Section 8: Concrete Overlays
Applying a concrete overlay on an HMA-surfaced pavement may be a viable rehabilitation strategy under certain circumstances. Where existing distress in an HMA-surfaced structure is confined to the HMA itself (mix rutting, shoving, washboarding, cracking), but otherwise the existing substructure is sound, a concrete overlay can offer a durable replacement surface. These circumstances may present themselves at controlled intersections or along open sections of highway. The process of applying a concrete overlay on an HMA-surfaced pavement is sometimes referred to as “whitetopping,” a term used by the American Concrete Pavement Association (ACPA). The ACPA further divides whitetopping into three sub-categories:
- Anchor: #WRXXRSYD
- conventional whitetopping, Anchor: #RFPARIKV
- concrete inlay, Anchor: #GLQAXALQ
- thin whitetopping.
Conventional whitetopping will use a slab with a thickness designed by the Rigid Pavement Design procedure (Chapter 8) placed on top of the existing HMA surfaced pavement. Minimum thickness for this overlay option is 7.0 in.
Concrete inlays may be placed on thicker HMA pavements that have been partially milled out. Depending on the proposed slab thickness, requirements might follow either those of conventional whitetopping or thin whitetopping.
Thin whitetopping will use slabs from 4.0 to 7.0 in. thick that are placed on an HMA surface that has been milled or otherwise prepared to enhance the bond. Refer to Chapter 8, Section 8, “Thin Concrete Pavement Overlay (Thin Whitetopping),” for the thickness design, slab size selection, and existing HMA support requirement. Concrete overlays thinner than 4.0 in. are not allowed under department guidelines. This may restrict the use of concrete overlays at certain curb and gutter intersections where vertical profile may not allow direct placement on top of the existing HMA structure, and milling to the appropriate depth may leave insufficient support.