Perpetual Pavement

Golder Associates designed a “Perpetual Pavement” for the new four-lane Red Hill Valley Parkway in Hamilton, southern Ontario. Golder’s project won the Willis Chipman Award from Consulting Engineers of Ontario in 2009.

The Perpetual Pavement is designed to last 50 years, whereas conventional asphalt pavements are typically designed to last 20 years. Until this project, there was very limited experience with these long-lasting pavements in Canada, so the design involved feasibility studies, mechanistic properties testing, and consultation with some of the world’s leading experts in pavements and materials.

A conventional pavement on a high volume highway will likely require two major rehabilitations over a period of 50 years. These, depending on the type of structure, may include milling and thick overlays, or the reconstruction of the asphalt layers.

By contrast, the perpetual pavement will likely require only two periodical resurfacings (milling and placement of a new surface course only), and these can generally be done overnight, which means much less disruption to traffic. The roadway’s durability also means savings in materials, with their associated environmental costs.

The unique aspect of the perpetual pavement is the combination of the asphalt layers. The Red Hill Valley Perpetual Pavement is a “bottom-up” design. The road is designed so that the tensile strength at the bottom of the asphalt does not exceed 70 microstrains, which should prevent fatigue cracking. The compressive strain at the top of the subgrade should not exceed 200 microstrains, which should prevent subgrade rutting.

The pavement consists of 370 mm of subbase, 150 mm of granular base and then several lifts of asphalt (see photo).

For the lowest lift, Golder developed a new Rich Bottom Mix (RBM), laid 80 mm thick, which gives excellent fatigue endurance. Above that is a 70 mm course of Superpave 25.0 and then 50 mm of Superpave 19.0. These high-quality binder courses provide a strong stone skeleton resistant to rutting. Finally, there is a 40 mm Stone Mastic Asphalt (SMA) surface course.

The mechanistic properties of the asphalt mixes had to be determined by laboratory testing at the mix design stage; Golder developed six special specifications for mix types. The contractor had to achieve tight tolerances with reasonable effort.

Construction traffic was strictly limited to avoid damaging newly placed lifts. There were no cold longitudinal joints, and the potential for segregation was eliminated by using a Shuttle Buggy material transfer vehicle.

An advanced monitoring system was built into the roadway that measures both traffic and pavement response. Since it opened in 2007, the parkway has carried around 80,000 vehicles a day, and the pavement has remained in excellent shape. Today more perpetual pavements are being constructed in Ontario and Alberta.

Client: City of Hamilton

Pavement/materials consultant: Golder Associates (Ludomir Uzarowski, P. Eng., Imran Bashir, P. Eng., Andro Delos Reyes)

Contractor: Dufferin Construction

Contract administrator: Philips Engineering