Processing at the wharf

When the hold is full, the vessel returns to port where the cargo is discharged into a processing plant. This is similar to the screening plant at an onshore sand and gravel pit. The aggregate is washed to separate out the various sand and gravel fractions. Any deleterious materials such as wood and metal, and large pieces of rock are removed. The aggregate is screened into different size fractions which are then selectively remixed in the correct proportions required for specific aggregate products. In some cases, value added products such as ready-mixed concrete are also produced at the wharf. The processis illustrated well on the BMAPA website.

Distributing products

The products are then distributed from the wharf to customers normally by lorry within a fairly limited distance from the wharf. A few sites distribute products by rail over longer distances. Some distribute part of the material by barges (e.g. recently from Thames wharves to London Docklands and the Olympics site). Since marine wharfs are usually located within cities where the demand for aggregates is high, most are used in the near vicinity thus reducing fuel use and consequent carbon emissions.