Development of an Overlay Design Procedure for Flexible Pavements in Indiana : Executive Summary

Abstract

A procedure for designing the thickness of asphaltic concrete overlays of flexible pavements was developed at Purdue University in response to a request from the Indiana Department of Highways (IDOH). The research included testing on 30 flexible pavement test sections. Two approaches to the problem were taken: an empirical approach which calculates the overlay thickness required to provide functional performance (ride quality and resistance to distress) over the life of the pavement, and a structural overlay method which calculates thickness required to prevent structural failure. Flexible overlay design Method 2 of the 1986 AASHTO Guide for the Design of Pavement Structures was selected for structural capacity design. Method 2 uses nondestructive testing (NDT) deflection data input to calculate overlay thickness. A negative value for overlay thickness indicates that sufficient structural capacity is present without adding an overlay. The functional performance approach used Indiana flexible pavement historical data to produce a regression equation relating overlay thickness to traffic, design life oil the overlay, pavement condition at the end of the design life, and estimated subgrade California bearing ratio. Various NDT deflection measurements, climate zone data, and pavement layer thickness variables were included in a variety of empirical analyses, but they were not significant in the analyses. Simultaneous use of the two design methods was recommended to IDOH. If values from both methods are positive, the larger value governs the design. If the structural value is negative, a thickness equal to the functional performance design may be milled and recycled back to the pavement.