New, blended slag cements gain in interest due to the increasing demand of reduced emission of carbon dioxide during cement production. These new cements are based mainly on recycled material such as slag. For a general application of this cement in structures, there is demand of deep knowledge on this new material, e.g. with regard to the structural performance at elevated temperatures.

The aim of the project is the development of new experimentally based material laws on the compressive strength of concrete at elevated temperatures. An extensive testing program was performed. The tests allowed the determination of the concrete’s compressive hot strength at 300°C, 500°C and 700°C and additional losses in strength during the cooling phase to ambient temperature. As test specimens, concrete cylinders made with an ordinary portland cement (CEM I), a portland-limestone cement (CEM II-A-LL) as well as a new supersulfated slag cement (SSC) were chosen. During the heating cycle, significant losses in the compressive strength were noticed, followed by additional losses of up to 30% during cooling from high- to ambient temperature.

Long term tests on the residual strength showed further losses in the concrete’s compressive strength up to 28 d after cooling to ambient temperature. In general, it was noticed that the material behaviour of the three types of cement used was very similar.

Further, the spalling behaviour of concrete cylinders made from these three cements was analysed. It was noticed that rapid heating did not cause explosive spalling at the concrete’s surface. However, one week after cooling to ambient temperature, significant post cooling spalling was noticed. The concrete cylinders made with the common cement (CEM I, CEM II-A-LL) were affected by post cooling spalling, while the surface of the cylinder made with the new slag cement (SSC) remained compact.