# Wireless Strain Gauge for Monitoring Bituminous Pavements
###### Abstract  
This paper introduces the implementation of a new device for measuring deformations at the surface layers of bituminous pavement. Using wireless technology, rechargeable remotely, low cost, and easily positioned in a layer by coring after pavement construction, this sensor makes it possible to obtain measurements of the deformation when a vehicle passes by. The development of the wireless sensor is presented as well as its advantages and limitations. It was then tested in the laboratory under a hydraulic press and in situ using a full-scale test of the mobile load simulator (MLS10 type). This system allows simple measurement, gives reliable results, and could be a useful device for the structural monitoring of pavement structures. strain gauge; wireless sensor; monitoring; instrumented pavement +
Footnote †: journal: Applied  
0000-0001-4600-799X/0000-0000-0000-0000-0000-0000-0000-0000-00000-0000-0000-  
different orientations concerning the direction of traffic. In France, [PERSON] et al. [7] have set up groups of three strain gauges (vertical, longitudinal, and transverse gauges) at different levels in the bituminous layers. [PERSON] et al. [8] used seven strain gauges. The longitudinal gauges at the base of the high-modulus asphalt concrete were damaged during construction (probably by the effect of the intense compaction of this material), and their measurements could not be used. [PERSON] et al. [9] set up, on an instrumented site in the Yvelines (France), 24 deformation sensors positioned at the base of the layer of bitumen. These deformation sensors are connected to a new generation of self-powered acquisition boxes developed especially for this application. Data analysis is performed on a remote data server, using a specially developed software suite. Also in France, [PERSON] et al. [10] implanted different types of deformation measurements in an experimental pavement pit to study the behavior of the structure under traffic simulator MLS10 tests (fiber optic network, longitudinal, and transverse deformation gauges under the pavement surface). [PERSON] et al. [11] developed an instrumented pavement core also equipped with optical fiber strain gauges. This was the first technique with set-up after the construction of the asphalt concrete layer. All the previously cited studies highlight that to ensure sufficient anchoring in the layers of bituminous materials, the gauges are most often installed during construction. These must be robust enough to withstand the stresses of compaction and the high temperatures of the installation process. To do this, these are installed on resin or aluminum supports or glued on a thin strip protected by a metal tube and layers of insulating material. To avoid damages during installation or to install sensors after construction, the gauges are sometimes carried over the cores of material extracted after construction and put back into place by gluing. Whether placed before or after construction, these gauges require wiring that is often difficult to make and maintain over time. Mechanical and/or thermal breaking may occur during the first installation of the sensor, as this requires careful cable insulation. A small transverse trench must be made and then covered with asphalt. This manipulation undeniably affects the uniformity of the surface. In both cases, a connection to a frame grabber is needed. With the progress made in recent years on wave transmission technologies, wireless sensors are increasingly used in the monitoring of engineering structures, such as bridges [12], buildings, railways [13; 14], or road structures [3; 15]. Many articles deal with their use in the dynamic and vibration fields [16; 17; 18] as well as in fatigue or damage problems [19; 20], detection of the presence of humidity [21], or even vehicle detection and counting [22; 23]. [PERSON] et al. [24] conducted a state-of-the-art survey on the structural condition monitoring of bituminous pavements using smart sensor networks.