Chloride Binding Capacity Of Concrete Research Articles

A study of chloride binding capacity of concrete containing supplementary cementitious materials

Chloride-induced steel corrosion is known to be a very common kind of deterioration of reinforced concrete. It is beneficial to bind free chloride ions to reduce the corrosion probability of the reinforcement embedded in the concrete. The binding capacity of the concrete varies according to its cementitious system. This paper investigates the chloride binding capacity of different kinds of supplementary cementitious materials (SCMs): Ground granulated blast furnace slag (GGBFS), Fly ash, and Metakaolin as a partial replacement of Ordinary Portland Cement (OPC). Different properties of concrete after chloride binding are assessed by carrying out the following tests: half-cell potential, accelerated corrosion test, compressive strength, rapid chloride penetration test, sorptivity test, measuring pH value of concrete, and XRD. The results showed that utilizing the SCMs in concrete can enhance the chloride binding capacity, especially those materials that have high quantities of aluminate and calcium in their chemical composition like GGBFS. Based on testing results, it’s recommended that the limit of the chloride content in the different codes should be revised regarding the binding capacity according to the type and quantity of the cementitious materials used.

Physics-informed deep neural network for modeling the chloride diffusion in concrete

Chloride diffusion in concrete is a complex chemo-physical process and it is of pivotal importance to forecast the initiation time of corrosion. But limited equations are accessible to simulate the chloride diffusion considering the nonlinear chloride binding capacity of concrete. This study proposes a physics-informed deep neural network to simulate the chloride diffusion mechanism and forecast the distribution of chloride concentrations in concrete. Physical laws are formulated as a loss term to guide the training process and to mitigate the data required for model training. The physical constraint loss (based on the governing equation and boundary conditions) and the training loss (based on the neural network) are then fused to produce the loss function. Different experimental cases are first employed to validate the proposed model and then the model is compared to numerical applications and purely data-driven approaches. Results revealed that the proposed model could effectively simulate the chloride transport behavior and forecast the diffusion coefficient of concrete with high precision over other states of art methods. The application of this method to the temporal and spatial domains of the chloride concentration within the concrete samples showed its potential as a powerful tool for investigating concrete properties.

Identification of chloride diffusion coefficient in concrete using physics-informed neural networks

The corrosion of steel caused by chloride is one of the important causes of the deterioration of reinforced concrete structures. In order to describe the transport behavior of chlorides in concrete and to make quantitative durability designs based on it, it is necessary to determine the chloride diffusion coefficient correctly. However, the commonly used analytical method is not suitable for the free chloride diffusion coefficient considering the nonlinear chloride binding capacity of concrete. In this study, by comparing the results of solving forward problems involving chloride transport equations using finite element method (FEM) and solving corresponding inverse problems using physics-informed neural networks (PINNs), it is verified that PINNs can be applied to identify the chloride diffusion coefficient in non-steady-state immersion tests and accelerated chloride migration tests considering no chloride binding, Langmuir binding, or Freundlich binding. The robustness of PINNs is verified by training with 5% and 10% noise data as observed data. The results of interpolation and extrapolation using PINNs trained successfully show its excellent generalization performance.

Effect of electric field intensity on chloride binding capacity of concrete

Determining the binding capacity of concrete to chloride ions has always been the focus of the durability study of reinforced concrete structures. In many cases, concrete interior is in the electric field environment, such as railway track affected by stray current, component under electrical chloride removal (ECR), and concrete in corrosion electric field. However, the influence of electric field intensity on the chloride binding ability of concrete has not been determined clearly and quantitatively. In this paper, an experimental study is conducted to investigate the evolution of chloride binding capacity under various electrical current densities. The results indicate that the binding capacity of concrete is degraded by the electrical field, and the amount of physical adsorption for chloride is far less than the that of chemical binding. Based on experimental data, the modified Langmuir isotherm is given, and the evolution of key coefficients is measured quantitatively. The research findings are of great significance to the accurate evaluation of subsequent transmission of chloride ions after the initiation of steel corrosion and corrosion protection effect by ECR technique.

Mechanical Performance and Constitutive Model Analysis of Concrete Using PE Fiber-Strengthened Recycled Coarse Aggregate.

To promote the sustainable development of the construction industry, concrete incorporating polyethylene (PE) fiber-strengthened recycled coarse aggregate (SRCA) and seawater and sea sand (SWSS) is prepared. The usage of SRCA significantly improves the mechanical performance of concrete. The strength is improved, and the failure mode of concrete cylinders is also remarkably altered. The incorporation of SWSS that alleviates the shortage of freshwater and river sand slightly reduces the mechanical strength of concrete at 28 and 90 days, while the replacement of cement by 35% limestone calcined clay cement (LC3) overcomes this drawback. The compressive strength of concrete is further enhanced, and the pore structure is refined. The introduction of LC3 also promotes the formation of Friedel’s salt, which could improve the chloride binding capacity of concrete using SWSS. Furthermore, the stress-strain relationship of sustainable concrete is analyzed, and the experimental results are compared with the commonly used constitutive models. The predictive constitutive models are proposed to effectively describe the mechanical performance of sustainable concrete.

Modeling of Chloride Binding Capacity in Cementitious Matrices Including Supplementary Cementitious Materials

The improvement in the chloride binding capacity of concrete has been shown to increase corrosion resistance. The addition of supplementary cementitious materials (SCMs) to Portland cement has been proven to increase the binding capacity, except for silica fume, whereas the impact of chemical additives is not extensively addressed in the literature. This work studies the influence of SCMs and chemical additives, i.e., calcium nitrite inhibitor (CNI), migrating corrosion inhibitor (MCI), and Caltite as a hydrophobic material, on binding capacity. The addition of both corrosion inhibitors (MCI and CNI) has minimal effect on the binding capacity, while the addition of Caltite reduces the binding capacity by limiting the contact of the samples with the salt in water due to its hydrophobic nature. In addition, the study compares the performance of the available fitting–binding models against the available experimental work in the literature, and shows that the Freundlich isotherm is the best fitting model for describing the relationship between the binding capacity and the free chloride. The study further relates the binding capacity to different compositions in cement and SCMs, and shows, by conducting quantitative analysis, that the Al2O3 content is the dominant factor affecting the binding capacity. Finally, this work proposes a new model, which uses Al2O3 content and free salt concentration to predict the bound chloride. The model shows adequate correlations to the experimental work and, further, can be used in service-life modeling of concrete.

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.

Chloride diffusion and binding in concrete containing NO2 sequestered recycled concrete aggregates (NRCAs)

This study investigates the effect of NO2 sequestered recycled concrete aggregates (NRCA) on chloride ion diffusion and chloride binding capacity of concrete. Two types of NRCAs were used as a partial replacement for natural fine aggregate in fresh OPC mixtures at 20% and 40% replacement levels by volume. Control mixtures with conventional recycled concrete aggregates (RCA) were also evaluated for comparison purposes. The water-permeable porosity, rapid chloride permeability, long-term chloride diffusivity, and chloride binding capacity of the test concrete mixtures were evaluated. Results showed that the presence of NRCA reduced porosity as well as both short-term and long-term chloride ion permeability compared to conventional RCA containing concrete. Most importantly, the addition of NRCAs enhanced the chloride binding capacity of concrete. Thermogravimetric and X-ray diffraction analyses demonstrated increased formation of Friedel’s and Kuzel’s salts in concrete due to the incorporation of NRCA. Based on the test results, a mechanism is proposed for the enhanced chloride resistance in NRCA incorporated concrete.

Chloride permeability and chloride binding capacity of nano-modified concrete

Chloride permeability and chloride binding capacity are two important factors for assessment of the rebar corrosion risk in reinforced concrete structures. In this work, the chloride permeability and chloride binding capacity of concrete modified with nano-SiO2 (NS), nano-CaCO3 (NC), multi-walled carbon nanotubes (CNT) were evaluated. The results demonstrate that incorporation of nanomaterials significantly decreases the chloride diffusion coefficients by refining the pore structure and reducing the pore volume. The experimental data strongly suggest the existence of a percolation threshold (critical porosity), below which the chloride permeability decreases dramatically. Addition of NS compromises the chloride binding capacity due to decreased pH value of pore solution, which results in dissolution of Friedel's salt. XRD suggests that adding NC restrains the formation of AFm phase, which is mainly responsible for the chemical binding. TG/DTG analyses confirm that adding CNT facilitates the formation of more amount of hydrates, thus enhancing the chloride binding. Addition of NS and NC leads to a decreased amount of Friedel's salt and thereby weakens the chemical binding.

Time-Dependent Model for Predicting Chloride Binding Capacity of Concrete with Crystalline Material

The aim of this study is to develop a time-dependent model for determining the chloride binding capacity of concrete with crystalline material (CM) with different water to binder (w/b) ratios, fly ash replacement proportions, curing times, and chloride exposure periods. The effect of CM on chemical and physical binding processes was considered in the development of the model. The model was developed based on the results of experimental analysis conducted by the authors. The values of chloride binding capacity predicted using the model fell within the R-squared values ranged from 0.842 to 0.982, which indicates satisfactory agreement with the experimental results.

Improving the chloride binding capacity of cement paste by adding nano-Al2O3: The cases of blended cement pastes

Chloride ingress is one of the main causes for the degradation of reinforced concrete structures. Increasing the chloride binding capacity of concrete is generally thought as a feasible way to restrain the chloride ingress. In our previous study, the γ-phase nano-Al2O3 (NA) was found to be beneficial for improving the chloride binding of plain Portland cement paste as a result of the formation of additional Friedel’s salt. Herewith, the cases of blended cement pastes were further investigated, into which supplementary cementitious materials (SCMs) were incorporated, including fly ash (FA), blast furnace slag (SL) and silica fume (SF). NA with a dosage of 1% and 2% was introduced to blended cement paste, and the chloride binding capacity of which were determined with the conventional equilibrium method. The results showed that the use of NA was even viable to improve the chloride binding capacity of blended cement pastes. X-ray diffraction (XRD)/Rietveld refinement method and thermogravimetric analysis (TGA) were performed to unravel the phase assemblages change upon exposure. It was revealed that besides the formation of more Friedel’s salt, the addition of NA could allow the enhanced physical binding of chloride as a result of the formation of C-A-S-H, i.e., the substitution of Si by Al in C-S-H gel.

Chloride Binding Capacity of Cement Paste Containing Layered Double Hydroxide (LDH)

Abstract The chloride binding capacity of concrete can affect the rate of chloride ingress, which ultimately determines the chloride-ion resistance. A layered double hydroxide (LDH) can absorb the chloride ions in cement paste and delay chloride ingress in the structure. A method for evaluating the chloride binding capacity of cement paste was used in the experiment reported herein. We compare Mg-Al LDH under different treatments (including CO32− series and NO3− series) in order to determine the chloride binding capacity of the LDH. The binding mechanism is explored in this article. The experimental results indicate that LDH processes have a remarkable chloride ion binding capacity. The addition of LDH can improve the chloride binding capacity of cement paste significantly. Cement paste containing roasted LDH has a better chloride binding capacity than that containing unroasted LDH or rehydrated LDH. Based on the comparison of LDHs with different anions, the chloride binding capacity of NO3− series LDH appears to be more powerful than that of CO32− series LDH.

Long term performance of chloride binding capacity in fly ash concrete in a marine environment

The capacity of binding chloride ions in fly ash concrete under marine exposure was studied. The free and total chloride contents in concrete were determined by water and acid-soluble methods, respectively. In order to study the effects of W/ B ratios, exposure time, and fly ash contents on chloride binding capacity of concrete in a marine site, a class F fly ash was used as a partial replacement of Portland cement type I at 0%, 15%, 25%, 35%, and 50% by weight of binder. Water to binder ratios ( W/ B) were varied at 0.45, 0.55, and 0.65. Concrete cube specimens of 200 mm were cast and placed into the tidal zone of a marine environment in the Gulf of Thailand. Consequently, acid-soluble and water-soluble chlorides in the concrete were measured after the concrete was exposed to the tidal zone for 3, 4, 5, and 7 years. It was found that the percentage of chloride binding capacity compared to total chloride content increased with the increase of fly ash in the concrete. The percentage of chloride binding capacity significantly decreased within 3–4 years after the concrete was exposed to the marine environment, and then its value was almost constant. The research also showed that the W/ B ratio does not noticeably affect the chloride binding capacity of concrete.