Abstract
Carbonization of concrete leads to a decrease in the alkalinity of concrete, an increase in the number of hydrogen ions in the pores, is one of the main factors that lead to corrosion of reinforcement, the formation of cracks and the subsequent reduction of load-bearing capacity of structures. The study of the depth of carbonization of concrete is to determine the pH of the pore liquid at different depths. There are devices with automatic maintenance of a given concentration of carbon dioxide, to determine the diffusion permeability of concrete to carbon dioxide, based on data on the rate of neutralization (carbonization) of concrete with carbon dioxide. Basically, this method is intended for use in the development of technology and design of concrete composition, providing long-term maintenance of structures in non-aggressive and aggressive gaseous environments, as chips are not prepared immediately before the test and after reaching the design age are placed in the installation with reagents for 7 days. But to determine the carbonization directly on the construction site or object often use the pH method, i.e. the indicator method of pH determination. To assess the concentration of hydrogen ions used acid-base indicators - organic substances – dyes, the color of which depends on the pH from the obtained results the algorithm of definition of depth of carbonization consists in the following actions. The improved formula of definition of depth of carbonization of concrete taking into account degree of aging and corrosion damages for what in the final formula the corresponding coefficients kst and kkor are entered: hcarb = {(2D˖C˖τ) / (mo˖kst ˖kkor)} 1/2, where the effective diffusion coefficient of CO2 in the concrete of the existing reinforced concrete structure, which is determined by the condition D = (mo˖δ2) / (2C˖t ). The thickness of the neutralized layer δ is determined experimentally on an existing structure using a physicochemical method (phenolphthalein solution or using depth gauges. .Concentration of CO2 in air C should be determined by chemical analysis of air samples taken directly from the structure or take ≈ 0.03%. Re. the ability of concrete mo is determined by the formula mo = 0.4 (C˖p˖f), taking the amount of cement, kg per 1m3, respectively, the strength of concrete. neutralization of concrete is equal to f = 0.5.
Highlights
Ivan Chebotar Director of PE "METCON" of UAS, Academic of the Ukrainian Academy of Sciences depth of carbonization of concrete taking into account degree of aging and corrosion damages for what in the final formula the corresponding coefficients kst and kkor are entered: hcarb = {(2DCτ) /} 1/2, where the effective diffusion coefficient of CO2 in the concrete of the existing reinforced concrete structure, which is determined by the condition D = / (2Ct )
Carbonization of concrete is a process of interaction with carbon dioxide (CO2) which results in the formation of calcium carbonate with a reduced pH of the liquid phase of concrete and the loss of passive action on concrete reinforcement (Fig. 1, 2) [1 − 4]
The carbonization process consists of a number of intermediate stages, starting from the surface of the concrete structure from the moment of its manufacture and attenuating as carbon dioxide penetrates into the concrete through open pores
Summary
Carbonization (neutralization) of concrete is a process of interaction with carbon dioxide (CO2) which results in the formation of calcium carbonate with a reduced pH of the liquid phase of concrete and the loss of passive action on concrete reinforcement (Fig. 1, 2) [1 − 4]. Despite the fact that carbonization occupies only 5...6% of destruction, but its prevalence in recent years in underground sewerhydraulic reinforced concrete structures has led to the need for urgent study of this important problem for the construction industry [4, 5]. Assuming that the concentration of CO2 in the pores of concrete varies linearly from the value of the concentration in the environment to zero in the zone of chemical interaction, and that the concentration gradient for small time intervals is constant, we can determine the effective diffusion coefficient by the formula
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