Current Situation Analysis and Development Trend of Intumescent Fireproof Coatings for Steel Structures: A Comprehensive Review

Abstract

Steel is indispensable to modern construction owing to its exceptional load-bearing capacity and design versatility; however, its mechanical properties degrade rapidly under elevated temperatures, making passive fire protection critically important. Intumescent fireproof coatings have emerged as the preferred passive fire protection system for structural steel, owing to their thin application profiles, aesthetic compatibility with architectural design, and demonstrated thermal insulation performance. Upon exposure to fire, these coatings undergo a series of sequential chemical and physical transformations, expanding many times their original thickness to form a low-density, carbonaceous char layer that thermally insulates the underlying steel substrate and significantly extends structural integrity time in a fire event. This review provides a systematic and comprehensive analysis of the current state of knowledge and the most recent development trends in intumescent fireproof coatings for steel structures. A systematic literature search was conducted using the academic databases Web of Science, Scopus, and Google Scholar. PubMed was additionally consulted for biomedical aspects related to the toxicity of flame-retardant additives and bio-based compound applications. The search was restricted to peer-reviewed journal articles published since 1 January 1996 as the primary inclusion window, though foundational pre-1996 classic works were also included where they constitute the intellectual basis for subsequent research. The principal chemical constituents — acid sources, char-forming agents, blowing agents, and binder resins — are examined in detail, together with the governing mechanism of intumescence. The roles of inorganic fillers, nanotechnology-derived additives including graphene, layered double hydroxides, and nanoclays, as well as emerging bio-based and sustainable formulation strategies, are critically assessed. The review further addresses durability and weathering performance, standardised fire testing protocols, regulatory qualification frameworks, and advanced modelling approaches. Key challenges including moisture sensitivity, topcoat compatibility, performance under natural fire exposures, and the environmental sustainability of coating formulations are identified. Future research directions are outlined, with emphasis on multifunctional coatings, computational design, and green chemistry platforms, all of which are shaping the next generation of intumescent fireproof coatings.