Chloride Concentration Profiles Research Articles

Assessment of Cryogenic Coring to Preserve Vertical Distributions of Trichloroethylene and Reaction Products in an Aquitard

AbstractThere is not a clear understanding of the extent by which naturally occurring reactions can attenuate trichloroethene (TCE) and its daughter products within low permeability zones (LPZs), and addressing this knowledge gap requires advancement of methods to accurately measure in situ volatile chemical concentrations. In this study, a soil coring method that freezes the soil in‐situ (a.k.a., cryogenic coring) was utilized to measure depth‐discrete distributions of TCE and its volatile reaction products through a TCE‐impacted silty clay aquitard, and results were compared with those from adjacent soil cores taken using a conventional coring approach. Vertical concentration profiles of TCE, cis‐1,2‐dichloroethylene (DCE), vinyl chloride (VC), ethane, and methane were all compared between the two coring methods, and results indicate the two coring methods recovered statistically equivalent concentrations of volatiles across most depths of the fine‐grained cohesive clayey soil at the study site. Biotic reductive dechlorination was the dominant TCE reaction pathway at the site; several reduced gasses that are possible markers for abiotic reduction were detected, but their concentrations and intervals of occurrence were not sufficiently consistent to indicate whether they were from abiotic TCE reduction or unrelated biological processes. Overall, cryogenic coring yielded improved recovery of sand lenses compared to conventional coring, but offered no apparent benefits for improved recovery of TCE and its volatile reaction products in the low permeability aquitard material at the site.

Effect of exposure conditions on the chloride concentration profiles in a marine concrete structure, studied by means of the kernel density estimation technique and a Gaussian–Lorentzian model

The corrosion of the embedded steel due to chloride action is one of the main degradation problems limiting the service life of reinforced concrete structures in a marine environment. Modelling chloride profiles into concrete is a key factor to predict durability of structures. Experimental profiles from the harbour of a Mediterranean city are here studied fitting them to a Gaussian–Lorentzian peak model. This model is suited for the observed peak-shaped profiles, yielding descriptive transport parameters for both the convective and the diffusive zones. The parameters of the diffusive zone are found to be in agreement with the solution of the Fick’s second law of diffusion. The obtained parameters describing the profiles are statistically analysed by means of the kernel density estimation technique in order to determine how exposure conditions affect these parameters. A criterion of probability density distributions overlapping is used to draw conclusions about how exposure time, orientation respect to sea, wind, and splash affect the height and location of the chloride peak concentration, and the transport coefficients in the convective and diffusive zones of the profiles.

Coupled model on the variation of diffusion coefficient and surface chloride concentration in reinforced concrete structures over time

Durability analyses and service life estimates of structures in a marine environment can be developed through the modeling of chloride concentration profiles. However, as surface chloride concentration and diffusion coefficient vary over time, especially due to the cement hydration process, modeling chloride profiles from structures with recent degradation ages requires an adjustment for the temporal dependence of these two physical parameters. The variation of the surface chloride concentration (Cs) as a function of time tends to show an increasing asymptotic behavior, while the diffusion coefficient (D) has a decreasing asymptotic tendency. For this reason, the power function, usually used to describe the diffusion coefficient, has problems for advanced ages, while the exponential function has difficulties at recent ages. Therefore, the key issue in this problem is the rate of change of Cs and D over time. This article presents the development of a single time-dependence model to simultaneously describe the decrease in D and the increase in Cs over time. The coupled model is a piecewise-defined function, with continuity of the function and its first derivative in the transition time between recent ages and more advanced ages, defined as 10 years. To validate the new model, data from structures under natural degradation were used. The results demonstrated the applicability of the coupled model with individual adjustments of the exponent α, which implicitly represents material properties and environmental parameters. However, in the absence of sufficient information, a standard α exponent of 0.25 per year can be adopted, demonstrating a moderate to strong adherence of the coupled model to the Cs and D data over time. Three stages of temporal dependence were identified: I – up to 10 years: marked increase in Cs and decrease in D over time; II – between 10 and 25 years: decrease in the variation rate of Cs and D; and III – from 25 years: stabilization of Cs and D.

Exploring the Detection of Cl- Penetration in Portland Cement Mortars via Surface Electrical Resistivity.

Surface electrical resistivity is a non-destructive technique that is sensitive to the microstructure of hydrated cement paste and the chemical composition of the pore solution in cement-based materials. In this study, a Wenner array was used to measure changes in mortar resistivity due to chloride ion diffusion as a function of electrode separation. Specimens were made from four mortar mixtures: 100% Ordinary Portland cement and 60% cement + 40% fly ash at two water/binder ratios of 0.55 and 0.40. The specimens were subjected to unidirectional chloride ion diffusion in a 2.8 M NaCl solution for 175 days. To determine the chloride penetration depth, three methods were used: silver nitrate spraying, chloride concentration profiles via potentiometric titration, and chloride concentration profiles via inversion of the resistivity data using the RES1D software (version 1.00.09 Beta). The results showed a linear relationship between the chloride ion penetration depth obtained via inversion of the surface electrical resistivity data versus the penetration depth from colorimetry and from chloride concentration profiling (both with R2 = 0.8612). Chloride penetration changed the conductivity of the pore solution; therefore, the resistivity decreased when increasing both the chloride concentration and the penetration depth. Inversion of surface resistivity data obtained with a Wenner array permitted non-destructive determination of chloride penetration. However, these results were obtained under laboratory environmental conditions and other scenarios must be addressed for wider applications.

Chloride penetration resistance of engineered cementitious composite (ECC) subjected to sustained flexural loading

This paper presents a research on the chloride penetration behavior of engineered cementitious composites (ECC) under sustained flexural loads. Three load levels, i.e. 30 %, 60 % and 75 % of the ultimate flexural load were used. Chloride diffusion depth and concentration profile were measured 30, 60 and 150 days after the specimen was exposed to NaCl solution and compared with pre-loaded specimens. Influence of the sustained local bending stress and microcracks were investigated. It shows that under sustained loads, the relationship between the surface chloride content and maximum normal tensile stress can be described using an exponential equation. A binary model was developed to explain the correlation among the chloride ion diffusion coefficient, maximum normal tensile stress and exposure time. Changes of capillary pore structure and phase compositions were measured using mercury intrusion porosimeter and X-ray diffraction, respectively. Unlike mortar, the fiber bridging of ECC helps with limiting crack width and thus the diffusion process, and the measured results were used to explain the observed penetration behavior of ECC. It is believed that the current study provides theoretical foundation for the durable design of the ECC/concrete composite structure.

New semiempirical temporal model to predict chloride profiles considering convection and diffusion zones

Chloride ions are primarily responsible for reinforcement corrosion in concrete structures in the marine environment. Thereby, analyses regarding chloride penetration into concrete are fundamental for service life estimates, in which the chloride concentration profiles provide quantitative information for prediction models. However, the conventional modeling method based on the solution of Fick's second law of diffusion usually only fits the diffusion profile zone and does not represent the convection zone. Therefore, this article shows a new model for complete chloride profile modeling. The semiempirical double exponential model was developed by approximating Fick's second law using the finite difference method and validated with chloride profiles from structures under natural degradation for more than 40 years. The double exponential model proposed can fit in the two profile zones, showing higher efficiency than Fick's model, and stands out for expressing the variation in chloride peak depth over time.

Time and Crack Width Dependent Model of Chloride Transportation in Engineered Cementitious Composites (ECC).

This paper aims to develop a chloride transport model of engineered cementitious composites (ECC) that can consider the influence of both exposure time and crack width. ECC specimens with crack widths of 0.1 mm, 0.2 mm and 0.3 mm were soaked into NaCl solution with periods of 30, 60, 90 and 120 days. The free chloride content profile was measured and used for the development of the transport model. Regression analysis was applied to build the time and crack width dependent models of apparent diffusion coefficient and surface chloride content. The results show that the crack width has significant influence on the free chloride concentration profile when it is above 0.2 mm and the time-dependent constant n decreases linearly with the crack width. The chloride transport model was obtained by subscribing the models of apparent diffusion coefficient and surface chloride content into the analytical solution of Fick’s second law. The model was further validated with the experimental results, showing a deviation within 20%. The findings of the presented study can enhance the current understanding on the chloride transportation in ECC.

Modelling of Chloride Concentration Profiles in Concrete by the Consideration of Concrete Material Factors under Marine Tidal Environment

The corrosion of reinforcement induced by chloride ions is one of the most significant causes of durability deterioration for reinforced concrete (RC) buildings. The concrete material factors, including the water-to-cement ratio (w/c) of concrete, as well as the content, shape, particle grading, and random distribution of coarse aggregate embedded in mortar, have a marked effect on chloride transport performance within concrete. However, comprehensive consideration for the effects of both w/c and coarse aggregate performances on chloride diffusion characteristics in concrete is scarce, especially regarding the chloride diffusion model of concrete. In this paper, an indoor exposure experiment exploring chloride ions intruding into mortar and concrete specimens with w/c = 0.4, 0.5 and 0.6 was carried out, in order to acquire the chloride diffusion parameters for concrete three-phases composites. Based on the numerical algorithm of random generation and placement of two-dimensional random convex polygon coarse aggregate, mesoscopic numerical models for concrete, considering various coarse aggregate contents as well as grading, were established. Using the numerical simulation method of finite element analysis for chloride transport in cement-based materials, which can replace some of the exposure tests, the influences of w/c, coarse aggregate content and grading on chloride diffusion performance in concrete mesoscopic models were systematically probed. According to the Fick’s second law, a chloride diffusion model by the consideration of w/c, volume fraction of coarse aggregate (VFCA), and maximum size of coarse aggregate (MSCA) was developed to assess the chloride concentration profiles in concrete under arbitrary w/c, coarse aggregate content, and coarse aggregate grading conditions. Certainly, the precision accuracy for this proposed chloride diffusion model was validated. The research results can provide theoretical support for chloride erosion behavior and structural durability assessment of concrete with different mix proportions.

Nonlinear regression using Gaussian-Lorentzian functions to empirical modeling of convective-diffusive chloride transport in concrete

Reinforcement corrosion due to chlorides action is the main problem regarding the durability of reinforced concrete structures present in the marine environment. Fick's second law of diffusion is used to model chloride concentration profiles in concrete for service life analysis, however, the material's properties, allied to environmental characteristics, create, close to the concrete surface, a zone where diffusion is not the chlorides transport mechanism, but also convection. Fick's second law of diffusion neglects the convective effect resulting in a large discrepancy between modeled and measured data, affecting the service life modeling of field marine structures. This study proposes an empirical chloride transport model, contemplating the convection-diffusion zones, through two Gaussian–Lorentzian functions using nonlinear regression in chloride profiles obtained from field structures located in different marine aggressive zones exposed to the marine environment for more than 40 years. The parameters of the two functions were interpreted in order to represent the physical perspective of the convective/diffusive process of chlorides penetration in reinforced concrete field structures for realistic and assertive modeling. The results showed that chosen functions can qualitatively and quantitatively describe the chloride transport in filed concrete structures, presenting better results than methodology based on Fick's second law of diffusion.

Experimental and theoretical investigation of chloride ingress into concrete exposed to real marine environment

Chloride-induced corrosion is a critical issue that influences the durability and mechanical performance of reinforced concrete (RC) structures exposed to marine tidal and splash environments. This paper presents an experimental and theoretical investigation on the chloride transport behavior in concrete exposed to an aggressive marine environment for up to 720 days. Field exposure tests were performed in marine tidal and splash zones, and free chloride concentration profiles for different types of concrete after several exposure times, i.e. 90, 180, 360 and 720 days, were obtained. The effects of the water-to-cement ratio, binder type, exposure environment and exposure time on the time dependency of the chloride diffusion coefficient (D) and surface chloride concentration (Cs) were analyzed and discussed. Based on the obtained results, a modified time-dependent prediction model of chloride ingress into concrete was established and validated by considering the time-dependency effect of material and environmental factors. The results indicate that the comparisons of the predicted chloride profiles using the developed time-dependent prediction model were in good agreement with the results of the real marine exposure test.

Reinforced Concrete Structure Performance in Marine Structures: Analyzing Durability Indexes to Obtain More Accurate Corrosion Initiation Time Predictions.

This paper presents a comparison of six index properties collected during durability inspections of five Mexican seaports. Typical durability indicators such as compressive strength, saturated electrical resistivity, ultrasonic pulse velocity, percent total void content, capillary porosity, and chloride concentration profiles were analyzed to obtain empirical correlations with the non-steady-state chloride diffusion coefficient. These indices were compared to determine correlation coefficients that are the most important for obtaining better corrosion initiation forecasting. Two models of corrosion initiation time (ti) were used: Fick’s second law of diffusion and the reported UNE-83994-2 (Spanish Association for Standardization, UNE) in which electrical resistivity was used to calculate concrete service life. The data from both models were cleaned using correlated variables, and the initial variables were compared with ti. The main result achieved was the verification of the feasibility of using correlations of variables to clean unnecessary data in order to calculate ti. Additionally, electrical resistivity was identified as one of the main durability indexes for in-service concrete structures exposed to marine environments. This is important because electrical resistivity is a non-destructive and reliable test that can be measured both in the laboratory and in the field very easily.

Exposure duration and sub-zero temperature effects on concrete chloride diffusion decay index and binding

Accurate prediction of corrosion initiation period and service life of reinforced concrete structures requires accurate determination of their chloride diffusion coefficient and binding capacity. Temperature and exposure duration affect these properties, but there is paucity of knowledge regarding the effects of long-term exposure to sub-zero temperatures. Hence, the effects of sub-zero temperature, T, and exposure duration, t, on the chloride diffusion decay index, m, and binding in ordinary Portland cement concrete are investigated. Non-steady natural diffusion tests are conducted at + 5, 0, −5 and −15 °C for 3, 6, 12 and 18 months, and at the end of each period, the total and free chloride concentration profiles are determined. The index m is found to vary over a wide range, it being directly proportional to T and inversely to t. It drastically deviates from the commonly assumed value of 0.2 in the literature. Chloride binding is found to obey the Freundlich isotherm. The coefficient α of the isotherm equals 1.0 ± 0.16 and is only slightly dependent on T or t while its exponent β varies from 0.178 to 0.502, without exhibiting a systematic relationship with either parameter. Binding is noticed to increase with drop in temperature for the first three months of exposure, but over longer exposure durations, no systematic relationship is observed.

Effect of polyethylene glycol on chloride binding in mortar

As a widely used chemical admixture, polyethylene glycol (PEG) is often added to concrete as a self-curing or shrinkage-reducing agent. PEG with a low molecular mass can inhibit the corrosion of chloride by increasing the viscosity of the pore solution. The chloride binding capacity of the cement matrix significantly affects the service life of reinforced concrete owing to its high correlation with the concentration of free chloride. However, the influence of PEG on the chloride binding capacity of cement-based materials remains unclear. Through chloride concentration profiles, the assessment of solid phase content based on the TGA/XRD/reference intensity ratio method, and SEM morphology analysis, this study reveals the influence of PEG on chloride binding in mortar. The addition of PEG significantly reduced the chloride binding capacity of the cement matrix. Complexing Ca2+ on the surface of calcium silicate hydrate (C-S-H), to occupy the adsorption sites of chloride, reduces the physical adsorption capacity and the chemical binding ability of the matrix by inhibiting the conversion of ettringite (AFt) to monosulfoaluminate (AFm). Moreover, the addition of PEG spheroidizes C-S-H and reduces its particle size, leading to loose packing of C-S-H in the mortar. Thus, the findings of this study suggest that when PEG is used in cementitious materials, caution and corresponding measures are needed to optimize its impact on durability.

Chloride Ingress into High-Performance Concrete Containing Graphene Oxide Nanoplatelets and Ground Granulated Blast Furnace Slag under Different Conditions of Water Pressure and Temperature

In this study concrete samples were made by addition of 0.1wt.% Graphene Oxide (GO) and 50wt.% Ground Granulated Blast Furnace Slag (GGBFS). Tests on mechanical and chloride permeation properties were conducted. Concrete samples exposed to pressurized 3.5% NaCl aqueous solution under time and temperatures. The water pressure was at 0.1, 0.3 and 0.7 MPa. The chloride concentration profiles at different conditions were measured. The results show that the addition of 0.1 wt.% GO and 50wt.% GGBFS increased the compressive strength of concrete sample by 19.9% during 28 days and 17.6% during 90 days compared to ordinary concrete sample. Concrete with a combination of 0.1wt.% graphene oxide and 50wt.% granular slag had an increase in flexural strength of 15% during 28 days and 13.6% during 90 days. A high reduction in electrical conductivity from 4012C to 1200C was observed for 90-days cured concrete containing GGBFS and GO compared to the ordinary concrete. Chloride ion content was substantially enhanced by increase in water pressure and exposure time. The convection-diffusion coupling is the main mechanism of the transfer of chloride ion in concrete in this research. The mix with 0.1wt.% GO and 50wt.% GGBFS was shown considerable performance on chloride penetration in concrete. This admixure reduced the chloride penetration by up to 17.6% in 90 days compared to ordinary concrete. Chloride ion penetration is curtailed when GO and GGBFS are added to ordinary concrete. Pozolanic reaction effects in concrete leading to the filling of the pores are factors in the proposed curtailment mechanism.

Chlorine isotope data of chlorides challenge the pore fluid paradigm

In order to examine the seawater-seafloor sediment interactions that influence the chemical composition of seawater through time, we examined hundreds of pore fluid geochemical analyses from 13 clay-rich sedimentary successions drilled by the ODP-IODP. Chemical trends such as monotonous increases in Ca2+, and decreases in Mg2+ and δ18O with depth are traditionally interpreted to result from water-rock interaction. In this view, the release of Ca2+ into fluids and the uptake of Mg2+ and 18O mainly results from the formation of low-temperature clays in the sediment and within underlying basalts. Chloride concentration profiles and isotopic compositions, however, suggest that different processes may influence pore water geochemistry. The data examined here show relatively constant chloride contents but with a systematic decrease in δ37Cl of chlorides with depth from 0 permil (the seawater value) down to −8.5 permil. The δ37Cl data are highly correlated with δ18O (with δ18O down to −5.7 permil).The δ37Cl-depletions of pore fluid chlorides are found in all studied sedimentary piles regardless of tectonic or sedimentary history. These trends cannot be explained by water–rock exchange reactions because minerals formed at low temperature have Cl contents that are too low to compensate for δ37Cl depletions observed in pore fluids. Accordingly, we hypothesize that fluid-specific processes are responsible for the δ37Cl-depletions of the fluids and that δ37Cl-enriched chlorides were expelled out of the sediments into the ocean. After reviewing the fluid-specific processes that are known to change the chlorine isotope ratios in chlorides, we rule out diffusion and gravitational isotope fractionations of chlorides could generate this isotope pattern. The flow of a δ37Cl -depleted fluid from the underlying basaltic basement into the sediments could explain the δ37Cl data. But the mechanism that produces depletion in δ37Cl of the fluid remains unknown. It cannot be chloride exchanges between fluids and rocks.Here we show that compaction-induced ion filtration of chlorides through clay-rich membranes can produce the observed pore fluid δ37Cl-depletions, with isotope fractionation factors ranging from 1.000 to 1.008 between the chlorides of the expelled fluid (the permeate) and those of the residual fluid (the retentate). We find that smectite-rich sediments are associated with higher isotopic fractionation factors, while illite/chlorite-rich sediments are associated with intermediate values and with clay-poor sediments associated with lower values. This suggests that chlorine isotope fractionation might be controlled by surface charge associated with specific clay minerals. Our calculations show that compaction-induced filtration has the capacity to produce 18O-depletion for oxygen isotope fractionation factors between the expelled fluid and the retentate ranging from 1.000 to 1.005. 18O-enrichment in the expelled fluid is in agreement with the experimental data of Haydon and Graf (1986). Overall, although further experimental work on both chlorine and oxygen isotopes is certainly needed, the results of this study indicate that ion-filtration should be considered as a potential mechanism for fractionating isotopic species in sediment pore waters, particularly for oxygen isotope ratios whose variations are often commonly attributed to water–rock exchange.

Interactions between deep formation fluid and gas hydrate dynamics inferred from pore fluid geochemistry at active pockmarks of the Vestnesa Ridge, west Svalbard margin

Seafloor seepage sites along the Vestnesa Ridge off west-Svalbard have been, for decades, a natural laboratory for the studies of fluid flow and gas hydrate dynamics along passive continental margins. The lack of ground truth evidence for fluid composition and gas hydrate abundance deep in the sediment sequence however prohibits us from further assessing the current model of pockmark evolution from the region. A MARUM-MeBo 70 drilling cruise in 2016 aims to advance our understanding of the system by recovering sediments tens of meters below seafloor from two active pockmarks along Vestnesa Ridge. We report pore fluid composition data focusing on dissolved chloride, stable isotopes of water (δ18O and δD), and the isotopic composition of dissolved boron (δ11B). From one of the seepage sites, we detect a saline formation water with two layers where gas hydrates were recovered. This saline formation pore fluid is characterized by elevated chloride concentrations (up to 616 mM), high B/Cl ratios (9 × 10−4 mol/mol), high δ18O and δD isotopic signatures (+0.6‰ and +3.8‰, respectively) and low δ11B signatures (+35.0‰), which collectively hint to a high temperature modification at great depths. Based on the dissolved chloride concentration profiles, we estimated up to 47% of pore space occupied by gas hydrate in the sediments shallower than 11.5 mbsf. The observation of bubble fabric in the recovered gas hydrates suggests formation during past periods of intensive gaseous methane seepage. The presence of these gas hydrates without associated positive anomalies in dissolved chloride concentrations however suggests that the decomposition of gas hydrate is as fast as its formation. Such a state of gas hydrates can be attributed to a relatively low methane supply transported by the saline formation water at present. Our findings based on pore fluid composition corroborate previous inferences along Vestnesa Ridge that fluids sustaining seepage have migrated from great depths and that the variable gaseous and aqueous phases through the gas hydrate stability zone control the distributions of authigenic carbonates and gas hydrates.

Salt and water profiles in surface dry-salting goat’s cheese during ripening

In order to determine the evolution of sodium chloride and water distribution profiles, surface dry-salting goat cheese was analyzed during a four-week ripening period. The concentration profiles of sodium chloride and water were analyzed according to the height and diameter of the cheese pieces and the response surface analysis was applied for the interpretation. Water distribution was higher on the outside of the pieces until the second week of ripening due to water movement caused by osmotic pressure gradients after NaCl uptake, after which there was surface dehydration. In the sodium chloride profile there was an initially rapid salt uptake by inward diffusion in the surface layers, which decreased as ripening advanced. Although the cheeses were turned over regularly, the salt and water distributions were unequal on the top and bottom surfaces in the early stages and vertical distribution was favored due to the gravitational effect. At the end of the study period the concentration of NaCl in the vertical direction was in equilibrium, while small differences persisted in the horizontal direction. The prediction of the evolution of the proposed models indicates that equilibrium of NaCl concentration would be reached after 35 days ripening.

Combined impact of carbonation and crack width on the Chloride Penetration and Corrosion Resistance of Concrete Structures

Chloride-induced corrosion of steel rebar embedded in concrete is one of the major concerns influencing the durability of reinforced concrete structures. It is widely recognized that the carbonation in concrete affects the chloride diffusivity and accelerates chloride-induced reinforcement corrosion. The service load-related cracks also have a dominant influence on reinforcement corrosion. This study aims to investigate the potential impact of concrete carbonation on the chloride penetration resistance, and the rate of corrosion, in RC structures subjected to service-related cracks, which is not yet fully understood within the literature. The experimental programme involves casting concrete prisms (100 × 100 × 500 mm) with different water-cement ratios of 0.4, 0.5 and 0.6 and with four different crack width ranges (0, 0.05–0.15 mm, 0.15–0.25 mm and 0.25–0.35 mm), developed through flexural loading of prisms. These samples were exposed initially to accelerated carbon dioxide (CO2) environment and then exposed to the accelerated chloride environment. Carbonation depth, chloride penetration, and the degree of corrosion (using half-cell potential and linear polarization resistance) were experimentally measured. The results indicated that (i): The depth of carbonation increases with the increase in crack width and w/c ratio, (ii) chloride penetration depth and chloride concentration profile in concrete structures increases significantly due to the influence of carbonation and (iii) half-cell corrosion potential and linear polarization resistance increases significantly when carbonated concrete samples are exposed to the chloride environment relative to the uncarbonated concrete samples.

High precision paleosalinity determination from measured porewater density

We have developed a density-based method for determining porewater salinity that can be performed shipboard on small volume samples with greater efficiency and precision than the currently available shore-based chloride titration technique. This approach is based on a recently developed water column method that determines salinity at the precision of a conductivity measurement through density measurements and the seawater thermodynamic equation of state. Diagenesis causes deviations in porewater composition from standard seawater values, affecting the density salinity relationship, that we correct for through precise measurements of each ion's concentration before converting measured density to chloride concentration. We account for the diffusive change in porewater chloride that occurs over time independent of diagenesis by optimizing diffusion modeled, sea-level determined bottom water chloride as a function of time to measured modern porewater and converting the best fit to salinity.We applied our density method to porewater samples extracted from adjacent long cores collected from the deep western North Atlantic, determining Last Glacial Maximum (LGM) bottom water paleosalinity in a region critical to understanding deep water mass distribution. High uncertainty is associated with current LGM bottom water salinity characterizations and their implications for LGM overturning circulation and climate. Density was determined to a precision of 2.3 × 10−6 g/mL, which translates to a relative uncertainty of 0.03% for LGM salinity. We compare the high precision chloride concentration profiles determined using our method to profiles determined from chloride titrations of parallel samples. Salinity change at our site between the pre-industrial and LGM is 3.07 ± 0.03 % and 3.65 ± 0.06 % when determined from density and 2.96 ± 0.12 % and 1.96 ± 0.21 % when determined from titrated Cl− for the two co-located cores analyzed. This is consistent with nearby deep Atlantic paleosalinity data (Adkins et al., 2002) and global sea-level-change determined salinity change (Clark and Mix, 2002). By comparing these uncertainties we demonstrate that porewater salinity can be determined to a higher precision and with increased reproducibility through our density protocol compared to titration-determined salinity. Application of our shipboard method at further locations will increase the resolution, precision, and accuracy of available LGM bottom water salinity reconstruction, improving the characterization of glacial deep water masses and overturning circulation.

Assessment of the Coupled Transport-Degradation Model for Concrete using Smart Sensors

The primary objective of this paper is to assess model-based simulation for the coupled transport-degradation behavior of concrete using smart sensing technologies and experimental investigations. Twenty humidity and temperature sensors were installed inside five cylindrical cement mortar specimens (120 mm diameter and 160 mm height) prepared with different water-cement ratios and aggregate volume fractions. The mortar specimens were then exposed to 8% sodium chloride solution on the specimen top surface and placed in an environmental chamber with programmable freezing and thawing cycle. Model-based simulations were obtained for the temperature and humidity variations with time, and the chloride concentration profiles and compared with the sensor and experimental measurements. The comparison shows that the temperature, relative humidity and chloride concentration predicted by the model had the same general trend of the sensor and experimental measurements, but the model underestimates their values. Validating model-based simulations is an essential step towards the integration of model-based simulations and sensors technologies for the structural health management of civil structures.