Some Stochastic Specific Features of Concrete and Reinforced Concrete Carbonization

Reliable calculation of concrete carbonization development is considered as a basis of forecasting corrosion of steel reinforcement and longevity of reinforced construction structures. Investigation results for stochastic specific features of carbonization in a protective concrete layer or its residual thickness in reinforced structures operating in airspace have been obtained for the last 20 years. In this case it is recommended for simulation of a protective concrete layer to use a normal law of distribution and a histogram which looks like distribution of extreme values is recommended for its residual thickness. Stochastic estimation for multiple measurements (1211 results excluding obviously unsuccessful ones) has made it possible to determine rather large values of variation coefficient (maximum values up to 0.34 with average index about 0.19) for indices of initial carbonization for С12/15−С20/25 concrete grades. At the same time these variation coefficients for С25/30 and С30/37 concrete grades have decreased up to 0.15 and 0.11, respectively. It has been established that density of distribution for random carbonization values of С12/15−С18/22.5 concrete grades being operated under conditions of agricultural premises with high aggressive environment corresponds, as a rule, to a normal law after excluding evidently unwanted values. In this connection use of maximum and minimum values of concrete carbonization in selections for estimation of variation coefficients differs from determination for the whole selection and it requires a corresponding correction. While operating С12/15−С18/22.5 concrete grades under conditions of agricultural premises in the period of 10−40 years average values of variation coefficients remain approximately constant with fluctuation up to ±0.01 with average value of 0.11−0.12. Spread in some variation coefficient values for concrete carbonization is decreasing from two to 1.25-fold within this period of time and later on it likely becomes stabilized. As a whole while determining duration of concrete protective layer carbonization it is necessary to take into account not only stochasticity of concrete protective layer and carbonization rate but also random values of concrete carbonization at specific carbonization rate and depth.