By Greg Harder, P.E. and Dwight Walker, P.E.
When the New York State Department of Transportation (NYSDOT) decided to upgrade the pavement on a section of I-87 near Albany, they took advantage of the opportunity to gain experience with warm mix asphalt (WMA.)
NYDOT Region 1 Materials Engineer Greg Wichser, P.E., chose to do a significant portion of the project with WMA to get away from a “demonstration project” mentality. Prior to this project, most WMA placed in NY had been bid as a small part of a larger project—or had been substituted for some of the hot mix, at no cost to the DOT.
Wichser had confidence in WMA technology but he wanted a better understanding of how production and placement would be handled and accomplished routinely (beyond the limited tonnage/production days for demonstration type projects). He also wanted a better representation of the bid numbers if WMA becomes more widely used. That was the main reason he bid such a large portion of the overall project as WMA.
“By deciding to bid such a large portion of this project with WMA, we were taking it from an experimental or demonstration phase to a real world scenario,” said Wichser.
The I-87 project runs from Exit 18 to Exit 24 in both directions (north and south). This entire section was last paved in 1998, one of the first Superpave projects placed by NYSDOT. The binder and wearing courses consisted of granite aggregates. The base was last paved in 1967 and is still in good condition. It utilized a limestone aggregate.
The surface course was showing surface cracks and some thermal cracks. During construction, stripping was observed in the existing binder and wearing courses; this may have contributed to the cracking on the project. The project was at that point where it was exhibiting distresses (very little of which was structural), and if let go for even a few more years, the roadway would deteriorate quickly. Further deterioration would lead to structural distresses and a maintenance nightmare.
The NYSDOT Region 1 position is that maintenance personnel cannot work efficiently on interstates under traffic, even with protection, traffic control, etc. So their strategy is to get to these projects before their condition reaches a point requiring a substantial amount of maintenance work. With this concern in mind, the remedial work was undertaken.
The HMA section runs from Exit 18 to exit 22 and is 12.7 miles long and 6 lanes wide (3 northbound and 3 southbound)—with 47,000 AADT and 12 percent trucks. The HMA section uses a 12.5mm mix (5.4 percent total AC) placed at 2 inches compacted depth requiring approximately 65,000 tons of mix.
The WMA section runs from Exit 22 north to Exit 24. This section is 11.7 miles long and 4 lanes wide (2 northbound and 2 southbound), with 23,000 AADT and 26 percent trucks. The WMA section uses the same 12.5mm mix (again 5.4 percent total AC) placed at 2 inches compacted depth requiring approximately 45,000 tons of mix.
The entire project, both HMA and WMA sections, is mill-and-fill. Two inches of material is being milled off and removed; two inches of new material is being replaced.
Kubricky Construction Corporation is the general contractor on this project and is doing the paving. Pallette Stone Corporation is the producer for the asphalt mixes used on the project. Both companies are part of the D.A. Collins organization.
Both the HMA and WMA mixes are produced through Pallette Stone’s Gencor drum plant, rated at 400 tons per hour. The plant has 1,200 tons of silo capacity ? three 200-ton silos and two 300-ton silos. The plant also has six cold feeds, as well as two Recycled Asphalt Pavement (RAP) bins. The plant has two 30,000-gallon asphalt storage tanks. One tank contains PG 64-22 and the other contains PG 64-22 with the LEA-Lite WMA additive. On good production days, the plant produces around 4,500 to 5,000 tons of mix. Both the HMA and WMA mixes used on this project contained 20 percent RAP. Pallette Stone processes the RAP on site by crushing it and screening it on a 9/16-inch screen so that all RAP being used currently is minus 9/16 inches.
Eric Winter, Pallette Stone’s Quality Control Manager, describes the WMA work as going very well. The mix volumetrics have been as good as or better than the same HMA. This project falls under an experimental work plan so no incentives/disincentives apply. But, if they did, the WMA would be averaging a 3 percent bonus—without a single deduction, so far.
Switching between the PG 64-22 and the WMA-modified binder was seamless. The PG 64-22 with LEA-Lite additive is coming from Gorman Asphalt, Ltd. out of Albany. LEA-Lite is a technology developed by McConnaughay Technologies, a division of Suit-Kote Corporation based in Cortland, NY. Suit-Kote is providing the LEA additive to Gorman Asphalt where they are adding it to each tanker by injecting the additive into the asphalt line during the truck loading process. LEA-Lite is a warm mix technology that allows a drop in temperature of 20?50¿F from conventional mix temperatures through the use of a chemical additive. Gorman uses a micromotion mass flow meter with printout to insure the proper dosage is met.
This project has both in-place and plant density requirements, as well as a rideability specification, but nothing regarding joint densities. Field densities for the WMA have not been an issue. In fact the contractor has been able to reduce the number of passes from one of the rollers by one pass and still obtain good densities.
To date everyone seems pleased with the project. Winter, the QC manager says, “Making the switch from HMA to the WMA has been seamless. Our plant volumetrics and field densities continue to be consistent—keeping us in a bonus situation.”
That is the type of experience, we all want on our projects.