# The Influence of Water on the Heat Loss of Hot Mix Asphalt
## 5 Final Conclusions  
The results prove that the adopted model and values of the heat transfer coefficient \(\alpha\) (calculated on the basis of experimentally obtained values of \(A\)) enable determination, with a good accuracy, of the temperature drops in the HMA layer. The average deviation between the measured and theoretical temperature was 6.6 \({}^{\circ}\)C. The result allows engineers to adjust the HMA laying process to difficult weather conditions and predict the time for necessary compaction.  
A constant value of \(\alpha\) can be adopted for practical purposes (for the total time period) depending on the precipitation rate, temperature difference between HMA and the surrounding environment and the characteristic length (\(d\)) which considerably simplifies the calculations.  
Large drops of temperature in a very short time in the HMA layer due to contact with water occur mainly near the surface. The influence of water (boiling and evaporation) is clearly visible in the comparison between the model and real conditions--the highest average deviation between the measured and theoretical temperature were noticed at the very surface of the HMA layer. The difference decreases towards the inside of the layer. At 1 cm from the surface the cooling down process is slow, showing that the proposed model to a good degree reflects the changes in the temperature in the HMA layer.  
Studies on the influence of water on the cooling down of the HMA layer allowed do determine the values of the heat transfer coefficient \(\alpha\) correlating them with \(T_{m}\) and characteristic dimension \(d\). In the case of water amount of 3 L/m\({}^{2}\)/h the \(\alpha\) coefficient corresponds to a convectional transfer (induced flow) at wind velocity of 3 to 12 m/s (Figure 5). Increase in the water amount up to 6 L/m\({}^{2}\)/h results in the increase of the \(\alpha\) coefficient value, which correlates to convectional transfer at the wind velocity of 4 to 24 m/s (Figure 5).  
The values of the heat transfer coefficient during cooling with water are influenced by the initial temperature of water and the HMA layer. The higher the average temperature (\(T_{m}\)), the more intense the heat exchange to the environment is (Figures 15 and 16). As a result, the surface will exhibit a much higher rate of cooling down. The differences in the temperatures inside the HMA layer are significantly lower. This is caused by a low thermal conductivity coefficient of the HMA layer.  
Rapid temperature drops at the surface of the HMA layer with a contact with water can be a cause of decreased interlayer bonding. Such phenomenon can take place in the case where the HMA layer will be laid on a wetted subfloor. Laying of the HMA on a subfloor with high water content should be avoided, and if necessary, the subfloor should be dried using local space heaters.  
Moreover, rolling the surface as soon as the paver has laid it will additionally counteract the penetration of precipitation water into the HMA structure, thus reducing the cooling rate and depth.  
Further research includes the preparation of real-size section of a road. The influence of water on cooling down of the HMA layer and its density will be evaluated for the different water content in the subfloor. The effectiveness of compaction as the influence of the number of road roller cycles on the compaction index will be studied  
[PERSON] conceived and designed the experiments; [PERSON] performed the experiments; [PERSON] and [PERSON] analyzed the data; [PERSON] and [PERSON] wrote the paper.  
This research received no external funding.  
The authors declare no conflict of interest.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Time Range [min]** & **Average Deviation \(\psi\) [\({}^{\circ}\)C]** \\ \hline
0–5 & 5.8 \\
5–60 & 5.6 \\
0–60 & 6.6 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Average deviation \(\Psi\) between the measured and theoretical temperatures in relations to the assumed time range for all analyzed samples.