Design of Thin Concrete Overlays

Two general design procedures are available for concrete overlays:

• The 1993 AASHTO Guide for Design of Pavement Structures, 4th Edition (AASHTO 1993) is applicable to the design of bonded concrete overlays.
• The current AASHTO Mechanistic-Empirical (M-E) procedure can be used for the design of bonded and unbonded concrete overlays of 4 inches (102 mm) in thickness or more and joint spacing greater than 12 ft (3.6 m), as implemented in the AASHTO Pavement ME Design software and described in the AASHTO MEPDG Manual of Practice (AASHTO 2015).
  
  

In addition, several procedures are available that specifically address the design of bonded concrete overlays of asphalt pavements:

• The BCOA-ME method and associated software, both of which were developed under FHWA Pooled Fund Study TPF 5-165 (University of Pittsburgh 2012; Vandenbossche, Dufalla, and Li 2013).
• AASHTO Pavement ME Design Version 2.3 includes an adaptation of the TPF 5-165 design procedure for thin, bonded concrete overlays of asphalt pavements with joint spacings greater than 5 ft (1.5 m).
• The American Concrete Pavement Association (ACPA) method and software, which can also be applied to bonded concrete overlays of composite (i.e., asphalt over concrete) pavements (ACPA 2006).
• The Colorado Department of Transportation (CDOT) method (Tarr, Sheehan, and Okamoto 1998).
  
  

Both the BCOA-ME method and the ACPA method are capable of designing bonded concrete overlays of existing asphalt pavements as thin as 3 inches (76 mm).

Finally, there are several procedures available for the design of unbonded concrete overlays of existing concrete pavements. Because those procedures typically produce thicker overlays, their application to thin overlay projects should be considered as a preliminary design. These procedures include:

• The Portland Cement Association (PCA) method (Tayabji and Okamoto 1985). The Minnesota Department of Transportation (MnDOT) method (MnDOT 2010), which uses an average of the Army Corps of Engineers Rigid Overlays for Airfields method (UFC 2001) and the PCA method as a recommended overlay thickness.