COLUMBIA — Along with giving taxpayers a smooth surface to drive on, the rehabilitation of Dripping Springs Road will test whether fabric makes asphalt last longer.
The Boone County Public Works Department will experiment with paving fabric on a half-mile stretch of Dripping Springs Road between Route VV and U.S. 63. The fabric, placed between the old and new layers of asphalt, costs $2 to $3 per square yard. But the theory is that it saves money by keeping water out of the road base and slowing the rate of cracking in the asphalt, county spokeswoman Porcshe Moran said.
"With the economy being the way it is now, it's very important for us to make sure we're using the money in the best way, to make sure it's really giving us the benefits that we think it gives us," Moran said.
Asphalt is generally impervious, but gaps allow water to travel down to a road's base, the undermost tier composed of dirt or rock, causing base failure.
"If the base rock gets wet, it basically ruins the road," Moran said.
Asphalt cracks at a rate of one inch per year. Derin Campbell, the county's interim director of Public Works, said that means it would take three years for cracks to appear in the top of a three-inch layer of asphalt.
"The paving industry says that the fabric is equivalent to about three-fourths of an inch of asphalt," Campbell said. "The rule of thumb is that for every inch of asphalt it takes one year for reflective cracking to make it through that inch."
Cracks in asphalt are called "reflective" because they reveal problems in the road base, Campbell said. Fabric bridges gaps at the top of an asphalt surface, covering them to distribute the weight of vehicles.
The Public Works Department began using the fabric sparingly about five years ago but has stepped up its use because it allows thinner layers of asphalt.
Still, Campbell said, not everyone is a believer. "In the past two or three years we've been having some debate whether it's worth it or not," Campbell said. "We're just trying to see for ourselves: Does it work? That's the purpose of the experiment."
Public Works has used the fabric before, and some employees feel it pays for itself, Campbell said. The county is testing the fabric to get better data on which to base the decision of whether to continue using the material.
Originally, the county planned to divide the half-mile section of Dripping Springs Road that’s being built into two parts, one with fabric underneath and one without. Instead, the county will create five 500-foot stretches of pavement that alternate between having and not having the fabric. The method was suggested by Missouri Petroleum, the St. Louis-based company that supplies the fabric.
"By doing it in strips we hope to get a truer test of the fabrics' capability," Campbell said.
An average of 1,175 vehicles travel Dripping Springs Road each day, Moran said. In recent years much of that has been construction traffic with heavy-load bearing trucks.
"The life of the asphalt's pretty much met its limit," said Justin Skouby, the construction inspector for Boone County who is overseeing the project.
Restoration of the road began the third week of August and will continue to the end of September. Moran said the project will cost $270,370. Aside from the new surface, the work also includes ditching, improvement and replacement of storm-water pipes, slope stabilization and driveway improvements.
"We're just fixing it up and hoping it will hold up under the traffic better," Campbell said.