One of the major north-south routes running across the state of Virginia is Interstate 81 with two lanes in each direction. Continues use since its initial construction in the late 1960s had a severe effect on the structural capacity of the supporting layers, especially the slow lane. Since the existing layer works consists of 200mm to 250mm thick asphalt on top of granular layers, this project was identified as an ideal candidate to implement foam bitumen stabilization and other recycling methods.
The slow lane indicated more severe failures than the fast lane, therefore separate designs were proposed for each lane. The design proposal of the slow lane were to first mill off 250mm of the existing pavement structure, mainly consisting of asphalt material, and transport it to a stockpile area. The granular layers, now exposed, was then cement stabilized in-place with a Wirtgen WR2400 and re-compacted to form a new cement stabilised subbase layer. The material milled of earlier was stabilized at the stockpile area using a KMA 220 mixing plant and transported back to site where a paver placed the newly stabilized material to -50mm of the final level (200mm thick), forming a new BSM base layer. A 50mm new asphalt layer was constructed last to the existing surface level, creating a smooth driving surface.
For the fast lane, mostly used by passenger vehicles, the top 50mm of asphalt was removed and disposed of followed by the in-placed foam bitumen stabilisation with the Wirtgen 3800 CR cold recycler fitted with an integrated paving screed to a depth of 120mm. Once compacted a 50mm asphalt layer was constructed on the stabilised material to the existing surface level.
Ground-breaking cold recycling technologies form Wirtgen were the key to success in this showcase project. The traffic on Interstate 81 flowed smoothly again after a short construction period where this resource efficient and environmentally friendly process was applied.