New Constructions

This section illustrates how to design a flexible pavement with a preliminary trial hot mix asphalt (HMA) thickness for the given subgrade type and TI. Table 1 lists the starting thicknesses for each subgrade type and a selection of TIs. Note that the table look up and interpolation or extrapolation (when necessary) has been programed into CalME for new pavements with HMA/AB/SG structure.

Table 1: Starting Point for Design of HMA Thicknesses (ft) with Minimum AB Thickness for

Different TIs and Subgrade Types (Passing 95% Reliability)

This table was developed by finding the minimum HMA thickness in CalME required for a given TI and subgrade type. The actual design should be determined by additional CalME runs for the desired reliability. The structure of the pavement consisted of a subgrade, the minimum specified aggregate base thickness for the subgrade type, and the minimum thickness of HMA required to satisfy the design. The HMA mix used depends on the climate zone and will meet the requirement for binder PG grade listed in Table 632.1 of the HDM. The AB used was the 2020 Standard AB Class 2. The other inputs used to generate the starting thicknesses are listed below in Table 2.

Table 2: Design Parameters

These starting point designs can be further refined by increasing the AB layer above the minimum and then adjusting the HMA layer thickness. It is recommended that the user try other structure types, for example replacing a portion of the HMA with RHMA-G or polymer modified mix following Caltrans standard practices. These changes may reduce the overall AC thickness required.