As aggregates are in building natural and artificial rock called grains. They either come from natural deposits or arise from the recycling of building materials or as an industrial by-product. The rocks are either round grain or in broken form .
The roughly equivalent terms concrete aggregate , mineral mixture , mineral mixture or mineral substance are no longer used in the standards. The more general term surcharge is often used synonymously.
Aggregates are processed together with a binding agent (often cement or lime ) and added water to make concrete and mortar . Asphalt is a mixture of aggregates and bitumen . Grain shape, strength and grading curve of the aggregate can have a significant influence on the properties of the building material.
The requirements for aggregates are defined, among other things, in DIN 18196 soil classification for structural purposes and the technical delivery conditions for aggregates in road construction, TL Gestein-StB, edition 2004 . The DIN 4226 surcharge for concrete has been replaced by the new European standard EN 12620 aggregates for concrete .
Aggregates for outdoor use must be sufficiently resistant to weathering and must only contain small amounts of constituents that can swell, disintegrate, dissolve or chemically react (such as marly and clayey grains, some clay and mica minerals , pyrite , marcasite , gypsum , calcium oxide , Magnesium oxide ). This property is also called spatial stability .
Aggregates must not be contaminated and contain no harmful amounts of metals or plastics and no substances of organic origin such as wood or plant residues. When extracting, processing and storing aggregates, care must be taken to ensure that they retain their properties and can continue to meet the requirements.
The TL-Gestein StB set of rules describes a large number of additional requirements for the aggregate, such as: B. bulk density, bulk density, resistance to shattering , to surface abrasion, to wear, frost resistance, reaction to alkali silica, etc.
Natural aggregates consist of mineral deposits that have only been mechanically processed . These include the unbroken gravel and sand , as well as broken aggregates such as gravel , chippings , crushed sand and rock .
Processing: Rock is extracted in the quarry and processed into a grain mixture with the help of crushers. Then sieves and other separating devices ( separators , etc.) separate the individual grain classes . Gravel and sand are extracted in gravel pits and also separated into individual grain classes by sieves. Gravel> 32 mm is partially crushed with crushers, which results in chippings and crushed sands. During the processing, the rocks are also washed in order to remove dirt and organic or cohesive components.
Industrially produced aggregates are of mineral origin that are produced industrially under the influence of thermal or other processes. The following aggregates come from industrial by-products:
- Blast furnace slag (HOS)
- Slag sand (HS)
- Steel mill slag (SWS)
- Slag from copper production (CUS / CUG)
- Foundry cupola slag (GKOS)
- Hard coal fly ash (SFA)
- Melting chamber granulate (SKG)
- Boiler ash from coal firing (SKA)
- Foundry residue (GRS)
- Household waste incineration ash (HMVA)
Recycled aggregates are created by processing inorganic material that was previously used as building material. This includes asphalts and concretes that have been removed, prepared and re-installed.
Thermosit is no longer on the market . You can still find it in renovations.
Aggregate for concrete and mortar
Among the aggregate for concrete and mortar refers to a mixture of broken or unbroken, the same or different large grains of natural or artificial mineral materials, in special cases even of metal or organic substances. They must be free of impurities (e.g. humus ) and harmful components (e.g. chlorides > 0.02%, see also alkali reaction ).
The aggregate generally has a higher strength than the cement paste . As high a proportion as possible in the end product (a high packing density ) leads to an increase in its strength and to a saving of the binding agent. However, if the fine sand is increased to increase the packing density , the proportion of binding agent must also increase in order to bind the fine grain and prevent the mixed mortar or concrete from becoming too stiff. A sensible compromise between packing density and fines has to be found.
Type of aggregate
The properties of a concrete aggregate are dependent on the type and texture of the rock that makes up the contract. However, this must be so strong that it enables the production of a concrete of the required strength.
- Normal surcharge
Surcharges with a gross density of 2200 to 3200 kg / m³ are called normal surcharges. Natural aggregates such as spherical and smooth sand (up to 2 mm grain size) and gravel from river deposits and moraines are mainly used for this . In addition, there are aggregates from quarries such as crushed stone , grit , crushed sand and filler (rock flour). But artificial additives such as blast furnace slag , broken clinker and recycled concrete chippings are also possible.
- Light surcharge
Aggregates with a gross density of less than 2200 kg / m³ are referred to as lightweight aggregates and are used for lightweight concrete and light mortars. As natural additives you use z. B. pumice , tuff , lava sand , lava gravel and diatomaceous earth as well as artificial additives z. As expanded shale , expanded clay , expanded glass , bulking mica , bulking perlite , fly ash , crushed brick , blast furnace slag (Hüttensandbims) and boiler sand . In special dry mortars (e.g. tile adhesives ), hollow microspheres made of glass, ceramic or plastic are also used.
- Heavy surcharge
Supplements are having a bulk density greater than 3200 kg / m³ referred to as heavy aggregates and heavy concrete used. As natural additives you use z. B. barite (barite), magnetite , hematite and limonite and as artificial additives z. B. scrap and heavy metal slag.
Composition of the aggregates
The grain composition of the concrete aggregate determines the density and the water requirements of a concrete mixture, which is necessary for sufficient workability. The grain composition of the aggregates is determined by sieving tests with test sieves and represented by grading lines which show the proportion of the aggregate in percent by weight that is smaller than the corresponding grain size . The addition can follow a continuous or discontinuous grading curve. For good processability, it is desirable to combine the grain sizes in such a way that their grading curve, as coarse or medium grain, lies in the favorable area 3 between lines A and B. With discontinuous grading lines U, a particularly dense packing of the aggregate grains is possible and thus a greater density can be achieved.
The largest grain is the largest aggregate diameter of an aggregate. Sieving is done with a (mostly rectangular) mesh opening that has this nominal value, which in general also allows (significantly) longer rock grains to pass through. The largest grain size is 8, 16, 32 or 63 mm. It should be chosen as large as possible, as this means that the addition of cement can be reduced due to the lower water requirement . The largest grain size is limited by structural constraints such as component dimensions and reinforcement density.
The concrete aggregates up to 0.125 mm or 0.25 mm together with cement and possibly other concrete additives form the flour grain content and primarily influence the workability and, under certain circumstances, the color, pore content and water tightness of the concrete.
Aggregate for asphalt
In road construction , aggregates are used for the construction of asphalt roads. Asphalt consists of minerals (rocks) and bitumen as a binding agent. If the type or quantity of these components is changed, the asphalt acquires different properties and can thus be adapted to the required conditions.
Requirements: When choosing the aggregate, the following must be taken into account: strength, affinity (adhesive behavior) towards binding agents, resistance to polishing, color, local availability, transport costs.
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
- as well as their respective national takeovers
- DIN 18196 Earthworks and foundation engineering - Soil classification for structural purposes
- DIN 4226 surcharge for concrete is replaced by the above-mentioned EN, except for DIN 4226-100: 2002 aggregates for concrete and mortar - Part 100: Recycled aggregates
- Technical delivery conditions for aggregates in road construction. 2004 edition, TL Gestein-StB, publisher: FGSV-Verlag, Cologne; implements the following European standards in Germany:
- Leaflet on the reuse of mineral building materials as recycling building materials in road construction (M RC)
- Leaflet on the use of household waste incineration ash in road construction (M HMVA)
- Definitions of terms, part road construction technology, edition 2003, FGSV-Verlag.
- Univ.-Prof. Dr.-Ing. K.-Ch. Thienel: Construction Chemistry and Construction Materials - Aggregates , page 20, Institute for Construction Materials, University of the Federal Armed Forces, Munich, spring trimester 2020
- G. Stehno: Baustoffe und Baustoffprüfung , p. 101, Springer-Verlag, 2013.