Cement and concrete

The basis of modern production of elements in concrete is cement powder, one of the most versatile binders. About 950 million tonnes of cement powder is produced each year around the world.

Concretes can vary greatly in their composition but those in general use are: high strength concrete, normal weight concrete, lightweight concrete, aerated concrete, and fibre reinforced concrete. Mostly, Portland cement is used but other cements are used in special circumstances. Concrete may be unreinforced, reinforced with steel or fibres or prestressed. Another important distinction is by method of production between cast-in-place concrete, which is poured into its final position on site, and precast concrete, which is poured and cured in a factory and must then be transported to site. Concrete elements can also be precast on site and lifted into their final position by crane. Methods are available for continuous casting of concrete, both vertically and horizontally.

The basic components of concrete are coarse and fine aggregate, cement powder and water; admixtures are sometimes added in too. Most often the fine aggregate is a sand. The quantities of aggregates, cements or admixtures which are used may vary in particular circumstances. A typical concrete is a two-phase material with 60-75% of coarse and fine aggregate, which is the filler material and 25-40% of cement paste, which is the binder. This paste is hardened and formed from the reaction of water and cement powder. Voids of free water and air occupy between one and ten per cent of the volume of the mix and have a major influence on the strength and other properties of the mix.

Notes:

coarse adj. крупный

fibre reinforced concrete фибробетон

phase n. фаза, этап, стадия

powder n. порошок

reaction n. реакция

Ответьте на вопросы к тексту.

1. What is one of the most versatile binders?

2. What kinds of concrete are there?

3. How can concrete be made stronger?

4. What is “cast-in-place concrete”?

5. What kind of concrete is poured and cured in a factory?

6. Where can precast concrete be made?

7. How can concrete elements be lifted into their final position?

8. What are the basic components of concrete?

9. What is fine aggregate?

10. What makes the concrete paste harden?

11. What does a typical concrete consist of?

12. What influences the strength of the mix?

Date: 2016-02-19; view: 731; Нарушение авторских прав