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PurposeThe purpose of the paper is to mathematically model and predict the characteristics of thermo-mechanically treated (TMT) rebar when subjected to elevated temperatures.Design/methodology/approachData were collected from a few selected studies for developing the constitutive relations. Using the exposed temperature and the duration of heating as independent variables, the empirical relations were developed for determining the changes in mechanical properties of TMT rebars at elevated temperatures.FindingsRecrystallization of TMT rebar crystals took place around 500 °C, which led to a decrease in the dislocation density along with the increase of large-sized grains, resulting in the degradation of strength. Up to a temperature range of 500 °C, the normalized fracture strength was higher, while the normalized fracture strain is not so high. This indicated a failure of brittle nature.Originality/valueThis is an original work done by others as a study to theoretically predict the mechanical behavior of TMT rebars when exposed to elevated temperature.HighlightsThe TMT bars showed brittleness characteristics up to 500 °C and showed ductility characteristics after that on account of its recrystallization and extensive tempering of the outer martensitic rim around that temperature.The comparison between the super ductile (SD) TMT and the regular TMT exhibit shows that the SD-TMT bars were about 1.5 times more ductile than the normal ones.

RCC structures under elevated temperatures/ fire conditions, results in the structural damage and sometimes leads to structural collapse. It is very difficult to predict the behavior of a concrete at elevated temperatures because the fire spread is random and the heating profile is unpredictable. Excessive heating of concrete over long duration will degrade in mechanical properties and lead to structural failure. In the present study, thermal protection coatings have been explored to reduce the conduction of heat/fire into the core of concrete for protection of the concrete linings and reinforcing steel. Experiments are carried out using Cermabond-569 and Low density ablative material (LDAM) coatings on M30 and M40 concrete structures with 2mm and 4mm thickness as per the specification of Hydro carbon fire curve. The temperature profile across the front and back surface are measured as a function of time. From Temp-Time plots, the temperature difference (∆T) between uncoated and coated samples was observed as 200 0 C for Cermabond and it is 140 0 C for LDAM coated samples. Increase in (∆T), was observed with respect to thickness of coating. Cermabond-569 coating has good adhesion, low porosity and low thermal conductivity compared to LDAM coating. It is concluded that for M30 and M40 RCC structures, Cermabond-569 coating is most efficient for high thermal/fire resistance at elevated temperatures.