The old cliché “where the rubber hits the road” could be paraphrased as “where the rubber is in the road” when describing a 1-inch asphalt wearing course recently placed on a section of I-91 in western Massachusetts. Installed by contractor Warner Bros. as part of an $11 million MassDOT resurfacing contract, the wearing course incorporated crumb rubber produced by grinding up approximately 75,000 scrapped rubber tires.
The contractor installed the Asphalt-Rubber Open Graded Friction Course (A-R OGFC) on both north- and southbound barrels of a busy (31,000 vehicles ADT), 11-mile segment of I-91 passing through the City of Northampton and the Towns of Hatfield, Whately and Deerfield. The wearing course capped 2-1/4 inches of mill-and-fill Superpave containing 20 percent recycled asphalt pavement (RAP), which was also installed under the contract by Warner Bros., a subsidiary of All States Materials Group.
OGFC Upgrades Highway Safety
In general, open graded friction courses boost highway safety, according to the Federal Highway Administration (FHWA Technical Advisory T 5040.31). FHWA notes that open graded friction courses have demonstrated a number of advantages over other high type surfaces:
They provide and maintain good high speed, frictional qualities; reduce the potential for hydroplaning and the amount of splash and spray; and improve the wet weather, night visibility of painted pavement markings.
However, OGFCs have had some problems with raveling with conventional asphalt, the Administration points out:
“An OGFC generally has a higher asphalt content than a dense graded mix and uses an equal or harder grade of asphalt. A very heavy asphalt film on the aggregate is essential for longevity. The film helps to resist stripping and oxidation of the asphalt cement.”
Rubber Can Improve OFGC Performance
Adding rubber to an OGFC design can improve pavement performance. The rubber in the asphalt mix of the Warner Bros. project is actually contained in the liquid asphalt binder, which is commonly referred to as “asphalt-rubber.” This contrast with a different process in which the crumb rubber is actually a dry additive mixed with the stone aggregate and referred to as “rubberized asphalt.”
Asphalt-Rubber binder is listed in ASTM D 8-88 Standard Definitions as:
"A blend of asphalt cement, reclaimed tire rubber, and certain additives, in which the rubber component is at least 15 percent by weight of the total blend and has reacted in the hot asphalt cement sufficiently to cause swelling of the rubber particles."
All States Materials Group manufactures an asphalt-rubber binder known as crumb rubber modified (CRM) asphalt that coats aggregate with a thick film, making it especially useful for mixes such as open-graded friction courses, according to the company.
“The CRM asphalt binder is composed of conventional liquid asphalt binder blended with 20 percent (by weight) rubber from recycled tires. The tire rubber is finely ground at ambient temperatures then blended with asphalt at temperatures exceeding 350 degrees Fahrenheit.”
All States explains that the high temperature causes oils in the asphalt to swell the elastomeric rubber polymer, resulting in a high-viscosity, elastic binder that produces a thick, highly cohesive and adhesive film on aggregates, improving not only highway safety, but other desirable features such as durability and resistance to oxidative aging, rutting, raveling, delamination and shoving, among other hazards.
More Mix Goes In Than Taken Out
The I-91 section that underwent resurfacing has north- and southbound mainlines consisting of two 12-foot travel lanes, a 4-foot inside shoulder and a 10-foot outside shoulder. Job specifications called for micromilling off 2-1/4 inches of existing pavement – and surprisingly, replacing this with 3-1/4 inches of asphalt mix. The contract’s specified thicknesses for milling and Superpave layers are designed to allow the existing guardrail to maintain a minimum height of 26 inches and therefore remain in place.
Subcontractor Garrity Asphalt Reclaiming of Bloomfield, Connecticut, micromilled the existing pavement. Garrity employed a Roadtec RX-900 Cold Planer powered by a 950hp Caterpillar engine, which can cut up to 8 feet wide and 14 inches deep. The machine was equipped with a micromilling drum that has 0.2 inch (just over 3/16-inch) cutter bit spacing for thin overlays and greater smoothness, and is also used on bridge decks for skid resistance. This contrasts with a standard milling drum that uses 5/8-inch cutter bit spacing for general purposes and deep cuts.
100,000 Tons of Asphalt Mix
Mainline paving was preceded by spot repairs using a 9.5 mm (3/8-inch stone) Superpave leveling course, followed by the placement of 2-1/4 inches of 12.5 mm (1/2-inch stone) Superpave surface course, and the final 1-inch, A-R OGFC wearing course.
In contrast, the specifications for the job’s 13 interchange ramps, two rest areas and two weigh stations called for micromilling off 2-1/4 inches of existing pavement and replacing this with 2-1/4 inches of the Superpave surface course. No A-R OGFC was added.
According to All States, the project required manufacturing and installing a total of 100,000 tons of asphalt mix. About 75,000 tons of this mix was used for spot leveling with 9.5 mm Superpave levelling course and the placement of 12.5 mm Superpave surface course across the entire area of the project including ramps and parking areas. These mixes incorporated 15 percent reclaimed asphalt pavement (RAP), which amounted to 11,250 total tons of recycled material.
Furthermore, the A-R OGFC placed as the final wearing surface on the highway travel lanes and shoulders totaled approximately 28,000 tons of asphalt mix. This 1-inch-thick porous mix was produced with 20 percent asphalt-rubber binder that incorporated about 450 tons of ground tire rubber.
Warner Bros. commenced work on the I-91 project in spring 2017, not long after receiving the MassDOT Notice to Proceed on May 12 for the approximately $10.9 million project. The Department’s Resident Engineer was John Burek, while Warner Bros. key personnel were Rich Brynda, Project Manager; Kevin Cislak, Paving Superintendent; and Eric Emond, Paving Foreman.
The contract limited work time to an 8-hour day, 5-day week, Monday through Friday, between 7:00 a.m. and 3:30 p.m., with no lane closures allowed after 12:00 p.m. on Fridays. In addition, all construction equipment had to be off the road by 3:30 p.m., including backrolling and removing traffic control setups.
For the paving portion of work, the contractor elected to use either of two Caterpillar pavers, an AP1055F and AP655F, depending on the width of placement at the time, plus a Weiler E1650 Material Transfer Vehicle (MTV) to accept mix from the plant. All asphalt mixes were produced by ASMG’s CMI 400EB drum plant and two Dillman 250-ton silos at the company’s River Road, Deerfield plant.
The company employed several Mack 10-wheel dump trucks to haul asphalt mix to the job site. Mix temperatures varied, depending on the type of material. The Superpave surface course mix left the plant at 275 degrees Fahrenheit +/- 25 degrees Fahrenheit and arrived at the MTV at about 265 degrees Fahrenheit, while the A-R OGFC left the plant at 285 degrees Fahrenheit +/- 25 degrees Fahrenheit and arrived at the MTV at approximately 275 degrees Fahrenheit.
Compaction requirements were also different: For the Superpave surface course, the contractor used a Caterpillar CB54B Compactor in vibratory mode for breakdown rolling, a Hamm 110i VV-HF for intermediate rolling, and the same Hamm for finish rolling. For the asphalt-rubber open-graded friction course (A-R OGFC), Warner Bros. used the Hamm 110i in static mode for breakdown rolling and the Caterpillar CB54B in static mode for finish rolling.
Results Win NAPA Awards
In addition to the designated paving work, the contract required adjusting or rebuilding drainage structures, installing new highway guardrail, and setting polyurea recessed pavement markings, plus constructing asphalt berm, resetting granite edging, and establishing safety controls. Other tasks included retrofitting bridge rail and setting up traffic data collection stations and erosion-sedimentation controls. Crews also placed milling mulch for shoulders and improved drainage structures and roadway shoulders, guardrails and signage, and final-striped the entire length of the job.
The project was completed in the fall of 2018.
According to Project Superintendent Brynda, final testing of both laboratory and field asphalt samples yielded excellent results on material composition and mix performance. Additionally, ride quality testing conducted across the entire area of the project showed superior results for pavement smoothness.
Robert Betsold, in charge of Technical Marketing for All States Materials Group, indicated that due to the exceptional results with several unique aspects of the paving portion of the project, it was awarded a Quality in Construction Award by the National Asphalt Pavement Association (NAPA) at their Annual Meeting on January 23, 2019. The project was recognized in the Over 50,000 Tons Category and was also given a Green Project designation for the use of green materials.
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