15. Choose a phrase from the list below that has the same meaning as the italicized phrase:

 mortar  depends upon  reinforced concrete  hardens  impurities  binder  construction  exposed to  employed  the density of the concrete

1. Concrete with metal bars in it to make it stronger was recognized as the best material for all types of structures.

2. The strength of plain concrete is directly affected by the quality of the cement, the strength and character of the aggregate, the quantity of cement in a unit volume and the relationship between the mass of the concrete and its volume.

3. In all structures not protected from the weather the reinforcing steel must be carefully and well secured so that it cannot be displaced while concreting.

4. The setting of cement is a chemical change brought about by the addition of water to the cement after which the mixture slowly becomes firm or stiff and increases in strength.

5. Portland cement was first used on a large scale in the process of building of the Thames tunnel in 1828.

6. When cement is mixed with water it forms a mixture used in building for holding bricks and stones together which hardens very firmly.

7. Aggregates are inert mineral materials, which, when surrounded and bonded together by a substance that makes things stick together, form the rock.

8. All aggregates which do not contain harmful substances of a low quality making aggregates less pure may be used for making concrete.

16. Fill in the blanks with the following prepositions or adverbs where necessary:

chiefly; from; rapidly; through; for; on; at; while; widely; in; with; into; under; of; to; with; by; also.

1. Concrete is made … thorough mixing such natural ingredients or aggregates as cement, sand and gravel or broken stone together … sufficient water … produce a mixture … the proper consistency.

2. It sets … water, can be poured … moulds so as to get almost any desirable form, and together … steel … reinforced concrete it has very high strength, and … resists fire.

3. Prestressed concrete is most … used … present … prefabricated blocks are employed … vast scale … skeleton structures.

4. Aggregates can be defined as a mass … practically inert mineral materials, which, when surrounded and bonded together … an ac­tive binder, form the rock.

5. Aggregates have three principal functions … the concrete: they provide a relatively cheap filler … the concreting material, or bind­er; they provide a mass … particles which are suitable … resisting the action … applied loads, … abrasion, … percolation … moisture … the mass, and … climate factors; they reduce volume changes resulting … the action … the setting and hardening … the con­crete mass.

6. The successful use … prestressed concrete use has been developed … during the last two decades.

7. Concrete is strong … compression but weak when used … tensile stresses.

8. Prestressed concrete is not only used … beams but is now em­ployed extensively … columns, pipes, and cylindrical water towers, storage tanks, etc.