Chloride Profiles Research Articles

In situ temperature-compensated ultraviolet spectrophotometry to estimate nitrate and chloride concentrations in estuarine seawater with different salinity and composition

Various methods have been proposed for in situ measurement of nitrate concentrations from the ultraviolet (UV) absorbance spectrum of seawater with stable salinity and constituents. However, salinity and temperature affect the UV absorption spectrum of seawater. In sea areas with large variability in salinity and water temperature, accurate nitrate ion concentration measurements remain challenging. We performed in situ measurements of nitrate, chloride, and bromide in estuarine seawater with different salinity compositions and applied water temperature compensation. First, the impact of water temperature on the UV absorbance of chloride, bromide, and nitrate was experimentally investigated and represented in a mathematical model. Next, chloride, bromide, and nitrate concentrations were estimated by suppressing the impact of residual components from the UV absorbance spectra of seawater using principal component regression (PCR). Hence, the chloride, bromide, and nitrate concentrations were determined by measuring the UV absorbance spectrum of seawater alone, without measuring water temperature and electrical conductivity. The proposed method was more accurate (±1.39 μM below 100 μM and ±0.90 μM below 20 μM) than the conventional method (±2.35 μM below 100 μM and ±1.88 μM below 20 μM) and PCR without water temperature compensation (±3.67 μM). In a field study, an in situ UV spectrophotometer with water temperature compensation was used to measure depth profiles of nitrate concentrations in estuarine seawater. We successfully measured the depth profiles of low chloride and high nitrate concentrations in the surface layer as well as high chloride and low nitrate concentrations in the lower layer. The proposed method enables in situ measurements of nitrate concentrations in waters with either stable or highly variable salinity and composition. Unlike conventional chemical analysis, our method can describe detailed spatiotemporal variations in nitrate concentrations.

Effect of Imperial Smelting Process Slag Addition in Self Compacting Concrete Concrete on the Efficiency of Electrochemical Chloride Extraction.

This paper presents the analysis of how ISP slag addition affects the effectiveness of chloride extraction from self-compacting concrete. Corrosion processes were initiated by chloride ions added to concrete by the method accelerated with an electric field. Corrosion of reinforcement was monitored using the method of linear polarization resistance (LPR). Polarization measurements of steel reinforcement and chloride profiles were analysed to evaluate the effectiveness of electrochemical extraction. Microstructural analysis was conducted on a specimen of concrete after migration and extraction of chlorides. The presence of chloride ions and the application of an electric field during migration were tested with respect to the changed microstructure of concrete evaluated on the basis of image analysis using a scanning electron microscope (SEM). The research contributes to a better understanding of the corrosion processes caused by the presence of chloride ions in concretes in which ISP slag was used as a substitute for sand in various amounts. Thanks to the treatments of concrete with already corroding reinforcement bars, it can be concluded that the moderate replacement of sand with ISP slag limited to 25% allows for the effective inhibition of corrosion processes taking place in these concretes. However, it is not possible to completely withdraw already started corrosion processes in steel. The observations of the microstructure of concrete in which sand was completely replaced with ISP slag indicate that after prolonged use of the chloride extraction process, we can expect a change in the microstructure and the formation of ettringite, which may cause the concrete structure to burst. The obtained information will contribute to the development of modelling methods for chloride ion extraction from a wide range of currently used concretes.

Deep learning-based prediction for time-dependent chloride penetration in concrete exposed to coastal environment

The application of deep learning methods in civil engineering has gained significant attention, but its usage in studying chloride penetration in concrete is still in its early stages. This research paper focuses on predicting and analyzing chloride profiles using deep learning methods based on measured data from concrete exposed for 600 days in a coastal environment. The study reveals that Bidirectional Long Short-Term Memory (Bi-LSTM) and Convolutional Neural Network (CNN) models exhibit rapid convergence during the training stage, but fail to achieve satisfactory accuracy when predicting chloride profiles. Additionally, the Gate Recurrent Unit (GRU) model proves to be more efficient than the Long Short-Term Memory (LSTM) model, but its prediction accuracy falls short compared to LSTM for further predictions. However, by optimizing the LSTM model through parameters such as the dropout layer, hidden units, iteration times, and initial learning rate, significant improvements are achieved. The mean absolute error (MAE), determinable coefficient (R2), root mean square error (RMSE), and mean absolute percentage error (MAPE) values are reported as 0.0271, 0.9752, 0.0357, and 5.41%, respectively. Furthermore, the study successfully predicts desirable chloride profiles of concrete specimens at 720 days using the optimized LSTM model.

Laboratory procedure for obtaining chloride profiles from concrete structures cores: a mathematical approach

Laboratory procedure for obtaining chloride profiles from concrete structures cores: a mathematical approach

Understanding Chloride Diffusion Coefficient in Cementitious Materials.

One of the key problems that affect the durability of reinforced concrete structures is the corrosion of rebar induced by chloride. Despite the complicated transport mechanism of chloride ions in cementitious materials, diffusion is still the key mechanism of chloride ingress. The determination of the chloride diffusion coefficient will help to predict the chloride profile inside the cementitious materials and estimate the service life with regard to chloride-induced corrosion. However, this paper shows that the chloride diffusion coefficient in the literature is sometimes misunderstood. Such a misunderstanding results in the overestimation of the chloride resistance of cementitious materials. To clarify the chloride diffusion coefficient, this paper first presents the steady- and non-steady-state diffusion equations in cementitious materials. The factors that influence the diffusive flux are identified. The effective and apparent diffusion coefficients are then clearly explained and properly defined. We also point out the obscure definitions of the effective diffusion coefficient in the literature. The varied definitions of the effective diffusion coefficient are the result of the consideration of different factors affecting the diffusion process. Subsequently, this paper discusses two natural diffusion test methods that are frequently employed in cementitious materials to measure the chloride diffusion coefficient. The influencing factors considered by the measured diffusion coefficients are analyzed in detail. Then, the diffusion coefficients determined in some of the studies are reviewed. It is shown that three typical errors could occur when numerically determining the diffusion coefficients.

Physicochemical Analysis of Chloride Diffusion and Adsorption in Water-saturated Concrete: Theory and Measurement

The theory of ionic diffusion in water-saturated concrete accompanying ion exchange with mobile or immobile adsorbed ions was constructed by using the general theory of diffusion and the condition of electrical neutrality. Analysis of the diffusion profile of chloride (Cl−) ions in concrete with the theory revealed that adsorbed Cl− ions in AFm and C-S-H are as mobile as free Cl− ions in the pore solution, so that the adsorption does not retard the ingress of Cl− ions. The existing test methods for determining the effective or apparent diffusion coefficient of Cl− ions were evaluated on the bases of the present theory and new experimental findings. It was revealed that steady-state electrochemical methods such as NTBUILD-355 and ASTM C1202 are not suitable for determining the diffusion coefficient, because the steady state methods expel preexisting diffusible ions which strongly affect the diffusion of Cl− ions. Moreover, the steady state methods overestimate the diffusion rate because the methods assume that adsorbed Cl− ions are immobile. The electrochemically-accelerated method NT BUILD 443 is also unsuitable for the diffusion test, because the acceleration is induced by the electro-osmotic flow of the external solution into concrete. The present diffusion theory necessitates the effective self-diffusion coefficient of not only Cl− ions but also all the other diffusible ions in concrete. A simple method of determining the effective self-diffusion coefficients of arbitrary ions in concrete from the diffusion profile of Cl− ions was presented.

DFT Simulation of Berberine Chloride with Spectroscopic Characterization – Biological activity and Molecular Docking against Breast Cancer

In this work, the structural and spectroscopic properties of the berberine chloride molecule were investigated using quantum chemical calculations based on density functional theory (DFT). Through molecular docking simulation, the breast cancer inhibitory properties of the title chemical were revealed. With the basis set at 6-311++G (d,p), the optimization was carried out and theoretically assigned vibrational frequencies were compared to the experimentally observed vibrational frequencies. The reactive behavior of berberine chloride was further examined using simulated calculations of the molecular electrostatic potential surface. Utilizing the HOMO-LUMO energies, the stability and molecular reactivity of the molecule were assessed and the calculated energy gap was 3.19 eV. The second order perturbation energy E(2) values of the molecule, which demonstrate the bioactivity of the berberine chloride, were determined using natural bond orbital analysis. The Mulliken atomic charge distribution confirms the molecule’s reactive site. The biological activities of berberine chloride were evaluated through in vitro and in silico methods. The antioxidant activity was tested through ABTS assay and the antibacterial test was performed through disk diffusion technique and the zone of inhibition was observed for berberine chloride molecule. The breast cancer inhibitory potential of berberine chloride was assessed through molecular docking simulation. Berberine chloride was docked against seven breast cancer associated proteins and the highest binding ability was observed against HER-2 protein with −9.1 Kcal/mol. The drug-likeness properties were predicted and safety profile of berberine chloride was revealed.

Parametrized division of exposure zone for marine reinforced concrete structures with a multi-class Boosting method

The analysis of marine reinforced concrete structures using chloride profile data is a commonly used exposure zone classification method. However, chloride profile data is multi-class, unbalanced and non-parametric, which makes it difficult for the commonly used machine-learning methods to construct an appropriate classification model. To solve this problem, chloride profile is parametrized by the minimum redundancy maximum relevance algorithm and a multi-class Boosting method using F-measure as inductive bias indicator to evaluate the weight of base classifiers is put forward. The method is based on field test data of the chloride profile over a period of 18 years in Hangzhou Bay, China. The method outperforms the original Boosting method with an average F-measure improvement of 6.2 %. The results show that parametric partitioning of the exposure zone is achieved and the distribution of the exposure zone satisfies the Weibull distribution.

Surface application of multifunctional compound to prevent and control combined chloride and carbonation corrosion in concrete

This paper presents the performance of a multifunctional generic compound, 4-Aminobenzoic acid (4ABA) as migratory inhibitor applied on hardened concrete surface to curb corrosion due to combined chloride and carbonated environment. Electrochemical techniques (LPR and EIS), gravimetric analysis were applied to evaluate the corrosion performance and the inhibition mechanism of 4ABA. Chloride and carbonation profiles were developed to investigate the dominant cause of corrosion during the exposure. Visual and microscopic analysis of concrete surface and rebar surface was also done. Compressive strength test was performed to study the effect of corrosion inhibitor on strength property of hardened concrete. Results confirm that 4ABA prolonged the passive state of rebar when used as preventive measure and restrained the on-going corrosion process when employed as repair strategy. Combined exposure by chlorides and CO2 leads to redistribution of chloride ions in concrete matrix. The results also conclude that during the combined exposure, chloride ions initiate the corrosion process and carbonation aggravates this process. Application of 4ABA does not influence the strength properties of concrete. ABA has performed the inhibition by protective layer development and shield formation against the negatively charged corrosive ions. Blended cement concrete system which was observed to be more vulnerable to corrosion was seen to attain similar corrosion resistance as OPC concrete after inhibitor application.

A Study on the Calculation of the Standard Recycling Cost of PVC Profiles and Flooring Waste in Korea

The Voluntary Agreement for Collecting and Recycling Plastic Waste (VA), including polyvinyl chloride (PVC) profiles and flooring materials, will be converted to an Extended Producer Responsibility (EPR) system from 2023. The objective of this study is to calculate the standard recycling cost and the recycling market size for preparing the new system. Among the total recycling companies participating in the VA, a cost analysis was conducted for 11 profile businesses (35% of the total businesses) and seven flooring businesses (58% of the total businesses). As a result, the standard recycling cost was calculated as 0.45 USD/kg for PVC profiles and 0.36 USD/kg for PVC flooring materials. As of 2020, the total market size is 1135 million USD (5.86 million USD for PVC profiles and 5.49 million USD for PVC flooring materials). Our research shows that few countries have nationally managed accurate data regarding PVC profiles and flooring waste. Compared to the European Union (EU), the total amount of recycled PVC products in Korea seems lower, but the recycling rate per capita is higher. This study can provide basic data about the recycling industry for the recycling academia and the manufacturing field.

Similarities and probability distributions of chloride convection zone depth in concrete exposed to cyclic drying-wetting environments

A methodology using parabolic fitting was proposed to regress three points in chloride profile and determine the depth of convection zone in concrete. Based on exposure tests, the influences of environmental exposure, exposure time and mixture proportion of concrete on probability distributions and statistical parameters of convection depth were studied. The similarity in probability distribution of convection depth was analyzed by the Kullback-Leibler divergence. It was found that the mean, coefficient of variation and distribution type of convection depth are significantly influenced by environmental condition. Convection depth in natural environment mostly follows the Gumbel (Type I) distribution, while it follows the Beta distribution in simulated environment. The probability density functions of convection depth in simulated environment at early exposure have high similarities with those in natural environment at later exposure.

Chloride diffusion along the interface between concrete matrix and repair materials under flexural loading

The interface will be the weakest part after the rehabilitation of old concrete substrate; however, the durability of the interface has been unclear. To fill this gap, this study designed three typical interfaces to simulate those in field projects, i.e., the concrete-repair concrete interface, the concrete-repair cementitious grout interface, and the concrete-repair cementitious grout interface under flexural loading. An improved salt ponding test and a self-designed loading device for simulating the chloride contamination environment coupled with the loading were proposed. Results showed that as the water to cement ratio (w/c) of concrete decreased, the difference in chloride profile was also reduced in each part of the repair system, which presented no obvious difference when the w/c was 0.4. The chloride ion concentration was distributed in an asymmetric inverted V shape in all cases along the perpendicular direction of the interface. Besides, the influenced area of crack at the interface in the prefabricated concrete substrate was 10–20 mm, while that in the cast-in-place concrete substrate was 5–10 mm, along the direction perpendicular to the interface. The crack widths between 0.08 and 0.11 mm posed no great threat to the chloride diffusion at the interface under flexural loads. The present study suggests that the interface is the weakest part, for both mechanical properties and durability of a repaired concrete system. A novel model was proposed to describe the in-depth mechanisms based on complicated microstructure characteristics and particle–particle interactions at the interface.

Chloride ion permeability of Ultra-high-performance fiber-reinforced concrete under sustained load

This work aims at investigating the effect of multiple microcracks in Ultra-High Performance Reinforced Concrete (UHPFRC) occurring in service conditions on the apparent chloride diffusion which is critical to guarantee the design lifetime. First, series of preliminary static bending tests were carried out on three UHPFRC beams to characterize their flexural response as well as their microcrack distribution measured by Digital Image Correlation (DIC). Then, a special test set-up was designed to apply and maintain a sustained bending moment on the UHPFRC beams. Finally, some accelerated migration tests were carried out on the micro-cracked UHPFRC beams under sustained bending load. The results showed different chloride penetration rates and profiles in tested UHPFRC beams under different loading levels, and the influence of the microcrack's width on the apparent chloride diffusion coefficient of the considered UHPFRC was clearly identified, which is a precious information for better predicting the service lifetime of a UHPFRC structure.

New semiempirical temporal model to predict chloride profiles considering convection and diffusion zones

Chloride ions are primarily responsible for reinforcement corrosion in concrete structures in the marine environment. Thereby, analyses regarding chloride penetration into concrete are fundamental for service life estimates, in which the chloride concentration profiles provide quantitative information for prediction models. However, the conventional modeling method based on the solution of Fick's second law of diffusion usually only fits the diffusion profile zone and does not represent the convection zone. Therefore, this article shows a new model for complete chloride profile modeling. The semiempirical double exponential model was developed by approximating Fick's second law using the finite difference method and validated with chloride profiles from structures under natural degradation for more than 40 years. The double exponential model proposed can fit in the two profile zones, showing higher efficiency than Fick's model, and stands out for expressing the variation in chloride peak depth over time.

Influence of corrosion inhibitors on two different concrete systems under combined chloride and carbonated environment

This paper presents the performance of three generic compounds, 4-Aminobenzoic acid (ABA), 2-Aminopyridine (AP) and Salicyaldehyde (SA) as migratory inhibitor on hardened concrete surface to curb corrosion due to combined chloride and carbonated environment. Two types of cement viz. portland cement and fly ash blended cement were used to prepare concrete mixes. Electrochemical techniques (LPR and EIS), gravimetric analysis were applied to evaluate the corrosion performance. Percolation ability of the inhibitors was assessed by UV–visible spectroscopy. Also, chloride profile and carbonation depth was analyzed after definite durations of exposure to identify the dominant cause of corrosion and effect of inhibitor application on these two parameters. Electrochemical and gravimetric results conclude that steel in blended cement is more vulnerable to corrosion as compared to portland cement. Obtained carbonation depth and chloride profile revealed carbonation had significant impact on the corrosion during combined exposure. Degradation of reinforced concrete due to corrosion occurs in two phases in combined environment. In the first phase, chloride ions initiate the corrosion process causing pitting corrosion and carbonation dominates this process during the second phase by aggravating the corrosion mechanism. Application of CoI reduces the corrosion rate effectively, where ABA displayed highest inhibition efficiency of 79.64% in portland cement and 88.31% in blended cement concrete, followed by AP and SA. The inhibition order followed the order of its concentration at rebar level showing direct relation between the two parameters. Optical examination of exposed concrete surface and extracted rebar’s surface validated the inhibition effect of the inhibitors. Reduction in the crack width was noticed on the concrete surface with inhibitor application. Blended cement concrete system which was observed to be more vulnerable to corrosion before the application of inhibitors was seen to attain similar corrosion resistance as portland cement concrete after inhibitor application.

Efeito da duração e pressão da cura por carbonatação do concreto em perfis de cloreto

Abstract Carbonation curing alters the characteristics of the concrete's microstructure and can interfere with the penetration of aggressive ions. The objective of this article was to evaluate the influence of CO2 pressure and carbonation cure time on chloride profiles. Concrete specimens were cured by carbonation with CO2 pressures ranging from 5 to 25 Psi, for a time within the carbonation chamber of 8, 24, and 36 hours. These concretes were subjected to 30 wetting and drying cycles in NaCl solution to stimulate the chloride ingress. The carbonation depth and the microstructure of the concrete were monitored over time. Chloride profiles were obtained and modeled by 4 mathematical equations. The results showed that the combination of less time and CO2 pressure during carbonation curing potentiated the reduction of chloride penetration in concrete. Also, the carbonation curing conditions of 5 and 10 Psi for 8 hours reduced the chloride diffusion coefficient.

Behavior of Engineered Cementitious Composites (ECCs) Subjected to Coupled Sustained Flexural Load and Salt Frost

The performance of engineered cementitious composites (ECCs) under coupled salt freezing and loaded conditions is important for its application on the transportation infrastructure. However, in most of the studies, the specimens were generally loaded prior to the freezing. The influence of sustained load was merely considered. To this end, four sustained deflection levels, i.e., 0%, 10%, 30% and 50% of the deflection at the ultimate flexural strength, and three salt concentrations (1%, 3% and 5%) were applied. Prior to the salt frost resistance test, the fluid absorption of ECC specimens under various conditions were measured. The changes in relative dynamic elastic modulus (RDEM) during the freeze-thaw cycles were captured. The depth and the content profile of free chloride were measured after the coupled sustained load and freezing and thawing cycles. It is shown that 3% NaCl solution leads to the largest deterioration in all cases. There is no visible flaking or damage occurring on the surface. The relationships between locally sustained flexural stress and RDEM loss and also locally sustained flexural stress and free chloride penetration depth were proposed and showed satisfactory results. It is concluded that when ECC is subjected to the FTCs under 1% de-ice salt solution, no depassivation of the steel is expected even under a large deflection level. In terms of 3% and 5% salt solution, the thickness of cover should be no less than 20 mm when a deflection level of 0.5 is applied.

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.

Influence of Chloride Transport Modes and Hydrated Cement Chemistry on Chloride Profile and Binding Mechanisms in Concrete

Influence of Chloride Transport Modes and Hydrated Cement Chemistry on Chloride Profile and Binding Mechanisms in Concrete

Chloride Diffusion Prediction in Concrete through Mathematical Models Based on Time–Dependent Diffusion Coefficient and Surface Chloride Concentration

This paper compared several mathematical models predicting chloride penetration in concrete by employing a time-dependent diffusion coefficient for a number of analytical solutions of Fick’s second law. We propose calibrated models that consider a time-dependent build-up of the surface chloride concentration Cs. Predicted values and measured values of chloride profiles from experimental results were compared, which showed that the calibrated models considering a time-dependent surface chloride concentration could significantly improve the correlation compared with the conventional models employing a constant surface chloride concentration. Moreover, we investigated several factors (i.e., skin effect, aging factor m, exposure conditions, curing conditions, water/binder ratio, and fly ash content) that may affect chloride penetration in concrete by adopting the calibrated models. The results showed conclusively that these factors also significantly affected the accuracy of the chloride penetration obtained by these calibrated models. Finally, the results predicted by the calibrated Tang–Gulikers model were proved to be reasonably accurate in concrete with a small water/binder ratio compared with the experimental data. It is concluded that the calibrated Tang–Gulikers model can be applied for predicting chloride penetration and solving relevant service-life problems resulting from chloride ingress in concrete.