The build-up of sediments in waterways constitutes a serious problem for navigation. In EU, dredged sludge is considered as a waste and is usually landfilled. However, river sediments could be a source of raw materials for... [ view full abstract ]
The build-up of sediments in waterways constitutes a serious problem for navigation. In EU, dredged sludge is considered as a waste and is usually landfilled. However, river sediments could be a source of raw materials for construction if the right pretreatment is applied.
In order to produce substitutes for building materials, the selection of the mineral pretreatment process first implies sediments characterisation in terms of particle size distribution, viscosity, chemical composition, mineralogy, organic matter content, micro-pollutants content (inorganic and/or organic) and distribution across particle size, leaching behaviour ,… These data are needed to design the appropriate process and to size the equipment.
The use of river sediments as a substitute for sand in a concrete formula will be demonstrated in the INTERREG project VALSE. This project regroups Walloon, Flemish and French partners who target to build a cycle track using sediments-bearing concrete. The pretreatment of the dredged sludge will consist in the partial dehydration and the deagglomeration of the sediments before adding into the concrete formula.
However, in many cases, a more complex mineral processing pretreatment is needed. Anthropogenic materials (plastic bottles, metal cans...) must be removed from the coarser fraction of river sediments by using trommels and vibrating screens. The sand, silt and clay fractions of the sediments may need to be separated then, using wet mineral processing techniques, prior to be used as raw materials for construction. Coarse sand (size from 2 mm to 250 µm) can be separated using a curved grid and fine sand (from 250 to 63 µm) can be separated using either a screw classifier or a bench of hydrocyclones. Then silt can be separated from clay using finer hydrocyclones which cut the material at 15 µm.
After separations, clay and silt are recovered in water suspensions which contain most of the pollutants, especially the heavy metals. Flotation techniques can be applied to remove the pollutants. At the end of the process, the solids are flocculated and filtered.
In many building applications, by means of a pretreatment, larger fractions of added sediments are made possible. For instance, the sand fraction can effectively be recycled into concrete, the silt fraction can be used in embankment or landscape butte, the clay fraction either in bricks or expanded-clay production.
This approach would contribute to circular economy objectives by reducing as far as possible the volume of sediments to be landfilled, and by reducing the demand of primary minerals.
Interaction and chemical compatibility with other materials and structures , Processing possibilities and logistics , Other (please speficy on the next page)
