# Development of Passive Fire Protection Mortars
## 3 Results and Discussion
### Short Steel Columns Specimens  
Regarding the protected square-section short steel columns (SSC), the assessment of the column temperature was based on the arithmetic average of the temperatures obtained from the 12 thermocouples welded to the steel column, which were distributed into three sections with four thermocouples each one (Figures 6 and 10). As an example, Figure 11 shows the temperature evolution in steel at the lower section of the column where temperatures were recorded (Figure 6). Based on Figure 10, it is possible to observe that the furnace temperatures slightly delayed the initial minutes concerning the ISO 834 standard fire curve. This part of the curve is difficult to reproduce in an electric furnace, and this becomes worse for larger furnaces (high initial thermal inertia). However, near 9 min after the beginning of the heating, the furnace temperatures followed close to the ISO 834 standard fire curve (ISO 834-1, 1999). Nevertheless, the evolution of temperatures inside the furnace over time was uniform in all fire tests, meaning that the tests were comparable. Based on Figure 11, it is possible to observe that the temperature development recorded in the four thermocouples of group 3 was similar. There is only a difference of 3.3 \({}^{\circ}\)C between the thermocouple with the highest (TH_12) and the lowest temperature (TH_9) at column failure. Figure 11: Evolution of the temperature of the four thermocouples in group 3 of specimen 5 of SSC. Figure 10: Evolution of the average temperature in the three groups of thermocouples in specimen 5 of SSC. Until the specimens became unstable, graphs were generated with the evolution of the vertical deformation of the specimen as a function of time (Figure 12) to identify the critical experimental temperature, as well as graphs of temperature evolution as a function of time (Figure 13). Table 8 shows the average temperature values acquired in the specimens after 15, 30, 60, and 90 min and the average temperature values for the failure instants of each specimen. The critical design temperature calculated according to EN 1993-1-2:2005 [41] for this short steel column was 586.7 \({}^{\circ}\)C.  
In Figure 12, the tested SSC2 failed at 17 min, SSC4 at 77 min, SSC6 at 84 min, SSC8 at 95 min, SSC12 at 102 min, and SSC14 at 91 min, corresponding to the temperature of 617, 531, 585, 572, 566, and 559 \({}^{\circ}\)C, respectively (see also Table 8). In Figure 13 and Table 8, it can be seen that the commercial mortar has a more effective thermal protection for lower temperatures (the highest delay in the temperature rise at the beginning of the test). However, for temperatures higher than 400 \({}^{\circ}\)C, its thermal capacity tends to decrease due to the degradation of the mortar (the highest temperature rise rate at the ending of the test). Figure 14 depicts the specimen before and after being tested. Regarding the instability modes of the steel columns, local instability was observed despite the column being a class 1 cross-section under fire conditions. Figure 12: Evolution of vertical deformation in the specimens of SSC as a function of time. Figure 13: Evolution of temperature in the specimens of SSC as a function of time. The results from Table 8 clearly show that the application of mortars works as a good thermal barrier to fire, since columns without passive fire protection failed after 17 min of testing, whereas the protected columns failed on average, beyond 81 min. Furthermore, the results also show that the thermal protection of mortars developed in the laboratory was more efficient than that provided by the commercial mortars. Finally, it appears that the introduction of the NS and MS slightly improved the thermal performance of the mortars developed in the laboratory. Table 8 shows that the specimen without passive fire protection presented a fire resistance rating (FRR) of 15 min (R15), and the protected specimens with the CM allowed a FRR of R60.