Surface Prep for Overlays

Surface Prep for OverlaysOverlays, whether they are structural or non-structural, make up a large portion of paving done on roads today. The degree of surface preparation for an overlay is dependent on the condition and type of the existing pavement. Generally, the existing pavement should be structurally sound, level, clean and capable of bonding to the overlay. To meet these prerequisites, the existing pavement is usually repaired, leveled by milling, preleveling or both. It is then cleaned and coated with a binding agent.

Generally, pavement overlays are used to restore surface characteristics like smoothness, friction and aesthetics or to add structural support to an existing pavement. However, even a structural overlay needs to be placed on a structurally sound base. If an existing pavement is cracked or provides inadequate structural support, these defects can often reflect through even the best-constructed overlay. Premature pavement failure in the form of deformations and cracks can result. To maximize an overlay’s useful life, failed sections of the existing pavement should be patched or replaced, and existing pavement cracks should be filled.

At most, overlays are designed to add only some structural support. The remaining structural support must reside in the existing pavement. Therefore, small areas of localized structural failure in the existing pavement should be repaired or replaced so this structural support is restored. Existing pavement failure can be caused by inadequate support or poor drainage. In these cases, the existing pavement over the failed area should be removed and the subgrade should be prepared as it would be for a new pavement.

Existing pavement crack repair methods depend upon the type and severity of cracks. Badly cracked pavement sections, especially those with pattern cracking or severe slab cracks, must be patched or replaced due to the fact that these distresses are often symptoms of more extensive pavement or structural failure. Existing cracks other than those caused by structural failure should be cleaned out by being blown out with pressurized air or swept. The cracks should then be filled with a crack-sealing material when the cracks are clean and dry.

Be warned: cracks less than about 10 mm in width may be too narrow for crack-sealing material to enter. The narrow cracks should then be widened with a mechanical router to accommodate the crack-sealing material. If the existing pavement has an excessive amount of fine cracks but is still structurally adequate, applying a general bituminous surface treatment (BST) or slurry seal instead of filling each individual crack may be the more economical way to go.

All in all, pavement repair should be extensive enough to provide an existing pavement with adequate structural support. Pavement management techniques should provide for overlays before an existing pavement has lost most or all of its structural support capability.