Parameter estimation approach applied to the characterization of an intumescent fire retardant paint

Intumescent paints are used as passive fire protection system in structural constructions. In particular they are widely used as fire retardant to protect structural steel elements. The thermal properties of intumescent paints are often unknown and difficult to be estimated since they vary significantly during the expansion process induced by the fire event; for this reason the fire resistance validation of commercial coatings is based on expensive, large-scale methods where each commercial coating/beam configuration has to be tested one by one. Adopting, instead, approaches based on the thermal modeling of the intumescent coating could provide a helpful tool to simplify the test procedure and to support the design of fire resistant structure as well. Inverse parameter estimation methodologies offer a robust tool to obtain this required information. The present investigation is focused on the assessment of such methodology applied to the restoration of the thermal properties which can be used to model the behavior of intumescent coatings. The parameter estimation procedure is first validated throughout its application to synthetic data derived with regard to an IPE 400 steel beam. The analysis is then completed throughout the application of the parameter estimation methodology to the experimental temperature history of protected steel beams subjected to a fire test according to EN 1363-1 and ENV 13381-4 standards. The results suggest that the approach suggested here, based on the modeling of the behavior of the intumescent paint by means of an equivalent thermal conductivity, could be suitable for quantifying the fire retardant effect of the protective coating.