Intumescent coatings used for the fire-safe design of steel structures: A review

Abstract

The mainstream use of intumescent coatings for the design of fire safe steel structures has fostered extensive research into the development of effective intumescent coatings and the assessment of their fire performance as thermal barrier to structural elements and materials. The research community has highlighted numerous challenges related to the current design framework based on standard fire resistance furnace testing and the current methodologies have been questioned due to its over-simplifications, limitations and uncertainties. In order to overcome these challenges, numerous research studies have proposed comprehensive approaches and methodologies to investigate the effectiveness of intumescent coatings exposed to a range of heating and fire conditions. This review covers the more recent developments in the field of fire testing and analysis of the fire performance of steel elements protected with intumescent coatings. Apart from the chemical formulation, the substrate boundary conditions, the applied coating thickness, the heating conditions and the fire test method appeared to be the key governing factors. All of them should be considered for a rigorous and systematic testing and design environment that allows the explicit quantification of the effectiveness of intumescent coatings.

Effects of substrate thermal conditions on the swelling of thin intumescent coatings

“…Thanks to its open environment, the experimental setup based on H-TRIS test method allowed for the visual inspection of the test samples during thermal exposure. As shown in Figure 5, upon heating, the coating underwent different phases, typical of intumescent reactions 9,29 . First, the virgin intumescent coating softens and gradually decompose: this can be observed by the change in colour from white to dark/black and the release of volatiles ("Thermal decomposition zone").…”

“…The first category, led by chemists and chemical engineers, focuses on the development and invention of new formulations and ingredients for more effective and reliable intumescent coatings 4,6,7,8 . The second category, led by fire safety engineers, focuses on investigating the overall insulating effectiveness of intumescent coatings as thermal barrier for different structural elements and materials 9 . Based on the research goal, the swelling of intumescent coatings is studied and assessed in different manners.…”

“…The temperature-dependent effective thermal conductivity defines an equivalent thermal barrier provided by the intumescent coating to the substrate material under a certain heating regime 5,[22][23][24] . This parameter incorporates several phenomena that occur in the intumescent coating, such as the swelling process, endo-and exothermic reactions 9,18 . In this way, the swelling of intumescent coatings is indirectly assessed in terms of a lower temperature rise in the protected material.…”

“…The entrapment of gases represent a fundamental process during intumescence in order to optimise the coating swelling. Several researchers have highlighted how the order and the matching of the chemical and physical processes are essential, as they must happen in an appropriate sequence, as the temperature is raised9,10,25 .…”

Exfoliated and functionalized boron nitride nanosheets towards improved fire resistance and water tolerance of intumescent fire retardant coating

“…melamine) 15–17 . Meanwhile, certain nanomaterials such as graphene, carbon nanotubes, etc., have been proved to be capable of improving the fire resistance of intumescent flame retardant coatings 18–21 . However, although BN is recognized as an effective flame retardant for polymeric materials, the BN‐modified IFR coating is rarely reported 22–24 .…”