The Properties of Concrete

Concrete must be hard, strong, durable, dense, non-porous, fire-resisting and economical.

Concrete has proved to be durable when made of good materials, well mixed, and properly cured. Failures can be found in concrete work, but the trouble is usually caused by poor material, faulty foundations, lack of knowledge of the properties of concrete or poor workmanship. For example, some cements will give better results in sea water than others. This fact had to be established by experience and experiments.

It is more difficult to secure durable reinforced concrete than mass concrete. This is due to the reinforcing steel and the additional water required to make the concrete flow around the steel bars. When moisture reaches the steel, it will rust and the expansion caused by the rust will crack the concrete, resulting in an unsightly structure and necessary repairs. In all structures exposed to the weather the reinforcing steel must be carefully placed and well secured so that it cannot be displaced while concreting. No metal should project to the surfaces. Small wires will soon cause rust spots on the surface of the concrete if they are exposed.

Concrete, to be durable, must be made of good materials, uniform in quality, mixed with a minimum amount of water, and properly placed and protected while curing. Concrete exposed to sea water and the rise and fall of water levels, especially in cold climates where ice forms on the structures, requires specials attention in the selection of the cement, aggregates, mixing, placing and curing.

With the use of dense aggregates the proportions which will produce the densest products are generally those which contain the maximum amount of coarse aggregate and still contain enough fine aggregate to produce a smooth surface. With porous aggregates used in the production of light weight units, the amount of material in the mix passing a 50-mesh sieve is generally limited and in addition more of the coarse aggregate is used to produce a unit of less density and lower weight. This is generally desirable for light weight units except where fire resistance or watertightness are important.

The strength of plain concrete depends upon the quality of the cement, the strength and character of the aggregate, the quantity of cement in a unit of volume, and the density of the concrete. Other things being equal the strongest concrete is that containing the largest amount of cement in a given volume of concrete, the strength of the concrete varying directly as the amount of cement. With a given quantity of cement in a unit of volume, the strongest concrete is that in which the aggregates are proportioned so as to give a concrete of the greatest density that is of the greatest weight per unit of volume. The strength of concrete also depends upon the methods used in mixing, upon the care taken in measuring the ingredients, and in mixing and placing the concrete. Concrete exposed to the air hardens more rapidly than protected concrete. The setting of cement is a chemical change brought about by the addition of water to the cement, the strength increasing very rapidly the first few days, after which the mixture slowly hardens and increases in strength.

Concrete has poor elastic and tensional properties, but it is strong in compression. Its tensile strength is only one-tenth of its compressive strength. The compressive strength of plain concrete varies between wide limits, depending upon the cement, the proportions of cement and aggregates, and the methods of mixing, and depositing, and the age.

2. Переведите на русский язык следующие английские словосочетания:

reinforced concrete; fire resistance; unsightly structure; density of the concrete; a minimum amount of water; the strength of concrete; a smooth surface; addition of water; light weight units; tensional properties

3. Найдите в тексте английские эквиваленты следующих словосочетаний:

недостаток знаний; особое внимание; свойства бетона; качество цемента; морская вода; количество цемента; уровень воды; химическое изменение; холодный климат; методы смешивания.

4. Найдите в тексте слова, имеющие общий корень с данными словами. Определите, к какой части речи они относятся, и переведите их на русский язык:

economics; desire; add; resist; care; hard; select; rapid; produce; mix.

5. Задайте к выделенному в тексте предложению все типы вопросов (общий, альтернативный, разделительный, специальный: а) к подлежащему, б) к второстепенному члену предложения):

6. Выполните анализ данных предложений, обратив внимание на следующие грамматические явления: числительные, времена групп Continuous и Perfect активного и пассивного залога; согласование времен; функции глаголов to be, to have; усилительные конструкции; неопределенные местоимения some, any, no и их производные:

1. Concrete has proved to be durable when made of good materials, well mixed, and properly cured. 2. For example, some cement will give better results in sea water than others. 3. No metal should project to the surfaces. 4. Concrete has poor elastic and tensional properties, but it is strong in compression. 5. Its tensile strength is only one-tenth of its compressive strength.

7. Ответьте на вопросы по тексту:

1. What kind of concrete must it be? 2. When has concrete proved to be durable? 3. What is the trouble of concrete work caused by? 4. What concrete requires special attention in the selection of the cement, aggregates, mixing, placing and curing? 5. What does the strength of plain concrete depend upon? 6. What is the strongest concrete? 7. What concrete hardens more rapidly?

8. Составьте аннотацию к тексту (2-3 предложения)

9. Составьте словообразовательный анализ текста

10. Составьте план текста и перескажите текст

Самостоятельная работа №5

1. Прочитайте и переведите текст:

Wood

Wood has been a highly used building material since prehistoric times. Among other highly used construction materials there are concrete, steel, brick, stone, and plastics. They all differ in their properties and in the methods of usage. Construction materials are known to differ in strength, hardness, fire- and corrosion-resistance durability, and, naturally, cost.

Being the oldest building material, wood is also known to be the only naturally growing organic material. Is wood strong? Hardly so, because wood always contains some water which decreases its strength. But after the wood is cut, the water content starts to evaporate and as the water content decreases the strength of the cut wood and its hardness start to increase. It is a well-known fact that the drier is the cut wood the greater is its strength and hardness.

Trees are known to grow naturally, which makes wood a constantly renewable natural resource. Among other advantages of wood there are its low cost, low weight, and high workability. But, as any other construction material, wood has its disadvantages. The main ones are the following – it is not fire-resistant, it easily burns. Besides, it easily decays.

Wood products. Wood used for construction purposes is usually changed into laminated wood or wood panel products. Large structural wooden members are produced by glueing small strips of wood together.

Wood in panel form is more advantageous for many building purposes than boards. Why is it so? First of all, because wood panels are much easier to install than boards. They require much less labour for the process of installation. Besides, swelling and splitting in panels are greatly decreased compared with boards. As to plywood panels, they are made up of thin wooden veneers glued together. It is of great importance to note that when wooden structures are designed the future stresses of their structural members must be predetermined.

Timber. Timber is wood, suitable for building and structural purposes.

Timber belongs to one of the oldest building materials. It has been from ancient times and is still produced from cut wood. Timber has always been highly usable in construction because of its many advantages. To these belong its strength, light weight, cheapness, and high workability. Its other advantage is that it belongs to natural resources and is naturally renewable. It is more so that about a third of the world is still considered to be covered with forests. Besides, timber is resistant to corrosion produced by chemical substances in the modern polluted atmosphere. One more advantage of timber is that it can be used for many construction purposes. But, naturally, timber has disadvantages and the main ones are that it is not fire-resistant and it easily decays; especially if it is not impregnated. Besides, freshly cut timber contains water that may cause great structural defects. Removal of water from timber is a necessary procedure that should take place before timber is used in practice. It increases strength and workability of the material and, of course, its durability.

What is timber mainly used for? Because of its many advantages it is highly used for producing window and floor frames, for flooring and roofing and for other various woodwork. There are over 4000 woods in common use throughout the world. The two main types of timber are hardwoods and softwoods. Of them, hardwoods are popular as materials used for decorative purposes: veneering in furniture and paneling. As to softwoods, they are mainly used for producing window and door frames and other kinds of woodwork. The best and most commonly used softwoods popular for structural work in many countries are redwood, whitewood, pine, red cedar, sequoia, beech and some others. As to the hardwoods, the best known ones include beech, birch, blackwood, chestnut, elm, mahogany, maple, myrtle, oak, rosewood, walnut and some others.

2. Переведите на русский язык следующие английские словосочетания:

corrosion-resistance; fire-resistant; organic material; laminated wood; decrease strength; plywood panels; well-known fact; floor frames; high workability; veneering in furniture.

3. Найдите в тексте английские эквиваленты следующих словосочетаний:

строительный материал; химические вещества; методы использования; легкий вес; природный ресурс; преимущества дерева; строительные цели; устранение воды; процесс установки; декоративные цели.

4. Найдите в тексте слова, имеющие общий корень с данными словами. Определите, к какой части речи они относятся, и переведите их на русский язык:

highly; install; construct; wood; use; nature; hard; fresh; advantage; decorate.

5. Задайте к выделенному в тексте предложению все типы вопросов (общий, альтернативный, разделительный, специальный: а) к подлежащему, б) к второстепенному члену предложения).

6. Выполните анализ данных предложений, обратив внимание на следующие грамматические явления: числительные, времена групп Continuous и Perfect активного и пассивного залога; согласование времен; функции глаголов to be, to have; усилительные конструкции; неопределенные местоимения some, any, no и их производные:

1. Wood has been a highly used building material since prehistoric times. 2. But, as any other construction material, wood has its disadvantages. 3. It has been from ancient times and is still produced from cut wood. 4. Timber has always been highly usable in construction because of its many advantages. 5. Removal of water from timber is a necessary procedure that should take place before timber is used in practice.

7. Ответьте на вопросы по тексту:

1. What are advantages of wood? 2. What are disadvantages of wood? 3. What elements are plywood panels made up of? 4. What is timber produced from? 5. Why is removal of water from timber useful for construction purposes? 6. What are the two main types of timber? 7. How much of the world’s land surface is considered to be covered with forests?

8. Составьте аннотацию к тексту (2-3 предложения)

9. Составьте словообразовательный анализ текста

10. Составьте план текста и перескажите текст

Самостоятельная работа №6

1. Прочитайте и переведите текст: