Thin-Lift Warm-Mix Protects Road

By Paul Fournier | September 28, 2010

Public works officials witnessed the debut of a new thin-lift maintenance mix on a road subject to high-volume traffic in Wellesley, Mass.

Aggregate Industries (AI) installed the maintenance mix on the access road to a busy recycling and transfer center during the demonstration hosted by the Wellesley Department of Public Works for highway officials from more than 20 municipalities and the Massachusetts Highway Department (MassHighway).

AI's Saugus, Mass., plant produced the material, a dense-graded, thin-lift, maintenance mix employing a high percentage of recycled asphalt product (RAP) and a proprietary warm-mix formulation modified with latex. Designed as an alternative to current roadway maintenance products, the mix is said to have a service life of 10 years, and because of its depth — less than 1 inch — preserves curb reveal and oftentimes eliminates having to raise such structures as catch basins.

Longer Workability

In addition, because of the warm-mix technology the material remains workable at lower temperatures than conventional hot-mix asphalt (HMA) pavements, providing an extended window for compaction operations according to Ron Tardiff, manager of materials research for the asphalt producer.

"Usually, a paving crew can't roll a standard HMA mix below 260 degrees, but with warm-mix technology, the mix can be rolled at a temperature as low as 220 degrees," said Tardiff. "This gives the crew more time to compact the mix."

Furthermore, for standard thickness HMA pavements, he said, the material can be produced at the plant at lower temperatures — say 270 degrees versus 310 degrees — saving on energy costs.

The new mix was developed as a joint effort by representatives of both industry and academe. The principal architects included: Ron Tardiff, AI's manager of materials research; Paul Montenegro, a Rhode Island pavement consultant; Fred Mello, a consultant for Rub-R-Road, a distributor for BASF latex polymers; and Professor Walaa Mogawer, P.E., director of the Materials Lab, Advanced Technology & Manufacturing Center of the University of Massachusetts, Dartmouth.

Good Candidate For New Mix

The Wellesley demonstration was the result of a search by DPW Director Michael Pakstis for an alternative pavement maintenance tool. Wellesley residents had been objecting to the use of chipseals because of the loose stones and rough texture associated with this type of surface maintenance treatment. On the advice of consultant Montenegro, Pakstis visited the laboratory of Professor Mogawer and was impressed by the facility's technological developments, including its work with thin-lift, warm-mix applications. After conversations with AI personnel, Pakstis decided to have the asphalt producer manufacture and install the mix on the busy recycling center access road. It was a good candidate for the application.

"That road gets a lot of traffic, about 1,200 residents' cars a day during the week, and up to 2,400 cars on Saturdays," he said. "And there are a lot of trucks hauling in construction and demolition debris, and others — including 100-yard trailers — hauling away transfer trash, recycled C&D, and baled products like cardboard and plastic items."

All told, he said, about 10,000 tons of trash and 8,000 tons of recyclables pass over the access road each year. The road takes a beating, but is still in reasonably good condition, with a conventional HMA pavement structure that had been recently crack sealed. He wanted to preserve the road's condition, and decided to try the thin-lift maintenance mix.

Thin-Lift Mix Added To Specs

For this application, AI installed a 3/4-inch-thick course of the mix, a dense-graded material containing 30-percent RAP and a proprietary warm-mix formulation modified with 1.5-percent latex. The latex, a product manufactured by BASF, The Chemical Company, improves the pavement's resistance to oxidation, raveling and rutting, according to Rub-R-Road's Fred Mello.

The paving crew installed the mix over the 1,100-foot-long, 24-foot roadway using a CAT 1055 paver, with a mix laydown temperature at about 275 degrees Fahrenheit. While the mix utilized warm-mix technology, it was laid down at the higher temperature because it was thin, and thin mixes cool faster.

The mix remained very workable for a long time, according to Pakstis.

"There were no problems laying down and rolling it. The officials watching the operation were impressed by its workability and the fact it was so thin," said Pakstis.

"Based on what we observed during the demonstration, we're adding this thin-lift mix to our specifications for asphalt maintenance treatments," he said.