# Efficacy of Fire Protection Techniques on Impact Resistance of Self-Compacting Concrete
## 3 Results and Discussion
### SCC Crack Analysis of SCC Specimens Subjected to High Temperature  
When concrete structures are subjected to elevated temperatures, there is a risk of thermal crack formation. The combination of high heat flux on the concrete surface, coupled with the thermal incompatibility between the mortar and aggregate, contributes to the formation of microcracks. To effectively manage these cracks, it is crucial to precisely measure their geometrical characteristics, including width, length, density, and pattern [40]. This study aims to analyse the crack pattern in SCC and explore potential strategies to control these cracks under standard fire temperature conditions. Figure 9a, b illustrates the failure patterns of SCC specimens, protected (FA/EPA/CPP and GGBFS/EPA/CPP) and unprotected (FA and GGBFS), exposed to elevated temperatures. Based on the fracture pattern observed at the point when the specimen failed, failure pattern comparisons are made. After being exposed to heating for 30 min, line crack failure was observed for the FA, FA/EPA/CPP, GGBFS, and GGBFS/EPA/CPP specimens. The specimens split into two sections along the line crack, indicating an apparent and sudden brittle failure followed by the formation of the first crack. It was observed that the line crack width was smaller in the case of the FA/EPA/CPP 30M specimens compared to the FA 30M specimens. However, the line crack width at failure in the FA/EPA/CPP 30M specimens was similar to that of the GGBFS 30M specimens. On the other hand, unprotected (FA 30M and GGBFS 30M) specimens showed surface microcracks that formed due to direct exposure to heat flux. The failure pattern observed in this case was similar to the brittle failure observed in plain cylindrical specimens under impact loadings at ambient conditions. The failure crack patterns display significant variations as the exposure temperature exceeds 30 min. At 60 min of heating, the role of CPP protection is significantly noticeable. Critical surface microcracks were observed on the unprotected (FA 60M and GGBFS 60M) specimens. The ultimate failure resulted from the formation of multi-line cracks that developed from the fracture zone, and finally, the specimen broke into three or more pieces. In contrast, thermal microcracks were absent on the surface of both the protected (FA/EPA/CPP 60M and GGBFS/EPA/CPP 60M) specimens. Even after the initial crack appeared, these specimens continued to withstand impact loads and absorb impact energy for additional blows. The final failure pattern was curved, with zig-zag rupture failures occurring over the SCC's weakest region due to prolonged exposure to heat. At 90 min exposure, the unprotected specimens (FA 90M and GGBFS 90M) exhibited a combination of cracking and failure. The failure pattern on the FA 90M specimen was characterised by a combination of curves and severe surface cracks that emerged from the fracture zone, resulting in a multi-curve cracking failure. Meanwhile, the GGBFS 90M heat-exposed specimens failed due to a combination of curve and line cracks and typical surface cracks seen in unprotected specimens. In contrast, the FA/EPA/CPP 90M specimens resisted developing various crack patterns. They failed through curve crack failure, similar to the failure mode observed in FA 60M specimens. The efficacy of the CPP layer was evident from the failure patterns, even after 90 min of heating. Finally, the GGBFS/EPA/CPP 90M specimens failed under multiple lines of cracks impeding the fracture zone. The most significant failure pattern was observed in unprotected specimens (FA 120M and GGBFS 120M) and protected specimens (FA/EPA/CPP 120M and GGBFS/EPA/CPP 120M) after 120 min of heating. The ultimate failure observed in these specimens resembled that of the unprotected specimens subjected to a 90 min heat exposure. It was noted that irrespective of specimen protection, the ultimate failure resulted from a combination of line and curve cracks originating from the fracture zone.