Chloride Concentration Profiles Research Articles

Perfiles de concentración del cloruro reconstruidos debajo del lecho marino en Hong Kong (China) y sus implicancias en los recursos de agua subterránea mar adentro

Offshore hydrogeology has been much less studied compared to onshore hydrogeology. The marine Quaternary system in Hong Kong (China) consists of interlayers of aquitards and aquifers and was part of the Pearl River Delta when the sea level was low before the Holocene. Core samples from six offshore boreholes were collected to measure the chloride concentration in the system by adding deionized water. A method was proposed to convert the sediment chloride into that of the original pore water. A one-dimensional sedimentation-transport model was developed to simulate the historical conservative transport of the reconstructed pore-water chloride. The model integrates present knowledge of stratigraphy and the historical evolution of the geological system. The chloride concentration profiles show that the chloride decreases from an average of 13,800 mg/L in the first marine unit to an average of 5,620 mg/L in the first aquifer. At the bottom of one borehole, the concentration is only 1,420 mg/L. The numerical model shows that the vertical chloride distribution is due to diffusion-controlled downward migration of seawater. The second marine unit obstructs the downward migration, indicating its low permeability and good aquitard integrity. The relatively fresh or brackish water in deep aquifers protected by the aquitard has the potential to be used as drinking water following some treatment, or at least as raw water with much cheaper desalinization compared with using seawater. The methodology and findings in this study are instructional for other coastal areas with similar geology and history in the South China Sea.

Comparing vertical profiles of natural tracers in the Williston Basin to estimate the onset of deep aquifer activation

AbstractComparing high‐resolution depth profiles of different naturally occurring environmental tracers in aquitards should yield consistent and perhaps complementary information about solute transport mechanisms and the timing of major hydrogeological and climatological events. This study evaluated whether deep, continuous profiles of aquitard pore water chloride concentration could provide further insight into the paleohydrology of the Williston Basin, Canada, than possible using high‐resolution depth profiles of stable H/O isotopes of water (δ18O, δ2H). Pore water samples were obtained from extracts of cores taken over 392 m of the thick Cretaceous shale aquitard. Water samples were also collected from wells installed in the underlying regional sandy aquifer (Mannville Group; 93 m thick) and from seepage inflows into potash mine shafts (to 825 m below ground). Numerical modeling of the 1‐D vertical Cl− profile supported diffusion dominated solute transport in the shales. The modeling also showed a similar time frame for development of the Cl− profile prior to activation of the aquifer as determined from the δ18O profile (20–25 Ma); however, it provided a significantly longer and potentially better‐constrained time frame for evolution of the profile during the activation phase of the aquifer (0.5–1 Ma). The dominant paleoevent reflected in present‐day profiles of both tracers is the introduction of glaciogenic meteoric water to the Mannville aquifer underlying the shale during the Pleistocene. The source area of this water remains to be determined.

The effect of chloride binding on the predicted service life of RC pipe piles exposed to marine environments

Chloride binding capacity has a significant effect on the service life of reinforced concrete (RC) pipe piles exposed to marine environments. Four typical chloride binding isotherms (i.e., null, linear, Langmuir and Freundlich binding isotherms) were reviewed in this paper. The effect of chloride binding on service life predictions of RC pipe piles, in terms of these different binding isotherms, was investigated. An experimental program was conducted to verify the theoretical predictions developed in the present study. The free and total chloride concentration profiles were presented for RC pipe piles exposed to submerged and splash zones for 5, 10 and 30 years. Furthermore, the predicted service life of RC pipe piles exposed to submerged and splash zones, using different binding isotherms, was also presented in this paper. The results of the present study indicated that the chloride binding has a more significant effect on the service life of RC pipe piles in submerged zone than in splash zone, and RC pipe piles in submerged zone display longer service life than those in splash zone.

Application of Two Different Methods for Determination of Water and Chloride Transport Parameters of Building Stones

The transport of 1M NaCl water solution in three different types of sandstones is studied For basic characterization of studied materials, their chemical composition, porosity, bulk density and matrix density are accessed. The chloride transport is analyzed using two different methods. In the first one, the chloride absorption coefficient is measured on the basis of a modified sorptivity concept. The second method consists in carrying out an inverse analysis of experimentally measured moisture and chloride concentration profiles, leading to the determination of chloride diffusion coefficient as a function of chloride concentration, and moisture diffusivity as a function of moisture content. The chloride transport properties obtained for the particular studied materials are compared and the observed differences are discussed.

Rhizon sampler alteration of deep ocean sediment interstitial water samples, as indicated by chloride concentration and oxygen and hydrogen isotopes

AbstractDespite their potential to inform past ocean salinity, δ18O, and temperature, high‐resolution depth profiles of interstitial water chloride concentration and hydrogen and oxygen isotopes exist in very few locations. One of the primary limitations to the recovery of these depth profiles is that traditional interstitial water sampling requires 5–10 cm whole rounds of the sediment core, which has the potential to interfere with stratigraphic continuity. The Rhizon sampler, a nondestructive tool developed for terrestrial sediment interstitial water extraction, has been proposed for efficient and nondestructive sampling of ocean sediment pore waters. However, there exists little documentation on the reliability and performance of Rhizon samplers in deep ocean sediments, particularly in regard to their effect on chloride concentration and oxygen and hydrogen isotopic measurements. We perform an intercomparison of chloride concentration and oxygen and hydrogen isotopic composition in samples taken using traditional squeezing versus those taken with Rhizon samplers. We find that samples taken with Rhizons have positive biases in both chloride concentration and stable isotopic ratios relative to those taken by squeezing water from sediments in a hydraulic press. The measured offsets between Rhizon and squeeze samples are consistent with a combination of absorption by and diffusive fractionation through the hydrophilic membrane of the Rhizon sampler. These results suggest caution is needed when using Rhizons for sampling interstitial waters in any research of processes that leave a small signal‐to‐noise ratio in dissolved concentrations or isotope ratios.

Multi‐species diffusion analysis in porous media under various dry density and temperature conditions: molecular dynamics simulation, homogenization analysis, and finite element method

SUMMARYIn porous media, chemical species that dissolve in pore water can be transported via diffusion mechanisms or advective fluxes, close to or far away from where precipitation occurs. In the case of a high‐level radioactive waste disposal system, compacted bentonite is used in a buffer material in an engineering barrier system to minimize the amount of specific nuclides that breach into the surrounding host rock. To minimize breaching, it is very important to understand the transport mechanism of multiple chemical species in porous media. In the following research, we introduced FEM analysis methods using the results of the molecular dynamics simulation and homogenization analysis (MD/HA) method. First, the diffusion coefficients of ions (Cl−, I−, and Na+) in different water layers of Na‐beidellite were calculated using the MD/HA procedure under various dry density (1.2, 1.6, and 2.0 Mg/m3) and temperature (293, 323, and 363 K) conditions. Next, using FEM analysis that used the MD/HA results as input parameters, the diffusion behaviors of ions in porous media were calculated. The results indicate that the diffusion coefficients of the interlayer water in Na‐beidellite are different from the diffusion coefficients under dry density conditions. Further, the concentration profiles (Ct/C0) of iodine and chloride are proportional to temperature but inversely proportional to dry density. Copyright © 2014 John Wiley & Sons, Ltd.

Experiments of Chloride Ingression in Loaded Concrete Members under the Marine Environment

AbstractThis paper presents the results of an experimental investigation on the effect of load on chloride diffusion in concrete members in tidal zone and salt spray zone which were simulated by using a self-designed tidal circulation device and a salt spray chamber. The concrete members were loaded by using self anchoring at both ends. The load conditions were 0, 0.3, and 0.5 times of the member’s flexural strength (ff). Chloride concentration profiles in concretes were determined after 35, 70, 120, and 180 days of exposure, respectively. Regression analysis of the experimental data was carried out by applying Fick’s law of diffusion to determine the diffusion coefficient (Dc) and chloride concentration on the surface (Cs). The results show that chloride diffusion has a big difference between the two zones; diffusion coefficient (Dc) is time dependent and gradually reduces over time; loads have a certain impact on diffusion; and tensile stress promotes chloride diffusion whereas compressive stress inhibi...

Palaeohydrogeological insights from natural tracer profiles in aquitard porewater, Great Artesian Basin, Australia

The value of using environmental tracer profiles in aquitards to quantify fluid flux and to reveal information about palaeohydrology is largely unknown for parts of the world that were not glaciated during the Cenozoic. We present deep, continuous vertical profiles of aquitard pore water chloride concentration and δ2H/δ18O composition from the western margin of the Great Artesian Basin, Australia, where upward leakage is the dominant groundwater discharge mechanism. At the deeper of the two sites studied, the Cl− and δ2H profiles exhibit a distinctive S‐shape, which we interpret as a shift in the upper concentration boundary condition over time. Numerical simulations are used to support an hypothesis that the shallow phreatic aquifer was more saline and more enriched in δ2H compared to current conditions prior to ∼120 ka, followed by an extended freshening phase from ∼120 to 20 ka, then a saline phase similar to current conditions for the last ∼20 ka. These timeframes correspond favorably with results of previous studies into the palaeohydrology of nearby playa Lake Eyre. At the shallower site, the tracer profiles decrease exponentially with depth. We explore several models for the evolution of these profiles and adopt one of long‐term salt input at ground surface. At both sites, tracer concentrations for groundwater sampled from the underlying artesian aquifer provide conclusive evidence that recharge occurred within the last 10–20 ka. Chloride was a more useful tracer than δ2H in this study, primarily due to lack of recent glaciation in central Australia to provide a dynamic δ2H tracer signal.

Modelling of chloride penetration into non-saturated concrete: Case study application for real marine offshore structures

The aim of this paper is to explain the chloride concentration profiles obtained experimentally from control samples of an offshore platform after 25years of service life. The platform is located 12km off the coast of the Brazilian province Rio Grande do Norte, in the north-east of Brazil. The samples were extracted at different orientations and heights above mean sea level. A simple model based on Fick’s second law is considered and compared with a finite element model which takes into account transport of chloride ions by diffusion and convection. Results show that convective flows significantly affect the studied chloride penetrations. The convection velocity is obtained by fitting the finite element solution to the experimental data and seems to be directly proportional to the height above mean sea level and also seems to depend on the orientation of the face of the platform. This work shows that considering solely diffusion as transport mechanism does not allow a good prediction of the chloride profiles. Accounting for capillary suction due to moisture gradients permits a better interpretation of the material’s behaviour.

A variable-order time-fractional derivative model for chloride ions sub-diffusion in concrete structures

Abstract This study proposes a new variable-order fractional diffusion equation model to describe the coupled chloride diffusion-binding processes in reinforced concrete, in which the order of fractional derivative term is a variable function instead of a constant in the standard fractional model. The concentration influence coefficient k is introduced to capture the effect of concentration dependency on chloride transport due to the chloride binding behavior. The two parameters in the proposed model can be determined directly by a statistical analysis of measurement data. Four test cases illustrate that the proposed variable-order fractional derivative model agrees significantly better with experimental data than the most commonly used traditional model governed by the classical Fick’s second law, especially when a large concentration coefficient k is involved. That proposed model is also verified by accurately predicting chloride concentration profiles in a period of 200 days.

Investigation on the geochemical dynamics of a hydrate-bearing pockmark in the Niger Delta

A joint industrial project with IFREMER and Total provides insights into the tectonic setting and the geochemistry of a large active pockmark offshore W-Africa in the Niger Delta. The study combines both geophysical (seismic) and geochemical data to infer the dynamics of a 300 m wide pockmark located at 667 m water depth. Two Calypso cores, one at the centre and one outside the pockmark, along with three box-cores, two inside the pockmark and one outside, were collected to study the geochemistry of gas hydrates, carbonates and pore waters. Two seismic lines, a 3D high resolution random line and a 2D high resolution seismic line, provide a good description of the plumbing of the system. The integrated results depict a very active pockmark characterized by several gas charged-bodies, a well identified BSR marking a hydrate accumulation zone, charged from deeper sources via a network of faults. Hydrates and carbonate concretions have been detected inside the pockmark while only the latter has been found outside. The hydrate analyses show that the hydrate-forming gases are of thermogenic origin, albeit overwhelmingly composed of methane. Pore-water analyses reveal the occurrence of anaerobic oxidation of methane coupled with sulphate reduction at shallow depth (∼200 cm). The chloride concentration profile exhibits both values lower than that of seawater which is inherent to hydrate dissociation after core recovery and positive anomalies (values 7% higher than that of seawater background) at the lowermost part of the core. The latter evidence suggests current or recent hydrate formation at this area. The carbonate dating provides additional temporal information and indicates that this pockmark has been active since ∼21 kyr.

Resolving Cl and SO4 Profiles in a Clay-Rich Rock Sequence

The chloride and sulfate concentration profiles in a 260 m thick clay-rich Mesozoic sediment sequence have been analyzed by various methods. Chloride data generally indicate a good consistency between different methods if anion exclusion is accounted for in leaching tests. For sulfate, however, there is an apparent inconsistency between leaching data and those obtained from the other methods, which points to the dissolution of a sulfur-bearing mineral. Traces of diagenetic gypsum seem to be a likely source, but other sulfur minerals cannot be ruled out.

Modeling Cl− Concentration and δ37Cl Profiles in Porewater Across a 250m-thick Indurated Argillite at the Tournemire URL (France)

Dissolved chloride in argillite porewater has been studied as a natural analogue for radionuclides potentially released from radioactive waste disposal. The Tournemire URL intersects impervious and compacted argillite. A previously obtained chloride concentration profile of intact rock is symmetric with a maximum concentration of 0.6±0.1 g/L, compared to 19 g/L for the original connate seawater. Dissolved chloride shows high δ37Cl values, ranging between +6 and +8‰ vs. SMOC. The modeled profile considers diffusive exchange between connate seawater and meteoric freshwater. Transport parameters were obtained by radial diffusion experiments. Numerical modeling was performed with the coupled reactive-transport code Hytec. Simulations suggest a diffusive-exchange time of 85±10 Ma for Cl, which correlates with a major erosional period. Simulated δ37Cl values between 1.002 and agree with observed porewater δ37Cl. This study strongly suggests that the dissolved chloride profile in the argillites results from diffusive exchange and indicates that unfractured argillites can provide good confinement.

Modeling the chloride concentration profile in migration test based on general Poisson Nernst Planck equations and pore structure hypothesis

The rapid chloride migration test is widely used in estimating the diffusivity of cement-based material. However, the concentration profile predicted in the conventional method was found different from the realistic one. In this paper, the current models attempting to describe the concentration profile are introduced. Experimental test is carried out to found the realistic concentration profile. A system of general Poisson–Nernst–Planck (PNP) equations is formed by considering the influence of electrophoreses, relaxation, etc. A new model is built up based on the general PNP equations and a hypothesis of pore structure to explain the realistic concentration profile. A semi-empirical model is simplified from the new model according to the experimental evidence. And the semi-empirical model is applied to analyze the influence of source concentration on the chloride penetrability.

Fixed bed reactors with three dimensional electrodes for electrochemical treatment of waters for disinfection

A fixed bed electrochemical cell was tested as reactor for treatment of waters by direct electrolysis. The aim was the development of a reactor configuration for effective and controllable primary and secondary disinfection. Stacks of titanium grids coated with Ru/Ir oxides or platinum were used as anodes and cathodes, respectively. The electrode packings were arranged in series, the system worked in continuous mode.The reactor was characterised for mass transfer (by the limiting current densities technique) and flow behaviour (by pulse-response curves with an inert tracer). Electrolyses were carried out with 100mgdm−3 of chloride ions, and current density ranging from 2.5 to 7.5mAcm−2.Active chlorine concentrations from 0.3 to 1.2mmoldm−3 were obtained in the reactor outlet, depending on the conditions. The higher value was measured with i=7.5mAcm−2 and flow conditions corresponding to a Reynolds number of 5: under these conditions, about 1mgdm−3 of chlorates were detected, otherwise the selectivity of the process towards active chlorine was about unit.A mathematical model at steady state was implemented, and pseudo first order kinetics was used to describe chemical and electrochemical reactions. The model allowed obtaining the concentration profiles of chloride and chloride oxidation by-products which were compared with experimental data, with good agreement in a wide range of flow rates. The configuration allowed a well-defined concentration profile: the active chlorine in the outlet was always 50% less than the value inside the reactor, allowing to exploit the process for primary and secondary disinfection.

Numerically and Experimentally Based Reliability Assessment of a Concrete Bridge Subjected to Chloride-Induced Deterioration

AbstractMaintaining an adequate safety level in concrete bridges under gradual degradation due to traffic and environmental actions is not only an expensive task, but also filled with some level of uncertainty. Degradation in itself is not easily quantifiable because numerous aspects reduce the load-bearing capacity of a concrete bridge. Furthermore, the effects of preventive maintenance and rehabilitation actions are difficult to predict. Chloride ion ingress is an important aspect of durability design and maintenance, especially in regions where winter salt is commonly applied for traffic safety. This paper introduces a feasible approach to analyze the effects of chloride-induced deterioration on the overall safety level, which is validated by the application to a real highway bridge, which was demolished after 38 years of service. Concrete samples were extracted from this bridge and chemical analyses were performed to determine the chloride concentration profile in the concrete. Once the present chlori...

Numerical simulation of ionic transport in cement paste under the action of externally applied electric field

This paper presents a numerical investigation on the penetration of chloride ions in a saturated cement paste with considering the interactions between different ionic species in pore solution. The work is performed by solving the equations of mass conservation of individual ionic species with electrostatic coupling of ions in a multi-component pore electrolyte solution. Unlike most of existing work where the electrostatic potential was determined based on the assumption of electro-neutrality, the present work uses the Poisson’s equation relating the spatial variation in the electric field to the charge distribution to determine the electrostatic potential. As numerical examples, chloride penetrations in saturated cement pastes of different initial concentrations are simulated. The results show that chloride concentration profiles are significantly different in the cement pastes of different initial concentrations. The dependence of chloride penetration on the initial composition of pore solution may explain why the experimentally obtained chloride diffusion coefficients published in literature varying from 10−12 to 10−10 m2/s.

Evaluation of Hydrophobic Concrete Coatings in Tropical Marine Environments

This paper reports a six-year field- and laboratory-based study carried out to compare the performance of three proprietary hydrophobic coating systems (silane- and siloxane-based coatings), designed to reduce chloride ingress and reinforcement corrosion. Their behavior in the laboratory was also compared by using concrete of two different mixes (water-to-concrete [w/c] = 0.40 and 0.65). Field tests were carried out on a Portland I cement concrete with a w/c ratio of 0.4 and exposed to a very aggressive tropical marine environment. Six reinforced concrete probes (two per coating) of 15 by 15 by 30 cm were placed in the exposure site. The rebars were placed into the probes to obtain concrete covers of 20, 25, and 30 mm. During the test period, evaluation of the environmental parameters was based on the methodology established by ISO Standard 9233. The evaluations of half-cell potential (Ecorr) and corrosion rates (icorr/linear polarization resistance technique) were determined monthly. Chloride concentration profiles were determined after a 5-year, 8-month exposure. The results showed that when siloxane-based coating is used, there is an improvement in the behavior of the concrete with respect to chloride ion penetration. The behavior of the coatings depends not only on the quality of the concrete, but also on the company who manufactured them.

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.

RCM: A new model accounting for the non-linear chloride binding isotherm and the non-equilibrium conditions between the free- and bound-chloride concentrations

In this paper a new theoretical model for the Rapid Chloride Migration test is presented. This model accounts for the non-linear chloride binding isotherm and the non-equilibrium conditions between the free- and bound-chloride concentrations in concrete. The new system of equations is solved numerically and compared to a simplified analytical solution, revealing a good agreement. Subsequently, numerical simulations are applied to experimental data on chloride concentration profiles in concrete obtained elsewhere. The binding parameters, the chloride mass transfer coefficient and the effective diffusion coefficient of chloride are estimated with these simulations. The non-linear binding coefficients correspond well to experimental data found in literature. The chloride mass transfer coefficient reveals a tendency to decrease in time during the application of electrical field across a concrete sample. The effective chloride diffusion coefficient ( D eff ) obtained in the present study is found to be in line with data obtained elsewhere. Finally, it is demonstrated that the values of the diffusion coefficient computed from the Rapid Chloride Migration test in the traditional way are overestimated.