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ТЕ Х Т В

fiber, gravity, massive, block, optimize, stress, distribute, optimal, press, service, conserve, reconstruction, resource, locally, confuse, term, stucco, contact, stable, asphalt, deposit, minor, competent, con­veyor, separate.

2. Запомните слова и словосочетания.

compressive stress — напряжение на сжатие;

tensile stress — растягивающее напряжение;

concrete delivery truck — машина для доставки бетона;

to reduce weight — уменьшать вес;

fire resistance — огнестойкость, жаростойкость;

to conserve resources —- сберегать ресурсы;

load bearing element — несущий элемент (конструкции);

anhydrous powder substance — безводное порошкообразное ве­ щество:

hydraulic render — гидравлический (затвердевающий в воде) нижний слой штукатурки; particulate material — зернистый материал;

uniform properties — неизменные/постоянные свойства;

specialty aggregate — специализированный заполнитель;

bedrock deposit — месторождение/залежь материковой породы;

earth-moving equipment — оборудование для землеройных работ;

belt conveyor — ленточный конвейер/транспортёр.

3. Прочитайте текст и выполните задания. More details about concrete, cement, and aggregate Part One

[Concrete has relatively high compressive strength, but signifi­cantly lower tensile strength. and as such is usually reinforced with materials that are strong in tension (steel reinforcing bars, steel fibers, glass fiber, or plastic fiber).]⁰ This concrete is then referred to as rein­forced concrete. To minimize air bubbles that would weaken the structure, a vibrator is used to eliminate any air that has been en­trained when the liquid concrete mix is pound around the ironwork.

Mass concrete structures include big buildings, gravity dams, large breakwaters, tornado shelters, etc. and are widely used in mod- ern massive construction. Concrete that is poured all at once in one block does not have weak points where it is 'welded' together. The size of building site is optimized as well, when a ready product is de­livered to the site by special concrete delivery trucks.

Prestressed concrete is a form of reinforced concrete that builds in compressive stresses during construction. It can greatly reduce the weight of beams or slabs by better distributing the stresses in the structure to make optimal use of the reinforcement.]⁰ For example, a horizontal beam will tend to sag down. If the reinforcement along the

bottom of the beam is pressed, it can counteract this: In pre-tensioned concrete, the prestressing is achieved by using steel or polymer ten­dons or bars that are subjected to a tensile force prior to casting, or for post-tensioned concrete, after casting.

Concrete is the safest, most durable and sustainable building ma­terial. It provides superior fire resistance, gains strength over time and has an extremely long service life (with its 100-year service life, concrete conserves resources by reducing the need for reconstruc­tion). Energy requirements for transportation of concrete are low be­cause it is produced locally from local resources, typically manufac­tured within 100 kilometres of the job site. [As a construction materi­al, concrete can be cast in almost any shape desired, and once har­dened. can become a structure (load bearing) element. ]⁰(1 750 п.зн.)

Part Two

The most important use ofcement is the production of mortar and concrete — the bonding of natural or artificial aggregates to form a strong building material that is durable in the face of normal envi­ronmental effects. [Concrete should not be confused with cement be­cause the term cement refers only to the anhydrous powder substance used to bind the aggregate materials of concrete.]⁰ Upon the addition of water and/or additives the cement mixture is referred to as concrete, especially if aggregates have been added.

Modern hydraulic cements began to be developed from the start of the Industrial Revolution (around 1800), driven by three main needs:

• Hydraulic render (stucco) for finishing brick buildings in wet climates.

• Hydraulic mortar for masonry construction of harbour works, etc., in contact with sea water.

• Development of strong concrete.

Construction aggregate, or simply 'aggregate', is a broad category of coarse particulate material used in construction. [Aggregates are used as stable foundations or road/rail base with predictable, uniform

properties, or as a low-cost extender that binds with more expensive cement or asphalt toform concrete.]⁰ Sources for this basic material can be grouped into three main areas:

• mining of mineral aggregate deposits, including sand, gravel, and stone;

• use of waste slag from the manufacture of iron and steel;

• recycling of concrete.

In addition, there are some minor materials that are used as special­ty lightweight aggregates — clay, pumice, perlite, and vermiculite.

Modern blasting methods enabled the development of quarries, which are now used throughout the world, wherever competent be­drock deposits o f aggregate quality exist. Large stone quarry and sand and gravel operations exist near virtually all population centres. [These are capital-intensive operations, utilizing large earth-moving equipment, belt conveyors, and machines specifically designed for crushing and separating various sizes of aggregate.]⁰

(1 700 п.зн.)

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