Fabric interlayers and Stress Absorbing Membrane Interlayers are allowed when placed between the original concrete surface and the overlay. Overlaid pavement with aggregate interlayers and open-graded AC are not included in this study. Pavements that have been overlaid more than once since they were originally constructed are not included. Sampling design factors for GPS-7A are moisture, temperature, subgrade type, traffic rate, original pavement type, overlay stiffness and overlay thickness. Sampling design factors for GPS-7B are moisture, temperature, subgrade type, traffic rate, original pavement condition level, original pavement type, and overlay thickness.
All factors have two levels except original pavement type which has three levels.
The table below shows how a section may evolve to obtain such a designation. An interlayer used to prevent bonding of the two slabs is required. The overlaid concrete pavement may rest on most base and subbase types or directly on the subgrade. Sampling design factors for this study are moisture, temperature, overlay thickness, original pavement type and overlay type. All factors have two levels except original pavement type and overlay type which have three.