UC Davis Institute of Transportation Studies

The conclusions from the backcalculation analysis are as follows:

The overall stiffness values of the two pavement structures indicated by the surface moduli are similar. The variation along the section is typical of that of other projects in which the pavement structure is relatively homogenous.

The average backcalculated stiffness of the cold foam material combined with the existing asphalt concrete layer below it is 1,778 MPa, with an 80 percent confidence range of 1,210 MPa to 2,660 MPa along the section tested.

The backcalculated stiffness of the cold foam mix is roughly 25 percent lower than that of the 37.5-mm asphalt concrete layer in the other structure. In both structures the layer in question was combined with the thin existing asphalt concrete layer below it for backcalculation.

The backcalculated CTB stiffness values of the two sections are very similar. The subgrade stiffness of the section using cold foam is slightly higher than the other section.

The coefficient of variation of the resilient moduli of Layer 2 (cold foam combined with existing asphalt concrete or 37.5-mm maximum size aggregate asphalt concrete) and Layer 3 (CTB) along the sections is relatively high (>30 percent) for both structures. This is likely due in part to variations in actual thickness compared to the assumed thickness, and in the case of the CTB, may indicate more damaged areas as well as variations in thickness. However, in both cases the variability is typical of structures with relatively homogenous structures. The coefficient