Pre-Overlay Repair

For overlays of asphalt pavements, pre-overlay repair operations are controlled by the type of overlay and the condition of the pavement after milling (if performed). For bonded overlays of asphalt, milling of the existing surface is conducted to promote good bonding and minimize shear stresses at the concrete–asphalt interface. For unbonded overlays of existing asphalt, milling may be required if there is shoving or rutting in excess of 2 inches (51 mm).

Typically, unbonded overlays of asphalt require very little pre-overlay repair. For bonded overlays of existing asphalt pavements, pre-overlay repairs after milling will focus on local issues such as potholes, areas of severe alligator cracking, and/or areas that indicate poor slab support. Transverse thermal cracks can be cleaned and filled to ensure proper support for the overlay under loading (Harrington and Fick 2014).

For overlays of existing concrete pavements, the required pre-overlay repairs will depend on the type of overlay selected (which in turn is decided primarily by the level of distress). For unbonded overlays of concrete, pre-overlay repairs should focus on providing a sound underlying structure for the interlayer and overlay, although Harrington and Fick (2014) note that some agencies choose to increase overlay thickness as an alternative to pre-overlay repair. For bonded overlays of concrete, pre- overlay inspection and repair should make certain that support conditions are uniform and that any existing distresses are accounted for. Voids under the existing slab should be stabilized, and existing cracks or patches should be addressed to ensure uniform bond between the overlay and existing slab.

In addition, prior to the placement of the interlayer, improvements to the existing pavement system to improve drainage may be warranted. These activities may include cleaning of existing drains or installing a retrofitted drainage system. Drainage should not be overlooked in the process, as Hansen and Liu (2013) observed poor drainage conditions in an extensive study of concrete overlays, and they were able to confirm the presence of pumping and base erosion that led to surface distresses (faulting and top-down cracking) and overall reductions in ride quality.