*Objectives*

As in-service roads advance with time, their initial mechanical properties (modulus, fatigue resistance, etc.) are highly affected. Traffic loads, environmental effects, such as temperature and moisture variations, and aging cause structural damage and surface wear. For this reason, it is important to measure the pavement response like deflection to predict pavement performance and continuously monitor the health of the pavement for condition-based maintenance decisions. Presently, deflections are mainly measured by the FWD and deflectograph, and the results are used for back-calculation of pavement layer properties. The drawback of these methods is that the measurements require to close the road to traffic, and that the road cannot be monitored continuously, measurements being made at best once a year. Using total deflection data obtained from accelerometers or geophones, as demonstrated in this paper, could facilitate the measurement of pavement response, and enable continuous monitoring of pavement condition.

To test the possibility to monitor pavement layer properties, deflection basins obtained from the geophone and accelerometer measurements, are used to back-calculate pavement layer moduli. For that purpose in this work, Section 2 presents the selection of suitable sensors for measuring the vertical displacement. Section 3 presents pavement response calculations, which are used to determine the theoretical deflection response of bituminous pavement, under heavy vehicle loading. Section 4 describes the laboratory tests done with the selected sensors and the experimental protocol. The sensor measurements are converted accurately to deflections using signal processing techniques, as described in Section 5. The sensors are also tested at the accelerated pavement facility as explained in Section 6 and using these responses, the pavement design software Alize is used for the back-calculation of pavement layer moduli, described in Section 7.
