Integrity and fire performance of intumescent coating protection of steel elements subjected to tensile deformations

Steel elements may be subjected to large deformations in case of fire or as a consequence of previous accidental events that triggered the fire, such as an earthquake or explosion. In such cases, fire protective intumescent coatings (ICs) applied on the steel elements can crack or detach and expose the steel to higher thermal effects than assumed in design. However, there is at present little knowledge on the entity of deformations that are tolerated by the IC and to what extent cracks in the IC may cause reduced fire protection performance. This project was aimed at advancing such knowledge by means of an experimental campaign, where four different types of ICs (one water-based, one solvent-based, and two epoxy-based) were evaluated. Tensile tests of free film coating specimens were performed to assess the stress-strain relationship of the coatings. Then, ICs were applied on 39 steel plate specimens, which were first subjected to different tensile strains and then tested in an electric furnace under constant heating rate. The damage of the IC after the tensile test was evaluated and graded and the performance of the strained specimens during fire exposure was assessed against the performance of unstrained reference specimens. The results show that, while the two water- and solvent-based ICs could tolerate tensile pre-strains levels up to 16% without significant visible damage at 20°C nor reduction of the insulating performance during fire, the two epoxy-based ICs showed large cracks and detachments when subjected to tensile pre-strain larger than 5-8% and were not able to provide the required fire protection.