V-18 19 th INTERNATIONAL SCIENTIFIC CONFERENCE “TRANSPORT 2009” ON THE BACKCALCULATION OF FLEXIBLE ROAD PAVEMENT MATERIAL PROPERTIES AND NEW METHODS Mehmet Saltan, Mustafa Karaşahin, Serdal Terzi msaltan@mmf.sdu.edu.tr sterzi@tef.sdu.edu.tr Faculty of Engineering-Architecture, Suleyman Demirel University, Isparta 32260, Faculty of Technical Education, Suleyman Demirel University, Isparta 32260 TURKEY Abstract. The determination of pavement layer structural efficiency is an important issue in determining the performance of existing road pavements and in performing pavement design and rehabilitation processes. In order to apply the most appropriate rehabilitation and management decisions, the most efficient method for determining the structural capacity of pavements should be utilized. As the theoretical approaches such as linear elastic analysis and finite element method used to determine the stress–strain relationships in pavement layers calculate the deflections for given mechanical properties, it is necessary to consider an inversion algorithm as a backcalculation tool. Over the years, several methodologies involving static, dynamic, and adaptive processes have been used for obtaining in situ pavement layer mechanical properties thorough Nondestructive Testing (NDT) measurements. This paper summarizes the basic backcalculation methods and new trends. Keywords: Flexible pavement; Backcalculation; Nondestructive Testing. 1. INTRODUCTION In recent years, highway and transportation agencies have an increased responsibility for the maintenance and rehabilitation planning of flexible pavements. Knowledge of the structural condition of the pavement is essential in order to assess the need for rehabilitation and the nature of the required treatment which may be a strengthening overlay, partial and/or complete reconstruction. Efficient and economical methods are required for determining the structural capacity of existing flexible pavements. Since highway infrastructure deteriorates, reconstruction and rehabilitation of the vast road networks have become increasingly important. Nowadays, a large proportion of highway funds are being used for maintenance, rehabilitation and reconstruction of pavements. The structural capacity of the existing pavement system needs to be evaluated as part of the rehabilitation design process. Considerable savings in rehabilitation cost can be made by predicting accurately the strength of the existing pavement system. Nondestructive Testing (NDT) and backcalculating pavement layer moduli are well-accepted procedures for the evaluation of the structural capacity of pavements (Chou, 1993). “Backcalculation” is the accepted term used to identify a process whereby the material properties such as elastic moduli, Poisson’s ratio, and layer thickness of individual pavement layers are estimated based on measured surface deflections (Gopalakrishnan, 2009). NDT enables the use of a mechanistic approach for pavement design and rehabilitation because in-situ material properties can be backcalculated from the measured field data through appropriate analysis techniques (Uzan et al., 1989). In order to backcalculate reliable moduli, it is essential to accomplish several deflection tests Mechanics ISSN 1312-3823 Transport issue 3, 2009 Communications article № 0405 Academic journal http://www.mtc-aj.com