Use of fibre-optic sensors in pavement condition monitoring

Abstract

Like any physical structure, roads require preservation, maintenance, and rehabilitation. Furthermore, the structural analysis of a road pavement is a significantly complex operation due to the variability of its subgrade characteristics and the traffic loads. Nowadays, the growing environmental concerns have directed scientific research to new fields, namely the development of techniques that increase the resilience of pavements. Therefore, the interest in developing sensors capable of precisely measuring strains and displacements has been growing, allowing the establishment of a more reliable relationship between the characteristics of the pavement and the loads to which it is subjected. Thus, the work presented here is part of the research project Rev@Construction, which aims to create a system for monitoring pavement performance in terms of strains and temperatures in real time. Real-time pavement monitoring with sensors can be considered to have a set of conditioning factors: the type of sensor (electrical or optical based); the conditions under which the sensor is incorporated in the pavement; the protection of the sensor system by using coatings and adequate fixing systems; and the influence of external conditions, such as temperature and moisture, on the quality of the results. The use of sensors based on optical fibre technology offers several advantages for real-time pavement monitoring, as observed in some recent applications, mainly with Fiber Bragg Grating (FBG) technology. This technology ensures immunity to electromagnetic fields and excellent accuracy in measurements, and given the reduced dimensions of the sensors, they may be less intrusive to the pavement. Attempts to include FBG sensors in pavement monitoring systems have shown that the central aspect that needs further investigation is how the sensors should be installed to ensure the maintenance of the sound mechanical condition of the cables and ensure an adequate transmission of stresses between the road pavement and the system itself, with enormous importance of the materials in which the sensors will be embedded. This work will present the results of a laboratory study developed to determine the best way to fix the sensors in asphalt specimens, considering the mentioned problems. Thus, a series of configurations for 4-point bending and wheel-tracking tests were executed to calibrate the system that will later be included in an actual pavement trial. The influence of external conditions on the results was assessed, as well as the configuration that ensures the most reliable stress transmission, according to the type, position, and number of sensors, as well as the effect of using protection materials (e.g., fibreglass coatings) and filling materials (e.g., polymeric resins). The most relevant results obtained and the future work will be presented at the symposium.