Ответьте на вопросы. [Portland cement is a basic ingredient of concrete, mortar, and plaster.]° It is the most common type of cement in general usage

А.

Part Two

[Portland cement is a basic ingredient of concrete, mortar, and plaster.]° It is the most common type of cement in general usage. It consists of a mixture of oxides of calcium, silicon, and aluminium.

Portland cement and similar materials are made by heating limestone (a source of calcium) with clay, and grinding this product (called clinker) with a source of sulfate (most commonly gypsum**).

Fine and coarse aggregates make up the bulk of a concrete mix­ture. [Recycled aggregates (from demolition, construction, and exca­vation waste) are increasingly used as partial replacements of natural aggregates, while a number of manufactured aggregates, including air-cooled blast furnace slag and bottom ash are also permitted.]⁰ De­corative stones, small river stones or crushed glass are sometimes added to the surface of concrete for a decorative finish, popular among landscape designers.

Combining water with a cementitious material forms a cement paste by the process of hydration. The cement paste glues the aggre­gate together, fills voids within it, and allows it to flow more freely.

[Chemical admixtures are materials in the form of powder or flu­ids that are added to the concrete (usually less than 5%) to give it cer­tain characteristics not obtainable with plain concrete mixes.]⁰

* Limestone is a hard sedimentary rock, composed mainly of calcium carbonate or dolomite.

** Gypsum is a soft material occurring in nature as crystals and transparent cleav­able masses called selenite. (1 250 п.зн.)

4. Соедините части предложений (AB), чтобы получить закон­ченное высказывание.

■ Aggregates may usually include...

■ The factors for selecting building materials are...

■ Cement consists of...

■ Recycled aggregates are increasingly used...

■ Concrete is composed of...

■ Cement paste is formed...

■ The most widely used types of concrete extensions are...

в.

■ their physical properties, availability, transportation ease, cost, environmental impacts, etc.

■ as partial replacements of natural aggregates.

■ mass concrete structures, reinforced and precast concrete.

■ cement, aggregate, water, and chemical admixtures.

■ by the process of hydration combining water with a cementi- tious material.

■ sand, natural gravel, and crushed stone.

■ a mixture of oxides of calcium, silicon, and aluminium.

Ø What natural substances have been used to construct buildings since earliest times?

Ø What sources can be all building materials generally catego­rized into?

Ø Whose concern is it to select appropriate materials for building purposes?

Ø How much concrete is produced each year?

Ø What are chemical admixtures added to the concrete for?

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