Concrete Chloride Research Articles

Diffusion resisting performance of concrete modified with sodium methyl silicate in saline soil area

• A new type of concrete mixed 2.4% sodium methyl silicate was prepared. • An instantaneous diffusion model of chloride ions in concrete was proposed. • The diffusion reducing performance of the new concrete were compared against ordinary concrete. • A useful means for the corrosion resistance of tunnel lining was proposed. Concrete of tunnel lining in saline soil area is subjected to compound salt attacks, which decrease the service life of tunnel. In this study, a new type of concrete mixed 2.4 % sodium methyl silicate was prepared to improve the compound salt damage resistance of concrete. The properties of the concrete, including chloride diffusion resisting performance, compressive strength, and water absorption, were investigated. The results showed that the chloride diffusion resisting performance of the concrete modified with methyl sodium silicate was notably better than that of normal concrete in compound salt solution. The maximum compressive strength had not changed significantly compared with normal concrete, while the occurrence of peak strength was delayed by about 30 days. The water absorption of the concrete modified with sodium methyl silicate was reduced by 21.09 % compared with the normal concrete. Moreover, chloride diffusion resisting mechanism of the concrete immersed in compound salt solution was elucidated. Furthermore, based on the Fick’s second law and experimental results, a time-varying diffusion model for predicting the chloride ion mass fraction of chloride in the concrete was proposed in this paper. The proposed approach is a useful means for the chloride diffusion resisting of concrete in some saline soil area of Western China.

A machine learning method for predicting the chloride migration coefficient of concrete

• Extensive model optimizations and performance evaluations are carried out. • XGBoost predicts the chloride migration coefficient with the highest accuracy. • XGBoost outperforms other five tree-based algorithms. • Fresh density and strength tests are predictors of the chloride migration coefficient. • The models can replace traditional laboratory-based concrete chloride migration tests. This work adopts a state-of-the-art machine learning algorithm, XGBoost, to predict the chloride migration coefficient (D nssm ) of concrete. An extensive database of experimental data covering various concrete types is created by gathering from research projects and previously published studies. A total of four D nssm models are developed depending on the number and type of input features. All models are verified with unseen data using four statistical performance indicators and compared to other five tree-based algorithms. The verification results confirm that the XGBoost model predicts the D nssm with high accuracy. The model has the potential to replace cumbersome, time-consuming and resource-intensive laboratory testing.

Experimental study of mechanical properties and durability of green concrete containing slag, waste rubber powder and recycled aggregate with artificial neural network

In this experimental study, the impact of using waste materials such as ground granulated blast furnace slag (GGBFS), waste rubber powder (WRP), and recycled concrete aggregate (RCA) were evaluated on the compressive, tensile and, flexural strengths and durability test of rapid chloride migration test (RCMT) of concrete. It was observed that the mechanical properties of concrete decreased by raising the proportions of recycled materials in all replacement ratios. Because of the adverse effects of the WRP and RCA on the cement matrix and the interfacial transition zone, the reduction of the mechanical properties is higher for the concrete specimens with both recycled materials. In the case of durability, the migration rate of chloride ions in concrete is reduced by increasing the WRP rates due to the blockage of micro-pores connections. However, adding the RCA has a negative effect on the durability performance of concrete. Regarding the simultaneous effect of slag, rubber powder, and recycled aggregate on the migration of chloride ions, it can be derived that durability of samples containing 20% slag, 2.5% rubber powder, and 25% recycled aggregate at the age of 7 days on average is 14.8% higher compared to the reference sample. As the age of the samples increases to 28 days, the migration of chloride ions in the samples reduced 9.5% compared to 7 days.

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.

Performance of Coral Aggregate on Mechanical and Durability Properties of Concrete - A Review

Coral concrete is a type of aggregate and is generally light and porous, with rough surface, little adherence to the attachments and high concentration of sea salts. Coral concretes are mainly required in the Construction of offshore structures. This types of aggregate complies low grade of strengths, little corrosive resistance and is highly brittle. These features influences the workability, mechanical properties, and durability properties of developed concrete. The objective is to analyse the performance of coral aggregate on workability, mechanical and durability properties such as (shrinkage, chloride) of concrete. In this backdrop, this paper gives an account of properties of low stability hydrated products of the Portland cement under sea condition, low strength and stiffness of coral aggregates having large connected porosity with weak interface microstructure between the cement matrix and coral aggregates. Keywords: Coral aggregate, Physical & Chemical Properties, Strength, Durability properties.

Influence of catholytes on the generation of steel corrosion in concrete with accelerated chloride migration method

In the aim of developing localized corrosion, artificial corrosion on a steel sheet coated with concrete was implemented through accelerated chloride migration with a constant applied voltage (20 V). Four chloride solutions (20 g/L NaCl) with different initial pH were used. The pH values and chloride concentrations of the solutions were recorded during the test. Electrochemical non-destructive measurements of corrosion potential (Ecorr) and apparent linear polarization resistance (Rp,app) of the steel sheet were made. The concrete cover was then removed to observe corrosion visually (autopsy). The corrosion products were characterized by XRD and SEM and the results showed that the migration of chloride ions in concrete was slowed down by hydroxide ions, which was highlighted by a reduction of chloride transport number. Whether chloride ions were present at the steel interface or not, corrosion occurred because of acidification at the steel sheet/concrete interface due to the anodic polarization. However, when chloride ions were present, the corrosion propagation phase started earlier and the corrosion rate was higher.

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.

Effect of nucleation seeding and triisopropanolamine on the compressive strength, chloride binding capacity and microstructure of cement paste

Free chloride ions in concrete can lead to serious corrosion of steel and properties deterioration of reinforced concrete structures. A successful control of free chloride ions is significant to the service life of concrete structures. In this work, the combination of triisopropanolamine (TIPA) and C–S–H seeds is used to improve the chloride binding capacity of cement paste as well as its compressive strength. Results show that the compressive strength was enhanced due to the early nuclei effect of C–S–H seeds and promotion of TIPA to hydration. The mineralogical composition and microstructure analyses demonstrated the improved chloride binding capacity of the cement paste to free chloride ions is mainly due to the formation of Friedel's salts phase and the physical adsorption behavior of gels. TIPA promotes the hydration of aluminum-containing minerals, indirectly contributing to the formation of Friedel's salts. The compactness of microstructure of cement pastes is improved by using TIPA and C–S–H seeds, contributing to the physical adsorption of free chloride and inhibiting its migration. This work provides a feasible approach for the effective control of free chloride in cement/concrete.

Chloride ion penetration behaviour in concrete containing an expansive additive and a calcium-aluminate-based additive

The effect of the material characteristics on the infiltration behaviour of chloride ions in concrete containing a combination of an expansive additive and a calcium-aluminate-based additive has been investigated. The same level of salt resistance as that of blast furnace slug cement was exhibited even for a small addition amount. In addition, the permeation behaviour of chloride ions was largely influenced by the immobilisation capacity and pore network. When these changes were dominant, the results suggested that the characteristics based on the Fick diffusion equations may not necessarily reproduce the actual permeation behaviour of chloride ions.

Concrete admixtures - sustainable concrete

Durability of concrete, an important part of the sustainability theme, was, is, and will be one of the main topics for large infrastructure projects like the Gotthard base tunnel. For such important structures a service life of more than 80 years is expected. The prevailing underground conditions like water ingress, aggressive waters etc. will influence the choice of the concrete system and mix design. Therefore, a focus is on the potential damage mechanisms on the concrete like chloride ingress or sulfate attack. A well-designed concrete will be durable concrete which can withstand various external attacks and achieves or even extends the designed service life of the concrete structure. Based on the knowledge that the main damaging mechanisms for concrete are based on water penetration into the concrete, various measures can be taken to achieve concrete structures with significantly reduced permeability. These measure ranges from reduction of the water/binder-ratio, increasing the density of the concrete using silica fume, to the use of special admixtures in order to increase the durability of concrete. In an extensive research program, the influence of mix design components e.g. different admixture types, water/binder-ratio on hardened concrete properties like chloride resistance (chloride migration coefficient), sulfate resistance and water conductivity have been tested and analyzed.

Numerical and Empirical Models for Service Life Assessment of RC Structures in Marine Environment

The service life prediction of reinforced concrete (RC) structures in marine environment is essential in structural repair and health monitoring. In this paper, a numerical model for predicting the service life of reinforced concrete is first developed which considering the time-varying boundary of chloride concentration, critical chloride concentration and density of corrosion current. Based on the model, the effects of water–cement ratio, reinforcement diameter, concrete cover thickness and critical chloride ion concentration on the service life and deterioration duration of RC structures are investigated. The key factors affecting the service life of reinforced concrete structures are determined. More importantly, based on regression analysis, a new simplified empirical model for predicting the service life of RC structures is also developed. It provides a fast assessment tool for practical engineers. Both the numerical model and empirical model validated are suitable for practical engineering applications. The results show that with the increase of water–cement ratio, the service life of reinforced concrete structure decreases exponentially. And with the increase of the thickness of the concrete cover, the service life, deterioration duration, and safety reserve increase linearly. However, the influence of the diameter of the reinforcing bar on the service life can be ignored.

Formation Factor Concept for Non-Destructive Evaluation of Concrete's chloride diffusion coefficients

Estimation of chloride diffusion coefficient (Drcm) is an integral part of service life assessment of vulnerable concrete structures due to chloride induced corrosion. This study focuses on the suitability of an alternate non-destructive, low-cost approach of estimating diffusion coefficients through electrical resistivity and formation factor as a replacement of conventional destructive migration tests. The variation in formation factor for 60 concrete mixes with different Supplementary Cementitious Materials (SCM) types (fly-ash, slag) and proportions (0–40%) along with multiple mix parameters (w/cm ratio and target slump) were studied after 365 days of curing. Drcm values predicted from formation factor approach were found to be in close proximity to the coefficients obtained from migration test but however, required certain modifications to ensure conservative estimations. Tentative modification factors were developed for each binder separately as well as for all blended mixes. Based on the obtained factored Drcm values using the modification factor, it was demonstrated that it is possible to ensure reliable and conservative estimation of corrosion initiation time of any mixes without the requirement of destructive testing.

The Effect of Carbonation on the Diffusion of Chlorides in Concrete:Experimental Analysis and Application in the Calculation

The Effect of Carbonation on the Diffusion of Chlorides in Concrete:Experimental Analysis and Application in the Calculation

Diffusion behavior of chloride in coral aggregate concrete in marine salt-spray environment

In this study, the chloride diffusion behavior of coral aggregate concrete (CAC) in a salt-spray environment was investigated. Ten concrete groups were designed using different mix proportions, and the concrete samples were exposed to a salt-spray environment for 180 days. The effects of the aggregate type, CAC strength grade, fly ash (FA) content, and basalt fiber (BF) content on chloride ion diffusion were analyzed. The results showed that the chloride concentration of CAC was higher than that of ordinary aggregate concrete. The chloride corrosion resistance of CAC could be effectively improved by adding 30% FA or 0.1% BF to the concrete mix, and the peak chloride concentration decreases by 15.9% and 16.3%, respectively. The peak chloride concentration of concrete appeared at 3–5 mm in the concrete and exhibited a power function increase with the exposure time. In addition, a model for calculating the peak chloride concentration was established. The chloride diffusion coefficient decreased with an increase in exposure time. When the BF content was 0.1%, the chloride diffusion coefficient was the smallest. X-ray diffraction and thermogravimetric analysis were performed to analyze the erosion products, and the deterioration mechanism of the CAC in the salt-spray environment was determined.

Combined Freeze-Thaw and Chloride Attack Resistance of Concrete Made with Recycled Brick-Concrete Aggregate.

The objective of this study was to investigate the physico-chemical properties of concrete made with recycled brick-concrete aggregate, which was the mixture from waste concrete and waste clay brick in a 7:3 ratio. Specifically, this paper investigated the mechanical properties, freeze-thaw resistance, and distribution of water-soluble chloride ions of concrete containing RBCA and fly ash (FA) against combined freeze-thaw and sodium chloride attack. Concrete containing RBCA replacement of natural coarse aggregate and fly ash replacement of Portland cement was subjected to 45 freeze-thaw cycles containing sodium chloride solution. It was discovered that the mechanical properties and freeze-thaw resistance to sodium chloride attack gradually decreased with increasing RBCA content. At the same time, a replacement level of 15% FA by weight resulted in significant improvements in compressive strength and resistance to combined freeze-thaw and chloride attack. Furthermore, using a replacement of 30% FA by weight markedly improved the resistance to chloride ion penetration of concrete due to the lowest water-soluble chloride content.

Exposure duration and sub-zero temperature effects on concrete chloride diffusion decay index and binding

Accurate prediction of corrosion initiation period and service life of reinforced concrete structures requires accurate determination of their chloride diffusion coefficient and binding capacity. Temperature and exposure duration affect these properties, but there is paucity of knowledge regarding the effects of long-term exposure to sub-zero temperatures. Hence, the effects of sub-zero temperature, T, and exposure duration, t, on the chloride diffusion decay index, m, and binding in ordinary Portland cement concrete are investigated. Non-steady natural diffusion tests are conducted at + 5, 0, −5 and −15 °C for 3, 6, 12 and 18 months, and at the end of each period, the total and free chloride concentration profiles are determined. The index m is found to vary over a wide range, it being directly proportional to T and inversely to t. It drastically deviates from the commonly assumed value of 0.2 in the literature. Chloride binding is found to obey the Freundlich isotherm. The coefficient α of the isotherm equals 1.0 ± 0.16 and is only slightly dependent on T or t while its exponent β varies from 0.178 to 0.502, without exhibiting a systematic relationship with either parameter. Binding is noticed to increase with drop in temperature for the first three months of exposure, but over longer exposure durations, no systematic relationship is observed.

Bond behaviors between copper slag concrete and corroded steel bar after exposure to high temperature

In this paper, the experimental investigation on degradation law of bond behaviors between copper slag concrete and corroded steel bar after exposure to high temperature was conducted. The bond behaviors such as bond strength, bond stiffness, peak slip displacement and average bond stress-slip curve between copper slag concrete and corroded steel bar after heating were analyzed with the change in heating temperature and corrosion rate of steel bar. Moreover, the distribution of free chloride ion in concrete was measured and the chloride ion diffusion coefficient was also calculated. At last, the bond-slip constitutive model suitable for high temperature damaged concrete and corroded steel bar was proposed. The test results showed that the chloride ion diffusion coefficient of high temperature damaged copper slag concrete increased with the increasing of copper slag replacing ratio and heating temperature. The bond strength between copper slag concrete and corroded steel bar decreased with the increasing of heating temperature and corrosion rate of the steel bar and decreased at an accelerated rate with the increasing of the copper slag replacing ratio, and the peak slip displacement gradually increased as the heating temperature increased. However, the bond stiffness increased first and then decreased with the increasing of heating temperature, and the bond stiffness also increased with the increasing of copper slag replacing ratio. At last, the accuracy of the bond-slip constitutive model established based on the test results was verified.

Investigation of composite silane emulsion modified by in-situ functionalized graphene oxide for cement-based materials

Silane coatings were ubiquitously utilized to protect the structure concrete against water and aggressive ions in marine environment. In this paper, a novel design method for silane-based nanocomposite is proposed to enhance the water repellence for silane coatings. The graphene oxide sheets (GO) were first functionalized by in-situ polymerization of dopamine (DA), and then isobutyltriethoxysilane emulsion coatings were fabricated by sol–gel method with incorporation of rGO-PDA. The PDA molecules, bridging the GO sheets and silane molecules by forming chemical bonds of –NH, CO-NH, and Si-O-C, construct amorphous and dense network structure in the emulsion. The laser particle size analysis shows that GO sheets modified by PDA were dispersed better in silane emulsion. Furthermore, the newly developed silane emulsions were sprayed on the concrete surface, while the water and ions resistance were tested to evaluate the effectiveness of coating materials. The silane emulsions modified by rGO-PDA generate higher hydrophobic effects on concrete surface. The surface contact angles can reach as high as 140° and the capillary absorption rate for water is reduced by 90%. In particular, as the rGO-PDA content is 0.2%, the modified silane emulsions exhibit the highest hydrophobicity. Additionally, the long-term sulfate attack and chloride penetration tests also confirm that as compared with coating without modification, rGO-PDA modified silane emulsions can effectively reduce transport rate of chloride and sulphate ion in concrete by nearly 70%, and alleviate concrete degradation in great extent. This paper presents new ideas for the research of nano-modification of composite silane coatings and provides technical guidance for the surface protection against concrete structures in marine regions.

Numerical and experimental research on the effect of rainfall on the transporting behavior of chloride ions in concrete

Reinforced Concrete (RC) structures eroded by chloride ions will reduce the chloride ion concentration on the concrete surface under the effect of sustained rainfall dilution and erosion, and there will be rainfall convection areas and peak chloride ion contents. In this study, the influence of rainfall environment on the transporting behavior of chloride ions in concrete is studied through capillary absorption test and rainfall experiment. A numerical prediction model of chloride ion transporting behavior in concrete was established by COMSOL Multiphysics based on the rainfall tests. The chloride behavior is analyzed and studied. It is found that the numerical simulation results are in good agreement with the experimental results, and the predicted models of chloride ion diffusion under different rainfall conditions are obtained, and the transporting behavior of chloride ions can be effectively predicted. The results also show that with the increasing of rainfall intensity and rainfall time, the chloride ion contents on the concrete surface decreases obviously. When the rainfall time and rainfall intensity increase, the chloride ion contents of concrete decreases, and the binding capacity of chloride ions in the matrix weakens. This research provides some resulting information of RC structures in rainy marine areas.

Analytical solutions of moisture‐chloride ion coupled transport in unsaturated concrete

AbstractStudies of chloride‐induced corrosion in reinforced concrete structures are performed based on the reliable predictions of chloride and moisture distributions in concrete. This paper adopted the Laplace Transformation and the inverse Laplace Transformation to obtain the analytical solutions of the moisture‐chloride two‐way coupled transport processes. Additionally, the model has involved with realistic material parameters to predict the internal distributions of relative humidity and free chloride ions in concrete samples. To illustrate the accuracy of the present model, the calculations were compared with the available experimental results, and good agreements were obtained. It indicates that the present analytical model can successfully characterize the two‐way coupling effects between chloride transport and moisture diffusion in concrete; and the model can provide the distribution profiles of both chloride and relative humidity in concrete, which are useful for predicting the service life of reinforced concrete structures.