Mar. 8, 1999 CHAMPAIGN, Ill. -- Plagued by potholes? A special composite patented by the University of Illinois -- and now commercially available -- may pave the way to smoother, longer-lasting roads.
Applied to concrete or asphalt surfaces, the material covers cracks like a huge adhesive bandage, reinforcing the surface and preventing the cracks from spreading and causing further damage.
"Seasonal and daily temperature changes are enemies of any road surface," said Barry Dempsey, a U. of I. professor of civil engineering and director of the university's Advanced Transportation Research and Engineering Laboratory. "Low temperatures cause pavement sections to contract, which creates new cracks and widens existing joints and cracks."
A common remedy is to spread a thin asphalt-concrete overlay on the damaged pavement, Dempsey said. "Because the overlay is fully bonded to the pavement, however, stresses cause the cracks to propagate up through the overlay. This 'reflection cracking' not only allows water to percolate into the pavement and weaken the base, but also contributes to rapid deterioration of the overlay."
The U. of I. material is engineered to effectively block the upward propagation of cracks, joints or potholes in existing pavement.
The composite consists of three layers: a low-stiffness geotextile as the bottom layer, a viscoelastic membrane layer as the core, and a very-high-stiffness geotextile as the upper layer. The materials work together to relieve stress at the crack and provide reinforcement to the overlay, thereby preventing the crack from propagating.
The material functions as a base isolation layer in the pavement overlay system, Dempsey said. "When thermal contraction occurs in the underlying pavement, the low-stiffness geotextile -- which is fully bonded to the pavement -- absorbs some of the horizontal movement. The sandwiched viscoelastic membrane layer allows movement between the top and bottom geotextiles, while the high-strength upper geotextile limits the stress in the overlay to which it is firmly bonded."
In 1994, after testing the composite's performance in the laboratory, Dempsey selected a field test site on a state highway near Rochelle, Ill. The composite was placed on a number of cracks and joints in the pavement, and its performance and durability were evaluated over time.
"When we developed this material, our goal was to keep cracks from spreading for three years," Dempsey said. "We have now completed five years of field testing, and the product's performance has surpassed our expectations. The material has effectively reduced the occurrence of reflective cracking by more than 75 percent."
An exclusive license to market the composite has been granted to Contech Construction Products Inc. of Middletown, Ohio.
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