Structural Characterization of Recycled Materials at the NCAT Test Track

Abstract

The functional and structural performance of two pavement recycling techniques: Cold Central-Plant Recycling (CCPR) and Cement Treated Base (CTB) from a Full Depth Reclamation (FDR) process, were evaluated under accelerated pavement testing (APT). Three test sections, consisting of a combination of CCPR and CTB layers built underneath a set of asphalt concrete (AC) layers, were built in 2012 at the National Center for Asphalt Technology (NCAT) Test Track. A total traffic of 20,055,247 ESALs was applied to each test section by a fleet of special tractor trailer rigs manually operated at a target vehicle speed of 45 mph. During this period, the evolution of the performance of each test section was evaluated periodically. Based on weekly visual inspections and field measurements it was identified that, after over 20 million ESALs, rut depth and ride quality (represented by the international roughness index or IRI) remained well below the limiting criteria used at the Test Track. Periodical falling weight deflectometer (FWD) testing and weekly stress and strain measurements (by means of embedded instrumentation) revealed the structural performance and pavement response of the test sections remained relatively constant over the application of traffic. Laboratory testing and FWD backcalculated modulus showed the CCPR is a temperature-dependent material, with slightly less temperature susceptibility than conventional AC. Similarly, based on the performance measurements, it was determined that the CTB significantly improved the response of the pavement under traffic loading. The obtained results were used to evaluate the structural contribution of the recycling technologies from a pavement design perspective. Based on empirical pavement design it was determined that the structural layer coefficients of CCPR ranged between 0.30 and 0.35, while those of CTB ranged between 0.20 and 0.25. Additionally, based on mechanistic analyses and the measured pavement responses it was determined that the correct combination of CCPR and CTB may result in a perpetual pavement. Although additional research is needed to support the previous statements, this research provided sufficient information on the performance and failure mechanisms of CCPR and CTB, indicating they may be used for high traffic applications.