# Numerical Assessment and Repair Method of Runway
## 5 Conclusions  
This study confirmed the scale of damage to the airfield pavement from a CBU attack through a field test and verified the result through numerical modeling. In the event of a CBU attack by a ballistic missile, when the cluster munitions are dispersed 20 km above the ground, it penetrates the concrete pavement at the terminal speed of about 500 m/s by free fall, and the penetration depth was calculated to be 33-39 cm using the formula. Assuming that the CBU does not penetrate the pavement, an explosive was penetrated and detonated at 33 cm under the simulated runway for the field blast test, and the test confirmed that the crater was 300 mm in diameter; the fracture zone was 155.8 cm on average from the center of the crater; and the fracture zone had an upheaval and cracks for up to 0-7 mm \begin{table}
\begin{tabular}{c c c} \hline \hline
**Repair Method** & \multicolumn{2}{c}{**Advantages and Disadvantages**} & **Applicability** \\ \hline \multirow{4}{*}{High-Early-Strength Concrete} & \(\blacksquare\) & Able to simulate the concrete’s strength early; \\  & \(\blacksquare\) & High durability after the repair; \\  & \(\blacksquare\) & Able to combine and construct based on the field’s need; \\  & \(\blacksquare\) & Decent storage time for the construction material; \\  & \(\blacksquare\) & Expensive and has weather restrictions for the construction. \\  & \(\blacksquare\) & High quality concrete same as the original pavement; \\ Precast & \(\blacksquare\) & Able to craft precast panel and store it permanently; \\ Concrete & \(\blacksquare\) & Can be constructed regardless of the weather; \\ (PCC) & \(\blacksquare\) & Expensive and must consider complex distribution; \\  & \(\blacksquare\) & Must remove more than the damaged part due to precast panel. \\  & \(\blacksquare\) & Easily applied; \\ FOD Cover & \(\blacksquare\) & Reusable; \\ Mat & \(\blacksquare\) & Short-lived and incompatible with some airplanes; \\  & \(\blacksquare\) & Unsuitable for small craters and needs to be replaced. \\  & \(\blacksquare\) & Economic initial construction fee; \\  & \(\blacksquare\) & Usable for any shape crater due to its flexibility; \\ Asphalt Concrete & \(\blacksquare\) & Sensitive to temperature change, therefore, incompatible with jets; \\  & \(\blacksquare\) & Different from original pavement and needs replacement; \\  & \(\blacksquare\) & Unusable for long term. \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Comparison and assessment of small crater repair methods. and 1-2 mm, respectively. The crater as a result of the modeling was 67.6 cm in diameter, and 67 cm in depth including the upheaval, and the displacement occurred throughout the base course. In addition, the height of the upheaval on the concrete pavement surface, caused by the impact of the explosion, was approximately 12 cm from the existing surface. Therefore, the model confirms that even some parts of the crushed stone and sand layer need repair, as the repair section is 1.8 m \(\times\) 1.8 m in size and approximately 84 cm in depth. If damage occurs down to the crushed stone and sand layer, considerable time is additionally required for repair. It is necessary to change the construction standards to prevent penetration damage to the pavement, in the event of an explosion, by increasing the strength or thickness of concrete. Furthermore, in order to repair such damage, it is appropriate to apply the high-early-strength concrete method, since this method can achieve a high level of strength early, has a long storage period for the materials, and has a shorter time for repair [3]. Conceptualization, I.H. ; methodology, I.H. ; software, I.H. ; validation, I.H., J.H. and S.K. ; formal analysis, I.H. ; investigation, S.K. ; resources, I.H. ; data curation, I.H. ; writing--original draft preparation, I.H. ; writing--review and editing, I.H. and J.H. ; visualization, S.K. ; supervision, I.H. ; project administration, I.H. ; funding acquisition, J.H. All authors have read and agreed to the published version of the manuscript.