In the largest project of its kind in the country, CEMEX UK is supplying cement from its Rugby cement plant and marine sand from the Bristol Channel to a major contract in Combe Down village near Bath.
The materials are being used in foamed concrete, which is being pumped and sprayed into historic abandoned mine workings beneath the village, to stabilise the mines which are close to the surface.
Work to safeguard the 1600 people who live in the village, including their dwellings, primary school, nursery, three churches and road infrastructure, commenced in 1999, when Bath and North East Somerset Council secured funding for a two-phased emergency stabilisation plan.
For the first phase of the project, which was concluded at the end of March, CEMEX UK supplied 64,000 tonnes of cement and 20,000 tonnes of sand for 160,000 cubic metres of foamed concrete that was pumped into approximately 25 hectares, the size of more than 50 football pitches, of the shallow underground mines.
This is the single largest application of foamed concrete in the UK. The cement and foamed concrete mixes were closely controlled on temperature and provided at a maximum of 35° Celsius to control cracking and heat development in the materials. Following extensive data collection, this was achieved by rotating materials between silos at two locations; Rugby and Newport.
CEMEX UK has also secured the contract to supply the second stage of the contract, which includes 90,000 tonnes of cement over a three-year period.
According to Hydrock's project manager, Dr Robert Narbett, CEMEX UK secured the contract based on its flexibility, and willingness to meet the challenging temperature logistics requirements: "All vehicles have to deliver within a tight time frame. Due to the site's proximity to housing and schools all deliveries, up to 25 per day from CEMEX, have to be made between 9.30am and 3.30pm to avoid rush hour traffic and comply with planning regulations."
The areas of immediate hazard have now been made safe, and work has started on the remaining 300,000 cubic metres of the mine, to secure and conserve the internationally recognised heritage, wildlife and environmental properties in Combe Down. Work on the mines is expected to be fully completed in 2010.
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CEMEX: CEMEX is a global building solutions company and leading supplier of cement, ready-mixed concrete and aggregates. In the UK, CEMEX also has a significant share of the asphalt, concrete block and mortar markets. The company has a national supply network in the UK with over 500 locations, to ensure that quality building materials is available to customers locally.
For more information, see www.cemex.co.uk or www.cemex.com
Hydrock: Hydrock is a leading national provider of consultancy and specialist contracting services for Construction, Infrastructure & the Environment. For more information, see www.hydrock.com
Combe Down mines:
Extraction in the Combe Down and Bathampton Down Mines ceased in the 1860s when reserves of Bath Stone for buildings in Bath, Bristol and London had been exhausted. It is estimated that less than 20% stone, rather than the recommended 40%, was left within the mine as roof support. This means that the roof is as little as one metre thick in places.
Following extensive trials of suitable infill materials, a lightweight (600kg/m3) foamed concrete was selected to prevent the potential settlement problems associated with large volumes of denser materials. With 70% of the fill material being foam, the number of material truck movements is greatly reduced, thus lessening the impact on the local environment. Specialist Foamed Concrete contractor Propump Engineering have supplied the main contractor, Hydrock, with a bespoke mixing and foaming system, which has enabled the foamed concrete to be pumped over one kilometre into the mine at rates of 200 cubic metres per hour.