Broken aggregates (formerly called mineral or aggregate ) are stones whose shape did not arise naturally, but which were artificially crushed, in contrast to broken stone or gravel and sand of natural origin.
Broken aggregates are obtained as primary material in quarries or gravel works and as secondary material from sorted construction rubble . A special form are artificial aggregates such as B. slag, they are the result of a technical process. The primary material in quarries is first extracted by blasting and then processed by crushing and classifying processes. The primary material is dredged in gravel works and, if necessary, processed into a marketable product through cleaning stages and also through crushing and classification processes. Gravel and sand can also be sold without being crushed if the distribution of the grain sizes is in line with the market and a round surface without edges and broken surfaces is required. Construction rubble as well as artificial aggregates must also be processed in order to relieve them of foreign matter. In this way, the desired grain size distribution is achieved and a minimum strength is ensured by uncovering crumbly components.
Depending on the grain size , one differentiates:
- Rock flour (also flour grain , stone flour or filler , fine fraction ) with grain sizes up to 0.063 mm.
- Crushed sand , also squeezed sand , is sand (fine aggregate) with grain sizes of 0 to 2 mm (asphalt application), 0 to 4 mm (concrete application) and 0 to 6.3 mm (SoB, HGT, paving and paving applications) ( according to the technical delivery conditions for aggregates in road construction TL Gestein-StB), previously 0 to 4 mm (according to DIN 4226); including fine crushed sand or fine crushed sand with grain sizes from 0 to 0.25 mm.
- Chippings (coarse aggregates) with grain sizes from 2 to 32 mm; including fine chippings with 2 to 8 mm. As high-grade chippings, double , i.e. H. denoted twice broken aggregates with an approximately cubic shape. As a result of the selection made in this way, only particularly hard rock grain remains, which should be broken over the entire surface as possible. Fine chippings are used in asphalt and concrete, mainly as a top layer (wearing layer). The starting material is gravel and hard rock (granite, basalt, quartz). The production takes place in chippings, which were mostly built directly in the extraction sites. A natural round stone of this size is called rolling .
- Gravel (coarse aggregate) with a grain size of 32 to 63 mm
- Scratching over 63 mm grain size
- The latter both correspond roughly to natural rubble ( stones and blocks ).
Broken aggregates are also considered natural aggregates , as the rocks were extracted from nature. Artificial aggregate (industrially produced aggregate) mostly comes from blast furnaces (blast furnace crushed sand, blast furnace slag chippings).
Rock meal ("primary rock meal")
Ground rock as a soil additive for the garden or organic farming is often referred to as primary rock flour in the trade . Frequently used parent rocks are diabase or basalt . Due to slow weathering, the silicates and feldspars they contain provide important minerals for plant growth in the long term, above all iron and magnesium from the silicates and calcium from the feldspars. Depending on the source rock, rock powder also contains other important trace elements such as copper, molybdenum, boron, nickel, zinc and cobalt. The primary rock flour, which is commercially available as fertilizer, is slightly alkaline .
Rock flour , in English also rock flour or glacial flour , is not only created through technical processing, but can also be created in a completely natural way. The English term glacial flour indicates that this rock flour is created by the sliding and grinding motion of a glacier on its underground rock. This rock flour is the explanation for the special color that various glacial lakes, such as Lake Louise and Peyto Lake in Canada, take on; see glacier milk .
Are used broken aggregates mainly in road construction and as aggregate for concrete or asphalt as well as gravel for subsequent rolling in asphalt and grit for winter maintenance. Larger grain sizes are used as block material ( scraps ), for example as backing for dry stone walls .
Norms and standards
- EN 12620 aggregates for concrete
- EN 13043 Aggregates for asphalt and surface treatment for roads, airfields and other traffic areas
- EN 13242 aggregates for unbound and hydraulically bound mixtures for civil engineering and road construction
- EN 13139 aggregates for mortar
- EN 13450 aggregates for track ballast