Recent Advances in Modification Strategies for Intumescent Fire-Protective Coatings for Steel Structures

Intumescent fire-protective coatings provide lightweight protection for steel structures by forming porous insulating char layers during fire exposure. However, their effectiveness is constrained by poor component compatibility, insufficient char stability and limited durability. This review first introduces coating composition and fire-protective mechanisms, followed by an analysis of the limitations of conventional systems. Modification strategies for acid sources, carbon sources, blowing agents, functional fillers, and binders are then systematically reviewed, with attention to surface modification, microencapsulation, biomass functionalization, and inorganic reinforcement. Multicomponent synergistic mechanisms are examined and the advantages and limitations of different approaches are discussed in relation to thermal insulation, char integrity, water resistance, and smoke suppression. The analysis highlights that effective protection depends on coordinated acid generation, carbonization, gas release, and matrix transformation, requiring a balance between expansion and char strength. Binders and interfaces connect component dispersion with protective-layer development and service durability. Future research should advance from individual-component modification toward multicomponent synergy, integrated organic–inorganic design, and environmentally responsible, durable formulations. This review provides guidance for linking formulation design to sustained fire protection of steel structures under relevant service and fire exposure conditions.