Approaches for the assessment of the residual strength of concrete exposed to fire

Generally, concrete structures have a high fire resistance. After fire, it is of economical interest to reuse the structure after appropriate repair based on a reliable assessment of the residual strength. This paper deals with some fundamental aspects of a scientific and systematic methodology to assess the damage and to estimate the residual concrete strength on the basis of the change in colour and the crack development. This method seems to be promising, but the number of cracks and the change in colour are influenced by the test set up. Furthermore, these relationships change when the concrete ages after heating. Other methods such as water immersion, the Rebound Index and microscopy also provide an adequate basis for the assessment of the temperature in heated concrete.