Papers by Keyword: Chloride

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.

Abstract: This study presents assessment of the environmental impact in terms of the CO₂ due to silane treatment for extending corrosion-free service life of concrete structures under chloride attack. To achieve this, there are two issues to be addressed; prediction of corrosion-free service life extension, and assessment of the amount of CO₂ emission. In predicting the corrosion-free service life extension, the behaviors of chloride diffusion before and after time-based silane treatment are considered. Then, the cumulative CO₂ due to silane treatment is accordingly calculated. The ratio of the corrosion-free service life extension to the cumulative CO₂ is defined as the effectiveness of silane treatment, and used to compare different silane treatment strategies.

Abstract: Recycled aggregates concrete (RAC) becomes an important participant in recycled materials. This study was performed in order to evaluate the effect of recycled coarse aggregates (RCA) on the chloride resistance of concretes with different coarse aggregates replacement ratio under wetting–drying cycles. Composition influence on the concrete were studied with different the addition of admixtures. The results indicate that the free chloride content decreased with the increasing of depth, whist it increased with the increasing replacement ratio of RCA at the same depth. Wetting–drying cycles accelerated the process of chloride diffusion. It was also found that the addition of admixtures can improve the ability of chloride resistance of concrete.

Abstract: Concrete is a material synonymous with strength and longevity and plays a vital role in the construction activity. Scarcity of natural sand and its fast rising cost have paved way for use of bottom ash, a residue being collected from the thermal power stations, as substitute for sand. Recent research shows that the mechanical properties of concrete containing bottom ash as a partial replacement of fine aggregate is suitable for construction. The various parameters involved are different percentage of bottom ash and grades of concrete. This present experimental study is made on chloride induced corrosion using accelerated corrosion test (ACT) and related durability properties such as water absorption & porosity, water sorptivity and rapid chloride penetration test (RCPT). Compressive strength test is performed in order to ascertain the mechanical property of bottom ash concrete. The above tests were conducted on the concrete specimens and the results were found comparable with the control concrete up to 20% replacement of bottom ash. Utilization of bottom ash in concrete becomes more significant in cost-saving and reducing the quantity of landfill, thus providing an economical and ecological way of conservation of natural resources.

Abstract: Molecular Dynamics was employed to investigate the interaction of calcium silicate hydrate (C-S-H), the primary hydration product of cement based materials, and chloride, causing severe durable problems of concrete. The 11Å tobermorite structure was chosen to describe the C-S-H structure and the CLAYFF force field was used. It is observed in the simulation that there are no bound chlorides at 303K, while a fraction of chlorides appear in the adsorption district of tobermorite/solution interface at 323K indicating the temperature increase can improve chloride sorption capacity of C-S-H. The formation of Ca-Cl cluster is found on the surface of tobermorite, which is assumed to promote the chloride sorption. The experimental results of sorption isotherms of C-S-H in CaCl₂ and NaCl aqueous solutions with the same chloride concentration have proved this point. Other researchers have made the same conclusion by means of molecular dynamics modeling, NMR tests or zeta potential experiments.

Abstract: This work aims at studying the passive behaviour of new alloy corrosion resistant steel Cr10Mo1 and plain carbon steel (as a reference), in simulating concrete pore solutions contaminated with different concentrations of chloride (0 M, 0.2 M, 0.6 M and 1.0 M, as NaCl). The electrochemical behaviour was evaluated by linear polarization resistance, d.c. potentiodynamic polarization and electrochemical impedance spectroscopy. The surface films composition was investigated by X-ray photoelectron spectroscopy (XPS). The results show that the passivity of the corrosion-resistant steel has no significant decline with chloride contents increasing, while carbon steel hardly passivates with chloride above 0.6 M. The primary constituents of the passive films formed on the corrosion-resistant steel and carbon steel are very different; the former contains both Cr and Fe oxides while the letter consists of only Fe species. Cr oxides, as the key components for the passive film on the corrosion-resistant steel, can still remain stable and protective under high concentration of chloride, which supports the excellent passive performances of the corrosion-resistant steel in severe conditions.

Abstract: This paper presents the environmental impact in terms of CO₂ and service life extension due to repairs by surface treatment on concrete structures exposed to time-dependent chloride attack. The service life extension is defined as the difference between the corrosion-free service life of concrete before and after surface treatment by silanes. The corrosion-free service life is predicted based on considering the mechanism of chloride diffusion which can be described using the partial differential equation (PDE) of the Fick’s second law. With the surface treatment, solving the PDE is complicated due to non-constant diffusion coefficient. Furthermore, if the diffusion coefficient is time-dependent, it is even more complicated to solve the PDE. Therefore, numerical computation by the Crank-Nicolson based finite difference method is introduced as a computational tool. From computation, the chloride profiles before and after different surface treatment strategies can be calculated considering time-dependent chloride attack. Furthermore, the environmental impact in terms of CO₂ due to surface treatment is also presented. Finally, numerical examples to calculate the service life extension after surface treatments and the environmental impacts are compared.

Abstract: Concrete structures are generally subjected to serious deterioration under harsh environment, even though the concrete materials exhibit inherently higher durability than any other construction materials. The service life of concrete structures is directly affected by the durability performance under various conditions. In this regard, many studies have been conducted on the deterioration of concrete structures under various environmental conditions. However, previous studies were confined mostly to the deterioration of concrete structures under single deteriorating factor such as chloride ingress only or sulfate attack only, although real environment is actually a combination of such factors. The purpose of the present study is, therefore, to explore the effects of combined deterioration due to chlorides and sulfates in concrete structures. To this end, comprehensive experimental program has been set up to observe the chloride penetration behavior under combined deterioration conditions of chlorides and sulfates. The test results indicate that the chloride penetration is more pronounced for the case of combined attacks of chloride and sulfates than the case of single chloride attack. The surface chloride content is found to increase with time and this phenomenon is also more pronounced under the combined exposure of chlorides and sulfates. The present study may allow more realistic assessment of durability for such concrete structures which are subjected to combined attacks of chlorides and sulfates.

Abstract: The main cause of premature deterioration of reinforced concrete structures is the corrosion of steel bars, induced by chloride ions (for example in marine environment) and/or by carbonation (atmospheric CO₂). At the same time, environmental-induced degradations of concrete can also affect the structure, such as sulphate attack. This can lead to the formation of ettringite, inducing expansion inside the materials and finally degradation. Carbonation, chloride and sulphate ingress are usually studied separately in the literature. This is not representative of in-situ conditions since they can occur at the same time and can have an influence on each other. In this paper, chloride ingress are studied for concretes and cement pastes partially carbonated or/and in presence of sulphate in chloride contact solution. The mixtures contain OPC alone or with supplementary cementitious materials (SCM). SCMs are here pozzolanic materials (Fly Ash or Metakaolin) or alkali-activated materials such as ground granulated blast furnace slag (GGBS). The materials, partially carbonated (2 months in chamber at 1.5 % of CO₂) or not, are put in contact with chloride solutions in presence of sulphate. This study focuses on the apparent chloride diffusion coefficients, as well as chloride binding isotherms which are obtained by the profile method. In addition, some aspects of the microstructure and of the pore structure are investigated, by using Mercury Intrusion Porosimetry and ²⁷Al NMR, in order to better understand the results obtained relatively to the apparent chloride diffusion coefficients and to the chloride binding. Chloride ingress increases when sulphates are present in the contact solution for all cement materials tested (partially carbonated or not). In addition, chloride ingress is faster when the material is partially carbonated before contact with chloride solution. It appears that both carbonation or presence of sulphate decrease chloride binding, thus explaining the results. The results show an evolution of the properties as a function of the cement replacement ratio by SCMs.

Abstract: In Japan, a number of existing prestressed concrete bridges are suffering chloride attack. Especially in the cases that bridges were constructed decades ago, grouts tending to bleed or swell were often used, and the grouting was not well done. As a result, ducts were not completely filled and voids remained. For the incompletely grouted zones, tendons were vulnerable and more severely corroded. To repair those bridges, effective and economic regrouting materials and method are requisite. Recently, a new repair grout has been developed in the authors’ group by mixing ion-exchange resin, a widely used polymer in water purification, into cement paste. Since IER can absorb chloride ions, IER mixed grout is promising to remove free chloride ions in the unfilled duct. In this study, the chloride ion diffusion properties of IER mixed grout was investigated experimentally. Tendons, which were preliminarily spread at the surface with chloride, were grouted using the IER mixed grout. After curing, the chloride amount in the grout was analyzed using potentiometric titration against silver nitrate. It was confirmed that IER effectively absorbed chloride ions from the surface of tendon, and thus is promising to alleviate the corrosion. Furthermore, to promote the practical use, other properties of the grout, such as strength, flowability and bleeding ratio, were test. It is found that as IER ratio increased strength and flowability tended to decrease but bleeding did not occur. When mix proportion and addition ratio of IER were adopted properly, those properties satisfied the acceptance criterias in design code.