International Technology Scanning Program
Federal Highway Administration
May 2009
Pavement engineering is traditionally a conservative field, but successful pavement engineers will constantly seek out proven innovative concepts with potential to improve pavement performance while reducing costs. Many pavement structures in the United States consist of more than one cementitious layer that requires separation. This could be a new concrete pavement (jointed or continuously reinforced) atop a cementitious base or, becoming increasingly popular, an unbonded concrete overlay.
In both cases, an interlayer is often required for separation. While hot-mix asphalt is commonly used for this purpose, associated constructability, cost, and performance issues need to be recognized.
The German highway community has more than 25 years of experience using an alternative interlayer made of a nonwoven geotextile. With proper selection and placement, these interlayers have resulted in excellent performance in separating new concrete pavement layers from the cementitious bases commonplace on the German motorway system. While this application also exists in the United States, the possibility of using the nonwoven geotextile as a separation interlayer in an unbonded concrete overlay system has also generated significant interest because of the potential cost savings involved.
This report documents the German experience and gleans better practices for using nonwoven geotextile interlayers between cementitious layers in the United States. The report covers field trials in Missouri and Oklahoma along with other information so that pavement engineers can make an informed decision on the viability of this innovative but proven alternative.
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