## 3 Results  
### Ice Melting Test  
We observed that the solid RDP melted rapidly into the ice (Figure 4). The RDP melting of ice was more pronounced using 5 g than using 0.5 g. In the first few minutes, the RDP-related melting rates were both elevated; however, these rates decreased markedly over the next 10 min (Figure 4). For 5 g of RDP, the melting rate was higher after 30 min, possibly because of the presence of pristine RDP still able to melt the ice and generate brine.  
The 5 g ice melting rate was greater than that of the 0.5 g samples, although the rate was not proportional to the RDP amount. The standard deviation after one minute was greater for 5 g (\(\pm\)0.02) than for 0.5 g (\(\pm\)0.01), possibly because not all of the 5 g of RDP was initially in contact with the ice, resulting in only partial effectiveness. When using 0.5 g, proportionally much more area of the RDP grains is in contact with the ice, allowing for complete melting. After 10 min, the residual dry RDP in the 5 g samples, which was initially inactive, comes into contact with the water or brine, promoting further melting. Unfortunately, this delay in ice melting negatively affects the time, cost, and quantity required for winter runway maintenance. Therefore, using excessive amounts of RDP does not offer a suitable solution.  
We then analyzed temperatures from the thermal video to understand RDP behavior in the Petri dish (Figure 5). Temperatures during the melting were not uniform or constant across the surfaces, ranging from \(-\)10 \({}^{\circ}\)C to just below \(-\)16 \({}^{\circ}\)C (Figure 5). There was an initial instantaneous temperature drop, an endothermic reaction from the salt dissolution [33]. The reaction can be described as follows: solid RDP + ice and then solid RDP + ice + brine, and it evolves quickly to a brine-ice interaction. The thermal images show that for 0.5 g of RDP, the grains were evenly distributed on the ice at 0 min. In contrast, for the 5 g samples, the grains were stacked. As the melting process continued, brine formed in both tests. We recorded a minimum temperature of \(-\)16 \({}^{\circ}\)C for the 5 g test, which corresponds to the peak effectiveness of the product. This temperature was reached after approximately 12 min  
Figure 4: Ice melting rate of the 5 g and 0.5 g sodium formate (NaFo) samples at \(-\)10 \({}^{\circ}\)C.  
and then increased until our final observation at 30 min. The minimum temperature of the 0.5 g RDP sample was approximately \(-13\)\({}^{\circ}\)C at around 7 min. The minimum temperature was lower for the 5 g sample than for the 0.5 g samples, consistent with the difference in RDP amounts. The difference between the initial test temperature (\(-10\)\({}^{\circ}\)C) and the lowest temperature observed on the thermal images was 3.4 \({}^{\circ}\)C for 0.5 g and 6.4 \({}^{\circ}\)C for 5 g. This temperature pattern can be explained by the endothermic dissolution of RDP and the melting ice related to poor thermal conduction and local convective effects in aqueous solutions below 0 \({}^{\circ}\)C [34]. The product temperature followed the same trend, with lower temperatures corresponding to higher melting rates. Thus, the correlation between the two methods supports the conclusion that higher melting rates resulted in lower temperatures. However, using 5 g to evaluate melting capacity, as recommended by the standard, may produce false results by exaggerating the endothermal reaction and causing an excessive temperature decrease.