Fire protection of steel structures is critical for extending the time it takes for the steel to reach the temperature where a considerable compromise of the yield strength is expected, typically between 500-600 oC depending on the section factor of the element. This conceivably increases the chances of firefighters in preventing the loss of lives.
Employing the cellulosic fire curve on the specimens in a gas furnace according to ISO 834 or ASTM E119 or BS476: Parts 21-23 or EN13381-8 standards assesses the fire performance of structural steel. Among the various solutions at hand for improving the fire performance of the steel structures, intumescent coatings are the most accepted and widely used across the industry .
The dehydration and esterification of the carbonizing agent by the acid source, and its later swelling/expansion as a consequence of the degradation of the foaming/spumific agent, produces the basis of these systems. Simplicity of application, thickness requirements, and aesthetics are the key benefits of these coatings in contrast to cementitious coatings or board systems.
However, their vulnerability to weathering (environmental conditions), the brittle nature of their residue at high temperatures, and predisposition of the char/residue to thermo-oxidation are issues that remain problematic and hinder further developmental activities in this field.
These issues have been addressed at varying levels and certain aspects of this work have been published [2-5]. The knowledge produced from the framework of these projects has led to:
- the development of ‘FiroShield’, a cost-effective fire-protective coating for steel and concrete structures.
- Transparent fire-retardant coatings for timber.
- Other technology disclosures (filed with NTUitive, NTU Singapore) include thin-film intumescence as well as the design and advancement of fire-retardant coatings that result in rigid residues after exposure to fire conditions.
From a scientific perspective, the information acquired from the aforementioned development and work is significant and useful for personnel involved in the design and development of generic fire-retardant coatings.
For instance, despite the regulatory requirement of testing the developed coatings as per large-scale tests like EN13381-8 or ASTM E119 or BS476: Part 21, during a majority of the studies in the field of fire-retardant coatings only coupon-level or materials-scale tests are conducted to understand their performance. This is due to the fact that most large-scale fire tests tend to be expensive, time-consuming, and demand a great number of resources.
The methodology which uses materials- and coupon-scale tests for corresponding the performance at the structural-scale raises questions on the associations between the innate flammability, thermal characteristics, and performance standard. The gravity of this issue increases considering the exposure to heating conditions on all sides at the structural-scale in contrast to bulk or coupon scale, and higher heat fluxes inflicted to the edges of an H or I steel section.
Non-uniform coverage of expanded char on those edges (depending on the section factor) further brings about through cracks, self-weight of char, the cohesion of char across the surface areas, and the mechanical load thrust on the column throughout the fire test. Thus, Ng et al. explore the fundamental relationships across these different scales of testing .
References and Further Reading
- Wang, Y., I. Burgess, F. Wald, and M. Gillie, Performance-based fire engineering of structures. 2012: CRC Press.
- Y.H. Ng, A. Dasari, and K.H. Tan. Fire-retardant coatings for concrete substrate: A comparison between one-dimensional and two-dimensional heat transfer. in 10th International Conference On Structures In Fire. 2018. Belfast, United Kingdom.
- Y.H. Ng, I.S. Zope, A. Dasari, and K.H. Tan, Correlating the performance of a fire-retardant coating across different scales of testing. Polymers, 2020. 12. https://doi.org/10.3390/polym12102271
- Anees, S.M. and A. Dasari, Acrylic-based fire-retardant coatings for steel protection: Employing the concept of in situ ceramization. Journal of Applied Polymer Science, 2020. p. 50299. https://doi.org/10.1002/app.50299
- Y.H. Ng, A. Dasari, K.H. Tan, and L. Qian, Intumescent fire-retardant acrylic coatings: Effects of additive loading ratio and scale of testing. Progress in Organic Coatings, 2021. 150: p. 105985. https://doi.org/10.1016/j.porgcoat.2020.105985
This information has been sourced, reviewed and adapted from materials provided by NTUitive.
For more information on this source, please visit NTUitive.