Free Chloride Concentration Research Articles

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.

Modelling of chloride binding related to hydration products in slag-blended cements

An improved hydration model of slag-blended cements, taking into account new insights, is used to estimate and quantify the hydration products of slag-blended cements. Individual chloride binding isotherms are used to correlate these amounts of hydration products with the amount of bound chlorides. A number of parameters are directly or indirectly taken into account when estimating the chloride binding ability of a slag-blended cement paste: cement composition, slag content, water/binder ratio, curing age, and free chloride concentration. The model allows the study of the breakdown of bound chlorides by hydration products and their source – either the OPC or the slag.

Analysis of chloride threshold from laboratory and field experiments in marine atmosphere zone

Studies focusing on chloride threshold analysis based on field experiments are still scarce. Although taking longer than laboratory experiments, they can help on setting chloride thresholds closer to realistic conditions. The present work analyses results from reinforced concrete specimens exposed in a marine atmosphere zone of the northeast coast of Brazil and also from specimens subjected to wetting and drying cycles in sodium chloride solution. After the process of corrosion had just been initiated, the concrete specimens were broken and the total and free chloride contents at the rebar level were measured and assumed as the chloride thresholds for starting corrosion. Results show that average total chloride threshold varies in a range between 1.82 and 2.45 (% cement weight) and between 0.88 and 1.58 (% cement weight) for laboratory and field exposure experiments, respectively. Environmental interaction contributes for these differences. On the other hand, a good correlation could be obtained between both experimental conditions, helping on transporting laboratory results to field conditions.

Chloride Diffusion in Limestone Cement Concrete Exposed to Combined Chloride and Sulfate Solutions at Low Temperature

The chloride diffusion in limestone cement concrete exposed to combined chloride and sulfate solutions at low temperature was studied. For this purpose, a normal Portland cement and two Portland limestone cements (15% and 35% w/w limestone content) were used for concrete preparation. The specimens were immersed in two combined chloride-sulfate solutions of different sulfate content, and stored at 5°C. The total and free chloride contents, as well as the chloride diffusion coefficients were determined for each concrete composition. The results show that the total chloride content and free to total chloride ratio are increased with time. The sulfate content of the corrosive solutions has not a clear effect on total chloride content and chloride diffusion coefficient. It seems that the lower sulfate content results, in general, in higher free to total chloride ratio values. The use of limestone in cement results in higher chloride concentrations in concrete and free to total chloride ratio values. In general, these phenomena are intensified for higher limestone content.

Corrosion behaviour of a Low Ni austenitic stainless steel in carbonated chloride-polluted alkali-activated fly ash mortar

This study concerns the corrosion behaviour of a low nickel and AISI 304 austenitic stainless steels embedded in alkaline activated fly ash mortars. They were carbonated and exposed for 650days to increasing amounts of chloride ions to simulate a highly corrosive environment. The corrosion process was monitored by applying the electrochemical impedance spectroscopy (EIS) technique and, at the end of the 650day exposure, by recording polarization curves on selected steel bars. After slab breakage, observations for detection of pitting attack and analysis of the total and free chloride contents in the mortars were carried out. These tests and some results obtained in simulated mortar pore solutions indicated that the fly ash mortars offered the rebars a higher protection against pitting attack than ordinary Portland cement mortar. The tests also evidenced the very good performances of the less expensive low nickel stainless steel.

Aminobenzoate modified Mg[sbnd]Al hydrotalcites as a novel smart additive of reinforced concrete for anticorrosion applications

A carbonate form of MgAl hydrotalcite, Mg(2)Al-CO3 and its p-aminobenzoate (pAB) modified derivative, Mg(2)Al-pAB, were synthesized and characterized by means of XRD, FT-IR and TG/DSC. The anticorrosion behavior of Mg(2)Al-pAB was evaluated based on open circuit potential (OCP) of carbon steel in simulated concrete pore solution and on chloride-exchange experiments. The results reported in this paper demonstrate that ion-exchange indeed occurred between chlorides and intercalated pAB anions, thereby reducing the free chloride concentration in simulated concrete pore solution. The simultaneously released pAB anions were found to exhibit the envisioned inhibiting effect and caused corrosion initiation of the steel to shift to higher chloride concentrations than without the modified hydrotalcites.

Chloride binding isotherm from migration and diffusion tests

Chloride binding is often described by chloride binding isotherm, which is closely related to the service life of concrete structures in chloride environments. Many methods have been proposed to determine chloride binding isotherm. Compared to other methods, chloride binding isotherms obtained directly from nonsteady-state diffusion tests seem closer to the reality. We studied the chloride binding isotherm from both nonsteady-state electrical-accelerated migration and diffusion tests at different temperatures. Twelve concrete mixes with different supplementary cementing materials and water-to-binder ratios of 0.35, 0.48 and 0.6 were cast for study. The specimens after diffusion (or migration) tests were sliced layer by layer, and acid-soluble and free chloride contents of each layer were measured. A chloride binding isotherm was obtained from one specimen. Experimental results indicated that electrical voltage had a slight effect on the chloride binding isotherm of concrete. Temperature had a positive effect on chloride binding. The higher the water-to-binder ratio was, the higher the chloride binding was.

The apparent and effective chloride migration coefficients obtained in migration tests

The apparent (Dapp) and effective (Deff) migration coefficients obtained in chloride migration tests are investigated in this study. The presented Dapp profiles in concrete show that the apparent migration coefficient is strongly concentration-dependent. As demonstrated, the binding of chlorides during the migration tests is very low at low free-chloride concentrations and therefore the chloride penetration front progresses throughout the concrete only slightly retarded by the binding. The diffusion flux during migration tests is shown to be insignificant compared to the migration flux. The DRCM obtained from the Rapid Chloride Migration (RCM) tests are found to be equal to the computed Dapp at the locations of the chloride penetration fronts, which gives an indication that the DRCM represents only the migration coefficient at the front. A linear correlation is found between the DRCM obtained from the traditional RCM model and the Deff obtained from the chloride transport model which includes non-linear chloride binding and concentrations in non-equilibrium.

Performance of Chloride Binding by Aluminate Hydrates in Cement-Based Composite Materials

The chloride binding capacity of aluminate hydrates in cement-based composite materials is investigated. The total chloride contents and free chloride contents were analyzed by acid-soluble method and water-soluble method. The chemical interaction of chloride with the hydrates of aluminate phases in cement was also studied by X-ray diffraction. Test results show that the monosulfate hydrate has chloride binding capacities, whereas ettringite has no capacity to bind chloride. The chloride binding by monosulfate hydrate is attributed to the formation of Friedel’s salt and Kuzel’s salt by the ion exchange of SO42- with Cl- and the nonlinear relationship can be represented best by a Freundlich isotherm.

Application of silver nitrate colorimetric method to non-steady-state diffusion test

NT build 443, or profile fitting method, is often used to measure the diffusion coefficient of chloride in concrete. However, this method is quite laborious and needs special equipment. Colorimetric method is a quick and simple method to measure the penetration depth of chloride by spraying 0.1 mol/L silver nitrate solution. The objective of this work is to study the possibility of the use of colorimetric method in the calculation of non-steady-state diffusion coefficient. Twelve concrete mixtures with different supplementary cementitious materials and water-to-cement ratios of 0.35, 0.48 and 0.6 were used for study. According to NT build 443, the concrete specimens were immersed in 165 g/L NaCl (2.8 mol/L) solution for 42 d. Both water-soluble (convert to free chloride) chloride and acid-soluble chloride at different layers of specimens were measured. The results show that the mean value of free chloride concentration at the color change boundary cd was 0.306 mol/L. The surface free chloride concentration cs was obtained by profile fitting method, which was 40% lower than the chloride concentration of exposure solution after an immersion period of 42 d. Chloride diffusion coefficients obtained by the colorimetric method was not well correlated with those obtained by profile fitting method.

Corrosion initiation of reinforced concretes based on Portland or GGBS cements: Chloride contents and electrochemical characterizations versus time

The ingress of chlorides in cylindrical reinforced concretes based on ordinary Portland cement (OPC) or ground granulated blast furnace slag cement (GGBS) has been investigated together with the corrosion behaviour of the steel rebar. Chloride exposure was obtained by wetting and drying cycles during one to two years. The evolution of total and free chloride contents versus time of exposure shows that GGBS concretes induced a delay in chloride ingress. Corrosion initiation of steel was evaluated through nondestructive electrochemical measurements (half cell potential and linear polarization resistance) versus time of exposure. For GGBS concretes, corrosion assessment was not reliable based on the ASTM standard or RILEM recommendations. For OPC concretes, the transition from passive to active corrosion was studied considering a drop of potential or a corrosion current threshold value. Considering this latter, total and free chloride contents larger than 2.2% or 0.7% by weight of cement were estimated.

Wetting Properties and Critical Micellar Concentration of Benzalkonium Chloride Mixed in Sodium Hypochlorite

IntroductionThe purposes of the present study were to (1) assess the effect of the addition of benzalkonium chloride to sodium hypochlorite on its wetting properties, contact angle, and surface energy; (2) determine the critical micellar concentration of benzalkonium chloride in sodium hypochlorite; and (3) investigate the influence of addition of benzalkonium chloride on the free chlorine level, cytotoxicity, and antiseptic properties of the mixture. MethodsSolutions of benzalkonium chloride, with concentrations ranging from 0%–1%, were mixed in 2.4% sodium hypochlorite and tested as follows. The wetting properties were investigated by measuring the contact angle of the solutions on a nondehydrated dentin surface by using the static sessile drop method. The pending drop technique was subsequently used to determine the surface energy of the solutions. The critical micellar concentration of benzalkonium chloride mixed in sodium hypochlorite was calculated from the data. When 2.4% NaOCl was mixed with benzalkonium chloride at the critical micellar concentration, 3 parameters were tested: free chloride content, cytotoxicity, and antibacterial effects against Enterococcus faecalis. ResultsThe contact angle (P < .001) as well as the surface energy (P < .001) significantly decreased with increasing benzalkonium chloride concentrations. The critical micellar concentration of benzalkonium chloride in sodium hypochlorite was 0.008%. At this concentration, the addition of benzalkonium chloride had no effect on the free chlorine content, cytotoxicity, or antibacterial efficiency of the mixture. ConclusionsThe addition of benzalkonium chloride to sodium hypochlorite at the critical micellar concentration reduced the contact angle by 51.2% and the surface energy by 53.4%, without affecting the free chloride content, cytotoxicity, or antibacterial properties of the mixture.

STUDIES OF THE EFFECT OF DIFFUSION-INDUCED CHLORIDE BINDING ON CHLORINATION LIFE PREDICTIONS FOR EXISTING REINFORCED CONCRETE BRIDGES

The chloride ions diffusion is one of important factors of corrosion of reinforced concrete (RC) structures. The total chloride concentration penetrated into concrete can be expressed as the sum of bound and free chloride concentrations. The principal purpose of this paper is to study the chlorination life prediction of existing RC bridges due to chloride binding effect. The investigation method is that the no binding, linear binding, Langmuir and Freundlich adsorption isotherms are substituted into the analytical solutions of linear (diffusivity D = constant) and non-linear (D ≠constant) diffusion equations associated with initial and boundary conditions, respectively. The chlorination life can be calculated from the analytical solutions through the Mathematica software. These theoretical models are used to apply the existing Lin-bian and Dah-jin RC bridges in Taiwan. The results of the present study show that the Langmuir adsorption isotherms is suitable for bridge deck with small concrete cover while the linear binding is suitable for pier and abutment with large concrete cover. The studied results can be provided as a crucial reference for engineering decision-making for repair, strengthening or demolition of existing RC bridges.

Evaluation of different methods for determination of properties of chlorine-based sanitizers

Chlorine-based sanitizers, such as electrolyzed oxidizing (EO) water, are used for the sanitation of food contact surfaces and the prevention of cross contamination in various food processing settings. Several different chlorine species are present in EO water, and these chlorine species are important to the antimicrobial efficacy. Measurements of free and total chlorine, hypochlorous acid (HOCl), hypochlorite ion (OCl−) and chloride were conducted on chlorinated water and EO water solutions using a variety of commercially available methods. The chlorinated and EO water solutions differed by pH, initial free chlorine concentration, chloride concentration and organic compound concentration. It was discovered that these factors influenced the methods used to measure the various chlorine species by differing amounts. The data from this study will help in determining the appropriate methods of measuring free chlorine, total chlorine and chloride in chlorine-based sanitizers under various conditions.

Resistance of concrete with blast-furnace slag against chlorides, investigated by comparing chloride profiles after migration and diffusion

The effect of partial replacement of ordinary Portland cement (OPC) by blast-furnace slag (BFS) on concrete’s resistance to chlorides was examined by comparing chloride profiles and colour change boundaries after non-steady state migration and natural diffusion tests, cfr. NT Build 492 and NT Build 443, respectively. Chloride profiles were obtained by means of potentiometric titration and the colour change boundaries by spraying 0.1 M AgNO3-solution. One OPC mixture and three BFS mixtures, with cement replacement levels of 50, 70 and 85 %, were tested. It was found that, compared to OPC concrete, migration coefficients of 50 and 70 % BFS concrete are decreased with 32 and 57 %, respectively. Diffusion coefficients are reduced by 66 and 50 %, respectively. Nevertheless, the chloride binding capacity of BFS concrete, determined from the difference between total and free chlorides, was lower than for OPC concrete. The results for 85 % BFS concrete differ from the results for 50 and 70 % BFS concrete, since higher migration and diffusion coefficients are found. Besides, free chloride concentrations at the colour change boundary (ccb), obtained after spraying with AgNO3-solution, amounted to 0.30 mol/l on average. There was no clear relation between the free chloride content at ccb and the BFS content.

The reduction of perchlorate anions in tap water using a fluidized bed bioreactor

The compounds that mainly interfere with perchlorate reduction in contaminated tap water, nitrate and dissolved oxygen (DO), were reduced using a fluidized bed bioreactor. Nitrate was reduced to below the maximum level of contamination adopted by the United StatesEnvironmental Protection Agency (EPA), 10 ppm, and the percentages of nitrate were 90, 84 and 80% for concentrations (conc.) of 25, 50 and 100 ppm perchlorate, respectively, after a 6 h hydraulic retention time (HRT). The DO concentration was reduced to less than 1 mg/L, which is considered to be appropriate for the maximum rates of perchlorate anion reduction, and the percentages of DO removed were 80, 83, and 88% for 25, 50, and 100 ppm perchlorate, respectively, after a 6 h HRT. The maximum reduction for perchlorate was obtained with an HRT of 6 h for the different concentrations of perchlorate anion contamination. This result was confirmed by increase in the concentration of free chloride and decrease in the pH values for UP water. The free chloride concentrations increased to 36, 47 and 58 ppm for the 25, 50 and 100 ppm perchlorate concentration, respectively, after the 6 h HRT. The pH values decreased to 6.01, 5.8 and 6.2 for the 25, 50 and 100 ppm perchlorate concentration, respectively, after the 6 h HRT. Key words: Fluidized bed bioreactor, free chloride, granular activated carbon, water treatment, perchlorate anion.

A New Smart Additive of Reinforced Concrete Based on Modified Hydrotalcites: Preparation, Characterization and Anticorrosion Applications

ABSTRACTA carbonate form of Mg-Al-hydrotalcite and its p-aminobenzoate (pAB) modified derivative (i.e.,Mg(2)Al-pAB) were synthesized and characterized by means of XRD and FT-IR. The anticorrosion behavior was evaluated based on open circuit potential (OCP) of carbon steel in simulated concrete pore solution and chloride-exchange experiments. The preliminary results shown in this study demonstrated that ion-exchange indeed occurred between chlorides and the intercalated pAB anions in Mg(2)Al-pAB structure, thereby reducing the free chloride concentration in simulated concrete pore solution. The simultaneously released inhibitive pAB anions were found to exhibit the envisaged inhibiting effect and caused corrosion initiation of the steel shifting to a higher chloride concentration than without the modified hydrotalcites.

Exposure levels to brominated compounds in seawater swimming pools treated with chlorine

Despite evidence of formation of brominated compounds in seawater swimming pools treated with chlorine, no data about exposure levels to these compounds have been reported. To address this issue, a survey has been carried out in four establishments (representing 8 pools) fed with seawater and devoted to relaxing and cure treatments (thalassotherapy centres located in Southeast of France). Carcinogenic and mutagenic brominated disinfection byproducts (trihalomethanes -THM- and halogenated acetic acids -HAA-) were quantified at varying levels, statistically related to organic loadings brought by bathers, and not from marine organic matter, and also linked to activities carried out in the pools (watergym vs swimming). Bromoform and dibromoacetic acid, the most abundant THM and HAA detected, were measured at levels up to 18-fold greater than the maximum contaminant levels of 60 and 80 μg/L fixed by US.EPA in drinking waters. The correlations between these disinfection byproducts and other environmental factors such as nitrogen, pH, temperature, free residual chlorine, UV 254, chloride and bromide concentrations, and daily frequentation were examined. Because thalassotherapy and seawater swimming pools (hotels, cruise ships,…) are increasing in use around the world and because carcinogenic and mutagenic brominated byproducts may be produced in chlorinated seawater swimming pools, specific care should be taken to assure cleanliness of users (swimmers and patients taking the waters) and to increase water circulation through media filters to reduce levels of brominated byproducts.

병원폐수의 전기화학적 처리시 무기응집제 주입 효과에 관한 연구

Effect of inorganic coagulants dosing on the performance of electro-chemical process was studied when treating hospital wastewater having low electrolyte concentration. It is thought that adding inorganic coagulants caused increase in concentration of electrolyte and this caused increase in free chloride concentration and consequently, caused increase in indirect oxidation effect. Thus, COD removal efficiencies more than doubled in percentage terms at the 2 hrs of reaction time and current density of 1.76 A/dm compared with the results obtained from the parallel experiments without adding inorganic coagulants. T-N removal efficiencies approximately doubled in percentage terms at the 2 hrs of reaction time and 700 ppm of coagulants addition and applied current density of 1.76 A/dm due to the increase of free residual chlorine such as HOCl caused by increase of electrolyte concentration through the addition of inorganic coagulants. Under the same experimental condition, more than 90% of T-P removal efficiencies was obtained. The reason can be explained that increase of chemical adsorption rate between phosphate and insoluble metal compounds caused by dissolved oxygen generated from anode by the increased electrolyte concentration through inorganic coagulants addition make a major role in improving T-P removal efficiencies. It can be concluded that inorganic coagulants addition as the supplemental agent of electrolyte is effective way in improving organic and nutrient salt removal efficiency when treating hospital wastewater having low electrolyte concentration.

RECONSIDERATION FOR A STUDY OF THE EFFECT OF CHLORIDE BINDING ON SERVICE LIFE PREDICTIONS

The major purpose of this paper is to use Kirchhoff’s transformation associated with Laplace’s transformation methods to obtain the analytical solution of the modified Fick’s second law of nonlinear diffusion equation with initial and boundary conditions provided by Martin-Perez et al. [A study of the effect of chloride binding on service life predictions. Cement and Concrete Research 2000; 30 (8): 1215-1223]. Based on experimented data and four kinds of chloride binding isotherm, i.e., no, linear, Langmuir, and Freundlich binding, results of free and total chloride concentration profiles calculated from the analytical solution are presented for a concrete structure suffered from two different exposure conditions: submerged in seawater and exposed to deicing salts during 6 months, 5 years, 30 years and 50 years, respectively. The difference between the analytical solution and the approximate solution obtained by Martin-Perez et al. used finite-difference method can be represented by percentage error. The percentage errors of Freundlich’s binding are higher than those of no binding and linear binding when both service life and concrete cover increase. The implication of answering for chloride binding in service life predictions is in detail discussed. The result of present study may offer as a critical reference of maintenance, strengthening, and demolition of concrete or reinforced concrete (RC) structures subjected to chloride-ion penetration.