Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: SUNDAY, October 8, 1995 TAG: 9510060044
SECTION: BUSINESS PAGE: F-1 EDITION: METRO
SOURCE: GREG EDWARDS STAFF WRITER
DATELINE: CHAMBLISSBURG LENGTH: Long
A county deputy even drove by to investigate.
Anyone would have been curious about the electronic gear being planted in the newly constructed roadway through open farm country. The concrete bunker dug into the embankment above the road at the edge of an alfalfa field added to the mystery.
But it was no military operation. The researchers - Virginia Tech professors and graduate students - are studying whether roads will last longer and cost less to maintain if specially designed plastic cloth and gridwork are built in underneath them.
Sponsors of the research, which will run for three years at a cost of $470,000, are the Virginia Center for Innovative Technology in Herndon; Atlantic Construction Fabrics of Richmond; the Virginia Department of Transportation; and an Amoco Corp. division in Atlanta that makes plastic cloth, "geotextiles," for use in road building and construction.
Tech laboratory studies indicated that the plastic fabrics work better than plastic grids in extending the life of paved roads, said Imad Al-Qadi, a Tech civil engineering professor who is a principal researcher on the Bedford project.
Researchers used an air piston to repeatedly apply 9,000 pounds of pressure to a 12-inch circle of pavement, a test that produces stresses similar to those inflicted by a tractor-trailer tire.
Then, to test those findings in the real world, the researchers built 450 feet of test strip on a road in Bedford County. They laid the strip in nine 50-foot-long sections, using various combinations of fabric and grids and different depths of base rock.
The site was chosen because the silty clay soils there are softer and less stiff than other soils and not as good for supporting roads.
A standard secondary highway in Virginia, a road that feeds main arterial roads, generally has six inches of base rock covered by three inches of asphalt. For the experiment, however, some sections of the test strip were designed to fail, with less base rock under the pavement, explained Tom Brandon, a Tech civil engineering professor.
Arthur Barnhart, a materials engineer with VDOT's Salem office, helped the Tech team find a suitable site for their research. Barnhart said the state is always interested in any technology that might improve roadway designs.
The main obstacle to wider use of geotextile and geogrid has been a lack of information about their long-term performance, said Ed Hopp, a research scientist with the Virginia Transportation Research Council in Charlottesville, VDOT's research arm. The Tech study could give the state more confidence in the materials' benefits, he said.
The Bedford County test strip, a stretch of Virginia 757 near its intersection with Virginia 616, was built last year when a curve was being reconstructed along a slightly new path.
The roadway was embedded with 200 electronic sensors that correlate the weight and speed of a vehicle with temperature, moisture and stresses and strains on the roadway.
Nearly 20 miles of wires feed the information from the road's sensors into a computer that transfers it by a modem each night to another computer at the Tech campus.
While the highway contractor, A.R. Coffey of Bedford, rebuilt the curve last year, the Tech team did much of the sensor installation at night under spotlights.
The researchers camped out in a farm field alongside the road as the work was under way. It rained several days during construction, and what should have taken two weeks to complete took two months, Brandon said..
Their work habits raised questions among nearby residents. One day, two curious people asked them if they were burying nuclear waste - something the government considered in Bedford County just a few years back.
On a recent sunny Saturday, Al-Qadi, Brandon and others on the research team were in Bedford County calibrating their instruments by loading a flatbed truck with concrete weights and running across the test roadway at different speeds. They measured the speed with a radar gun. The weight of a vehicle, its speed and the inflation of its tires all play a role in how much damage it will inflict on a road, Al-Qadi said.
If the field tests uphold the laboratory findings, the savings from using the plastic fabric in road construction are going to be "tremendous," Al-Qadi said. The material may almost double the normal 20-year design life of a road, he said.
|n n| The cost of building a two-lane road varies depending on the location and terrain but runs roughly $700,000 per mile, not including the cost of buying land for the right-of-way, according to VDOT. The cost of adding the geotextiles, which sell for 60 cents a square yard, is roughly $8,500; less than 2 percent of total construction costs. The fabric, however, can save as much as $35,000 in maintenance costs over the life of the pavement, Al-Qadi said.
Some of the research results so far are surprising to many people in the road building industry, Randy Thomas, engineering manager for Atlantic Construction Fabrics, said. "Everybody thought that geogrid was the only way to increase the life of pavement," he said.
Geogrid is designed to give reinforcement under the road in the way that steel bar is used to strengthen concrete. Tech researchers found in the laboratory, however, that for extending the life of a road it's more important to keep the road-base stone separate from the underlying soils. For that, geotextiles are thought to be the best solution. The textiles also help distribute the load on a road.
Thomas' Virginia-based company sells both geogrid and geotextiles. The textiles cost roughly half as much as geogrid, but Thomas said it's to the company's benefit to find the most cost-effective materials for its customers.
Rennie DiLoreto, president of the company, told the Virginia Center for Innovative Technology's newsletter that the Tech research has resulted in $2 million in additional sales for his company this year. The company has added 40 employees so far in 1995, he said.
VDOT has not been specifying geotextiles or grids in roadway designs, but Roanoke-area contractors are familiar with it.
Mike Branch, vice president of Branch Highways Inc. of Roanoke, said his company has used geofabric and geogrid for years to stabilize temporary roads at construction sites. The company also has used them in sanitary landfill liners as a drainage layer, he said.
North Carolina called for geofabric on two projects on Interstate 40 between Raleigh and Wilmington that Adams Construction Co. of Roanoke worked on and the roadway seems to be holding up well, said Jack Lanford, president. "From a contractor's perspective, I think they have a good future," he said.
Amoco, one of the Tech research sponsors, bought Phillips Petroleum Co.'s geotextile business a year and a half ago and is one of several makers of geotextiles.
Phillips touted the benefits of using fabric in paving roads in television advertisements several years ago. That fabric, however, was being laid within the asphalt and not underneath the base rock as the Tech researchers are doing.
|n n| The use of geotextiles is growing at about 5 percent a year, said Rick Valentine, an Amoco engineer. In 1992, he said, 105 million square yards were used nationwide and that figure is expected to climb to 120 million square yards this year.
Except that it's black to protect it against sunlight, the cloth looks like the fabric used in plastic feed sacks familiar to farmers. Amoco also weaves the lighter weight feed-sack fabric at its mills, Valentine said.
The soil on which a road is built has to be moderately weak for the use of the textiles to be economically practical, Valentine said. Ten percent to 15 percent of the soils in the United States are in that range, he said. If a road's base rock is mixed with those kinds of soils it can lose up to 80 percent of its strength to support the pavement and traffic, he said.
Geogrids don't prevent base rock and soil from mixing, but are useful in certain situations; roads over sandy soils such as those in Tidewater regions, for example, Valentine said. Or for reinforcement in projects such as the prefabricated wall along the flyway from Hershberger Road to the Roanoke Regional Airport, where the grids were used, Tech's Brandon said.
Brandon said the main goal of the research is a design method for geotextiles that could be used by state highway departments nationwide.
by CNB