VAA Virginia Asphalt Fall/Winter 2021

16 FALL/WINTER 2021 Material Unit Unit Cost, $ Assumed Density, lbs/ft 3 Asphalt surface (SMA) Tons 106 146 Asphalt base (dense graded) Tons 95 146 CCPR Tons 45 136 FDR Square Yard 8 - Aggregate Base Tons 20 152 Table 1 Unit Costs and Densities for Economic Analysis. Material CCPR S12 2003 N3 2003 N4 AC 4.4 9.1 8.9 CCPR 4.3 - - Agg Base - 6.0 6.0 FDR 7.8 - - Pavement Section Cost, $/SY $44.20 $56.52 $55.37 Structural Number (SN) 5.40 4.74 4.64 Structure Normalized Pavement Section Cost, $/SY/SN $8.18 $11.93 $11.93 Table 2 Economic Analysis Results. PAVEMENT RECYCLING density for each material required to con- vert from a weight-based unit cost ($/ton) to an area-based pavement section cost ($/ SY). The upper part of Table 2 shows the as-constructed layer thicknesses of Section S12 and the two sections constructed in 2003 that did not include CCPR or FDR: 2003 N3 and 2003 N4 (coincidentally, the 2003 sections were also located on Sections N3 and N4 and the year of construction is used to differentiate them from the CCPR sections built in 2012). The lower part of Table 2 shows the pavement section cost ($/ SY), the pavement structural number (SN) and the structure normalized pavement section cost ($/SY/SN). The pavement sec- tion cost was calculated by using the values shown in Table 1. The structural number was calculated by using typical VDOT pavement design values. Finally, the struc- ture normalized pavement section cost was calculated by dividing the pavement section cost by the structural number to normalize the section costs with respect to structural capacity. By observing this normalized cost, it can be seen that Section S12, built using pavement recycling techniques, was approx- imately 30% less expensive per square yard. In addition to cost, the environmental implications of the pavement structure are important to consider. The percent recycled content for each section shown in Table 2 was calculated as a weighted average per inch of material. Section S12 contained 76% recycled material; the two sections constructed in 2003 contained none. To characterize the environmental benefits of pavement recycling at NCAT completely, a life-cycle assessment (LCA) is needed. Although this has not yet been completed, the Federal Highway Admin- istration released a case study in 2020 that did investigate VDOT’s I-81 project constructed in 2011 that included a similar combination of CCPR and FDR and were the same RAP source as Section S12. The authors calculated that materials and initial construction energy demand were reduced approximately 50 to 70%, and Global Warm- ing Potential (GWP) was reduced by 40 to 70% compared to a “conventional” design ( https://www.fhwa.dot.gov/pavement/ sustainability/case_studies/hif19078.pdf) . One of the goals of VDOT’s pavements research program is to implement research findings into the business practices of VDOT. The findings of the research conducted at NCAT directly led to the use of pavement recycling techniques for the widening and reconstruction of Segments II and III on I-64 near Williamsburg. Both the widened and the reconstructed lanes used the combination of CCPR over an FDR foundation to produce a pavement structure having approximately 70% recy- cled materials. The work performed on Segments II and III included approximately 71 and 83 lane miles of recycled pavement, respectively. These quantities made them the second largest pavement recycling proj- ects globally at the time of their respective construction. VDOT continues to look for applications where pavement recycling can rehabili- tate existing pavements and construct new lanes. By implementing the results of pave- ment research, VDOT is leading the nation in using pavement recycling techniques on high-volume roadways. △ continued from page 15 By implementing the results of pavement research, VDOT is leading the nation in using pavement recycling techniques on high-volume roadways.