Asphalt overlay over rigid pavement

The asphalt overlay laid on worn rigid pavements involves (entails) the concept of correcting functionally related surface defects rather than exclusively strengthening the pavement to carry future traffic load. In all cases, asphalt overlay on rigid pavements is very much affected by reflective cracking. 

Asphalt overlay is rarely laid directly on rigid pavement without any pre-treatment or maintenance of the existing surface. Even if the surface is almost free of distresses, reflective cracking at the joints are expected to appear after a certain period. 

More often, the existing concrete surface shows (displaces) some kind of distress (settlement, joint failures, cracking, etc.). In this very common case, it is vital to first determine the causes and then repair the distress areas before applying the asphalt overlay. 

In order to control or minimise reflective cracking, one of the following techniques are employed, before laying the asphalt overlay  

Rubblisation is a technique that involves breaking the pavement into fragments varying in size from 25 mm at the surface to more than 300 mm at the bottom of the layer or below the reinforcement. 

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Asphalt Institute deflection procedure for asphalt overlay over rigid pavements... 

Reflective cracks occur in overlays laid to rehabilitate old cracked flexible pavement (Figure 15.5). Typical reflective cracks also appear in asphalt overlays on rigid pavements, flexible pavements with cement-bound bases or asphalt overlays constructed over tied shoulders or widenings. 

It covers asphalt or concrete overlays of flexible or rigid pavements as well as asphalt overlays of rigid pavements with an existing asphalt overlay and concrete overlay over a flexible pavement. In particular, it covers the following ... 

The Asphalt Institute deflection procedure for asphalt overlay design over rigid pavements is considered as a supplement to the effective thickness design method. It is used to determine if corrective actions to minimise pavement deflection, particularly at the joints, should be initiated prior to overlay construction this is only in the case when rubblisation, or crack (brake) and seat, has not been selected. 

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