Construction Aggregates
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Expert | Impartial | Innovative Mineral Planning Factsheet Construction aggregates This factsheet Aggregates are the most commonly used Manufactured aggregates — aggregates of provides an construction minerals in the UK. They are mineral origin resulting from an industrial overview of widely distributed with a range of potential process involving thermal or other modification aggregates supply sources and, while a low cost product, are used e.g. slag. in the UK. It forms in very large quantities. They are essential for part of a series constructing and maintaining what is literally Recycled aggregates — aggregates resulting on economically the physical framework of the buildings and from the processing of inorganic materials important minerals infrastructure on which our society depends. previously used in construction e.g. that are extracted construction and demolition waste. in Britain and is Aggregates are normally defined as being primarily intended hard, granular1 materials which are suitable In Britain, however, it is common practice to inform the for use either on their own or with the addition to distinguish between primary aggregates land-use planning of cement, lime or a bituminous binder in and alternative sources, such as secondary process. It is not construction. Important applications include aggregates and recycled aggregates. a statement of concrete, mortar, roadstone, asphalt, railway planning policy ballast, drainage courses and bulk fill. European Primary aggregates are produced from naturally or guidance; nor Standard (BS EN12620) defines aggregates occurring mineral deposits, extracted specifically does it imply as ‘granular material used in construction. for use as aggregates and used for the first time. Government Aggregates may be natural, manufactured or Most construction aggregates are produced approval of recycled.’ These are further defined as: from hard, strong rock formations by crushing any existing or to produce crushed rock aggregates or from potential planning Natural aggregates — aggregates from mineral naturally occurring particulate deposits such as application in the sources which have been subject to nothing sand and gravel. The most important sources of UK administration. more than physical processing (crushing and crushed rock in Britain are limestone (including sizing). dolomite), igneous rock and sandstone. Sand June 2019 and gravel can be either land-won or marine dredged. Primary aggregates fall within the 1 However, a proportion of aggregates sales are for European definition of natural aggregates. The constructional fill or other uses where soft and non- term aggregate mineral is also used for any Gravel aggregate. granular material may be acceptable or even specified. naturally occurring material that is suitable for aggregates use. Some rock types, notably limestone/dolomite, are suitable for both aggregates and non-aggregates applications. Secondary aggregates are usually defined as (a) aggregates obtained as a by-product of other quarrying and mining operations, such as china clay waste, slate waste and colliery spoil (minestone), or (b) aggregates obtained as a by-product of other industrial processes, such as blast furnace/steel slag, coal-fired power station ash, incinerator ash, and spent foundry sand. In European specifications, mineral waste sold as aggregates is classified as natural aggregates, and by-product aggregates derived from industrial processes are classed as manufactured aggregates. Recycled aggregates are an important source of aggregates in Britain. They arise from various sources including demolition or construction of buildings and structures, or 1 Aggregates Expert | Impartial | Innovative Mineral Planning Factsheet Construction aggregates from civil engineering works. Other forms of use of recycled aggregates, it is likely that the recycled aggregates are asphalt planings from major proportion of future aggregates demand resurfacing roads, and railway track ballast. will be supplied from primary sources because ‘Recycling’ involves the removal of deleterious there are limitations on the availability of materials, such as fines, wood, plastic or metal material to be recycled into aggregates. and processing by crushing and screening as required so that it can be reused, often for less Aggregates have a wide range of uses in demanding applications. Once a material is construction. Table 1 shows sales of primary processed into a saleable product it becomes a aggregates by major end-use in 2014. Data resource rather than a ‘waste’. for more recent years are not available. Most aggregates are used in the production of Demand concrete for buildings and civil engineering structures, or as roadstone in road building, Aggregates are used in construction and they repair and maintenance. Aggregates are also are the largest tonnage of material used by used in mortars and finishes in construction, as this sector. Demand is driven by activity in railway track ballast and as constructional fill. the construction industry and the economy as a whole. The relationship is not simple and The main use of sand and gravel is for concrete demand forecasting has proved to be difficult. (63% of the total sand and gravel sold). Other Past forecasts have proved to be too high or uses for sand include mortar and for gravel too low. It is difficult to forecast far ahead with include drainage layers or construction fill. any reliability and, therefore, it is important that The main use for crushed rock is as roadstone estimates are regularly reviewed and revised. in road construction (40% of the total crushed rock sold), where it is either coated with Efficient and effective transportation, affordable bitumen in asphalt or used uncoated. A further housing and investment in essential assets, such 15% of crushed rock is used in concrete. as new and improved roads, rail links, airport facilities, homes, flood defences and water Concrete is made from a mixture of water, air, and sewage facilities, all consume aggregates. cement, coarse aggregates (natural gravel, Thus there will be a continuing demand for crushed limestone or other hard rock) and fine aggregates. Despite a substantial increase in the aggregates (generally quartz sand, but limestone Principal uses Thousand tonnes Sand & gravel* Crushed rock Total % Concrete aggregates 35 381 14 279 49 660 32.1 Other screened, graded aggregates 6 555 19 572 26 127 16.9 and surface dressings Roadstone, coated 181 17 597 17 778 11.5 Roadstone, uncoated – 22 179 22 179 14.4 Building/asphalting sand 6 960 – 6 960 4.5 Railway ballast – 2 990 2 990 1.9 Armourstone/gabion – 976 976 0.6 Constructional fill 7 052 20 831 27 883 18.0 Total sales 56 129 98 423 154 552 100 Table 1 Great Britain: Sales of primary aggregates by major end-use, 2014. Source: Annual Minerals Raised Inquiry, Office for National Statistics (ONS) *including marine dredged Aggregates Aggregates 2 Expert | Impartial | Innovative Mineral Planning Factsheet Construction aggregates sand and other crushed rock fines are also the railway track, and provides a free draining used). The water and cement form the paste base. Fine aggregates (generally fine-grained binder, whilst the aggregates form an inert filler. sand) are used in mortar, to bond masonry or Fine and coarse aggregates are added either as a surface plastering and rendering material. separately or as combined ‘all-in’ aggregates. The properties of the aggregates used influence Some rocks suitable for use as aggregates, the mix proportions and the performance of notably limestone/dolomite, have a wide the concrete. Particle size, form and shape range of industrial applications, such as in the are important. For example, finer sand sizes manufacture of chemicals, as a flux in iron and require more cement, which has additional steelmaking and in the reduction of sulphur cost implications because cement is the most dioxide emissions from coal-fired power expensive component of concrete. (See also the stations. Quarries supplying limestone and Factsheet on Cement Raw Materials.) dolomite for industrial and agricultural uses invariably also supply crushed rock aggregates Modern flexible road pavements consist from material that is unsuitable for high of discrete layers. The sub-base provides quality industrial use. (See also Factsheets on strength and a solid platform, the binder Industrial Limestone and Industrial Dolomite.) course is the main load-bearing layer and Many crushed rock aggregates quarries also the surface course protects the lower layers produce small amounts of building stone and from the weather and provides an even, conversely some building stone quarries supply skid resistant running surface. Aggregates modest quantities of aggregates as by-product used in road pavement construction may be of quarrying and processing building stone. unbound or bound by a bituminous (asphalt) (See also Factsheet on Building Stone.) or cementitious binder. Unbound layers are usually used for the sub-base but may Specifications occasionally be used for the whole structure in minor roads. Over 95% of Britain’s roads are The suitability of aggregates for a particular asphalt roads. A wide range of crushed rock purpose depends principally on their physical types, as well as natural gravel and sand and and mechanical properties, although for certain secondary and recycled aggregates, some applications mineralogical or chemical are used as roadstone. Well-cemented properties are also important. For general limestones and sandstones