4. Ask questions to the following sentences in pairs. Use the expressions: I wonder, as far as I know, in fact, it is hard to say, to my mind, I believe, I suppose.

1. Concrete is a dense material composed of cement and aggregate mixed with water. 2. The cement is hardening and thus making the particles of the aggregate adhere close to each other. 3. The concrete is filled into the formwork immediately after mixing. 4. Surplus water weakens strength of the concrete. 5. Curing is the proper time during which the concrete is kept humid.

5. Say whether it is true or false:

1. Concrete is seldom used as a building material in modern construction. 2. Concrete consists of cement used as a binding agent and aggregate. 3. The setting and hardening of concrete are due to chemical reactions between the lime and mixing water. 4. The concrete is filled into the formwork immediately after setting. 5. The formwork is taken away as soon as the concrete has become hard enough.

V. Post-reading activities:

1. Make up a dialogue using the text “Concrete” according to the following steps:

1) definition; 2) composition; 3) hardening; 4) application;

5) factors which influence the quality.

2. Be ready to speak about “Concrete”.

3. Lexical test. Choose the wright translation:

1) application	1) превосходный
2) close	2) близкий
3) fabrication	3) применение
4) immediately	4) влиять
5) influence	5) выбирать
6) remove	6) удалить
7) select	7) немедленно
8) strength	8) изготовление
9) superlative	9) прочность
10) surplus	10) излишек
	11) заполнитель
	12)cхватывание

VI. Supplementary Reading.

1. Read and retell the text: water

It is by the addition of water that concrete is rendered workable and hardenable. The water must be clear. It must not contain any impurities such as oil, particles of bog-earth and peat. The effect of water content is concrete on the strength of concrete is frequently underrated. If the amount of water added is small, not all cement particles can harden. If an excessive quantity of water is added, small voids are left reducing the strength of the concrete.

Water in cement

Every concrete mix requires a certain quantity of water to ensure the thorough hydration of the cement and the necessary workability to permit placing. The strength of concrete with given cement (when fully consolidated) is contingent upon the water cement ratio.

Test conducted to determine the effect of water-cement ratio on compressive strength of concrete shows that a typical Portland cement concrete in a wet mix may attain only 70 per cent of the strength of a dry mix at the age of 1 year at earlier age the difference is more strongly marked. The positive quantity of water required to produce strong concrete is subject to the fol­lowing variable factors; 1) The proportions of the mix; 2) the grading of the fine and coarse aggregates; 3) the type of cement us4d, and the workability desired.

The water is transmitted into the mass from three sources: 1) the sand, 2) the coarse aggregate, 3) the water added to the concrete mixer.

The moisture content of the fine and coarse aggregate is sub­ject to wide variation. Consequently, to produce isotropic con­crete it is necessary to offset the varying quantity of water in the aggregates by adjusting the amount of water added at the mixer.

LESSON 10