Basic Approach for the Diagnosis of Concrete after Fire Exposure

Concrete structures have a good fire resistance. After the fire, depending on the amount of damage, they may be repaired and reused. However, knowledge is needed to do this in a systematic and scientific way. This paper describes the parameters influencing the residual compressive strength of heated concrete. Since this strength decreases with temperature, the temperatures inside the concrete need to be known to assess the remaining load bearing capacity of concrete members. Two assessment techniques are discussed in this paper. Firstly, the colour alterations of the concrete surface and of the aggregates are measured, from which colour paths are derived. The shape of these paths allows to distinguish different temperature zones. Secondly, due to thermal decomposition of the cement matrix and thermal cracking at the interfacial transition zone, an increase of the porosity is found. This internal damage can be measured by the weight increase found after immersing concrete cores under water.