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  1. Answer the following questions:

1) What is tensile strength of Portland cement in a day and in three days? 2) What is the compressive strength of Portland cement in a day and in three days? 3) What is the initial and final setting time? 4) Is rapid-hardening cement employed in cold weather? 5) What is the composition of Portland blast-furnace cement? 6) Which colour is high alumina cement? 7) What does high alumina cement contain?

  1. Comprehension and Word Study.

  1. Translate into Russian:

Strength, compressive strength, ultimate, ultimate tensile stress, early stages of hydration, more expensive, to pass to a ball mill for thorough incorporation, fine grinding.

  1. Translate into English:

Сравнительная быстрота, первоначальное схватывание, менее подвержен чем, схватываться примерно с той же скоростью, получать прочность очень быстро благодаря химической активности, он требует очень влажных условий выдерживания.

  1. Say whether it is true or false:

1) The initial setting time is less than 50 minutes and the final setting time is more than 30 minutes. 2) The colour of white cement is due to the raw materials used and special precaution taken in its production. 3) White Portland cement is more expensive than ordinary cement. 4) Portland blast-furnace cement is used for ornamental purposes. 5) High alumina cement sets at about the same rate as Portland cement, but gains strength very slowly. 6) High alumina cement requires very wet curing conditions.

4. Complete the following sentences:

1. The initial setting time is not less than five minutes and the final setting time … . 2. The chemical composition and chemical characteristics of white Portland cement are similar to … . 3. Portland blast- furnace cement is a mixture of … . 4. This cement sets at about the same rate as Portland cement, but … . 5. Owing to the chemical activity after hardening, it requires …

  1. Post-reading Activities.

  1. Discuss with your partner the text “Types of Portland Cement”.

  2. Be ready to speak about “Types of Portland Cement”.

  1. Supplementary Reading.

  1. Read and translate the text y, write 10 questions to the text.

White cement

White (nonstaining) cement is made from the raw materials as standard Portland cement, carefully selected, however, for their very low iron oxide content. It is made by the same process as standard Portland cement.

Ordinarily, the low iron oxide content would make a quick-setting cement, but this is overcome by the use of higher content of silica and lower lime content. White Portland cement hardens at a slightly slower rate than standard gray Portland.

Pozzuolana

Pozzuolana is a volcanic clay, or tuff, consisting of clay and gravel and containing approximately 35 per cent of soluble silica, which, when mixed with burned lime and water, bonds with the lime and forms a cement capable of resisting the action of water.

The ancient Romans, who practiced building in the water to a great extent, discovered a material which, when incorporated with lime, either with or without sand, possessed the property of hardening very rapidly, even under water. This was a kind of earth found at Puteoli (the modern Pozzuoli), to which was given “pozzuolana”.

A substance called tarrass (terras or trass) found near Andernach, in the vicinity of the Rhine, possesses the same quality as pozzuolana. It is this material that has been principally used by the Dutch, whose subaqueous structures are equal, if not superior to those of any other nation in Europe.

Various substances such as baked clay and calcined green-stone (an igneous rock), reduced to powder, afford a moderately good materials for water cements (hydraulic cements).

Pozzuolanic materials (natural) include pozzuolana, volcanic ashes and tuffs, basalts, diabases, syenites, gabbros, trasses, etc.

Up to 30 per cent of the cement in Portland cement concrete can be replaced by trass without perceptible loss of strength.

When this amount is added to a normal mixture, the tensile and compressive strength of the concrete as well as impermeability are improved.

LESSON 6

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