Effective Chloride Diffusion Coefficient Research Articles

Six-Year-Old Ecological Concrete in a Marine Environment: A Case Study

The durability of ecological concrete in a marine environment is of concern for the coastal and offshore construction industry. The properties of such concrete taken from a marine structure were studied. Specimens of six-year-old submerged ecological concrete were taken from a breakwater located in the East Mediterranean Sea. The specimens were analyzed for their biological carbonate deposition cover, chloride effective diffusion, carbonation, compressive strength, and mineralogy. About 57% of the surface was found to be covered by biogenic-deposited carbonates. The effective chloride diffusion coefficient and the carbonation rate were found to be reduced proportionally to the biogenic-carbonate cover, relative to the prediction by a standard model. No significant change in compressive strength was detected. Most of the aluminates were found in non-crystalline minerals. No evidence of a sulfate attack was found. In conclusion, the effect of the biological growth on the concrete surface is mainly a reduction of effective diffusion, and no negative effects were detected.

Assessment of Durability Indicators for Service Life Prediction of Portland Limestone Cementitious Systems Produced with Permeability-Reducing Admixtures

Supplementary cementing materials (SCMs) and the challenges associated with admixture compatibility and durability performance are continuous challenges for the construction industry. Utilizing SCMs has apparent benefits in reducing the carbon footprint and improving the durability performance of concrete structures. This work investigates the performance of mortars composed of Portland limestone cement, calcium carbonate, butyl stearate, and oleic acid. The effort focuses on transport properties using electrical resistivity, chloride migration, porosity, and water permeability measurements. Then, various methods based on the last parameters are compared to assess the changes in the effective chloride diffusion coefficient and the intrinsic liquid water permeability. Measurements for drying shrinkage, thermal expansion, and compressive strength are conducted to verify durability and mechanical performance. The effect of the admixture addition on the service life of a structure fully submerged in marine exposure conditions is then evaluated using Fick’s second law of diffusion and the approach described by FIB model code 34. The results indicate that incorporating calcium carbonate, butyl stearate, and oleic acid in mortar mixtures provides enhanced durability compared to plain Portland limestone cement mortars.

The role of chloride binding mechanism in the interpretation of chloride profiles in concrete containing limestone powder

The effect of limestone powder addition on the chloride binding capacity of concrete was evaluated. The results indicate that the chloride binding capacity becomes weaker as the limestone content increases due to decreased physical adsorption and chemical binding. XRD patterns indicate that adding limestone restrains the formation of monosulfate (AFm), thereby undermining the chemical binding. Thermogravimetric analyses (TGA) validate that despite limited participation of calcite in the hydration reaction, it is significant enough to change the stoichiometry of the cementitious systems and restrain the formation of Friedel's salt. The ratio between the apparent and effective chloride diffusion coefficients increases with decreasing chloride binding. A modified diffusion model was proposed based on Fick’s second law coupled with Freundlich adsorption isotherm on water-accessible pore surfaces to predict the chloride profile. The model exhibits a consistent trend that an enhanced chloride binding, higher tortuosity and lower porosity contribute to a lower chloride content.

Experimental Study on Effective Chloride Diffusion Coefficient of Cement Mortar by Different Electrical Accelerated Measurements

This study investigated the effective chloride diffusion coefficient of cement mortar with different water-to-cement ratio (w/c) under electrical accelerated migration measurement. The cumulative chloride concentration in anode cell solution and the cumulative chloride concentration drop in the cathode cell solution was measured by RCT measurement and the results were further used to calculate the chloride diffusion coefficient by Nordtest Build 355 method and Truc method. The influence of w/c on cement mortar’s chloride coefficient was investigated and the chloride diffusion coefficient under different determination methods were compared with other researchers’ work, a good consistency between this work’s results and literatures’ results was obtained. The results indicated that the increased w/c of cement mortar samples will have a higher chloride diffusion coefficient. The cumulative chloride concentration drop in the cathode cell solution will have deviation in early stage measurement (before 60 h) which will result in overestimation of the effective chloride diffusion coefficient.

Effective and Apparent Diffusion Coefficients of Chloride Ions and Chloride Binding Kinetics Parameters in Mortars: Non-Stationary Diffusion-Reaction Model and the Inverse Problem.

A non-equilibrium diffusion–reaction model is proposed to describe chloride transport and binding in cementitious materials. A numerical solution for this non-linear transport with reaction problem is obtained using the finite element method. The effective chloride diffusion coefficients and parameters of the chloride binding are determined using the inverse method based on a diffusion–reaction model and experimentally measured chloride concentrations. The investigations are performed for two significantly different cements: ordinary Portland and blast furnace cements. The results are compared with the classical diffusion model and appropriate apparent diffusion coefficients. The role of chloride binding, with respect to the different binding isotherms applied, in the overall transport of chlorides is discussed, along with the applicability of the two models. The proposed work allows the determination of important parameters that influence the longevity of concrete structures. The developed methodology can be extended to include more ions, electrostatic interactions, and activity coefficients for even more accurate estimation of the longevity.

Field Validation of Concrete Transport Property Measurement Methods.

Reinforcing steel corrosion, caused by chloride ingress into concrete, is the leading cause of reinforced concrete deterioration. One of the main findings in the literature for reducing chloride ingress is the improvement of the durability characteristics of concrete by the addition of supplementary cementitious materials (SCMs) and/or chemical agents to concrete mixtures. In this study, standard ASTM tests—such as rapid chloride permeability (RCPT), bulk diffusion and sorptivity tests—were used to measure concrete properties such as porosity, sorptivity, salt diffusion, and permeability. Eight different mixtures, prepared with different SCMs and corrosion inhibitors, were tested. Apparent and effective chloride diffusion coefficients were calculated using bound chloride isotherms and time-dependent decrease in diffusion. Diffusion coefficients decreased with time, especially with the addition of SCMs and corrosion inhibitors. The apparent diffusion coefficient calculated using the error function was slightly lower than the effective diffusion coefficient; however, there was a linear trend between the two. The formation factor was found to correlate with the effective diffusion coefficient. The results of the laboratory tests were compared and benchmarked to their counterparts in the marine exposure site in the Arabian Gulf in order to identify laboratory key tests to predict concrete durability. The overall performance of concrete containing SCMs, especially fly ash, were the best among the other mixtures in the laboratory and the field.

Phenomenological model for quantifying concrete chloride diffusion coefficient

Compressive strength and the chloride diffusion coefficient are the common and principal performance measures for designing durable concrete structures. Hence, a comprehensive and consistent phenomenological model is put forward that quantifies a concrete’s effective chloride diffusion coefficient based on the tortuosity factor, aggregate volume fraction, porosity, cement paste chloride diffusion coefficient, compressive strength, cement and cementitious material content and composition. The phenomenological model results are first shown to depict chloride ion diffusion phenomena in porous media. Experimental data reported in the scientific literature are then used to evaluate visually and statistically the accuracy and precision of the phenomenological model. The model results are found statistically equal to experimentally quantified chloride diffusion coefficient values to a 95% confidence level and possess high accuracy and precision for a wide range of concrete mixture proportions, composition and age. The model average percent error is less than the standard test method repeatability and the COV of the reproducibility. The standard error, samples mean, and R2 are found to be 0.41 × 10−12 m2/s, 1.46 × 10−12 m2/s and 0.94, respectively.

Effect of pore structures on gas permeability and chloride diffusivity of concrete

10 concrete specimens with different water-binder ratios and admixtures were manufactured to analyze the relationship between permeability and microstructure of the test concrete. The gas permeability coefficient and effective chloride diffusion coefficient of concrete were measured by Cembureau method and ASTM C1202 test respectively. In addition, the pore structure of concrete was determined by mercury intrusion porosimetry (MIP) and nuclear magnetic resonance (NMR) respectively. Results show that water-binder ratio and admixture have negligible effect on the distribution of pore size below 10 nm. Besides, the addition of admixtures can decrease the porosity of concrete effectively, except basalt fiber. Moreover, there is an obvious correlation between gas permeability (chloride diffusivity) and porosity of the test concrete. A higher proportion of pore within range of 1–100 nm can be obtained by NMR than that by MIP. The results are opposite when the pore size is >100 nm. There is a good correlation between gas permeability coefficients and contributive porosity with pore diameter of 10–1000 nm, meanwhile, chloride diffusivity is well dependent on contributive porosity with pore diameter of 100–1000 nm. The addition of admixtures will change the relationships between two global permeability coefficients and microstructure parameters of concrete.

Chloride ingress in a belite-calcium sulfoaluminate cement matrix

This paper reports an assessment of the performance of calcium sulfoaluminate-based cementitious materials in chloride-rich environments while addressing the importance that insightful mix proportioning can have on chloride ingress performance. Belite-calcium sulfoaluminate pastes and mortars were prepared at 4 different calcium sulfate to ye'elimite ratios (ranging from 0 to 2) and the properties of the matured matrix (i.e. porosity and binding capacity) were assessed. A comparative assessment was made of the effective chloride diffusion coefficient in belite-calcium sulfoaluminate mortars through commonly used migration (NT Build 492) and diffusion (NT Build 443) accelerated testing protocols. The influence of paste porosity was apparent in NT Build 492, where lower performance was noted for the low sulfate mixes. These results were in contrast with NT Build 443 observations and are attributed to the short testing period of the migration method in which the potential binding affinity of the hydrates is restricted.

Sensitivity analysis of chloride ingress models: Case of concretes immersed in seawater

Reinforced concrete structures exposed to a marine environment deteriorate as a result of chloride-induced corrosion of the steel rebars. A wide variety of models to predict chloride ingress in water-saturated concretes have already been developed to understand and predict the underlying transport processes. The majority of these models focus on the initiation period of chloride-induced corrosion in order to predict the service life of reinforced concrete structures. They require information on the concrete properties, the concrete cover thickness, the definition of corrosion initiation, etc. These models combine well-known mechanisms, i.e. diffusion of relevant ions, electrical interactions between ions, and interactions between these ions and the solid matrix. As the mechanisms to consider are well identified, the objective here is to perform a probabilistic analysis of some common models. A general framework is proposed to calculate a reliability service life for reinforced concrete structures under chloride attack in case of continuous immersion in seawater. Then a sensitivity analysis is performed in terms of the most relevant mechanisms and influencing input data. The results point out the crucial role of the concrete cover thickness, the critical chloride content and, to a lesser extent, the effective chloride diffusion coefficient. The difficulty to use the Freundlich isotherm for chloride binding is highlighted; it seems to be due to the non-linearity of the description which is still difficult to control.

Comparison of existing chloride ingress models within concretes exposed to seawater

Numerous models to predict chloride ingress within concretes for different environmental conditions (immersed in seawater, located in the tidal zone or exposed to sea spray) have already been developed. Thanks to a benchmark, the objective of this paper is to contribute to the choice of a reliable engineering model for predicting chloride ingress in the case of saturated conditions. This study focus on a comparison between various physico-chemical models which rely on different approaches to account for transport phenomena and binding of chloride ions onto the cementitious matrix. The authors draw special attention to models using a limited number of input data (3 or 4): accessible-to-water porosity ( $$\phi _{\text{w}}$$ ), effective chloride diffusion coefficient ( $$D_{\text{Cl}^-}$$ ) and one or two parameter(s) characterizing the physical binding of ions Cl−. They are determined through the analysis of two simple and repeatable experimental tests: $$\phi _{\text{w}}$$ is measured directly by hydrostatic weighing and the other parameters are fitted by inverse analysis performed of a total chloride content (tcc) profile at a given exposure time. An application of the method and a comprehensive comparison between predicted chloride profiles and experimental data (tcc profiles at other ages than the one used for the fitting and free chloride concentration profiles) have been carried out for two mortars and seven concretes exposed to laboratory or in-situ conditions. The performance of the studied models is assessed thanks to statistical tools and recommendations are pointed out for the development of new numerical models.

Influence of polymer proportion on transfer properties of repair mortars having equivalent water porosity

This study analyzes the influence of polymers proportion on the durability indicators of mortars patch repair modified with poly-ethyl acrylate styrene acrylamide (PEASA) and having similar water porosity (in the range 16, 5–18 %). To assess mortars durability, this work was based on the comparison of durability indicators (porosity, permeability, capillary absorption, effective chloride diffusion coefficient) of four repair industrial materials and one reference mortar. Results indicate that water porosity on its own is not sufficient to understand the transfer properties behavior of these materials. There is evidence that material performance depends on polymers proportion which have an important role in microstructure and pore size distribution. The use of PEASA aqueous dispersions, enabled polymer film formation to yield a monolithic matrix phase with a network structure in which the hydrated cement phase and polymer phase interpenetrate into each other. This eventually helps to improve flexural strength and durability properties of mortar repair.

Performance-based assessment of durability and prediction of RC structure service life: transport properties as input data for physical models

This paper deals with an approach based on durability indicators (DIs), intended for the assessment of the durability and the prediction of the service life (SL) of reinforced concrete structures with respect to reinforcement corrosion. The methods of assessment of the DIs, more specifically of the transport properties effective chloride diffusion coefficient and “intrinsic” liquid water permeability, are first investigated. Direct experimental methods, indirect methods based on simple analytical formulas, as well as numerical inverse analysis which involves the same physical models as used for prediction, are compared. Very good agreement is pointed out between the results obtained by the various methods for a broad range of materials. The effect of SCM, as well as of accelerated carbonation in the case of permeability, is also investigated. 1-D numerical models of moisture or ionic isothermal transport are then introduced, where the selected DIs are the main input data. Simulations carried out with the moisture transport model are compared to moisture profiles measured by gamma-ray attenuation, in order to validate the model and the input data (permeability). With regard to chloride ingress, examples of application of the multispecies transport model (saturated conditions) are provided for concentration profile prediction, in lab and in field conditions, as well as SL prediction.

Influence of cracking on chloride diffusivity and moisture influential depth in concrete subjected to simulated environmental conditions

Although Fick’s second law is always applied to predict chloride profiles in concrete due to its simple mathematical expression, it takes no consideration of cracking affects. However, concrete structures are not always crack-free, therefore clarifying the internal environment and relevant chloride diffusivity in cracked concrete is essential to predict chloride ingress since cracking always has a negative impact on concrete durability. In present work, series of experimental investigations on two coefficients (i.e., chloride diffusion coefficients and moisture influential depth) affecting chloride profiles at cracked concrete were carried out. For the investigation of chloride diffusivity, Electron Probe Micro Analysis (EPMA) was used to extract the accurate chloride concentration via area scanning, line scanning, and point scanning. In addition, specimens with two different types of mix (i.e., ordinary concrete and blast furnace slag concrete) and with two different exposed times (i.e., 30days and 60days) were tested for different surface crack patterns. Crack width investigated in present work ranges from 0.05mm to 0.20mm. Furthermore, the effective chloride diffusion coefficient for cracked concrete was calculated under the law of flux conservation by taking consideration of both crack patterns and concrete mixtures. On the other hand, for the investigation of moisture influential depth, a series of laboratory experiments with different cracking specimens were conducted to clarify the influence of external artificial weather on the relative humidity distribution in concrete crack, including periodic changing of external relative humidity and temperature, fog and rainfall simulation environments, the drying phase after precipitation.

Chloride ion penetration into mortar containing ceramic waste aggregate

In this study, the chloride ion penetration tests on mortars made of ceramic waste aggregates (CWAs) was conducted by using a silver nitrate (AgNO3) solution spray method and a rapid chloride migration test (steady-state condition). The CWAs used in the experiment are ceramic electrical insulator wastes supplied by an electric power company in Japan, which were crushed and ground to various sizes prior to the replacement of fine aggregates. The influence of the CWAs was evaluated through the tests on four series of mortar as follows: (1) mortars made of different fine aggregates, (2) mortars made of the CWA having a different range of particle sizes, (3) mortars made of the CWA at a different quantity, and (4) mortars made of the CWA at a different replacement ratio. From the experimental results, it is found that the CWA mortars are more effective in the resistance of chloride ion penetration than a typical mortar made of river sand. The depth of chloride ion penetration in the CWA mortars is decreased either when the amount of the CWA is increased or the particle size of the CWA is decreased. In addition, the effective chloride diffusion coefficient of the CWA mortar is lower than that of the river sand mortar.

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.

Multi-scale prediction of the effective chloride diffusion coefficient of concrete

The N-layered spherical inclusion theory is applied to develop a multi-scale model to predict the effective diffusion coefficient of chloride ion in concrete. The model treats concrete as four-phase composite materials consisting of matrix phase, aggregate phase, ITZ (interfacial transition zone) and their homogenization phase. With hardened cement pastes characterized by three parameters such as the porosity, tortuosity and constrictivity, the effect of the cement paste microstructures and ITZ on the chloride diffusivity in concrete is taken into account and the porosity distribution function and effective chloride diffusion coefficients of the ITZ are given in the model based on the cement particle distribution characteristics of the ITZ in concrete. To validate the proposed model, the diffusion coefficient of chloride ion by the steady-state migration test is measured on a series of mortar and concrete specimens and good agreement between the model and experiment is obtained. In addition, the model predicts that the chloride diffusivity of concrete composite materials depends on the chloride diffusion coefficient of the matrix and ITZ, volume fraction of the aggregate and ITZ, with the volume fraction of the ITZ influenced by aggregate size distribution, the volume fraction of aggregate and thickness of the ITZ.

Easy assessment of durability indicators for service life prediction or quality control of concretes with high volumes of supplementary cementitious materials

This paper investigates whether durability indicators (DIs), more specifically transport properties, can be assessed by simple methods, e.g. direct experimental methods or indirect methods based on analytical formulas, for every type of concrete. First the results of electrical resistivity and apparent chloride diffusion coefficient obtained by direct measurement on a broad range of materials, particularly on high-volume supplementary cementitious materials (SCM) mixtures, are discussed. Then, various methods, in particular methods based on these last parameters, are compared for the assessment of effective chloride diffusion coefficient and “intrinsic” liquid water permeability, including for the latter a sophisticated method based on numerical inverse analysis. The good agreement observed between the various methods points out that simple methods can allow DI assessment with sufficient accuracy. Moreover, the available values of electrical resistivity, effective/apparent chloride diffusion coefficients and “intrinsic” liquid water permeability can be included in a database. Throughout the paper, the specificities of high-volume SCM mixtures are highlighted.

Influence of initial curing conditions and exposure environments on chloride migration in concrete using electrochemical method

To investigate the influence of initial curing conditions and exposure environments on chloride ions’ migration in concrete, the specimens that were cured in different conditions and placed in several marine environments were studied. The amount of chloride ions passing through the specimen’s section was monitored in the accelerated chloride migration test. The effective chloride diffusion coefficients (D e) were calculated from the steady-state on the basis of Nernst-Planck’s equation. The results indicated that the initial curing conditions and the wet-dry interval of external environments have coupling influence on effective diffusion coefficient of chloride ion significantly. D e reflected the density and pore connectivity of concrete. The co-effects of the initial curing condition and following exposure environment should be taken into account in durability design for concrete structure located in marine environment.

AgNO3 spray tests: advantages, weaknesses, and various applications to quantify chloride ingress into concrete. Part 2: Non-steady-state migration tests and chloride diffusion coefficients

This paper forms the second part of a series devoted to the analysis of the capabilities of AgNO3 spray tests, in view of using them for various issues, within the framework of the evaluation and the prediction of chloride-induced corrosion risks. More precisely, the Maultzsch procedure (spraying of 0.1-N AgNO3 solution + K2CrO4) and the use of AgNO3 alone have been investigated on a broad range of concretes. In this second part, the feasibility of colorimetric techniques on saturated specimens cast in laboratory, after non-steady-state migration tests carried out in various conditions is discussed. Colorimetric methods have been applied to the determination of the average penetration depth. In addition, the detection threshold of these techniques has been investigated. Moreover, colorimetric methods have been applied to the calculation of apparent and effective chloride diffusion coefficients from non-steady-state diffusion and migration tests. The results then obtained have been compared to the values obtained by other types of methods.