Papers by Keyword: Chloride

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Authors: Xin Zhu Zhou, Jian Jun Zheng
Abstract: Practical experience and observations suggest that corrosion affected reinforced concrete (RC) structures are more prone to cracking than other forms of structural deterioration. Concrete cracking incurs considerable costs of repairs and inconvenience to the public due to interruptions. This gives rise to the need for prediction of the time to surface cracking of concrete in order to achieve cost-effectiveness in maintaining the serviceability of RC structures. The intention of this paper is to develop a numerical method for predicting the time to surface cracking of corrosion affected RC structures. In this method, concrete with embedded reinforcing steel bars is modeled as a thick-wall cylinder. With an exponential curve modeling the energy dissipation process in concrete, the element transfer matrix is derived analytically. The time to surface cracking is then determined by solving the nonlinear problem numerically. Finally, the validity of this numerical method is verified by comparing with experimental results collected from the research literature.
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Authors: Sotiris Tsivilis, A. Asprogerakas
Abstract: In this paper the diffusion of chloride ions through limestone cement concrete is studied. The Portland limestone cements have many benefits and the new European Standard EN 197-1 identifies 4 types of Portland limestone cement containing 6-20% limestone (types II/A-L and II/A-LL) and 21-35% limestone (types II/B-L and II/B-LL), respectively. Portland limestone cements of different fineness and limestone content (0-35% w/w) have been produced by inter-grinding clinker, gypsum and limestone. Six concrete mixtures were prepared and the Nordtest Method (accelerated chloride penetration) was applied for the determination of penetration parameters for estimating the resistance against chloride penetration into hardened concrete. The diffusion equation of Fick’s second law was used for the determination of the effective chloride transport coefficient. It is concluded that Portland limestone cement concrete indicates competitive behavior with the Portland cement concrete. Limestone content up to 15% has a positive effect on the concrete resistance against chloride penetration.
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Authors: Tassia Fanton, João A.M. Bender, Leandro G. Blois, Franciele Müller, André T.C. Guimarães
Abstract: The chloride diffusion coefficient indicates the capacity of a particular type of concrete to resist chloride penetration and is therefore used to predict the service life of a particular reinforced concrete structure exposed to environments containing this type of aggressive agent. Its experimental determination is time-dependent and time-consuming. For that reason, our study analyzes the characteristic behavior of the diffusion coefficient (D) of concretes in the saturated condition by testing higher NaCl concentrations and lower contamination ages than those used in standardized tests, in addition, the objective is to analyze the behavior of surface chloride concentration (Cs) over time. Therefore, it was concluded that for concrete dosed with pozzolanic cement, the Cs value varied with increasing tendency at higher ages. In addition, the D value obtained by the proposed method presented values ​​close to those obtained by standardized tests at contamination ages of 21 and 35 days.
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Authors: T. Sundararajan, Eiji Akiyama, Kaneaki Tsuzaki
Abstract: Crevice corrosion experiments on pure iron were carried out in a 0.5 M acetate buffer with varied chloride concentrations. Changes in resultant currents and morphology due to crevice attack were explained by IR potential drop mechanisms. The specimens experienced potential drop inside the crevice, which resulted in the formation of passive, active, and hydrogen evolution regions. The passive region did not exist in the electrolyte containing 0.05 M and 0.5 M chloride. Hydrogen evolution, which occurred inside the crevice was measured on rear side of the specimen using hydrogen permeation test. The results suggest that the hydrogen produced inside the crevice is measurable using a permeation test. The entry of diffusible hydrogen showed a significant increase with the addition of chloride into the acetate buffer.
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Authors: Dong Jin Wan, Dan Qu, Hua Xiao, Yong De Liu, Ting Lu, Wen Qing Xu
Abstract: Hydrotalcites (HT-X) of different Mg/Al ratio (X is Mg/Al molar ratio, 3 and 4) was synthesized by co-precipitation method. Calcined HTLCs (CHT-X) at 500°C have been shown to recover their original layered structure by taking up chloride ion from aqueous solution. Adsorption of chloride by CHT-X was investigated in batch mode. The kinetics study showed that the pseudo-second-order kinetics model could be used to describe the adsorption process satisfactorily. The equilibrium isotherm showed that the Langmuir model gave a better fit to the experimental data than the Freundlich model. The maximum adsorption capacity of CHT-3 was 83.33 mg/g; CHT-4 was 90.09 mg/g .The samples of different Mg/Al ratio have different crystallite size, thus showing different adsorption capacity. As the Mg/Al ratio increases from 3 to 4; the electric charge density between the layers becomes weaker; the interlayer spacing increases; the sample shows greater adsorption capacity. The HT-X where characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), electron dispersive X-ray analysis (EDX).
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Authors: Shohana Iffat, Abul Bashar Emon, Tanvir Manzur, Syed Ishtiaq Ahmad
Abstract: Durability means the resistance to physical or chemical deterioration of concrete resulting from interaction with environment (physical deterioration) or interaction between constituents (chemical deterioration) of concrete. A durable concrete ensures corrosion resistance of embedded steel which in turn ensures a better longevity of the structure as a whole. Concrete in structures in the coastal areas are the most susceptible to chemical deterioration as sea water, with high concentration of chloride ions, has quite a detrimental effect on durability of concrete. In these cases, the lower the chloride permeability, the better the durability of concrete. As instruments for standard chloride permeability test is very expensive, an experiment has been conducted to carry out Rapid Chloride Permeability Test (RCPT) using improvised apparatus made of readily available low-cost materials. Several RCPT tests were performed using this simple method and results showed marked variation in chloride permeability for concrete with different quality.
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Authors: Xiao Yong Wang, Han Seung Lee
Abstract: This paper presents a model for chloride diffusion in cracked concrete. This numerical model includes two parts: hydration model and chloride diffusion model. The hydration model starts with mix proportion of concrete and considers both Portland cement hydration and pozzolanic activity. By hydration model, the evolution of properties of cement paste is described as function of curing age. Furthermore, based on general effective media theory and composite spheres assemblage model, the effective diffusivity of chloride ions in concrete without crack is obtained. Finally based on crack distribution in cracked concrete and finite element methods, the diffusion of chloride ions in cracked concrete is predicted. The prediction results agree well with experiment results.
661
Authors: Do Gyeum Kim
Abstract: This study analyzed the impact caused by the change in the physical properties and fine structure of concrete by setting compressive strength, void ratio and permeability as the index to express the physical properties and geometric structure of concrete and then by analyzing the physical properties according to the mix properties of concrete, and secured the data to estimate the corrosion time of structure rebar by analyzing the chloride diffusion speed according to the change in the chloride diffusion speed and physical properties depending on mix properties.
367
Authors: Qi Xiao, Rui Wang, Lei Xu
Abstract: SnO2 thin film on the glass fiber was prepared by the ethanol solvent and crystalline tin chloride based Sol-gel method, including the process of solution preparation, fiber dip-immersing, gel reaction and annealing. The sol was prepared by alcoholysis reaction of 0.9mol/l chloride- ethanol solvent under 80°C. A thin film of sol was prepared by dip-immersing process, then a post annealing process with various temperatures and time was adopted to form a stable crystallized film on the surface of the glass fiber. X-ray diffraction, scanning electron microscope (SEM) and fiber electric resistance measurement were utilized to characterize the transmittance and resistivity of the thin film With the rising of annealing temperature, the transmittance of the thin film was firstly increased and then decreased while the resistivity changed adversely. At last, an optimized annealing process with 550°C and 3h was chosen.
194
Authors: Han Seung Lee, Hwa Sung Ryu
Abstract: The durability of a concrete structure is most significantly influenced by the corrosion of reinforcing bars, rather than by the deterioration of concrete itself. The corrosion of reinforcement bars due to chloride serves as a main deterioration factor at the interface between the bars and the concrete in the concrete structure. Accordingly, the corrosion inhibitors are widely used to improve the resistance to chloride penetration into reinforced concrete. Corrosion inhibitors are generally divided into the anode-type inorganic inhibitors and anode-cathode-type organic inhibitors, in terms of the reaction type. It is known that when the Cl-:OH- concentration ratio exceeds 0.6%, film on passive state metal on the bar-concrete interface is damaged and local corrosion starts regardless of the chloride ion content. In this study, the performance of the corrosion inhibitor was examined using a potentiostat, with chloride ion contents of 1.2kg/m3 (as reference), 2.4kg/m3, and 4.8kg/m3. The variables were the inhibitor type, Cl-:OH- molar ratio according to the addition of anode-type inorganic corrosion inhibitor (four ratios: 0.0%, 0.3%, 0.6% and 1.2%), and ratio compared to the standard anode-cathode-type organic corrosion inhibitor liquid (four ratios: 0.0, norm 1/2, norm, norm 2 times). As a result, with the anode-type inorganic nitrite corrosion inhibitor, the corrosion inhibition performance was verified with a corrosion potential of -0.30V at a molar ratio of 0.3% or higher when the chloride ion content was 1.2kg/m3, and at a molar ratio of 0.6% or higher when the chloride ion content was 2.4kg/m3 or 4.8kg/m3. With the anode-cathode-type organic corrosion inhibitor, the corrosion inhibition performance was very good at half the standard quantity (0.42kg/m3) regardless of the chloride ion content. From the added corrosion inhibitor quantities, the anode-cathode-type organic corrosion inhibitor had a better corrosion inhibition performance than the anode-type inorganic nitrite corrosion inhibitor.
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