The reaction to fire of coated UHPC slabs was evaluated in a laboratory fire test using the “WKI method”. The back side of an unprotected 1cm-thick UHPC sample reaches up to 350°C after 15 minutes. In contrast, the best base formulation and dry application of 1.1kg/m² was able to drop the temperature to 213°C after 15 minutes. The intumescence formed a crack-free, homogenous, compact foam with a white crown and formed an almost pointed dome shape. There were no open hollow spaces to be observed (Fig. 1). All the test specimens maintained unreacted coating under the produced isolating foam.
In the next step, processing or dispersing additives were added to the basic BB3 recipe. With recipe BB21 it was possible to improve the fire protection effect throughout the entire exposure time (Fig. 2). The BB21 sample displayed homogenous foaming without cracks or breaks.
The increase in volume of the fire protection coating (regardless of the substrate) was assessed using thermo-mechanical analysis (TMA). This allows conclusions to be drawn on whether the chosen binder allows intumescence, at which temperature this begins and how high the formulation foams up. The TMA curve also provides information on the stability of the foam.
Fig. 3 summarizes the results from the TMA and the lab trials. The highest foaming level, the most stable foam and the best protection were achieved with fire protection coating BB21.
Two recipes were provided to the iBMB for further analysis in furnace trials. UHPC column segments were tested under standardized fire conditions. The results showed that high-performance fire protection coatings can achieve improvements, but that these improvements currently do not go far enough. Further development work could not be carried out due to budget restrictions. More development work could be the subject of later research projects.