Critical Chloride Concentration Research Articles

Updating Durability Models for Concrete Structures in Chlorine Environment Based on Detection Information

The assessment of concrete structure durability in chlorine environments is significantly impacted by the uncertainty inherent in existing durability models. It introduces an integrated approach for updating these models based on the detection information of existing structures. This approach narrows the gap between theoretical predictions and observed structural durability. Specifically, we refined the probability model of critical chloride content by analyzing steel bar corrosion sample proportions using Bayesian theory for greater accuracy. The enhanced model enables more reliable life expectancy prediction, forming a solid foundation for maintaining and strengthening existing structures. This method was demonstrated through a case study of a reinforced concrete industrial building with a service life of 12 years.

A novel LDHs-VB3- inhibitor for rebar corrosion in simulated concrete pore solution: Synthesis, performance and mechanism

Developing novel chloride-trapping inhibitors is of great significance for enhancing the durability of marine concrete structures. In this study, a novel LDHs-VB3- inhibitor was synthesized through the ion exchange method. Then, the corrosion inhibition mechanism of LDHs-VB3- inhibitor for rebar in the whole process of release - capture - adsorption - retardation was studied using experiments and density functional theory (DFT) simulations. The chloride ion exchange test demonstrates that the LDHs-VB3- inhibitor has a chloride trapping capacity of 35.5 mg/g in the saturated Ca(OH)2 solution containing 0.14 M NaCl, implying that it could capture Cl- in concrete pore solution. According to the electrochemical tests, the critical chloride concentration of rebar in the simulated concrete solution containing LDHs-VB3- falls within a range of 0.22 M–0.28 M, which is much higher than that in the solution without LDHs-VB3- (0.10 M–0.14 M). DFT simulations indicate that LDHs-VB3- exhibits more positive binding energy and uneven binding forces in contrast to LDHs-Cl-. Consequently, VB3- could be easily replaced by Cl- and then released into the pore solution of concrete. Moreover, the released VB3- could adsorb on the α-Fe2O3 surface in a concrete environment via the interaction of surface Fe atoms with N and O atoms of VB3-. The preadsorbed VB3- could diminish the interaction of Cl- with the α-Fe2O3 surface by reducing electron transfer, thereby mitigating the risk of passive film breakdown and retarding the chloride-induced corrosion of rebars.

Steel corrosion and critical chloride content in concrete with calcined kaolinite clay, fly ash, and limestone powder under natural and accelerated marine environments

This study aims to investigate steel corrosion and critical chloride content in concrete with calcined kaolinite clay, fly ash, and limestone powder. The chloride diffusion coefficient and compressive strength of concrete, and weight loss of steel were measured after the specimens were exposed to the tidal zone in a real sea environment for 1 and 2 years. The depassivation time of the embedded steel and the critical chloride content of the concrete under an accelerated marine environment were investigated in the laboratory. The test results revealed that the coefficient of chloride diffusion and critical chloride content of concrete and weight loss of steel decreased with increasing calcined kaolinite clay contents. Although utilizing calcined kaolinite clay in concrete mixtures reduced critical chloride content (0.655% by wt. of binder for OPC and 0.573 to 0.427% by wt. of binder for C15 to C45) because of the lower portlandite content, it caused a longer rebar depassivation time (46 days for OPC and 63 to 237 for C15 to C45). The ternary binder systems of cement, calcined clay, and fly ash demonstrated the best overall performances, i.e., the lowest chloride diffusion coefficient (0.29 ×10−12 m2/s) and the highest compressive strength of the concrete (38.7 MPa), and no weight loss of embedded steel at 2 years of exposure.

Electrochemical behavior of zinc in alkali-activated fly ash solution

To study the passivation process and chloride-induced corrosion mechanism of galvanized steel in alkali-activated fly ash (AAFA) solution, pure zinc was chosen as the working electrode. Moreover, two other simulated concrete pore solutions, e.g., saturated Ca(OH)2 solution and ordinary Portland cement (OPC) solution were also tested for comparative purposes. Based on various electrochemical measurements and surface characterization techniques, the passivation capability and the chloride-induced corrosion behavior of zinc and its critical chloride concentration were investigated. Although no calcium hydroxyzincate (CHZ) was formed for zinc in AAFA solution due to the lack of sufficient calcium ion, a zeolite-like adsorption layer as well as a silicate gel adsorption layer could be formed on the zinc surface. Accordingly, compared with the other alkaline solutions, enhanced corrosion resistance was evident for zinc in AAFA solution even in the presence of high chloride concentration. These findings of this study serve as the first step towards enhancing our understanding of the possible application of galvanized steel in alkali-activated materials exposed to harsh marine environments.

Coconut coir dust extract as a novel green corrosion inhibitor for carbon steel in the chloride-contaminated concrete pore solution

The potential of coconut coir dust to inhibit corrosion, especially the pitting of rebars in concrete was tapped by electrochemical techniques. Electrochemical impedance spectroscopy and linear polarization results show that both deionized water and ethanol extracts of coconut coir dust can slow down corrosion development by forming a protective film even after long-term exposure to chloride and the latter performs better and is more stable. Cyclic potentiodynamic polarization results further show that ethanol extract at a concentration of 0.1 g/L can significantly delay the initiation of pitting. This inhibitor has exhibited the highest inhibition efficiency, which can be sustained at over 90 % even after six months of immersion in solutions with high chloride concentration, but increasing the concentration of the inhibitor does not result in any additional improvement in its efficiency. Critical chloride concentration for corrosion initiation prediction and corrosion resistance evaluation was also discussed.

Chloride-induced corrosion patterns of reinforcements in simulated pore solutions of calcium sulfoaluminate cement concrete: An analytical study

The widespread use of calcium sulfoaluminate cement (CSA) for rapidly repairing marine structures exposed to high chloride levels has spurred limited investigation into the corrosion behavior of reinforcements in low-pH CSA systems. To address this knowledge gap, researchers conducted a comprehensive study on the impact of primary ions within CSA (OH−, SO42−, and Al(OH)4-) on steel rebars in simulated pore solutions (SPSs). The investigation employed various analytical methods such as Mott-Schottky/cyclic polarization curves, corrosion current, impedance spectrum analyses, and microstructural examinations. The results demonstrate that SO42− diminishes the corrosion resistance of reinforcements by depassivating them, consequently reducing the critical chloride concentration (Ccrit). However, this influence is mitigated with elevated OH− or Al(OH)4− concentrations. Furthermore, the presence of Al(OH)4- in the pore solution contributes to an increased Ccrit by stabilizing alkalinity via OH− hydrolysis. Based on the empirical findings, the researchers developed an empirical formula for Ccrit, offering insights into estimating the service life of CSA-based concrete structures in real marine environments.

On the corrosion parameters acquired through potentiodynamic scans of carbon steel rebar in simulated pore solution and mortar

This study developed a methodology for quantifying the corrosion parameters such as corrosion potential, corrosion current density and Tafel slopes for rebar in simulated pore solutions and mortar with realistic rebar conditions. We quantitatively investigated the impact of depassivation duration, chloride concentration, carbonation, and relative humidity on these parameters. Specifically, in partially saturated mortar, it was observed that the critical chloride content lacked a distinct threshold. The degree of depassivation, as indicated by shifts in corrosion parameters due to chloride ions and carbonation, was influenced by humidity.

Chloride ion diffusion in saturated lightweight aggregate concrete: A numerical investigation

The durability of structural LWAC exposed to chloride environments remains a subject of debate due to its porous inclusions and the unresolved transport mechanisms. This paper aims to investigate the diffusion behavior of chloride ions in LWAC by establishing a numerical model at the mesoscale. LWAC was considered a two-phase material comprising lightweight aggregates and mortar matrix. The diffusion coefficients of chloride ions for the mesoscopic components in LWAC were derived using the composite sphere model. A parametric study was conducted to further explore the chloride ion diffusion process, taking into account the aggregate shape, water-to-cement (w/c) ratio, diffusivity of aggregate, aggregate content, and grading. The results suggest that the quality of the mortar matrix had the most significant impact on the chloride ion diffusion in LWAC, while the effect of aggregate diffusivity was influenced by the w/c ratio. By incorporating exposure conditions and critical chloride concentration suggested by the existing design model, the effects of different exposure conditions on the LWAC structures were studied. LWAC structures showed shortest service life in Tidal and Splash environment, and limits on the cover thickness and the maximum w/c ratio of LWAC structures were given by the mesoscopic numerical model.

Effect of Stress on the Critical Chloride Content of Steel Bar in Simulated Concrete Pore Solution

Effect of Stress on the Critical Chloride Content of Steel Bar in Simulated Concrete Pore Solution

Service life prediction and time-variant reliability of reinforced concrete structures in harsh marine environment considering multiple factors: A case study for Qingdao Bay Bridge

Chloride attack is the primary cause of performance deterioration and life attenuation of reinforced concrete (RC) structures in marine environments. In an attempt to accurately predict the reliability and service life of RC structures under the co-effects of multiple factors, a comprehensively modified chloride-transport-based model is proposed in this paper. Based on Fick's second law, a multifactor integrated deterministic chloride transport model is developed considering the time dependence, concrete mix proportion, chloride binding capacity, freeze–thaw cycles, sustained load, temperature, humidity and concrete deterioration. Based on extensive literature review combined with the results of multitudinous long-term field exposure tests used in the durability design of Hong Kong-Zhuhai-Macao Bridge and Shenzhen-Zhongshan Bridge, the probability distribution types and parameter values of the governing variables are determined. Taking Qingdao Bay Bridge as an example, the time-variant reliability index, failure probability and reliability-index-based corrosion initiation are determined by using the equivalent normalization method (JC method) and Monte Carlo simulation technique for different environmental zones including atmospheric/splash/tidal/submerged zones. The sensitivity of the reliability index to the control variables and the effects of age index, chloride binding capacity, numbers of freeze–thaw cycles, stress level and concrete deterioration on the reliability index are quantitatively investigated. The results show that the time-variant reliability of different environmental zones is sequenced as: atmospheric zone > submerged zone > tidal zone > splash zone; the sensitivity of reliability to the governing variables sequenced as: concrete cover thickness > surface chloride concentration > chloride diffusion coefficient > critical chloride concentration; the time dependence of the diffusion coefficient has a significant effect on the time to corrosion initiation and cannot be ignored in the predictive model for both the high-performance or ordinary concrete; the number of freeze–thaw cycles and the tensile stress level are relatively insensitive but substantially detrimental to the reliability of corrosion initiation.

Durability of concrete incorporating recycled coarse aggregates: carbonation and service life prediction under chloride-induced corrosion

The use of recycled aggregates (RA) is growing due to the environmental problems associated with extracting natural aggregates (NA) and the disposal of construction and demolition waste (CDW). However, the service-life prediction of recycled coarse aggregate concretes remains incipient. Thus, this study aimed to evaluate the effects of different replacement contents of NA by RA (25, 50, and 75 wt%) on physical (water absorption, porosity, and bulk density), mechanical properties (compressive strength and modulus of elasticity), microstructure (evaluated by X-ray microtomography), accelerated carbonation, and chloride penetration of concrete. A service life prediction analysis of RA concretes was conducted based on the chloride profile obtained and considering the application of different concrete surface treatments. The RA contents evaluated increased the carbonation and chloride diffusion coefficients by 75.7% and 43.0%, respectively, compared to the reference concrete. Nevertheless, reductions of approximately 50% on the critical chloride concentration depth of RA concretes are estimated considering the application of acrylic-based surface treatment. Therefore, applying surface treatments is promising to increase RA concretes' durability and service life, contributing to its wide use and dissemination feasibility.

Sensitivity analysis of a physicochemical model of chloride ingress into real concrete structures subjected to long-term exposure to tidal cycles

In marine environments, reinforced concrete structures are exposed to tidal conditions and therefore susceptible to chloride ingress. Reliable models of transport are crucial in order to evaluate the service life of these structures. Unlike engineering models based on Fick's 2nd law and empirical coefficients, this study proposes a model based on a physicochemical description of the transport phenomena and on some assumptions restricting the number of inputs to 9 parameters and the computational costs. This model is validated for a long exposure to tidal cycles (28 years). Then, the sensitivity analysis, based on the Morris method, is performed through 100 simulations of tidal exposure considering different sets of the 9 input parameters. According to the critical times of initiation of corrosion predicted, the most sensitive parameters are the critical chloride concentration and the chloride diffusivity factors. The effects of moisture sorption and chloride binding parameters are moderate after long exposure. Then, the results of the simulations are compared to data of the literature in terms of convection depths and total chloride concentrations at the limit of the convection / diffusion zones. Finally, by quantitative considerations, the analysis goes further, providing analytical relations expressing the convection depth and the associated total chloride concentration as functions of input parameters. These provide physically informed guidelines in using an engineering model based on Fick's 2nd law in order to estimate the critical time of initiation of corrosion.

Toward effective utilization of fly ash and multi-binder system with fly ash in concrete

This paper describes first the situation of fly ash in various ASEAN countries. Then the development of fly ash utilization in Thailand is discussed, which includes fly ash specification, standards on durability and service life design for fly ash concrete, and in the final, study results of application potential of various off-spec fly ashes are elaborated. Characteristics of fly ash in different ASEAN countries are different and have different problems. Thailand has 2 major sources of fly ash which have significantly different properties, especially CaO content (high and low CaO). Therefore, the standard specification of the Thai fly ashes classifies the fly ashes based on both quality classes (Classes 1, 2, and 3, with class 1 having the highest quality) and CaO content (high and low CaO). The effects of the fly ash were considered in the durability and service life design standard, for example in estimating the diffusion coefficient of chloride, critical chloride content, carbonation coefficient, and sulfate resistance. Lastly, examples of comparative study results on some off-spec fly ashes (high free lime, dumped wet, and high LOI fly ashes) are demonstrated.

Accelerated test device and method for critical chloride concentration initiating steel depassivation in cement-based materials

Abstract In order to overcome the disadvantages of traditional test devices and methods, new accelerated test device and efficient test method for critical chloride concentration (Ccrit) initiating steel depassivation in cement-based materials were developed. Based on the theory of electromigration, a new accelerated test device for Ccrit was invented first by combining with the chloride electromigration system and electrochemical test system. Then the influences of applied voltage and continuous power-on time on electrochemical parameters including open-circuit potential, polarization resistance, and corrosion current density during the steel depassivation process were investigated. Moreover, an efficient test method for Ccrit was proposed based on the quantitative criterion in terms of corrosion current density. Analysis results show that Ccrit can be measured quickly and accurately based on the accelerated test device and method by selecting appropriate applied voltage (e.g., 3–6 V) and continuous power-on time (e.g., 48–72 h).

Long-term performance of reinforced concrete under a de-icing road environment

In the middle of 1990, over 30 different mixes of concretes with eight different binders and water-binder ratios of 0.3 to 0.75 were exposed to a highway environment with a heavy de-icing salt spread for the examination of long-term performance, including chloride penetration, reinforcement corrosion and frost attack. This paper presents the results from this long-term study regarding chloride penetration and reinforcement corrosion. The results show that the chloride penetration in concretes under a de-icing salt road environment is much weaker than that in concretes under marine splash environment in Sweden. The estimated critical chloride content for the corrosion initiation is about 0.3 % by mass of binder for rebars with uncracked concrete cover. Considering the chloride redistribution in the surface zone, ClinConc model has been modified so that it can present a better description of the chloride profiles in the concretes at such an exposure site.

Evaluating the effects of environmental aging on the pitting corrosion of steam turbine blade steels

AbstractA flow loop has been setup to allow simulation of operating conditions in a steam turbine during transitions in water chemistry between on‐load (deaerated) and off‐load (aerated) environments. Electrochemical noise measurements were performed to establish the critical chloride concentration for pitting of 403 12Cr stainless steel. The results were confirmed by comparative measurements of corrosion potential and visual observation of pitting. X‐ray photoelectron spectroscopy was used to quantify changes in the passive film due to transient environmental conditions. The critical chloride concentration for pitting with/without pre‐exposure to on‐load conditions has been measured and the impact of environmental aging is discussed.

A Comprehensive Investigation on the Effects of Surface Finishing on the Resistance of Stainless Steel to Localized Corrosion

The present research investigates the influence of surface roughness imparted by cold surface finishing processes on the localized corrosion resistance of stainless steel. Five different alloys were studied: ferritic AISI 430, martensitic AISI 430F, austenitic AISI 303, AISI 304L, and AISI 316L. It was demonstrated that the grinding process, executed on previously cold drawn bars, leads to an improvement in corrosion resistance according to the results obtained with electrochemical tests, namely, potentiostatic and potentiodynamic tests in chloride-rich environments, the salt spray test, and long-term exposure in urban and marine atmospheres. This allowed us to establish a trend among the different alloys regarding the resistance to pitting corrosion, which was assessed according to pitting potentials, critical chloride contents, and pitting initiation time. All the tests confirmed that surface finishing, as well as alloy chemical composition, is an important factor in controlling the corrosion resistance of stainless steel.

Effect of cation type on corrosion of steel treated by DNA corrosion inhibitor in simulated concrete pore solution

The purpose of this study is to evaluate the influence of cation types on the rust resistance performance of new nucleic acid corrosion inhibitors in simulated concrete pore solution. Four common chlorinated ice salts (sodium chloride (NaCl), potassium choride (KCl), calcium chloride (CaCl2) and magnesium chloride (MgCl2)) were selected to study the corrosion behaviour of chloride ions by linear polarisation resistance method, electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy. The results show that the cationic type will affect the thickness of the passivated film on the steel surface and the compactness of the passivated film formed by iron oxide and nucleic acid rust inhibitor. The type of cations affects the critical chloride concentration of nucleic acid inhibitor, following Na+ ≈ K+ > Ca2+ > Mg2+.

Effect of carbonation on chloride transportation parameters in cementitious materials

ABSTRACT Many studies have only studied carbonation and chloride penetration separately, and study dealt with synergy interaction between these is very rare. This study is devoted to examining the chloride penetration parameters of carbonated cementitious materials, i.e. (a) surface chloride content, (b) chloride diffusivity, (c) chloride adsorption capacity and (d) critical chloride content linked with reinforcement corrosion directly. These chloride transportation parameters were expressed as a function of time in each condition because these depend on the mixing proportional properties and the degree of cement hydration. This study is expected to be useful to develop a chloride penetration model of carbonated concrete in the future.

Stainless Steels as Sustainable Solution for Concrete Reinforcement - From Laboratory to Practice

Stainless steel reinforcing bars show excellent corrosion resistance in concrete exposed to harsh environments. In this combined electrochemical and surface analytical work, an explanation for this behavior is proposed. XPS surface analytical results (thickness, composition of the passive film and of the interface beneath the film) obtained on black steel, FeCr alloys, and a series of stainless steels after exposure to alkaline solutions simulating concrete are reported. Pitting potentials were determined in the same solutions with electrochemical experiments. It is shown that the pitting potentials of the steels can be related to the Cr (III) oxy-hydroxide and Mo (VI) content in the passive film. It is proposed to calculate a Cr and Mo oxide equivalent similar to the well-known pitting resistance equivalent number (PREN). A correlation between the critical chloride content in concrete (reported in literature for CEM II A/LL and CEM I) and the pitting potential for carbon steel, Fe12%Cr alloy, DIN 1.4301 and DIN 1.4571 stainless steels is proposed to link results of solution analysis and performance in concrete.