Chloride Ion Diffusion In Concrete Research Articles

Factors Influencing Chloride Ion Diffusion in Reinforced Concrete Structures.

Reinforced concrete structures are prone to the corrosion of steel bars when exposed to chloride-rich environments, which can severely impact their durability. To address this issue, a comprehensive understanding of the factors influencing chloride ion diffusion in concrete is essential. This paper provides a summary of recent domestic and foreign research on chloride ion transport in concrete, focusing on six key factors: water-binder ratio, additive content, crack width, ambient temperature, relative humidity, and dry-wet cycles. The findings show that the diffusion coefficient of chloride ions in concrete increases with a higher water-binder ratio and decreases with increased additive content. Additionally, wider cracks result in a greater diffusion of chloride ions. The permeability resistance of concrete to chloride ions decreases with rising temperature and humidity, and dry-wet cycles further accelerate the diffusion of chloride ions. The article concludes by discussing various anti-corrosion measures, such as the use of corrosion inhibitors, surface coatings, and electrochemical treatments, to ensure the longevity of the structure. Finally, directions for future research are proposed.

Effect of Micro-Cracks on Chloride Ion Diffusion in Concrete Based on Stochastic Aggregate Approach

For concrete structures in offshore areas, chloride ion erosion is one of the main factors affecting durability. It is crucial to evaluate the chloride ion permeability resistance of concrete structures. In this paper, a finite element simulation of the chloride ion diffusion process in concrete is conducted. A mass diffusion finite element model based on a random aggregate approach is established to investigate the influences of an aggregate, the interface transition zone, and micro-cracks on the chloride ion diffusion coefficients in concrete. The results show that the mass diffusion finite element analysis based on the exponential function model and the power function model can effectively simulate the chloride ion diffusion process in concrete. In addition, the data reveal that volume fraction and distribution aggregates considerably affect chloride ion diffusivity in concrete. Also, the interface transition zone significantly accelerates chloride ion diffusion in concrete. Moreover, this acceleration effect exceeds the barrier effect of an aggregate.

Study on time range of definite integral in derivation process of chloride ion diffusion theoretical model of concrete

In the study of the durability of concrete structures, the chloride ion diffusion coefficient (Dt) is a key parameter that directly affects the prediction of concrete's service life. This study aims to explore the relationship between the chloride ion diffusion coefficient in concrete and the "curing age (tref)" and "exposure time (t)." By conducting long-term curing and seawater exposure experiments on three different mixes of high-performance concrete samples, we collected experimental data with a curing age of 3 years and a seawater exposure time of 4.5 years. Through in-depth analysis of these data, we found that there is a significant power function relationship between the chloride ion diffusion coefficient and exposure time, while the relationship with curing age is not significant. This finding suggests that in the derivation of the concrete chloride ion diffusion theory model, the time range of the definite integral of Dt should be from 0 to t, rather than from tref to tref+t. Furthermore, we have validated the concrete life prediction model using actual data from the Swedish Marine Exposure Station, further confirming the accuracy and reliability of our research results. This study provides a more scientific and accurate theoretical basis for the durability assessment and service life prediction of concrete structures.

Simulation Approach for Random Diffusion of Chloride in Concrete under Sustained Load with Cellular Automata

Steel bar corrosion caused by chloride is the major reason for concrete structure durability failures in a corrosive environment. An accurate simulation of chloride ion diffusion in concrete is hence critical to durability design, maintenance, and reinforcement of concretes in erosive environments. To accurately simulate actual chloride ion diffusion in concretes, an improved three-dimensional neighborhood type is proposed according to the mechanism of chloride ion diffusion in concrete, and a three-dimensional cellular automaton model (3D CA model) for describing the diffusion process of chloride in concrete is established based on this neighborhood type. The accuracy and correctness of simulation results obtained from the 3D CA model were verified by comparison with Fick’s second law analytical solutions. Based on the 3D CA model, an improved modified 3D CA model is developed (3D RTCA model) which takes into account random chloride ion distribution in concrete, the time dependence of the coefficient of chloride ion diffusion, and the structure stress level effect on chloride ion diffusion. Numerical simulation results reveal that the 3D RTCA model has higher calculation accuracy in predicting long-term concentration of chloride in concretes, and the simulation results are closer to experimental findings than analytical results obtained based on Fick’s second law. Compared with Fick’s second law analytical solutions, the 3D RTCA model can reflect more truly the cross-sectional stress level effect on chloride ion diffusion through simple local evolution rules. Besides, the 3D RTCA model can genuinely describe the randomness and uncertainty of the chloride diffusion process. The 3D RTCA model developed in the current study provides a novel perspective and method to investigate chloride ion diffusion in concrete from structural level.

Experimental Study on Chloride Ion Diffusion in Concrete Affected by Exposure Conditions.

The transport mechanism of chloride ions in concrete is relatively complicated since the erosion process is influenced by many factors. To investigate the effect of exposure conditions on the chloride ion diffusion property, three exposure conditions (long-term immersion in static sodium chloride solution, long-term immersion in circulating sodium chloride solution and dry–wet cycles in circulating sodium chloride solution) were considered in chloride ion diffusion experiments. Experimental results indicated that the chloride ion content at a certain depth increased with erosion age. The chloride ions in static sodium chloride solution transported more rapidly than those under dry–wet cycle conditions. Moreover, the chloride ion content of concrete under dry–wet cycles of the circulating sodium chloride solution was slightly higher than that under long-term immersion in the circulating solution. Based on Fick’s second law, empirical equations for the chloride diffusion coefficient and chloride content at the surface of concrete were proposed by fitting experimental data, and the values of correlation coefficients of different exposure conditions were suggested. By comparison with the experiment results, it was verified that the calculation formula had better applicability. This method could be used to predict and analyze the chloride ion content under different exposure conditions.

Application of ANN for prediction of chloride penetration resistance and concrete compressive strength

Self-consolidating concrete is considered as one of the greatest developments in concrete industry. It has several advantages over conventional concrete such as minimized voids, ease of pour into congested formworks and complex shapes and absence of mechanical vibrations. One of the major problems with concrete structures is the corrosion of steel reinforcement due to penetration of chemicals like chloride. Most of the standard tests to determine chloride penetration levels are performed at 28-days. It is desired that some rapid means of determination of chloride ion diffusion in concrete are available for design and quality assurance purposes. In present study Artificial Neural Networks (ANNs) are developed for prediction of chloride penetration level and compressive strength of SCC mixes. ANN developed for prediction of chloride penetration used 294 data points for training and validation. This trained ANN was used to verify chloride penetration level of twenty experimentally evaluated SCC specimens of varied composition. Similarly, ANN developed for prediction of compressive strength used 1031 data points for training and validation of network. Compressive strength values predicted by ANN were compared with experimentally evaluated compressive strengths of thirty-three SCC specimens of varied composition. Both ANNs use relevant input parameters for training and validation of networks. A comparison between experimentally evaluated and ANN predicted values is presented in the paper for different combinations of learning rate and momentum of network. The trained ANNs were able to predict chloride iron penetration levels and compressive strength based on selected input parameters to an acceptable extent.

Experimental Study on Chloride Ion Diffusion in Concrete under Uniaxial and Biaxial Sustained Stress.

The existence of axial and lateral compressive stress affect the diffusion of chloride ions in concrete will lead to the performance degradation of concrete structure. This paper experimentally studied the chloride diffusivity properties of uniaxial and biaxial sustained compressive stress under one-dimensional chloride solution erosion. The influence of different sustained compressive stress states on chloride ion diffusivity is evaluated by testing chloride concentration in concrete. The experiment results show that the existence of sustained compressive stress does not always inhibit the diffusion of chloride ions in concrete, and the numerical value of sustained compressive stress level can affect the diffusion law of chloride ions in concrete. It is found that the chloride concentration decreases most when the lateral compressive stress level is close to 0.15 times the compressive strength of concrete. In addition, the sustained compressive stress has a significant effect on chloride ion diffusion of concrete with high water/cement ratio. Then, the chloride diffusion coefficient model under uniaxial and biaxial sustained compressive stress is established based on the apparent chloride diffusion coefficient. Finally, the results demonstrate that the chloride diffusion coefficient model is reasonable and feasible by comparing the experimental data in the opening literature with the calculated values from the developed model.

Chloride ion erosion experiment research in cracked concrete

For the study of chloride ion erosion in cracked concrete, this essay tries to take advantages of relevant trails to build up concrete chloride ion diffusion model based on the Fick’s second law. The parameter of this model is easy to be set, and many factors such as the effect of cracks are taken into consideration in this experiment. The concept of “chloride ion diffusion coefficient of equivalent apparent” is introduced to simplify the calculation. It can help simplify the calculation process, and get a more accurate test result, as well as facilitating the practical application of this parameter.

The effect of tensile fatigue on chloride ion diffusion in concrete

Fatigue damage is one of the most important factors impacting the chloride diffusion coefficient in concrete. In this paper, chloride ion diffusion in concrete was experimentally studied using a modified apparatus based on the rapid chloride migration (RCM) test to measure the diffusion coefficient. The effect of fatigue damage on chloride ion diffusion coefficient was analyzed using residual tensile strain, fractal damage factor (defined based on fractal dimension of damage propagation fronts) and damage-responsive variable resistance as self-variables to characterize fatigue damage. The chloride ion diffusion coefficient increases exponentially as residual tensile strain increases. An initial degradation point occurs at approximately 25με. The diffusion coefficient increases exponentially with increasing fractal damage factor. The initial degradation point and steep degradation point occur at 30% and 50% fractal damage factor, respectively. An exponential increase in the ion diffusion coefficient is also observed as the damage-responsive variable resistance, (RCCP+RCP), decreases, with 3.25×106Ωcm2 and 2.1×106Ωcm2 being the initial degradation point and steep degradation point, respectively. The three exponential functions suggest strong correlation between the three damage variables and chloride ion diffusion coefficient.

Understanding the interacted mechanism between carbonation and chloride aerosol attack in ordinary Portland cement concrete

An experimental study is carried out with the aim to understand the interacted mechanism between carbonation and chloride aerosol attack in ordinary Portland cement (OPC) concrete. Effects of carbonation on the chloride profile, the chloride binding capacity and the chloride diffusion coefficient are evaluated. Besides, effect of chloride aerosol attack on the carbonation rate is investigated. Concrete specimens with three water-to-cement ratios (0.38, 0.47 and 0.53) are fabricated in this work. Tested results demonstrate that carbonation remarkably affects the chloride profile, reduces the chloride binding capacity, and also accelerates the rate of chloride ion diffusion of concrete. Besides, the presence of chloride aerosol can lead to lower the carbonation depth and increase the pH value of carbonated concrete. Microscopic properties such as morphology, porosity, and pore size distribution for the contaminated concretes are explored by scanning electron microscope and mercury intrusion porosimetry, which provide strong evidence to these research findings.

Chloride ion diffusion of structural concrete under the coupled effect of bending fatigue load and chloride

Through the bending fatigue load test and static load test on concrete specimens in a chloride environment, we, in this research, studied the law of chloride ion diffusion in concretes under the coupled effect of bending fatigue load and chloride. The results showed that the concrete chloride ion diffusion coefficient was higher under bending fatigue load than that under static load at the same load level. When the load level was greater than 47%, the amplification was very obvious. Under the coupled effect of bending fatigue load and chloride, the service life of the concrete structure would be greatly shortened.

Durability Design of Marine Concrete Structure Considering the Influence of Load

In this paper, based on accelerated testing indoors, under the action of bending tensile stress on a marine high-performance concrete chloride ion diffusion coefficient, the results show that: Subjected to bend under the action of tensile stress and do not withstand the test piece chloride diffusion coefficient increases with increasing stress levels, different tensile stress and does not bear the stress of the concrete chloride ion diffusion coefficient ratio (Dη/D0) exponential relationship with the stress level (η). In addition, addition, for a domestic Bridge, preliminary design to determine typical parameters of components and their environment is proposed to consider the durability of concrete structure load control index calculation method, to establish a "design life - chloride ion diffusion coefficient controlled targets" the correspondence between, for similar projects designed to provide a reference durability.

콘크리트의 염화물이온 확산성상에 미치는 온도의 영향

The long term integrity of concrete cask is very important for spent nuclear fuel dry storage system. However, there are serious concerns about early deterioration of concrete cask from creaking and corrosion of reinforcing steel by chloride ion because the cask is usually located in seaside, expecially by combined deterioration such as chloride ion and heat, carbonation. This study is to investigate the relation between temperature and chloride ion diffusion of concrete. Immersion tests using 3.5% NaCl solution that were controlled in four level of temperature, i.e. 20, 40, 65, and 90℃, were conducted for four months. The chloride ion diffusion coefficient of concrete was predicted based on the results of profiles of Cl- ion concentration with the depth direction of concrete specimens using the method of potentiometric titration by AgNO3. Test results indicate that the diffusion coefficient of chloride ion increases remarkably with increasing temperature, and there was a linear relation between the natural logarithm values of the diffusion coefficients and the reciprocal of the temperature from the Arrhenius plots. Activation energy of concrete in this study was about 46.6 (W/C = 40%), 41.7 (W/C = 50%), 30.7 (W/C = 60%) kJ/mol under a temperature of up to 90℃, and concrete with lower water-cement ratio has a tendency towards having higher temperature dependency.

Research on chloride ion diffusivity of concrete subjected to CO2environment

Carbonation is a widespread degradation of concrete and may be coupled with more severe degradations. An experimental investigation was carried out to study the effect of carbonation on chloride ion diffusion of concrete. The characteristic of concrete after carbonation was measured, such as carbonation depth, strength and pore structure. Results indicated that carbonation depth has a good linear relation with square root of carbonate time, and carbonation can improve compressive strength, but lower flexural strength. Results about pore structure of concrete before and after carbonation have shown that carbonation could cause a redistribution of the pore sizes and increase the proportion of small pores. It also can decrease porosities, most probable pore size and average pore diameters. Chloride ion diffusion of concrete after carbonation was studied through natural diffusion method and steady state migration testing method respectively. It is supposed that the chloride ion concentration of carbonation region is higher than that of the sound region because of the separation of fixed salts, and chloride ion diffusion coefficient was increased due to carbonation action evidently.

The transport properties of concrete under the simultaneous coupling of fatigue load and environment factors

A set of coupling experimental instrument was designed to study the transport properties of chloride ion in concrete under simultaneous coupling action of fatigue load and environmental factors. Firstly the water-saturated performance of modern concrete was investigated, then diffusion performance of chloride ion under different stress levels and different temperature were studied respectively; meanwhile, the time-dependent behavior of the chloride ion diffusion in concrete was also researched. The results showed that the saturation degree of concrete can reach as high as 99%. Besides, diffusion coefficient of chloride ion increased with increasing of the stress level and temperature, and when the stress level and temperature are at 0.6 and 60 ° respectively, the diffusion coefficient is 6.3×10−14 m2/s, moreover the diffusion coefficient of chloride ion in concrete decreased with time under the simultaneous coupling action of fatigue load and environment factors.

Durability of sea-sand containing concrete: Effects of chloride ion penetration

This paper describes an orthogonal experiment on the effect of water/cement ratio, water consumption per cubic meter, curing time, and type of sand on the response “resistance to chloride ion penetration”. A sea-sand containing concrete was used for the trials. An analysis of chloride ion diffusion coefficients at different factor levels was performed. A predictive model of chloride ion diffusion in concrete is developed through regression analysis. The experimental results show that when the water/cement ratio varies from 0.45 to 0.60, and the water consumption per cubic meter varies from 185 to 215 kg, and the curing time varies from 30 to 180 d then the size of the effects fall in the order (most significant first): curing time, type of sand, water consumption per cubic meter, and water/cement ratio. Chloride ion penetration is reduced, and better durability of the concrete is observed, with longer curing times, less water consumption per cubic meter, and a smaller water/cement ratio.

Aggregate influence on chloride ion diffusion into concrete

An attempt is made to predict the probable effect of the aggregate on chloride ion diffusion into saturated concrete. It is shown that if the chloride ion diffusion coefficient of an aggregate ranges from 0.2 to 10 times that of the cement paste matrix, then this could result in variations in the concrete chloride ion diffusion coefficient of up to 10:1. Such a variation is equivalent to a change in free water-cement ratio from 0.77 to 0.45.

ASSESSMENT OF CHLORIDE DIFFUSION IN HIGH STRENGTH CONCRETE USING THE ACCELERATED IONIC MIGRATION TEST

ABSTRACT The diffusivity of chloride ions through high strength concrete has been studied. A simple potential difference has been applied to accelerate the CI− diffusion through concrete. Test variables have included the strength of concrete, the applied electrical potential, and the pozzolan. A modified equation and numerical method are used to compute the diffusion coefficients of chloride ions in concrete. Test results show that the effective diffusion coefficients are between 2.53×10−14m2/sec and 9.84×10−14m2/sec for concrete with compressive strength between 62.5MPa and 91.1MPa. The slag refines the internal pores of concrete by pozzolanic reaction, and reduce the chloride ion diffusion in concrete. For high strength concrete, the computed effective diffusion coefficients are not significantly affected by the applied electrical field intensity.

Determination of the Effective Chloride Diffusion Coefficient in Concrete via a Gas Diffusion Technique

A new experimental technique based on gas diffusion through a thin sample specimen is presented to evaluate the effective chloride diffusion ion in concrete. The counterdiffusion of two gases, helium and nitrogen, through a concrete disc is used to establish the porosity-to-tortuosity ratio of the concrete. From measurements of the porosity via porosimetry, the tortuosity of the concrete can be determined. The effective chloride ion diffusion in concrete is a function of the porosity-to-tortuosity ratio and the diffusion coefficient of chloride ion in water which is a known value. The test takes 3 to 4 hours to complete. Excellent results were obtained when correlated with the conventional diffusional measurement techniques for different water-cement ratios and cement content.