July 8th, 2011 by Deirdre Dudley-Owen
This article by Deirdre Dudley-Owen and Steve Roussel of Ronez Ltd. was published originally in the June/July 2011 issue of Contact
Guernsey granite has been used to build homes, churches, fortifications, island infrastructure, as well as being used in the streets of Southampton and in the alleys, roads and embankments of the City of London.
In 1869 The Guernsey Star wrote “it is somewhat remarkable that while the stone trade has been so material an element in our commerce, its existence has scarcely been known to the generality of our population.”
By the late 1900’s, Guernsey’s quarrying industry employed over 1,970 stone workers. Granite exports provided an income for quarry owners, carters, stone breakers, dressers as well as blacksmiths, carpenters and shipping companies. Today few people comprehend the scale of this former major island industry.
The modern day activities of quarrying raw materials and the secondary industry of recycling and reuse of construction and demolition waste, glass and pulverised fuel ash has evolved over the years. Ronez was one of the first local companies to recognise the commercial value of recycling and reuse.
In environmental terms, quarrying of local stone by Ronez for local use, is a low carbon, low environmental impact industry. Ronez extracts and uses granite to supply the island with bitumen macadam, ready mix concrete, concrete blocks and paving as well as building stone. The need to import aggregates and the amount of fuel used for transport is reduced effectively reducing the carbon footprint of local buildings and island infrastructure projects such as harbour walls, sea defences and roads.
Les Vardes quarry is the only working quarry left in the island out of 268 in 1930. Its recent operation restarted in 1962.
An average day sees several thousand blocks produced at the Vale Monmains site, made mainly of locally quarried materials. Ronez began to recycle demolition waste in 1996 when they installed a crushing plant at the Monmains site. The plant has processed over 400,000 tonnes of building demolition arisings since 1996, material which otherwise would have gone to landfill at Longue Hougue, also extending the use of finite stone reserves within the island.
Currently builders are charged £4.50 per tonne to tip demolition materials and rubble separated from skip waste by skip companies at Ronez yard. This is turned into various grades of secondary aggregate for reuse. Ronez employ a number of systems to control contamination and ensure the quality of the aggregate produced. All incoming material is weighed over the weighbridge and a delivery ticket is issued to the customer. A CCTV camera is positioned above the weighbridge allowing the surface of the load to be inspected by the operator; on the ground inspections also take place periodically. The driver is then issued with a ticket and drives to the yard where the material is tipped into a stockpile. From the stockpile the demolition arisings are loaded into the crushing plant feeder by a 16 tonne hydraulic excavator. At this stage any granite boulders are separated to be either sold as decorative rockery stone or taken to Les Vardes for processing. Once fed into the recycling plant material is first crushed to minus 90mm by a jaw crusher, it then passes under an magnet where ferrous metal is removed before passing over a two deck Chieftan screen, which sorts the crushed material into sizes. A wheel loading shovel is then used to stack the various aggregate products into stockpiles and load customers’ trucks. Within the crushing plant are two manual picking stations where operators can inspect the feed material and remove plastic, wood, non ferrous metal and other extraneous material. Wherever possible these are sorted separately for further recycling.
As well as recycling demolition waste Ronez is also involved in the recycling of the coloured glass collected within the States recycling programme. The glass is crushed to -4mm at the States Works site at Bulwer Avenue. At this size it no longer contains any sharp shards, but is effectively a ‘green sand’.
The crushed glass is taken to Les Vardes Quarry, where it is blended by loading shovel into granite sub-base, used in the construction of roads and other civil projects. The proportion of glass within the mix is less than 25% recommended in Highways Agency Guidance. The use of crushed recycled glass reduces the proportion of either local or imported dust or sand that would otherwise be required to meet the islands building industry needs.
Another product which is reused by Ronez is Pulverised Fuel Ash or PFA. PFA is a by-product of the burning of coal for power generation and is a recognised cement replacement. The PFA is imported in a dedicated bulk cement ship, the MV Ronez, and stored in silos next to St Sampsons Harbour. By introducing a proportion of PFA into ready-mix concrete Ronez reduce the amount of Portland cement used. This has environmental benefits as the process for making Portland cement is energy intensive and also produces CO2.
Our architecture and cultural heritage owes much to quarrymen and stonemasons, and even a casual observer will see that from the random rubble used to build the sturdy tower of St Michel du Valle in about 1150, to the great stones used to build the islands fortifications and harbours, nothing is wasted. This bears testament not only to the skill of the stonemason, but also to the stewardship of our local environment. The activities carried out by Ronez continue to uphold this tradition of wasting nothing and contributing to the production of low carbon building materials as well as reducing waste going to landfill.