Heat dissipation and effective compaction time of floating bead amended asphalt mixture during the construction stage of pavement under low-temperature conditions
This paper investigates the impact of floating beads on temperature dissipation during the construction stage and their influence on the effective compaction time of asphalt pavements.As a high thermal resistance ma-terial,floating beads have been used in asphalt pavements in permafrost region to reduce heat absorption and mit-igate thawing induced settlement during the operational stage.However,limited research has focused on the in-fluence of floating beads on temperature dissipation during the construction stage and their impact on the effec-tive compaction time of asphalt pavement.The addition of floating beads alters the thermo-physical properties of the asphalt mixture,thereby affecting pavement compaction and heat transfer to the frozen soil subgrade.During the compaction process of asphalt mixtures,the material undergoes a transition from a loose state to a dense state,resulting in decreased porosity and increased strength.Consequently,the thermo-physical parameters of the asphalt mixture dynamically change throughout the construction stage of asphalt pavement.This study con-siders the asphalt mixture modified with floating beads as a composite material comprising coarse aggregates,as-phalt matrix,and air.Laboratory tests are carried out to measure the thermo-physical parameters of the three components in the modified asphalt mixture.The Williamson formula is utilized to calculate the thermo-physical parameters of the modified asphalt mixture in both dense and loose states.To analyze the temperature field in the asphalt pavement and the heat flux entering the soil subgrade,a finite element model is developed.The model takes into account different floating bead contents and paving thicknesses.Based on the numerical results,a mul-tivariate regression analysis is performed to identify the key factors influencing temperature fields during con-struction stage of asphalt pavement.This analysis leads to the derivation of an empirical equation for estimating the temperature of the asphalt mixture.The research findings reveal that the inclusion of 15%volume of floating beads reduces the thermal conductivity of the asphalt mixture by 78%,while exhibiting negligible changes in spe-cific heat capacity(i.e.,less than 1%).With an increase in air temperature 0 °C,10 °C,20 °C,30 °C,the addi-tion of 15%floating beads enhances the effective compaction time by 21.1%,20.2%,17.5%,and 16.8%in the dense state,and by 21.6%,21.2%,20.3%,and 18.7%in the loose state.Compared to the dense state,the effective compaction time in the loose scenario is approximately 1.7 to 2.1 times longer.Hence,in low-tem-perature conditions,re-compaction and final compaction are crucial to be promptly and continuously completed to achieve the specified compaction level within the designated timeframe.Furthermore,the inclusion of 5%,10%,15%volume of floating leads to a reduction of 1.9%,3.1%,and 6.4%in heat flow to the subgrade in the dense state,and a reduction of 3.5%,7.3%,and 12.8%in the loose state.These results demonstrate the bene-fits of adding floating beads in mitigating heat disturbance to the soil subgrade during the construction stage.By minimizing heat flow,the potential adverse effects on the frozen soil subgrade are significantly reduced,contrib-uting to the overall durability of the asphalt pavement.In conclusion,the addition of floating beads alters the thermo-physical properties of asphalt mixtures,thereby influencing the compaction process and heat transfer dy-namics.The findings in this study provide valuable insights for optimizing construction practices of asphalt pave-ment,including adjusting compaction procedures and ensuring appropriate timeframes for effective compaction.Moreover,the benefits of floating beads in reducing heat flow to the subgrade indicate their potential for enhanc-ing the long-term performance of asphalt pavements in challenging environmental conditions.Overall,this re-search contributes to the understanding of the thermo-physical behavior of asphalt mixtures containing floating beads and provides guidance for the design and construction of resilient asphalt pavement in permafrost regions.
floating beadsasphalt pavementconstruction qualityeffective compaction timepermafrost region
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