Современные проблемы промышленного и гражданского строительства на занятиях английского языка. Кузьмина Е.В. - 29 стр.

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after the water has been added and the process of hardening lasts for about

twenty-eight days. The process is called concrete curing. The characteristics of

concrete depend upon the quality of the materials used, grading of the

aggregates, proportioning and amount of water. The most important

requirements for concrete are: it should be hard, strong, durable, fire-resistant

and economical. Concrete can be divided into two classes: mass or plain

concrete and reinforced concrete (ferro-concrete) where it is necessary to

introduce steel. Plain of mass concrete can be used for almost all building

purposes. Ferro-concrete us used in buildings bridges and arches, dams and

dock-walls, for structured under water, for foundations, columns, girders,

beams. The use of concrete and ferro-concrete is almost universal.

Builders now produce two types of new building materials: alkali-slag

concrete and silica concrete. In alkali-slag concrete cement is replaced by a

mixture of granulated blast-furnace slags and sodium and potassium

compounds. The fillers can be sand or sandy loams containing various amounts

of clay, which usually cannot be used with conventional cement. The new

material has been tested successfully and is now being used for irrigation

systems, roads, pavements and other structures. Silica concrete is light, fire-

resistant and acid-proof. It contains no cement whatever. Silica concrete is

widely used in aviation and in under water constructions.

The term “Concrete” is used to describe a dense material composed of

cement and aggregate mixed with water.

The density of the aggregate. Therefore there is a broad division of

concrete types into:

a) Dense concretes – composed of heavy aggregates.

b) Light-weight concretes – composed of light aggregates.

The aggregates are graded in size from fine to coarse in order to reduce

the amount of void space to be filled by cement. There are “cellular” concretes

made by using materials which foam of form gas during the mixing of the

concrete. These give a product of very light weight, because after setting it

contains a large number of small voids.