Photothermal determination of thermal properties of concrete - a method evaluation

Abstract

The evaluation of thermal properties is probably an underrated tool for the onsite health monitoring of concrete structures. While the influence of water content on the thermal behaviour is obviously, a specific correlation with microcrack-density or carbonization state can be suspected. For further investigations, a robust measurement method is needed to characterize the thermal behaviour of concrete – under lab conditions as well as onsite. The photothermal approach offers a possibility to realize a real onsite measurement. Here, the surface to be investigated is heated shortly by a laser pulse and the cooling down is contactless recorded by an infrared camera or pyrometer. The obtained temperature transient allows the calculation of the thermal effusivity of the heated material. Especially this parameter - the thermal effusivity - is very sensitive to characteristic material modifications because it is the simple product of density, thermal conductivity and specific heat capacity. This contribution presents the application of the photothermal approach on three different concrete types. The obtained results were compared with those of a commercial device for laboratory investigations. Both agreed well within the estimated uncertainty ranges and therefore demonstrate the applicability of the photothermal method for this kind of investigations. First results of a concrete sample with different water contents support the potential of this method for the characterization of concrete in general.