Building fires can lead to tremendous damages and losses to society. With the determination to protect building structure from fire, various methods have been proposed. In particular, the use of intumescent coatings has been extensively used in protecting structural material from fire. The intumescent coatings mechanism specifically the charring and forming process has been recently investigated using various techniques. Unfortunately, the characterization of the resulting carbonaceous char layer has not been fully explored. This is highly necessary considering its significant role in shielding construction materials from the heat. In a recently published work, the role of both thermal and structural analyses of the char in predicting intumescent behaviors have been considered. However, it does not offer enough solution to technical challenges associated with diagnosis of internal char forming processes.
To this end, Case Western Reserve University researchers: Dr. Jiyuan Kang, Professor Fumiaki Takahashi and Professor James T’ien from the Department of Mechanical and Aerospace Engineering explored the expanded and charred intumescent coatings using a morphological structural characterization method based on computer tomography. Their main objective was to explore the feasibility of the method for characterizing chars of different intumescent coatings and to enhance their structural properties and insulation performance. The obtained data would thus be useful in developing accurate numerical models. The work is currently published in the journal, Fire Technology.
The research team initiated their experiments by obtaining intumescent char specimens from a radiation cone device, which were used in measuring the thermal insulation performance. Next, three different coatings were exposed to three different incident heat fluxes after which a computer tomography scanner was applied to the charred materials to generate high-resolution three-dimension reconstructed images. The central regions of the scanned images were divided into three layers: top, middle, and bottom for further analysis using the image processing technique. The measured char properties were correlated and compared to the previously observed thermal insulation performance.
The char depth, type of coating and the incident heat flux were the main factors observed to significantly affect the morphological structure of expanded and charred intumescent coatings. However, the pore size of the tested samples varied in the range of 0.352mm to 0.424mm thus exhibited no major impact. Comparing the performance of the sample coatings: the first water-based coating formed a highly porous coating with connected pores, the different water-based sample formed a shell-void structure with a relatively lower porosity than the former sample while the epoxy-based coating formed a middle layer sandwiched between the denser layers and exhibited relatively high porosity. Additionally, epoxy-based coating produced pore with smaller diameters as compared to water-based coatings. Despite being high, the incident heat flux moderately affected the pore sizes.
In summary, Dr. Jiyuan Kang and colleagues at Case Western Reserve University presented a new computer tomography-based analysis method together with a three-dimensional structure characterization technique for quantitative and qualitative analysis of the morphological characteristics of expanded and charred intumescent coatings. This is a non-intrusive method that has overcome some of the previously encountered challenges such as diagnosing the fragile chars without breaking the structure. The approach, therefore, offers a detailed structural characterization method for the development of new formulations leading to advanced numerical modeling. For instance, the transient variations of the transmitted heat flux and internal temperature and the char properties will adversely help in future validation of numerical models.
Kang, J., Takahashi, F., & T’ien, J. (2019). Computer Tomography Based Structure Characterization of Expanded Intumescent Coatings for Fire Protection. Fire Technology, 55(3), 689-712.Go To Fire Technology