Complete the sentences by filling in the correct word that fits a statement (gap fill). Choose the appropriate words from the word bank given below
A. properties B. cost-effective C. energy D. rebar
E. concrete F.stringentG. consolidation H. formwork
I. transferred J. treatment K. thickness L. particles
1. If the concrete is to be reinforced, the steel …… must already be in place.
2. Concrete can be …… in buckets by a crane or by wheelbarrow.
3. Concrete that is to be pumped has more …… requirements for workability.
4. Larger aggregate …… will tend to be driven downward.
5. Underconsolidation is more common, resulting in less-than optimal …….
6. The two most common methods of …… are vibration and roller compacting.
7. Vibration is a mechanical process that transfers pulses of shear …… to the concrete.
8. There is growing use of self-consolidating …… which flows freely.
9. Roller compaction is a simpler and more …… technique that is suitable for roads and very large mass concrete structures.
10. Finishing refers to any final …… of the concrete surface after it has been consolidated.
UNIT 5 The Concrete Construction Process (Part III)
Read, translate the following text and be ready to fulfil the tests:
Floating and troweling
Floating and troweling is a process of compacting and smoothing the surface which is performed as the concrete is starting to harden. This would be standard procedure for driveways and sidewalks. After concrete has hardened, mechanical finishing can be used to roughen the surface to make it less slippery or to polish the surface as a decorative step to bring out the beauty of a special aggregate such as marble chips.
A recently developed process, which is growing in popularity, involves the use of concrete dyes and surface molds to emulate the appearance of bricks, decorative pavers, or even ceramic tile. When done properly this type of decorative concrete is almost indistinguishable from the real thing.
Curing
Once concrete has been placed and consolidated it must be allowed to cure properly to develop good final properties. As the concrete hardens and gains strength it becomes less and less vulnerable, so the critical time period is the first hours and days after it is placed. Proper curing of concrete generally comes down to two factors, keeping it moist and keeping it supported. Hydration of cement, as the word itself implies, involves reaction with water. To cure properly, the cement paste must be fully saturated with water. If the relative humidity level inside the concrete drops to near 90%, the hydration reactions will slow, and by 80% they will stop altogether. This will not only prevent the concrete from gaining its full strength, but it will also generate internal stresses that can cause cracking.
To keep concrete moist, it can be covered with plastic or damp fabric to prevent evaporation, or sprayed periodically with water. Spraying is particularly helpful, because the original mix water is not enough for the cement to hydrate fully. The additional water will not penetrate through a thick concrete structure, but it will help create a stronger surface layer. Pools of water should not be allowed to form on the surface, however, as this will leach and degrade the concrete underneath.
When concrete is placed using formwork, there is generally a desire to remove the formwork as quickly as possible to continue the construction process. However, if this is done too soon, the fresh concrete will deform under its own weight. This will lead to a loss of dimensional tolerances, cracking, or even a complete collapse. Similar problems occur if loads are applied to the surface of a floor or slab too early.
The weather plays an important role in the curing process. Hot windy weather leads to rapid evaporation and thus particular care must be taken to keep the concrete moist. Cold weather causes the concrete to harden much more slowly than hot weather. This delays the construction process, but leads to better concrete in the long run, because the hydration products develop differently at different temperatures. If fresh concrete freezes, however, it will likely be destroyed beyond repair.
Read and memorize the active vocabulary to the text:
Active Vocabulary
1. floating (здесь) сглаживание
2. troweling затирка
3. smoothing сглаживание
4. to roughen делать шероховатым
5. to emulate подражать
6. indistinguishable неразличимый
7. to cure исправлять; затвердевать (о бетоне)
8. vulnerable уязвимый
9. humidity влажность
10. cracking растрескивание
11. evaporation испарение
12. penetrate просачиваться, проникать
13. leach выщелачивать
14. dimensional пространственный, размерный
15. tolerance допустимое отклонение, допуск
16. slab плита
17. moist влажный
18. to cause вызывать
19. to harden затвердевать
20. to delay задерживать, препятствовать
21. to destroy разрушать
22. repair ремонт, восстановление
CONTROL TESTS
TEST I
Decide whether these statements are true or false:
1. a). Floating and troweling is a process of roughening the surface.
b). Floating and troweling is a process of curingthe surface.
c). Floating and troweling is a process of compacting and smoothing the surface.
2. a). Once concrete has been placed and consolidated it must be compacted.
b). Once concrete has been placed and consolidated it must be allowed to cure properly.
c). Once concrete has been placed and consolidated it must be mechanically finished.
3. a). As the concrete hardens and gains strength it becomes less vulnerable.
b). As the concrete hardens and gains strength, this will generate internal stresses.
c). As the concrete hardens and gains strength, pools of water should be allowed to form on the surface.
4. a). Cold weather causes the concrete to evaporate rapidly.
b). Cold weather causes the concrete being destroyed beyond repair.
c). Cold weather causes the concrete to harden much more slowly than hot weather.
5. a). Proper curing of concrete generally comes down to two factors, evaporation andsmoothing.
b). Proper curing of concrete generally comes down to two factors, keeping it moist and keeping it supported.
c). Proper curing of concrete generally comes down to two factors, holding to dimensional tolerances and avoiding cracking.
TEST II
Match words in columns A and B (synonym match):
A B
1. driveway a). bending b). track
c). mold d). density
2. appearance a). depth b). technique
c). exterior d). growth
3. slippery a). rigid b). equal
c). strong d). sliding
4. dye a). paint b). strain
c). curve d). size
5. to saturate a). to distinguish b). to support
c). to sate d). to found
6. to spray a). to waste b). to perfuse
c). to measure d). to transfer
7. additional a). reliable b). harmful
c). vertical d). extra
8. to remove a). to delete b). to mount
c). to level d). to depend
9. to cause a). to gather b). to determine
c). induce d). to place
10. repair a). purpose b). precision
c). variation d). restoration
TEST III
Select the best possible answer out of the choices from the list to the statements (multiple choice):
1. After concrete has hardened, … .
a. it must be allowed to cure properly.
b. it must be fully saturated with water.
c. mechanical finishing can be used to roughen the surface.
d. it must be sprayed periodically with water.
2.If the relative humidity level inside the concrete drops to near 90%, … .
a. it can cause cracking.
b.the hydration reactions will slow.
c. it becomes less vulnerable.
d.it will likely be destroyed beyond repair.
3. To keep fresh and young concrete moist, … .
a. it should be sprayed once with water.
b. floating and troweling must be implemented.
c. mechanical finishing can be used.
d. it can be covered with plastic or damp fabric to prevent evaporation.
4. To cure properly, the cement paste … .
a. should be placed using formwork.
b. must be placed and consolidated as quickly as possible.
c.must be fully saturated with water.
d. should not be sprayed with water.
5.If fresh concrete freezes, … .
a. it will generate internal stresses that can cause cracking.
b.it will help create a stronger surface layer.
c. it will prevent the concrete from gaining its full strength.
d. it will likely be destroyed beyond repair.
TEST IV