The Texas Department of Transportation (TxDOT) has awarded a two-year $1,119,312 grant to Dr. Stefan Romanoschi to investigate the performance of asphalt mixes containing RAP (Recycled Asphalt Pavement) and RAS (Recycled Asphalt Shingles). He is leading a team of researchers from the University of Texas at Arlington and the Texas Transportation Institute. The project starts in May 2012 and will continue until April 2014.

TxDOT's current specifications permit the use of both RAP and RAS, but there is little evidence that these mixes give comparable performance to those mixes that do not incorporate any recycled materials. RAP is the material obtained after milling distresses asphalt pavements, while RAS results from damaged asphalt shingle roofs. Concerns have been raised about mixes which are now "drier," more difficult to compact and more susceptible to both reflection and fatigue cracking. There is an urgent need to conduct a rapid evaluation of these materials and this can readily be performed using Accelerated Pavement Testing (APT) technology.

Accelerated Pavement Testing (APT) is the "controlled application of wheel loading to a layered pavement structure to determine pavement response and performance under controlled, accelerated accumulation of damage". In APT, experimental pavement structures are build full-scale with conventional construction methods and loaded with conventional truck wheels and above the legal load limits. The accelerated loading is done by applying quickly a large number of load cycles (>100,000 per week), to induce failure to the experimental pavements in a few weeks or months.

APT is the research tool that links pavement research conducted in the laboratory and on in-service road sections. When laboratory research results are directly implemented in practice by building in-service pavement sections, there is the risk that these sections will fail prematurely and therefore, significant replacement or rehabilitation costs occur. APT singles out the damaging effect of wheel loads since when subjected to accelerated loading pavements are not affected by long-term climatic effects. Dr. Stefan Romanoschi, Associate Professor in Civil Engineering, has run the APT research program at Kansas State University between 2001 and 2007 when he joined UTA. He managed the most cost effective APT program in the country; it generated in total about $ 3 million during his tenure.

APT is not currently available in Texas. The University of Texas at Arlington is establishing a Pavement Research Center focused on APT research which can be used for a range of rapid pavement evaluations. Funds have been obtained from the UT System and ground has been allocated to house and operate the APT device, called the Pavement Testing Machine (PTM). The manufacture of the APT device and establishing the facility is currently underway and this will be developed only with internal funds from UT Arlington.

As part of the new research grant, twelve asphalt pavement test sections using Texas mixes in typical TxDOT pavement structures will be constructed. These mixes will have different levels of RAP and RAS; the goal is to validate the cracking and rutting potential of both control and RAP/RAS modified mixes within a controlled APT program.

The research project is expected to yield practical results that will have an immediate impact on TxDOT methodology for selecting the constituent materials and designing asphalt mixtures that will contain RAP and RAS for both new flexible pavement construction as well as for asphalt concrete overlays. The successful completion of this research will lead to a better understanding of the performance of mixes that contain RAP and RAS and optimum utilization of these materials. This will have a major positive impact on extending the life of the asphalt overlays constructed in Texas. It could also lead to significant benefits to TxDOT in terms of reduction of the costs for maintaining the Texas highway network, protecting the environment and improving the safety and comfort of road users.

Dr. Romanoschi, a research associate and two Ph.D. students will be working on the project.