Surface Chloride Ion Research Articles

Advances in Modeling Surface Chloride Concentrations in Concrete Serving in the Marine Environment: A Mini Review

Chloride corrosion is a key factor affecting the life of marine concrete, and surface chloride concentration is the main parameter for analyzing its durability. In this paper, we first introduce six erosion mechanism models for surface chloride ion concentration, reveal the convection effect in the diffusion behavior of chloride ions, and then introduce the corrosion mechanisms that occur in different marine exposure environments. On this basis, the analysis is carried out using empirical formulations and machine learning methods, which provides a clearer understanding of the research characteristics and differences between empirical formulas and emerging machine learning techniques. This paper summarizes the time-varying model and multifactor coupling model on the basis of empirical analysis. It is found that the exponential function and the reciprocal function are more consistent with the distribution law of chloride ion concentration, the multifactor model containing the time-varying law is the most effective, and the Chen model is the most reliable. Machine learning, as an emerging method, has been widely used in concrete durability research. It can make up for the shortcomings of the empirical formula method and solve the multifactor coupling problem of surface chloride ion concentration with strong prediction ability. In addition, the difficulty of data acquisition is also a major problem that restricts the development of machine learning and incorporating concrete maintenance conditions into machine learning is a future development direction. Through this study, researchers can systematically understand the characteristics and differences of different research methods and their respective models and choose appropriate techniques to explore the durability of concrete structures. Moreover, intelligent computing will certainly occupy an increasingly important position in marine concrete research.

ANOVA-guided assessment of waste glass and limestone powder influence on ultra-high-performance concrete properties

Ultra-high-performance concrete (UHPC) possesses remarkable structural and durability characteristics, yet its widespread acceptance is hindered by cost inefficiency and environmental concerns. To address these challenges, this study investigates the impact of waste glass and limestone powder as partial substitutes for silica fume and cement in UHPC. For this, three distinct formulations are studied (Control, Optimized-1, and Optimized-2), representing different dosages of waste glass and limestone powder. The research focuses on six critical properties (compressive strength, modulus of elasticity, ultrasonic pulse velocity, initial surface absorption, density absorption, voids, and chloride ion penetration) evaluated at different ages (1, 7, 28, and 90 days for compressive strength, and 7, 28, and 90 days for the remaining properties). So, a total of 171 test specimens were examined, with 3 samples for each age and formulation. Statistical analysis, using ANOVA, assessed and confirmed the significance of the factors in the experimental results. The findings provide comprehensive insights into the UHPC formulations, highlighting the influence of waste glass and limestone powder on specified properties over varying ages. The research reveals that, despite the optimized blends exhibiting lower compressive strength values, all mixes surpass the 150 MPa threshold for cylindrical samples at the 90-day mark. Moreover, the Control mix consistently outperforms the optimized blends in modulus of elasticity at all ages, meeting ACI 239 criteria. The void content analysis shows encouraging trends, with all formulations displaying voids of less than 5% on the seventh day, improving during the curing process. Notably, Optimized-2 demonstrates superior performance over the Control mix after 90 days. Chloride ion penetration is minimal for all blends after 90 days, confirming the effectiveness of mineral admixtures. ANOVA analysis confirms significant impacts of formulation and age on various UHPC characteristics, emphasizing the consistent reduction in performance with alternative mineral additions. The interaction between formulation and age implies variations in property evolution, suggesting potential convergence with alternative formulations.

Language model enhanced surface chloride concentration determination for concrete within splash environment based on limited field records

Chloride ion is severely harmful to reinforced concrete (RC) structures in marine environments. For maintaining the durability and safety of the designed RC structures, the determination of chloride ion concentration on concrete surfaces is critical. Currently, surface chloride ion concentration can be determined using empirical formulas and machine learning (ML) approaches. However, these approaches only rely on the numerical information within field records, disregarding valuable semantic and background information in the records, leading to low accuracy. Meanwhile, in splash environments, it presents a significant challenge to obtain chloride ion concentration records due to the complex environment and high costs involved. Therefore, based on limited field records of surface ion concentrations in splash environments, and utilizing a state-of-the-art language model (LM), this study proposes an LM-based information generation (LMIG) model to improve the accuracy of determination of surface chloride concentrations on RC structures. This paper utilizes the numerical and semantic information in 70 sets of field records to fine-tune the LMIG model and generates 200 sets of high-quality records. These records are then used to train ML algorithms for predicting chloride ion concentrations on concrete surfaces. After conducting comparative research, it was found that incorporating records generated by the LMIG model significantly enhances the accuracy of the ML algorithm. Specifically, the predictive accuracy using the random forest algorithm increased by 33.1%. Furthermore, this paper also conducts a comparative study on the LMIG model and the generative adversarial network (GAN)-assisted data-driven method. The results demonstrate that integrating semantic and numerical information into the LMIG model shows significant advantages in enhancing ML algorithms’ accuracy.

Chloride ion permeability of concrete containing recycled composite powder from building demolition waste

Buildings in the marine environment are vulnerable to chloride ion erosion, which threatens the service life of concrete structures. To facilitate the application of concrete containing construction demolition waste in the marine environment, recycled composite powder concrete (RCPC) was prepared using recycled composite powder as cement substitute. The chloride ion permeability of RCPC was evaluated by chloride ion diffusion test and rapid chloride ion migration test (RCM). The chloride ion permeability of RCPC continued to enhance with growing content of recycled composite powder. During the immersion age, the surface chloride ion content of the samples containing recycled composite powder increased by an average of 18.3–65.3% over the control group, with a corresponding average increase in chloride ion diffusion coefficients ranging from 17.0% to 31.5%. The chloride ion migration coefficients in the RCM test raised by 9.5–24.7%. A series of microscopic tests such as nuclear magnetic resonance (NMR), X-ray diffraction (XRD) and scanning electron microscope-energy dispersive spectrometer (SEM-EDS) suggested that the total porosity increased by 11.9–29.5% with the addition of recycled composite powder. The chloride ion diffusion coefficients exhibited a linear increase with growing total porosity and porosity of capillary pores, whereas an exponential increase with the porosity of transitional pores. The poor reactivity of the recycled composite powder resulted in a looser microstructure and weakened chloride binding capacity, and these factors boosted chloride ion transport. A chloride ion diffusion model of RCPC considering the time dependence of chloride ion transport was developed, and the reliability of the model was verified by experimental data.

Experimental Study and Numerical Analysis of Chloride Ion Diffusion in Hydrotalcite Concrete in Chloride Salt Environment.

Hydrotalcite, known as layered double hydroxides (LDHs), is a new type of admixture used to delay the corrosion of reinforcement. The aim of this study was to investigate the chloride ion diffusion behavior of C30 concrete with varying amounts of calcined hydrotalcite (0%, 2%, 4% and 6%) in a chloride salt environment. The NT-Build 443 test was adopted to characterize the one-dimensional accelerated chloride ion penetration of concrete. The distribution of chloride ion concentration in hydrotalcite concrete with different mix proportions immersed in sodium chloride solution for 30 days and 60 days was determined, and the chloride ion diffusion coefficient and surface chloride ion concentration were fitted based on Fick's second law to establish the chloride ion diffusion model considering the influence of multiple factors. This model was validated using COMSOL Multiphysics finite element software. The results show that concrete mixed with LDHs can meet its compressive strength requirements and that the resistance of concrete with 2% calcined hydrotalcite to chloride ion penetration is the best with a 19.6% increase in the 30-day chloride ion penetration coefficient. The chloride ion diffusion process under chloride salt immersion conditions is in accordance with Fick's second law. The chloride ion concentrations calculated with COMSOL software and the test results are in good agreement, which verifies the reliability of the chloride ion diffusion model.

Experimental and numerical analysis of chloride ion transportation in concrete under bending load with reverse seepage

The paper investigates a new technique, named as Reverse-seepage and Saturation based Active Anti-corrosion Technology (RS-AAT), for preventing chloride ion invasion within the marine concrete under the loading effect. By the indoor model experiments, the effect of RS-AAT on chloride ion invasion within the marine concrete under 10%, 20%, and 30% ultimate bending loads are explored and the results indicate that RS-AAT can effectively reduce 24.36% and 27.29% in chloride ion concentration in the compression and tension regions, respectively. Otherwise, the use of RS-AAT can effectively decrease the surface chloride ion concentration. Furthermore, the chloride ions convection-diffusion model with loading effect is established based on the mesoscopic structure theory of concrete pores and the K-C model, of which variability is verified by comparing with the experimental results.

Deicing performance of cement pavement concrete mixed with chlorine salt antifreeze material

This study explores a cost-effective and efficient method for snow melting and deicing using a concrete pavement structure with pre-mixed chloride-salt antifreeze material. The mixed design method for road cement concrete with chloride-type antifreeze material is investigated by encapsulating NaCl and CaCl2 in organic resin capsules. The snow melting and deicing efficacy of cement concrete with chloride antifreeze material is evaluated through an automatic tracking measurement system. The results indicate that NaCl-type antifreeze material is more effective in reducing the freezing point of concrete surface solution than CaCl2-type antifreeze material. A composite antifreeze material (4% NaCl + 1% CaCl2) provides the strongest snow melting and deicing ability. An outward migration and diffusion model of chloride ion in cement concrete with antifreeze material is established to calculate the chloride ion diffusion coefficient, surface chloride ion content, and decay rate of concrete. The effective age of snow melting and deicing is analyzed using this model.

Protective Performance of Coated Reinforcement in Coral Concrete under Dry/Wet Cycling.

The actual protective performance of the coated reinforcement in coral concrete was investigated by measuring the chloride ion diffusion coefficient, electrochemical analysis, and numerical simulation. The test results show that the corrosion rate of coated reinforcement in coral concrete under the action of wet and dry cycles is kept at a low level, and the Rp value is always greater than 250 kΩ·cm2 during the test period, which is in the uncorroded state and has good protection performance. Moreover, the chloride ion diffusion coefficient D is in accordance with the power function relationship with the wet and dry cycle time, and a time-varying model of chloride ion concentration on the surface of coral concrete is established. The surface chloride ion concentration of coral concrete reinforcement was modeled as a time-varying model; the cathodic zone of coral concrete members was the most active, increasing from 0 V to 0.14 V from 0 to 20 years, with a large increase in potential difference before the 7th year, and a significant decrease in the increase after the 7th year.

Experimental Study on the Influence of Transverse Crack on Chloride Ingress in Concrete Slab Track of High-Speed Railway.

The concrete track slab and the base slab of the high-speed railway CRTS II track structure are prone to transverse cracks in the initial service period, which are subjected to environmental action and train load. In order to investigate the influence of transverse cracks on chloride ingress of concrete track slab and base slab in a coastal environment, drying-wetting cycle chloride erosion tests were carried out on reinforced concrete track slab and base slab specimens with cracks ranging from 0 mm to 0.6 mm, subjected to continuous bending moment. The chloride ion concentration of concrete along the depth direction was collected during the test process. The experimental results show that the chloride ion concentration of concrete at the crack section is much higher than that at the intact section, and it increases with the increase of crack width in the range of 0.2 mm to 0.6 mm. A chloride diffusion coefficient model of cracked concrete is proposed for slab track based on the experimental results, which can comprehensively consider the effects of surface chloride ion concentration, chloride binding effect, time-varying effect, temperature, relative humidity, and transverse crack width.

Superior sensing sensitivity of ZnFe2O4 nano-octahedrons and sensing reaction molecule mechanism of polar ZnFe2O4 {111} surfaces

A solvothermal process prepared ZnFe2O4 nano-octahedrons with {111} crystal planes exposed. In the gas sensing performance experiment, the product showed good sensing activity towards ethanol, acetone or triethylamine. The sensitivity of the nano-octahedrons is further enhanced by adding 3-coordinated Zn atoms (Zn3c) on the exposed (111) crystal plane after the surface chloride ions and hydroxyl groups are removed by hydrogenation. The atomic-scale gas-sensitive mechanism is proposed using Zn3c atoms as sensitive response active sites. It is believed that the Zn3c plays three roles: adsorbing the O2 molecule, generating free electrons, and catalyzing the reaction between O2 and the gas being measured. The sensing mechanism, in which unsaturated metal atoms are reactive sites, explains the sensor's increased sensitivity, which is the basis for developing a high-performance gas detector.

Chloride corrosion resistance of cement mortar with recycled concrete powder modified by nano-silica

In the marine environment, the service life of coastal structures can be significantly reduced on account of chloride corrosion. This study employed nano-silica (NS) to improve the chloride corrosion resistance of mortar samples prepared with recycled concrete powder (RCP). The free chloride ion concentration and mechanical strength of mortar samples in 3.5% NaCl solution up to 12 months were measured. Rapid chloride migration (RCM) and electric flux experiments were carried out. Compared with the pure RCP mortar, the 2% NS incorporated RCP mortar experienced a significant decrease in the chloride ion diffusion coefficient, electric flux and corrosion rate of internal rebar. Moreover, the RCP mortar with 2% NS also had the slowest increase in the free chloride ion concentration and surface chloride ion concentration. The addition of RCP in cement mortar reduced the chloride corrosion resistance, while the inclusion of 2% NS compensated for the RCP induced degradation, resulting in an improvement in chloride corrosion resistance. The X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), and scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS) results showed that the addition of RCP and NS consumed Ca(OH)2 to generate more C-S-H gels and C-A-S-H gels and thereby improved the physical chloride-binding ability of the sample. In addition, the formation of Friedel’s salt via the combination of chloride ion with aluminosilicate further improved the chlorine ion corrosion resistance.

Soft template promoted microphase separation in anion exchange membrane of electrodialysis

This work reports a novel, effective, soft template strategy that can fabricate good-performance anion exchange membranes (AEMs) for electrodialysis application. Specifically, 1,2-ethanedisulfonic acid (EDA) is used as a small-molecule, soft template to promote microphase separation in multi-cation functionalized poly (2,6-dimethyl-1,4-phenylene oxide) membranes through electrostatic interaction between quaternary ammonium groups and sulfonic acid groups. The enhanced microphase separation has been confirmed by transmission electron microscopy (TEM) and small angle X-ray scattering studies. The prepared TPPO-2S-x membranes (where x represents the mass percent of EDA) were tested in the electrodialysis device for desalinating 0.1 M NaCl solution. Among them, the TPPO-2S-1 membrane gave the highest ED current efficiency (92.90 %), the lowest energy consumption (4.08 kWh kg−1), and the largest Cl− transport number (0.98); these performance results are better compared with those of the TPPO-2S-0 membrane (89.29 %, 4.39 kWh kg−1, and 0.98), which is not processed by soft template strategy. Although the TPPO-2S-4 and TPPO-2S-7 membrane show more obvious microphase separation than TPPO-2S-1, the current efficiencies of their ED devices are lower and the energy consumptions are higher due to their undesirable surface area resistance and chloride ion transport number. The investigation demonstrates that the soft template strategy is effective to improve membrane performance in ED devices.

Effect of reverse water pressure on chloride penetration within finite concrete during drying-wetting cycles

Chloride ions invasion in a finite RC structure is significantly controlled by the hydraulic head difference between the seawater and the soil sides. In this study, the mechanism of chloride convection-diffusion penetration within the finite RC structure under the coupled effect of drying-wetting marine environment and reverse water pressure is investigated by indoor experiments and numerical modelling. The indoor exposure experiment is designed to characterize the temporal-spatial variation of chloride convection-diffusion behaviors in concrete. A chloride invasion model by considering the coupled effect of drying-wetting cycles and reverse water pressure via the COMSOL Multiphysics software is developed. The results indicated that, by comparing the application of reverse water pressure to natural drying-wetting cycles, the concrete surface chloride ion concentration is significantly reduced, and the growth of the unsaturation zone is clearly limited. Seepage pressure gradient restrains the inward transport of chloride ion in time and space within the RC structure further.

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.

Preparation technology, mechanical properties and durability of coral aggregate seawater concrete in the island-reef environment

For the island-reef engineering construction background in the South China Sea, the research studied the preparation technology, mechanical properties and chloride ion diffusion behavior of coral aggregate seawater concrete and discussed the steel bars corrosion behavior of coral aggregate seawater concrete (CASC) and reliability analysis of service life, which provide a low cost, high durability CASC and its application technology for island-reef engineering. The results showed that: according to the theory of grout concrete and the design principle of high-performance concrete, the cube compressive strength (fcu) of CASC can reach C80. Uniaxial compression whole stress-strain curve of CASC with different strength grades and constitutive relation were obtained. The “three high” Cl− diffusion characteristics, high initial chloride ion content (C0), high surface chloride ion content (Cs) and high apparent chloride ion diffusion coefficient (Da) in CASC, were established, which easily result in steel bars corrosion. It suggests to choose organic newly coated steel bars, which the thickness of the concrete protective cover is greater than 5.5 cm, concrete strength grade is greater than C50 and use “slow-release effect of micropump” of coral aggregate to pre-absorb and incorporate the amino alcohols inhibitor, which can significantly reduce steel bars corrosion of CASC structures. Finally, the study determined the durability design methods of CASC structures that meet the 20–100 years of service life requirement.

Numerical model of the effect of water vapor environment on the chloride transport in concrete

Chloride ions are known as one of the most crucial factors for rebar corrosion in reinforced concrete (RC) structures exposed to marine environments under drying-wetting cycles. In this condition, the chloride ion content in unsaturated concrete will change under the coupled effect of diffusion and capillary suction. This study simulates the atmosphere zone of the marine environment to explore the law of the chloride transmission behavior under the context of constant temperature and humidity. To analyze the effect of different drying-wetting ratios on the chloride ion profile in the concrete by conducting the dry-wet cycle tests. It is found that the most unfavorable drying-wetting ratios for RC structures in this study is 1:5.5. A finite element numerical model of chloride ion transmission based on Fick’s Ⅱ law was established by COMSOL Multiphysics. It can be used to predict the range of concrete surface chloride ion concentration, and dynamic change of the distribution of chloride ion concentration inside the RC structures under different drying-wetting cycles over time. The comparison of experiment data and simulation results verify that the chloride diffusion prediction model has a good correlation.

Experimental and numerical analysis of chloride transport in finite concrete under reverse water pressure

This paper investigates chloride ion convection–diffusion transport in the finite RC structure under reverse water pressures. The chloride ion penetration in concrete is examined experimentally and theoretically. One-dimensional experiments are designed to reveal the characters of the time-varied behaviors of surface chloride ion concentration and the chloride ion penetration under different reverse water pressure in the concrete. A numerical solution of the chloride ion convection–diffusion penetration is also established by finite element method (i.e., FEM) via software entitled COMSOL Multiphysics. The K-C model is attempted to be used for the assess of the permeability of concrete. The results suggest that the reverse water pressure can weaken the accumulation of chloride ion on the concrete surface and effectively prevent the chloride ions from invading into the concrete. The results of this paper offer much-needed insights into this growing discussion in the field of assess of durability of finite marine RC structure.

Influence of the rainfall intensity on the chloride ion distribution in concrete with different levels of initial water saturation

Reinforced concrete (RC) structures located in coastal salt spray areas are subjected to rainfall erosion and chloride ion corrosion throughout the year. Consequently, this study simulates a rainfall environment with artificial rainfall simulation devices and applies a potentiometer to determine the chloride ion concentration. The microstructures and chemical compositions of the concrete were revealed through microscopic experiments. The research results show that with a greater rainfall intensity, the surface chloride ion concentration decreases more obviously, the surface chloride ion loss is more serious, and the chloride ion binding capacity becomes weaker. As the saturation decreases, the binding capacity of chloride ions also decreases. This study can provide some theoretical ideas for the durability design of PC structures in rainy environments.

A novel liquid precipitation route to synthesize high-quality cobalt carbonate with low chloride ions concentration

Herein, high-quality cobalt carbonate is synthesized by employing a novel liquid phase precipitation route, where CoCl2 and ammonium bicarbonate solutions are used as the raw material and precipitator, respectively. The morphology of primary and secondary particles and agglomeration due to their nucleation and growth are influenced by the stirring speed, reaction temperature and pH value. Furthermore, the influence of process parameters on physiochemical properties has been systematically studied by measuring apparent density, FSSS particle size, specific surface area and chloride ions concentration. Under optimal processing conditions, i.e., stirring speed of 100 rpm, pH value of 7.0-7.1 and a reaction temperature of 55 °C, the as-synthesized cobalt carbonate rendered an apparent density of 0.74 g/cm3 and chloride ions concentration of 19 ppm. The results reveal that the washing efficiency of chloride ions is affected by the morphology of primary particles and stacking mode of the secondary particle in cobalt carbonate. In general, the higher BET specific surface area of cobalt carbonate results in lower chloride ions concentration.

Experimental and cellular-automata-based analysis of chloride ion diffusion in reactive powder concrete subjected to freeze–thaw cycling

Natural soaking and accelerated freeze–thaw cycling experiments were conducted using NaCl solution to study chloride ion diffusion in reactive powder concrete. The chloride ion diffusion coefficient for specimens subjected to natural soaking was calculated using Fick’s second law. That for specimens subjected to freeze–thaw cycling was calculated using a newly proposed method that considers the damage resulting from freeze–thaw cycling. The coefficient first decreased and then increased as the number of cycles increased. A cellular-automata-based two-dimensional chloride ion diffusion model that considers the time dependence and impact of freeze–thaw cycling damage was established. The chloride ion diffusion and distribution in reactive powder concrete subjected to natural soaking and freeze–thaw cycling in NaCl solution were simulated using Matlab program that was based on the proposed model. The boundary condition for the cellular-automata model should be the surface chloride ion concentration instead of the chloride ion concentration of the solution. The acceleration of chloride ion diffusion due to freeze–thaw cycling damage can be well-simulated by introducing the freeze–thaw damage factor. A comparison of simulation and experimental results showed that this model can simulate and predict chloride ion diffusion in reactive powder concrete effectively.