Search

The durability of recycled aggregate concrete (RAC) in the marine environment is mainly influenced by chloride attack. In this paper, the chloride transport law in RAC with different recycled coarse aggregate (RCA) contents was investigated by dry-wet cycling tests considering RCA volume fractions. A five-phase randomly convex polygonal aggregate model was built through a self-compiled program and then a mesoscopic numerical method was established by finite element software development. The proposed numerical model was validated by experimental results and data from other scholars. The impact of interfacial transition zone (ITZ), RCA, new mortar and old mortar were studied. The results showed that: 1) As the thickness of ITZ grows, the chloride diffusion coefficient increases in RAC. When the thickness of the ITZ rises from 25 µm to 100 µm, the chloride diffusion coefficient rises by 37%; 2) The diffusion coefficient of ITZ and mortar have a positive impact on the diffusion of chloride ion in RAC; 3) The chloride diffusion coefficient of RAC is positively correlated with the volume fraction of RCA (V RCA). The chloride diffusion coefficient increases by 102.0% as the V RCA increases from 0% to 50%. The proposed mesoscopic model not only effectively simulates the chloride attack process but also can be used to simulate other ionic attack behaviors and mechanical properties of RAC. [ABSTRACT FROM AUTHOR]

This study investigates the synergistic effects of chloride ions, carbonation, and relative humidity on rebar corrosion in mortar, elucidating the complex interactions at the rebar-mortar interface. Findings reveal that chloride ions and carbonation significantly alter the volumetric water content and resistivity of mortar, leading to non-binary corrosion behaviour through area effect, ohmic control, and anode-to-cathode ratio. In chloride-free, non-carbonated mortar, the area effect dominates, whereas the presence of chloride introduces ohmic control and a saturation-dependent anode-to-cathode ratio. In carbonated mortar, a distinctive ohmic control mechanism emerges, governed by local ionic conductivity. This study highlights the critical need to consider these combined effects for accurate prediction and mitigation of rebar corrosion in concrete structures. By advancing the understanding of these mechanisms, the research provides valuable insights for improving the durability of reinforced concrete structures exposed to harsh environmental conditions. • Effects of carbonation and chloride on water retention and resistivity in mortar. • Water affects corrosion by area effect, ohmic control, and varying anode-to-cathode ratio. • Different water saturation-dependent corrosion potential in non-/carbonated mortar. • Ohmic control in chloride-rich carbonated mortar is not governed by bulk resistivity. [ABSTRACT FROM AUTHOR]

Shortly after casting, offshore reinforced concrete structures are exposed to sulfate and chloride ions without undergoing any proper curing procedures, which are crucial for enhancing their strength and durability. Furthermore, there persists a lack of comprehensive understanding concerning the coupled impact of the attack of sulfate and chloride ions on cementitious materials with current existing research still yielding conflicting outcomes. This paper investigates the influence of curing on the chemical interactions between low-carbon cementitious materials (substituting 45 % of cement with industrial by-products like slag, fly ash, and metakaolin to reduce CO 2 emissions) and coupled sulfate and chloride ions. To achieve this, powder samples were obtained from prismatic-shaped specimens of ordinary Portland cement (CEM I) paste, binary, ternary, and quaternary blends. Some solid specimens were ground into powder after 24 hours post-casting while others were powdered after a 90-day curing period. Subsequently, the acquired powders underwent exposure to chloride, sulfate, and sulfate-chloride solutions over a duration of 25 days. Results indicate that curing time does not alter the interplay between sulfate and chloride ions in the cementitious matrix. Sulfate presence accelerates chloride ion ingress, while chloride presence mitigates sulfate attack in both uncured and pre-cured samples. However, the curing process accelerates sulfate attack, proven through excessive ettringite and gypsum formation, high consumption of portlandite and AFm, diminution of sulfate ions concentration in the attacking solution after 5 days of exposure, increase of pH of more than 0.5 units, aspect changes observed through visual inspections, and porosity distribution changes showed by an increase of 10 % of the total porosity in the reference mix. Additionally, curing promotes the formation of Friedel's salt, thereby attenuating chloride ions ingress. [Display omitted] • Chemical interactions of sulfate-chloride attack are highlighted. • The presence of sulfate accelerates the chloride ingress in the materials. • Chloride diffusion mitigates the sulfate attack in the materials. • Curing duration does not affect the sulfate-chloride coupling chemical process. • Raman spectroscopy serves as a quick chemical characterization technique on solutions. [ABSTRACT FROM AUTHOR]

The practical application of Cu(II)-catalyzed Fenton-like reaction (Cu(II)/H 2 O 2) exhibits a low efficiency in the degradation of refractory compounds of wastewater. The impact of chloride ions (Cl−) on Fenton-like reactions have been investigated, but the influence mechanism is still unclear. Herein, the presence of Cl− (5 mM) significantly accelerated the degradation of benzoic acid (BA) under neutral conditions. The degradation of BA follows pseudo-first-order kinetics, with a degradation rate 7.3 times higher than the Cu(II)/H 2 O 2 system. Multiple evidences strongly demonstrated that this reaction enables the production of reactive chlorine species (RCS) rather than HO• and high-valent copper (Cu(III)). The kinetic model revealed that Cl− could shift reactive species from the key intermediate (Cu(III)-chloro complexes) to RCS. Dichlorine radicals (Cl 2 •-) was discovered to play a crucial role in BA degradation, which was largely overlooked in previous reports. Although the reaction rate of Cl 2 •- with BA (k = 2.0 × 106 M−1 s−1) is lower than that of other species, its concentration is 10 orders of magnitude higher than that of Cu(III) and HO•. Furthermore, the exceptional efficacy of the Cu(II)/H 2 O 2 system in BA degradation was observed in saline aquatic environments. This work sheds light on the previously unrecognized role of the metal-chloro complexes in production the RCS and water purification. [Display omitted] • The presence of Cl− enhanced the degradation of BA in Cu(II)/H 2 O 2 system. • The unstable Cu(III)-chloro complexes serve as the origin of chlorine species. • Model is developed to describe the kinetics of Cu(II)/H 2 O 2 /Cl− interactions. • Cl.• and Cl 2 •- are the primarily reactive species responsible for BA degradation. [ABSTRACT FROM AUTHOR]

• F − and Cl− ions distinctly impact cold-rolled steel, AA5754, and Zn corrosion rates. • Thermodynamic calculations support observed corrosion behaviours. • Complexation with F − modifies passivation dynamics, especially in AA5754. • Cl− leads to pitting in AA5754; F − extends the limiting current density range. • Zn corrosion is driven by buffering agent NH 4 HCO 3 rather than F − and Cl−. This study investigates the effects of fluoride and chloride ions on the corrosion of cold-rolled steel, aluminium alloy AA5754, and zinc, using ammonium bicarbonate as a buffer at pH 4 and compares electrochemical findings with thermodynamic calculations of E -pH diagrams. The distinct electrochemical behaviours of fluoride and chloride ions were confirmed, with fluoride-induced corrosion leading to the significant complex formation on cold-rolled steel and AA5754, the latter leading to a narrowing of the Al passive region. However, a comprehensive analysis of all ionic species in the solution (F−, Cl−, NH 4 + and HCO 3 −) and their complex equilibria reveals that zinc's corrosion is primarily influenced by the overall ionic strength of the solution and further complexation with the buffering agent at higher pH levels, should these conditions occur during corrosion. In addition, this analysis also highlights the subtle differences in the stabilization effects of open circuit potential on cold-rolled steel and AA5754. The results underscore the importance of considering the overall solution equilibrium in thermodynamic analyses and provide a foundation for further research on the role of F- and Cl- ions in zirconium conversion coatings. [Display omitted] [ABSTRACT FROM AUTHOR]

In this paper, a new approach of bidirectional electro-migration rehabilitation (BIEM) using pulse currents was proposed. The effect of the duty cycle and frequency of the square wave pulse current on the BIEM was investigated. The results showed that the desalination efficiency was improved by 10 % with the decrease of duty ratio and frequency. Furthermore, With the increase of duty ratio and frequency, the hydrogen permeation of steel bars decreased by 28.5 %. More uniform desalination efficiency was obtained by using pulse current. The half-cell potential of the rebars was also measured and it was higher for the samples using pulse currents than for those using direct currents, indicating a lower risk of corrosion after pulse current treatment. The pH value of the concrete also increased during the BIEM process. • The amount of hydrogen permeation in the rebars of concrete repaired by pulse current is reduced. • Increasing frequency and decreasing duty cycle of pulse current make the desalination efficiency distributed more evenly. • Decreasing frequency and duty cycle of pulse current will increase the efficiency of chloride ions removal. [ABSTRACT FROM AUTHOR]

• The postnatal GABA shift is the last in a sequence of developmental GABA shifts. • The molecular mechanism for triggering the postnatal GABA shift remains unresolved. • Sensory input may be crucial in determining timing of the postnatal GABA shift. • The impact of GABA signaling is controlled by network activity and connectivity. GABA is the major inhibitory neurotransmitter that counterbalances excitation in the mature brain. The inhibitory action of GABA relies on the inflow of chloride ions (Cl−), which hyperpolarizes the neuron. In early development, GABA signaling induces outward Cl− currents and is depolarizing. The postnatal shift from depolarizing to hyperpolarizing GABA is a pivotal event in brain development and its timing affects brain function throughout life. Altered timing of the postnatal GABA shift is associated with several neurodevelopmental disorders. Here, we argue that the postnatal shift from depolarizing to hyperpolarizing GABA represents the final shift in a sequence of GABA shifts, regulating proliferation, migration, differentiation, and finally plasticity of developing neurons. Each developmental GABA shift ensures that the instructive role of GABA matches the circumstances of the developing network. Sensory input may be a crucial factor in determining proper timing of the postnatal GABA shift. A developmental perspective is necessary to interpret the full consequences of a mismatch between connectivity, activity and GABA signaling during brain development. [ABSTRACT FROM AUTHOR]

This paper presents a study on the durability testing of a concrete facility located within the North Bay Port region, which has been in service for 200 months. Based on the results of 20 sets of concrete samples, an improved Kolmogorov-Smirnov (K-S) test method and gross error discrimination method are proposed to analyze the random distribution functions of the apparent chloride diffusion coefficient (D app) and the apparent surface chloride concentration (C s), and further explore the time-varying characteristics of chloride ion transmission in concrete. The research shows that the improved K-S method presented in this paper can effectively reduce the probability of type II errors by selecting a rational sample size, which can also improve detection efficiency. When the sample size does not exceed 10, the 2 σ criterion proposed in this paper can effectively identify and eliminate gross errors. In general, D app and C s follow the log-normal distribution, while the time factor (m) follows a normal distribution parameter. The value of C s basically stabilized after exposure to 80 months, whereas D app tended to stabilize after exposure to 100 months. The value of m obtained through fitting short-term experimental data is typically overestimated, and its value decreases as the exposure time prolongs. Therefore, m should also be considered a time-varying parameter that decreases with time. The tested RC structure will begin to experience rebar corrosion after 48.5–60 years of exposure to the marine environment based on the probabilistic assessment. • The 2 σ criterion was introduced to identify and rectify significant errors. • The improved K-S method was developed to minimize the likelihood of type II errors. • Chloride profiles were extracted from 200 months aged harbor concrete structures. • Both D app and C s demonstrated a good fit with the log-normal distribution. [ABSTRACT FROM AUTHOR]

• Sodium-chloride ion difference (SCD) affected pH as well as PaCO 2 and lactate. • The effects of SCD, PaCO 2 , and lactate for pH regulation were independent. • Prevention of SCD decrease may be important for maintaining normal pH. In the Stewart approach, the difference between the cation and anion concentrations, especially between sodium, accounting for the majority of cations, and chloride, comprising the majority of anions, is an important factor in pH regulation. This study investigated the effect of sodium–chloride ion difference (SCD) on pH regulation comparing with those of PaCO 2 and lactate. Arterial blood gas samples measured at our pediatric intensive care unit of a tertiary children's hospital between January and June 2020 were included. Samples that met the following criteria were excluded: samples collected from patients taking potassium bromide and samples with lactate concentration of >25 mmol/L. From the eligible data, pH was chosen as the dependent variable and SCD, lactate, and PaCO 2 as independent variables, and then, a multiple regression analysis was performed. In total, 5360 samples were included. Of these, five samples were excluded according to the exclusion criteria. Finally, 5355 samples were analyzed. As the variance inflation factors were <2.0 for all three variables, there was no multicollinearity. The following model was derived: pH = 7.384 + [0.97 × SCD (mEq/L) − 0.66 × PaCO 2 (mmHg) − 1.33 × Lac (mmol/L)] × 10−2 (adjusted R-squared = 0.73; P value < 0.001). Based on the standardized partial regression coefficients (β), pH was affected in the order of PaCO 2 (β PaCO2 = −0.95), SCD (β SCD = 0.72), and lactate (β lactate = −0.33). The prevention of SCD reduction, together with respiratory and metabolic management, is important for pH regulation. [ABSTRACT FROM AUTHOR]

This study developed a methodology for quantifying the corrosion parameters such as corrosion potential, corrosion current density and Tafel slopes for rebar in simulated pore solutions and mortar with realistic rebar conditions. We quantitatively investigated the impact of depassivation duration, chloride concentration, carbonation, and relative humidity on these parameters. Specifically, in partially saturated mortar, it was observed that the critical chloride content lacked a distinct threshold. The degree of depassivation, as indicated by shifts in corrosion parameters due to chloride ions and carbonation, was influenced by humidity. • A critical review of rebar corrosion parameters in solution and concrete. • A non-submerged two-step potentiodynamic test method on rebar corrosion in mortar. • Long-term effect of chloride-induced depassivation in simulated pore solutions. • Measurements of corrosion parameters in simulated pore solutions and mortar. • Effects of chloride, carbonation, and relative humidity on the corrosion parameters. [ABSTRACT FROM AUTHOR]

• Analysis of UAE environment for main deterioration. • Evaluation of temperature-dependent migration coefficients. • Derivation of activity energy of chloride ion in concrete. • Quantification of temperature effect on strength and migration. • Evaluation of cross-over in strength development. In this study, strength and chloride migration tests were conducted considering nuclear power plant concrete exposed to high temperature and chloride ingress. Two temperature grades (20 ℃ and 50 ℃) were considered for curing and diffusion testing. In the curing at high temperature, cross-over behavior appeared for strength development from 7 to 14 days, however lower migration coefficients were evaluated under high temperature curing conditions. This was because even if cement hydrates were not completely stable, the absorption of chloride was still effective and the pore structure improved due to accelerated hydration. Migration test referred to NT-BUILD 492 method was performed on 40 MPa and 27 MPa concrete of 91 days curing. Activation energy for two strength grades was individually obtained during migration test with chaining temperature to 50 °C. The obtained results were compared with the previous results considering test method (diffusion and migration) and mix proportions. [ABSTRACT FROM AUTHOR]

• FSGC showed 38.1% to 114.2% higher strength than FGC mixes irrespective of NaCl concentration. • Influence of Cl- ions in reducing strength of GPC decreased in the presence of slag and later curing ages. • Steel bar embedded in NaCl added FSGC showed lower E cor and I cor values than FGC mixes. • Formation of C-S-H gel and higher aluminosilicate gels in FSGC confirmed its improved performance over FGC mixes. The evaluation of corrosion behaviour of rebar and changes in microstructure evolution in geopolymer concrete (GPC) in the presence of chloride ions form an important aspect of durability investigation. For this purpose, an experimental investigation was undertaken to examine the corrosion of reinforcing steel and changes in microstructure development of fly ash based geopolymer concrete (FGC) and fly ash-GGBS based geopolymer concrete (FSGC) containing chloride ions. Corrosion behaviour was evaluated through corrosion potential (E cor) and corrosion current density (I cor) and microstructural changes of GPC were examined at various ages and that at rebar level by XRD, EDS, FTIR, and FESEM analyses. Test results revealed that chloride ions had significant influence on consistency, strength, and microstructure of GPC. NaCl improved the consistency of GPC mixes. FSGC mixes showed 38.1% to 114.2% higher strength than FGC mixes at all ages irrespective of NaCl concentration. Further, GPC mixes exhibited lower strength with increase in NaCl concentration at all ages. Rebar embedded in FSGC specimens exhibited mostly less negative E cor and lower I cor compared to FGC specimens. Results of chloride analysis revealed lack of chloride binding in GPC mixes. Higher peak intensity of aluminosilicate gels and presence of C-S-H gel in FSGC mixes as identified from XRD analysis and higher atomic Ca/Si ratio in FSGC mixes obtained from EDS analysis confirmed the improved performance of FSGC mixes in terms of higher strength, lower corrosion activity and lower chloride content over FGC mixes. [ABSTRACT FROM AUTHOR]

Chlorate ion ClO 3 − is formed as a result of the complex chemical interaction of ozone with chloride ion in aqueous solution. In neutral and basic solutions, chlorate is the main product. In acid solutions, the main product is molecular chlorine Cl 2 , and the yield of chlorate is 50–100 times lower. Dependencies have been studied of chlorate formation rate on significant experimental factors: concentrations of initial substances, ozone and chloride ion, acidity (pH), ionic strength and temperature of the reaction solution. The kinetic laws of chlorate generation have been established, and the expressions are given for rate constants of chlorate formation as functions of temperature and ionic strength. When tert-butanol is added to the reaction system, the formation of chlorate ceases, which is an evidence of the crucial role of free radical reactions in this process. Image 1 • Chlorate ClO 3 − is the main product of reaction between ozone and chloride solutions. • Kinetics of ClO 3 − formation was comprehensively investigated. • Radical scavenger tert-butanol stops chlorate formation. [ABSTRACT FROM AUTHOR]

• Chloride ions in exposure solution significantly affected formation of compounds in concrete as indicated by XRD results. • OPC exhibited 4.82 and 2.02 times higher apparent chloride diffusion coefficient than PPC and OPC plus fly ash. • PPC exhibited better performance against corrosion as compared to OPC plus fly ash followed by OPC. • Developed empirical relations for OPC and PPC predicted the I corr with higher degree of accuracy for OPC plus fly ash. • Developed empirical relation between E 0 and I corr predicted well the I corr values reported in literature. This study aims to investigate and correlate durability parameters in concrete exposed to external chloride. Tests for corrosion, chloride diffusion, and X ray diffraction (XRD) analysis were performed. Based on results, ordinary Portland cement (OPC) exhibited 4.82 and 2.02 times higher apparent chloride diffusion coefficient than Portland pozzolana cement (PPC) and OPC plus fly ash. Reinforced concrete specimens made with PPC showed better performance against corrosion as compared to those made with OPC plus fly ash followed by OPC. Concentration of chloride ions in exposure solution significantly affected microstructure of concrete as indicated by formation of compounds from XRD results. Developed empirical relationships between durability parameters for OPC and PPC predicted well the corrosion current density for OPC plus fly ash that was independent of model development. [ABSTRACT FROM AUTHOR]

Highlights • Coupling effect of mechanical load and environment load had influence on the durability performance of concrete structure. • Water and chloride penetration into concrete decreased firstly and then increased with the increase of applied load. • Applied load had an obvious influence on the frost resistance of concrete. • Coupling effect had more obvious influence on high water/ratio concrete. Abstract In cold coastal area, the destruction mechanism of reinforced concrete structures is mainly governed by a combination of factors such as self-loading, freeze–thaw and chloride erosion. In this study, ordinary cube concretes (C30 and C50, while w/c = 0.53 and 0.35 respectively) underwent a coupling effect of pressure load with stress ratio of 0, 0.3 and 0.5 and freeze–thaw cycles, following by capillary water absorption test and chloride penetration test. Concrete samples with 0.3 f c showed the best water and chloride penetration resistance under the coupling effect, followed by samples with 0.5 f c and 0 f c , which is consistent with the conclusion that under load only. Water and chloride ions penetration increased sharply when freeze–thaw cycles was over 100 times, which is different with samples without load. Outside part of concrete showed higher permeability and chloride content than inside part. MIP results confirmed that stress played an important role in the water absorption and chloride penetration of concrete under the coupling effect. These results provide important new insights into the permeability of concrete under a coupling effect. The applied load performed a more important role on the service life prediction of concrete structure. [ABSTRACT FROM AUTHOR]

• Cation type associated with chloride ions significantly affected compressive strength of concrete. • Boundary potentials of different zones of corrosion were obtained in presence of chloride salts and corrosion inhibitors. • Corrosion inhibitors influenced the effect of cation type of chloride salts on passivity of reinforcing steel. • Cation type associated with chloride ions affected free chloride ion and bound chloride ion concentrations. • Sodium nitrite was more effective in enhancing passivity of steel than di-Sodium hydrogen phosphate. In this research, effect of cation type of chloride salts on corrosion behaviour of steel was determined by potentiodynamic polarization test in concrete powder electrolyte solution in presence of corrosion inhibitors. Results showed that cation type of chloride salts not only affected compressive strength of concrete but also passivity of steel and chloride binding. The decreasing trend of bound chloride concentration was C B: CaCl 2 > C B: MgCl 2 > C B: NaCl. Formation of various compounds in concrete was confirmed through XRD and FTIR spectroscopy analyses. Sodium nitrite was more effective in enhancing passivity of steel than di-Sodium hydrogen phosphate. [ABSTRACT FROM AUTHOR]

Abstract Electrochemical Chloride Extraction (ECE) is one of the key ways to enhance the durability of concrete structure which suffered or are suffering from chloride attack. To deeply understand the influence of various factors on chlorine removal efficiency, this paper presents a numerical study to characterize transport and distribution of each ion during ECE. A plain concrete specimen was used as an example to investigate the influence of various factors on the efficiency of ECE of one side anode. These factors were: time, current density, ratio of cover thickness and side length, initial chloride ion concentration, and ratio of cross-sectional area of reinforcement to cross-sectional area of specimen. In addition, the quantitative relationship model between these factors and total electrochemical desalination efficiency are also proposed. Good agreement between the present the quantitative relationship model of total desalination efficiency and the FEM solution illustrates reliability and accuracy of the proposed relationship model. Highlights • ECE process efficiency of one side anode is discussed. • The influence of key factors on the efficiency of ECE is clarified. • The total ECE efficiency model are proposed. [ABSTRACT FROM AUTHOR]

Abstract Accelerated migration tests which are commonly used to measure chloride diffusion in ordinary cement-based materials cannot be directly applied to composite with very low permeability, such as Ultra High-Performance Fiber Reinforced concretes (UHPFRC). In order to assess the UHPFRC enhancement on the structural durability, there is a critical need to accurately assess the permeability level of the material to chloride ions. The objective of this work is to adapt an existing set-up of accelerated chloride migration test in order to (i) better characterize the resistance of chloride ion penetration in UHPFRC; and (ii) to compare the resistance of chloride ion penetration between UHPC and UHPFRC. The material characterization, the set-up modifications of the existing accelerated migration test, the results are presented. In conclusion, the modification of the test-set-up allowed to accurately measure chloride transport of very low permeability UHPFRC and to shed light on the effect of the fiber reinforcement. [ABSTRACT FROM AUTHOR]

Abstract Reinforced concrete structures experience severe durability degradation when subjected to alkali–silica reaction (ASR) and chloride attack. A special electrochemical rehabilitation treatment, containing lithium compound anolyte, has been developed to drive lithium ions into concrete composites and remove chlorides simultaneously, for mitigating both the ASR-induced cracks and the chloride-induced reinforcing steel-bar/fiber corrosion. In this study, the efficiency of the impregnation of lithium ions and the removal of chloride ions through a specific electrochemical treatment is numerically evaluated, which results into the distribution profiles of all typical ionic species. A heterogeneous numerical model, which treats concrete as a three-phase composite, is presented to examine the response of inner structures, especially the interaction between active aggregates and lithium ions that are supposed to mitigate ASR. The ionic interaction between different species, binding and the electrochemical reaction at electrodes are also considered. Through a detailed modelling of multi-phase and multi-species, a systemic parametric analysis based on a series of significant factors during electrochemical treatment (e.g., current density, treatment time, temperature, cathode position and concentration of lithium solution) reveals some important tendencies of ionic electromigration in concrete structures, which are supposed to guide the field applications. [ABSTRACT FROM AUTHOR]

This study compares the resistance against chloride-induced steel corrosion of two alkali-activated materials (AAMs) and a CEM III concrete. The AAMs studied are: a metakaolin activated with sodium silicate (AAMK), and a GGBS activated by sodium carbonate (AAS). In order to study the corrosion of the reinforcement due to chloride, electrochemical measurements were performed on reinforced samples kept in a humid room (passive conditions) and samples dried (40 °C) before their immersion in a 35 g/l chloride solution (active conditions). AAMK showed the highest transfer properties whereas AAS and CEM III showed similar performance. The highly interconnected porous network of AAMK concrete presented low resistance to the penetration of chloride ions and very low resistivity compared to CEM III and AAS concrete. AAS had a finer porosity and a high chloride fixation capacity, which led to better resistance to chloride penetration and high resistivity. However, in AAS, sulfide ions from the slag dissolution led to low corrosion potential compared to values measured in traditional concrete. The drying of these samples at 40 °C caused a drop in the resistivity and a sharp increase in the chloride migration coefficient, which was explained by damage of the material. No corrosion products were observed after 2 years on rebars embedded in AAMs (AAMK and AAS). However, in CEM III reference concretes, pits of corrosion were identified when the reinforced samples were split. AAMs seemed to provide good protection of the reinforcement regarding chloride corrosion in immersed samples. [ABSTRACT FROM AUTHOR]

The high concentration of salt in organic wastewater has a strong inhibitory effect on the removal of pollutants. A method for the efficient removal of trace pollutants in high-salinity organic wastewater was developed. This study investigated the effect of the combination of permanganate [Mn(VII)] and calcium sulfite [S(IV)] on pollutant removal in hypersaline wastewater. The Mn(VII)-CaSO 3 system removed more pollutants from high-salinity organic wastewater than from normal-salinity wastewater. Chloride (increasing from 1 M to 5 M) and low concentration of sulfate (increasing from 0.05 M to 0.5 M) significantly enhanced the system's resistance to pollutants under neutral conditions. Despite the fact that Cl− can combine with the free radicals in the system and reduce their efficiency in removing pollutants, the presence of chloride ions greatly enhances the electron transfer rate in the system, promoting the conversion of Mn(VII) to Mn(III) and significantly increasing the reaction rate of Mn(III) as the primary active species. Therefore, chloride salts can greatly enhance the removal of organic pollutants by Mn(VII)-CaSO 3. Although sulfate does not react with free radicals, a high concentration of sulfate (1 M) will affect the formation of Mn(III), which greatly weakens the removal effect of the entire system on pollutants. The system can still have a good pollutant removal effect with mixed salt. Altogether, this study demonstrates that the Mn(VII)-CaSO 3 system offers new possibilities for the treatment of organic pollutants in hypersaline wastewater. [Display omitted] • Mn(VII)-CaSO 3 system performs well under acidic conditions, but poorly under neutral and alkline conditions. • Higher SMX removal rates were obtained in high-salinity wastewater. • Chloride and low concentration sulfate enhanced the removal of pollutants by Mn(VII)-CaSO 3 system. • Mn(III) is considered as the main active substance against high salinity. [ABSTRACT FROM AUTHOR]

• Barrier protection from galvanized steel in sulfate-rich grout can be compromised. • Sulfates in alkaline solution develop poor coverage of calcium hyroxyzincate. • Corrosion development of galvanized steel captured by EN technique. Corrosion mitigation strategies for structural steel bridge elements including post tensioned steel components include the use of galvanized steel. The zinc alloy layers and subsequent precipitation of a dense surface oxide in alkaline environments provide beneficial barrier protection to mitigate corrosion. However, severe corrosion of galvanized steel components in contact with sulfate-rich deficient cementitious grout was documented to occur in less than 8 years of bridge service. Electrochemical testing and material characterization showed that the presence of sulfates in alkaline solutions allow for prolonged zinc activity and hindered passivation by the incomplete surface coverage and the precipitation of large sized calcium hydroxy zincate. OCP, LPR, and electrochemical noise (EN) testing showed greater corrosion activity of galvanized steel in chloride and sulfate solutions. EN identified local corrosion activity of the zinc associated to the porous nature of the surface oxide layer. [ABSTRACT FROM AUTHOR]

Due to the essential roles of glutamate, detection and response to a large range of extracellular concentrations of this excitatory amino acid are necessary for the fine-tuning of brain functions. Metabotropic glutamate receptors (mGluRs) are implicated in shaping the activity of many synapses in the central nervous system. Among the eight mGluR subtypes, there is increasing interest in studying the mGlu 3 receptor which has recently been linked to various diseases, including psychiatric disorders. This receptor displays striking functional properties, with a high and, often, full basal activity, making its study elusive in heterologous systems. Here, we demonstrate that Cl − ions exert strong positive allosteric modulation of glutamate on the mGlu 3 receptor. We have also identified the molecular and structural determinants lying behind this allostery: a unique interactive “chloride-lock” network. Indeed, Cl − ions dramatically stabilize the glutamate-induced active state of the extracellular domain of the mGlu 3 receptor. Thus, the mGlu 3 receptors’ large basal activity does not correspond to a constitutive activity in absence of agonist. Instead, it results mostly from a Cl − mediated amplified response to low ambient glutamate concentrations, such as those measured in cell media. This strong interaction between glutamate and Cl − ions allows the mGlu 3 receptor to sense and efficiently react to sub-micromolar concentrations of glutamate, making it the most sensitive member of mGluR family. [ABSTRACT FROM AUTHOR]

Industrial effluent is largely being used for irrigation of crops. Hence, monitoring its pollution level is essential to check its suitability for the purpose. We propose a simple and highly sensitive Fiber Bragg grating (FBG) sensor to determine the concentration of Chloride (Cl) and Lead (Pb) ions present in the treated waste water effluent of sugar factories. It is based on the principle of shift in the Bragg wavelength of an etched FBG with change in the ambient refractive index. The etched FBG was calibrated by known concentration of solutions containing the element under study and then was used to quantify the element in the waste effluent. Proper reagents were used for selective determination of the element. The concentrations of Cl and Pb ions in the effluent sample determined by our designed FBG sensor are 95.73 ppm and 0.008 ppm respectively which are in good agreement with the results obtained by APHA (American Public health association) standard techniques employed for wastewater analysis. Sensitivities of Cl and Pb sensors are calculated as 0.76 pm/ppm and 38.6 pm/ppm respectively. Sensitivity of the sensor for Pb ions being about 50 times greater than that for Cl ions, suggests a higher sensitivity of sensor in lower range of concentration in ppm. Limit of detection of our sensor for Cl and Pb are 1.2 ppm and 0.003 ppm respectively which are lower than that of APHA techniques, suggesting the superiority of our sensors. Simple working, miniaturization, cost-effectiveness and ability of online measurement are the most important features of FBG chemical sensors that give them an edge over existing techniques for continuous effluent monitoring. [ABSTRACT FROM AUTHOR]

The leaching of a chalcopyrite-bearing ore in sulfate solutions typical of heap leaching systems with various additives present was investigated. The catalytic effects of Ag ions and other additives, which included ethylene glycol, chloride ions and a wetting agent, were investigated experimentally for potential synergistic effects. It was established that the benefit of low Ag ion concentrations on Cu extraction can be enhanced significantly by the presence of additional components in the leach solution. The presence of Ag ions and ethylene glycol resulted in increased Cu extraction compared to just Ag ions. It was observed that in the presence of both chloride ions and Ag ions, the Cu extraction was significantly higher at high chloride concentrations than at lower concentrations. A strong synergistic effect on Cu extraction was observed also between Ag ions and a wetting agent. Cu extractions exceeding 80% after 10 days were observed when Ag ions and the wetting agent were both present. Only a small amount of the wetting agent was required to produce this result. [ABSTRACT FROM AUTHOR]

The chloride ion (Cl − ), a very common monatomic anion, has high ecological toxicity at high concentrations because of its non-biodegradability, and can easily migrate from landfill site into the surrounding environment. Four lab-scale landfill simulation reactors were established to investigate Cl − release behavior: the anaerobic landfill mode (R1), the semi-aerobic landfill mode (R2), the anaerobic landfill with leachate re-circulation mode (R3), and the semi-aerobic landfill with leachate re-circulation mode (R4). The landfill operation modes had a great influence on the release of Cl − . In 256 days, the cumulative release amounts of Cl − in the four reactors were 64.52, 132.07, 56.10, and 33.1 g for R1–R4, respectively. Once air enters anaerobic landfill, the leachate Cl − concentration may sharply increase. The highest leachate Cl − concentrations were 6.6 g L −1 in anaerobic reactor and 18 g L −1 in semi-aerobic reactor. However, the leachate re-circulation can maintain the release of Cl − at dynamic equilibrium state. Theoretically, the Cl − release behavior from anaerobic landfill with leachate re-circulation (R3) will be continuous. In contrast, under the other conditions, it can be anticipated to occur once the leachate recirculation stops (R1) or when the landfill encounters air incursion (R2 and R4). The semi-aerobic operation modes had significantly lower COD/Cl and NH 4 -N/Cl ratios than the anaerobic modes. This indicates that the Cl − pollution risk from semi-aerobic modes is lower than that from anaerobic modes. [ABSTRACT FROM AUTHOR]

Both Cl − and base can affect PMS activation to produce reactive chlorine or oxygen species, but the overall effects of chloride on this emerging PMS/base technology in saline wastewater treatment are unknown. Here effectiveness of PMS/base, PMS/Cl − and PMS/base/Cl − is compared with a gradient concentration of chloride and alkalinity, by probing the degradation of methylene blue (MB). Both PMS/base and PMS/Cl − systems can rapidly degrade MB due to the generation of singlet oxygen and reactive chlorine, respectively. Interestingly, dye degradation and adsorbable organic halides (AOX) formation are inhibited in the PMS/base/Cl − system as high concentrations of Cl − and base co-exist. Reaction of PMS with chloride diminishes the effective concentration of PMS by base activation, whereas in return high alkalinity decreases the oxidation capacity of reactive species. Therefore, this finding may have significant technical implications for evaluating the applicability of the emerging PMS/base technology and optimizing the conditions for AOX abatement in PMS-based processes. [ABSTRACT FROM AUTHOR]

The dissolution of screened samples of pure malachite in dilute (0.033 to 0.15 M) sulfuric acid solutions has been shown to be rapid and the kinetics of dissolution are consistent with rate-determining chemical reaction on the surface of the shrinking particles. There is no evidence of mass transport controlled dissolution even at the highest rates. The rate is inversely proportional to the particle size and increases with increasing acidity. However, the relationship between the rate and the acid concentration is not linear but is directly proportional to the proton activity as obtained from pH measurements. The effect of the addition of chloride ions on the rate is relatively small and it appears to involve a specific effect of chloride at low concentrations and the effect of chloride on the proton activity at high concentrations. The rate increases with increasing temperature and the activation energy of 53.6 kJ mol −1 is in the range expected for a rate-determining chemical reaction. A simple fundamental rate equation has been developed that will allow prediction of the dissolution curves for any particle size at any acid concentration and temperature within the range studied. From a practical perspective, these results suggest that heap leaching of malachite in dilute acid should present no chemical problems and that there is little advantage to be gained from the addition of chloride ions to increase the rate of leaching. [ABSTRACT FROM AUTHOR]

Chloride ion is known to accelerate corrosion in numerous metallic systems, although it is not well understood why. Using first-principles methods, such as density functional theory, it is possible to directly compute the energy of adsorption for chloride, and, using a thermodynamic framework based on statistical mechanics, to predict the environmental conditions under which it may be anticipated that chloride could displace other ions (such as hydroxide, incipient oxide, or other potentially corrosion inhibiting species) from the bare metal and/or oxide surface. By reviewing the literature, as well as performing some original density functional theory calculations, the authors present in this work the dependence of the surface coverage for H 2 O, OH, O and Cl on the electrochemical potential, pH and chloride concentration for a number of metallic systems, including nickel, iron, magnesium and aluminum, to predict the fundamental surface processes that may related to the role of chloride in potentially interfering with processes such as repassivation and metal dissolution. It is found that under some conditions certain metals can possess zones of mutual stability where both chloride and hydroxide may be coadsorbed, whereas other metals appear to have intrinsic resistance to chloride adsorption. Variations among the available first-principles adsorption energies obtained from different sources indicate that uncertainty analysis is necessary moving forwards. An analogous approach could be taken to consider the interaction of chloride with clean and defective oxide and/or hydroxylated surfaces. [ABSTRACT FROM AUTHOR]

The ultrasonic velocity in concrete and the concentrations of ions at different depths along the directional flow of ion erosion were measured under the joint effect of seepage flow and stress fields. The permeability of sulfuric acid and chloride ions in concrete under different pressure head and load were analyzed (pressure head and load are perpendicular to each other). The results show that the concentrations of chloride ion and sulfate ion in different depths of concrete were increased to a certain extent either under the water head pressure or load effect. The differences in water head can induce the variation of ions concentration in the surface layer of concrete and the influenced depth can reach up to 60 mm. The load imposed a similar effect on the ions concentration of different layers and the directions of ion erosion, respectively. The ultrasonic testing results of corroded concrete are consistent with the results of ions concentration measured by spectrometry. [ABSTRACT FROM AUTHOR]

A new kind of fluoro-chloride glass was successfully prepared based on fluoroaluminate glass modified by various Cl − . The reductions of phonon density and OH − content revealed by the measured Raman and FTIR spectra show that structural changes caused by the Cl − ions have an effect on the optical properties. With increasing chloride content, the thermal stability factor ΔT showed an increase trend, indicating a better thermal stability of the host. Meanwhile, according to Judd-Ofelt calculation, the intensity parameter Ω 2 increased, which indicates a stronger covalency and local asymmetry of the coordination bonds around the Er 3+ ions after introduction of Cl − . Noticeably, the lifetime (3.48 ms) of Er 3+ : 2.7 μm obtained in the chloride-rich glass (AYF-8Cl) is the longest in reported glass systems, along with obvious enhanced fluorescence intensity. All the results suggested that the fluoro-chloride glasses hint its potential applications in laser materials, especially in 3 μm wavelength. [ABSTRACT FROM AUTHOR]

Chloride transport in the gel pore determines the durability of concrete material. In this paper, experiments and molecular dynamics (MD) simulation were utilized to systematically investigate chemical composition (calcium to silicate ratio C/S) influence on the transport and adsorption behavior of water, calcium and chloride ions confined in the nano-pores of calcium silicate hydrate (C-S-H). The immersion experiments indicate C-S-H samples with higher C/S ratio have better chloride adsorption capability and the zeta potential measurements proved the calcium ions can determine the surface potential in the system and strongly affect the chloride adsorption. In the MD simulation, with increasing C/S ratio, the long surface silicate chains are broken to defective short chains that can provide more non-bridging oxygen sites to accumulate surface water molecules and calcium atoms. There existed strong spatial correlation between surface calcium and chloride ions in the radial distribution function patterns, which confirms that the surface calcium plays critical role in chloride adsorption. Furthermore, the interaction mechanism between calcium and chloride ions can be categorized into two parts, the stronger one caused by the formation of ionic pairs Ca-Cl (within 3 Å), and the weaker interaction at larger distance (around 4-6Å). Therefore, high calcium concentration in the vicinity of surface contributes to stronger chloride adsorption, more Ca-Cl accumulation and longer resident time. [ABSTRACT FROM AUTHOR]

For calculating ion transport in electro-migration experiments in concrete, the pore space is divided between free pore water and a double layer that compensates the surface charge of minerals lining the pore. The concentrations of counter-ions and co-ions in the double layer are averaged in a Donnan layer, which allows to solve the flux equation of the individual ions. A numerical model is developed for transient states, with the harmonic mean of the chemical activity coefficients and the physical parameters to adapt cell sizes in zones with high concentration gradients. Diffusion coefficients of the ions are corrected for temperature and ionic strength with an empirical equation with three parameters optimized on published transport numbers and specific conductances. The current and the Cl – breakthrough is calculated in an electro-migration experiment with a concrete sample. The surface charge is positive in the experiment, enhancing and reducing the diffusivity of anions and cations. [ABSTRACT FROM AUTHOR]

A study of the kinetics of the anodic oxidation of chloride ions on the surface of lead-silver anodes used for the electrowinning of zinc has shown some interesting and practically important results. Oxidation of chloride does not occur on a PbSO 4 surface but occurs readily on a PbO 2 surface. Oxidation of chloride occurs at the mass-transport controlled rate at the operating potentials of anodes during the electrowinning of zinc in the absence of manganese in the electrolyte. However, the rate of oxidation of chloride ions is significantly lower in the presence of manganese ions in the concentration range 1 to 5 g/L. These results have been compared with plant observations that confirm the lower rate of chlorine generation in the presence of manganese. The use of periodic current reversal does not increase the rate of oxidation of chloride ions in the presence of manganese ions. The rate of anodic oxidation of chloride in the presence of manganese ions is too low to be of practical value in controlling the chloride levels during the electrowinning of zinc. [ABSTRACT FROM AUTHOR]

Passivity breakdown and the pitting behavior of ultra-high strength 300 M and S280 steels, which are commonly employed for aircraft landing gear, in the presence of chloride has been explored and compared, and the data were interpreted using the point defect model (PDM). The breakdown behavior was studied using cyclic potentiodynamic polarization while SEM and digital confocal microscopy were employed to explore the micro morphology and depth distribution of pits. The cumulative distributions in the breakdown voltage are near-normal, which are consistent with the PDM, assuming the distributions of potential breakdown sites in terms of the cation vacancy diffusivity for different concentrations of chloride are normal. Compared to 300 M, S280 steel exhibits shallower pitting and is more resistant to breakdown. From the potential scan rate dependence of the breakdown potential, the critical areal cation vacancy concentration, ξ , resulting in passivity breakdown, is 8.6 × 10 13 No.cm −2 for 300 M and 2.4 × 10 13 No.cm −2 for S280. These values are structurally in close agreement with the calculated results, considering the vacancy condensation is either on the cation sublattice of the barrier layer or on the steels lattice. [ABSTRACT FROM AUTHOR]

The formation and nature of hydrogen bonding in the adsorption of chloride ions on activated carbon (AC) were investigated. The cause, nature and existence conditions for hydrogen bonding were analyzed by Fourier transform infrared spectroscopy (FTIR), chemical bond theory and chemical equilibrium measurements and calculations. The experimental results revealed the existence of COOH groups on the surface of the AC. There was a large π bond in the carboxyl groups, and the charge transferred from the O in the O H of the molecule to the C, resulting a in positively charged H. The hydrogen bonding occurred between the strong electropositive H atom and a strong electronegative Cl atom, and the bond energy was 34.87 kJ mol −1 K −1 . The stability of the hydrogen bond depended on the solution pH, pH values <4.0 were in the hydrogen bond forming region, and pH values >10.0 were in the hydrogen bond non-forming region. In the non-forming region, Van der Waals forces played an important role in the adsorption of chloride ions. The pH range from 4.0 to 10.0 was the transition region in which hydrogen bonding and Van der Waals forces were the two primary modes of attractions. Hydrogen bonding explained the change in the adsorption capacity of the chloride ion as the pH changed and the weak effect of SO 4 2− . [ABSTRACT FROM AUTHOR]

• Description of the sensing principles of chloride ingress monitoring by a radiofrequency dielectric probe. • Decoupling the influence of water and chloride ingress is possible with the proposed method. • Ability of the method to monitor diffusion of chloride in concrete at different depths. The origin of rebars corrosion in concrete infrastructures is frequently associated with the ingress of chloride ions present in water. This is particularly the case of infrastructures located in marine environments or exposed to deicing salts. The present study aims at developing a radio-frequency dielectric sensor dedicated to free chloride ingress monitoring in a well-defined volume of the material. A resonant method operating in a wide frequency range is selected to separate the effects associated with the variation of the real part of the dielectric permittivity and tangent loss. As it will be shown, the method provides useful information on the presence of free chloride in concrete and can be used for the monitoring of chloride diffusion. For this purpose, considering the variation of the transmission parameter S12 value presents clearly some advantages with respect to the frequency shifts of resonances. This allows to decouple water and chloride content. [ABSTRACT FROM AUTHOR]

Chloride ingress is considered as the most responsibility to steel corrosion for offshore concrete structure during service. Fly ash has been shown to effectively enhance the resistance of concrete to chloride penetration. Despite the numerous contributions of investigation regarding the chloride migration behavior of fly ash blended concrete composites by using rapid chloride migration (RCM) test, there is still a lack of critical understanding of curing age effect on the chloride migration in fly ash concrete under RCM testing system. The present study aims to investigate the effect of curing age on the resistance of fly ash blended concrete to chloride ion under RCM test, also considering the factors of water-to-binder ratio and fly ash content at the same time. Based on the RCM tested results, it is found that the effect of curing age condition on the chloride migration resistance is depended on the amount of fly ash incorporated in concrete. Short term curing age can lead to increase the chloride migration coefficient of concrete with low fly ash content. But resistance to the chloride migration can still be enhanced at this curing stage when high percentage of fly ash is supplied. Long term curing age can benefit the chloride migration resistance, regardless of how much fly ash is used in concrete. However, this positive effect becomes less significant when increasing the curing time at the late curing stage. The concrete microstructure is also explored to elucidate the macro-behavior of chloride migration. [ABSTRACT FROM AUTHOR]

The vertical profiles of chloride ion (Cl − ) concentration and oxygen and hydrogen isotopic ratios in pore fluids of basin-fill sediments in the southern Kumano Basin were examined. A model has been proposed to explain those profiles in conjunction with published data by invoking diffusion and advection of freshwater from methane hydrate dissolution. The model requires a low initial Cl − concentration in the old accretionary prism below the basin before the basin began to fill with sediments. It also requires little or no methane hydrate formation in the old accretionary prism. Given these requirements, an upward fluid advection rate of 1 × 10 −12 m/s has been estimated which is very low compared to other accretionary prisms. Our data suggests that the tectonic compaction of the basin-filling sediments and fault activity under the basin sediments have not been that active recently in the Kumano Basin. [ABSTRACT FROM AUTHOR]

In this paper the development of free Cl − content in various types of concrete was monitored by means of the embedded Ag/AgCl electrode. Moreover, the bound as well as total Cl − contents were determined through volumetric method. Besides, these mechanisms about the Cl − diffusion in different types of concrete are analyzed and discussed. Results revealed that real-time monitoring of free Cl − concentration in concrete was achieved based on the measurements of potentials of embedded electrodes and the diffusion law of free Cl − content followed Fick’s second law. In addition, the Freundlich isotherm was recommended to describe these relationships between free Cl − content and bound as well as total Cl − concentrations. As for the types of concrete with the addition of mineral admixture, lower total porosity and larger locked porosity have been found out. However, much more efforts should be paid to develop low-cost, robustness and long-term reliable Cl − selective sensors in order to achieve the wide application in concrete environment. [ABSTRACT FROM AUTHOR]

A rapid, robust, and routinely applicable HILIC based HPLC-UV assay was developed for the quantitative determination of the L -Lysine content of Atorvastatin lysine active substance. During the method validation it turned out that with UV detection at 200 nm, the method is also capable for the direct determination of chloride ions. To the best of our knowledge, the phenomenon of chloride determination by short wavelength UV detection had only been once highlighted earlier in the literature. A wide range of the potential applications are demonstrated as well as the validation of the method as a routinely usable assay for residual chloride determination is also given. • A rapid, robust HILIC-UV method for the determination of lysine and chloride content. • Validated assay for residual chloride determination in API salts. • Direct detectability of chloride ion by UV is a rarely highlighted phenomenon. [ABSTRACT FROM AUTHOR]

The growing worldwide demand for copper implies the need to process increased amounts of its ores. Chalcopyrite is the most abundant copper mineral, but due to its refractory nature it presents slow kinetics and low metal recovery when submitted to hydrometallurgical processes. Researchers have proposed the application of high temperatures and the use of reagents such as sodium chloride in order to overcome such refractoriness. Within hydrometallurgy, bioleaching has been suggested as an economic and environmental alternative to traditional chemical processes. However, most acidophilic microorganisms used in bioleaching cannot tolerate high chloride concentrations - similar to those found in seawater. Therefore, this review aims to present the main aspects of these systems, as the application of chloride in bioleaching is still a challenge. Nevertheless, if this problem is overcome, chloride bioleaching can become an alternative to process low grade chalcopyrite- bearing ores and tailings, particularly when saline waters are used in bioleaching processes to reduce the demand for fresh water. • Bioleaching with chloride is an alternative to overcome chalcopyrite passivation. • Chloride ions may be toxic for some acidophilic microorganisms. • Saline waters could be used in bioleaching to reduce the demand for fresh water. [ABSTRACT FROM AUTHOR]

• The chloride content in RCP mortar is evaluated at different immersion time. • The relationship between macro performance and microstructural characteristics of NS enhanced RCP mortar is established. • The effect of NS on the chloride corrosion resistance of RCP mortar is investigated. • An optimal NS dosage of 2% reflected by the greatest chloride corrosion resistance is obtained. 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. [ABSTRACT FROM AUTHOR]

• Raman mapping was employed to investigate the carbonation depth in a microscale. • The redistribution of the chloride due to carbonation was detected, and a chloride accumulation zone was found before the carbonation front, which directly caused the corrosion. • The corrosion mechanism of reinforcing steel in cement paste containing chloride under a CO 2 diffusion scenario was discussed and demonstrated in a schematic. Desalinated sea sand concrete (DSSC) is increasingly used to mitigate the shortage of natural river sand. However, one major concern lies in the corrosion risks of steel reinforcement embedded in DSSC under combined chloride and carbon dioxide attacks. To understand the corrosion mechanism, the corrosion process of steel reinforcement embedded in the cement paste containing chloride ions (Cl−) was monitored by electrochemical measurements, during which pH, Cl− profile and corrosion products were examined simultaneously. Raman spectroscopy was employed to evaluate the carbonation depth in microscale. Tests results showed that corrosion was initiated before the carbonation front reached the steel reinforcement. Interestingly, it was the carbonation-induced Cl− redistribution rather than the decrease of pH that dominated the corrosion initiation. Before the carbonation front, a Cl− accumulation zone was identified, and the corrosion mechanism was revealed. This study shall advance the understanding of the corrosion of steel reinforcement in DSSC for durability design of reinforced concrete structures. [ABSTRACT FROM AUTHOR]

• Cl- in the NaCl/Na 2 SO 4 blended solution can inhibit SO 4 2- transport into cement-based materials. • The formation of Friedel's salt consumes the calcium aluminate hydrate, which can indirectly influence the production of ettringite. • Stray current can break the chemical equilibrium of ion concentration in pore solution, which resulted in the decomposition of ettringite and Friedel's salt. • Friedel's salt can transform into ettringite at a specific condition. • The amounts of ettringite and Friedel's salt in specimens were significantly changed over the exposure time under the effect of stray current. When infrastructure is exposed to a complicated environment containing stray current, chloride and sulfate, it may be subjected to severe degradation. In order to analyze the interaction of different factors and the degradation mechanism of cement-based materials in a complicated environment, the blended solution with four molar concentration ratios of Cl-/SO 4 2- (0, 0.5, 1, and 2) were prepared to simulate a range of aggressive medium. Meanwhile, 40 V DC (direct current) electrical field was applied to cement-based materials to simulate stray current. After exposure, the transport properties, macro-properties, and microstructures of specimens were observed and measured. Additionally, the types and amounts of degradation products were tested to further analyze the degradation mechanism of cement-based materials. Experimental results show that chloride in the blended solution could inhibit SO 4 2- transport into cement-based materials, causing the SO 4 2- concentration in a specimen to decrease with the increase of Cl-/SO 4 2- ratio. Therefore, the specimens appeared less degraded in terms of macro-properties. But the results of microstructural analysis showed that degradation products and cracks were generated in the interior of specimens. Friedel's salt was detected in the specimens exposed to the solutions containing chloride. The formation of Friedel's salt consumed calcium aluminate hydrate, which caused the amount of Al-phase involved in the formation of ettringite to reduce. Consequently, the amount of ettringite was reduced, and the degradation of compressive strength and appearance was also reduced. Additionally, an electrical field could induce the ion concentration in pore solution to change and even break the ion chemical equilibrium, which resulted in the decomposition of ettringite and Friedel's salt. However, Friedel's salt can also transform into ettringite at a specific condition. Therefore, the amounts of ettringite and Friedel's salt in specimens were changed over the exposure time. [ABSTRACT FROM AUTHOR]

Corrosion of steel bars by chloride ions is one of the main reasons for determining the service life of marine concrete. In this work, the effects of calcium to silicon (C/S) ratio and SO 4 2− concentration on Cl− adsorption in calcium silicate hydrate (C–S–H) gels were systematically studied by molecular dynamics simulations. Atomic-scale results show that higher C/S ratio induces more Cl− adsorption. The presence of SO 4 2− not only reduces the Cl− adsorption but also buffers the adsorption caused by increasing C/S ratio. The Cl− adsorption is caused by the attraction of interlayer Ca (Cah) and hydroxyl groups in low C/S gel, while in high C/S ratio C–S–H gel is mainly contributed by Cah. More Cl− adsorption at the C–S–H interface ensures less Cl− accumulation in zones surrounding the reinforcement. The insights into ion adsorption behaviour should provide useful information for prolonging the durability of marine concrete by designing appropriate compositions. [Display omitted] • The effects of C/S ratio and SO 4 2− on Cl− adsorption in CSH gel were revealed by MD. • The higher the C/S ratio, the more Cl− adsorption at the CSH gel interface. • The adsorption of SO 4 2− is attracted by Na+, reducing adsorption of Cl− in CSH. [ABSTRACT FROM AUTHOR]

Friedel's salt is an AFm phase playing a major role in immobilizing chloride ions in cement-based materials. This phase exhibits a displacive phase transition between 30 and 40 °C. Data on the physical properties of Friedel's salt and their temperature dependence is lacking in the literature. Here, we perform molecular simulations to compute Friedel's salt's elastic constants, heat capacity, and thermal expansion. AFFF, a force field focusing on AF-phases in cement systems, is extended to account for phases with chloride. We capture the temperature transition with the simulations, provide the thermoelastic properties as a function of the temperature, and assess the dynamics of water and chloride in Friedel's salt. Such information can be readily used in multiscale modeling requiring data on Friedel's salt thermoelastic properties. • Thermoelastic properties of Friedel's salt are provided. • Property temperature-dependence is quantified. • Quantum corrections are needed to get Friedel's salt heat capacity. • Dynamics of water and chloride in Friedel's salt are quantified. [ABSTRACT FROM AUTHOR]

This investigation focuses on sodium biphosphate (Na 2 HPO 4 ) as corrosion inhibitor for construction steel. All the tests are carried out in a solution that simulates the composition of the pores in chloride-contaminated carbonated concrete. The carbonated solution (CS) contained Na 2 CO 3 (0.0015 mol L −1 ), NaHCO 3 (0.03 mol L −1 ) and NaCl (0.1 mol L −1 ), resulting in [Cl − ]/[OH − ]=10000. Inhibited solutions (IS20, IS60 and IS100) incorporated 20, 60, and 100 mmol L −1 Na 2 HPO 4 respectively. These were labeled IS20, IS60 and IS100 respectively and result in [HPO 4 2− ]/[Cl − ] = 0.2, 0.6, and 1. Cyclic voltammograms and anodic polarization curves were complemented with micro-Raman spectroscopy and XPS, to evaluate the surface film composition. The results show that chloride contamination promotes active corrosion. When phosphate ions are incorporated, steel becomes passive with a more positive corrosion potential (Ecorr), and pitting presents as the predominant form of localized corrosion. Raman spectra show a broad band, centred in 982 cm −1 , suggesting that phosphates incorporate to the passive film. Phosphates are also present in the corrosion products. The surface film becomes more protective to pitting for the highest biphosphate content. However, after pitting no repassivation was detected. After over one month in immersion, steel remains passive in the condition IS100, with inhibition efficiency higher than 99%. In contrast, in the case of IS60 and IS20, pitting was detected. It can be concluded that phosphate ions are good candidates to be used as corrosion inhibitors for steel in chloride-contaminated concrete. [ABSTRACT FROM AUTHOR]

The present work focuses on the corrosion behaviour of scratched epoxy coated carbon steel in simulated pore solution (SPS) containing varying % of chloride ions (added as NaCl) by localized electrochemical impedance spectroscopy (LEIS). LEIS results indicate that the |Z| at the scratch is decreased significantly with an increase in % of Cl − ions in SPS, which is evidenced by the formation of a depressed semicircle in the LEIS Nyquist plots. The intermediate corrosion products involved in the local corrosion process appears to be a function of the % of Cl − ions present in SPS. The competition between the aggressive Cl − ions and the inhibitive OH − ions and the extent of decrease in pH at interface determines the rate of corrosion. The LEIS maps acquired at 10 Hz provides a better understanding of the involvement of the anodic and cathodic areas on the local corrosion process of scratched epoxy coated carbon steel. The continuous decrease in |Z| at the scratch is due to the higher extent of dissolution of Fe at the scratch while the change in |Z| over the coating is determined by the extent of dissolution of Fe and accumulation of corrosion products over the coating due to the high bulk pH of SPS. No significant decrease in |Z| at the scratch is observed when the % of Cl − ions in SPS is 0.05. However, when the % of Cl − ions in SPS is increased beyond 0.05%, a significant increase in the corrosion rate of scratched epoxy coated carbon steel is observed. Hence, 0.05% NaCl can be considered as a threshold level of chloride ions in SPS. A pictorial model is proposed to explain the local corrosion process and mechanism of scratched epoxy coated carbon steel in chloride containing SPS. [ABSTRACT FROM AUTHOR]

0.3 wt % ammonium fluoride (NH 4 F) or ammonium chloride (NH 4 Cl) was added to ethylene glycol (EG) as an active ingredient for the formation of anodic oxide comprising of ZrO 2 nanotubes (ZNTs) by anodic oxidation of zirconium (Zr) at 20 V for 10 min. It was observed that nanotubes were successfully grown in EG/NH 4 F/H 2 O with aspect ratio of 144.3. Shorter tubes were formed in EG/NH 4 F/H 2 O 2 . This could be due to higher excessive chemical etching at the tip of the tubes. When fluoride was replaced by chloride in both electrolytes, multilayered oxide resembling pyramids was observed. The pyramids have width at the bottom of 3-4 μm and the top is 1-2 μm with 10.7 μm height. Oxidation of Zr in EG/NH 4 Cl/H 2 O 2 was rater rapid. The multilayered structure is thought to have formed due to the re-deposition of ZrO 2 or hydrated ZrO 2 on the foil inside pores formed within the oxide layer. XRD result revealed an amorphous structure for as-anodized samples regardless of the electrolytes used for this work. [ABSTRACT FROM AUTHOR]