Computer Tomography Based Structure Characterization of Expanded Intumescent Coatings for Fire Protection

Intumescent coatings are used to protect structural steel from fires. In this study, morphological characteristics of expanded and charred intumescent coatings, which is a key factor of its thermal insulating mechanisms, have been studied using a computer tomography (CT)-based analysis method. Specimens of the charred materials are prepared by a laboratory-scale mass-loss cone heating method for measuring thermal insulation performance. Three types of coatings are exposed to three constant incident heat fluxes (25 kW/m2, 50 kW/m2, and 75 kW/m2) for 2 h. The micro-CT scanning technology is applied on the charred materials to generate 3D reconstructed images with 20 µm resolution by ImageJ software. By using an image processing technique, the central region of each scanned 3D model is divided into three horizontal layers at different depths: top, middle and bottom. The morphological structure varies significantly with the type of coatings, the incident heat flux, and the depth in the char, but the median value of pore size (i.e. equivalent diameter) for all tested samples varies within a narrow range (0.352 mm to 0.424 mm). The qualitative morphological observations as well as the quantitative pore properties (i.e., 3D porosity, size distributions, and sphericity) are obtained. The present non-destructive structure analyses method is useful to assist in new formulation developments and to advance numerical modeling.