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The by-products from the extraction of china clay from decomposed granite, consisting largely of two distinct materials: 'Stent', which is waste rock, and 'Tip Sand'. China clay tip sand is defined as the washed material produced as a by-product during the extraction of China Clay (kaolin) from kaolinitic granite, predominantly comprising quartz with some mica, and is relatively consistent from within each source production [HD 35/04].
Based upon the Specification for Highway Works [MCHW Volume 1] and the Design Manual for Roads and Bridges [HD 35/04], china clay sand can be recycled into:
Recycled China clay waste has been extensively incorporated into various concrete products as a replacement for virgin materials including in concrete mixtures and in precast concrete products. Projects where these materials have been used include:
Approximately 3 Mt of English china clay was produced in 1999 in the South West of England, of which 87% was exported. English china clay extraction operations are concentrated around the granitic source rock of the South West of England. The largest producer operates 17 open pits in the UK; 14 of which are situated in Cornwall (12 are concentrated in the St Austell area). The remaining three pits are located in Devon and the South West side of Dartmoor [English China Clays International Ltd, 2002].
The tonnage data are sourced from the DCLG survey  and refer to china clay aggregate (china clay sand and stent combined).
*China clay sand and stent estimate is based on approximately 9 tonnes of waste being generated for every tonne of good china clay. This waste typically comprises (dependant on the quality and age of deposit) 4 tonnes of coarse china clay sand, 2.5 tonnes of coarse rock material (stent), 1.5 tonnes of overburden, and 1 tonne of fine residue [DCLG, 2007].
Located in South West England. China clay is removed by directing high-pressure jets of water at a weathered granite cliff face. The water runs into the bottom of the pit and is pumped up to a treatment plant that settles out the china clay. The grain size and quality of the china clay sand arising may vary between sources, but generally it is only likely to require basic grading and washing processes, as would be applied to other natural aggregates, prior to use. Stent would require crushing and screening for use as an aggregate [Coventry et al, 1999].
There has been historic perceptions of china clay waste having weathered, low quality material. This is characteristic of sources only in the area of South Dartmoor and there is a long history of satisfactory use in ready mix concretes over much of Cornwall and Devonshire [Marsh, 2006]. Quality control and specifications should be agreed prior to accepting consignments.
Located in the South West of England, total stockpile quantities of up to 600 Mt, but much of this is not available. Recent work on potentially usable stockpiles indicates a broad estimate figure of 150 Mt [DCLG, 2007].
China clay sand and stent have been predominately used in the South West of England, which has a finite requirement for such aggregates. Aggregate use has been steady at its current level [DCLG, 2007].
There is commercial and sustainability potential for using china clay waste as secondary aggregate as it is exempt from the Aggregates Levy, the main constraint and hindrance on its use was the geographic location of its source. Improvements in rail transport, for example deliveries to the London Olympic site are by rail directly to the batching plant, and investment in the Port of Par has resulted in china clay waste becoming more competitive.
The downloadable pdf document tells you if and where these materials can be used in any construction projects covered by the Aggregain site, as well as providing additional information regarding the materials.
Coventry, S., Woolveridge, C. and Hiller, S., (1999). The Reclaimed and recycled construction materials handbook, CIRIA report C513, London.
English China Clays International Ltd, (2002). UK’s biggest mineral exporter is English China Clays, International Mining and Minerals: Volume 3 (29), pp-125-128, May 2002.
Highways Agency, Welsh Assembly, Scottish Executive and the Department of the Environment for Northern Ireland. Design Manual for Roads and Bridges: Volume 7, Section 1, Part 2, HD 35/04 Conservation and use of secondary and recycled materials. The Stationery Office, London.
Highways Agency, Welsh Assembly, Scottish Executive and the Department of the Environment for Northern Ireland. Manual of contract documents for highway works: Volume 1, Specification for highway works, The Stationery Office, London.
Department for Communities and Local Government, (2007). Survey of Arisings and Use of Alternatives to Primary Aggregates in England, 2005 - Other materials, DLCG, London. Available from the DCLG Website.
Sherwood, P.T, (1995). Alternative materials in road construction. Thomas Telford Publications.
Marsh, B., (2006). Concrete for a Sustainable Future, The Institute of Concrete Technology One Coleman Street – A Case Study in the Use of Secondary Materials in Concrete
Olympic Delivery Authority (2009). Sustainable design and construction update, ODA 2009/295. Available from ODA Website: www.london2012.com