Construction aggregate
From Wikipedia, the free encyclopedia
Construction aggregate, or simply, aggregate, is the broad category of basic materials used in construction, including sand, gravel, crushed stone, slag, and recycled concrete. Aggregates are a basic resource, necessary for any kind of modern construction. Aggregates are the basic input materials to concrete and asphalt. Additionally, aggregates are used as base materials under foundations and roads.
The American Society for Testing and Materials publishes an exhaustive listing of specifications for various construction aggregate products, which, by their individual design, are suitable for specific construction purposes. These products include specific types of coarse and fine aggregate designed for such uses as additives to asphalt and concrete mixes, as well as other construction uses. State transportation departments further refine aggregate material specifications in order to tailor aggregate use to the needs and available supply in their particular locations.
Sources for these basic materials are limited to three main areas: Mining of mineral aggregate deposits, including sand, gravel, and stone; Use of waste slag from the manufacture of steel, and; recycling of concrete, which is itself chiefly manufactured from mineral aggregates.
[edit] History
Mankind has used sand and stone for foundations for thousands of years. Significant refinement of the production and use of aggregate occurred during the Roman Empire, which used aggregate to build its vast network of roads and aqueducts. The invention of concrete, which was essential to architecture utilizing arches, created an immediate, permanent demand for construction aggregates.
[edit] Modern production
The advent of modern blasting methods enabled the development of quarries, which are now used throughout the world, wherever competent bedrock deposits of aggregate quality exist. In many locales, good limestone, granite or other quality stone bedrock deposits do not exist. In these areas, natural sand and gravel are mined for use as aggregate. Where neither stone, nor sand and gravel, are available, construction demand is usually satisfied by shipping in aggregate by rail or barge. Additionally, demand for aggregates can be partially satisfied through the use of slag and recycled concrete. However, the available tonnages and lesser quality of these materials prevent them from being a viable replacement for mined aggregates on a large scale.
Large quarry and sand and gravel operations exist near virtually all population centers. These are capital-intensive operations, utilizing large earth-moving equipment, belt conveyors, and machines specifically designed for crushing and separating various sizes of aggregate, to create distinct product stockpiles.
Aggregate is needed for any kind of construction, mineral aggregates will be used in ever-increasing quantities as long as economies remain stable. Roads require continual maintenance and rebuilding. Homes, offices, warehouses, shopping centers, and workplaces all require foundations composed of aggregate, as well as concrete footers, asphalt parking lots, manufactured bricks, blocks and poured walls. Corporations which specialize in mining and processing aggregates are likely to grow and consolidate. In fact, the purchase of small aggregate companies by large, global corporations is the dominant trend in the industry. As less-developed countries build their infrastructure, the worldwide demand for construction aggregates will continue to grow. This demand will increasingly be met by global aggregate companies such as Hanson Aggregates, Martin Marietta Aggregates, Vulcan Materials Company, Lafarge, Oldcastle, and Cemex.
