Chloride Ion Diffusion Research Articles

Statistic investigation on chloride ions distribution based on numerical reconstruction of in situ meso-structure of concrete

To study the non-uniform corrosion of steel rebar induced by chloride ions invasion under marine environment, the three-dimensional characteristic distribution of aggregates and pores in concrete was numerically extracted and reconstructed through X-ray CT technique. Based on the 3D in-situ meso-structure model of concrete, the random characteristics of chloride ions transport in concrete was investigated by numerical simulation. Through a fitting and hypothesis test on the concentration distribution histogram of chloride ions, a reliable probability density distribution function of chloride ions concentration was proposed. And the influence of ITZ and aggregate shape on the random diffusion of chloride ions was studied. The research indicates that that the spatial distribution of coarse aggregates and pores is the main reason leading to the non-uniform distribution of chloride ions. The chloride ions concentration under a certain time follows the Lognormal distribution. The discreteness of chloride ions distribution in concrete decreases when the interfacial transition zone is not considered in the model. And an increase of the irregularity of aggregate shape will cause an increase in the tortuosity of chloride ions transport path, and the discreteness of chloride ions distribution will enhance accordingly.

Chloride ion diffusion in saturated lightweight aggregate concrete: A numerical investigation

The durability of structural LWAC exposed to chloride environments remains a subject of debate due to its porous inclusions and the unresolved transport mechanisms. This paper aims to investigate the diffusion behavior of chloride ions in LWAC by establishing a numerical model at the mesoscale. LWAC was considered a two-phase material comprising lightweight aggregates and mortar matrix. The diffusion coefficients of chloride ions for the mesoscopic components in LWAC were derived using the composite sphere model. A parametric study was conducted to further explore the chloride ion diffusion process, taking into account the aggregate shape, water-to-cement (w/c) ratio, diffusivity of aggregate, aggregate content, and grading. The results suggest that the quality of the mortar matrix had the most significant impact on the chloride ion diffusion in LWAC, while the effect of aggregate diffusivity was influenced by the w/c ratio. By incorporating exposure conditions and critical chloride concentration suggested by the existing design model, the effects of different exposure conditions on the LWAC structures were studied. LWAC structures showed shortest service life in Tidal and Splash environment, and limits on the cover thickness and the maximum w/c ratio of LWAC structures were given by the mesoscopic numerical model.

Research on crystalline admixtures for low carbon buildings based on the self-healing properties of concrete

The increasing fascination surrounding low carbon construction materials has propelled self-healing concrete into the realm of vital technologies for attaining low carbon objectives. This investigation through artificial cracking and precompression experiments demonstrates the efficacy of two specific crystalline admixtures (CAs), namely L-aspartic acid (LAA) and Ethylenediaminetetraacetic acid (EDTA), in augmenting the self-healing characteristics of concrete. The flexural and compressive strength as well as chloride ion diffusion coefficient tests, were used to evaluate the mechanical properties and durability, and the microstructures was analyzed by X-ray diffraction (XRD), differential thermogravimetric analysis (TG-DTG), scanning electron microscopy (SEM), Bruno-Emmett-Teller (BET) and mercury intrusion pore size measurement (MIP). The findings indicate that the optimum dosage for both LAA and EDTA is determined to be 0.5%. At this dosage level, these admixtures effectively fill the pores by stimulating the production of hydrated calcium silicate gel (CSH) and calcium carbonate, leading to a reduction in porosity, enhanced concrete compactness, and successful activation of the self-healing mechanism. Moreover, the incorporation of these admixtures results in improved strength grade and enhanced resistance against chloride ion penetration.

Study on Lifetime Performance Evaluation of a Precast Prestressed Concrete Frame in Chloride Environments.

This study established a comprehensive framework for evaluating the lifetime performance of precast prestressed concrete frames exposed to chloride environments. The proposed analytical framework enabled a scientifically grounded and rational assessment of both the service life and residual load-carrying capacity of precast prestressed concrete frames in chloride environments. It further served as the foundational basis for making informed decisions regarding the repair and maintenance of pertinent structures. Based on Fick's second law, this evaluation framework established the probability distribution of the corrosion initiation time and cracking time of reinforced concrete structures due to corrosion expansion in a chloride environment. Additionally, based on the fragility analysis model and results of a precast prestressed concrete frame in a chloride environment, a practical method for evaluating the time-varying seismic performance of the precast structure considering the influence of corrosion was proposed. Furthermore, by employing the path probability model and reliability theory, time-varying reliability models were proposed to predict the three limit states of the precast prestressed concrete frame. According to the analysis results of a four-story planar frame, it could be seen that the corrosion initiation time and normal service limit state were highly sensitive to the chloride ion diffusion coefficient of the composite layer in precast concrete structures. Compared to cast-in-place structures, the presence of a composite layer in precast concrete structures could lead to more severe degradation of the time-varying seismic performance of the precast prestressed concrete frame.

Study on Chloride Diffusion Behaviors of Recycled Concrete of Random Aggregates

Based on the chloride ions (Cl−) diffusion model and aggregate grading theory, PYTHON and COMSOL are used to construct a mesoscopic model of recycled concrete random polygon aggregate and verify its validity in combination with existing experimental results. The diffusion law of Cl− in recycled concrete and the law of influence of critical factors on the Cl− erosion resistance are studied by calculating and analyzing the Cl− erosion resistance of recycled concrete under different working conditions such as the diffusivity of new and old mortar, the thickness of old mortar and the replacement ratio of recycled aggregate. The results show that the simulation results agree well with the test results, and the method can better reproduce the Cl− diffusion process inside the recycled concrete. There are discontinuous features based on the relationship curves between the Cl− concentration and the depth of the recycled concrete. The Cl− concentration inside the concrete gradually increases with the increase of the diffusion rate of the old and new mortars. The resistance behavior of the recycled concrete to Cl− attack decreases with the increase of the thickness of the old mortar.

Diffusion coefficient and tortuosity: Brownian Motion

The objective of this research is to determine the chloride ion diffusion through Brownian motion using images. The research also aims at the search for diffusional physical tortuosity due to Brownian motion to understand the transport flow of the chloride ion. Through micro-CT scanned images of concrete samples, a 3D reconstruction is performed for the representative element and define its microscopic properties. The implementation of the Brownian motion of the chloride ion particles in the porous network of the representative element considered the initial diffusion coefficient defined by the Stokes-Einstein equation. The diffusion coefficient is an important parameter for predicting the depth of attack of the chloride ion and its displacement due to Brownian motion helps to define the tortuosity of this diffusive transport. The research used computational modeling with MATLAB® software. The results show diffusion due to Brownian motion and tortuousness.

Multi-scale microstructure quantitative characterization and anti-erosion performance of PHC pipe pile

Pre-stressed high-strength concrete (PHC) pipe pile is widely used in many large-scale projects, thus their durability has attracted more and more attention. However, in most studies, PHC pipe pile is regarded as the same as ordinary reinforced concrete, ignoring the effect of special construction processes and hollow shape on its microstructure and anti-erosion performance. In this paper, the real PHC pipe pile was cored and cut to investigate the multi-scale microstructure and the anti-erosion performance of PHC pipe pile concrete layer. The results shown that pore content first increases and then decreases with PHC pipe pile from the outer layer to the inner layer (5F → 1F) by CT, BSE and LF-NMR results, and the pore content changes most significantly around the rebar in PHC pipe pile. In rebar interfacial transition zone (ITZ), the thickness of the voids in PHC pipe pile is greater than that of normal reinforced concrete under the same water-binder ratio condition. Additionally, the content of un-hydration products in aggregate ITZ is obviously greater than that in rebar ITZ. Furthermore, the chloride ion diffusion coefficient of the concrete on the outside of the PHC pipe pile is slightly larger than that on the inside, which is closely related to the higher pore connectivity of the concrete on the outside of the PHC pipe pile. Moreover, it was found that centrifugation can not only reduce the water-binder ratio of PHC pipe pile but also affect the radial pore structure of PHC pipe pile concrete, including porosity and pore connectivity. This work finally indicated that the microstructure of PHC pipe pile concrete is quite different from that of normal reinforced concrete, providing a theoretical basis for establishing the diffusion model of PHC pipe pile concrete.

Research on improving the durability performance of damaged concrete with mineral admixtures

AbstractConcrete can be damaged under long‐term chloride ion action. This article uses mineral admixtures to repair the damaged concrete, and then conducts durability performance tests. Multi‐dimensional chloride ion diffusion tests were conducted under different salt solution immersion environments. The resistance of concrete to chloride ion corrosion was evaluated through RCM chloride ion penetration test, and the internal chloride ion concentration of concrete with different diffusion dimensions was detected through chemical titration analysis. Taking the SW test group as an example, after soaking for 3 months, the three‐dimensional diffusion chloride ion concentration of the SW test group is 2.55 times that of the one‐dimensional diffusion. Under the same three‐dimensional diffusion conditions, at a depth of 10 mm of concrete erosion, the chloride ion concentration of the SW test group after soaking for 3 months is 1.76 times that of the chloride ion concentration after soaking for 1 month. Experiments have shown that multi‐dimensional diffusion can significantly increase the concentration of chloride ions inside concrete, and this effect becomes more pronounced with the increase of erosion time and dimension.

Experimental Study and Numerical Analysis of Chloride Ion Diffusion in Hydrotalcite Concrete in Chloride Salt Environment.

Hydrotalcite, known as layered double hydroxides (LDHs), is a new type of admixture used to delay the corrosion of reinforcement. The aim of this study was to investigate the chloride ion diffusion behavior of C30 concrete with varying amounts of calcined hydrotalcite (0%, 2%, 4% and 6%) in a chloride salt environment. The NT-Build 443 test was adopted to characterize the one-dimensional accelerated chloride ion penetration of concrete. The distribution of chloride ion concentration in hydrotalcite concrete with different mix proportions immersed in sodium chloride solution for 30 days and 60 days was determined, and the chloride ion diffusion coefficient and surface chloride ion concentration were fitted based on Fick's second law to establish the chloride ion diffusion model considering the influence of multiple factors. This model was validated using COMSOL Multiphysics finite element software. The results show that concrete mixed with LDHs can meet its compressive strength requirements and that the resistance of concrete with 2% calcined hydrotalcite to chloride ion penetration is the best with a 19.6% increase in the 30-day chloride ion penetration coefficient. The chloride ion diffusion process under chloride salt immersion conditions is in accordance with Fick's second law. The chloride ion concentrations calculated with COMSOL software and the test results are in good agreement, which verifies the reliability of the chloride ion diffusion model.

Development of cementitious capillary crystalline waterproofing agents and durability study of concrete in the presence of chloride with sulfate in aqueous environment

In this study, the chemical composition of cementitious capillary crystalline waterproofing agents (CCCW) was developed by using the water penetration resistance test method. Response to impermeability by first permeability and self-healing properties by second permeability, five effective single components were obtained: Ethylene diamine tetraacetic acid (EDTA), l-aspartic acid, sodium sulfate, sodium silicate and nano-silica. With the help of chloride ion diffusion coefficient measurement and sulfate attack resistance test, it investigates the effect of five components on the durability of the concrete matrix. According to the differential thermogravimetric analysis (TG), X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis methods, the waterproof mechanism of each component acting in the matrix was proposed. Finally, also combined with the results of macroscopic performance and microscopic analysis designed orthogonal experiments, the results show that the optimal blending of five waterproofing agent components up to 300% increase in substrate impermeability. The optimal amount of each component is 0.5% EDTA, 2% l-aspartic acid, 3% sodium sulfate, 2% sodium silicate, and 2% nano-silica.

Hybrid machine learning-based model for predicting chloride ion concentration in coral aggregate concrete and its ethically aligned graphical user interface design

The chloride ion concentration distribution in coral aggregate concrete (CAC-CC) holds significant importance for evaluating CAC performance, assessing rebar corrosion, and understanding chloride ion diffusion. Thus, this study employs hybrid machine learning algorithms to establish predictive models for CAC-CC under three environmental conditions (salt spray zone, tidal zone, and underwater zone) and evaluates the accuracy and generalization ability of these models. The results demonstrate that the genetic algorithm-optimized support vector regression (GA-SVR) model provides predictions closer to the actual values, exhibiting smoother error fluctuations. The GA-SVR model also exhibits smaller mean and standard deviation in the residual distribution. Furthermore, the GA-SVR model excels in five performance evaluation metrics, with R2, MAE, MAPE, MSE, and RMSE values of 0.986, 1.25e-2, 3.24e-2, 0.276e-3, and 1.66e-2, respectively. Hence, the GA-SVR model emerges as the optimal choice for CAC-CC prediction. Additionally, this work utilizes Shapley Additive Explanations (SHAP) to assess the contribution of eight features. The analysis reveals that the water-binder ratio and the pre-wetted water to total water ratio are the two most critical features. Moreover, an increase in the pre-wetted water to total water ratio and a decrease in the water-cement ratio hinder chloride ion diffusion. Mechanistic analysis of the feature contribution to CAC-CC is further explored in this study. Based on the GA-SVR model, a graphical user interface for CAC-CC has been developed, enabling visualization of CAC-CC predictions. This research introduces a novel approach to optimize CAC performance and predict chloride ion concentration, laying the foundation for CAC application in reef construction.

Fractal derivative model with time dependent diffusion coefficient for chloride diffusion in concrete

More research and experiments have indicated that, under different water cement ratios, the binding effect of concrete on chloride ions and the blocking effect of hydration on chloride ions are clearly dominant. During this time period, the diffusion rate of chloride ions will increase or decrease with time, resulting in the classical Fickian diffusion law no longer being applicable. This study establishes an improved fractal model with a time-dependent diffusion coefficient for chloride diffusion in concrete. An explicit solution is derived in terms of the complementary error function. The proposed model is verified by fitting the chloride ion concentration data from different concrete immersion tests. The results show that the fractal model can fit the data in different spatial scales, and the corresponding prediction accuracy is rather high when compared to the three integer order models with constant, variable diffusion coefficient, and curing age. Therefore, the fractal derivative model is feasible in describing the anomalous diffusion of chloride ions in concrete.

Experimental Study on Long-Term Mechanical Properties and Durability of Waste Glass Added to OPC Concrete.

This study aims to achieve the sustainable utilization of waste glass resources through an investigation into the influence of three types of admixtures, namely waste glass powder (WGP) (G), waste glass powder-slag (G-S), and waste glass powder-fly ash (G-F), on the mechanical properties and durability performance of waste glass concrete. The experimental results demonstrate that the exclusive use of WGP as an admixture led to the relatively poor early compressive strength of the concrete, which decreased with an increase in dosage. However, at medium to long curing ages, the strength of the waste glass concrete could equal or even surpass that of ordinary concrete. When dual admixtures were employed, the G-S group exhibited higher compressive strength compared to the G-F group. Specifically, within the G-S group, a glass powder dosage of 15% yielded higher compressive strength, and after 180 days, the dual admixture groups exhibited greater strength than ordinary concrete (G0); the compressive strength of the tG1S1 group was 44.57 MPa, and that of the G0 group was 40.07 MPa. The chloride ion diffusion coefficient showed a varying trend with an increase in WGP dosage, initially decreasing and then increasing. The concrete's resistance to erosion was maximized when the glass powder dosage reached 30%. As the WGP dosage increased, the overall frost resistance decreased. For a total dosage of 30%, the optimal glass powder dosage in both G-S and G-F groups was found to be 15%.

Effects of incorporating silica glass powder as a supplementary cementitious material on selected properties of portland cement mortar

The use of waste glass powder as a partial replacement for cement is an emerging practice for sustainable cement-based construction. Several studies have demonstrated that finely ground-powdered glass could be an interesting supplementary cementitious material (SCM). However, the performance of such material is influenced by the chemical composition of glass and its pozzolanic reactivity. In this context, the goal of this study is to investigate the use of silica-glass powder (SGP), which is characterized by a high content of silica (>96%), as a partial replacement of Portland cement in mortar. In this research work, mortars containing 7.5%, 10, 12.5, 15 and 20% SGP in replacement of an amount of cement, with three different water-to-binder ratios of 0.55, 0.60 and 0.65 are studied. Selected properties have been investigated at both fresh and hardened stages, which include workability, air content, flexural and compressive strengths estimated by destructive and non-destructive methods, water absorption by capillarity, permeability to chlorides and chloride ions diffusion. The experimental results confirm that incorporating SGP improves the mechanical strength of the mortar, notably in the long-term, and can considerably enhance its durability properties, especially by a decrease in sorptivity of the mortar and by an increase of its resistance to chloride ions diffusion. Correlations between selected physical and mechanical properties and certain durability indices are also established and discussed in this study.

Analysis of corrosion rate, inhibition efficiency, and economic cost of XD3 reinforced concrete related to inhibitor and plasticiser types

The main problem in concrete structure is rebar corrosion, which is caused by the penetration and diffusion of chloride ions into reinforced concrete structures; therefore, it is essential to give the most attention to preventing or limiting the impact of this condition. So, in order to find a practical solution to the problem of corrosion of rebar, the current article focuses on demonstrating the beneficial effects of green and calcium nitrate inhibitors on chloride-induced corrosion. Thus, this paper presented an analytical procedure based on corrosion rates and the economic cost to evaluate the efficacy of such an inhibitor. Ten samples with various concrete mixtures were divided into two groups according to the type of plasticiser and inhibitor have been immersed in an aqueous solution of 3.5 wt% sodium chloride at room temperature for 18 months. The optimal results in which the corrosion rate was significantly reduced were for the two groups of concrete mixtures, first group was (C2), which contains 3 wt% orange peels extract inhibitor mixed with 2.4 wt% Oxydtron as water-resisting admixture, and the second group was (E2) included 3 wt% calcium nitrate inhibitor with 2.4 wt% Oxydtron as water-resisting admixture. These two groups samples have been showed more excellent corrosion resistance against the saline solution after the completed immersion period. The inhibition efficiency analysis showed that there is a direct relationship between the inhibitor concentration and the efficiency of corrosion inhibition. However, the inhibition efficiency in the case of samples containing calcium nitrate inhibitor was higher than their counterparts containing green inhibitor extract. Finally, the economic cost analysis showed that the cost of the green inhibitor extract-containing samples was lower than that of the calcium nitrate inhibitor-containing samples.

Feasibility of using iron-rich phosphoaluminate cement to prepare anti-corrosive coatings for rebars

The anti-corrosive coating has been taken as an effective measure to keep rebars from corrosion. In this study, the iron-rich phosphoaluminate cement (IR-PAC) based anti-corrosive coating for rebar was prepared. The Cl- diffusion coefficient, strength against abrasion, and impact ductility of IR-PAC mortar were tested, with ordinary Portland cement (OPC) and sulphoaluminate cement (SAC) mortar as controls. The experimental results demonstrated that the chloride ion diffusion coefficient of IR-PAC was the lowest at any age. Compared with OPC and SAC, the strength against abrasion of IR-PAC at 90 d increased by 19.19 % and 14.32 %, respectively. The impact ductility of IR-PAC at 28 d increased by 28.21 % and 17.37 %, respectively. IR-PAC had good resistance to Cl- penetration, excellent strength against abrasion and impact ductility, which assisted the coating in blocking Cl- intrusion and resisting damage. The optimum SCMs based coating for rebar is as follows: 10.08 % Fly ash (FA), 0.1 % nano-silica (NS), and 0.65 % superplasticizer (SP). The coatings prepared with this formulation were used for electrochemical experiments. The rebars coated with IR- PAC had good corrosion resistance, which proved it is feasible to use IR-PAC to prepare anti-corrosive coatings for rebars.

Effectiveness of various types of coating materials applied in reinforced concrete exposed to freeze–thaw cycles and chlorides

This study assesses the durability of coated and uncoated concrete surfaces protected with four different coating materials: water-soluble (BW), solvent-based (BR), mineral (MI), and epoxy (EP). The durability assessment includes evaluating the absorption rate of water, pull-off adhesion strength, and coating material thickness. Concrete samples were subjected to immersion in regular water and a 7% urea solution, followed by cyclic freezing and thawing. Furthermore, the diffusion of chloride ions in concrete was evaluated using the impressed voltage method, with the samples exposed to the aging process immersed in a 3.5% NaCl solution. The results indicate that EP and BW coatings were significantly affected by the presence of urea and freeze–thaw cycles, resulting in a 43% and 47% reduction in pull-off adhesion strength, respectively. Notably, the MI-coated concrete samples exposed to urea solution and the freeze–thaw cycles exhibited a significant reduction in the absorption rate due to the accumulation of crystals on the coating surface, resulting in reduced porosity of the material.

Multifactorial Diffusion of Chloride Ions in Concrete considering the Non-linear Voltage Distortion of Other Species

AbstractOne of the most relevant deterioration mechanisms of reinforced concrete (RC) structures is the corrosion of steel bars by chloride ions. The service life of structures could be extended by monitoring this process. The lack of correlation data between chloride ion diffusion and the electrical field has meant that alternative methods have been developed in this paper. One such method considers diffusivity and the electrical field as non-constant, although they are usually assumed constant, that is, without there being any variability of the involved factors. Therefore, a multi-factorial diffusivity that accounts for the material characteristics and environmental variations is adopted. In addition, an innovative stochastic approach to evaluate the variation of the electrical field while accounting for the non-linear voltage distortion, which considers a multispecies model, has been proposed. More complete 1D/2D electro-mechanical models that are solved by advanced numerical and analytical solutions for electro-mechanical diffusion have been developed. Results show that spatiotemporal numerical models estimate the chloride concentration well, estimating more reliable scenarios to provide information on the safety situation of the structure and make it more sustainable by employing successful preventive treatments.

Chloride ion diffusion and distribution characteristics in recycled coarse aggregate concrete under uniaxial and biaxial pressure

Under uniaxial compression, recycled coarse aggregate leads to complex internal stresses (simultaneous uniaxial, biaxial, and multiaxial tensile and compressive stresses at the micro scale) and even micro cracks in concrete, which poses difficulties in accurately predicting the chloride ion diffusion of recycled concrete. By changing the compressive stress level and bi-directional stress ratio of concrete, a self-developed biaxial compression device was used to test the chloride ion diffusion coefficient of recycled concrete under different stress states. In order to analyze the influence of various factors on chloride ion diffusion, DIC digital image technology and microcrack statistics technology were used to analyze the influence of concrete micro deformation on its chloride ion diffusion coefficient under load, and X-ray fluorescence technology was used to accurately analyze the concentration distribution of chloride element in different positions of concrete. The pore structure inside recycled concrete was characterized through experiments, and a real three-dimensional multi-scale model of concrete and the statistical characteristics of porosity at different scales were obtained. Finally, a theoretical model was established to predict the chloride ion diffusion coefficient under biaxial compressive loads, achieving accurate prediction of chloride ion diffusion coefficient close to practical engineering.

DURABILITY PERFORMANCE OF HPC CONTAINING MK AND GGBS FOR MARINE ENVIRONMENT: A REVIEW

High performance concrete (HPC) is designed to serve certain purpose and overcome certain environmental condition that normal concrete cannot achieve. Many supplementary materials in varieties of proportions have been incorporated to make HPC. This review study considered the partial replacement of cement by Metakaolin (MK) and Ground Granulated Blast-furnace Slag (GGBS). It provides information on the composition of marine environments and the mineral reactive admixtures as well as their usage while highlighting their behavior relating to chloride ion penetration, sulfate attacks and permeability. The scope of this study considers outstanding research articles, from 1980 to 2022, as well as major books on Marine Environment, Concrete Technology and Civil Engineering Handbooks as to reveal the various techniques that engineers and researchers have used to optimize concrete performance in marine environment. This study found out that the incorporation of MK and GGBS greatly improves HPC in marine environment but the pattern of their influence varies per the durability parameter; the increment in quantity of each mineral admixture incorporated in the concrete were found to have either progressive or retrogressive effect towards chloride ion diffusion and gas permeability but progressive enhancement trend when resisting sulfate attacks. Also, water to binder ratio greatly influence the HPC in relation to the admixtures. It is concluded that MK level from 10% to 15% and GGBS level from 40% to 60% have optimal performance in most harsh conditions of marine environment.