Concrete

Beton ([beˈtõ], [beˈtɔŋ] Austronesian and partly Bavarian [beˈtoːn]; Swiss and Alem. 1st syllable stressed [ˈbetɔ̃], from the synonymous French. Word béton,) is a building material mixed as a dispersion with the addition of liquid from a binder and aggregates. The hardened concrete is also called artificial stone in some contexts.

Normal concrete contains cement as a binder and aggregate (formerly aggregate) as an aggregate. The addition water (formerly mixing water) initiates the chemical setting process, i.e. hardening. In order to influence the workability and other properties of the concrete, concrete additives and concrete admixtures are added to the mix. Most of the water is chemically bound. The complete drying of the mixture may therefore only take place after hardening.

Fresh concrete can be considered as a two-material system consisting of liquid cement paste and solid aggregate. Cement paste hardens to form cement stone. This forms the matrix that surrounds the aggregate.

Today, concrete is mainly used as a composite material in combination with a tensile reinforcement. The combination with reinforcing steel or prestressing steel results in reinforced concrete or prestressed concrete. More recent developments are fibre concrete with the addition of steel, plastic or glass fibres, as well as textile concrete, which contains knitted fabrics (textile) made of alkali-resistant AR glass or carbon fibres.

The impact of concrete production on the environment has so far been considered problematic. The concrete industry is one of the main emitters of greenhouse gases that cause global warming. Concrete production is responsible for about 6 to 9 % of all man-made _{CO2 emissions}, which is three to four times the magnitude of all air traffic. Significant quantities of water, gravel, cement and sand are consumed worldwide for the production of concrete. The global supply of suitable sand is becoming increasingly scarce, primarily due to concrete production.

Basic characteristics and use

Normal concrete usually has a compressive strength of at least 20 Newtons per square millimetre (N/mm²). Concrete with lower strength is used for the production of clean layers, backfill and in gardening and landscaping. High performance concrete reaches strengths of over 150 N/mm².

Unreinforced concrete, on the other hand, can only absorb low tensile stresses without cracking, as its tensile strength is only about one tenth of its compressive strength. Tensile stresses are therefore usually absorbed by inserted bars or meshes of reinforcing steel that have a tensile strength of over 400 N/mm². This combination has proven to be advantageous for several reasons:

• Concrete and steel have similar coefficients of thermal expansion, so that no temperature-induced stresses occur in the composite material,
• the basic pH value of the concrete prevents corrosion of the steel,
• In the event of a fire, concrete prevents the rapid loss of strength of unprotected steel due to temperature.

Typical applications of reinforced concrete:

• Foundations, (basement) walls, slabs, columns and ring beams in general building construction,
• Skeletal supporting structures of high-rise buildings and commercial buildings,
• Transport structures such as tunnels, bridges and retaining walls.

Unreinforced concrete is used for gravity walls, curved gravity dams and other compact, massive structural components that are loaded predominantly in compression. Larger tensile stresses must either be avoided by design or there must be no risk from fracture of the material. This is the case, for example, with smaller prefabricated elements such as blocks for masonry construction or (exposed aggregate) concrete slabs in horticulture. Due to its low cost, arbitrary formability and comparatively high density of about 2400 kg/m³, concrete is also used for counterweights on cranes and for breakwaters.

The shrinkage of the component volume during drying and due to chemical processes must be taken into account. The degree of shrinkage depends on the composition of the starting material. A certain amount of creep occurs in all loaded components and describes the increasing deformation under load over time.

Distinguishing Features

Concrete can be distinguished on the basis of various characteristics. Common distinctions are according to

• the dry bulk density in light concrete, normal concrete and heavy concrete,
• the strength, with the compressive strength taking the most important role,
• the place of production in site or ready-mixed concrete,
• the intended use in, for example, waterproof concrete, underwater concrete,
• the consistency in classes from stiff to (very) flowable,
• the type of compaction in vibrated concrete, tamped concrete, rolled concrete, flowing concrete, poured concrete, shotcrete, ...
• the type of aggregate in sand concrete, gravel concrete, crushed concrete, ...
• the hardening state into the fresh concrete that can still be processed, the green concrete that has already been placed and compacted, the young concrete whose hardening has already begun and finally the hardened hardened concrete,
• the requirements for quality assurance in formulated concrete (production class R according to ÖNORM 4200 or class B I according to DIN 1045) and concrete after suitability testing (production class E or class B II according to DIN).

Like concrete, mortar is a mixture of a binder, aggregate and additives or admixtures. The difference is in the size of the aggregate, which in the case of mortar must not exceed 4 mm in diameter. There is an overlap in the case of spray plasters and masonry mortars, which in special cases may contain a maximum aggregate size of up to 16 mm, and in the case of screed, which is usually mixed with 8 mm aggregate size.