Bound Chloride Ions Research Articles

Influence of surfactants on chloride binding in cement paste

The influence of surfactants on chloride binding in cement paste has been investigated in this paper. Three surfactants, such as TEA-Lauryl sulfate (TEALS), sodium dodecyl benzene sulfonate (SDBS) and dodecyl polyglucoside (DPG) were used to represent as cationic, anionic and nonionic surfactants, respectively. The chloride binding was determined using the equilibrium method proposed by Tang Luping. X-ray powder diffractometer (XRD) was applied to characterize the phase structures of as-obtained paste specimens. It has been found that TEA-Lauryl sulfate (TEALS) increases the chloride binding, but sodium dodecyl benzene sulfonate (SDBS) and dodecyl polyglucoside (DPG) reduce the chloride binding. All the surfactants mainly affect the physical absorption of chloride ions, and exert a minor influence on the chemical binding of chloride ions. Freundlich isotherm can better describe the relationship between the amounts of bound chloride ions in cements with various surfactants and free chloride concentration than Langmuir isotherm. Besides, the later addition of surfactant has an effect on the chloride binding similar to the former addition of surfactant.

Carbonation of concrete made with dredged marine sand and its effect on chloride binding

River sand (RS) has been overly exploited to meet demand in the construction industry, particularly in China. Chloride salt in dredged marine sand (DMS) is the primary concern that limits the use of DMS in reinforced-concrete (RC) structures. This paper developed an interaction model between the carbonation behaviour and chloride ions in DMS concrete compared with RS concrete. In this research, the test results indicated that the chloride ions introduced by DMS can reduce 20–50% carbonation of the DMS concretes. A higher carbonation resistance can reduce the possibility of steel bar corrosion in the concrete. The process of concrete carbonation can alter the state of chloride ions in the concrete and their concentrations. During the carbonation process, the bound chloride ions would become free, and their concentration in carbonated concrete could increase by up to 200% compared to that of uncarbonated concrete when the chloride ion concentration was less than 3% by cement mass. Therefore, the effect of carbonation on chloride ions must be considered with respect to the durability when DMS concrete is designed for use in RC structures.

Influence of elevated temperature on release of bound chlorides from chloride-admixed plain and blended cement pastes

This paper is aimed to evaluate the influence of elevated temperature on the release of bound chloride ions from pastes made of ordinary Portland cement alone and a mixture of ordinary Portland cement and the partial replacements of cement with 10% silica fume (SF) and 50% ground granulated blast furnace slag (GGBS). Three ratios of water to binder (W/B) and four levels of total chloride ions were applied. The contents of free chloride ions and pH values in the pastes at different temperatures (0°C, 20°C, 40°C and 60°C) were determined by the measurements in the suspensions with 1:10 mass ratio of triturated paste powders to water. The results indicate that the increase of temperature can release partially the bound chloride ions. The amount of released chloride ion is dependent on the W/B ratio, content of total chloride ions and temperature range. Besides, the released chloride ions for the partial replacements of cement with 10% SF and 50% GGBS exhibits different trends with the temperature range. Furthermore, the influences of 10% SF and 50% GGBS on the corrosion risk of reinforcing steel at different temperatures are discussed by means of the index of Cl−/OH−.

Friedel's salt formation in sulfoaluminate cements: A combined XRD and 27Al MAS NMR study

Four different binders based on calcium sulfoaluminate cements have been submitted to accelerated chlorination through ionic exchange on hydrated pastes, in order to investigate their ability to chemically bind chloride ions that might reduce chloride penetration. The composition of hydrated cements before and after the treatment was evaluated by means of an X-Ray Diffraction–27Al Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopy combined study, allowing to take into account even partially amorphous phases and to make quantitative assumption on the relative abundance of the different aluminium-containing phases. It was found that low SO3 Sulfoaluminate–Portland ternary systems are the most effective in binding chloride ions and the active role played by different members of the AFm family in chloride uptake was confirmed. Moreover, a peculiar behavior related to the formation of Friedel's salt in different pH conditions was also established for the different cements.

Chloride binding isotherms of various cements basing on binding capacity of hydrates

This study investigated the chloride binding isotherms of various cement types, especially the contributions of C-S-H and AFm hydrates to the chloride binding isotherms were determined. Ordinary Portland cement (OPC), Modified cement (MC), Rapid-hardening Portland cement (RHC) and Low-heat Portland cement (LHC) were used. The total chloride contents and free chloride contents were analyzed by ASTM. The contents of C-S-H, AFm hydrates and Friedel's salt were determined by X-ray diffraction Rietveld (XRD Rietveld) analysis. The results showed that OPC had the highest chloride binding capacity, and, LHC had the lowest binding capacity of chloride ions. MC and RHC had very similar capacities to bind chloride ions. Experimental equations which distinguish the chemically bound chloride and physically bound chloride were formulated to determine amounts of the bound chloride basing on chloride binding capacity of hydrates.

Testing a novel method to identify salt production pottery via release and detection of chloride ions

A recently published analytical technique to detect chloride ions in ceramic vessels that were used to produce salt is replicated (Horiuchi et al., 2011). The method involves releasing bound chloride ions permanently retained by the vessel via a chemical exchange reaction with ammonium fluoride, following the removal of all unbound salt with water. The chloride concentration is measured in solution and used to quantify the amount of salt that was bound to the ceramic matrix. Our data suggest that this method is not a viable way to consistently discriminate salt-making pottery, as the detected chloride may not be derived from salt production activities, but from the ceramic material of the pot itself. We employ experimental vessels in which salt-making was simulated, in addition to analyzing excavated sherds from two Chinese and one North American site known to have been involved in salt production. The method proposed by Horiuchi et al. is not able to distinguish salt-making and non-salt-making vessels from one another.

Chloride ion penetration into concrete under hydraulic pressure

The lining concrete of subsea tunnel services under combined hydraulic pressure, mechanical and environmental loads. The chloride ion and water penetrations into concrete under hydraulic pressure were investigated. The experimental results indicate that the water penetration depth, chloride ion transportation depth, and the concentration of chloride ion ingression into concrete increase with raised hydraulic pressure and hold press period. But the chloride ion transportation velocity is only 53% of that of water when concrete specimens are under hydraulic pressure. The chloride transportation coefficient of concrete decreases with hold press period as power function. And that would increase 500%-600% in chloride transportation coefficient when the hydraulic pressure increases from 0 to 1.2 MPa. The hydraulic pressure also decreases the bound chloride ion of concrete to about zero. Besides, the low water-cementitions materials and suitable content of mineral admixture (including fly ash and slag) improve the resistance capacity of chloride penetration, and binding capacity of concrete under hydraulic pressure.

Charge Transfer and Polarization for Chloride Ions Bound in ClC Transport Proteins: Natural Bond Orbital and Energy Decomposition Analyses

ClC transport proteins show a distinct "broken-helix" architecture, in which certain α-helices are oriented with their N-terminal ends pointed toward the binding sites where the chloride ions are held extensively by the backbone amide nitrogen atoms from the helices. To understand the effectiveness of such binding structures, we carried out natural bond orbital analysis and energy decomposition analysis employing truncated active-site model systems for the bound chloride ions along the translocation pore of the EcClC proteins. Our results indicated that the chloride ions are stabilized in such a binding environment by electrostatic, polarization, and charge-transfer interactions with the backbone and a few side chains. Up to ~25% of the formal charges of the chloride ions were found smeared out to the surroundings primarily via charge transfer from the chloride's lone pair n(Cl) orbitals to the protein's antibonding σ*(N-H) or σ*(O-H) orbitals; those σ* orbitals are localized at the polar N-H and O-H bonds in the chloride's first solvation shells formed by the backbone amide groups and the side chains of residues Ser107, Arg147, Glu148, and Tyr445. Polarizations by the chloride ions were dominated by the redistribution of charge densities among the π orbitals and lone pair orbitals of the protein atoms, in particular the atoms of the backbone peptide links and of the side chains of Arg147, Glu148, and Tyr445. The substantial amounts of electron density involved in charge transfer and in polarization were consistent with the large energetic contributions by the two processes revealed by the energy decomposition analysis. The significant polarization and charge-transfer effects may have impacts on the mechanisms and dynamics of the chloride transport by the ClC proteins.

촉진염화물 확산계수의 시간의존성을 고려한 고성능 콘크리트의 염화물 침투 해석기법

촉진 염화물 확산계수는 최근 들어 염화물 거동 평가를 위하여 많이 사용되고 있다. 촉진 염화물 확산계수는 겉보기 확산계수와 마찬가지로 재령에 따라 감소하는데, 이 연구에서는 공극률을 이용하여 촉진확산계수의 감소를 구현하였다. DUCOM 프로그램을 이용하여 15 배합에 대한 공극률을 도출하였으며, 이를 회귀분석하여 재령 270일 동안 감소하는 염화물 확산계수를 모델링하였다. 또한 자유염화물과 구속염화물간의 관계인 비선형 구속능을 고려하여, 고성능 콘크리트내의 염화물 거동을 평가하였다. 기존의 실험자료인 180일간 염화물에 침지되어 있는 시편을 이용하여, 이 연구에서 제안한 기법의 검증을 수행하였다. 제안된 기법은 다양한 물-시멘트비 및 혼화재(고로슬래그 미분말 및 플라이애쉬)를 가진 고성능 콘크리트의 염화물 거동을 적절하게 평가하였다. 또한 혼화재료를 사용한 콘크리트의 경우, 확산계수의 시간의존성이 뚜렷하므로 염화물 거동 해석시재령에 따른 염화물 확산계수의 감소를 반드시 구현해야 함을 알 수 있었다.

Effect of Stray Current on Chloride Binding Mechanism in Concrete

In this article, simulation tests of chloride binding were made under the condition of sodium chloride as an internal admixture while loaded with stray current externally. Through the potential titration method, free chloride ion concentration Cf 、 total chloride ion concentration Ct and chloride binding rate RCl were determined. The results show that: With the increase of the strength and action time of the stray current, the number of internal free chloride ions in the cement paste increases while that of the corresponding bound chloride ions reduces significantly, leading to the decrease of chloride binding rate. The relationship between chloride binding rate and the two can be shown as follows respectively:RCl=50.754e(-I/28.258)+42.532、RCl=63.427 e(-T/8.238)+27.325.

Effect of Mineral Admixtures on Chloride Binding Mechanism in Concrete

The chloride binding mechanisms of different mineral admixtures under the condition of stray current and NaCl solute were researched. The electric potential titration was used to measure the content of total chloride ions and free chloride ions. The results show that using of mineral admixture could effectively inhibit the destructive action of the stray current to the stability of bound chloride ion in cement paste. Among all, the most effective mix proportion on chloride-induced corrosion is the mixture with only slag, then the double mixing of fly ash and slag, the last comes the mixture with only fly ash.

Corrosion inhibition of steel in concrete with natural inorganic minerals in corrosive environments due to chloride attack

The purpose of this study is to assess the corrosion resistance of a reinforcing concrete bar from chloride attack when the concrete is blended with a natural inorganic mineral admixture.To this end, specimens with chloride ion contents resembling the chloride attack environment were prepared, and an autoclave accelerated corrosion test was conducted. The electrochemical values of the steel bars (i.e., half-cell potential and polarization resistance) were measured, and the measured polarization resistances were used to derive equations to determine the corrosion rate of the reinforcing bar. After curing for accelerated corrosion, the steel bars in concrete were analyzed with respect to corrosion shape, corrosion area rate, and corrosion weight loss rate.The results of the analysis showed that the concrete blended with a natural inorganic mineral admixture could control chloride-induced damage more thoroughly than the non-blended concrete under the same corrosive environments, regardless of the coating thickness. The improved corrosion resistance is attributed to the fact that the concrete blended with a natural inorganic mineral admixture could bind chloride ions and inhibit bleeding, thus prohibiting the formation of pores in the lower part of the reinforcing bar.

Cooperation between bound waters and hydroxyls in controlling isotope-exchange rates

Mineral oxides differ from aqueous ions in that the bound water molecules are usually attached to different metal centers, or vicinal, and thus separated from one another. In contrast, for most monomeric ions used to establish kinetic reactivity trends, such as octahedral aquo ions (e.g., Al(H 2O) 6 3+), the bound waters are closely packed, or geminal. Because of this structural difference, the existing literature about ligand substitution in monomer ions may be a poor guide to the reactions of geochemical interest. To understand how coordination of the reactive functional groups might affect the rates of simple water-exchange reactions, we synthesized two structurally similar Rh(III) complexes, [Rh(phen) 2(H 2O) 2] 3+ [ 1] and [Rh(phen) 2(H 2O)Cl] 2+ [ 2] where (phen) = 1,10-phenanthroline. Complex [ 1] has two adjacent, geminal, bound waters in the inner-coordination sphere and [ 2] has a single bound water adjacent to a bound chloride ion. We employed Rh(III) as a trivalent metal rather than a more geochemically relevant metal like Fe(III) or Al(III) to slow the rate of reaction, which makes possible measurement of the rates of isotopic substitution by simple mass spectrometry. We prepared isotopically pure versions of the molecules, dissolved them into isotopically dissimilar water, and measured the rates of exchange from the extents of 18O and 16O exchange at the bound waters. The pH dependency of rates differ enormously between the two complexes. Pseudo-first-order rate coefficients at 298 K for water exchanges from the fully protonated molecules are close: k 0 298 = 5 × 10 −8(±0.5 × 10 −8) s −1 for [ 1] and k 0 298 = 2.5 × 10 −9(±1 × 10 −9) for [ 2]. Enthalpy and entropy activation parameters (Δ H ‡ and Δ S ‡) were measured to be 119(±3) kJ mol −1, and 14(±1) J mol −1 K −1, respectively for [ 1]. The corresponding parameters for the mono–aquo complex, [ 2], are 132(±3) kJ mol −1 and 41.5(±2) J mol −1 K −1. Rates increase by many orders of magnitude upon deprotonation of one of the bound waters in complex [ 1] because of the close proximity of a transferable proton that can convert the bound hydroxyl to a bound water. This interconversion allows the oxygen to exchange as a bound water, rather than as a bound hydroxyl, which is slow at near-neutral pH conditions.

Binding of externally supplied chlorides in micro silica concrete under field exposure conditions

Abstract Chloride binding has remarkable influence on the chloride penetration and hence, on the time to corrosion initiation in reinforced concrete structures. Previous studies have mainly looked at the chloride binding from internal sources in laboratory, which is not representative of practical situations. The current work focuses on the chloride binding characteristics of concrete samples exposed to an external source of chlorides from the sea water at Persian Gulf region. Some of the important parameters including w/c ratio, silica fume replacement and effect of chloride concentration on chloride binding were investigated in order to provide insight into the distribution of free and bound chloride ions after a long-term exposure. The results of the current study suggest that the chloride binding capacity increases with increasing the w/c ratio and chloride concentration but decreases by using silica fume. A general equation was also developed correlating the total and bound chloride in order to obtain more accurate service life prediction.

Chloride transference during electrochemical chloride extraction process

Chemical titration method and lab-made chloride probes were jointly adopted to investigate the effects of water-to-cement (W/C) ratio and the impressed current density on chloride transport for cement-based materials during electrochemical chloride extraction (ECE) process. The dissolution of bound chlorides and the effect of current density on dissolution were analyzed. The variations of chloride concentration at different depths and the chloride transference process were monitored. Test results show that W/C ratios adopted have slight influence on chloride extraction, while chloride extraction efficiency is mainly determined by the impressed current density. During ECE process a portion of bound chloride ions dissolved and the amount of bound chlorides released is directly proportional to current density.

Different effects of fly ash and slag on anti-rebar corrosion ability of concrete with chloride ion

In this paper, we have studied the anti-rebar corrosion ability of high-strength concrete (HSC), which were made by one or two mixed fly ash and slag. The different effects of fly ash and slag on concrete anti-rebar corrosion ability were discussed in chloride ion-contaminated condition. The results indicate that the effects of slag on concrete anti-chloride ion penetration ability are more excellent than that of fly ash at the same content. When the content of fly ash is 10%, the corrosion-inhibition action is not obvious; when the content is higher than 25%, this effect is remarkable. Corrosion-inhibition action of slag is better than that of fly ash. Slag is not like fly ash that has obvious effect on anode curves Tafer slope, so its contribution to restraining rebar in concrete corrosion is the result of high concrete anti-chloride ion penetration ability and binding chloride ion. Their “superimposition effect” can be realized only at reasonable content and proportion condition.

A mathematical model for electrochemical chloride removal from marine cast iron artifacts

The aim of this article was to theoretically study diffiusion and migration of chloride ions during electrochemical chloride removal. The proposed model would enable optimization of its application by predicting the optimal treatment time and current combination. A mathematical model for simulating the transport behavior of chloride ions was developed by consideration of diffiusion and migration of chloride ions when a constant DC current density was applied through the marine cast iron artifacts. The corresponding tests were conducted to validate the mathematical model. This model predicted the data of the extraction ratio of the chloride ion that correlated satisfactorily with the experimental values. An important issue in electrochemical chloride removal was to understand how chloride ions moved, taking account of diffiusion and migration of chloride ions and the release of binding chloride ions. The effiects of the treatment time, externally applied current density, chloride diffiusion coefficient, and rate constant of release of binding chloride ion on chloride removal are studied. The specific quantitative details applied to one-dimensional model were discussed here. This article has proposed a mathematical model for the first time, which was showed to be a useful tool that can reveal the ionic transport mechanism and optimize the application during electrochemical chloride removal.

Structure of acid-sensing ion channel 1 at 1.9 Å resolution and low pH

Acid-sensing ion channels (ASICs) are voltage-independent, proton-activated receptors that belong to the epithelial sodium channel/degenerin family of ion channels and are implicated in perception of pain, ischaemic stroke, mechanosensation, learning and memory. Here we report the low-pH crystal structure of a chicken ASIC1 deletion mutant at 1.9 A resolution. Each subunit of the chalice-shaped homotrimer is composed of short amino and carboxy termini, two transmembrane helices, a bound chloride ion and a disulphide-rich, multidomain extracellular region enriched in acidic residues and carboxyl-carboxylate pairs within 3 A, suggesting that at least one carboxyl group bears a proton. Electrophysiological studies on aspartate-to-asparagine mutants confirm that these carboxyl-carboxylate pairs participate in proton sensing. Between the acidic residues and the transmembrane pore lies a disulphide-rich 'thumb' domain poised to couple the binding of protons to the opening of the ion channel, thus demonstrating that proton activation involves long-range conformational changes.

Electro-chemical chloride extraction: Influence of C 3A of the cement on treatment efficiency

The aim of this study was to clarify whether the C 3A content of cement had a significant effect on electrochemical chloride extraction (ECE) treatment efficiency. It is known that a higher C 3A content in a cement gives it superior chloride complexing ability resulting in the formation of an “insoluble” calcium chloro aluminate compound. ECE was applied using cylindrical specimens made from concrete containing two levels of C 3A (4.3% and 9.05%). Specimens were 5 cm in diameter and 10 cm in height. Steel was placed in the axial direction with an embedded length of 7 cm. These specimens were immersed in an NaCl solution and dried in a stream of air at 40 °C for 10 months. The corrosion was monitored by half-cell potential and polarization resistance measurements. After steel depassivation, ECE was applied for 20, 30, 40 and 50 days using a constant current density of 1 A/m 2 of steel. At the end of the treatment, the specimens were maintained at 20 °C and 70% RH in order to observe the evolution of the steel (electrochemical measurements). The results show that, after 30 days of treatment, the chloride content remained constant in the specimen. This was probably due to OH − ion formation on the steel. The OH − ions “contribute” to the current transport, decreasing the ECE efficiency. Concerning the C 3A content, ECE efficiency was slightly affected by C 3A because only a part of the bound chloride ions was released. From the point of view of corrosion, half-cell potential showed a shift in the positive direction, indicating little corrosion activity at 20 °C and 70% RH. However, polarization resistance measurements showed that 2 months post treatment corrosion rates were significant, although the corrosion rate decreased from 6 μA/cm 2 to 2.5 μA/cm 2.

Monomeric and Polymeric Amines as Dual Reductants/Stabilisers for the Synthesis of Gold Nanocrystals: A Mechanistic Study

AbstractUniform, monodisperse gold nanocrystals have been prepared in a single‐step synthesis by the addition of secondary and tertiary alkylamines, or a cationic polymer containing these moieties, to dilute solutions of gold tetrachloraurate. The acidic pH resulted in the formation of quaternary ammonium sites, scavenging loosely bound chloride ions from the tetrachloraurate species, lowering the overall potential and reducing AuIII to nanocrystalline Au0. The secondary amino groups then served to stabilise the particles, preventing aggregation and collapse of the colloidal system. Addition of further capping groups was thus not required. The particles were characterised by UV/Visible spectroscopy, HR‐TEM, X‐ray diffraction, electrochemical potential and pH measurements (Eh‐pH) and FTIR. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)