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Tarmac invest in state-of-the-art processing technology at key East Anglian sand and gravel operation

Located on the outskirts of the Essex county town from which it takes its name, Colchester Quarry is Tarmac's largest and most important unit in the East Anglian region, with sand and gravel, ready-mixed concrete, asphalt, recycling, dry silo mortar (DSM) and landfill operations, together with a regional administration office, all occupying various parts of the site. The site has been in existence for around 35 years, although it originally comprised two discrete and separately owned quarries.

(Bellhouse and Stanway) located on either side of Warren Lane. Later, having both been acquired by Tarmac, the two sites were combined and their operations linked by field conveyor via a tunnel under the road.

Until recently extraction operations were centered on the former Stanway site, with material being conveyed to Bellhouse for processing and distribution. However, with diminishing useable material at Stanway and significant reserves still remaining beneath the 20-year-old Bellhouse processing plant, some two and a half years ago Tarmac took the decision to, in effect, reverse the operation.

In order to release the sterilized deposit at Bellhouse, the company opted to construct a brand new state-of-the-art sand and gravel plant on previously worked land at Stanway, shut down and dismantle the Bellhouse processing facility and then reverse the existing field conveyor to supply the new plant, thereby adding to (and eventually supplanting) the current supply of raw feed from the Stanway site.All of these changes were permissible under the site's existing planning consent.

Based on previously successful projects one of the two main contracts for the new processing plant was awarded to DUO Manufacturing. The brief from Tarmac was to design, build, install and commission a new 360 tonnes/hr washing plant capable of producing two sizes of gravel (20mm and 10mm) and two grades of sand to precise specifications, the latter comprising up to 85% of the plant's total output.

The equipment supplied and installed included two Metso Ellivar 13 twin-deck and triple-deck screens; three belt feeders, a 90m long recovery conveyor, a 37m long feed conveyor, a 40 tonne live capacity surge bin and a 39m long closed circuit conveyor. A vibrating tray feeder and an inverter driven 150 tonnes/hr Ore Sizer vertical shaft impactor completed the specification.