Текст A

Building materials of the past were wood and masonry - brick, stone, or tile, and similar materials. The builders bound the layers together with mortar or some other binder. They sometimes used iron rods to strengthen their buildings. The columns of the Parthenon in Athens, for example, have holes in them for iron bars that have now rusted away. The Romans used natural cement that they made from volcanic ash.

Steel and cement, the two most important building materials now, appeared in the nineteenth century. People had been producing steel, an alloy of iron and an amount of carbon, up to that time by a difficult process that limited its use. After the invention of the Bessemer process steel was available in large quantities.

The important advantage of steel is its tensile strength; that is, it does not lose its strength when it is under a calculated degree of tension - a force which pulls materials apart. New alloys have further increased the strength of steel and eliminated some of its problems, such as fatigue, which is a tendency for it to weaken as a result of constant changes in stress.

Modern cement, which we call Portland cement, appeared in 1824. It is a mixture of limestone and clay. Builders mix it with sand, aggregate (stones, crushed rock, or gravel), and water to make concrete. Different proportions of these materials produce concrete with different strength and weight. Concrete is very versatile; builders can pour, pump, or spray it into all kinds of shapes. And while steel has great tensile strength, concrete has great strength under compression. Thus, the two building materials complement each other.

Notes:

Athens n. ['xTqnz] Афины

Bessemer process n. ['besImq ֽprqVses] бессемеровский процесс

complement v. дополнять

invention n. изобретение

Parthenon n. ['pRTinqn] Парфенон

pump v. качать, закачивать (насосом)

Roman n. римлянин

volcanic ash n. вулканический пепел

Ответьте на вопросы к тексту.

1. What were the main building materials of the past?

2. What did the builders use to bind the layers together?

3. Who used iron rods to strengthen their buildings?

4. Which columns have holes for iron bars?

5. Who used natural cement?

6. When did the two most important building materials appear?

7. When was steel available in large quantities?

8. What is the important advantage of steel?

9. What has increased the strength of steel?

10. When was Portland cement invented?

11. What is Portland cement?

12. What do builders do to make concrete?

13. What makes concrete a versatile building material?

14. Why do concrete and steel complement each other?

Date: 2016-02-19; view: 511; Нарушение авторских прав