Chloride Transport In Concrete Research Articles

Influence of hydraulic pressure on pore structure evolution and chloride transport in concrete

To study the influence of hydraulic pressure on pore structure evolution and chloride transport behavior in concrete, the mass transport depth, chloride concentration, and pore characteristics of specimens with different water-cement ratios were investigated using silver nitrate spraying, potentiometric titration, the mercury intrusion porosimetry (MIP) method, N2 adsorption method, and laser confocal microscopy. The results showed that chloride concentration increases as the hydraulic pressure and the water-cement ratio increase. As this hydraulic pressure increases, the difference between water and chloride ion transport distinctive characteristics becomes conspicuously pronounced, extending from 5.2 mm to 25.4 mm in distance. The hydraulic pressure changes the pore structure of the concrete, leading to a surge in the specific surface area, larger porosity, and average pore diameters. Notably, ink-bottle-type pores emerge prominently and the proportion of fine mesopores and capillary pores markedly rises after the application of hydraulic pressure. Furthermore, a relationship between chloride diffusion coefficient and hydraulic pressure is suggested. A relationship between the modified permeability coefficient and hydraulic pressure is constructed based on the mesoporous contribution β to express the hysteresis effect of chloride.

Experimental and Numerical Study on Chloride Transport in Unsaturated Concrete: Highlighting Temperature, Humidity, and Mineral Admixtures.

Chloride transport within concrete is critical for the durability of reinforced concrete structures; however, its diffusion under the coupling action of temperature and humidity has not been fully comprehended. Therefore, in this work, the coupling effects of temperature, relative humidity, and mineral admixtures on chloride transport in concrete were investigated through experimental and numerical simulation work. The results show that the chloride diffusion coefficient decreases with the decreased temperature and growth of relative humidity; however, the chloride concentration on the concrete surface is increased with the growth of temperature and relative humidity. Moreover, compounding about 15% fly ash (FA) and 30% granulated ground blast furnace slag (GGBS) to replace the cement is the most beneficial for improving the antichloride capacity of concrete, considering also the strength. In addition, the numerical simulation considering the coupled effect of temperature and relative humidity of chloride transport in concrete has good agreement with that of experimental results.

Mesoscopic characteristics and spatiotemporal variability of chloride transport in concrete

Chloride-induced corrosion is the leading cause of structural performance deterioration and life decay in marine environments. This paper delves into the mesoscopic characteristics and spatiotemporal variability of chloride transport in concrete. We conducted extensive mesoscopic simulations to reveal the effects of ITZ and aggregate volume fraction, morphology, size, and particle quantity on chloride transport. We identified the probability characteristics of chloride concentration and diffusion coefficient based on statistical analysis of the mesoscopic simulation results. We proposed a novel probabilistic framework and predictive model for chloride diffusion coefficients incorporating aggregate parameters like volume fraction and particle size. The findings of this study demonstrate that the chloride transport shows noteworthy spatiotemporal variability; the aggregate size effect, aggregate particle quantity effect, and the local effect of large aggregates are all significant characteristics of the chloride transport in addition to the pre-discovered dilution effect, tortuosity effect, and ITZ effect. The chloride diffusion coefficient approximately follows a log-normal distribution, whereas the chloride concentration roughly follows a normal or log-normal distribution. The findings in this work are instrumental in predicting the probabilistic chloride transport and service life of reinforced concrete structures.

Stray current induced ITZ effect on chloride transport in concrete

Understanding the influence of interface transition zone (ITZ) on chloride migration characteristics in concrete under coupled stray current and high hydraulic pressure is essential to solve the durability problem of ultra-deep buried infrastructures (40 m-100 m). Herein, an advanced test system is developed and the chloride migration characteristics of deeply buried concrete is comprehensively investigated. Specimens were casted with the same aggregate volume content but different aggregate size distribution. The ITZ between aggregate and cement matrix was measured from BSE (back scattered electron imaging) images, and the ITZ thickness was measured by Vickers hardness. The silver nitrate spray was used to determine the chloride migration front, and the effective diffusion coefficient was calculated. The results showed the concentric expansion and overflow method based on BSE images were effective ways to determine ITZ porosity distribution. The significant increase of ITZ thickness and porosity on concrete reaction surface under stray current environment was observed and defined as “stray current induced ITZ effect”, which was considered to be the fundamental reason for the distinct differences in chloride migration depth and effective diffusion coefficient of specimens with different aggregate gradations.

Reusing thermoactivated construction waste spoil as sustainable binder for durable concrete: Microstructure and chloride transport

Construction and demolition waste is predominantly comprised of construction spoil. However, the proper recycling of this construction spoil in a manner that maximizes its value has historically received insufficient attention. Therefore, the objective of this study investigated the micro-structure and chloride transport of cement concrete including thermoactivated construction spoil powder (CSP) as a substitute for cement. The results highlights that the un-treated CSP consisted of massive inert components, and active metakaolin and amorphous components were generated in thermoactivated CSP after 800–1200 ℃ activation treatment. Mixing un-treated CSP negatively impacted the micro-structure and strength development of concrete, but the thermoactivated CSP blended paste had improved micro-structure and better strength than the un-treated CSP blended paste. Incorporating un-treated CSP raised the chloride transport in concrete. At the constant replacement ratio of CSP, the thermoactivated CSP blended concrete had lower chloride transport than the un-treated CSP blended concrete, and decreasing the particle size of thermoactivated CSP could further decline the chloride transport in thermoactivated CSP blended concrete. The concrete with 1200 ℃-activated CSP even had lower chloride transport than the reference concrete. The mix of un-treated CSP up to 30% reduced the chloride binding capacity of concrete, but the thermoactivated CSP blended concrete had superior chloride binding capacity to the un-treated CSP blended concrete. Particularly, the concrete with 20% thermoactivated CSP and 10% active metakaolin/silica fume had similar strength and lower chloride transport than reference concrete. By optimizing the thermoactivation temperature, replacement ratio, and particle size of CSP, it was possible to prepare a durable concrete with low chloride transport.

Estimation of safe cover thickness to steel reinforcement in coastal structures addressing several tidal stations

Corrosion of steel in reinforced and prestressed concrete members exposed to a marine tidal zone is a serious durability problem. This study presents a methodology for rationally estimating the safe cover thickness for steel in concrete structures exposed to the tidal zone. The proposed methodology was implemented for the case of six Indian coastal stations using 100-year-long simulations of chloride transport in concrete. Real-time meteorological and tidal height data were used for simulating the model boundary conditions. Using simulated results of chloride threshold depths (CTDs), safe cover thickness to steel was assessed. Estimated safe cover thicknesses to steel across coastal stations differed significantly (25–30 mm), indicating a need for corrosion vulnerability zonation of coastlines. Conventionally used tide models were improved by superimposing with an annual component of astronomical tides, which expanded the range of wet-dry regimes simulated by the tide models. The study also compared the chloride ingress predictions from the modified tide models with those from real tides. The superimposed tide model was found to be a better approximation of real tides than the diurnal tide model. The modified tide models very well simulated chloride ingress around the critical sections in the tidal zone.

Evaluation of Concrete Bulk Resistivity as the Key Performance Index for Chloride Transport in Concrete and Rate of Hydration

Evaluation of Concrete Bulk Resistivity as the Key Performance Index for Chloride Transport in Concrete and Rate of Hydration

Numerical Modeling of Chloride Transport in Concrete under Cyclic Exposure to Chloride.

Concrete structures under cyclic exposure to chlorides entail a higher risk of embedded steel corrosion along with accelerated ionic ingress from the environment. This study proposes a coupled transport model considering moisture and chloride distribution in concrete to investigate the influence of a cyclic exposure condition on chloride penetration. In this model, pore size distribution to quantify the effective pore space for moisture and chloride mobilizations was determined to establish the governing equation for chloride transport through non-saturated concrete. From the simulation results, the rate of chloride penetration increases with decreasing ambient humidity levels due to the enhanced chloride convection. Finally, the coupled transport model was verified by comparing in-situ data, showing reasonable correlations with 0.83 and 0.93 of determinant coefficients for 22 and 44 years of exposure, respectively, while those obtained from LIFE 365 were much lower.

Revealing the nature of concrete materials using soft computing models

The durability of materials has long been a topic undergoing intense study in civil engineering. This paper used a novel approach to foster current research in two aspects: identifying dominant concrete properties and simulating chloride transport in concrete. Machine learning methods have proven to have remarkable abilities to approximate complex functions, which provides a potential tool for realizing the above ideas. This paper used deep neural networks to identify dominant concrete parameters and simulate the transport process by integrating physical constraints into models. Results showed that deep neural networks combined with physical constraints could effectively identify material properties with high accuracy (relative error <1%) and simulate the aggression of chloride. This study also demonstrated that machine learning models could be interpretable. In addition, this paper also explored the influence of time intervals of detection datasets, the size of datasets, and the noise in datasets (−5%–5%) on the convergence of identification. Results showed that short time intervals and big datasets could accelerate convergence while the noise in datasets had negligible influences on this method. In addition, with exact physical constraints, this method could predict the performance of materials without the assistance of any dataset.

Effects of coupled heat and moisture and load damage on chloride transport in concrete

This paper presents thoroughgoing research on chloride transport in damaged concrete. The effects of temperature and temperature gradient on chloride transport were investigated, along with the effects of relative humidity, humidity gradient, concrete damage and exposure time. The higher the temperature and the greater the humidity gradient were, the quicker the chloride transport was. Moisture transport increased as concrete damage increased, while chloride transport decreased incrementally. Considering the effect of coupled heat and moisture on chloride transport in concrete, a chloride transport model was established and verified by experiments. Chloride profiles in damaged concrete were related to temperature, temperature gradient, relative humidity and humidity gradient. The chloride attack rate decreased with increasing concrete damage and exposure time. Hence, coupled heat and moisture as well as concrete damage had significant effects on chloride transport in damaged concrete, and the effects of concrete damage on chloride transport should be considered when determining chloride profiles in damaged concrete.

Numerical model of the effect of water vapor environment on the chloride transport in concrete

Chloride ions are known as one of the most crucial factors for rebar corrosion in reinforced concrete (RC) structures exposed to marine environments under drying-wetting cycles. In this condition, the chloride ion content in unsaturated concrete will change under the coupled effect of diffusion and capillary suction. This study simulates the atmosphere zone of the marine environment to explore the law of the chloride transmission behavior under the context of constant temperature and humidity. To analyze the effect of different drying-wetting ratios on the chloride ion profile in the concrete by conducting the dry-wet cycle tests. It is found that the most unfavorable drying-wetting ratios for RC structures in this study is 1:5.5. A finite element numerical model of chloride ion transmission based on Fick’s Ⅱ law was established by COMSOL Multiphysics. It can be used to predict the range of concrete surface chloride ion concentration, and dynamic change of the distribution of chloride ion concentration inside the RC structures under different drying-wetting cycles over time. The comparison of experiment data and simulation results verify that the chloride diffusion prediction model has a good correlation.

Combined Effect of Stray Current and Sustained Compressive Loading on Chloride Transport in Concrete

As with the leakage of stray current in the surrounding medium, the chloride transport in concrete is influenced by the stray current and loading of the subway structure. This paper presents the results of the experimental study on the chloride transport properties of concrete under the combined action of stray current and sustained compressive loading. First, an experiment was setup to explore the chloride transport in the subway structure as the concrete specimen embedded with steel under test current and study the influence of the existence of steel on the chloride transport profiles in concrete under stray current. Then, to investigate the combined effect of stray current and loading on the chloride transport properties, an improved experiment was designed with stray current and sustained compressive loading. The chloride transport profiles were measured, respectively, subjected to different stray currents and compressive stress levels. The experimental results indicated that stray current and sustained compressive loading have a significant influence on the chloride transport properties of concrete, and the loading threshold existed as the turning point of the chloride transport rate. Based on the experimental data and migration theory, the prediction model of chloride transport in concrete under stray current and sustained compressive loading was established and verified by the experimental measurements, and the steel corrosion-induced cover cracking was studied, and the comparison indicated that the numerical results were consistent with the experimental results.

Reliability analysis of corrosion initiation in reinforced concrete structures subjected to chlorides in presence of epistemic uncertainties

This paper presents a methodology for assessing the corrosion initiation in reinforced concrete (RC) structures subjected to chlorides, with a focus on the influence of epistemic uncertainties inherent to input parameters. Epistemic uncertain parameters were modeled using fuzzy probability theory. The chloride penetration was modeled using a finite element solution of the coupled heat transfer, moisture and chloride transport in concrete. The environmental conditions were modeled using a stochastic process. The reliability analysis was undertaken using a hybrid fuzzy Monte Carlo simulation. As an illustration, the durability of concrete basins of a newly constructed waste water treatment plant, with respect to reinforcement corrosion, was examined. The time to corrosion initiation was found to approximately follow a generalized extreme value distribution with fuzzy parameters. The stochastic modeling of exposure conditions accelerated the corrosion initiation. The time to corrosion initiation is highly sensitive to the epistemic uncertainty in the threshold chloride level in concrete. Reducing this uncertainty will result in an important improvement in accuracy. The proposed method is suitable for durability assessment of recent RC structures with little or no available performance data.

Chloride transport behavior in bending-shear section of reinforced concrete beam under combined effect of load and environment

This paper investigated the combined effects of different sustained loads and environmental conditions on chloride transport behavior in bending-shear section of reinforced concrete beam. It also compared the chloride transport pattern between bending-shear section and pure bending section based on published literatures. In this study, the tested reinforced concrete beams were subjected to 10%, 16%, 22% and 28% of ultimate bending load using spring-loaded system. For each load, the chloride content was measured on different depths of two specimens under chloride immersion and drying-wetting cycle conditions for 60 days, respectively. The results show that for the given depth and load, the specimens under drying-wetting condition had higher chloride content than those under immersion. The drying-wetting condition facilitated the chloride transport in concrete. The restrictive effect of depth on chloride transport in tension zone was larger than in compression zone. Experimental condition is the most effective factor on chloride transport in compression zone, comparing with depth and load. The corrosion of chloride was mainly on bending-shear section when the load is within 10–16% of the ultimate flexural capacity, while it was on pure bending section when the load is from 22 to 28% of the ultimate flexural capacity.

Modeling the effect of temperature gradient on moisture and ionic transport in concrete

Most reinforced concrete structures are under the influence of environmental conditions, such as temperature fluctuations, moisture and chloride variations simultaneously. Thus, the moisture transfer in concrete is driven by the moisture gradient as well as the temperature gradient. Similarly, the ionic transfer in concrete is driven by the concentration gradient of the ion as well as the temperature gradient. This paper developed an analytical solution that can be used for the moisture or the chloride transport in concrete considering the effect of temperature gradient. The effect of mass transfer on the thermal conduction was not considered, so the problem is simplified as a one-way coupled problem. The analytical model was validated by using two CASE studies, in which realistic material parameters of concrete were used, the parameters were obtained from experiments in the literature. The comparisons between analytical results and experimental results showed good agreement. It indicated that the present model can successfully characterize the effect of temperature gradient on moisture transfer and the effect of temperature gradient on chloride transport in concrete.

Effect of Crack Characteristics on Chloride Transport in Concrete: An Overview

Effect of Crack Characteristics on Chloride Transport in Concrete: An Overview

Chloride Transport in Concrete under Flexural Loads in a Tidal Environment

AbstractA long-term exposure test of reinforced concrete (RC) beams with different flexural loads in a tidal environment has been conducted by taking the influence of time-dependent chloride diffus...

Modeling Chloride Transport in Concrete at Pore and Chloride Binding

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Chloride transport in concrete under sustained flexural loading

Chloride transport in structural concrete has been found to be both stress- and time-dependent. Several models have been developed to take into account the time dependency of the chloride diffusivity of concrete. However, less is understood about the stress dependency and the interaction between the two dependencies. Experiments were conducted to investigate chloride transport in concrete subjected to different tensile stress levels and different periods of wet–dry cycling exposure (56, 112, 168 and 224 d). Two key parameters were investigated – surface chloride content (Cs) and the apparent chloride diffusion coefficient (Da). It was found that regardless of the tensile stress level, the values of Da and Cs respectively decreased and increased with time due to the continuous hydration of cement and the periodic surface wetting with chloride solution. However, both the decreasing and increasing rates were found to be dependent on the tensile stress levels. Both Da and Cs increased with the tensile stress level due to the opening of pores and the development of microcracks in concrete. Practical models were developed to reflect the above time and stress dependency of Da and Cs, as well as their interactions. The models were validated through comparisons of the experimental and predicted chloride profiles of all the tested specimens.

Prediction of initiation time of corrosion in RC using meshless methods

Degradation of reinforced concrete (RC) structures due to chloride penetration followed by reinforcement corrosion has been a serious problem in civil engineering for many years. The numerical simulation methods at present are mainly finite element method (FEM) and finite difference method (FDM), which are based on mesh. Mesh generation in engineering takes a long time. In the present article, the numerical solution of chloride transport in concrete is analyzed using radial point interpolation method (RPIM) and element-free Galerkin (EFG). They are all meshless methods. RPIM utilizes radial polynomial basis, whereas EFG uses the moving least-square approximation. A Galerkin weak form on global is used to attain the discrete equation, and four different numerical examples are presented. MQ function and appropriate parameters have been proposed in RPIM. Numerical simulation results are compared with those obtained from the finite element method (FEM) and analytical solutions. Two case of chloride transport in full saturated and unsaturated concrete are analyzed to test the practical applicability and performance of the RPIM and EFG. A good agreement is obtained among RPIM, EFG, and the experimental data. It indicates that RPIM and EFG are reliable meshless methods for prediction of chloride concentration in concrete structures.