NCAT Research Leads to Improved Use of CCPR in VDOT Project
Tuesday, April 3, 2018
Posted by: Kristi Olson
During the 2018 NCAT Test Track Conference that ran from March 27-29 in Auburn, Alabama, highlighting results from NCAT’s sixth testing cycle, the practical application of the testing and research conducted on the track was highlighted by several presentations on Virginia Department of Transportation’s (VDOT) cold central plant recycling projects.
University of Auburn Civil Engineering Professor David Timm led off with a presentation to attendees on the Virginia CCPR and Stabilized Base Experiment at the NCAT Test Track.
With an estimated 10 million plus tons of stockpiled RAP in Virginia, in 2011 VDOT decided to construct a pavement recycling project on I-81. This project, implemented based on lab-based materials characterization, performed so well that VDOT began thinking about long-term performance. In 2012, the decision was made to sponsor three sections at NCAT that resembled the I-81 project, with a focus on instrumentation response. Two sections were installed on the north part of the track, N3 and N4, and one on the south side, S12, as follows:
Performance measurements at the track included weekly inspection for cracking, rutting, and ride quality. Instrumentation was placed above the subgrade layer and above the aggregate/stabilized base layer and falling weight deflectometer (FWD) testing was conducted several times per month to measure the structural capacity.
||University of Auburn Civil Engineering Professor David Timm demonstrates FWD testing on the VDOT sections at the NCAT Test Track facility.
With these sections now having gone through two cycles at NCAT, all sections have demonstrated excellent performance, outperforming expected lives with greater than 18 million ESALs so far. With support from FWD and strain measurements, it was determined that CCPR could be treated like asphalt concrete in mechanistic modeling. Based on testing, it was also found that section S12 is expected to be a perpetual pavement using existing criteria.
Virginia Transportation Research Council Associate Principal Research Scientist Brian Diefenderfer then provided attendees with additional information on VDOT’s implementation on I-81 and I-64. Based on the performance results on the installed NCAT test sections, with perpertual type performance from Section S12 and no observable surface distresses after nearly 20 million ESALs, in 2016 the decision was made by VDOT to move forward with CCPR with a stabilized base on their I-64 project.
|| Virginia Transportation Research Council Associate Principal Research Scientist Brian Diefenderfer shared information about VDOT’s CCPR project at the NCAT Conference and, pictured left, at the 2017 ARRA Semi-Annual Meeting.
The S12 test section included subgrade and stabilized base layers with 100 percent recycled content, a CCPR layer with 30 percent recycled content, and a top layer with 12.5 percent recycled content. Overall, the test section was 80 percent recycled. With similar recycled content, when implemented VDOT opted for a 12 inch stabilized based layer topped by a 2 inch open-graded drainage layer (OGDL), 6 inch CCPR layer, and 4 inch asphalt concrete top layer.
Segment I of the project, consisting of the widening and overlay of 5.6 miles of existing jointed concrete, was completed in 2017. The existing lanes in the project consist of full depth reclamation of existing base materials, while the new lanes utilize imported crushed concrete or RAP that is stabilized in the FDR process. Segment II, consisting of the widening and reconstruction of 7.08 miles is estimated to be completed in Spring 2019, and beginning this summer, Segment III will consist of 8.3 miles and is expected to be completed in 2021.
The CCPR with stabilized base of existing and new lanes has costs of $40 to $61 per square yard, compared to the $80 per square yard anticipated with the original plan including an 8 inch layer of cement treated aggregate, 2 inch OGDL, and 12 inch layer of asphalt concrete. Structural value for the two approaches was nearly equivalent (7.06 compared to 7.08, respectively). In total, Diefenderfer shared that VDOT estimated a total cost savings of about $15 million with the CCPR approach, or a 36% lower cost with no appreciable difference in structural value.
This project will be highlighted at the upcoming ARRA Semi-Annual Meeting, October 15-18, 2018, in Norfolk, Virginia. A narrated tour through the I-64 project and demonstration at the CCPR plant is planned for the event.