Thermal Path Reconstruction for Reinforced Concrete Under Fire

In post-fire investigation, the damage of fire-exposed concrete is usually related to the temperature time-history. This paper presents the results of an experimental investigation on reinforced concrete, cement pastes and mortars exposed to fire, aimed at identifying the benchmarks necessary to reconstruct the thermal path 15 dry core samples were obtained from a real fire damaged structure and compared to other reference dry cores collected in not damaged zones of the same structure. In addition, 16 irregular spalling samples were collected and investigated. In order to assess changes in mineralogical composition and microstructure modifications due to temperature, 20 cubic cement pastes samples and 20 prismatic mortars specimens were realized and exposed to temperature ranging from \(200\,^{\circ }\hbox {C}\) up to \(800\,^{\circ }\hbox {C}\) with a gradient of \(10\,^{\circ }\hbox {C}\)/min and keeping the maximum temperature for 1 h. Optical and Scanning Electron Microscopy, X-Ray Diffraction, Thermoanalysis and MIP porosimetry along with Helium picnometry allowed to investigate the damage degree and the mineralogical changes of the concrete and other cement based materials. Calibrated Colorimetry could determine fire temperature in the different parts of the samples due to colour changes in the mineralogical phases and in the microstructure of cement materials. The absence or presence of some specific minerals (like Portlandite), the colorimetric variations and other microstructural features are markers capable of assessing the temperature reached with high accuracy. The approach and the data showcased in this work can be useful for post-fire investigations, for theoretical and numerical models tuning and to optimize the structural retrofitting.