ABSTRACT
Intumescent Coatings (IC) are protective materials that provide the thermal insulation of steel structures. When exposed to fire, IC generally react to fire by expanding in thickness by 15 to 30 times in a standard test, to form a carbon “char” with low thermal conductivity, which essentially forms an insulating layer reducing the rate of heat transfer and extending the time necessary to reach the critical failure temperature of the underlying steel. Moreover, during the process the IC change their chemical, physical and also thermal properties. Among the main problems for IC there is the dependence of thermal response (chemical reaction) under different fires. In particular, the dissolution of the IC, resulting in a reduction of performance, can occur for heating curves with thermal gradients lower than Standard fire curve ISO 834 (EN 1363-2) close to the IC initiation temperature. For this reason, in EN 1363-2, a slow heating curve (smouldering curve) is also defined. This work shows an experimental program that could allow to characterize the thermal properties of the IC, based on the measurements of thickness variation during different fire conditions (ISO 834 and Smouldering curves) and highlighting the parameters which mostly affect the thermal behavior of IC-protected steel members. The research is aimed to allow analytical or numerical modelling of steel members protected by IC through a finite element thermal analysis. This modelling could be useful for the fire designers, since it allows to take into account the presence of the IC also when the Structural Fire Safety Engineering approach (SFSE) is applied, according to the modern fire regulations. The experimental results show that the behaviour of IC depends on the initial thickness, on the section factor and only slightly on the input fire curves.
