Distribution Of Chloride Ions Research Articles

Study on the Effect of Water–Binder Ratio on the Carbonation Resistance of Raw Sea Sand Alkali-Activated Slag Concrete and the Distribution of Chloride Ions after Carbonation

The excessive extraction of river sand has led to significant ecological issues. Moreover, the environmental impact and resource demand of cement production have increasingly turned the spotlight on sea sand as a viable alternative due to its abundance and ease of extraction. Concurrently, alkali-activated binders, a novel type of low-carbon cementitious material, have gained attention for their low energy consumption, high durability, and effective chloride ion fixation capabilities. However, they are susceptible to carbonation. Introducing a controlled sea sand amount can raise the materials’ carbonation resistance, although carbonation may raise the concentration of free Cl− within the structure to levels that could risk the integrity of steel reinforcements by accelerating corrosion. In this context, the current study investigates sea sand alkali-activated slag (SSAS) concrete prepared with varying water–binder (W/B) ratios to evaluate its impact on flowability, mechanical strength, performances, and chloride ion distribution post-carbonation. The results demonstrate that the mechanical property of SSAS concrete diminishes as the water-to-binder ratio increases, with a more pronounced reduction observed. The depth of carbonation in mortar specimens also rises with the W/B ratio, whereas the compressive strength post-carbonation initially decreases before showing an increase as carbonation progresses. Furthermore, carbonation redistributes chloride ions in SSAS, leading to a peak Cl− concentration near the carbonation front. However, this peak amplitude does not show a clear correlation with changes in the W/B ratio. This study provides a theoretical foundation for employing sea sand and alkali-activated concrete.

Simulation of concrete cracking and chloride diffusion under uniaxial compression

The dispersion and randomness of concrete cracking under compressive loads make it challenging to predict the diffusion rate of chloride ions. In this paper, the cohesive element method was employed to quantitatively calculate and determine the form and width of dispersed cracks in concrete. These results were found to be consistent with the real concrete crack forms obtained using digital image correlation (DIC) technology. The findings indicate that both the form and width of the cracks significantly impact the diffusion of chloride ions within the concrete. Chloride ion diffusion is enhanced when the cracks are closer to the penetration side or when there are more cracks present in the concrete. Additionally, an increase in axial load amplifies the randomness of chloride ion distribution at the same penetration depth. While coarse aggregates can impede chloride ion penetration, wider cracks lead to a higher concentration of chloride ions within the concrete. Our results contribute to a deeper understanding of chloride ion diffusion in cracked concrete under varying stress levels.

Chloride ion permeation and electrochemical impedance response of red mud-coal metakaolin geopolymer concrete

In geopolymer concrete, chloride ions largely contribute to the surface passivation of steel reinforcement and accelerate its corrosion. However, real-time nondestructive testing of chloride ion diffusion has not been widely conducted. Therefore, this study determined the distribution of chloride ions in red mud-coal metakaolin geopolymer concrete with different water-binding ratios under natural immersion conditions. The electrochemical properties of geopolymer concrete in a sodium chloride environment were examined by electrochemical impedance spectroscopy (EIS) and the relationship between these properties and the chloride ion diffusion coefficient was established. The experimental results showed that the contents of free chloride ions, total chloride ions, and bound chloride ions gradually decreased with increasing penetration depth; total chloride ions and free chloride ions increased at the same depth with increasing water-binder ratio; and bound chloride ions decreased with increasing ratio. In addition, the contents of free chloride ions, total chloride ions, and bound chloride ions gradually increased with the increase of the immersion age. The EIS results showed that there was a significant correlation between the diffusion coefficient and the electrochemical parameters. Therefore, EIS is suitable for detecting the diffusion of chloride ions in geopolymer concrete.

Statistic investigation on chloride ions distribution based on numerical reconstruction of in situ meso-structure of concrete

To study the non-uniform corrosion of steel rebar induced by chloride ions invasion under marine environment, the three-dimensional characteristic distribution of aggregates and pores in concrete was numerically extracted and reconstructed through X-ray CT technique. Based on the 3D in-situ meso-structure model of concrete, the random characteristics of chloride ions transport in concrete was investigated by numerical simulation. Through a fitting and hypothesis test on the concentration distribution histogram of chloride ions, a reliable probability density distribution function of chloride ions concentration was proposed. And the influence of ITZ and aggregate shape on the random diffusion of chloride ions was studied. The research indicates that that the spatial distribution of coarse aggregates and pores is the main reason leading to the non-uniform distribution of chloride ions. The chloride ions concentration under a certain time follows the Lognormal distribution. The discreteness of chloride ions distribution in concrete decreases when the interfacial transition zone is not considered in the model. And an increase of the irregularity of aggregate shape will cause an increase in the tortuosity of chloride ions transport path, and the discreteness of chloride ions distribution will enhance accordingly.

Chloride ion diffusion and distribution characteristics in recycled coarse aggregate concrete under uniaxial and biaxial pressure

Under uniaxial compression, recycled coarse aggregate leads to complex internal stresses (simultaneous uniaxial, biaxial, and multiaxial tensile and compressive stresses at the micro scale) and even micro cracks in concrete, which poses difficulties in accurately predicting the chloride ion diffusion of recycled concrete. By changing the compressive stress level and bi-directional stress ratio of concrete, a self-developed biaxial compression device was used to test the chloride ion diffusion coefficient of recycled concrete under different stress states. In order to analyze the influence of various factors on chloride ion diffusion, DIC digital image technology and microcrack statistics technology were used to analyze the influence of concrete micro deformation on its chloride ion diffusion coefficient under load, and X-ray fluorescence technology was used to accurately analyze the concentration distribution of chloride element in different positions of concrete. The pore structure inside recycled concrete was characterized through experiments, and a real three-dimensional multi-scale model of concrete and the statistical characteristics of porosity at different scales were obtained. Finally, a theoretical model was established to predict the chloride ion diffusion coefficient under biaxial compressive loads, achieving accurate prediction of chloride ion diffusion coefficient close to practical engineering.

Analysis of the Effect of Applied Load on Crevice Corrosion Behavior

A two-dimensional numerical model incorporating solid mechanics, electrochemistry, mass diffusion, and ion migration processes is developed to investigate the load effect on the crevice corrosion. The model is a transient model of crevice corrosion occurring in cracks of 304 stainless steel in a dilute NaCl solution, and the interaction between stress and electrochemical corrosion was considered. By solving the multiphysical coupling model in COMSOL, the effect of applied load on electrochemical corrosion in the crack tip region was calculated, and the local corrosion current density in the crack tip region with stress concentration within the crack was also calculated by using the Tafel relationship. The distribution of Fe2+ ion, Na+ ion, CL− ion, and H and O2 substance concentrations within the crack cavity is predicted by the equation analysis of substance transport. The results show that metal oxidation is more clearly affected by plastic deformation, the rate of hydrogen evolution reaction increases with stress enhancement, and the oxygen absorption reaction is not affected by stress strain. The distribution of iron ions, hydrogen, and oxygen within the crack is affected by the electrochemical reaction rate, and the distribution of iron ions, sodium ions, and chloride ions is affected by the electrolyte potential.

Effect of carbonation curing on distribution and binding capacity of chloride ions in cement pastes

Carbonation curing of concrete is an effective measure to reduce CO2 emissions, but it can adversely affect chloride binding capacity of cement pastes and its durability. In this study, the chloride ion content and phase assemblages of cement pastes under three curing conditions: standard curing, carbonation curing, and mixed curing (7-day carbonation curing and 21-day standard curing) were investigated based on combined macroscopic and microscopic methods. The chloride ions were introduced into cement pastes either through internal incorporation during the mixing process or from external penetration during its immersion in chloride contained solutions. Experimental results show that a large number of internally incorporated chloride ions were accumulated in the surface layer of pastes due to moisture evaporation during carbonation curing process. The transport of internally incorporated chloride ions in the paste under the mixed curing process was affected by the coupling effects of carbonation and capillary suction, resulting in inward migration of chloride ions. The external chloride ions from the solution penetrated into paste through initial diffusion and subsequent capillary suction during carbonation curing and mixed curing processes. Neither internally-incorporated nor externally-penetrated chloride ions could be bound in the carbonated zone, and the Friedel's salt could not be formed either. Due to the decrease of carbonation effect along the penetration depth and inward migration of chloride ions, the bound chloride ion content increased and formed a peak value in the inner layer.

Chloride Ion Corrosion Resistance of Innovative Self-Healing SMA Fiber-Reinforced Engineering Cementitious Composites under Dry-Wet Cycles for Ocean Structures

To evaluate the chloride ion corrosion resistance of proposed innovative self-healing concrete based on shape memory alloys (SMA) and engineering cementitious composites (ECC), a total of 2 kinds of 22 specimens were prepared. Chloride ion corrosion tests of self-healing SMA-ECC concrete under dry-wet cycles were carried out. It was found that the chloride ion erosion depths of SMA-ECC were significantly smaller than that of MC, and the growth rate of erosion depth of SMA-ECC was obviously smaller than that of MC after 15 dry-wet (dry and wet) corrosion cycles. The chloride ion content of SMA-ECC vanished at the erosion depth more than 10 mm, which was consistent with the test result of AgNO3 solution color-rendering test. Test results indicate that, compared to marine concrete (MC), SMA-ECC has a better chloride ion corrosion resistance behavior. Moreover, the chloride ion concentration of SMA-ECC at a chloride ion erosion depth of less than 10 mm decreased more significantly than that of MC, indicating that almost all chloride salt solution reacted in the outer layer of SMA-ECC, which is consistent with the conclusions of 4.1 and 4.2. Finally, based on the erosion distribution of chloride ions and Fick’s second law, a calculation model describing the relationship between the apparent chloride ion diffusion coefficient and the boundary condition of the chloride ion content was proposed.

Chloride ion control of under-constructing concrete structure based on ECE with different electric field intensities

Electrochemical chloride extraction (ECE) technology can effectively reduce the harmful chloride ions in concrete and decline the durability failure risk of concrete structures. In this study, early-age sea-sand concrete was treated by ECE with strong electric field and conventional electric field, respectively. The chloride ion content analysis and microscopic observation were adopted to evaluate the durability improvement effect with ECE treatment. The results showed that at the early ages of 3, 5, and 7 d, the chloride ions were drastically reduced upon the application of a strong electric field for 40, 80, and 120 min or the conventional electric field for 15 d. Treating time of ECE with strong electric field is 0.19 %–0.56 % of that of ECE with conventional electric field. Under a strong electric field, the distribution of residual chloride ions in specimens was more uniform. Application of an electric field during the curing period caused the directional migration of ions and subsequently changed the pore structure and microhardness of the specimen. However, these changes were recovered with the continuous hydration of concrete during the curing period. Finally, based on engineering cases, the field implementation schemes of the strong electric field and conventional electric fields were analyzed. The energy consumption of ECE with strong electric field is 17.8 %–53.3 % of that of ECE with conventional electric field. The results of this study provide the technical means for the timely treatment of excessive chloride ion concentration in sea-sand concrete structures.

Distribution of chloride ions along the flight path of aircraft (Overview)

Based on the analysis of the literature, the number of corrosive particles entering the aircraft engine with air has been determined. It is shown that the atmosphere of the continents has the smallest number of chlorides, their maximum content on the seashore, the troposphere above 10 km has a stable amount of aerosol particles. A method for estimating the chloride content has been developed to predict the rate of sulfide-oxide corrosion of parts of the hot TRD tract.

Enhanced Passivity and Resistance to Pitting of New Cr-Fe-Co-Ni-Mo Multi-Principal Element Single-Phase Alloys

Extensive thermodynamic calculations exploring the large composition space of the Cr-Fe-Co-Ni-Mo system were performed in order to design new multi-principal element single-phase fcc alloys with enhanced passivity and resistance to localised corrosion.This presentation will cover several aspects from design to production, passivation, surface analysis and pitting resistance of alloys with up to 15 at.% Mo . The newly designed and produced quinary alloys, Cr25Fe25Co5Ni40Mo5 and Cr15Fe10Co5Ni60Mo10 (at.%) show superior resistance to localised corrosion in chloride solution. The chemical states, composition and stratification of passive films were investigated by X-ray Photoelectron Spectroscopy (XPS) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). The resistance to pitting was measured after pre-passivation of the alloy surfaces in Cl--free acidic solution.Stratification of the passive films was observed, with Cr, Fe, Ni,Mo oxides and hydroxides in the outer layer and Cr oxide in the inner layer.The amounts and distribution of chloride ions that penetrated into the passive films were also investigated. In-depth profiles show that, on the Mo-bearing alloys, chloride ions do not penetrate the Mo-enriched outer layer of the oxide film.A direct link between the structural and chemical nature of passive films and the resistance to pitting in chloride solution was observed. This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (advanced grant agreement # 741123)

Simulation Approach for Random Diffusion of Chloride in Concrete under Sustained Load with Cellular Automata

Steel bar corrosion caused by chloride is the major reason for concrete structure durability failures in a corrosive environment. An accurate simulation of chloride ion diffusion in concrete is hence critical to durability design, maintenance, and reinforcement of concretes in erosive environments. To accurately simulate actual chloride ion diffusion in concretes, an improved three-dimensional neighborhood type is proposed according to the mechanism of chloride ion diffusion in concrete, and a three-dimensional cellular automaton model (3D CA model) for describing the diffusion process of chloride in concrete is established based on this neighborhood type. The accuracy and correctness of simulation results obtained from the 3D CA model were verified by comparison with Fick’s second law analytical solutions. Based on the 3D CA model, an improved modified 3D CA model is developed (3D RTCA model) which takes into account random chloride ion distribution in concrete, the time dependence of the coefficient of chloride ion diffusion, and the structure stress level effect on chloride ion diffusion. Numerical simulation results reveal that the 3D RTCA model has higher calculation accuracy in predicting long-term concentration of chloride in concretes, and the simulation results are closer to experimental findings than analytical results obtained based on Fick’s second law. Compared with Fick’s second law analytical solutions, the 3D RTCA model can reflect more truly the cross-sectional stress level effect on chloride ion diffusion through simple local evolution rules. Besides, the 3D RTCA model can genuinely describe the randomness and uncertainty of the chloride diffusion process. The 3D RTCA model developed in the current study provides a novel perspective and method to investigate chloride ion diffusion in concrete from structural level.

Test and theoretical prediction of chloride ion diffusion in recycled fine aggregate mortar under uniaxial compression

A combined test device was developed to investigate the effect of microcracks on rapid chloride ion diffusion in mortar with recycled fine aggregate under uniaxial compression loading. Deformation and microcrack growth were statistically evaluated using the digital image correlation (DIC) method. The chloride ion distribution and porosity in mortar with different proportions of natural and recycled fine aggregates were investigated by micro X-ray fluorescence (μXRF) and mercury intrusion porosimetry (MIP), respectively. Chloride ion transportation was affected by pore structure and natural fine aggregate content. The diffusion coefficient decreased and then increased with increasing compression load and reached the minimum at stress of 0.4 fc-0.5 fc. A statistical specific crack area method based on DIC is proposed for the first time, based on which the chloride diffusion coefficient in mortar with recycled fine aggregate can be predicted.

Mathematical statistics algorithm in the bending performance test of corroded reinforced concrete beams under fatigue load

Abstract Harsh environments such as alternating wet and dry conditions and cyclic loading cause erosion in steel bars, leading to severe damage to structures. Steel bars are also prone to bending under long-term fatigue loads. This paper establishes the bending performance test of corroded reinforced concrete (RC) beam under fatigue load based on the mathematical–statistical algorithm. It investigates the influence of heavy load on the fatigue performance of damaged RC beams, the influence of corrosive environment on the fatigue performance of RC beams, the degree of corrosion of steel bars in concrete beams under fatigue loading, and the distribution of chloride ions. The study results found that the stress ratio has a significant effect on the maximum crack width of the specimen beam. The greater is the stress ratio, the longer the fatigue life. This directly affects the performance of the specimen beam under fatigue loading. For this reason, we should pay special attention to the impact of corrosion on the fatigue performance of a structure during the design of steel bars.

Combined Freeze-Thaw and Chloride Attack Resistance of Concrete Made with Recycled Brick-Concrete Aggregate.

The objective of this study was to investigate the physico-chemical properties of concrete made with recycled brick-concrete aggregate, which was the mixture from waste concrete and waste clay brick in a 7:3 ratio. Specifically, this paper investigated the mechanical properties, freeze-thaw resistance, and distribution of water-soluble chloride ions of concrete containing RBCA and fly ash (FA) against combined freeze-thaw and sodium chloride attack. Concrete containing RBCA replacement of natural coarse aggregate and fly ash replacement of Portland cement was subjected to 45 freeze-thaw cycles containing sodium chloride solution. It was discovered that the mechanical properties and freeze-thaw resistance to sodium chloride attack gradually decreased with increasing RBCA content. At the same time, a replacement level of 15% FA by weight resulted in significant improvements in compressive strength and resistance to combined freeze-thaw and chloride attack. Furthermore, using a replacement of 30% FA by weight markedly improved the resistance to chloride ion penetration of concrete due to the lowest water-soluble chloride content.

Durability Investigation of Carbon Fiber Reinforced Concrete under Salt-Freeze Coupling Effect.

In order to study the durability behavior of CFRP (carbon fiber reinforced polymer) reinforced concrete, three category specimens (plain, partially reinforced, and fully reinforced) were selected to investigate its performance variation concerning chlorine salt and salt-freeze coupled environment, which included the microscopic examination, the distribution of chloride ion concentration, and the compressive properties. By observing the microscopic of the specimens, the surface and cross-section corrosion deterioration was examined with increasing exposure time, and the physical behavior of CFRP and core concrete were discussed. The chloride ion diffusion test exerted that the chloride ion concentration in plain specimens is at least 200 times higher than that of fully reinforced specimens. Therefore, the effectiveness of CFRP reinforcement will be proved to effectively hinder the penetration of chloride ions into the core section. The formula of the time-dependent effect of concrete diffusivity with salt-freeze coupling effect was presented and its accuracy verified. A time-varying finite element model of chloride ion distribution was established by using ABAQUS software. It can be seen from the axial compression test that the strength loss rate of three categories of specimens was varied when subjected to the corrosion environment. Therefore, it is proved that CFRP reinforcement can effectively reduce the deterioration of the specimen’s mechanical properties caused by the exposure environment. The research results can provide technical reference for applying the CFRP strengthened concrete in a severe salt-freeze environment.

Mineral Additives to Enhance Early-Age Crack Resistance of Concrete under a Large-Temperature-Difference Environment

The large temperature difference condition in Northwest China threatens a myriad of concrete structures during construction, with the daily temperature varying by around 40 °C. To investigate the macro-mechanical properties and microstructural characteristics of concrete containing different amounts of mineral admixtures under such harsh conditions, this investigation used an environmental chamber to simulate a saline soil erosion environment with a large temperature difference. Four types of concrete containing different proportions of fly ash and slag were prepared and exposed in the environmental chamber with a daily temperature change of −5~40 °C to investigate their compressive strength, flexural strength, and fracture properties. Moreover, the X-ray diffraction (XRD) characteristics, microscopic morphological characteristics, pore structure characteristics, and post-erosion chloride ion distribution characteristics were also observed and recorded. Results showed that the mineral admixture could improve the early strength development of the concrete and effectively improve the fracture performance of the concrete. The average compressive strength growth rate of concrete from day 3 to day 14 was 83.25% higher than that of ordinary concrete (OC) when 15% fly ash and 15% slag were added. In addition, the fracture energy of the concrete was maximized when 15% fly ash and 20% slag were added, which was 50.67% higher than that of OC; furthermore, the internal compactness and pore structure were optimized, and the resistance to saline soil erosion was strong. This provides a basis for the practical application of compounded mineral admixture-modified concrete in an arid environment with a large temperature difference and saline soil erosion.

Influence of rebar geometry on the steel-concrete interface of reinforced concrete

This paper investigates the effects of rebar geometry, namely the rib and diameter of rebar, on the steel–concrete interface (SCI) and corrosion initiation of reinforcing steel. Cutting-induced damage on the SCI is also studied using various W/C ratios, cutting wheels and rebar diameters. Interfacial porosity and the distribution of chloride ions at different locations with respect to the rib of vertical rebar and the phase distribution of the SCI of horizontal rebar with various diameters is quantified. The results show that a macroscopic gap can be found below the rib of vertical rebar. Corrosion initiation of vertical rebar is associated with interfacial porosity at different locations with respect to the rib of vertical rebars. Local water content near the SCI of horizontal rebar is increased when using a larger rebar diameter. Cutting-induced damage can be reduced by decreasing the water to cement ratio and rebar diameter.

Corrosion Inhibition of Mg Alloy ZEK100 Sheet Metal by Dissolved Lithium Carbonate

The extent of corrosion inhibition of Mg alloy ZEK100 in 100 mM NaCl (aq) imparted by dissolved Li2CO3 (aq), with a particular focus on Li incorporation into the surface film that forms under activated anodic dissolution (anodic polarization) was determined. Dissolved Li2CO3 reduces corrosion by a factor of ∼12 when added at a concentration (100 mM) just below saturation. Effective inhibition involves suppressing the transition to filament-like corrosion, and associated anode/cathode activation, initiating at local breakdown sites. Such suppression is linked to the formation of Li-doped MgO as a corrosion product film during activated anodic dissolution. When formed by anodic polarization, the film composition also significantly affects the chloride ion distribution with the film. Without Li incorporation, chloride ions tend to enrich at the film/metal interface, whereas with Li incorporation, chloride ions tend to be uniformly distributed within the film.

Effects of alternating stray current on chloride transport in cement-based materials

A series of tests were conducted to investigate the effects of alternating stray current on chloride transport in cement-based materials (mortar). The chloride distributions in the mortar after the conditioning of immersion in 35 g/L NaCl solution or coupled with direct/alternating stray current within 14 days were gained. Test results show that: (1) The distribution of chloride ions along the depth in mortar shows an exponential shape, after the conditioning of immersion in 35 g/L NaCl solution or coupled with direct or alternating stray current within 14 days; (2) Comparing with the immersion in the NaCl solution without stray current, the transport of chloride in the mortar under DC electric field is significantly accelerated. The maximum chloride content in the mortar under this environment was almost seven times higher than that in the condition without current; (3) The chloride contents at different depths of the mortar in the AC electric field are slightly less than those in the solution without electric field and are much less than that with direct stray current.