The top highway and public works officials from over 40 cities and towns in eastern Massachusetts recently witnessed a demonstration of new pavement technology in Salem, the “Witch City” and one of the state's oldest communities, as part of a technical meeting of the Essex County Highway Association (ECHA).
The ECHA demonstration took place near the Congress Street Bridge at historic Pickering Wharf, not far from the Custom House where Nathaniel Hawthorne once worked as port overseer and the location he used as a setting for the beginning of The Scarlet Letter.
More than 60 officers and members of the association filed out of the Finz Restaurant following several speaker presentations to watch the demonstration in the city noted for its witchcraft trials of 1692. But the demonstration they had come to view this day focused on the future, not the past, showcasing an emerging pavement maintenance technology that turns conventional thinking on its head – the placement of a very thin layer of polymer-modified asphalt mix at lower than normal temperatures that provides a longer than usual time for compaction.
As the public works officials watched, an Aggregate Industries' (AI) paving crew under the direction of General Superintendent Mike Little sprayed an asphalt emulsion tack coat Grade RS-1 on the existing pavement, then employed a CAT 1055B paver to place the overlay, a special mix in several ways. First, it was designed to be very thin – 7/8-inch to 1-inch thick after compaction. Secondly, it was at least 50 degrees Fahrenheit cooler than a conventional hot mix asphalt (HMA), which has a standard plant production temperature running between 300 and 350 degrees. Third, it featured warm-mix asphalt technology incorporating a polymer additive. And fourth, it had a high concentration of recycled asphalt pavement (RAP), up to 30 percent by weight of total aggregate.
“We used warm-mix technology because thin lifts cool fast, and we wanted enough time for proper compaction,” said Ron Tardif, AI's materials and research manager. Superintendent Little confirmed that they got the time they needed.
“The mix was placed at about 285 degrees, and we were still rolling it at 220 degrees,” said Little, a 35-year veteran of asphalt production and paving. Compaction was obtained with a 10- to 12-ton HYPAC static steel roller, which was kept as close as possible to the paving machine.
After the demonstration, Mark Nikitas, AI's marketing and communications manager, told the ECHA group that thin-lift asphalt is used as a maintenance treatment over roads that are structurally sound but may require a facelift, display fatigue cracking or are showing signs of oxidation. Applied in time to such roads, he said, the process can extend the useful life of the pavements at least eight years.
Not suitable for the treatment, he added, are roads with sub-base failure, drainage problems, extensive cracking, or surfaces susceptible to rutting and shoving.
Helping to make thin-lift asphalt treatment successful is its incorporation of warm-mix technology that extends the temperature range of workability and hence the degree of compaction. There are a number of proprietary warm-mix processes under development or in production. First used in Europe, warm-mix technology was introduced to the U.S. in 2003 at the annual convention of the National Asphalt Pavement Association (NAPA), with the first public demonstration of warm mix taking place at the World of Asphalt in 2004. Since then, industry groups such as NAPA and federal agencies including the Federal Highway Administration have been engaged in research and have conducted demonstrations of the processes throughout the country.
The proprietary technology demonstrated to the ECHA group employs a latex polymer injected directly at the asphalt plant.
“It's an SBR latex, a styrene butadiene rubber made by BASF Corporation,” explained Fred Mello, a representative of Rub-R-Road, whose company distributes the product to HMA producers. “Essentially it's a synthetic version of natural rubber that adds strength to the mix, helps it resist raveling and rutting, and makes it more flexible in winter and stiffer in summer,” he said.
In addition to the paving demonstration, the technical meeting featured presentations by several speakers on a broad range of topics. Among these were Keyspan and National Grid power company representatives discussing the handling of downed power lines and other safety issues, Woodard & Curran spokesman David White explaining storm water regulations and challenges, and Worcester Public Works Commissioner Robert Moylan making the case for reforming environmental regulations related to the Clean Water Act permitting process.
The Salem meeting was but one of a number of ECHA meetings scheduled for 2008. Some are held to inform its members of the latest developments in highway design, construction and maintenance; to provide training; introduce new public works programs; offer updates on federal and state legislation; and present student scholarships. And some are held for purely social reasons. On June 5, for example, the association was scheduled to hold its annual clambake at Tucks Point in Manchester-by-the-Sea, MA, and on August 5 the group intends to hold its golf tournament at the Gannin Country Club in Lynn, MA. A fall meeting is planned for December 4, but the location is yet to be determined.
Founded in 1969, The Essex County Highway Association is focused on advancing highway permitting, design, construction, operation, and maintenance in the 45 Essex County communities. With an original membership of just eight, ECHA today has more than 100 members including highway officials, public works directors, engineers, and highway superintendents. In addition, the organization is supported by equipment manufacturers and distributors, consulting engineers, and pavement and other contractors. (See list of officers and directors in accompanying box.)