This project focuses on collecting and verifying reliable deformation data of asphalt pavements by using Fiber Bragg Grating sensors. These sensors are already integrated in a bicycle path at the University of Antwerp (project CyPaTs at Campus Groenenborger). FBG is a new technology for measuring deformations in a material, e.g. by external loading. In asphalt pavement, the service life of the lower positioned asphalt layers is directly related to these deformations, loadings and rest periods between loadings. Nowadays, this service life is monitored by Falling Weight Deflection (FWD) measurements only for primary road network and each two years. These measurements are time-consuming, expensive and the road needs to be closed for a certain time. The FBG technology could give a solution to measure these deformations continuously for a lower cost. Moreover, FBG will give more insight in the deformation under all available conditions (temperature of the road, different loadings, rest periods). In order to predict service life, an asphalt response model needs to be developed, based on a monitoring program over at least 1 year. The project will allow to determine long-term ageing and healing properties of the pavement.
In this project both technology domains will be used: FBG data will give the deformations in the structure in such a way that the parameters of a visco-elastic plastic asphalt model are optimized continuously.
The installed FBG monitoring system of CyPats will be used in this project. Data will be gathered by means of a monitoring campaign in normal conditions (climate) and forced-conditioned on site; calibrated loadings and rest periods. These data will be used for fitting the parameters of a simple response model by Young modulus. The data can be used in future work for parametric fit in more complex models, e.g. a visco-elastic (Burgers) and a visco-elastic plastic model (Huet-Sayegh). A first step will be taken in this project.
A challenge to be encountered is to distinguish the effect of ageing and healing, e.g. increase of resistance to deformation during a rest period after a loading set. In current models these are not taken into account and the expected service life has to be estimated by doing FWD tests with a lot of variance in results. Moreover, in the FBG setting, the ageing is monitored continuously. This will give insight in the ageing mechanism in time of asphalt pavements allowing to use this factor as fundamental knowledge. The ageing factor will be used in a complex response model and in a prediction model for estimated service life. Moreover in the future, with this knowledge, a new ageing method under laboratory conditions can be developed based on the measurements on site.
The project work program consists of 3 workpackages. The first workpackage focuses on the signal processing of optical FBG spectra i.e. how to determine the peak shifts in order to obtain a correct strain value. workpackage 2 focuses on the identification of the Young modulus from FBG vibration measurements using the so-called inverse modelling approach to identify the mechanical material properties of the different layers of the asphalt, starting from a simple elastic Young's modulus model. Workpackage 3 deals with the monitoring of the Young modulus in time on the asphalt pavement structure of CyPaTs bicycle path during 24 months, and relating these to more complex models.