Chloride Concentration Profiles Research Articles

The dark side of the hyporheic zone: depth profiles of nitrogen and its processing in stream sediments

1. Although it is well known that sediments can be hot spots for nitrogen transformation in streams, many previous studies have confined measurements of denitrification and nitrate retention to shallow sediments (<5 cm deep). We determined the extent of nitrate processing in deeper sediments of a sand plains stream (Emmons Creek) by measuring denitrification in core sections to a depth of 25 cm and by assessing vertical nitrate profiles, with peepers and piezometers, to a depth of 70 cm. 2. Denitrification rates of sediment slurries based on acetylene block were higher in shallower core sections. However, core sections deeper than 5 cm accounted for 68% of the mean depth-integrated denitrification rate. 3. Vertical hydraulic gradient and vertical profiles of pore water chloride concentration suggested that deep ground water upwelled through shallow sediments before discharging to the stream channel. The results of a two-source mixing model based on chloride concentrations suggested that the hyporheic zone was very shallow (<5 cm) in Emmons Creek. 4. Vertical profiles showed that nitrate concentration in shallow ground water was about 10–60% of the nitrate concentration of deep ground water. The mean nitrate concentrations of deep and shallow ground water were 2.17 and 0.73 mg NO3-N L−1, respectively. 5. Deep ground water tended to be oxic (6.9 mg O2 L−1) but approached anoxia (0.8 mg O2 L−1) after passing through shallow, organic carbon-rich sediments, which suggests that the decline in the nitrate concentrations of upwelling ground water was because of denitrification. 6. Collectively, our results suggest that there is substantial nitrate removal occurring in deep sediments, below the hyporheic zone, in Emmons Creek. Our findings suggest that not accounting for nitrate removal in deep sediments could lead to underestimates of nitrogen processing in streams and catchments.

Assessment of seawater mixing in a coastal aquifer by high resolution electrical resistivity tomography

Seawater intrusion is a major problem in urbanized coastal regions of India which is due to over exploitation of groundwater for various purposes. This study was carried out with the objective of assessing the zone of mixing between seawater and groundwater in the coastal aquifer in south of Chennai, Tamil Nadu, India using high resolution electrical resistivity tomography. High resolution electrical resistivity tomography was carried out in five profiles perpendicular to the sea using IRIS make SYSCAL Pro-96 system with 2.5 m or 5 m inter-electrode separation. The maximum length of the profile was 170 m which resulted in a depth of investigation of 28.7 m. The apparent resistivity measured in this area varies from 0.3 ohm-m to 30,000 ohm-m. The apparent resistivity of saturated zone decreases towards the sea, indicating the influence of seawater. This was also confirmed by measuring the electrical conductivity of groundwater, which gradually increases from 156 μS/cm to 3430 μS/cm towards the sea. Further, the concentration profiles of electrical conductivity, sodium, chloride and chloride / bicarbonate ratio are compared with the high resolution electrical resistivity tomography profile. The distance of influence of seawater is comparatively high in northern part than in southern part of the area. The high resolution electrical resistivity tomography was effectively used to determine the effect of seawater mixing with groundwater.

Anodic corrosion inhibitors against chloride induced corrosion of concrete rebars

The effect of anodic inhibitors [calcium nitrate Ca(NO3)2, calcium nitrite Ca(NO2)2 and potassium nitrate NaNO2] has been evaluated using cylinders with steel rebars exposed to the following environments: in the marine tidal zone, at roof top and in air of 38°C and 90% relative humidity for 4 years. The experiments showed that the half cell potentials were more negative than the visual inspections proved when anodic inhibitors are used. Inhibitor dosage on 3–4% of cement weight seems sufficient to protect the rebar against corrosion. Capillary absorption experiments showed that the concrete porosity was unaffected by the inhibitors. The concentration profiles of chloride, nitrite and nitrate were investigated with respect to leaching. However, it was difficult to find the background level of nitrite due to possible chemical alteration.

APPLICATION OF THE RESPONSE SURFACE ANALYSIS METHOD TO THE STUDY OF SALT AND WATER PROFILES IN GOAT'S CHEESE SALTED IN LAYERS

ABSTRACTWith the purpose of determining sodium chloride and water distribution profiles, a series of analyses were carried out on goat's cheese that had been salted by a traditional method from the province of Jujuy (Argentina). This process consists of distributing layers of dry salt between layers of curd of a constant height during the moulding operation. The sodium chloride and water concentration profiles were analyzed in relation to the height and distance of the cheese samples from the center. The response surface analysis methodology was used to interpret the results. The highest water concentration was obtained in the lower external zone, this being connected to the gravitational effect of syneresis and its contact with the cheese inside the container. In the sodium chloride profile, it was observed that the upper zone of the cheese presented the concentration furthest from the average value. This indicates that salt and water distribution can be improved by increasing the frequency of turning the cheeses after salting.PRACTICAL APPLICATIONSA fundamental variable in the formulation and control over the cheese manufacturing process is the salt concentration and its profile within the product. In the case of the goat cheese, which is traditionally manufactured in the province of Jujuy, the salting is mostly made by dry salt distribution. The product have a variable salt content and heterogeneous flavor. A detailed understanding of the factors that influence in the salt distribution must allow producers to optimize the salting stage and thus improve the quality of the final product. An analysis of the salt and moisture concentration profiles developed throughout the mass transfer process is a good method to clarify the reach of the mechanisms involved in it.

Distribution of Chloride Accumulation in Marine Tidal Zone along Altitude

In this paper a new mathematical model of chloride transport in concrete under dry-wet cycling conditions is developed. The model considers the hysteresis of moisture evaporation and the accumulation of chlorides at the concrete surface. Unimodal distribution of chloride accumulation in marine tidal zones along altitude can be derived based on the sensitivity analysis for the proposed model—that is, with the increment of altitude, the accumulation of chloride is first aggravated for the increasing drying time proportion and accelerated evaporation rate, and then weakened for the reduction of contact time with a chloride-contained reservoir and the declining saturation of pores in concrete. The proposed model has been validated by experiments carried out in both the laboratory and the field. In laboratory tests, concrete specimens were exposed to dry-wet cycles in an artificial environmental chamber (AEC) for 2 to 3 months and then chloride concentration profiles were measured. In field tests, measurements were directly taken from a concrete harbor deck that was 55 months old. The comparison of the laboratory and field data with the model predictions demonstrates that the proposed model can be used to predict the transport of chlorides in the marine tidal zone.

Salt transport and storage parameters of renovation plasters and their possible effects on restored buildings’ walls

Three systems of brown coat-renovation plasters for restoration of building structures damaged by moisture and salt efflorescence are analyzed, and their properties are compared with reference lime plaster. In the experimental part, measurement of bulk density, matrix density, open porosity, pore distribution curves, chloride binding isotherms, moisture and chloride concentration profiles is performed. The obtained data are used in the calculations of moisture dependent moisture diffusivity and concentration dependent chloride diffusion coefficient. The experimental and computational results show that all three systems can have beneficial influence on the restored building structures but they should be used with caution, taking into account the properties of the material of load bearing wall and the conditions for water and salt transport in the wall including their possible sources after reconstruction. The measured water and salt transport and storage parameters may contribute to the improvements in service life assessment if they are used as input parameters in computational modeling of water and salt transport and accumulation in the load bearing wall-renovation plaster system.

Computational modelling of coupled water and salt transport in porous materials using diffusion–advection model

The diffusion–advection model taking into account not only the influence of water flow on salt transport but also the effect of bonded salt on pore walls is used for the description of coupled moisture and chloride transport in lime plaster. Moisture and chloride concentration profiles are determined experimentally and subjected to inverse analysis making possible to identify the moisture diffusivity as a function of moisture content and salt diffusion coefficient as a function of salt concentration. The results of experimental and computational investigations show that the moisture diffusivity of lime mortar increases fast with increase in moisture content, its maximum value being about 10 −6 m 2/s, which indicates very fast moisture transport in that material. The chloride diffusion coefficient of lime mortar is found very high, in the range 10 −6–10 −5 m 2/s. This can be explained by the action of additional driving forces, namely the surface diffusion and osmosis, which accelerate the chloride transport. The obtained results should find use in computational modelling of the damage of lime plasters in historical buildings caused by combined action of water and salts.

Investigations on the chloride migration in consequence of cathodic polarisation

AbstractAt the Institute for Building Materials Research (ibac) in Aachen and the Federal Institute for Materials Research and Testing (BAM) in Berlin a joint research project is currently running with the aim to develop a numerical model which describes cathodic protection (CP) of reinforced concrete. Special project focus is the CP of the rear reinforcement layer. The resulting model shall include the impact of chemical alterations at the steel surface and within the adjacent concrete on the polarisation behaviour of reinforcement, which are induced by long‐term application of CP. The investigations presented in this paper aim to clarify open aspects on the migration of chloride ions due to small electric fields as applied in CP of steel in reinforced concrete structures. A comparatively new method, laser induced breakdown spectroscopy (LIBS), was applied in order to determine chloride concentration profiles on laboratory specimens as one of several model parameters for a mathematical description of CP of the rear reinforcement of reinforced concrete structures. The paper concerns migration tests using non‐saturated specimens under laboratory conditions at constant voltage and the application of the experimental parameters on FEM‐calculations. The presented results suggest the conclusion that even comparably small electric fields, as applied in CP of steel in concrete, may lead to significant and sustainable reduction in chloride concentration at the surface of the reinforcement.

Lake Malawi sediment and pore water chemistry: Proposition of a conceptual model for stratification intensification since the end of the Little Ice Age

Sedimentary records of salinity indicators are largely used to reconstruct past climatic changes in lacustrine systems where chemistry is sensitive to hydroclimatic conditions. In large fresh lakes of the East African Rift such as Lakes Tanganyika and Malawi, salinity is often considered constant and other paleoclimatological proxy data are used. However, a relation between lake surface chloride concentration and hydroclimatic regime was previously demonstrated at the century scale in Lake Tanganyika. This relation is transposed to Lake Malawi on the base of similarity between hydrochemical budgets of both lakes that are computed for the whole lake and epilimnion. Whereas numerous physico-chemical difficulties make generally debatable use of lake pore water chemistry, as illustrated here by diffusion modelling, the dissolved chloride concentration profile from a core sampled in northern Lake Malawi is considered as a potential indicator of limnological–hydroclimatic condition changes for the last 200 years. A decrease in pore water chloride concentration between 1840 AD and present situation is directly associated to a metalimnetic water salinity decrease. The chronology of this event is synchronous with diatom productivity change demonstrated by Johnson et al. (2001) at the end of the Little Ice Age (LIA). A conceptual model of Lake Malawi, based on salinity, organic carbon and its “dead” watershed contribution, lake-level and productivity changes since the mid 19th century is presented. A new scenario is proposed, based on thermal stratification reinforcement at the end of the LIA. Lake productivity and chemistry depend on stratification strength, water column mixing rate and on climatic variability. During the LIA, nutrient distribution profiles were more homogeneous with depth due to the climatically (colder and drier climatic conditions than today) induced destabilisation of the mixing barrier. The productive system is then auto-supplied and does not require external silicon supply while chloride concentration is higher due to closure of the basin. Stratification has become more stable since the end of the LIA, as in nearby Lake Tanganyika where it is linked to air temperature global increase. Results demonstrated that chloride is a suitable indicator of the present and past hydroclimatic and hydrodynamic regimes. This work shows that in Lake Malawi, assessment of “dead” carbon (or old “refractive watershed carbon”) contribution to the TOC is a key parameter to set chronological frame from 14C ages.

Removal of potassium chloride from ion-exchanged solution containing potassium clavulanate by diafiltration with nanomembrane and its modeling

When an ion-exchange chromatography process is employed for the recovery of potassium clavulanate (KCA) from fermentation broth, the resulting KCA solution usually contains a large amount of KCl due to the use of a concentrated elution buffer. In this study, nanofiltration (NF) with NF200 membrane has been carried out in a diafiltration (DF) mode to remove KCl from the ion-exchanged KCA solution, and a multistage version NF model has been proposed to represent this process. In this model, the effect of temperature on clavulanate degradation during the filtration has been incorporated. For the determination of model parameters associated with NF and clavulanate degradation, separate series of experiments at different concentrations, pressures and temperatures were performed. The clavulanate rejection could be assumed to be constant with no loss of modeling accuracy based on the experimental data. The chloride rejection was represented as a function of its concentration simply by nonlinear fitting. For the estimation of solution flux, the reflection coefficient and effective volume charge density were calculated by using the Speigler–Kedem model together with the Teorell–Meyer–Sievers model. Model prediction of clavulanate and chloride concentration profiles was in good agreement with the experimental data. It was also demonstrated that KCl could be removed effectively by NF in a DF mode.

Performance of concrete in XS1, XS2 and XS3 environments

An extensive chloride-profiling programme was undertaken over an eight-year period on nine concrete pier-stems placed at a marine location to represent XS1, XS2 and XS3 environmental exposure conditions as defined in European Standard EN 206-1. The pier-stems were 2·0 m high and octagonal in plan with each vertical face 0·66 m wide and were constructed in groups of three (one each placed at the locations defined above): one group, which was used as a benchmark, represented plain Portland cement concrete; the second group had a waterproofing agent (Caltite) added at the time of mixing; and the third was treated with silane. Chloride concentration profiles were taken at a number of locations on each pier-stem, which were subsequently used to evaluate the temporal change in effective diffusion coefficient and surface chloride concentration for the different exposure conditions. In addition, it allowed assessment of the relative performance of the plain concrete, Caltite concrete and silaned concrete pier-stems with regard to chloride ingress.

Effect of the environment temperature on the chloride diffusion through CEM-I and CEM-V mortars: An experimental study

This paper documents the influence of the temperature level (5, 21 and 35 °C) on the chloride penetration through cementitious materials. Mortars based on CEM-I and CEM-V type cements are tested. Results on chloride binding, chloride diffusion coefficients together with total chloride concentration profiles after 6 months of immersion are presented. It is shown that the change of total chloride concentration profiles with the temperature is due to the change in chloride diffusion coefficients.

The relation between electrokinetics and chloride transport through cement-based materials

The objective of this study is to determine how the use of an electrokinetic technique (migration) has an impact on chloride transport through cement-based materials. Electrokinetic transport of ions is the transport of ions under the influence of an electrical current, and is also named migration. The paper emphasizes the impact of electrokinetics on the total chloride concentration profile through saturated mortar both in transient regime, and in steady state during chloride penetration, and chloride extraction. For chloride decontamination, an explanation is proposed for the different shapes of the curves representing the chloride mass flow rate and the amount of chloride extracted in time from the mortar, measured with or without an electrical current. The efficiency of the electrokinetic dechloruration is proposed in terms of amount of removed chloride.

Peat porewater chloride concentration profiles in the Everglades during wet/dry cycles from January 1996 to June 1998: field measurements and theoretical analysis

AbstractWater quality is a key aspect of the Everglades Restoration Project, the largest water reclamation and ecosystem management project proposed in the United States. Movement of nutrients and contaminants to and from Everglades peat porewater could have important consequences for Everglades water quality and ecosystem restoration activities. In a study of Everglades porewater, we observed complex, seasonally variable peat porewater chloride concentration profiles at several locations. Analyses and interpretation of these changing peat porewater chloride concentration profiles identifies processes controlling conservative solute movement at the peat–surface water interface, that is, solutes whose transport is minimally affected by chemical and biological reactions. We examine, with an advection–diffusion model, how alternating wet and dry climatic conditions in the Florida Everglades mediate movement of chloride between peat porewater and marsh surface water. Changing surface water–chloride concentrations alter gradients at the interface between peat and overlying water and hence alter chloride flux across that interface. Surface water chloride concentrations at two frequently monitored sites vary with marsh water depth, and a transfer function was developed to describe daily marsh surface water chloride concentration as a function of marsh water depth. Model results demonstrate that porewater chloride concentrations are driven by changing surface water chloride concentrations, and a sensitivity analysis suggests that inclusion of advective transport in the model improves the agreement between the calculated and the observed chloride concentration profiles. Published in 2007 by John Wiley &amp; Sons, Ltd.

Modeling of chloride diffusion in hetero-structured concretes by finite element method

With a two-dimensional structure model, the finite element method was used to simulate the chloride diffusion behavior in a heterogeneous concrete composed of two phases with distinct diffusivities, compared with its derived homogeneous medium that was given a single effective diffusion coefficient by the mean field theory. In contrast to the smooth chloride concentration profiles for the homogeneous medium, a three-dimensional concentration distribution network has been found in the hetero-structured concrete, characterized by a complicated band-like profile along the diffusion depth. Moreover, it features an undulating and narrowing width as the diffusion time and diffusion depth increase. The modeling results also manifest that the chloride diffusion in hetero-structured concretes appears to lag behind that for the homogeneous ones, showing an increasingly notable discrepancy between the two chloride concentration profiles as the diffusion proceeds. Nonetheless, such a concentration difference may be remarkably reduced when the chloride binding and time-reducing effect of diffusivity are supposed to happen within the cement paste phase of the hetero-structured concrete and its derived homogeneous medium.

Effects of Initial Surface Treatment Timing on Chloride Concentrations in Concrete Bridge Decks

In consideration of concrete cover thickness and the presence of stay-in-place metal forms (SIPMFs), research was done to determine the latest timing of initial surface treatment applications on concrete bridge decks subjected to external chloride loading before chlorides accumulate in sufficient quantities to initiate corrosion of the reinforcing steel. Chloride concentration data for this research were collected from 12 concrete bridge decks located within the Interstate 215 corridor in Salt Lake City, Utah. Numerical modeling was used to generate a chloride loading function and to determine the diffusion coefficient of each deck. On the basis of average diffusion coefficients for decks with and without SIPMFs, chloride concentration profiles were computed through time for cover thicknesses of 2.0 in. (50.8 mm), 2.5 in. (63.5 mm), and 3.0 in. (76.2 mm). The results of the work show that the average diffusion coefficient for bridge decks with SIPMFs is approximately twice that of decks without SIPMFs and that, on average, each additional 0.5 in. (12.7 mm) of cover beyond 2.0 in. allows an extra 2 years for decks with SIPMFs and 5 years for decks without SIPMFs before a surface treatment must be placed to prevent excessive accumulation of chlorides. Although the data generated in this research are based on conditions typical of bridge decks in Utah, they clearly illustrate the effect of cover depth and the presence of SIPMFs. This information may be especially valuable to bridge engineers and managers responsible for programming surface treatments on concrete bridge decks.

Prediction of chloride ingress into saturated concrete on the basis of a multi-species model by numerical calculations

A multi-species model based on the Nernst-Planck equation has been developed by using a finite volume method. The model makes it possible to simulate transport due to an electrical field or by diffusion and to predict chloride penetration through water saturated concrete. The model is used in this paper to assess and analyse chloride diffusion coefficients and chloride binding isotherms. The experimental assessment of the effective chloride diffusion coefficient consists in measuring the chloride penetration depth by using a colorimetric method. The effective diffusion coefficient determined numerically allows to correctly reproduce the chloride penetration depth measured experimentally. Then, a new approach for the determination of chloride binding, based on non-steady state diffusion tests, is proposed. The binding isotherm is identified by a numerical inverse method from a single experimental total chloride concentration profile obtained at a given exposure time and from Freundlich's formula. In order to determine the initial pore solution composition (required as initial conditions for the model), the method of Taylor that describes the release of alkalis from cement and alkali sorption by the hydration products is used here. Finally, with these input data, prediction of total and water-soluble chloride concentration profiles has been performed. The method is validated by comparing the results of numerical simulations to experimental results obtained on various types of concretes and under different exposure conditions.

Distinct developmental changes in the distribution of calcium, phosphorus and sulphur during fetal growth‐plate development

Gradients in the concentrations of free phosphate (Pi) and calcium (Ca) exist in fully developed growth zones of long bones and ribs, with the highest concentrations closest to the site of mineralization. As high concentrations of Pi and Ca induce chondrocyte maturation and apoptosis, it has been hypothesized that Ca and Pi drive chondrocyte differentiation in growth plates. This study aimed to determine whether gradients in the important spectral elements phosphorus (P), Ca and sulphur (S) are already present in early stages of development, or whether they gradually develop with maturation of the growth zone. We quantified the concentration profiles of Ca, P, S, chloride and potassium at four different stages of early development of the distal growth plates of the porcine femurs, using particle-induced X-ray emission and forward- and backward-scattering spectrometry with a nuclear microprobe. A Ca concentration gradient towards the mineralized area and a stepwise increase in S was found to develop slowly with tissue maturation. The increase in S co-localizes with the onset of proliferation. A P gradient was not detected in the earliest developmental stages. High Ca levels, which may induce chondrocyte maturation, are present near the mineralization front. As total P concentrations do not correspond with former free Pi measurements, we hypothesize that the increase of free Pi towards the bone-forming site results from enzymatic cleavage of bound phosphate.

Microstructure, Microchemistry, and Prediction of Long-Term Diffusion Behavior of Chloride in Concrete

Microstructural and microchemical features of two types of concrete are investigated employing electron and ion optical techniques. The first type is the concrete cured in seawater or normal water. The second type is concrete cured in normal water and exposed subsequently to seawater. Major constituent phases of concrete and differences in their distribution due to different curing media are identified. Chloride profiles in different concretes are evaluated using the proton induced x-ray emission technique. Diffusion coefficientD was calculated by modeling the diffusion process and comparing with measured profiles.D, thus estimated, is found to be ∼1.8×10−9 m2/s, which is higher than the reported values of ∼10−11 to 10−13 m2/s. The faster diffusion of chloride in seawater-cured concrete can be attributed to the availability of water medium in wet concrete, in the initial stages of the hydration of cement. The prediction of the concentration profile of chloride in a layer of 100 mm of 28% fly ash containing concrete over concrete exposed to seawater is carried out. For the worst scenario, analytical estimates of the concentration of chloride as a function of time at a distance of 100 mm in the fly ash containing concrete were made. The concentration profiles of chloride expected after 40 years in the fly ash-containing concrete were also estimated using diffusion coefficient values available in the literature.

Chemical stratification in thermally stratified lakes: A chloride mass balance model

In thermally stratified lakes, nutrient-enriched hypolimnion and a nutrient-depleted epilimnion is a common feature. Vertical mixing between these layers affects geochemical and biological processes. We used chloride ion as an inert tracer to model the main factors controlling the chemical stratification and to identify lake-wide mixing processes. The stratified lake is treated as two completely mixed reservoirs separated by the thermocline. Based on the long-term records of temperature, hydrochemical, and hydrological data from Lake Kinneret (Israel) and Lake Biwa (Japan), monthly hypolimnetic and epilimnetic chloride concentrations were predicted and tested against measured chloride concentration profiles. Water-volume exchange between the layers during the thermocline deepening was calculated using mass balance. We found that changes in the epilimnetic and hypolimnetic inventories of an inert tracer (chloride) correspond quantitatively to the calculated water mass exchange, and as such, reflect mixing. Our inert-tracer-approach provides a basis for an operational means of quantifying the vertical mixing process in thermally stratified lakes independently from the heat budget.