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22. Write an abstract of the chapter, I. E. Express the idea of the chapter in some sentences.

23. Render the text in English.

Древесина относится к весьма распространенному строительно­му материалу, применяемому с глубокой древности. Отличительной особенностью этого материала всегда остается высо­кая прочность и упругость при сравнительно малой плотности, что обеспечивает невысокую массу изготовляемых из него конструкций при относительно большом коэффициенте конструктивного качест­ва. К тому же такие конструкции обладают надежной химической стойкостью в средах, которые агрессивны по отношению к стали и бетону. Имеется ряд и других положительных качеств у древесины как строительного материала: легкость технологической обработки с приданием изделиям практически любых форм; надежная склеива­емость и хорошая гвоздимость; малая теплопроводность.

Следует также отметить достаточно широкое распространение лесных пород для получения качественной деловой древесины, главным образом, пиломатериалов. Немалую пользу приносят и побочные продукты деревопереработки и лесопиления – стружка, дробленка, опилки и др. Их используют в качестве компонентов различных строитель­ных конгломератов – древесностружечных плит, древесноволокни­стых плит, арболита, ксилолита и т. п.

У древесины имеются и серь­езные недостатки: анизотропность, легкая возгораемость, подверженность к загниванию в переменно-влажностных условиях, повышенная гигроскопичность с возможным короблением и разбу­ханием, но они преодолеваются техническими средствами: пропит­кой антисептиками, введением антипиренов, прессованием, склеива­нием тонких элементов и др. Кроме того, возможно создание благоприятных эксплуатационных условий для соответствующих строительных конструкций. Поэтому в России, богатой лесными массивами, древесина всегда была и остается одним из основных строительных материалов, особенно для жилищного строительства. Используют ее при устройстве перекрытий, стен, строительных ферм, полов, дверных и оконных заполнений и др.

Unit 2

1. In pairs answer the following questions:

  • Do you know any valuable properties of concrete?

  • Why is concrete more fit for foundation?

2. Write phonetic symbols for the following words, pay attention to their correct pronunciation and read them aloud:

abrasion; binder; cement; concrete; consequently; cylindrical; moister; percolation; pour; pumice; reinforce; sufficient; thorough.

3. Learn new words and phrases.

beam

балка, брус, перекладина

binder

зажим, связывающее вещество

gravel

гравий

impurity

грязь, загрязнение, примесь

prestressed concrete

предварительно напряженный бетон

reinforced concrete

железобетон

tensile stress

растягивающее напряжение

to bond

связывать, соединять

to denote

значить, обозначать, различать

to derive (from)

происходить

to resist

сопротивляться, противостоять

to sag

оседать, обвивать, падать

4. Translate the following words and phrases into Russian:

aggregate; compression; cross-sectional area; devoid of; elastic limit; on the other hand; on vast scale; proper consistency; relatively cheap filler; steel bar; tensile stress; to assist in; to result from.

5. Make up your own sentences using the words and phrases from tasks 2-4.

6. Skim the text and say what the general idea of the text is.

7. When skimming divide the text into parts.

Concrete is perhaps the most widely spread building material used nowadays. Concrete is an artificial stone, made by thorough mixing such natural ingredients or aggregates as cement, sand and gravel or broken stone together with sufficient water to produce a mixture of the 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 concrete it has very high strength, and also resists fire. Prestressed concrete is most widely used at present while prefabricated blocks are employed on vast scale for skeleton structures.

Aggregates for concrete

By the simple definition from the dictionary "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 action of applied loads, of abrasion, of 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 weathering, 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, cinder, pumice and others can be used.

Prestressed concrete

Prestressed concrete is not a new material. Its successful use has been developed rapidly during the last two decades, chiefly because steel of a more suitable character has been produced. Concrete is strong in compression but weak when used for tensile stresses.

If, therefore, we consider a beam made of plain concrete, and spanning a certain distance, it will at once be realized that the beam's own weight will cause the beam to "sag" or bend. This sagging at once puts the lower edge of the beam in tension, and if the cross­ sectional area is small, causes it to break; especially if the span is relatively large.

If, on the other hand, we use a beam of similar cross-section, but incorporate steel bars in the lower portion, the steel will resist the tensile stress derived from the sag of the beam, and thus assist in preventing it from breaking.

In prestressed concrete steel is not used as reinforcement, but as a means of producing a suitable compressive stress in the concrete. Therefore any beam (or member) made of prestressed concrete is permanently under compression, and is consequently devoid of crack under normal loading, or so long as the "elastic limit" is not ex­ceeded.

Prestressed concrete is not only used for beams but is now em­ployed extensively for columns, pipes, and cylindrical water towers, storage tanks, etc.

8. Compare your number of parts with that of your fellow students.

9. Read and translate each part using a dictionary.

10. Underline the sentences that best sum up the main idea of each part and use key words from them to make plan of the text in order to retell it according to your plan.

11. Find Russian equivalents to the following words and phrases in the text:

the most widely spread building material; concrete; an artificial stone; aggregates; cement; gravel; sufficient; the proper consistency; valuable properties; can be poured into moulds; reinforced concrete; high strength; resists fire; prestressed concrete; prefabricated blocks; on vast scale; practically inert mineral materials; bonded together by an ac­tive binder; provide; bind­er; the action of applied loads; abrasion; percolation of moisture; reduce; harmful impurities; pebbles; gravel; slag; cinder; pumice; compression; tensile stresses; a beam; spanning a certain distance; to sag; to bend; the cross­ sectional area; steel bars; derived from the sag of the beam; assist; devoid of crack; loading; is employed for.

12. Match pairs of words having similar meanings.

assist

objective

scale

originate

sag

degree

derive

carefully

denote

dirt

stress

ensure

impurity

support

thoroughly

pressure

sufficient

enough

provide

symbolize

purpose

fall