Long term research programme asphalt dike revetments

assignment/short description

In The Netherlands, asphalt is used as revetment for 600km of dikes, mostly sea dikes. In 2007, The Ministry of Transport, Public Works and Water Management and STOWA (Dutch acronym for the Foundation for Applied Water Research) started an extensive research programme to inspect, manage and test the safety of the older asphalt dike revetments. Approximately 70% of this 600km of asphalt is over 30 years old and must be tested extensively every five years.

Reason

The main reason for this study was the fact that the tests did not detect the bad quality of the asphalt of the “Friese Waddenzeedijk”. It is very difficult to spot the aging of asphalt during visual inspection. In addition, falling weight deflectometer measurements failed to show the weakest spots.

Cooperation

The on-going research programme is lead by the research institute Deltares. Some parts of the programme are executed by experts of this institute and other parts by KOAC-NPC and Delft University of Technology. Deltares has a broad experience in asphalt dike revetments, experience we can apply on a large scale by working together with other parties.

Method

During the safety assessment, both the strength and the load aspects were taken into consideration. We are now working on a method to determine the remaining lifetime of the asphalt. The consequences of the new testing method for older asphalt, which is now being developed, are not yet clear. Testing and inspection have to be incorporated in a systematic management method. The expertise on aging asphalt will also be incorporated in cooperation with the the local water managers, who are now developing maintenance management systems. Furthermore, we will focus on safeguarding the expertise that is needed for functional specifications. An addendum to the Technical Report “Asphalt for Dikes” will be written and is expected to be completed in 2010.

Safety and cost savings

By using the newly developed testing method, inspection method and complete management method, the safety of especially the older asphalt dike revetments can be guaranteed much better. Also, the remaining life of the asphalt can be estimated more accurately. This will lead to a considerable saving in costs of 0,5 million Eur pro kilometer.

Field inspection

Field inspection of the “Friese Waddenzeedijk (traject Westhoek-Zwarte Haan)” early 2006. Experts are worried by the condition of the damaged asphalt. A decision still had to be made whether or not the quality of the asphalt would be good enough after reparation of the weak spots. Laboratory tests showed that the mechanical quality of the asphalt’s weak spots quickly deteriorated. In 2006, the entire asphalt dike revetment was replaced.