Professional sealing of drill core extraction points
Which process and which backfill materials are suitable for permanently and durably sealing drill core extraction points?
BASt has awarded an external research project to the Bergische Universität Wuppertal for the professional sealing of drill core extraction points. As part of the research project, a wide variety of mix variants were initially investigated and evaluated in the laboratory as backfill material for drill core removal points. The evaluations (of the results of the various tests) led to the selection of two mix variants, which were used on duraBASt as backfill material. The loading section with the filled core extraction points was loaded with the Mobile Load Simulator MLS30.
The loading program provides overrun loading with a Super-Single standard truck tyre and a wheel load of 50 kN. The arrangement of the drill core removal points was based on a specially developed scheme in order to map different load situations. The centrally arranged drill cores are driven over the entire surface (two positions per mix variant), the shifted drill cores only halfway (three positions per mix variant). In addition, this scheme enables measurements to be carried out during the test in order to examine the backfilled extraction point in detail.
The investigations are intended to provide information on which methods and which backfill materials are suitable for permanently and durably closing off drill core extraction points.
The load area was loaded with the MLS30 for two months (corresponding to 1.6 million rollovers). The researcher team examined the load field and in particular the filled cores at regular intervals.
After around seven weeks of loading one million loading cycles were performed. During this time, the load was interrupted at pre-defined intervals in order to perform various measurements for documentation purposes. The Accelerated Pavement Tests (APT) run until mid-August 2018 and was completed after 1.6 million rollovers. The project will be finished end of 2018.
In summary, a positive conclusion can be drawn from the load tests with the MLS30 on the duraBASt. The closures of both variants have survived the high stresses of 1.6 million overrolling operations in nine weeks at high air temperatures. There were no breakouts or total failure of the surface layer replacement materials. In the rolling lane, both the hot mix (HMG) and the cold mix (KMG) performed well. Settlement took place at approximately the same level as the surrounding original structure. Only the tread marks of the super single tyre on the surface of the closure variant made of HMG have a negative impact, but can be explained by the true-to-track load under extreme boundary conditions. At the edge of the rolling track, HMG delivers better results than CMM. In the overrolled area, the height of both closure variants is also equal to that of the surrounding original construction. Outside the loaded area, strong compressions are observed, especially in the CMM closure variant.