Performance Evaluation of Fireproof Paint and Spray-Type Fireproofing Materials via Heating Experiments
Article information
Abstract
Various strengthening methods are applied to ensure the fire resistance performance of structures. Specifically, steel-framed structures should be fireproofed as they are relatively less fire-resistant than concrete structures. In general, sprayed fireproof materials and fireproof paint are widely applied to improve the fire resistance of steel structures. Fireproof paint improves fire resistance performance by forming an air insulation layer on the surface of members along with volume expansion due to chemical reactions during a fire. This in turn delays the rate of flame temperature transfer to the steel members. In the case of spray-type fireproofing materials, the fire resistance performance of structural members is improved by the insulation performance of the material itself without physical changes. In this study, the fire resistance performance of refractory materials (fireproof paint and spray-type fireproof materials) was experimentally evaluated with respect to exposure temperature, and the differences in insulation performance with respect to each material were confirmed. Additionally, based on the experimental results, the necessity for improving the performance certification system of current fireproof materials was suggested.
1. Introduction
Various countries have established institutional requirements to ensure the fire safety performance of buildings to minimize casualties in the event of a fire. In South Korea, the Building Act specifies the minimum fire resistance performance according to the use and scale of the building. For concrete members, with a certain cross-sectional size, it is possible to apply them as fire-resistant structures without additional fireproofing. However, for steel-framed structures, fireproofing is mandatory [1-3]. Fireproofing materials include gypsum board, concrete encasement, concrete blocks, and fire-resistant coatings. Specifically, fire-resistant coatings are generally applied on-site for their constructability and space utilization. Fire-resistant coatings can be applied using fireproof paint or fireproof spray methods. Fireproof paint exposed to high temperatures undergoes a chemical reaction that causes the paint to expand. The expanded area forms an insulating air layer that delays the temperature rise of the structural member, thereby ensuring the fire resistance of the structure [3]. Conversely, spray-type fireproofing materials realize fire resistance via the inherent insulating properties of the material without undergoing physical changes. Generally, the performance testing of fireproofing materials is conducted according to the current standards, specifically KS F 2257 standard fire conditions, by determining whether the temperature measured on the substrate exceeds the average of 538 °C or maximum of 649 °C during the required fire resistance performance time. However, performance analysis with respect to the exposure temperature of specific materials should evaluate various behavioral characteristics, including the insulating effect, under conditions where the substrate temperature exposed to the target temperature is reached. The aim of this is to evaluate the insulation effect based on exposure temperature for two types of fireproof paint (acrylic-based and epoxy-based) and spray-type fireproofing materials (cement-based and gypsum-based).
2. Heating Experiment of Fireproof Materials
The specimens used in this study were prepared by applying different fireproof reinforcement materials to the surface of steel plates with dimensions of 100 × 100 mm and thickness of 20 mm, according to the variables listed in Table 1. Acrylic-based paint and gypsum-based spray-type fireproofing materials were applied to general building structures, while epoxy-based paint and cement-based spray-type fireproofing materials were used for plant facilities with relatively high fire intensity, such as hydrocarbon fires. For each target temperature experiment, three specimens were prepared for each variable. The thicknesses of the paints and spray-type fireproofing materials, which were used as variables, were those that had received performance certification domestically. Specifically, the epoxy-based paint included an UL 1709 certified product. The target temperature settings were based on 500 °C, the critical temperature at which the effective yield strength reduction factor of structural steel decreases, as suggested by Eurocode [4]. Simultaneously, 300 °C was also considered, the temperature at which visible discoloration of concrete, commonly used with steel, occurs.
Experimental Variables
In each experiment, the furnace was heated at a rate of 5 °C/min to reach the target internal average temperature. As shown in Figure 1, after the internal temperature reaches the target temperature, a 2 h temperature maintenance period is set to allow the unreinforced specimen's internal temperature to reach a steady state at the target temperature. Then, natural cooling was allowed to occur.
Heating rate.
The experiments for the two types of fireproofing materials are conducted separately, and the furnace temperature data for each experiment are shown in Figure 2. In the fireproof paint experiment, the temperature increase is stable according to the target temperature input values, as shown in Figure 1. However, the increase in temperature slightly increases above the target temperature. Additionally, in the sprayed material experiment, the furnace output was unevenly applied during the experiment, resulting in varying temperature rise rates in certain sections. However, it was observed that the furnace temperature rose similarly to the target temperature. Each specimen had a K-type thermocouple installed at a depth of 10 mm in the center of the steel. Furthermore, Figure 2 shows the temperature of the uncoated specimens used in each experiment. As previously mentioned, depending on the temperature rise and output of the furnace, the temperatures of the uncoated specimens measured in each experiment were observed to be higher or lower than the target temperature according to the actual maximum temperature of the furnace.
Temperature of furnace and non-coating specimens.
3. Experimental Results and Discussion
In this study, heating experiments are conducted on specimens with the application of variables listed in Table 1. It was confirmed that in all specimens, the fireproof paint exhibited its characteristic expansion, forming an insulating air layer on the steel plate surface. However, as shown in Figure 3, the expansion shape varies according to the type of paint. This phenomenon was most pronounced in FP_A1, where the paint thickness was relatively thin. The epoxy-based paint uniformly expanded on all specimen surfaces. Additionally, in some epoxy-based paint specimens, the fireproof paint detached, exposing the steel plate and causing a rapid temperature rise (Figure 3(c)). Conversely, in the experiments with spray-type fireproofing materials, it was observed that they exhibited insulating performance without external changes, as mentioned earlier.
Expansion shape of fireproof materials after heating experiment (target temperature: 800 ℃).
As previously mentioned, The fundamental reason for using fireproof paint and spray-type fireproofing materials is to ensure the fire resistance of steel-framed structures by forming an insulating layer on the surface of the steel members. This is realized by utilizing the materials' inherent characteristics and their intumescent behavior under high-temperature exposure. Figure 4 shows the maximum temperature at the center of all steel specimens according to the internal temperature via actual heating under the target temperature condition. However, the maximum temperature inside the heating furnace for target temperatures of 300 and 400 °C in Figure 2(b) is expressed using the average value of the measured values in the latter half of the experiment. Furthermore, it was considered that the temperature distribution is not even due to the instability of the heating furnace output.
Temperature of specimen with respect to furnace temperature.
In the fireproof paint tests, it was generally observed that thicker paint layers resulted in a thicker insulating air layer when exposed to fire, leading to superior insulation effects. Conversely, in the spray-type fireproofing material experiments, it was found that the specimen temperatures were significantly lower even when considering the relatively lower furnace temperatures. To analyze this phenomenon more clearly, the insulation performance for each experiment is shown in Figure 5. Figure 5 illustrates the ratio of the steel temperature of each reinforced specimen to the temperature of the unreinforced specimen. It was confirmed that, in general, specimens with thicker reinforcement exhibited superior insulation performance. Additionally, as shown in Figure 4, the insulation performance of the spray-type fireproofing material specimens was relatively superior.
Insulation performance with respect to fireproof material.
According to ASTM E119 [5] and KS F 2257-6 and 9 [6,7], the performance criteria for "fire resistance tests of structural steel beams/girders/columns" require that the average temperature at any four points on the steel member does not exceed 538 ℃ (1,000 ℉) or that the maximum temperature at any single point does not exceed 649 ℃ (1,200 ℉). As shown in Figure 4, the results of the experiments conducted in this study show that some specimens fail to satisfy these conditions. This can be attributed to the fact that ASTM E119 and KS F 2257 standards typically apply the standard fire curve used for fire resistance tests of building structural members, as shown in Figure 6. Conversely, the experiments in this study exhibited a relatively low heating rate (5 °C/min). However, the heating time was extended, which likely caused this phenomenon. The standard fire curve shown in Figure 6 simulates a fire after a flashover, resulting in a very high initial temperature rise rate. Subsequently, tests are conducted for 1 to 3 h, depending on the required fire resistance performance time of the structural member. The performance of fireproof paint is determined based on whether the critical temperature shown in Figure 4 is reached, guiding the development and production of fireproof paint products to consider these fire conditions. However, in actual fire scenarios, the maximum temperature may be lower than the standard fire curve, and the fire duration may be relatively longer. The type of potential combustibles and fire load can vary significantly depending on the structure's purpose and scale. For instance, plant facilities are open spaces with various structures, where flashover does not occur. Furthermore, the fire intensity, combining fire duration and flame temperature, can be significantly high depending on the quantity and type of combustibles. Considering this, performance tests of fireproof paint are sometimes conducted using the hydrocarbon fire curve shown in Figure 6. In this study, the FP_E2UL product was tested under such conditions. The FP_E2UL product reached the critical temperature in the 800 ℃ target temperature experiment, with a total heating time of approximately 280 min, including approximately 160 min of temperature rise and 120 min of temperature maintenance.
Standard fire curve.
Regarding fire exposure duration, the fire at Daegu Seongseo Industrial Complex in South Korea in 2023 took approximately 240 min to extinguish. In other industrial and warehouse fires in South Korea, it often took over 180 min from the time of fire occurrence to suppression. The experimental results and fire case studies in this research suggest that relying solely on the standard fire curve to determine the fire resistance performance of structural members with fireproof paint- irrespective of the structure's purpose and scale-may not ensure sufficient performance in real fire situations. This potentially leads to member failure and structural collapse.
4. Conclusions
In this study, the behavior characteristics of fireproofing materials under varying exposure temperatures were analyzed, and the existing performance recognition system for fireproofing materials was reviewed based on the analysis results. Two types of fireproofing materials, which are commonly used, were selected for this purpose, and material heating experiments were conducted, where the coating thickness of the reinforcement material was set as a variable. The experimental results highlighted the issues with the performance criteria of ASTM E119 and KS F 2257 for "fire resistance tests of structural steel beams/girders/columns" and led to the following supplementary opinions:
- Depending on the structure's purpose and scale, it is necessary to apply test regulations on fire duration, including the standard fire curve, to respond to fire scenarios in plant facilities and various industrial facilities. This can be sufficiently addressed via the process of verifying the thermal insulation performance of fireproof paint under various fire scenarios through material-level testing prior to structural member-level testing.
- Given that actual structures are subject to continuous load applications and deformations, it is necessary to consider situations, such as local failure of members, due to the deterioration of insulation performance caused by detachment and blistering of fireproof paint during performance tests under load conditions.
- Additional research is required on the deterioration of thermal insulation performance of fireproof coatings over fire exposure time. Specifically, it is necessary to identify the causes of surface spalling observed during experiments and to develop preventive measures.
Notes
Author Contributions
Methodology, Experiment, Investigation, Analysis, Writing and Modification: Hyun Kang, Review: Oh-Sang Kweon. All authors have read and agreed to published version of the manuscript.
Conflicts of Interest
The authors declare no conflict of interest.
Acknowledgements
This work is supported by the Korea Institute of Civil Engineering and Building Technology(KICT) grant funded by Ministry of Science and ICT(Grant No.20240189-001).