Вариант 3

1. Прочтите и переведите текст Concrete (I)

Concrete may be considered an artificial conglomerate of crushed stone, gravel or similar inert material with a mortar which has the capacity of hardening into a rocklike mass. The basic materials for making concrete are cement, aggregate and water. Cement is the most essential material and the most important one for making concrete of high quality. Cement is made of limestone and clay. It is calcined at high temperature and ground up into powder. Depending on the kind and composition of the raw materials different types of cement are obtained. Portland cement, blast furnace cement are suitable for putting up marine structures (structures under water).

Concrete is made by mixing cement, water, sand and gravel in the right amount. The binding agent used is a paste of Portland cement and water, in suitable proportions. When water is added to the cement, hydration takes place. This causes the whole mixture to set and harden, forming a solid mass.

The sand, gravel (or broken stone) are termed "aggregate". As soon as it is thoroughly mixed it is poured into forms. Cement starts hardening one hour after the water has been added and the process of hardening lasts for about twenty-eight days. The process is called concrete curing.

Concrete becomes hard by the chemical combination of cement and water, during which process it is necessary to prevent as far as possible evaporation of the water from the surface of the concrete; this is called "curing", and is accomplished by covering the concrete, as soon as it can be done without damaging the surface, with damp cloths, wet straw, wet sand, etc., kept wet by sprinkling, or by immersing in water.

II. Ответьте на следующий вопрос:

What is concrete curing?

Вариант 4

1. Прочтите и переведите текст Reinforced concrete

Reinforced concrete is a building material that combines advantageously the load-bearing abilities of concrete and of steel, which differ greatly in mechanical properties. Similar to other rock materials concrete operates well in compression, but is brittle and poor in tension. Tensile strength of concrete is equal to 1/15 - 1/10th of compressive strength, so that it is bad practice to use it in units subjected to tensile stresses, since the units must be made very heavy. But steel, which is very strong in tension, is capable of resisting tensile forces that may arise in reinforced concrete units.

Reinforced-concrete items are most advantageous in units subject to bending, when both tensile and compressive stresses take place. Steel resists the former, and concrete, the latter, so that the composite unit successfully withstands the bending loads. In this manner the load resisting abilities of steel and of concrete are combined in a single material – reinforced concrete.

The successful combination in reinforced concrete of two materials with greatly differing properties is based on the following factors: strong bond of concrete with steel reinforcement so that the two materials offer a combined resistance to loads; almost equal thermal expansion coefficients of steel and concrete, this making reinforced concrete a monolithic item; concrete is not only non-aggressive with respect to steel, but even protects it against corrosion.

Depending on the reinforcing technique and the state of reinforcement, distinction is made between common and prestressed reinforced concrete.

II. Ответьте на следующий вопрос:

What are advantages of reinforced concrete?