Sustainability Assessment Of Recycled Asphalt Mixtures In Texas

The pavement practitioners use more recycled materials in asphalt mixtures in order to compensate for the high price of petroleum products and save the limited resources of virgin materials. Reclaimed Asphalt Pavement (RAP) and Recycled Asphalt Shingles (RAS) have been in wide use in asphalt mixtures for several decades. Public perception on the utilization of recycled materials is that the mixtures become more cost effective and more environmental friendly. This is true when the initial stage of construction of pavements is assessed. However, a mixture that costs less and/or burdens the environment less at the beginning may require more frequent rehabilitation because of poor performance. Therefore, in order to have a comprehensive idea of the sustainability of a mixture, its entire life cycle should be evaluated. The objective of this research was to assess the sustainability of three recycled asphalt mixtures and of a mix not containing recycled materials. The recycled mixtures were labeled as "High RAP", "RAP&RAS-WMA" and "BMD". The "High RAP" mixture had 19 percent fractionated RAP. The "RAP&RAS-WMA" had 15 percent RAP and 3 percent RAS while the production technology was WMA. The "BMD" mixture had 15 percent RAP, 3 percent RAS and slightly higher binder content. The virgin mixture was "Type D" which is a common dense-graded mixture in Texas. Twelve pavement sections were constructed from these four mixtures to evaluate their resistance to rutting, fatigue cracking and reflection cracking. The Accelerated Pavement Testing machine of the University of Texas at Arlington was employed to perform the full-scale testing. The results of field sections were then utilized to determine the service life of the mixtures for initial construction and subsequent required overlays. The life cycle environmental burden and cost of each mixture were also calculated. Field results suggested that rutting is not a concern for these mixtures. The virgin control mixture had the second best performance in resistance to both fatigue cracking and reflection cracking. The life cycle environmental assessment of mixtures showed that the "BMD" mixture had the least environmental impacts and was followed by the "Type D", the "RAP&RAS-WMA" and the "High RAP" mixtures. The same ranking of mixtures was observed in life cycle cost analysis. Among different construction phases, the "Materials Production" phase had the highest energy consumption and carbon dioxide emission, mainly due to the bitumen production process.