VAA Spring/Summer 2020

18 SPRING/SUMMER 2020 The project conditions permitted a 25- calendar day, full-closure of the runway to complete the milling and paving opera- tions with $3,000/day liquidated damages. The construction specifications included P-401 asphalt mix with all grades +/- ½" of plans and profile milling areas noted in the plan to accomplish a 2 ½" final surface lift of asphalt. Longitudinal cold joints were limited to 3 for the runway and required a 6" re-mill of each cold joint to provide a vertical edge for paving the next lane. Before full production of the final asphalt surface, a 300' x 37.5' test section was required to demonstrate the contrac- tor’s ability to achieve the project specifi- cations. The minimum densities were 96.3% for the mat and 93.3% for the joints. The PWL - Method of Estimating Percent- age of Material Within Specification Limits were specified for acceptance and payment of the asphalt. Before the start of work, W-L created a GPS model of the planned surface to compare with the existing surface eleva- tions. After dividing and marking the existing surface, milling operations were performed with GPS (millimeter preci- sion) of high areas. Areas that were significantly low were then paved in 1 ½" lifts to reach the bottom of the 2 ½" surface lift. One last GPS milling pass was performed on the entire runway to provide a uniform 2 ½" final mat. Before place- ment of the last mat, the entire surface was coated in PG64-22 liquid followed by a non-woven fabric to reinforce the pave- ment structure. The final surface course was placed using two tandem pavers that also incorporated the GPS model, result- ing in final grades within 0.02' of planned grade, which was half of the allowed tolerance. This process also reduced the number of cold joints to one at the centerline of the runway. The project utilized over 13,000 tons of P-401, with 100% of tonnage meeting the PWL specification. Project Execution and Outcomes Understanding the importance of the project and the risks associated with a PWL specification, W-L selected two of its’ senior Paving foremen and crews to perform the paving operations. Several planning meetings were held to discuss means and methods before starting the project. Additionally, mix designs were submitted △ continued from page 17 Mountain Empire Airport, Smyth County, Virginia (photo courtesy of Mountain Empire Airport) Echelon Paving the Runway Installation of Paving Fabric prior to Overlay MOUNTAIN EMPIRE AIRPORT