Equipment World Digital Magazine
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Virginia's I-81 North America's first highway reconstruction combining cold in-place recycling, cold central- plant recycling, and full-depth reclamation all in one project is now performing "excellently," according to a 2015 TRB paper. 1 The Virginia Department of Transportation rebuilt the sec- tion of I-81 in the shadow of the Blue Ridge Mountains in 2011. In Phase I, VDOT rehabili- tated a 3.7-mile section of I-81 southbound near Staunton using cold in-place recycling, cold central-plant recycling and full- depth reclamation. The high- profile project used cold milling machines, a reclaimer, a por- table cold-mix plant and a cold recycler, in addition to rollers and asphalt pavers. The processes were per- formed both "in place" within the roadbed and adjacent to the highway, and contractors re- used existing material from the underlying road structure. The driving surface received a new overlay of hot-mix asphalt. After rebuilding the shoulders to accommodate work zone traf- fic, the top 10 inches of asphalt from the right-hand lane were removed using two large cold mills, and brought to a mobile cold recycling plant near the interstate, adjacent to the work zone. There the materials were stabilized with a combination of foamed asphalt and portland cement using cold central-plant recycling (CPR). Meanwhile, a subcontractor stabilized the revealed, exist- ing aggregate subbase – which had deteriorated to the point of causing damage to the overlying bound layers – with 3 percent lime kiln dust, a reclaimed in- dustrial byproduct, to a depth of 12 inches using a reclaimer. The stabilized materials were com- pacted in-place with padfoot and smooth drum rollers. The milled, recycled materials from the mobile cold-recycling plant then were used to pave a new base course over the stabilized aggregate subbase to a 6-inch compacted depth. This later was topped with a 4-inch intermediate course of conven- tional hot-mix asphalt and a 2-inch surface course of stone- matrix asphalt. In Phase II of the project, a larger cold recycler performed cold in-place recycling (CIR) in the left-hand passing lane. For this work, the top 2 inches of the pavement was milled and the next 5 inches was recycled in situ using foamed asphalt and portland cement as the stabiliz- ing agents. It then was topped with a 2-inch hot-mix asphalt intermediate course and a 2-inch surface course of stone- matrix asphalt. "The section of pavement re- habilitated by the three in-place recycling methods continues to perform well after nearly three years of heavy interstate traffic," report the authors. "To date, ap- proximately 6 million equivalent single axle loads have been ap- plied. The initial performance of the I-81 pavement section reha- bilitated with in-place recycling techniques can be considered excellent." Roller-compacted concrete with asphalt overlay Roller-compacted concrete (RCC) is accepted for mass place- ments of concrete, such as truck road science | continued April 2015 | EquipmentWorld.com 64 1 Initial Performance of Virginia's Interstate 81 In-Place Pavement Recycling Project, by Brian K. Diefenderfer, Ph.D., P.E., Benja- min F. Bowers, Ph.D., Virginia Center for Transportation Innovation and Research, Charlottesville, and Alex K. Apeagyei, Ph.D., P.E., University of Nottingham, England. Photo: Tom Kuennen