Interlayer Placement

Interlayers help mitigate reflection cracking and reduce peak pressures due to vehicle loads. Interlayers for unbonded concrete overlays are typically constructed using 1 to 2 inches (25 to 51 mm) of asphalt. Recently geosynthetic fabric interlayers have become a popular, more economic option. While the placement of asphalt interlayers is well understood, the use of geotextile interlayers is fairly recent and placement practices vary from agency to agency. Rasmussen and Garber (2009) detail general guidelines for geotextile interlayer installation, which include:

• The geotextile should lay smoothly, without obvious wrinkles and folds.
• The geotextile should be installed no more than 2 to 3 days before the placement of the concrete.
• No more than three layers of geotextile should overlap at any Field trials in Missouri and Oklahoma of fabric interlayers included wetting (but not saturating) the geotextile prior to overlay placement.
  
  

Finally, for both bonded and unbonded overlays, interlayer placement may also include “daylighting” or connecting the interlayer to conduits for adequate layer drainage where drainage capacity is a concern.