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Concrete is perhaps the most widely spread building material used nowadays. Concrete is an artifi-cial stone, made mixing such natural ingredients or aggregates as cement, sand and gravel or broken stone together with sufficient water to produce a mixture of proper consistency. It has many valuable properties. It sets under water, can be poured into moulds so as to get almost any desirable form, and together with steel in reinforced details it has very high strength, and also resists fire. Prestressed concrete is most wide-ly used at present while prefabricated blocks are employed on vast scale for skeleton structures.
Aggregates for concrete.
By the simple definition “aggregates are the materials, such as sand and small stones that are mixed with cement to form concrete”. In other words aggregates can be defined as a mass of practically inert mineral materials, which, when surrounded and bonded together by an active binder, form the rock. This rock is denoted by the general term concrete.
Aggregates have three principal functions in the concrete: they provide a relatively cheap filler for the concreting material, or binder; they provide a mass of particles which are suitable for resisting the ac-tion of applied loads of abrasion, or percolation of moisture through the mass, and of climate factors; they reduce volume changes resulting from the action of the setting and hardening of the concrete mass.
All aggregates, both natural and artificial, which have sufficient strength and resistance to weather-ing, and which do not contain harmful impurities may be used for making concrete.
As aggregates such natural materials as sand, pebbles, broken stone, broken brick, gravel, slag, cin-der, pumice and others can be used.
4. Задайте вопросы к следующим предложениям
1. Concrete is an artificial stone.
2. It has many valuable properties.
3. Concrete can be poured into moulds.
4. It resists fire.
5. Concrete is used for skeleton structures.
6. Aggregates have three functions
5. Выпишите из текста предложения с модальными глаголами.
6. Заполните пропуски соответствующими модальными глаголами
1. They... not do this work themselves.
2 You...take my dictionary.
3 Why... I give you my money?
4 She ..not speak any foreign language.
5 He...to help them, they need his help.
7. Выпишите из предложения все глаголы во времени Present Simple.
It sets under water, can be poured into moulds so as to get almost any desirable form, and together with steel in reinforced details it has very high strength, and also resists fire.