Improving Pavement in America
Pavement engineers are constantly seeking out proven innovative concepts with the potential to improve pavement performance while reducing costs. An example of such a concept is the use of a nonwoven geotextile as an alternative to hot-mix asphalt (HMA) between cementitious layers. Proven by German engineers to be effective, this concept is not common or widespread in the U.S. However, as part of a recent effort to demonstrate the use of nonwoven geotextile interlayers as concrete pavement interlayers, initial recommendations for materials specifications and better construction practices were developed. Implementation of a nonwoven geotextile interlayer was successful in two recent field trials in Missouri and Oklahoma. The material proved to be cost effective, required minimal training and equipment during construction, and could be placed rapidly. As a result, nonwoven geotextiles have the potential to be a viable alternative to more conventional materials as an interlayer in the U.S. pavements.
- Separation – keeps discontinuities (cracks or joints) in the underlying cementitious layer from reflecting to the surface layer. This requires a material that possesses a degree of compliance that can accommodate the anticipated movements in the base layer.
- Drainage – channels away water that infiltrates into the pavement structure at the surface. The concept is that water should drain into the interlayer and then along the (cross-) sloped surface to the pavement edge. Because of this, German practice requires that the geotextile either terminate next to a drainage layer or be daylighted (allowing the egress of water). The drainage function also requires that the geotextile have enough permeability to allow a minimum flow rate in three dimensions.
- Bedding – reduces bearing stresses and the effects of dynamic traffic loads. This function also requires a geotextile material that has some degree of compliance, but not so much that inadequate support stiffness results.
- Cost Savings – lower cost for material and installation.
- Expedited Construction – rapid installation, with firsthand observations revealing installation rates exceeding that of paving.
- Ease of Construction – requiring a minimum of training and equipment
In Germany, nonwoven geotextile interlayers have been used in concrete pavements for more than a quarter of a century. During that time, German engineering has proven nonwoven geotextiles placed between a concrete pavement surface and a cement-treated base (CTB) reduces bonding, facilitates subsurface drainage, and minimizes bearing stresses.