After the face profiling survey, the explosives supervisor prepares the area. Using an air operated drilling rig, vertical holes are drilled 15 metres down and charged with explosives to provide a well fragmented blast pile.
Sirens are sounded to make sure that everyone nearby is warned. A final safety check is carried out and only when the final all clear is given does the shot firer set off the explosives. The quarry face is loosened by controlled blasting. A typical blast can fragment up to 20,000 tonnes.
The material produced which is less than 40 inches in diameter is transported to the primary crusher - oversize material must first be broken into a workable size.
The rock is loaded into dumpers by a large 80 tonne excavator and transported to the processing circuit for crushing and sizing. Boulders which are too big for the crusher are set aside for secondary breaking at a later date.
The Hercules Trommel effectively separates the ragstone and hassock, which is then conveyed in two separate product streams for further crushing, screening and washing, producing a series of graded products.
Screening and washing
In the screening and washing process, material passes over a series of screens to rinse and separate the various sizes. Stones too large to pass through the largest openings are re-routed to a crusher and then screened again until they are correctly sized.
Different grades of stone are transported from beneath the respective screens by conveyors onto stockpiles. They are stored until they are loaded onto trucks to be delivered to customers or mixed to make concrete.
The best blocks of primary rock are used for Kentish Ragstone building stone. They are sawn into dimensional slabs by primary saws and then hand finished by skilled stonemasons to a variety of finishes.
Construction and demolition waste, trench arisings and waste asphalt are all returned to Hermitage for sorting and processing to produce a suite of high quality recycled aggregate for use in construction and road building.
Two fully computerised batching plants operate within the quarry. A full range of concrete mixes and screeds can be produced as well as bespoke mixes, including self compacting, waterproof, foamed concrete and fibre reinforced concrete.
Part of the Hermitage model is to restore the land back to original levels. This is facilitated by importing ‘inert’ waste coupled with sub soils and top soils into the void created by quarrying to achieve the required levels.
While the quarry continues to be worked, restoration is also ongoing where extraction has ceased. Here at Hermitage this enables us to have high quality agricultural land and woodland which creates an excellent habitat for plants and wildlife.
Head Office address:
Gallagher Group, Leitrim House, Little Preston
Aylesford, Kent ME20 7NS
Gallagher Aggregates Ltd., Hermitage Quarry
Hermitage Lane, Maidstone, Kent ME16 9NT