Study of heating carbonized and non-carbonized concrete to assess reinforced concrete structures fire resistance

Purpose. Concrete carbonization, resulting from corrosion damage to the main elements of the precast reinforced concrete structure, drastically reduces the performance characteristics of reinforced concrete structures (RCS), especially under high temperature conditions. In this regard, it is of interest to study heating carbonized and non-carbonized concrete and its optimization. The given research is aimed at experimental investigation of the effect of carbonization process on the change of thermal diffusivity (α, mm2/s) and depending on the density of the material (ρ), acidity of the medium (pH), and thermoregulatory parameters of the process such as follows: temperature (T), specific heat capacity (C) and thermal conductivity (λ). The objects of the study were concrete samples taken in the carbonization zone, transition zone and the zone of the initial (control) concrete sample. Methods. To study the behavior of carbonized concrete, when being heated, the authors used the experimental method of synchronous thermal analysis. The obtained results were processed by dispersion and regression-correlation analysis, as well as Brandon's method. Findings. Based on the obtained research data, the optimization of experimental results (Brandon's method) was carried out and on its basis the corresponding parametric equations describing in the temperature range 293-1 123 K and acidity of the medium pH = 4÷12 the change of thermal diffusivity of carbonized concrete depending on its density and such thermo-physical parameters of the heating process as C, λ, T were obtained. Research application field. The obtained results of regression analysis of the thermal diffusivity of concrete temperature dependence can be used in solving the thermal engineering problem of fire resistance by numerical methods. Conclusions. Based on the optimization results, it was found that the concrete carbonation process could be represented by three mutually dependent zones: non-carbonized and carbonized zones and an intermediate transition zone between them. The experiments proved that heating concrete samples within the temperature range 293–1 123 K is accompanied by a change in thermal diffusivity depending on the pH of the environment, sample density and such thermo-physical parameters of the sample as temperature, heat capacity and thermal conductivity.