Evaluation of rutting performance of asphalt concrete layers using multi-depth deflectometers (MDD)
The multi-depth deflectometer (MDD) is an linear variable differential transformers (LVDT) deflection measuring device which is retrofitted into pavement layers. A maximum of six modules may be installed in a single 1.5 inch (3.8 cm) diameter hole. The modules are clamped against the sides of the hole at the required depths and the center core is attached to an anchor located approximately seven feet below the pavement surface. The MDD can measure the permanent deformation (rutting) of each layer in the pavement system. By placing multiple modules in a single hole, the vertical strains induced in pavement layers can be measured. This paper presents the evaluation of the rutting performance of asphalt concrete layers in various flexible pavement structures as well as the traffic measurement using weigh-in-motion (WIM) device installed in the field. It has been found that, at least for reasonably stiff supporting materials, most pavement rutting is confined in the asphalt concrete layer. In addition, the majorportion of the total surface permanent deformation in the flexible pavement stems from the upper part (top 3.6 inches (9.1 cm)) of the asphalt concrete layer. The permanent deformations from base, subbase, and subgrade layers were negligible if any.
Keywordsmulti-depth deflectometer (MDD) performance permanent deformation
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