# Freezing and Thawing Processes of Highways in Kazakhstan
## 3 Results and Discussion
### Freezing and Thawing  
Freezing depth is an important characteristic of asphalt concrete roads operating in cold climate regions. It corresponds to points in the pavement and subgrade (subgrade) at which the temperature is approximately 0 \({}^{\circ}\)C. Thus, within the freezing depth, a part of the road is in a frozen state, and outside it, the temperature has a positive value. It is useful to have more detailed information about the processes of freezing and thawing of pavement and soil base layers, since the strength and deformation characteristics of pavement materials and soil, as a rule, change significantly due to temperature variation and the amount of phase state of moisture contained in them. It turned out that during the considered cold period on the selected section of the road, the freezing process follows a complex pattern (Figure 6). Around 27 October 2021, the freezing of the surface of the asphalt concrete pavement occurred, and on November 16 it reached a freezing depth of 44 cm, i.e., the freezing rate was 2.32 cm/day. Then, the freezing rate increased sharply to 14.75 cm/day, with which freezing reached a depth of 103 cm in 4 days; then, over the next 12 days, the freezing rate gradually decreased to a depth of 137 cm. The average rate in this period of time was 2.83 cm/day. Then, for a long time (95 days), from a depth of 137 cm to a depth of 219 cm, freezing proceeded at an even lower average rate of 0.86 cm; at the most recent characteristic freezing interval, the rate had a minimum value of 0.33 cm/day, and a maximum freezing depth of 227 cm was reached. The thawing process follows a simpler regularity: both \"bottom-up\" and \"top-down\" thaws take place, which begin at approximately the same time points (27-30 March 2022); the descending branch of thawing occurs almost uniformly, at an average rate of 6.25 cm/day from the surface of the asphalt concrete pavement to a depth of 220 cm; the average rate of the ascending branch of thawing is 0.9 cm/day. The temperature distributions over the depth of the pavement and the subgrade at different characteristic times are shown in Figure 7. These time points are not chosen randomly; they are the times at which some characteristic physical processes take place, which are associated with the freezing and thawing of the pavement and the subgrade: 27 October 2021--the beginning of freezing of the asphalt concrete pavement; 16 November 2021--the beginning of freezing of subgrade; 30 November 2021--the beginning of freezing of the subgrade at a constant rate (at a depth of 130 cm); 27 March 2022--the beginning of thawing of the asphalt concrete pavement; 30 March 2022--maximum freezing depth (227 cm); 1 April 2022--the beginning of thawing of subgrade (at a depth of 62 cm). Figure 5: Graphs of temperature changes in the lower part of the subgrade. This figure clearly shows that with the onset of the cold period, the temperature distribution curves shift towards lower temperatures. Within 20 days (from 27 October 2021 to 16 November 2021), the surface temperature of subgrade soil (at a depth of 62 cm) drops from 8.5 \({}^{\circ}\)C to 0 \({}^{\circ}\)C. Despite the short period of time (only 5 days from 27 March 2022 to 1 April 2022), the temperature in the lower asphalt concrete layers (depth 20-30 cm) during the thawing period changes significantly (from \(-3\) \({}^{\circ}\)C to \(+4\) \({}^{\circ}\)C). Figure 6: Freeze and thaw curves for pavement and subgrade. Figure 7: Temperature distribution curves in pavement and subgrade at different characteristic times. Moreover, according to the aforementioned method, the patterns of the freezing-thawing process at measuring stations located near the settlements of Oskemen, Balkhash, Kosshy, Kazaly, Almaty, Ucharal, and Zaisanwere studied. These stations represent different climatic conditions in the regions of the Republic of Kazakhstan. For example, the village of Kosshy is located near the city of Astana, which belongs to central Kazakhstan.