Hassan Salama

Backcalculation of Permanent Deformation Parameters Using Time Series Rut Data from In-Service Pavements

Time series of rut data from 109 in-service pavement sections in the Long-Term Pavement Performance (LTPP) Special Pavement Study-1 (SPS-1) experiment were used to predict the permanent deformation parameters for the VESYS mechanistic-empirical rut model. This was accomplished by matching the rut performance curves versus time being matched for each section with a commercially available iterative solver. To ensure uniqueness of each sections permanent deformation parameters (PDPs), the transverse surface profiles were used to match the most likely contributions by layer according to the criteria proposed in the NCHRP Report 468. On average, the contribution to the total surface rutting from the various pavement layers was as follows: 57% from the asphalt concrete layer, 27% from the base layer, and 16% from the subgrade. These results confirmed that the contribution to the total rutting from asphalt concrete and base layers is important and needs to be included in any mechanistic-empirical design procedure.

A Laboratory Investigation of the Effect of Multiple Axle and Truck Configurations on HMA Mixture Rutting

ABSTRACT Few studies have investigated pavement damage resulting from different axle and truck configurations, and they were generally limited to single and tandem axles. The unconfined compression cyclic load test with loading cycles that simulate different axle and truck configurations was used to examine their relative effect on permanent deformation of an asphalt mixture. The laboratory investigation indicates that the rutting damage due to different axle configurations is approximately proportional to the number of axles. However, the effect of rest period between axles groups within a truck configuration is significant. Calculating truck rutting damage by simply summing the vertical permanent deformation corresponding to its constituent axle groups results in erroneous predictions. The application of Miners rule results in improved truck rutting damage predictions for a wider range of truck configurations, although it does not account for the effect of rest periods within a truck configuration. Finally, unique HMA rutting damage curves, which can be used for any axle or truck configuration, were developed using strain and energy response parameters.