Sand and crushed stone are used in almost every road, rail line and building in the UK. Before they can be used, raw material from a quarry, gravel pit or demolition site has to be crushed, washed and graded to a set specification.

The equipment that does this has changed a lot over the past twenty years. Plants now use more automation, recycle most of their water and handle recycled material as well as quarried stone.

Crushing Material Down to Size

Processing usually starts with crushing. A jaw crusher takes the largest rock and squeezes it between a fixed plate and a moving plate, producing a coarse product that can go onto a conveyor.

Cone crushers then reduce the material further by compressing it inside a rotating chamber, which suits hard, abrasive stone such as granite.

Where a well-shaped, cubical product is needed, operators often use . These throw material against breaker plates at high speed so it breaks along natural weaknesses. Shape affects performance, because flaky or elongated stone needs more cement paste in concrete and packs less tightly in a road base.

Crushed or dug material usually carries clay, silt and organic matter. Left in, these weaken concrete and stain finished surfaces, so they have to be washed out.

brings several stages together in one flow. Feed is wetted and scrubbed first, sometimes in a log washer or attrition cell where paddles rub particles against each other to strip off clay.

Slurry pumps then move the mix to hydrocyclones, which use centrifugal force to separate sand from the lighter silt. Cyclone linings are made from rubber or polyurethane to resist wear, and replacing them is one of the main running costs on site.

Finally, dewatering screens vibrate the sand on fine mesh until it is dry enough to stockpile and sell. Some older sites still use bucket wheel setups for this stage.

Screening sets the product range. Vibrating screens with two or three decks split material into separate sizes, and spray bars rinse each size as it travels along the deck.

Each product has to fall within a grading curve, which is the size distribution set out in the relevant standard. Many decks now use polyurethane panels instead of woven steel mesh, as they last longer, run more quietly and can be swapped quickly when worn.

Setting up the decks correctly on an aggregate screen is often the difference between a stockpile that meets specification and one that has to be reprocessed or sold as lower-value fill.

Recycling the Water

Washing aggregates uses large volumes of water, so most modern plants recycle it. Dirty water from the plant flows into a thickener, where a flocculant makes fine particles clump together and settle.

Clear water overflows from the top and goes back to the plant, while the thickened sludge is pumped away. Many sites now put this sludge through a filter press, which squeezes it into a solid cake that can be moved with a loading shovel. This reduces the need for large settling lagoons.

Automation and Remote Monitoring

Programmable logic controllers manage start-up and shutdown, so conveyors, pumps and screens come on and off in the right order.

Sensors track motor loads, bearing temperatures, water flow and tank levels. Engineers can view this data remotely, which helps them spot a blocked chute or a failing bearing before it causes a long stoppage.

More plants are now built from modular, skid-mounted sections that are tested before delivery and connected on site. This shortens installation and makes it easier to move equipment when a deposit is worked out.

The same approach has helped the growth of recycled aggregates. Construction and demolition waste can be crushed, screened and washed to remove plaster, wood and plastics, with some plants using upward water currents to lift out lightweight contaminants.

Fines recovery systems then capture sand that would otherwise be lost to settling ponds, so more of the material can go back into new construction.

Choosing the Right Setup

No two sites use exactly the same layout. The right combination of crushers, screens and washing stages depends on the feed material, the products the site needs to sell and the space and water available.

Most operators work with a supplier of to test samples of their material first. The results show which stages are needed and how the plant should be sized before any equipment is ordered.