FLEXIBLE PAVEMENT OVERLAY DESIGN PROCEDURES--VOLUME 2. USER MANUAL

This report is a user's manual for the design of flexible overlays of flexible pavements. Detailed instructions are given on obtaining the necessary input data and entering this data into the completely computerized design package. The design procedure is based on fatigue cracking criterion and nondestructive evaluation of the existing pavement. Input is required from the following areas: 1) dynamic deflection testing, 2) limited condition surveys, 3) projected future traffic in terms of equivalent 18 Kip (80kN) axle loads, and 4) material characterization. The condition of the existing pavement is determined from dynamic deflection measurements using 3-4 layer elastic layer theory to characterize the existing pavement. The condition survey is limited to determination of the presence or absence of class 2 and 3 cracking, and the extent of this cracking, when present. Materials characterization requires the determination of layer thicknesses, estimation of layer Poisson's ratios, estimation of the stress dependency relationship of base and subgrade moduli, and estimation of the asphalt modulus-temperature relationship. Guidelines are presented for the solution of these parameters when laboratory testing is not available. In contrast with most other design methods, pavement evaluation and overlay thickness determination are done at each location where dynamic deflection measurements were made. This allows the pavement engineer to consider alternate repair strategies, such as improvements in drainage, recycling or reconstruction, in areas requiring thick overlays, and may consequently result in more economical solutions. This report is Volume 2 of a two-part series. The first is: Flexible Pavement Overlay Design Procedures-Evaluation and Modification of the Design Method, Volume 1 (FHWA-RD-81/032). (FHWA)