Pavements need constant rehabilitation when they deteriorate with time and approach the end of their expected service lives. Overlay is the most prevalent treatment that restores its desirable condition and extends its life span of serviceability, especially for roads subjected to moderate and heavy traffic. Overlay composite design remains a major challenge due to difficulties in characterizing the complex behavior and assessing the existing condition of a combination of asphalt concrete (AC) and Portland cement concrete (PCC) layers over a soil subgrade. Deflection based design using falling weight deflectometer (FWD) deflection data offers an effective approach for overlay thickness design for composite pavements. It utilizes the deflection measurements of the pavement surface which can be used to back-calculate the subgrade and overlay composite properties and allows one to estimate the structural capacity of the existing pavement. However, the prevailing deflection based design procedure generally treats the AC and PCC as a single layer during the back-calculation and, as a result, frequently leads to less than satisfactory, usually over-conservative, design for overlay composites. The principal objective of this research is to develop improved FWD deflection based design strategies for overlay composite pavements. It is proposed that a three-layer linear elastic model be used for back-calculation of the moduli of all three layers: subgrade, PCC and AC. The structural capacity of the existing pavement is estimated using pavement surface deflections measured by FWD, the most commonly used pavement non-destructive testing (NDT) device. In the present study actual FWD deflection data for eleven construction projects are used to back-calculate the moduli of three layers. The three-layer model allows the composite pavement structure to be modeled more accurately. The elastic moduli of the asphalt concrete layer and the underlying Portland cement concrete can both be back-calculated, instead of combining them into one. The results show that the three-layer model produces higher effective thickness than the two-layer model for the same pavement structure, thereby reducing the required overlay thickness. However, there are a number of factors that can strongly influence the final overlay design thickness. The effects of computational error tolerances in back-calculation, temperature at FWD testing and variations in FWD deflection data are found significant and may cause unreliable design results and hence, two strategies to avoid excessively large or small back-calculated moduli are also explored: imposing moduli bounds and relaxing the precision convergence; they have been found very effective in mitigating the effect of large variations in deflection data. The statistical variations observed in the overlay design are also evaluated and two models are explored to improve the overall design procedure from the statistical perspective: Monte Carlo method and Point Estimation method. The effective thicknesses of existing pavement computed from reliability analysis are similar to those obtained from the proposed design method. This demonstrates the validity of the proposed design method and also the applicability of reliability based design in case the statistical parameters are available or can be obtained from engineering judgment.

The composite overlay design procedure currently used by ODOT sometimes produces very large overlay thicknesses that are deemed structurally unnecessary, especially for composite pavements already with thick asphalt overlays. This study was initiated to investigate the cause(s) and to develop a revised procedure. The current ODOT pavement overlay thickness design procedure is based on the structural deficiency approach recommended by the 1993 AASHTO Pavement Design Guide. The current procedure uses a simple, closed form procedure to back-calculate the subgrade modulus and the effective modulus of the existing pavement structure from the measured Falling Weight Deflectometer (FWD) surface deflections. The simplistic treatment of the AC and PCC layers as a combined layer in the back-calculation model was found to significantly underestimate the moduli of the existing pavement. A three-layer elastic model is adopted in lieu of the two-layer model used in the current procedure for back-calculation. The three-layer model allows the composite pavement structure to be modeled more accurately. The elastic moduli of the asphalt concrete layer and the underlying Portland cement concrete can both be back-calculated, instead of being combined as one. A revised overlay design procedure has been developed. A comparison of the revised procedure and the current procedure shows that the three-layer model produces higher effective thickness than the two-layer model for the same pavement structure. Therefore, the required overlay thickness is reduced. The revised design software has been implemented into a design software program, which also offers an optional feature that takes into consideration the temperature effects on the asphalt concrete moduli.

Design related project level pavement management - Economic evaluation of alternative pavement design strategies - Reliability / - Pavement design procedures for new construction or reconstruction : Design requirements - Highway pavement structural design - Low-volume road design / - Pavement design procedures for rehabilitation of existing pavements : Rehabilitation concepts - Guides for field data collection - Rehabilitation methods other than overlay - Rehabilitation methods with overlays / - Mechanistic-empirical design procedures.

ODOT initiated this research study to determine (1) the impact of milling off portions of the existing pavement on the structural capacity of the remaining pavement and (2) whether currently recommended HMA structural coefficients adequately reflect the structural properties of new HMA overlay materials. The study mainly focused on the impact of milling on the design of HMA overlays over existing flexible pavements and composite pavements. Volume I of the report deals with this main study focus area. During the course of the study, an additional focus area was added to the project to investigate the impact of completely milling off existing HMA layers in composite pavement systems on unbonded overlay design. Volume II of this report deals with impact of milling on unbonded overlays. Volume I describes the structural evaluation of individual flexible and composite pavement projects located at different sites throughout Ohio, as well as an analysis of the evaluation results to develop enhancements to the ODOT HMA overlay design procedure as needed. The report presents detailed descriptions of the projects evaluated, field testing procedures employed, procedures adopted for analyzing field testing data and other data collected, structural evaluation results, analysis of results, and recommendations for improvements of the current ODOT overlay design procedure. Volume II presents descriptions of the data collected, data analysis, observations, and recommendations for improvements of the current ODOT overlay design procedure.

Changing economic conditions have led to a need for more objective means of prioritizing pavement resurfacing needs and for determining the required thickness of resurfacings. Both of these issues have been addressed in the study for which this document constitutes the final report. Earlier reports on the study were directed at the development of a pavement maintenance rating system and a tentative method for designing the thickness of overlays. The present report is divided into two parts. The first deals with field trials and verification of the pavement rating system and the second with further development of thickness design procedures. Among the major findings of the study are : 1. An objective rating system can be used to provide a common basis of comparison of pavements between various raters. 2. Methods for designing the thickness of overlays based on the volume of traffic and the existing pavement structure, or on a combination of the two, appear to be practical. Material developed in the study is being used in an inventory of Virginia interstate pavements.

Experimental composite pavements were constructed at MnROAD in Minnesota and the University of California Pavement Research Center at Davis, where the pavements were instrumented and monitored under climate and heavy traffic loadings. A composite pavement consisting of HMA over jointed plain concrete also was constructed in the field by the Illinois Tollway north of Chicago. At the Tollway, extensive field surveys were performed on 64 sections of the two types of composite pavements. This project also evaluated, improved, and further validated applicable structural, climatic, material, and performance prediction models, and design algorithms that are included in the AASHTO MEPDG and DARWin-ME, CalME, NCHRP 1-41 reflection cracking, NCHRP 9-30A rutting, and the Lattice bonding model. The current DARWin-ME overlay design procedure for HMA/PCC and a special R21 version of the Mechanistic-Empirical Pavement Design Guide (MEPDG [v.

Masters Theses in the Pure and Applied Sciences was first conceived, published, and disseminated by the Center for Information and Numerical Data Analysis and Synthesis (CINDAS)* at Purdue University in 1957, starting its coverage of theses with the academic year 1955. Beginning with Volume 13, the printing and dis semination phases of the activity were transferred to University Microfilms/Xerox of Ann Arbor, Michigan, with the thought that such an arrangement would be more beneficial to the academic and general scientific and technical community. After five years of this jOint undertaking we had concluded that it was in the interest of all concerned if the printing and distribution of the volumes were handled by an international publishing house to assure improved service and broader dissemination. Hence, starting with Volume 18, Masters Theses in the Pure and Applied Sciences has been disseminated on a worldwide basis by Plenum Publishing Corporation of New York, and in the same year the coverage was broadened to include Canadian universities. All back issues can also be ordered from Plenum. We have reported in Volume 40 (thesis year 1995) a total of 10,746 thesis titles from 19 Canadian and 144 United States universities. We are sure that this broader base for these titles reported will greatly enhance the value of this impor tant annual reference work. While Volume 40 reports theses submitted in 1995, on occasion, certain uni versities do report theses submitted in previous years but not reported at the time.