Investigation of the thermal parameters of reclaimed asphalt materials with applications to asphalt recycling

Abstract

Asphalt concrete is the third most widely used resource in the world, next to Portland Cement Concrete and water. In the United States alone, over 550 million tons of hot mix asphalt (HMA) are produced at more than 4,000 asphalt plants across the country. With over 94% of the paved roads in the United States surfaces with asphalt concrete, it's safe to say asphalt pavement is what America drives on. However, a majority of today's pavement projects are geared towards rehabilitation and reconstruction of existing pavements, rather than construction of new roads. While it is true that asphalt pavement is 100% recyclable and it is the most recycled material in America, the reality is most roads contain no more than 20% recycled material. There are many factors that prohibit new road construction in excess of 20% recycled content, and this thesis aims to explore just one of those factors - the thermodynamics of hot mix asphalt pavement recycling. Most research that is investigating the use of high amounts of Reclaimed Asphalt Pavement (RAP) have been based on empirical trials. This work has approached the issue of pavement recycling by measuring the thermal properties of recycled asphalt, examining the thermodynamic limits of asphalt drum mixing, and by modeling asphalt mixing drums using finite element techniques to determine the amount of time required to achieve full melting inside of asphalt drums. It was found that for many different drum configurations, there is insufficient retention time for RAP to reheat. This insufficient heating could cause premature failures in asphalt pavements using high percentages of RAP. A secondary goal of this thesis is to explore the benefits of using the waste mining material, taconite tailings, in new asphalt pavements. This research shows there is thermodynamic benefit gained by using taconite tailings because they can be heated faster than traditional aggregates. This heating supplies more heat to RAP, which in turn, may allow for more of the recycled asphalt pavement to be incorporated into new asphalt pavements.