Alternative sources of aggregates

Harrison, D.J.; Steadman, E.J.. 2003 Alternative sources of aggregates. Nottingham, UK, British Geological Survey, 22pp. (CR/03/095N) (Unpublished)

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In most countries aggregates for construction are produced from the crushing and processing of hard rocks (mainly limestones, igneous rocks and sandstones) or from the extraction and screening of unconsolidated deposits of sand and gravel. The availability of aggregate sources varies from place to place within a country, depending on the geology. There are two main sources of aggregates in Jamaica; sand and gravel from alluvial deposits, especially from the active river channels, and limestone. The latter dominates in the north and west of Jamaica and the major producers of sand and gravel are in the south and east of the island. River sand is often in short supply and is generally the only available source of natural fine aggregate, an essential component of concrete and other building products. There is considerable pressure in many countries to use secondary and recycled aggregates in construction because of the environmental problems associated with the production of primary aggregates. There is particular concern about the environmental effects of instream sand and gravel mining and thus there is a need to know to what extent alternative materials can augment or replace sand and gravel from this source. In Jamaica, the alternative sources include, marine sand and gravel, manufactured sand, river terrace deposits and recycled aggregates. There has not been any production of marine aggregates in Jamaica but the environmental concerns of onshore extraction and land-use pressures require marine sources to be seriously investigated. Offshore sources are thought to exist off the mouth of the Yallahs river in Saint Thomas, Jamaica, but have not been investigated in detail. The Yallahs has formed a fan-delta onshore and this feature extends for a further two kilometres offshore. The onshore deposits consist of interbedded, poorly sorted, coarse gravels and sands which are over 30 m thick and which are extensively quarried, with extraction concentrated in the main river channel. The sediments offshore are thought to be similar in lithology and thickness to the land-based deposits and there is current interest in dredging marine aggregates from the mouth of the Yallahs river. However, a range of resource assessment, environmental impact, production and investment issues need to be addressed prior to any development. Fine aggregate can be manufactured by crushing and processing hard rocks such as limestone and sandstone to produce fine grained (sand-sized) material. The degree to which such crushed rock sand can replace natural sand varies with rock type, the degree of quarry processing used and end-use. Nevertheless, in many parts of the world such material is a major source of fine aggregate. In Jamaica, ‘stone dust’ is produced as a by-product of limestone quarrying and is used, principally, in concrete block making and in asphalt products. The quality of the ‘stone dust’ is, however, variable and may perform poorly as fine aggregate. A few quarries wash the sand to remove fines and this significantly improves its quality. Sand is also produced from crushing river gravels at several sites, but this is coarse-grained and at the limits of specifications. Jamaica has large resources of rocks that can be crushed to produce manufactured sand, but improvement in quarry crushing and processing plant is required to consistently produce manufactured sand of acceptable quality. In Jamaica, substantial resources of sand and gravel occur within the floodplain and terrace deposits and beneath the agricultural lands of the major river valleys. These deposits are not currently worked for sand and gravel aggregates; extraction is largely restricted to the river 1 channel deposits. It is common practice in many parts of the world for sand and gravel to be dug from such alluvial deposits. Indeed, in many countries they are the preferred source of fluvial sand and gravel as in-stream mining is restricted by environmental constraints. Development of the floodplain and terrace deposits in Jamaica will ease the pressure on mining of river channel deposits, reducing the impacts of river extraction. Nevertheless, there are environmental and other impacts associated with the working of river terrace deposits. If these resources are to be developed in future, a range of studies will be required, including exploration surveys, hydrogeological investigations and environmental and social impact assessments. Many mineral wastes fulfil the technical requirements to substitute for primary aggregates and many governments are now encouraging greater use of mineral wastes as aggregates. Concrete, bricks and asphalt, for example, may be crushed and screened to produce secondary aggregates that can be used in construction. Recycling concrete rubble not only reduces environmental impacts of new aggregate production, but also avoids impacts associated with disposal. In Jamaica, the degree of recycling of mineral waste materials into secondary aggregates is very small, although some construction and demolition waste is used as fill. In conclusion, there are several potential sources of alternative aggregate materials in Jamaica. There are, however, large resources of natural primary aggregate materials, although their extraction creates considerable environmental problems. The planning and management of aggregate resources must be based on the consideration of all possible sources. Therefore, the viability of alternative materials needs to be considered when formulating aggregate resource management plans.

Item Type: Publication - Report
Programmes: BGS Programmes > Economic Minerals
Funders/Sponsors: British Geological Survey
Additional Information. Not used in RCUK Gateway to Research.: This item has been internally reviewed, but not externally peer-reviewed.
Date made live: 26 Mar 2020 13:45 +0 (UTC)

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