Aggregate dredging is used for the purpose of collecting sand or gravel from onshore or offshore locations, to be used as building materials. These marine aggregates are the “raw ingredients” for materials such as concrete, and are widely used in the construction industry. With the global population rising, the demand for construction aggregates is also increasing.
What sets aggregate dredging apart from other forms of dredging, are the properties of the dredged materials. For example, aggregates are much coarser than the sands associated with capital dredging applications and have a higher value. The specific sand and gravel types used for concrete production can be found in rivers and offshore deposits dating back to the Ice Age.
Onshore sand and gravel dredging solutions
Depending on the grain size and required production capacity, the onshore dredging of aggregates is done either by a cutter suction dredger (CSD) or a grab dredger. CSDs have the advantage of a higher production rate and the ability to discharge the slurry by pipeline over long distances. The discharge distance can be extended further with the addition of booster stations.
Grab dredgers are mainly used for smaller quantities and operations at larger depths. Since these dredgers are less prone to wear, they are also better suited to coarser gravels. Both vessel types usually deposit the dredged materials directly into a processing plant for washing, sizing and dewatering. This ensures that the right grain sizes are distributed to their relevant applications.
Offshore dredging of marine aggregates
The offshore dredging of aggregates is performed by gravel dredgers, which are a special type of trailing suction hopper dredger (TSHD). Since the profitability of this type of operation widely depends on production rates, the TSHDs used for marine aggregate dredging are mainly larger vessels. In general, they range between 80 to 150 metres in length and are equipped with special installations.
Screening installations improve the quality of the dredged materials stored in the hopper and, as a result, increase the value per tonne brought back to shore. For rapid discharging, they are equipped with high capacity dry self-unloading systems. These ensure that the vessel is on its way back to the dredging site within a couple of hours.