Advanced Mechanics in Pavements : Applications to Damage and Improved Maintenance – MACADAM

The aim of this MACADAM research project is to develop a software dedicated to pavement surface layer design. The resulting tool will enable engineers to mitigate pavement surface damage due primarily to traffic loading. In France, a tremendous budget is allocated to pavement maintenance, upwards of 10 billion euros for urban areas alone. The extent of the underlying economic and environmental impacts, plus the lack of a rational method for designing such a maintenance system, has made this issue a key societal challenge. The first step to bringing tyre-pavement contact modelling in line with actual field measurements makes use of a tribological approach; this objective can be quickly achieved by means of a joint research laboratory effort (involving LaMCoS for contact mechanics and GEMH for pavement mechanics and engineering). Three main work packages can be defined: 1) tyre-pavement modelling (Work Package 1, WP1); Accelerated Pavement Testing (APT) validation (WP2); and design and production of a traffic simulator (WP3).
Tyre-pavement contact modelling, including thermo-visco-elasto-plastic behaviour in the pavement surface layer, will lead to the software "SAMRoad", which simulates actual tyre-pavement contact in order to derive stress and strain fields in the first layer. Several test identifications, relying on both monotonic and cyclic loading, will be necessary for APT material characterisation. Pavement modelling with SAMRoad will yield the surface layer rut depth. The main advantage of a semi-analytical model is to run a simulation in little time compared to the 3D finite element model, which necessitates lengthy computations. SAMRoad will incorporate tangential forces, thus making it possible to consider braking, acceleration and turning configurations.
The experimental Work Package will entail an APT assessment of the SAMRoad model. The current construction of a pavement pit 3 m by 8 m by 2 m deep inside the new research facility will serve to test a pavement 1.90 m wide by 8.0 m long. The FABAC traffic simulator will be run under both rutting and fatigue cracking conditions. The APT results will then be compared with SAMRoad model output. This WP will be limited to a rutting/cracking assessment of SAMRoad in the case of traffic without any tangential loading.
Work Package 3 will address the tangential loading for a singular pavement area (e.g. slope, turn, rest area). For this WP, we will be required to study and build a specific simulator once the MACADAM project has been launched. This initial simulator will be designed at the lowest cost, hence a second-hand truck axle will be used. The edge of the pavement pit will be built to accommodate the simulator frame anchor so as to apply horizontal and vertical loads on the truck axle. The axle will be guided by a large central beam to enable round trip loadings on a 4-meter track.
Upon completion of the project, SAMRoad will be capable of designing surface layers according to the lifetime calculation with rutting and/or fatigue cracking criteria. The MACADAM simulator will be capable of simulating damage for a single pavement area (e.g. turn, braking, slope). Pavements will be the first case studied and the focus of a demonstrator for 30,000 roundabouts across France. A backup solution is possible, as the MACADAM simulator can be replaced by several APT with FABAC, to obtain a comprehensive rutting validation.