Crews shut down lanes for completely closed night work zones.
Pick and choose
For a mill-and-thin overlay project using 40% RAP in the mix, Hartnett selected an older asphalt pavement considered to be in fair condition, merely in need of resurfacing. The approximately 3,000 linear ft of the North Service Road and westbound ramp onto I-290 in Worcester had seen no preservation treatments in the past.
“It showed no signs of deterioration,” Berkley agreed. “There was some oxidation and some surface cracking.”
Berkley explained the pavement was the correct one for the treatment. “The purpose of this project is a pavement preservation instead of a rebuild.”
A thin overlay’s purpose is not to fix structural problems, but to extend an existing pavement’s life, thus the minor cracking and oxidation of the chosen pavement could be resolved with the simple 1-in. mill and well-designed thin overlay.
Originally, the test section was going to be included in a MassDOT district-wide resurfacing contract. When the budget was expended prior to completing the work in mid-2016, the North Service Road project had to be pushed to a later date. October 2016 saw the project come to fruition.
Design and produce
Mogawer prepared a Superpave 9.5-mm Sustainable Thin Overlay (SP9.5 STO) mix design, which is appropriate for lift thicknesses ranging from 0.75 to 1.5 in. The mixture comprises coarse aggregate, fine aggregate, mineral filler as needed and a PG 64-28 asphalt binder typical to Massachusetts specifications. A maximum of 40% RAP incorporates a rejuvenator at a dosage of 6% by weight of recycled binder. The draft specification allows MassDOT District 3 to increase the amount of RAP it would typically include in a surface layer.
Montenegro explained, “Nationally, on a simple percentage basis, most DOTs allow up to 20% RAP in surface course mixes,” he said. “When mixes include a higher percentage of RAP than that, the pavement can experience the early onset of premature cracking due to the stiffness of the aged binder. Industry can offset that brittleness with a softer binder grade or rejuvenators. Mogawer is using the rejuvenator in the lab, and now it needs to be put to the test in the field. MassDOT District 3 and P.J. Keating opted to use it in the field for a pavement in Worcester.”
As mentioned above, the specification used for the North Service Road mill-and-fill project is a provisional one. Once enough projects use and prove the efficacy of the specification, Mogawer can assist in developing a spec that allows for the use of whatever rejuvenator is in a producer’s arsenal.
In this case, the restorative agent P.J. Keating added to the mix was Delta S, which is a small-molecule dispersion inside a plant-based oil. The plant-based oil penetrates the asphalt binder and carries the rejuvenator in to soften the binder.
