Concrete overlay over rigid or flexible pavement

19 CONCRETE OVERLAY OVER RIGID OR FLEXIBLE PAVEMENT 

Concrete overlay on rigid or flexible pavement is not a common practice as asphalt overlay. However, when concrete overlay is used, it is distinguished into thin overlay (50 to 100 mm) and thick overlay ( 150 mm) construction. 

Thin concrete overlay over either flexible or rigid pavement presupposes intact pavement surface and ensures good bond between the old surface and the concrete overlay. 

Thick concrete overlay is also applied over damaged surfaces and is most commonly applied over existing rigid pavements. 

In the case of thick concrete overlay, the new slab needs to be free to move horizontally to deter the appearance of reflection cracks. The above can be achieved with the provision of an interlayer, which can be a polythene membrane or an asphalt interlayer. The use of an asphalt interlayer is preferred if the underlying concrete pavement has a significant remaining integrity (Thom 2008). 

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