A little history on the subject

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The Assyrians and Babylonians used clay as the bonding sub­stance. The Egyptians used lime and gypsum cement. An analysis of ancient Egyptian pyramids has shown that concrete was employed in their construction.

Roman architects invented Roman concrete and used it in buildings where it could stand on its own and support a great deal of weight. The first use of concrete by the Romans was sometime after 273 ВС. Ancient Roman concrete was a mixture of lime mortar, pozzolana [2], water, and stones. The ancient builders placed this mixture in wooden frames where it hardened and bonded to a facing of stones or (more frequently) bricks. When the framework was removed, the new wall with a rough surface was very strong. This surface could be smoothed and faced with attractive stucco or thin panels of marble or other co­loured stones. Concrete construction proved to be more flexible and less costly than building solid stone buildings. The materials were readily available and not difficult to transport. The wooden frames could be used more than once, allowing builders to work quickly and efficiently.

The widespread use of concrete in many Roman structures has en­sured their survival to the present day. The Baths of Caracalla in Rome are just one example. Many Roman aqueducts and bridges have masonry cladding on a concrete core, as does the dome of the Pan­theon.

In 756, British engineer John Smeaton made the first modern con­crete by adding pebbles as a coarse aggregate and mixing powdered brick into the cement. In 1824, English inventor Joseph Aspdin in­vented the first true artificial cement — Portland cement by burning ground limestone and clay together. The burning process changed the chemical properties of the materials and stronger cement was created, which has remained the dominant cement used in concrete production.

* Pozzolana is a type of volcanic ash used for mortar or for cement that sets under water.

(1 600 п.зн.)

TEXT С

1. Переведите интернациональные слова.

metal, major, structural, profile, specific, section, composition, me­chanical, regulate, corrosion, thermal, expansion, assembly, insula­tion, design, typically.

2. Запомните слова и словосочетания.

structural framework — несущий каркас, каркасная конструкция;

external surface covering — облицовка;

metal alloy — металлический сплав;

structural building material — конструктивный строительный ма­териал;

chemical composition — химический состав;

carbon steel — углеродистая сталь;

high-strength low alloy steel — высокопрочная низколегированная сталь;

quenched steel — закалённая (при быстром охлаждении) сталь;

tempered steel — закалённая/отпущенная сталь;

thermal expansion — тепловое расширение;

structural integrity — конструктивная целостность;

external insulation — внешняя/наружная изоляция;

raw material prices — цены на сырьё.

3. Прочитайте текст и выполните задания.

Building Materials (II)

Metal is used as structural framework for larger buildings such as skyscrapers, or as an external surface covering. There are many types of metals used for building. Steel is a metal alloy whose major com­ponent is iron, and is the usual choice for metal structural building materials. It is strong, flexible, and if refined and treated well, lasts a long time.

[Structural steel is steel construction material, a profile, formed with a specific shape or cross section and certain standards of chemical composition and mechanical properties. ]⁰Structural steel shape, size, composition, strength, storage, etc., is regulated in most industrialized countries. The standard commonly used structural steels are:

• carbon steels

• high-strength low alloy steels

• corrosion resistant high strength low alloy steels

• quenched and tempered alloy steels.

The properties of steel vary widely, depending on its alloying ele­ments. [Care must be taken to ensure that thermal expansion of struc­tural elements does not damage wall and floor assemblies of a build­ing.]⁰ When heated, steel expands and softens, eventually losing its structural integrity. Given enough energy, it can also melt. Structural steel requires external insulation (fireproofing) in order to prevent the steel from weakening in the event of fire. Heat transfer to the steel can be slowed by the use of fireproofing materials.

[As raw material prices fluctuate, often so does building design.]⁰ During times of lower steel prices, more steel and less concrete is used, and vice versa. However, both materials are typically used to­gether. While both steel structures and reinforced concrete cement structures have their pros and cons, the steel structures have better strength and can be easily dismantled. (1 480 п.зн.)

Дата добавления: 2014-12-29