Keywords: pavement, interface flaw, crack, dynamic, falling weight deflectometer.

Vectors of economy and culture, roads have a vital role in all industrialized countries. Road networks evolved at the dawn of the twentieth century and continued to extend with the fast growth of automobile traffic and technology, and the equipment and materials used in their construction. In France, the so-called flexible pavements are the most common structures. They constitute more than half of the motorways and national roads and almost all the secondary road network. These structures are constantly subjected to various types of mechanical and thermal loading which lead to damage. Without maintenance, this damage may in the long term threaten the integrity of the structure resulting in a significant maintenance cost. In this context, non-destructive testing provides an ideal means to test the pavement structure in a rapid and convenient manner [1].

This paper explores the possibility of extending the use of a non-destructive testing device named the falling weight deflectometer (FWD) to the detection of defects in road structures [2,3]. The FWD test consists of reproducing the dynamic impulse load similar in magnitude and duration to a moving truck, and evaluating the pavement's response by measuring the surface deflection (deflection basin) using nine sensors [4]. It is usually used to evaluate the structural condition of a pavement by back-calculating the pavement material properties from the measured dynamic response of the pavement surface and is used in this paper in an original way to locate interface flaws, absence of the tack coat and transverse cracks.

The modelling part is based on a three-dimensional finite element model that shows the ability to obtain an accurate response prediction and enables the verification of the effectiveness of FWD tests associated with back-calculation programs to evaluate the pavement material properties. Moreover, instead of the maximum deflection the numerical simulation allows the exploitation of the full deflection time histories. Beside its role in evaluating the structural condition of a pavement, the possibility of finding other potential uses of the FWD has been explored. The first and second derivatives of the deflection basin and a spectral technique based on the difference between healthy and damaged pavement responses in the frequency domain have proven effective as criteria for identifying and locating defects of damaged pavements. A means of application in field work which will significantly improve the usefulness of the FWD and provide a most precise diagnosis of the pavement state still remains.

1

CERTU, "Matériels et méthodes d'auscultation des chaussées urbaines", in French, report, Engineering Department of Civil Aviation, 2005.

2

S. Chea, "Contribution à l'auscultation structurelle des chausses mixtes: Détection de défauts d'interface à l'aide de la déflexion", Thèse de doctorat, INSA de Rennes, 2007.

3

M.J. Sansalone, W.B. Street, "IMPACT-ECHO, Nondestructive Evaluation of Concrete Masonry", Bullbier press, 1977.

4

A. El Ayadi, "Apport de l'analyse dynamique pour le diagnostic de chaussées", PhD thesis, In French, University of Limoges, 2010.

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