Marine Dredged Aggregates Processing

The processing of marine dredged aggregates is no different in principle from the processing of land-won sand and gravel, indeed the materials are almost identical. However, the dredged aggregates have a low content of the clay and silt so that there is no need for a log-washer or scrubber barrel. The dredged aggregate does not contain soluble chloride salts but obviously the associated seawater does. Simple drain- age is generally inadequate to reduce the chloride content to a satisfactory level for concrete aggregates.

Therefore, marine dredged aggregates are usually washed with fresh water to reduce the content of the chloride ion to acceptable levels before processing by sizing and crushing as for land-won sand and gravel. This washing is commonly affected by screens support- ing polymer screen mats, to resist corrosion, and equipped with water sprays. The chloride content of the fresh water, which is usually recirculated, is closely monitored using specific ion electrodes or conductivity probes to determine the need to replace the water in the circuit. Silt and clay is removed from the wash water circuit by thickeners and blended with the products as permitted by the relevant specifications. Saline water is dis- charged to the sea, estuary or sewer although in one case it is planned to regenerate fresh water by reverse osmosis.