Effects of thermally modified asphalt concrete on pavement temperature

摘要

This study investigates the feasibility of mitigating temperature-related issues, such as heat island effect, ice layer formation and thermal distresses of asphalt pavement, by controlling thermal properties of hot mix asphalt (HMA). Expanded polypropylene (EPP) beads and graphite powder are selected as the additives to change the thermal properties of HMA, and their effects on thermal and mechanical properties are evaluated experimentally. The test results show that the EPP modified HMA yields a reduction in thermal conductivity, heat capacity and indirect tensile strength up to 17, 32, and 27%, respectively. Conversely, replacing a part of traditional fillers with graphite powder increases indirect tensile strength and thermal conductivity up to 40 and 43%, respectively. A series of heat transfer analysis was conducted using a finite difference heat transfer model to investigate the effects of the thermally modified HMA on the pavement temperature gradient and surface temperature. The simulation results show that the amplitude of daily surface temperature variation reduces as the HMA thermal conductivity increases. The HMA containing 4.8% graphite by volume of the mixture reduces the daily surface temperature amplitude by 8.1% in the summer simulation and 9.6% in the winter simulation. The graphite modified HMA also has 1.5 degrees C lower maximum pavement surface temperature than the non-modified HMA in the simulation for a summer day at Texas. This implies that the modified HMA with improved thermal conductivity, such as the graphite modified one, is effective in mitigating thermal cracking, rutting and urban heat island effect. In addition, the improved indirect tensile strength of graphite modified HMA will bring extra extension of pavement service life. The parametric study for wide ranges of thermal conductivity and heat capacity shows that the daily temperature amplitude on a pavement surface can be reduced up to 28.9% by selecting highly conductive aggregates and graphite powder.