According to the AASHTO guide of pavement structures

The AASHTO guide of pavement structures (AASHTO 1993) provides the most comprehensive overlay design methods for rehabilitating/strengthening flexible or rigid pavements. 

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  

In all cases, to determine the overlay thickness, the following is required functional evaluation of the existing pavement, structural evaluation of the existing pavement, determination of design subgrade resilient modulus, M, and traffic analysis (past and future traffic). 

All existing pavement design and construction details (thickness and material type of each layer, subgrade soil information, etc.) are also required. 

Despite the collected information on the existing pavement, coring and materials testing are strongly recommended to determine the resilient modulus of the subgrade, M, (or CBR), the elastic modulus of the asphalt, and the concrete modulus of rupture, S, in most cases. 

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