External Chloride Ions Research Articles

Development of Environmental Monitoring Sensor for Steel Corrosion in Concrete based on Micro-Electro-Mechanical Systems (MEMS)

Many bridges located near marine environments usually have high risk to lose their structural performance due to corrosion of reinforcing bars with chloride attack. While a huge amount of budget to maintain may be consumed for the structural maintenance methodologies, an efficient monitoring system for Reinforced Concrete (RC) structures in the corrosive environment is strongly demanded. Thus, structural health monitoring in real situations is significant for bridge asset management. The alternative way for preventing severe damage propagation is proactively monitoring the environmental condition containing chloride ion and its effect on the durability of concrete structures, for which numerous methods have been conventionally suggested such as dry gauze method to capture chlorides in air. In this study, Micro Energy Harvester (MEH) based on Micro-Electro-Mechanical Systems (MEMS) is technically applied to develop a sensor to identify the corrosion environment with chlorides in the exposure condition. MEMS is a rapidly evolving device, which enables to monitor the changes in natural frequency and amplitude at nodal locations of the targeting structure due to vibration-based electrostatic power generation induced by the corrosive environment. The purpose of this research is to develop a system for detecting the high corrosion-prone areas and finding the suitable metal sheet material for various chloride ion conditions, using the metal sheet as a cantilever structure for the MEMS device. 4 types of metal, aluminium, copper, iron and zinc are considered for the parametric experiments. Several scenarios are considered including chloride ion concentration, temperatures, and wet and dry conditions to compare the dominant frequency changes of each metal sheet and determine their sensitivity to corrosion environment. From the preliminary results, iron and zinc have a significant drop in frequency with the elapsed exposure period, which indicates that they are highly sensitive to the external chloride ion environment. These results offer an innovative and proactive approach to structural health monitoring for further developed applications. It enables prompt maintenance and early detection of potential issues for corrosion of steel bars in concrete, ensuring the longevity and safety of RC bridge structures.

Chloride penetration resistance and chloride binding capacity under different application environments of ferroaluminate cement

Free chloride is a crucial factor that threatens the long-term performance of marine concrete structures. The resistance of cement to chloride penetration and its capacity to bind chloride are important parameters for assessing the ability of cement-based materials to resist chloride invasion. Ferroaluminate cement (FAC) has considerable application potential in concrete used for marine structures; however, its resistance to chloride invasion and mechanism of chloride binding have not yet been revealed. In this study, the chloride diffusion coefficient and chloride binding capacity of FAC, for both internal and external chloride ions, are experimentally investigated and compared with that of ordinary Portland cement (OPC). The results show that the chloride diffusion coefficient of FAC mortar is approximately 2.5 times lower than that of OPC mortar. FAC exhibits finer overall pore distribution and the number of pores with sizes within 10–100 nm is reduced, which is responsible for its notably lower chloride diffusion coefficient. The chloride binding capacity of FAC to internal chloride ions is slightly lower than that of OPC, and a portion of the chloride ions are chemically bound by reacting with ye'elimite during hydration. The chlorides bound by physical adsorption constitute a dominant portion of the entire bound chloride content. In the case of external chloride ions, the bound chloride content of FAC is lower than that of OPC. The chemical chloride binding capacity of FAC is comparable to that of OPC and the lower physical adsorption capacity for chloride in FAC leads to a weaker chloride binding capacity compared to that of OPC.

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

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

Investigation on the chloride ion erosion mechanism of cement mortar in coastal areas: From experiments to molecular dynamics simulation

• The influences of chloride ions on the phsysical and mechanical properties of cement mortar were analyzed. • The mechanism of bound and free chloride ions on the cement mortars properties were investigated in long-term erosion. • The effect of chloride ions in pores on C S H adsorption was investigated by molecular dynamics simulation. Chloride salts in groundwater are a serious threat to the durability of underground reinforced concrete structures in coastal areas. In order to effectively improve the durability performance of underground structural concrete in coastal areas, physical and mechanical properties such as compressive strength, water absorption rate and chloride ion permeability of cement mortar were studied. The influence laws of mineral additives such as fly ash, ground granulated blast-furnace slag and chloride ions on the relevant properties of cement mortar were analyzed. The effect of chloride ions on these physical and mechanical properties was investigated. The main hydration product categories of cement mortar were derived using microscopic analysis (XRD). The internal microstructure and the surface morphology of cement mortar were obtained by scanning electron microscopy (SEM). The effect of chloride ions in pores on C S H adsorption was studied by using molecular dynamics simulations. The results showed that chloride ion erosion increased the compressive strength of cement mortars doped with FA and GGBS at 28, 100, and 180 days by 2.76 %, 14.32 %, and 7.83 %, respectively. Chloride ion erosion moderately increased the compressive strength of cement mortar doped with FA and GGBS at all curing period. After chloride ion erosion, the electric fluxes of the four groups of specimens at 180 days decreased by 30.37 %, 31.64 %, 23.22 % and 17.41 %, respectively. After the addition of mineral additive, the bound chloride ions changed the influence law of water absorption rate of cement mortar, and reduced the electric flux of cement mortar. The molecular dynamics simulations revealed that the chloride ions in the pores weakened the physical adsorption of external chloride ions by C S H, resulting in the easier passage of external chloride ions through the pores. Microscopic analysis showed that the Friedel's salt generated by chloride ions attacking the cement-based materials filled communicating pores, which may be one of the reasons for the reduced electric flux of the cement mortar.

Evaluation of the Surface Performance of Mortar Matrix Subjected to Sodium Chloride Solution Modified with Hybrid Nanosilica Cement Paste

In order to prolong the service life of cement-based materials subjected to external chloride ion attacks, two kinds of methods, a surface treatment and chloride immobilization, were combined by fabricating a nanosilica-modified cement paste and coating it on mortar samples as a surface treatment material (HSM). The protective effect of the HSM was evaluated according to its surface hardness, and an RCM test was carried out, which indicated that the attached layer could both increase the surface hardness and decrease the chloride diffusion coefficient. Then, the chloride immobilization mechanisms were illustrated in terms of chloride blocking resistance, chemical binding and physical binding X-ray diffraction (XRD), and thermogravimetric/derivative thermogravimetric (TG/DTG) and thermodynamic modeling. The results showed that the hybrid nanomaterials that modified the cementitious surface treatment materials may effectively improve the chloride-resistant property of a matrix with content of no more than 1%. This research outcome could provide evidence that hybrid nanosilica can be applied in surface treatment technology.

Study of anti-chlorine corrosion of anion exchange resin based superhydrophobic cement mortar in chloride salt environment

Anti-corrosion of reinforced concrete structures in the chloride salt environment is an important issue. Especially the corrosion damage of reinforced concrete by chloride ions seriously affects the safety of concrete structures and quality of the material’s appearance. In this paper, the chlorine corrosion resistance of superhydrophobic anion exchange resin cement mortar in a chloride environment was investigated. The chlorine corrosion resistance of different samples was compared by electrochemical experiments and chloride distribution test. The results show that the as-fabricated mortar has better corrosion resistance to chloride salt attack than the reference sample at a 98.60% increase in corrosion resistance rate. AgNO3 color development experiment and free chloride ion concentration measurements show that the as-fabricated mortar can not only adsorb chloride ions inside the mortar, but also effectively inhibit the penetration of external chloride ions. This internally and externally coordinated anti-corrosion cement mortar is expected to extend the service life of reinforced concrete in chloride salt environments.

Numerical simulation of electrochemical mechanism of steel rebar corrosion in concrete under natural climate with time-varying temperature and humidity

In order to analyze and predict the corrosion ratio and rust layer distribution of steel rebar embedded in reinforced concrete under time-varying climatic conditions, a self-balancing steel corrosion model was established by connecting the environmental temperature, humidity, external chloride ions and oxygen concentration to the potential distribution and current density of the steel using finite element method. The model covered the whole corrosion process of steel rebar in concrete under natural climate, including the steel rebar depassivation, steel corrosion propagation and the rust layer expansion on the surface of steel rebar. In the proposed model, the microcell and macrocell corrosion were coupled by electrochemical polarization, and the cathode-to-anode area ratio was determined by the time-varying chloride distribution at the rebar surface. Taking the diffusion of chloride ions and oxygen in concrete into account, the distribution of corrosion potential of reinforcement, the change of corrosion current density of reinforcement, and the distribution of rust layer on the surface of reinforcement can be obtained based on the variation of natural temperature and humidity. The proposed model was validated utilizing the experimental data from the literatures. On this basis, a discussion about the influence of long-term climatic environments on the corrosion kinetics were conducted. The results suggest that environmental temperature and relative humidity affect the steel corrosion process mainly by affactting the chloride and oxygen diffusion coefficients, concrete resistivity, and concentration of dissolved oxygen in concrete pore solution. The corrosion current density of steel in concrete is sensitively influenced by the environmental temperature more than relative humidity. Although the initial exposure time has a significant impact on the accumulation process of chloride on steel surface within one climatic cycle, it has little influence on the final chloride distribution at the end of the period. However, the initial exposure time remarkably influences the evolution profile of rust layer thickness during the climatic cycle. The steel rebar initially exposed to a higher temperature suffers from more severe corrosion than that initially exposed to a lower temperature.

Electrochemical chloride extraction on reinforced concrete contaminated external chloride: Efficiencies of intermittent applications and impacts on hydration products

This paper aims to assess the efficiency of electrochemical chloride extraction (ECE) using the intermittent application and its impacts on cement hydration products in concrete contaminated external chloride ions. Continuous application (Mode 1) and two modes of intermittent application (Mode 2 and Mode 3) were conducted for 10 weeks. The results indicated that while the final efficiencies of chloride extraction on three modes were approximate, the charge efficiency, which is the content of chloride removed per one unit charge applied, was much greater on samples using Mode 2 and Mode 3 than that in Mode 1. Portlandite content in concrete at the electrodes increased after the treatment. The decomposition of C-S-H was proportional to the cumulative applied charge number. By using a much less applied charge number, Mode 2 and Mode 3 caused less decomposition of C-S-H in concrete than that in Mode 1. The accumulation of NaOH in concrete near the steel reinforcement was observed. Intermittent applications can apparently alleviate the adverse impacts of ECE treatment on C-S-H. Furthermore, the total cumulative charge number employed should not exceed 800–900 A h/m2.

The effects of aging in seawater and SWSSC and strain rate on the tensile performance of GFRP/BFRP composites: A critical review

• The tensile properties of GFRP/BFRP after exposure in sea water/SWSSC are discussed. • The degradation degree increases with the exposure time, temperature and alkalinity. • The impact strength and fatigue life are reduced due to the exposure in seawater. • The dynamic performance and failure mode are obviously influenced by strain rate. • The future research needs are proposed for the FRP used in seawater/SWSSC. Replacing metallic materials (typically carbon steel bars) with fiber reinforced polymer (FRP) composites to reinforce marine concrete structures can effectively resolve the corrosion issue of carbon steel due to external chloride ions and moisture. However, the corrosion-free nature of FRP material cannot guarantee its desirable durability in the marine structures. In order to better understand the durability performance of FRP composites, this paper summarizes the quasi-static tensile properties of FRP composites after exposure in simulated seawater and seawater sea sand concrete (SWSSC) environments, and the dynamic performance of the FRP materials. It is found the degradation degree of FRP composites increases with the exposure time, temperature, stress level and alkalinity/salinity of the immersion solution. Currently, the investigations on the dynamic tensile properties of FRP composites after long-term exposure tests are quite limited. Hence this study identifies the possible research needs by summarizing the investigations on the degradation of FRP’s dynamic performance after seawater exposure and the strain rate sensitivity of glass/basalt fiber reinforced polymer (GFRP/BFRP) composites under dynamic loading. The impact strength, Young’s modulus and fatigue life will all be diminished due to exposure in seawater. And both the mechanical performance and failure mode of the FRP composites are obviously influenced by the applied strain rate. This study identifies the current knowledge gap and can serve as a valuable reference for further investigation on the long-term performance, especially the long-term dynamic tensile properties of FRP composites in seawater and SWSSC environments.

Key inhibitory mechanism of external chloride ions on concrete sulfate attack

To explore the key inhibitory mechanism of external chloride ions on concrete sulfate attack, long-term partial- and full-immersion experiments of concrete in chloride solutions and chloride and sulfate composite solutions were performed. As corrosion time begins, visual inspection, compressive strength, and ultrasonic velocity were periodically observed or tested. Moreover, the micro-morphology, the contents of Cl and S elements in concrete, and the transport speeds of Cl− and SO42− ions through concrete were investigated by using scanning electron microscope, X-ray fluorescence spectrum, and chemical analysis. Chloride ions neither have corrosive effects on concrete nor effects on concrete physical and mechanical properties, which is the prerequisite for chloride ions in inhibiting concrete sulfate attack. In the case of combined solutions, the transport speed of Cl− ions into concrete is evidently higher than that of SO42− ions. Then, chloride ions enter concrete early and form Friedel's salt with AFm or with C3A and Ca(OH)2 in concrete, which inhibits the transport of SO42− ions into concrete and reduces the formation of expansive corrosion products of ettringite or gypsum. Thus, the sulfate attack on plain concrete is alleviated. Based on the inhibitory mechanism of Cl− ions on concrete sulfate attack, the presence of Cl− ions cannot completely avoid concrete sulfate attack but can partially reduce sulfate risk on concrete.

Key role of external chloride ions in regulation of fast sodium channels in rat cerebellum Purkinje neurons.

A decrease in the external chloride ion concentration to 4 mM caused a decrease in the fast sodium current to 85-100% in rat cerebellum Purkinje neurons in the whole-cell configuration using the patchclamp method. This effect did not depend on the main cation from the internal side of the cell membrane (120 mM of potassium or cesium) and also appeared when Cl- was substituted with sulfate (SO2-4) or phosphate (H2PO4-) anion outside of the cell. The effect was reversible after washing out the low chloride by the standard saline.

Both degradation and AOX accumulation are significantly enhanced in UV/peroxymonosulfate/4-chlorophenol/Cl− system: two sides of the same coin?

External chloride ion may lead to AOX accumulation in UV/PMS process, although 4-CP degradation was accelerated.

Calcium-dependent chloride current in rat cerebellar Purkinje cell membranes

The presence of calcium-dependent potential-activated chloride currents in the membranes of freshly isolated rat cerebellar Purkinje cells (12-15 days) was shown by the whole-cell patch clamp technique. Chloride currents appeared in a sodium-free external solution and reversibly disappeared in the absence of external chloride and calcium ions.

An Efficient Environmentally-Friendly Materials for Concrete Building Protection

The concrete building protection materials is widely in the hydraulic and bridge engineering. In the external environment, water, chloride ion, deicing salt and freeze-thaw cycle is the greatest enemy of the concrete builidng , leading to concrete corrosion damage. we found that silane materials is an efficient materials for building protection ，water absorption rate of silicone protected specimens is no more than 0.004 mm/min0.5and the chloride diffusion coefficient was clearly reduced. The silane can penetrate into a few centimeters below the surface of the concrete structure to provide long-term protection. So the silane materials is considered the most suitable for concrete protection.

Iontophoretic Transdermal Delivery of Glycyrrhizin: Effects of pH, Drug Concentration, Co-ions, Current Intensity, and Chemical Enhancers

The aim of the present study was to evaluate the feasibility of transdermal delivery of glycyrrhizin, an agent used in the treatment of chronic hepatitis C, by cathodal iontophoresis using Ag/AgCl electrodes in vitro. The effects of donor pH (pH 4-7), concentration of drug (0.025-0.2% (w/v)), concentration of external chloride ions (Cl(-)) (0-133 mM), current strength (0-0.5 mA/cm(2)), and permeation enhancers (urea and Tween 80) on the skin permeability of glycyrrhizin were examined in in vitro skin permeation studies using porcine ear skin as the membrane. The cumulative amount of permeated glycyrrhizin and the steady-state skin permeation flux of glycyrrhizin across porcine skin increased in a pH-dependent manner. The skin permeability of glycyrrhizin was independent of the concentration of drug and competed only with a high external Cl(-) concentration. The skin permeation flux of glycyrrhizin increased with the current (R(2)=0.8955). The combination of iontophoresis and enhancers provided an additive or synergistic effect, and a skin permeation flux of about 60 µg/h/cm(2) was achieved. The plasma concentration of glycyrrhizin in humans, extrapolated from the in vitro steady-state permeation flux across porcine skin, was within the therapeutic level. These results suggest that cathodal iontophoresis can be used as a transdermal drug delivery system for glycyrrhizin using reasonable patch sizes and acceptable levels of current intensity.

Synthesis and Hydrolysis of a cis-Chlorohydrin Derived from a Benzo[a]pyrene 7,8-Diol 9,10-Epoxide

(+/-)-7beta,8alpha-Dihydroxy-9beta,10beta-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (DE-1) undergoes reaction with anhydrous HCl in dioxane to yield predominantly ( approximately 94%) a single chlorohydrin. This chlorohydrin was assigned structure 9, in which the chloro goup at C-10 is located cis to the C-9 hydroxyl group, on the basis of its (1)H NMR spectrum. This result is in contrast to the reaction of a diastereomeric benzo[a]pyrene 7,8-diol 9,10-epoxide (DE-2) with HCl, which yields only trans-chlorohydrin 8. The hydrolysis of cis-chlorohydrin 9 in 10:90 dioxane-water solutions yields the same ratio of tetrols ( approximately 89% cis/11% trans) as that formed by acid-catalyzed hydrolysis of DE-1. This result again contrasts with the hydrolysis of trans-chlorohydrin 8, which undergoes hydrolysis to give tetrols in a ratio different from that from acid-catalyzed hydrolysis of DE-2. A marked common ion rate depression in the hydrolysis of cis-chlorohydrin 9 is observed, which shows that hydrolysis proceeds via an intermediate carbocation that has a sufficient lifetime to be trapped by external chloride ion. The observation that DE-1 reacts with HCl to give mainly the cis-chlorohydrin is rationalized by quantum chemical calculations that suggest that the cis-chlorohydrin is more stable than the epimeric trans-chlorohydrin.

Anomalous effect of anthracene-9-carboxylic acid on calcium-activated chloride currents in rabbit pulmonary artery smooth muscle cells.

1 Ca(2+)-activated Cl(-) currents (I(Cl(Ca))) evoked by K(+)-free pipette solutions containing 500 nM Ca(2+) were recorded in rabbit pulmonary artery smooth muscle cells. A voltage step protocol in which the cells were stepped to +70 mV and then to -80 mV produced outward and inward Cl(-) currents respectively that exhibited distinctive voltage- and time-dependent kinetics that remained consistent for the recording period. 2 Application of the Cl(-) channel inhibitor anthracene-9-carboxylic acid (A-9-C, 500 micro M), produced a small inhibition of the maximum outward Cl(-) current at +70 mV (21+/-10%) but augmented the amplitude of the instantaneous inward relaxation at -80 mV by 321+/-34% (n=12). 3 The current recorded in the absence and presence of A-9-C reversed at the theoretical Cl(-) equilibrium potential and the reversal potential was shifted by about -40 mV upon replacement of external chloride ion by the more permeant anion thiocyanate. Currents in the absence and presence of A-9-C were similarly affected by 100 micro M niflumic acid. 4 Augmentation of the inward current at -80 mV by A-9-C required prior depolarization, i.e. A-9-C did not simply activate a Cl(-) current at negative membrane potentials. Moreover the degree of augmentation was independent of the internal Ca(2+) for concentrations between 100 nM and 1 micro M Ca(2+). 5 The data from the present study confirm previous observations that the inhibitory effect of Cl(-) channel blockers is modified when [Ca(2+)](i) is maintained at higher than normal resting concentrations.

Diffusion of a mixture of cations and anions dissolved in water

In service life modeling of concrete, the ion transport in the pore solution is crucial. The main deterioration phenomena associated with ions in the pore solution are (1) corrosion due to external chloride ions reaching the embedded reinforcement bars; (2) carbonation due to presence of dissolved carbon dioxide (which will form carbonic acid with water) supplied from the surrounding air; and (3) leaching of hydroxide ions from the pore solution to the surrounding environment. Models dealing with diffusion of ions are usually based on the mass balance equations for the individual diffusing ions together with constitutive relations for the mass density flows and for the mass exchange among the constituents. The important consequences of electroneutrality among the diffusing ions, however, is often omitted in models dealing with diffusion of ions in the pore solution of concrete. Here a method will be examined that allows diffusion of different ions in water, which satisfies both the electroneutrality requirement and the mass balance laws. For simplicity the effect of built-up electric double layers on the charged pore walls will not be treated.

Modulation of a calcium-activated chloride current by Maitotoxin

The effect of Maitotoxin (MTX) on the calcium-activated chloride current (ICl-Ca) from Xenopus oocytes was studied, applying the two-electrode voltage clamp technique. MTX increased the current amplitude at all the voltages explored and reduced the time to reach the maximum current level (time to peak). At low toxin concentrations (15 pM), both effects were fully reversible. Activation of ICl-Ca by MTX was secondary to the increment in the intracellular Ca 2+ concentration induced by this toxin, since incubation of the oocytes with the cell-permeant Ca 2+ chelator BAPTA-AM, greatly reduced the effect of MTX on ICl-Ca. Furthermore, external chloride ions removal also diminished the MTX effect on the current, strongly suggesting that the main current activated by MTX is ICl-Ca. Subsequent applications of a fixed toxin concentration after toxin washout resulted in enhanced ICl-Ca, suggesting that the toxin effect potentiates.

Retinal glial cell glutamate transporter is coupled to an anionic conductance.

Application of L-glutamate to retinal glial (Müller) cells results in an inwardly rectifying current due to the net influx of one positive charge per molecule of glutamate transported into the cell. However, at positive potentials an outward current can be elicited by glutamate. This outward current is eliminated by removal of external chloride ions. Substitution of external chloride with the anions thiocyanate, perchlorate, nitrate, and iodide, which are known to be more permeant at other chloride channels, results in a considerably larger glutamate-elicited outward current at positive potentials. The large outward current in external nitrate has the same ionic dependence, apparent affinity for L-glutamate, and pharmacology as the glutamate transporter previously reported to exist in these cells. Varying the concentration of external nitrate shifts the reversal potential in a manner consistent with a conductance permeable to nitrate. Together, these results suggest that the glutamate transporter in retinal glial cells is associated with an anionic conductance. This anionic conductance may be important for preventing a reduction in the rate of transport due the depolarization that would otherwise occur as a result of electrogenic glutamate uptake.