СМ 2021-2022: Concrete: Concrete

Concrete

Concrete is an artificial stone resulting from hardening of a rationally chosen mixture of:

•binding material,

•water

•aggregate (sand and crushed stone or gravel).

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•The mixture of these materials before it hardens is called concrete mix.

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•Particles of sand and crushed stone form a stone carcass in concrete.

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•When cement paste hardens, it binds the aggregate into an artificial stone, or concrete.

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•Concrete combined with steel reinforcement is called reinforced concrete.

Concrete is one of the major building materials in all branches of modern construction, which is due (обусловлено) to the reasons given below:

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•possibility of controlling the properties of concrete within a wide range by using appropriate (соответствующих) ingredients and by special mechanical, physical and chemical processing techniques;

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•possibility of a complete mechanization of concrete preparation and placing processes;

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•economical efficiency (экономичностью бетона) of concrete, since 80 to 90% of its volume are occupied by aggregates from local stone materials.

By the maximum size of aggregate, concretes are subdivided into:

•fine-grained (мелкозернисытый) varieties with aggregates of up to 10 mm in site

•coarse grained (крупнозернисытый) varieties, the maximum size of aggregates ranging from 10 to 150 mm.

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•Strength and durability are major characteristics of the quality of concretes.

•By compressive strength, concretes fall into a number of grades.

•Heavy concretes have strength grades between 100 and 600,

•lightweight ones, between 25 and 300,

•extra-heavy ones, from 100 to 200.

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•Durability of concretes is evaluated in terms of their frost resistance. By this characteristic, concretes are subdivided into grades:

•heavy concretes, from 50 to 300;

•lightweight concretes, from 10 to 200.

According to the kind of binding material, concretes are available in the following varieties:

•cement concretes manufactured from hydraulic binding materials, such as portland cement and its varieties;

•lime-sand concretes, from lime binders in combination with silicate or aluminate compounds;

•gypsum concretes, from gypsum-anhydride binding materials; concrete from organic binding materials.

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•Heavy concrete is manufactured from cement and common dense aggregates,

•Lightweight concrete, from cement and natural or artificial porous aggregates.

•A variety of lightweight concrete is cellular concrete which is a hardened mixture of a binding material, water, line silicate component and pore-forming agent.

•Lime-sand concretes are obtained by mixing lime and quartz sand and subsequently hardening moulded items in autoclaves at pressures between 0.8 and 1.2 MPa and temperatures from 170 to 200°C.

By application, concretes are divided into the following kinds:

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•common, for concrete and reinforced concrete supporting elements of buildings and installations (columns, beams, plates);

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•hydraulic engineering for dams, sluices, facing of channels, etc.(гидротехнические для строительства дамб, шлюзов, облицовки каналов и т.д.);

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•for walls of buildings and light floors;

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•for floors and road surfaces and bases;

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•for special purposes, such as acid- and heat-resistant superheavy concretes, the latter being for biological shielding; extra-heavy concretes are manufactured from cement and special aggregates of high bulk density.

•Cement. Heavy concretes are prepared from portland cement, pla- sticized portland cement, portland cement with hydraulic admixtures, slag portland cement, etc.

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•The type of cement is chosen according to the demands placed upon concrete (strength, frost resistance, chemical stability, water impermeability, etc.).