VAA Spring/Summer 2020

VAASPHALT.ORG 29 THE SCIENCE OF RECYCLING However, given that this layer was only 2 inches thick, it would not have been possible to place the 0.5-inch-thick strain gauges before the construction of the OGDL layer without causing problems for the creation of that layer. As an alternative, the researchers decided to place the strain gauges at the bottom of the CCPR layer and determine the maximum strain by modeling. On five dates from June 2019 to December 2019, trucks from the VDOT Williamsburg Area Headquarters were loaded with sand or aggregate to the desired axle weights and were driven over the instrumented section by agency personnel as part of the public traffic stream. The researchers used a synchronized timestamp from a video camera, recording the passing traffic and the data acquisition system to determine when the test vehicle crossed the instru- mented section, as shown in Figure 3. Edge Stripe Centerline Pressure cell on top of OGDL Pressure cell on top of subgrade Horizontal asphalt strain Temperature probe array TDR moisture probe array Direction of Traffic Center of Wheel Path 3.5ft 20ft 2ft 2ft 1.5ft 2.5ft 4ft Figure 2. Plan view of the instrumented test section. Figure 3. VDOT tandem-axle dump truck traveling over instrumented section. △ continues on page 30