Keywords: impact-echo, ground penetrating radar, falling weight deflectometer, flexible pavements.

This paper relates to the non-destructive testing of a pavement. An experimental pavement (APT) was designed [1] for studying the behaviour of different types of flexible pavements, monitoring their evolution over time and locating artificial defects built during the construction such as compacting defects of unbounded granular material, bond defects between bituminous layers and transverse cracks. This pavement was instrumented with various sensors that allow the measurement of: temperature and moisture in the individual layers and at their interfaces.

The diagnosis tools presented here are based on the mechanical waves, impact echo (IE) and falling weigh deflectometer (FWD) and electromagnetic wave (GPR) propagation and were tested on the experimental pavement:

• The FWD is a nondestructive testing device usually used for the evaluation of the structural state of road pavements. Deflections measured using nine sensors make it possible to estimate the modulus of each layer with the help of the basin of defection. In this paper, FWD is mainly used for the localization of the defect by analyzing the measured dynamic signals [2]. The measurement results show the influence of temperature and the possibility of estimating the presence of defects.
• The impact-echo method is often used to determine the positions of intermediate and large defects within concrete structures [3]. For this method, the challenges raised are more heavily concentrated in the roads sector. Regarding the technique itself, the difficulties involved relate to the use of bituminous materials, whose properties evolve as environmental conditions change (i.e. loading temperature and frequency). Our objectives are to investigate the impact response of asphalt concrete and to study the feasibility of using the impact-echo method to detect the occurrence of the pavement structure delamination. The results show that: higher temperatures (above 20°C) significantly affect the impact response; experimental results are in good agreement with the expected theoretical response and that the method could successfully locate delaminations within a layered asphalt concrete structure.
• The radar technique allows the measurement under continuous conditions the thickness of the pavement layer which is an important parameter in the monitoring of roads, and especially in FWD analysis [4]. In addition, amplitude analysis was used to investigate the potential of the GPR technique to locate defects such as compacting defects of unbounded granular material and bond defects between bituminous layers.

These methods can be finally coupled to better estimate the state of damage of the pavement.

1

A. El Ayadi, A. Phelipot-Mardelé, B. Picoux, A. Millien, C. Petit, "Implementation of an experimental pavement for the study of nondestructive testing techniques", Proc conf Non-Destructive Testing in Civil Engineering 2009, Nantes, France, Paper 191, 2009.

2

A. El Ayadi, "Apport de l'analyse dynamique pour le diagnostic de chaussées", PhD. Thesis (in French), Université de Limoges, 2010.

3

M. Sansalone, N.J. Carino, "Impact-Echo: A Method for Flaw Detection in Concrete Using Transient Stress Waves", NBSIR 86-3452, National Bureau of Standards, Sept 1986.

4

S. Lahouar, I.L. Al-Qadi, "Automatic detection of multiple pavement layers from GPR data", NDT&E International, 41, 69-81, 2008. doi:10.1016/j.ndteint.2007.09.001

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