Design And Performance Of Composite Heat-induced Structure In Plateau Permafrost Region

In the plateau permafrost region,it is an important way to realize the stability of permafrost subgrade by reducing the solar radiation income of asphalt pavement and inducing the heat to radiate upward in the surface layer.Based on the principle of gradient thermal conductivity structure,a composite heat-induced structure based on the surface reflection layer and the integrated gradient thermal conductivity in the pavement surface and interior was proposed.In order to achieve the thermal conductivity gradient distribution of the composite heat-induced structure in the pavement,a certain dosage of floating beads was added into the surface mixture to control the thermal conductivity gradient of the pavement.Based on the requirements of pavement performance,the dosage of floating beads was not more than 37.5%of the volume of mineral powder.By using ABAQUS software,the gradient thermal conductivity structure was designed and analyzed,and the composite heat-induced structure was verified.The results show that compared with the control group,the optimal gradient thermal conductivity structure reduces the heat absorption of subgrade by 10.77%in warm season,and the annual net heat absorption of subgrade decreases by 11.53%.The average temperature of subgrade decreases by 0.916℃in warm season.Compared with the control group,for the composite heat-induced structure,the heat absorption of subgrade in warm season decreased by 34.27%,and the annual net heat absorption decreased by63.31%.The average temperature of subgrade decreased to 2.591℃in warm season.The coating formula and structure were optimized,and the thermal conductivity of the coating was matched with the gradient thermal conductivity structure in the pavement by using high thermal conductivity anti-skid particles.Part of the parameters and properties of the coating were tested,and it was determined that the anti-skid properties were basically recovered when the amount of anti-skid particles was 200g/m~2.By the indoor irradiation test,the effects of reflective coating,gradient thermal conductivity structure and composite heat-induced structure were verified and analyzed.The results showed that compared with carbon black,the surface cooling ratio of the reflective coating was increased by90.58%and 100.39%by chrome black or Paliogen Black,and the bottom cooling was increased by90.99%and 96.19%,respectively.Compared with the single gradient thermal conductivity structure,the composite heat-induced structure can significantly improve the active cooling effect in asphalt pavement.The cooling efficiencies of the surface,top layer,middle layer and bottom layer of the optimal composite heat-induced structure scheme are 28.74%,47.58%,29.21%and 21.57%respectively,which are significantly higher than the cooling efficiencies of the single gradient thermal conductivity structure.Meanwhile,the cooling efficiencies of the gradient thermal conductivity structure is-2.92%,13.10%,14.06%and 12.25%,respectively.The composite heat-induced structure is an integrated cooling structure with high efficiency and rapid cooling effect for both surface and pavement interior.It is expected to provide a more efficient heat dissipation structure for the asphalt pavement in the plateau permafrost region to reduce the thermal damage of the asphalt pavement,enhance the thermal stability of the subgrade in summer.