A new approach to determine the maximum temperature of fire damaged reinforced concrete building elements

When a fire has damaged a reinforced concrete structure, an engineer has to work out a proper and efficient repair strategy. Because of the effect of the fire on the structural properties of the concrete and the steel, it is important to know the maximum temperature reached. Actually, methods like x-ray diffraction, thermogravimetry and mercury intrusion are used for this investigation. These methods can only determine a few temperature steps and can't provide a stepless thermometer. From these methods no step-less heat exposure can be drawn. For the first time the FTIR spectroscopy was used to determine the maximum temperature. This method has the advantage that the amorphous structures can be examined. It is shown that the wavenumber of the Si-O-stretching mode is a function of the temperature. The wavenumber decreases with increasing temperature. It should be noted that this correlation is independent from the time the sample is exposed to temperature. The decreases of the wavenumber is probably due to the fact that the Si-O-Si-chains of the CSH phases do depolymerise until monosilicate b-C2S.