Pavement Rehabilitation

Tack Coats

When overlaying, a tack layer might as well be put on an existing asphalt to guarantee sufficient holding of the overlay to the existing asphalt surface. True tack cover requisition might be basic to lifelong asphalt exhibition.

Levelling

The existing asphalt ought to be made as smooth would be prudent before being overlaid. It is demanding to make up rise divergences or smooth out trenches by differing overlay thickness. For adaptable overlays, HMA will almost always differentially conservative; a dependable guideline is that ordinary blends will minimized pretty nearly 6 mm for each 25 mm (0.25 crawls for every 1 crawl) of uncompacted thickness (TRB, 2000). Along these lines, before connecting the last surface course the existing asphalt is commonly leveled by one or both of the emulating techniques:

Applying a leveling course (HMA pavements). The first lift applied to the existing pavement is used to fill in ruts and make up elevation differences. The top of this lift, which is relatively smooth, is used as the base for the wearing course.
Milling (HMA pavements). A top layer is milled off the existing pavement to provide a relatively smooth surface on which to pave. Milling is also commonly used to remove a distressed surface layer from an existing pavement.
Diamond Grinding (PCC pavements). A thin top layer can be milled off of an existing pavement to smooth out relatively small surface distortions prior to flexible or rigid overlay.

Leveling Course - HMA Pavements

Leveling courses (or prelevel) are initial lifts placed directly on to the existing pavement to fill low spots in the pavement (Figure 2). Typically, pavers use an automatic screed control, which keeps the screed tow point constant regardless of the tractor unit vertical position. This allows the paver to drive over a rough, uneven pavement yet place a relatively smooth lift with extra HMA making up for low spots in the existing pavement.

Although leveling courses can help produce a smoother pavement, they suffer from discussed differential compaction and therefore may not entirely solve the smoothness problem.Leveling course lifts need to be as thick as the deepest low spot but not so thick that they are difficult to compact. Because it is not the finalwearing course, leveling course elevation and grade are sometimes not tightly specified or controlled. However, contractors and inspectors alike should pay close attention to leveling course thickness because an excessively thick leveling course can lead to large overruns in HMA and thus large overruns in project budget.