Identification of Elastic Response of Asphalt Pavements Layers Using Deflectometric Tests With Different Load Levels

It is a unusual practice in national new pavement designs and rehabilitations to consider the nonlinear elastic behavior of the materials that constitute or will constitute the pavement layers. However, the linear elastic response is a simplification of the actual pavement layers behavior, since the materials used in the structure have stiffness dependent on the stress state (granular layers and subgrade) or on the temperature and time of load application (asphalt concrete). In view of this, this paper aims to study the elastic behavior of the pavement structures of two monitored sites in the city of Santa Maria/RS, through tests with FWD equipment, applying four different levels of loading on the full extension of these two sites. In these structures, the pavements showed a tendency to stiffening with increasing load acting at initial measuring distances (near the FWD load application point), which represent the elastic compression of all layers that make up the pavement. The measuring distances farther from the load application point, referring to the elastic compression of the subgrade, indicated, in most cases, a tendency to linear behavior of the load-deflection relationship in both sites. The backcalculated resilience modulus confirmed the impressions drawn from the load-deflection relationships, indicating the nonlinear elastic behavior of the granular layers (base and sub-base) of the analyzed sites, with resilience modulus directly proportional to the increase of the confining stress. The subgrade of the experimental sites exhibited varied behavior, and could be simplified by linear elasticity, without considerable loss. The same fact happened for the asphalt concrete material used in the pavement of site 1. For site 2, the backcalculated modulus indicated asphalt concrete stiffness dependent on the vertical surface stress increment at the center of the load plate.