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| It's thin,
it's fast, it's cost effective - and it's here. Hailed as "the newest pavement
innovation outside of Superpave in 15 years," a European paving process which has
recently hit U.S. shores may mean a long and happy marriage of hot mix (HMA) and
emulsified asphalt. It is being touted as a revolutionary pavement maintenance process.
First introduced in the United States in 1992, the Nova Chip process is spreading across
the country. It's a relatively simple technique: A layer of heavily-modified emulsion is
applied to the road surface, and within three seconds, a layer of HMA is screeded onto the
emulsion. In this instant, the water driven from the emulsion cools the HMA, setting both
materials and providing a bond to the underlying surface. How the process works The Nova Chip process appears as a normal paving process except the paver is much larger than we're used to seeing in America. The paver holds the emulsion in a tank and the HMA in auger chambers which run the length of the machine. It is self-contained, other than the HMA, say Nova Chip experts in the U.S.
Terry Crouthamel of Shore Slurry Seal, Coopersburg, PA, says that is because of the speed of the operation. Work can proceed two to three times the laydown rate of normal HMA, he explains. He says conventional hand tools are used, with the exception of the lute, which is not applicable to the Nova Chip process. Instead, a strong rake with a steel shank is used because the material gets very stiff very quickly.
The material stretches aggregates, say Nova Chip fans. Because less aggregate material is used, it can be beneficial any place where there is a shortage of good quality aggregates. That, in turn, conserves trucking time, fuel, and wear and tear. One stipulation: Top notch control of all aspects from aggregate quality, to asphalt quality, to equipment, and laydown are a must, according to Crouthamel. The fans are going wild Today, four machines exist in the U.S. market to support some 12 contractors using the process in more than eight states. "This market will grow even more rapidly in the coming years with the availability of an American built machine for the 1998 construction season," says Crouthamel, adding that some 700 lane miles (1100 kilometers) have been completed in the United States. Nova Chip has been evaluated over the past three years by a number of state departments of transportation and local municipalities that have placed the product over asphalt and concrete surfaces with traffic counts from 100 to 100,000 vehicles per day. "The list of satisfied customers is growing," says Crouthamel.
"With the outcome of this testing, Nova Chip is growing into a wearing surface of choice due to the many benefits provided by this innovative product," he says. Process makes its way to the eastern seaboard Jack Hill of Midland Asphalt Corp.,Tonawanda, NY, has been in the business for two years. After "exploring the possibilities" with test projects in '93 and '94, Hill joined Midland Asphalt in 1995, and together with Brad Banks, formed a separate division of the company solely to perform the Nova Chip process. Now doing highway work, the company's projects range from small villages, to residential subdivisions, to state highways, to the New York State Thruway, Hill repeats. He describes the process as "very well received" by his agency customers. "Many of our agency customers have had us back repeatedly each year," he says. "The product meets certain criteria in the pavement maintenance business, and when we can satisfy the warrants established by the contracting agency's needs, our interaction with the customers has been very positive." For instance, on the Thruway project, Midland ground shallow rebates - a notch cut at the beginning and the end of a job so the elevation of the new pavement is the same as the existing pavement - to transition the mix. The crew also ground down plastic marking stripes.
Hill emphasizes the fact that although this process is not intended to improve the structural value of the road, it has its place. "The product is not a construction item; it is a maintenance item," he says. "If an agency has catch basins and manholes, they don't want to adjust, this product doesn't require that they do that. They also don't have to adjust curbing," he adds. "It meets certain conditions for restoring acceptable friction values if the pavement is polished or bleeding up through. We've done projects on steep hills where friction is needed. But if the surface is open country, like a typical rural highway, this product may not fit the agency's needs. Other pavement treatment options certainly should at least be considered and evaluated in these rural settings," Hill explains. And the cost? "It fits midway between the cheapest and most expensive overlay products," he says. "You don't use as much aggregate as you would with a hot mix overlay. You use one-half to one-third the amount of aggregate. If good quality aggregate is hard to get, you only have to acquire one half to one third of what a hot mix project would require. Nova Chip contractors stress that the aggregate used in the process must be of high quality. Plus, the producer of the hot mix asphalt must use the aggregate which meets specifications. It must be 100 percent fractured and cubical. The more cubical the aggregate, the better. New York State has critical standards for aggregates used in asphalt mixes and those which are used for rut avoidance, heavy duty, or high friction mixes generally work well for the Nova Chip process. Hill says trap rock is a superb material for this process, even better than steel slag because it is not porous and won't break down like slag can. In Jamestown, NY, high friction aggregates are hard to come by. Hill says contractors there have to truck their aggregates from Buffalo, NY, 75 miles (120 kilometers) away. On a Nova Chip job there, Midland's crew used 60 pounds per square yard (27 kilograms per square meter) of aggregate, versus 150 pounds per square yard (70 kilograms per square meter) which Hill says would have been needed for an HMA overlay. "Sometimes your surface needs a 1.5 inch (39 mm) overlay to improve its strength, and in that case, HMA is the better choice," he says. "Nova Chip generally does not add any strength to the pavement section and when the increased strength is not driving the decision of which surfacing treatment to use, this process may very well be the choice," he adds. In Greene County, NY, which covers Catskill, the highway department supervisor is a proponent of the process and has used Nova Chip for three consecutive seasons. The area is mountainous, hilly and has many curves and steep intersections. It is the site of many accidents where people go sliding off the road in rainy and snowy weather. "Nova Chip has been a big plus for accident prevention there," says Hill.
Midland completed nearly 1 million square yards (836,125 square meters) of work in 1995 and '96. "In 1993, we did 48,000 square yards (40,130 square meters); in '94, we did 140,000 square yards (117,000 square meters). In '95 we were a driveway short of 1 million square yards (836,125 square meters), and we expect a good year in '97," says Hill. This year the company will venture into Canada to work. "This is a new concept in Canada - it's new technology everywhere. This is probably the newest pavement innovation outside of Superpave in 15 years," says Hill. Going like gangbusters in Texas The area was well lit and portable HMA plants were onsite. "The process works well at night," says Crouthamel, "because neither sun nor chemicals are necessary." "It can be drizzling outside and the process works due to the interaction of the two materials," he says. On this job, the crew worked the first couple of nights with the highway open and police on the scene. All seemed to go well enough until one car speeding through the workzone nearly hit a police officer. Local officials decided then to close the work site each night at 9 p.m. On the second job, located between Corpus Christi and Gregory, Texas at the bottom of the Causeway Bridge, Nova Chip was used over an existing road which had polished out. "The friction values in the Nova Chip process made it viable," says Peterson. "The work on this job was completed in four and a half days," he says, "because the process moves so quickly." "It can be laid so much faster," says Peterson. The train moves at a rate of 50 to 180 feet per minute (15.25 to 60 meters per minute), depending on the machine used. The American model paves the fastest of the three on the market, according to Peterson. The crew paved one lane at a time and closed down two. "One day we paved two lanes and closed one, then switched traffic onto the new pavement put down the day before," Peterson explains, adding that the work was done in two sections, with the Causeway Bridge in between. By 3 p.m., the crew shut down for traffic. "The set plan was to pave so much per day," he says. "We ended up paving what was intended. Because Nova Chip is a thin layer, there is no drop-off between lanes to contend with," he adds. "At the end of the day, we pulled the cones down, moved our barricade trucks, and opened the pavement to traffic," he repeats.
"It's very versatile in its applications," he says. "A lot of small towns like it because of its durability - it lasts a long time. States like it because of the reduced hydroplaning. Plus, it is said to be a lot quieter than normal asphalt - almost 3 decibels lower than HMA," he adds. Peterson, Crouthamel and Hill see a growing market for the Nova Chip process, but they don't see it as an opportunity to replace hot mix asphalt entirely. "HMA will always have its place," says Peterson, adding that Bay has a full HMA construction division. "Nova Chip will take away from HMA in some areas, but it will also fill a gap in some areas, too." Reprinted courtesy of Asphalt Contractor May 1997 |
As the
paver pushes the dump truck along, emulsion is applied at 0.15gallon to 0.35 gallon per
square yard (0.6 liter to 1.3 liter per square meter), at 175°F (80°C). The HMA is
placed at 280° to 315°F (140°C to 160°C ) or cooler, depending on the ambient
temperature. Nova Chip is designed around an average 0.5 inch (12.5 mm) material
depth with a maximum depth of 1.5 inches (39 mm). The material is compacted with a static
8 to 10 ton (7.25 to 9 metric ton) roller, depending on the thickness of the mat. On a hot
day, the roller sits 50 to 100 feet (1.5 to 30 meters) behind the paver; on a cooler day,
it may sit right up behind the paver. The paving equipment runs from 60 to 120 feet per
minute (18 to 36 meters per minute) at varying widths. The paver screed is hydraulically
extendible, so the process matches the existing pavement panel. Although it's a train configuration, the elements in the Nova Chip process are
much the same as in conventional HMA paving, except a larger crew is required.
Once
the process has been completed, the pavement can be opened to traffic quickly - within
about 5 minutes.
Right
now, Bay contracts out with Shore Slurry for crew members to perform the Nova Chip
process. However, Peterson says because the process is becoming so popular in Texas, Bay
will dedicate a whole crew to Nova Chip paving in the near future.