Dynamic Field Assessment of Short Term Bearing Capacity for Cold Recycled Layers

The need to apply in situ cold recycling techniques for flexible pavement rehabilitation arises in response to economic, environmental and operational issues. Where a pavement is in a distressed state there is always an option to recycle the existing material and obtain benefits in terms of lower construction costs, improved durability and reduction in the negative effects that construction has on the environment. The possibility offered by foam bitumen stabilized layer to allow immediate construction of the upper layers of the pavement is often in contrast with times requested by the traditional testing techniques. In this regards the use of Light Weight Deflectometer (LWD) systems offers the possibility to evaluate short term bearing capacity of cold recycled layers for quality control/quality assurance (QC/QA) activities. Moreover, this allows a large amount of data to be recorded rapidly, thereby guaranteeing a more detailed investigation and the possibility to identify homogeneous sections and, in extreme cases, to re-work the layer before the pavement is completed. This paper reports the results of several experiences on validation of innovative field testing systems for recycled layers. Different curing time periods were taken into account, as far as the influence of the anisotropic factor induced by compaction: different tracks for each lane were tested at different curing periods, both for lime-cement stabilized subbase and foamed asphalt recycled layers, to obtain the development of the stiffness and a higher resolution of bearing capacity mapping. Comparison of results obtained with LWD immediately after compaction with Falling Weight Deflectometer (FWD) was also performed at an Italian international airport. The results obtained appear very promising for upcoming insertion of the methodologies into existing technical prescriptions and specifications.