Effect Of Chloride Binding Research Articles

Effect of chloride binding and sulfate ion attack on the chloride diffusion in calcium sulfoaluminate-based material under seawater environment

The diffusion of chloride ions in reinforced concrete under the seawater environment will affect the physical or mechanical properties and durability. Sulfate ions also influence the diffusion of chloride ions by generating expansion products through physical and chemical reactions. Further research on the effects of chloride binding and sulfate ion attack on chloride ion diffusion will deepen the understanding of concrete failure mechanism. In this paper, a quaternary blend based on calcium sulfoaluminate (CSA) cement was prepared and laboratory immersion tests were conducted in artificial seawater with varying salt concentrations. Initially, chloride ion concentration measurements and XRD tests were conducted at different corrosion ages and salt concentrations. Subsequently, the chloride binding properties of CSA-based materials was quantified through the analysis of chloride ion concentration and the phases of hydration products. Meanwhile, the corrosive effect of sulfate ions on chloride ion diffusion was determined corresponds to the content of expansive hydration products. Furthermore, numerical simulations were employed to evaluate the impact of sulfate ion corrosion, chloride binding, and their combined effects on chloride ion diffusion, and the results were compared with free chloride ion concentration (Cf). The results indicate that the total chloride ion concentration (Ct) exhibits a linear relationship with increasing salt concentrations of seawater in CSA-based materials. Meanwhile, the bound chloride ion concentration (Cb) follows a logarithmic growth pattern. The chloride binding rate experiences a linear decline with the increase of chloride ion concentration in the artificial seawater. Additionally, the relationship between Cf and Cb or Ct can be described using different isothermal adsorption models for the CSA-based materials. Among these models, the Langmuir model is suitable for characterizing the relationship between Cf and Cb, while the Freundlich model is suitable for describing the relationship between Cf and Ct. Furthermore, it is noteworthy that sulfate ion attack and chloride binding exert nearly equivalent effects on the diffusion of chloride ions in CSA-based materials at short corrosion age and low chloride ion concentration. However, the corrosive impact of sulfate ions gradually evolves into the dominant factor in the progression of corrosion over time and the increase in seawater salt concentration.

A multi-phase mesoscopic simulation model for the long-term chloride ingress and electrochemical chloride extraction

Electrochemical chloride extraction (ECE) is one of the effective methods to remove chloride and prolong the service life of reinforced concrete (RC) structures. To fully understand the mechanisms of the long-term chloride ingress and subsequent ECE treatment of RC structure, a multi-phase mesoscopic numerical model is proposed. Unlike most of existing models, the long-term chloride ingress and the effect of chloride binding are considered in the proposed model, and the transport of chloride is simulated through a novel diffusion-migration-reaction process. The numerical simulation results show that the adsorption capacity of concrete to chloride decreases with the increase of chloride ingress time. Interestingly, the free chloride concentration on the surface of concrete decreases dramatically, and the maximum value appears in the concrete protective cover after ECE treatment. Furthermore, ECE treatment time, current density and concrete protective cover have significant influences on ECE treatment efficiency. Besides, the quantitative relationship models between these factors and ECE treatment efficiency have been developed. Moreover, the use of stirrup can improve the efficiency of ECE treatment. The research outcomes reveal previously ignored fundamental aspects of the ECE treatment and provide insights for the durability prediction of RC structures.

Chloride binding capacity of green concrete mixed with fly ash or coal gangue in the marine environment

Wide application of green concrete mixed with supplementary cementitious materials (SCMs) can result in the reduction of energy consumption and carbon dioxide emission from cement production. Adequate aluminum in SCMs can improve the chloride binding capacity of green concrete to decrease the free chloride concentration in pore solution, reduce the corrosion risk and enhance the structural durability. Thus, high-aluminum fly ash (FA) and coal gangue (CG) can be regarded as potential SCMs for reinforced concrete structures exposed to the marine environment. This study investigated the chloride binding capacity of FA and CG concrete in the marine environment and the effects of the environment (salt fog and tidal zone) and water to cement ratio (w/c) on the chloride binding capacity. The replacement ratios of cement by FA or CG were designed to be 0%, 10%, 20%, and 30%. The results indicated that FA and CG could significantly improve the chloride binding capacity and the optimal contents of both SCMs are in a range from 20% to 30%. The chloride binding capacity is time-dependent and can be described well by linear binding isotherm. Furthermore, the chloride binding capacity in salt fog is lower than that in the tidal zone and the binding capacity increases with an increase of w/c. Finally, a semi-empirical model was proposed to evaluate the chloride diffusion and predict the chloride concentration considering the effect of chloride binding.

A refined, self-consistent Poisson-Nernst-Planck (PNP) model for electrically induced transport of multiple ionic species through concrete

A fundamental re-look of the use of Poisson-Nernst-Planck (PNP) model for predicting electrically accelerated ionic transport through concrete is carried out. The PNP model is augmented with concentration-based diffusion coefficients and explicit considerations of transport path in the formulations since the electric field is distributed only along the connected pore path. The geometric tortuosity obtained from electrical property measurements is modified with a multiplicative correction factor that is a function of the ratio of dominant pore sizes in the specimen. Idealized models of the pore structure are used to arrive at this correction factor, which ranges between 1.5-to-3.0 for typically used concretes. Time-dependent changes in boundary conditions induced by the electrode reactions are also accounted for. The effect of chloride binding as a time-dependent process during the test, is also ascertained. The model is verified on a series of concretes of different water-to-cement ratios and containing different cement replacement materials (fillers and/or reactive materials) subjected to the non-steady state migration test.

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

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

The effect of chloride binding on the predicted service life of RC pipe piles exposed to marine environments

Chloride binding capacity has a significant effect on the service life of reinforced concrete (RC) pipe piles exposed to marine environments. Four typical chloride binding isotherms (i.e., null, linear, Langmuir and Freundlich binding isotherms) were reviewed in this paper. The effect of chloride binding on service life predictions of RC pipe piles, in terms of these different binding isotherms, was investigated. An experimental program was conducted to verify the theoretical predictions developed in the present study. The free and total chloride concentration profiles were presented for RC pipe piles exposed to submerged and splash zones for 5, 10 and 30 years. Furthermore, the predicted service life of RC pipe piles exposed to submerged and splash zones, using different binding isotherms, was also presented in this paper. The results of the present study indicated that the chloride binding has a more significant effect on the service life of RC pipe piles in submerged zone than in splash zone, and RC pipe piles in submerged zone display longer service life than those in splash zone.

The Effects of Chloride Binding on the Behavior of Cellulose-Derived Solutes in the Ionic Liquid 1-Butyl-3-methylimidazolium Chloride

The structure and diffusion of various linear and ringed solutes are examined in two different solvents, the ionic liquid 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) and SPC/E water, using molecular dynamics (MD) simulations. The formation of distinctly ordered local solvent environments around these solutes is observed. Specifically, spatial distribution functions reveal significant ordering of the solvents around the solutes with chloride-hydroxyl group interactions largely dictating these arrangements. Further, a breakdown of the hydrogen bonds that develop between the solute and solvent is provided, showing a relationship between the presence of additional functional groups and the distribution of hydrogen bonds. The diffusivities of the solutes were determined in water at 298 K, 1 bar and [BMIM]Cl at 400 K, 1 bar. The results show that the solutes were approximately 10-100 times more diffusive in water than in [BMIM]Cl. Within [BMIM]Cl, diffusivity appears to decrease with increasing strength of the hydroxyl groups present. Additionally, the free energies of solvation of the solutes are determined with COSMO-RS, providing information about their tendencies in forming aggregates. These results are then compared with MD results in which aggregation is quantified through the use of a dispersion measure. Though all solutes remained relatively dispersed in each of the solvents, those with hydroxyl groups were seen to be the most highly dispersed in the solvent [BMIM]Cl. Further, the dynamic dispersal of a large solute aggregate into [BMIM]Cl was studied, finding that solutes with hydroxyl groups tend to form complexes with the chloride ions. If strong enough, these chlorides can actually bind multiple solutes together into long chains, inhibiting their dispersal in solvent. It is believed that the formation of these chloride-solute complexes is largely responsible for the decreased diffusivity and elevated dispersion seen in simulations with [BMIM]Cl.

Effect of Chloride Binding on the Thermal Trimer−Monomer Conversion of Halorhodopsin in the Solubilized System

Halorhodopsin from Natronomonas pharaonis (NpHR) acts an inward-directed, light-driven chloride pump and forms a homotrimer. To evaluate effect of trimeric assembly, that is, intermolecular interaction, on the control or modulation of light-driven chloride pumping activity of individual HRs, it is important to understand the thermal and chloride sensitivity of trimer dissociation and the structural stability of HR. In this study, the thermal dissociation of NpHR trimer to monomer in a dodecyl beta-d-maltoside-solubilized system was investigated, using size-exclusion chromatography and visible absorption. In the absence of Cl(-), NpHR retained the trimer assembly at 25 degrees C but dissociated to the monomer with an increase in temperature to >40 degrees C. On the other hand, in the presence of Cl(-), the trimer assembly was maintained at 40 degrees C. The dissociation of the trimer to the monomer after incubation at 40 degrees C, which was determined via size-exclusion chromatography, depended on the Cl(-) concentration and showed a sigmoidal isotherm. From this isotherm, the apparent dissociation constant for Cl(-) was estimated to be 22 mM with a Hill coefficient of 2.2. A similar isotherm was obtained when SO(4)(2-) was used instead of Cl(-) with a dissociation constant of 94 mM. On the other hand, thermal dissociation of the NpHR trimer to the monomer in the absence of Cl(-) proceeded by two components: the fast component is susceptible to the changes in temperature and detergent concentration, and the slow component is accompanied by bleaching at the same time. Activation energies of the fast and slow dissociation components and bleaching were 57.8, 35.3, and 40.5 kcal/mol, respectively. The presence of a second chloride-binding site with a Hill coefficient of approximately 2 at the surface of NpHR to control the trimer-monomer conversion was discussed.

Chloride resistance of concrete and its binding capacity – Comparison between experimental results and thermodynamic modeling

Abstract The chloride resistance of concrete mixtures produced with different binders and water-to-binder ratios is determined by three different methods (natural chloride diffusion, accelerated chloride migration and conductivity measurement). The influence of mix design and type of binder are evaluated and related to porosity. The effect of chloride binding on chloride resistance is assessed by thermodynamic modeling and compared with chloride content measured with acid and water extraction. Chloride resistance depends on the type of binder and on water-to-binder ratio. Chloride content measurements and thermodynamic modeling both show that chloride binding is strongly related to the hydration degree of the cement and of the mineral admixtures. However, the decisive parameter for chloride resistance in all the tests is the permeability while the influence of chloride binding is less important.

Characterization and oxygen binding properties of des-Arg human hemoglobin

The role of chloride in the stabilization of the deoxy conformation of hemoglobin (Hb), the low oxygen affinity state, has been studied in order to identify the nature of this binding. Previous studies have shown that arginines 141alpha could be involved in the binding of this ion to the protein. Thus, des-Arg Hb, human hemoglobin modified by removal of the alpha-chain C-terminal residue Arg141alpha, is a possible model for studies of these interactions. The loss of Arg141alpha and all the salt bridges in which it participates is associated with subtle structural perturbations of the alpha-chains, which include an increase in the conformational flexibility and further shift to the oxy state, increasing oxygen affinity. Thus, this Hb has been the target of many studies of structural and functional behavior along with medical applications. In the present study, we describe the biochemical characterization of des-Arg Hb by electrophoresis, high-performance liquid chromatography and mass spectroscopy. The effects of chloride binding on the oxygen affinity and on the cooperativity to des-Arg Hb and to native human hemoglobin, HbA, were measured and compared. We confirm that des-Arg Hb presents high oxygen affinity and low cooperativity in the presence of bound chloride and show that the binding of chloride to des-Arg does not change its functional characteristics as observed with HbA. These results indicate that Arg141alpha may be involved in the chloride effect on Hb oxygenation. Moreover, they show that these residues contribute to lower Hb oxygen affinity to a level compatible with its biological function.

Effects of material and environmental parameters on chloride penetration profiles in concrete structures

On the basis of the transport mechanism of chloride ion, a prediction model of chloride penetration into concrete structures has been developed. The model includes the diffusion of chloride and its dependences on temperature, age, relative humidity, chloride binding and chloride convection by moisture transport. The experimental program has been set up to verify the model developed in the present study. Several series of concrete specimens were immersed in 3.5% chloride solutions for 15 weeks, and the chloride profiles of the specimens were measured and compared to the predicted chloride profiles. In addition, field measurements have been also conducted. From 10-year-old bridge piers, the chloride profiles in concrete under tidal zone were measured and compared with the predicted chloride profiles. The effects of chloride binding, relative humidity, temperature, exposure condition, and age-dependence on the chloride penetration in concrete were clarified from the present analyses. It was found from the present study that all these variables affect greatly the chloride penetration profiles in concrete. The comparison of the laboratory and field test data with the present theory confirms that the proposed model can be realistically used to predict the penetration of chloride ions into concrete structures under sea environments. Further, these results may be efficiently used for the realistic assessment and design for durability of concrete structures.

Influence of diffusion coefficient on chloride ion penetration of concrete structure

This paper proposes a modified diffusion coefficient that considers the effect of chloride binding and evaporable water on the diffusion coefficient. A finite element method (FEM) program based on the modified diffusion coefficient estimates chloride concentration according to concrete depth, and external and internal conditions. The predicted chloride concentrations were compared with experimental values. The modified diffusion coefficient, which is a function of chloride binding, evaporable water content and diffusion coefficient, varies greatly according to the water–cement ratio. Also, C 3A content, which has an influence on the chloride binding content, changes the modified diffusion coefficient. The FEM program using the modified diffusion coefficient estimates experimental chloride concentrations within a good accuracy. The numerical analysis of the internal and external conditions shows that the most effective way to reduce chloride ion penetration is to decrease water–cement ratio.

Theoretical assessment of the steady state diffusion cell test

The steady state diffusion cell test is often used to determine the chloride ion diffusion coefficient in cementitious materials. It involves the measurement of the flux of chloride ions through a specimen under near steady state conditions. It has been noted that such a test may also provide data which characterises the chloride binding capacity of the specimen. In this work a numerical model of chloride diffusion subject to the effects of chloride binding is used to assess the effect of deviations from the steady state on the data obtained from a diffusion cell test. It is noted that there will be a tendency to underestimate the diffusion coefficient, although good practice should limit this error. The predicted error in the chloride binding isotherm is smaller than that in the diffusion coefficient. Furthermore, the influence of errors in the effective porosity on model predictions is limited as the resulting effect on the values of the calculated parameters describing chloride diffusion and binding counteract each other.

Ionic diffusion across an interface between chloride-free and chloride-containing cementitious materials

One end surface of a cylindrical specimen of hardened OPC paste of water/cement ratio 0·5 was cemented to that of a similar specimen which contained 2% chloride ion by weight of cement, added as sodium chloride. The total chloride contents, as well as the concentration profiles across the interface of potassium, sodium, chloride and hydroxyl ions in the pore solution phase, were determined. It was found that the sodium concentration profile could be interpolated by Fick's Second Law to a good approximation. By assuming a Lungmuir-type relationship between the free and bound chloride, the effect of chloride binding on diffusion was incorporated into diffusion equations derived from Fick's First Law and mass conservation. This also yielded a good characterization of the free chloride profile. The concentration profile of hydroxylions in the pore solution was more complex than those for sodium and chlorideions, but it could be modelled by assuming that hydroxyl ions move simply to preserve the charge balance in response to the movements of other difising ions in the system.

Diffusion of chloride and hydroxyl ions in cementitious materials exposed to a saline environment

One end surface of a cylindrical specimen of hardened OPC paste of water/cement ratio (w/c) 0·5 was exposed to 1 mol/l NaCl solution saturated with Ca(OH)2. The free hydroxyl, free chloride and total chloride concentration profiles were determined after 100 days of exposure by analysis of the paste at various depths from the exposed surface. Attempts were made to characterize these concentration profiles by Fick's laws. It was found that the total and free chloride profiles could be interpolated by Fick's second law to a fairly good approximation, but the hydroxyl concentration profile near the exposed surface deviated from such an interpolation. It was also confirmed that the relationship between free and bound chloride could be approximately represented by the Langmuir adsorption isotherm. The effect of chloride binding on chloride diffusion was determined by consideration of mass conservation, and this yielded a good characterisation of the free chloride profile. It is suggested that a reasonably accurate estimation of the experimentally determined hydroxyl concentration may be obtained from charge balance consideration after diffusion of all the other ions besides hydroxyl has been modelled.