Papers by Keyword: Concrete Corrosion

Abstract: It was defined that structural elements of a building made from electrically conductive concrete may reduce their performance characteristics due to the corrosion environment. The main reasons for that process are supplement corrosion factors such as a wide range of temperature, humidity as well as chemical agents in the environment. In this article results of different properties (mechanical, electrical) of electrically conductive concrete are discussed including their alterations due to sulphate attack. Also, microstructure as well as physical and chemical properties of modified concrete have been considered after being exposed to sulphate attack (Na₂SO₄) for 112 days. That component has been used for modeling the sulphate attack environment. Compressive strength, rate of the corrosion process, the volume of absorbed SO₄^2– ions from a water-based solution of Na₂SO₄ was defined in order to analyze the effect of sulphate attack. Scanning electron microscopic investigation, energy dispersive spectroscopy, differential thermal analyses were applied for observing morphology and properties changes of modified samples. To assess the influence of sulphate attack on mineral composite materials the approach was suggested and this method might be useful to foresee the durability of concrete while exposing it to the high corrosion environment. In addition to that, a possible method of protection for electrically conductive concrete from sulphate attack was also considered in the article.

Abstract: This paper considers the basic methods of physical-mathematical modeling that are used to describe the processes of non-stationary mass transfer of "free calcium hydroxide" in concrete structures placed in a liquid environment with a defined flow rate. The boundary value problem of "free calcium hydroxide" mass conductivity in dimensionless variables is obtained. To demonstrate the possibilities of the obtained solution, we will carry out a numerical experiment: in which the fluctuation in the field of dimensionless concentrations by the different values of the Fourier number, in accordance with the theory of similarity, will be considered as an indicator of the process time. The study indicated the results of calculating the concentration distributions "free calcium hydroxide" over the dimensionless thickness of the concrete structure at Fourier numbers 0.01; 0.1; 0.2; 0.5 and 1. The study also provides an example of determining the time of reaching the coastal structure surface critical concentration "of free calcium hydroxide" leading to the beginning of high-basic cement concrete. Analysis of the solution also makes it possible to determine the duration of the service life of a reinforced concrete structure, which is determined by the processes occurring at the interface: in concrete - mass conductivity (k), and in the liquid phase - mass transfer (β).

Abstract: The paper considers methods of physical and mathematical modeling that can be used to describe the processes of non-stationary mass transfer of free calcium hydroxide in buried concrete and reinforced concrete structures of coastal zones. The authors proposed a mathematical model of mass transfer in an unrestricted two-layer plate in the form of a system of parabolic partial differential equations with boundary conditions of the second kind at the "concrete-liquid" interface and of the fourth kind at the "concrete-soil" interface. In terms of the results of experimental studies of the mechanisms for reducing the quality of concrete due to exposure to sulfate and acidic environments, using the obtained solutions of the mathematical model, it becomes possible to select the optimal composition of concrete with high anticorrosion properties.

Abstract: A study of the joint work of cement concrete and material winding fiberglass composite reinforcement with different types of coatings and types of windings was conducted. The type of periodic profile winding is presented, which increases the adhesion of the material of glass fiber reinforcement winding with cement concrete. It has been established that the winding of the periodic profile improves the strength properties of the composite reinforcement material. The influence of aggressive media on the adhesion of fiberglass rods with different types of surface preparation from cement concrete is estimated.

Abstract: The corrosion is one of the main deterioration reasons of structural concrete and reinforced concrete. The corrosion is a consequence of unsatisfactory construction maintenances, poor diagnosis of defects' causes and no fracture control of concrete structures and also incorrect repair specifications and incorrect products and techniques selecting for the repair inevitably lead to the concrete structures' deterioration. The most countries are taking care to developing of the national standards for using as manuals for the protection and repair of concrete structures against corrosion to avoid these negative factors. The article authors are offering the comparative analysis of the harmonized Russian state standards and Eurocodes for the protection and repair of concrete structures against corrosion.

Abstract: The maturity behavior of cement mortar specimens with different concrete additives during the 28 day curing period has been examined using the AC Impedance technique. The main focus of this part of the study is to understand the impedance and capacitance behavior of the steel rebar in cement mortar using different additives during the early stages of hydration process. In this respect, two sets of specimens were prepared: One set consist of two graphite electrodes surrounded by a carbon steel rod for AC Impedance measurements. Another set consisted of two carbon steel setup that has been used for monitoring corrosion of two steel reinforcement bars embedded in cylindrical mortar specimens. The specimens are placed in a salt fog (spray) cabinet for 1,000 hrs.Galvanic current between the two coupled electrodes has been measured using zero resistance ammeter (ZRA) to monitor the extent of corrosion. The in-situ measurement was carried out in a sequential manner over a periodical basis of up to 1,000 hrs of salt fog cabinet exposure. Different mortar mixes were studied including ground granulated blast furnace slag (GGBS) and silica fume (microsilica) as additives and calcium nitrite as corrosion inhibitor and chloride as a contamination species. This data helps in understanding the corrosion activities at the rebar-concrete when interface combined with salt fog test according to (ASTM B117), which can be further correlated with the atmospheric and marine corrosion of steel rebars in concrete. The overall results have indicated the tendency of the admixture to show different hydration processes during the early stages of concrete curing. The interfacial impedance spectrums and galvanic current testing clearly identifies and documents this process for each material.