| A mechanistic design procedure for Full-Depth asphalt concrete AC pavements for highways is proposed and validated. The procedure is based on ILLI-PAVE, a stress dependent finite element computer program, coupled with appropriate transfer functions.; Two material design criteria are considered: AC flexural fatigue cracking and subgrade rutting. Fatigue cracking is controlled by limiting the tensile strain at the bottom of the AC layer. Subgrade rutting is controlled by limiting the stress-ratio at the AC-subgrade interface. Algorithms were developed relating pavement response parameters (stresses, strains, deflections) to AC thickness, AC moduli, and subgrade moduli. Two fatigue equations were calibrated with ILLI-PAVE algorithms and data from the AASHO Road Test bituminous wedge sections. Miner's hypothesis is used to develop a "closed form" solution for predicting pavement life. Weighting factors are developed and validated. Relationships between weighting factors and mean monthly air temperatures are established. From the WF-MMAT relationship a "design season condition" is determined. The design season condition is represented by the effective AC dynamic modulus and the subgrade resilient modulus corresponding to late spring or early summer.; The proposed mechanistic design procedure requires AC thicknesses less than those required by IDOT, the Asphalt Institute, and the Shell procedures. The thickness discrepancies vary depending on traffic and subgrade support. |
