Formulation of artificial aggregates from dredged harbour sediments for coastline stabilization

Coastal erosion is a common phenomenon along the shores of the member states of the European Union. In 2004, approximately 20,000 km of coastlines, accounting for 20% of the whole of the EU coastline, were considered particularly affected by this phenomenon. Coastal erosion and shoreline retreat already affect a significant proportion of the French coast, the beaches in the north of France being no exception, and will probably increase during the 21st Century because of climate change. Because erosion is often accentuated by sedimentary deficits, artificial beach replenishment often represents an appropriate engineering solution for coastline stabilization. Meanwhile, large quantities of sediments are dredged every year from ports, with approximately 25 to 45 million tons of sediments (dry matter) per year being dredged for the maintenance of harbours. The purpose of the study presented in this article is to report on the potential use of artificial aggregates formulated with harbour sediments in order to recharge beaches and/or nearshore environments. The manufacture of the aggregates consisted of several stages, beginning with the characterization and the preparation of the sediment before the fabrication of aggregates by extrusion, associating the sediments with a specific hydraulic binder. Various parameters, such as water content of the mixing sediment, the cement content and the shape of the aggregates, were taken into account, in order to ensure the criteria regarding the strength of these aggregates are entirely fulfilled. The first simulations in a wave flume are encouraging and reveal the possibilities for use of the aggregates in coastal engineering.