A rational overlay design method for flexible pavements in arizona, which includes roughness, fatigue, and plastic deformation models, has been developed. The roughness model is based on an analysis of the change in roughness because of overlay and the rate of change in roughness after overlay for typical arizona roads. The fatigue model uses a shift factor to adjust existing fatigue criteria for the rate of crack development of pavements in the state. The plastic deformation model ensures that the overlay is thick enough so that expected traffic loads will not induce significant plastic deformations in underlying layers. The three design models are incorporated into a microcomputer program for cmputing the optimum overlay thickness, estimating the remaining life of an existing pavement, evaluating the life of a user-specified overlay, and performing economic analyses. Twenty in-service pavement sites were selected from arizona highways covering various geographical and environmental regions, soil types, pavement conditions, and traffic volumes. Nondestructive tests were performed on these sites using the falling weight deflectometerat several stress levels, as well as dynaflect tests. The layer elastic moduli were back calculated and adjusted for temperature. Asphalt concrete cores and undisturbed subgrade samples were collected and tested in the lab for modulus and other properties. The overlay design procedure has been verified with typical pavement sections in the state. Although the procedure in its current form applies to conditions in arizona primarily, the design concepts can be used with conditions in other states. This paper appears in transportation research record no. 1286, Design and evaluation of rigid and flexible pavements 1990.
Abstract