Improvement of the calculation and experimental method of evaluation of carbonization of reinforced concrete structures of sewerage underground systems

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 k_st and k_kor are entered: hcarb = {(2D˖C˖τ) / (m_o˖k_st ˖k_kor)} 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 = (m_o˖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 m_o = 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.