Testing & producing HiMA mix
Kraton supplied D0243 polymer in pellet form to NuStar Energy’s New Jersey asphalt facility, where it was added to liquid asphalt to yield HiMA binder. This binder was shipped to the North Clarendon, VT, asphalt mix plant of Pike Industries. The 3.5-ton Cedarapids plant was used to manufacture both Type C surface treatment mix and the HiMA-binder mix for the demonstration.
A member of the Oldcastle Materials Group, Pike is a 140-year-old asphalt producer/paving contractor with more than 40 asphalt plants and 20 crushing facilities throughout northern New England. The company also operates several fully equipped testing laboratories staffed by engineers and quality control technicians.
For comparison purposes, the demonstration called for placing one inch of PMTOL mix containing virgin aggregate on the first mile of the two-mile section, and one inch of PMTOL mix containing 25% RAP on the second mile. To facilitate production of the latter, Pike set up an Astec screening system to feed RAP directly to the batch plant.
The crushed 38-inch stone (9.5mm) required by PMTOL specifications was supplied by precast concrete manufacturer J.P. Carrara & Sons Inc. of Rutland, VT, while Pike supplied the necessary natural sand and RAP from its own stockpiles. Pike technical personnel tested pavement materials in the company’s laboratories at its Barre, VT, office and at company headquarters in Belmont, NH.
Months before the thin-lift demonstration took place in Danby, Pike laboratory staff tested native aggregate and RAP for physical and chemical qualities to ensure the stone would meet PMTOL specifications. Technicians also conducted standard tests on the RAP, checking aggregate gradation and binder content among other characteristics.
In addition, Pike personnel experimented with different aggregate, and samples of HiMA binder provided by Professor Mogawer, to create various blends in order to produce PMTOL mix characteristics. They also ran several batches of these blends through the Cedarapids plant to study process reactions.
Working with Dr. Mogawer, they were able to verify that both all-virgin aggregate and 25% RAP blends would meet PMTOL specifications.
They also got approval from VTrans for the mix design. During mix production for the demonstration, VTrans personnel took samples of plant mixes and had them delivered to the Highway Sustainability Research Center for analyses by Dr. Mogawer and his staff.
Tandem paving and rolling
US Route 7 at the demonstration location is 44-feet wide, with two 12-foot travel lanes and two 10-foot shoulders. Pike used its own fleet of Mack tri-axle dump trucks to haul the mix from North Clarendon, supplementing these with contract haulers when needed.
The decision was made to pave the 10-foot shoulder and 12-foot travel lane simultaneously to obtain smooth longitudinal joints. A Terex Cedarapids was used to pave the shoulder while a CAT AP-1055D paved the travel lane. The pavers operated in tandem, with the Terex Cedarapids always in the lead.
Three rollers operating in non-vibratory mode provided compaction – a CAT CB534D breakdown roller, CAT CB434 intermediate roller, and a HYPAC roller. As with the pavers, the rollers operated in tandem, going from shoulder to travel lane and back – again, this was to ensure a smooth joint.
For the remaining 912 miles of Pike’s maintenance contract, a special paver was used to install the Type C surface treatment mix, which contains ½-inch maximum stone and 4.9 % binder and is placed over fresh-sprayed asphalt emulsion.
Pike trucks delivered plant mix to a specialty spray paver provided by Gorman Bros. of Albany, NY. This self-priming paver sprayed asphalt emulsion on the road surface immediately before it laid down the Type C overlay.
Monitoring the overlay
The performance of NEPPP’s thin-lift PMTOL mix used on the U.S. Route 7 demonstration is being monitored by VTrans and compared with the performance of the Type C surface treatment. VTrans’ Fowler wants to see if they can get the same durability and same installation cost per square yard from one-inch-thick HiMA-modified overlays that they’re getting from conventional 112-inch overlays.