof concrete. There are unseen drawbacks to simple practices of concrete rooftop vegetation in common residential buildings, specifically the presence of aggressive agents in treated water from the public water supply, which is commonly used to irrigate the vegetation in such buildings. The effect of vegetation on the concrete roof and its influence on various salient aspects, specifically the durability of concrete, is discussed in this paper. The influence of chlorides and sulphates present in the municipal treated water used for watering plants and shrubs on the durability of concrete is also presented. Moreover, the chloride threshold value of the reinforcement is between 0.1% and 1.5%. The total charges passed through concrete are also reduced to less than 1000 Columbus with the addition of agricultural by-products. In addition, root intrusion tendency of commonly grown plants on rooftop and corrosion due to agricultural chemicals are also mentioned. In the latter sections, remedial measures are highlighted to minimize the negative impacts of rooftop vegetation on the durability of concrete. In addition, to highlight the impact of chlorides on the roof concrete, the study also presented the chloride permeability and service life of blended concrete.

The Influence of CaCl2-Blended Acrylic Polymer on Steel Rebar Corrosion and Acid Attack Resistance of Mortar

A realistic forecast of the impact of CaCl2-blended acrylic polymer (CP) emulsions on steel reinforcement corrosion is difficult without a detailed study. This is traceable to the conflicting effects of cement additives on the chloride threshold value, pore solution chemistry, and matrix resistivity. Hence, in the study reported herein, the actual influence of 0.5–1.5 wt% CP on rebar corrosion was assessed via an accelerated corrosion test. The macrocell current, half-cell potential measurements (HCP), reinforcement cover crack propagation, and rebar deterioration were monitored. The resistance of mortar specimens to acid-induced degradation was also evaluated over time. The corrosion test results indicate that steel rebar corrosion initiation in the mortar expedited as the CP dosage in mixtures increased. Consequently, the time required for the CP-modified specimens to crack shortened. Moreover, non-uniform rebar section loss and surface crack width widening were also observed in CP-modified mortar specimens. However, X-ray diffraction (XRD) analyses of the plain Ref and 1.5% CP corrosion byproduct residues indicated that key phases such as akaganeite, goethite, lepidocrocite, hematite, and magnetite were quantitatively similar. Interestingly, the addition of 1.0–1.5% CP to mixtures enhanced the acid attack resistance of mortars. For now, these results indicate that CP should only be used as a chemical admixture in unreinforced cement composites.

Durability life prediction of RC piles subjected to localized corrosion in chloride environments

In this study, an analytical model for evaluating the durability life of reinforced concrete (RC) piles subjected to localized corrosion under chloride attack is proposed. The localized corrosion process is divided into three stages, and a predictive method is presented to predict the durability life of the pile by calculating the time of each stage. The time of each stage is determined based on the chloride diffusion model, the pitting corrosion model and the crack propagation model. The effects of the water-cement ratio, concrete cover thickness, pile concrete quality, relative humidity, chloride threshold level, pitting factor, corrosion current density and initial surface chloride ion concentration on the various stages of localized corrosion and the durability life of the pile are investigated. The analysis results show that the effects of the water-cement ratio and concrete cover thickness on the durability life of the pile are the most significant in the corrosion initiation stage. The durability life is increased by a reasonable choice of both concrete water-cement ratio and concrete cover thickness with constant concrete quality. The durability life of the pile increases with increasing concrete cover thickness, concrete quality, chloride threshold value and limit crack width, while it decreases with increasing water-cement ratio, relative humidity, corrosion current density and initial surface chloride concentration. The influence of the pitting factor is minimal and is mainly in the pit nucleation stage.

Galvanic Corrosion Study between Tensile-Stressed and Non-Stressed Carbon Steels in Simulated Concrete Pore Solution

The present study investigated the galvanic effect between tensile-stressed and non-stressed carbon steels, in addition to the influence of the tensile stress on the passivation and corrosion behavior of steel in a simulated concrete pore solution. Three different levels of tensile stress, ranging from elastic to plastic stress on the surface, were applied by adjusting the displacement of C-shape carbon steel rings. Different electrochemical measurements including the open circuit potential (OCP), the electrochemical impedance spectroscopy (EIS), the zero-resistance ammetry (ZRA), and the cyclic polarization were performed. Based on the results of EIS, the tensile stress degraded the resistance of the oxide film in moderate frequencies while enhancing the charge transfer resistance in low frequencies during passivation. As corrosion propagated, the stressed steel yielded a similar charge transfer resistance to or an even lower charge transfer resistance than the non-stressed steel, especially in the case of plastic tensile stress. The galvanic effect between the tensile-stressed and non-stressed steels increased the chloride threshold value of the tensile-stressed steel, although the susceptibility to pitting corrosion was exhibited after being corroded.

Quantitative Non-Linear Effect of High Ambient Temperature on Chloride Threshold Value for Steel Reinforcement Corrosion in Concrete under Extreme Boundary Conditions.

This paper investigates the effect of high ambient temperatures on the chloride threshold value for reinforced concrete (RC) structures. Two commonly available carbon steel rebars were investigated under four different exposure temperatures (20 °C (68 °F), 35 °C (95 °F), 50 °C (122 °F), and 65 °C (149 °C)) using environmental chambers at a constant relative humidity of 80%. For each temperature, six different levels of added chloride ions (0.00%, 0.15%, 0.30%, 0.60%, 0.90%, and 1.20% by weight of cement) were used to study the chloride threshold value. Corrosion initiation was detected by monitoring the corrosion potential and corrosion rate using electrochemical techniques. The water-soluble (free) and acid-soluble (total) chlorides were determined using potentiometric titration according to the relevant ASTM standards. The threshold chloride content for each exposure temperature was determined by analyzing the corrosion potential, corrosion rate, and chloride content of each specimen. The results showed that the chloride threshold values were significantly temperature-dependent. At temperatures of 20 °C (68 °F) and 35 °C (95 °F), the chloride threshold value (expressed as free chlorides) was approximately 0.95% by weight of cement. However, as the temperature increased to 50 °C (122 °F), the chloride threshold decreased significantly to approximately 0.70% by weight of cement. The reduction in the chloride threshold value became more dramatic at an exposure temperature of 65 °C (149 °F), decreasing to approximately 0.25% by weight of cement. The trends were similar for the rebars from the two sources, indicating that the rebar source had little influence on the chloride threshold value.

A Comparison between Ultrasonic Guided Wave Leakage and Half-Cell Potential Methods in Detection of Corrosion in Reinforced Concrete Decks

This article presents the advantages and limitations of a recently developed Ultrasonic Guided Wave Leakage (UGWL) method in comparison to the well-known Half-Cell Potential (HCP) method in their ability to detect corrosion in reinforced concrete (RC) bridge decks. This research also establishes a correlation between UGWL data and chloride content in concrete RC slabs. Concrete slabs submerged in a 10% NaCl solution were monitored using both methods over a period of six months. The chloride content from the three cores (0.84, 0.55, and 0.18%) extracted from the slab after the 6-month long process all exceeded the chloride threshold values suggested in ACI 318, which is 0.05 to 0.1% by weight of concrete. Further, the UGWL method detected changes due to corrosion approximately 21 days earlier than the HCP method.

Influence of chloride cations on pore solution chloride and critical chloride threshold of carbon steel rebar

ABSTRACT As part of ongoing research to validate the efficacy of a potentiodynamic polarization technique of determining the critical chloride threshold (CCRIT) value of steel reinforcing bars exposed to chloride-contaminated concrete, the present work reports CCRIT values of carbon steel exposed to NaCl, CaCl2 and MgCl2. The increasing use of locally available multi-chloride anti-icing agents in Ontario during the winter season, which are brine solution with ~21% chloride as NaCl, CaCl2 and MgCl2, resulted in a need to understand the impact of these salts on the threshold values. The potentiodynamic polarization method allowed the influence of these salts on CCRIT values of carbon steel rebar to be determined in a significantly shorter period than existing standard methods. Cement pastes with varying admixed chloride as NaCl, CaCl2 and MgCl2 were cast with 0.5 w/cm ratio and their pore solution content was expressed after 28 days curing for cation and anion analyses. The resulting pore solution composition revealed increasing Ca, K and Na cations and increasing chloride and sulphate anions when the cement pastes were admixed with chloride as NaCl. However, sulphates decreased in the pore solution when the pastes were prepared with CaCl2 and MgCl2. The consequence of the latter findings was that the threshold values by mass of pore solution of the carbon steel rebar exposed to these chloride compounds were significantly lower than bars exposed to pore solution with NaCl. Nevertheless, the conversion of these values to percentage by mass of cementitious materials gave surprisingly similar values for all three chlorides

Chloride-induced corrosion of reinforcement in simulated pore solution of geopolymer

Studying the chloride-induced corrosion of reinforcement in geopolymer is of great significance to the corrosion prevention of marine engineering. In this paper, the chloride-induced corrosion experiments of reinforcement in five solutions with different compositions and concentrations were carried out. The chloride threshold value that lead to initiate depassivation of the reinforcement was proposed. The phenomena of localized corrosion and the corrosion current density were further analyzed. The results show that the chloride threshold value Ccrit increases with the increase of alkaline of electrolyte. Ca(OH)2 can maintain the alkalinity of pore solution. Thus the reinforcement immersed in Ca(OH)2 solution can be repassivated, which enhances the stability of the passivated film. The results further show that the reinforcement in geopolymer exhibited significantly higher corrosion resistance, however, the stability properties of the passivation film of reinforcement in cement is better than that of reinforcement in geopolymer.

Initial-corrosion condition behavior of the Cr and Al alloy steel bars in coral concrete for marine construction

To improve the corrosion resistance of the steel matrix, 1% and 3% Cr and 1% Al are added to ordinary carbon steel for the design of a corrosion-resistant alloying composition. And based on the principle of electrochemical tests, a method for determining the depassivation of Cr and Al alloy steel bars in coral aggregate concrete (CAC) is established. The equivalent circuit model was used based on the electrochemical impedance spectroscopy (EIS) results to characterise the corrosion behaviour of the Cr and Al alloy steel bars and determine their corrosion resistance and the protective effect of the steel bar passivation film. The corrosion resistance of the Cr1 reinforcement to chloride increases by 37.67%, that of the CrAl reinforcement increases by 64.08%, and that of the Cr3 reinforcement increases by 171.82% with respect to that of the HPB 400 bar. The polarisation curves of the alloy steel bars with different Cr and Al contents in CAC were recorded by linear polarisation resistance (LPR), and the time variations of the corrosion potential and corrosion current in the low-alloy steel bars containing Cr and Al were analysed. In addition, the free chloride ion concentration and pH value of the CAC were measured while the Cr and Al alloy steel bars were rusting. The chloride threshold values (% by weight of concrete) of the HPB 400, Cr1, CrAl, and Cr3 steel bars are 0.515%, 0.718%, 0.950%, and 1.084%, and the chloride thresholds (Cl−/OH− ratio) are 0.288, 0.382, 0.502, and 0.693, respectively. Initial-corrosion condition behavior of the Cr and Al alloy steel bars in CAC was obtained. There is considerable scientific value and application significance attainable from the examination of the corrosion mechanism and behavior of corrosion-resistant steel bars in a harsh marine environment.

Corrosion of rebar in concrete. Part III: Artificial Neural Network analysis of chloride threshold data

Active corrosion of carbon steel in reinforced concrete occurs when the chloride ion concentration exceeds the chloride threshold (CT). CT is affected by many physical and chemical parameters including primary variables (pH, corrosion potential, breakdown potential, and temperature) and secondary variables (cemenet composition, concreete porosity, and water/cement ratio). A Kohonen-self organized map (KSOM) and regression artificial neural network (ANN) coupled methodology was developed to find the missing values of independent variables in the sparse database and for quantitatively evaluating the effects of these variables on CT values that are expressed in %TotalCl/cem (or %FreeCl/cem), and [Cl−]/[OH−].

Investigations of accelerated methods for determination of chloride threshold values for reinforcement corrosion in concrete

ABSTRACT Testing the critical chloride content (C crit) in laboratory samples or in samples retrieved from structures enhances the understanding of rebar corrosion initiation in concrete and can result in a significant improvement of predicting the residual service life of ageing structures. A possible drawback of test methods for C crit is that they can be time-consuming. In this work, different accelerated methods for C crit testing are studied and compared. It is found that the acceleration method influences the test results. The results are discussed with respect to evaluation of existing structures and service life modelling.

Corrosion of rebar in concrete. Part II: Literature survey and statistical analysis of existing data on chloride threshold

The literature is reviewed with respect to defining, measuring, and interpreting the chloride threshold (CT). CT was defined with a strong fundamental basis in the Point Defect Model. which also dictates the nature of the statistical analysis of surveyed CT values. A database of CT for various primary and secondary independent variables has been established. Statistical analyses reveal that CT is lognormally distributed, in accordance with the PDM, with most probable values being 0.85, 0.69, and 1.19 for %total Cl/cem, %free Cl/cem, and [Cl−]/[OH−], respectively. The breakdown and corrosion potentials follow normal distributions with means of 0.056 and -0.322 VSCE, respectively.