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020301 > 020301d Trans And Placement Of Concrete > Flashcards

020301d Trans And Placement Of Concrete Flashcards

1
Q

Construction joint and cold joint are similar. T or F

A

T

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2
Q

At the outset of any large project, who is employed to determine the exact legal location of the structure?

A

A legal surveyor

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3
Q

A legal surveyor is required to determine the elevation of the foundation or main floor to ensure that it is not placed too high or too low. T or F

A

T

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4
Q

At what stage should the wall form be marked with a pour height?

A

After one side is in place

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5
Q

Why are nails placed along the pour line?

A

To establish the top of pour of the chalk line is covered by fresh concrete.

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6
Q

Why are stakes cut flush with the top of form edges?

A

So the screed can ride on top of the form without hitting the stake.

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7
Q

In what three ways may slope be expressed?

A
  1. Rise to run 2. Grade percent 3. Total slope
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8
Q

What placement method is used for quick and efficient slab placement?

A

Wet screed

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9
Q

Screed chairs support what screed system?

A

Screed rail

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10
Q

What is wet screed?

A

A method by which the fresh concrete is used to establish a screed that can be followed.

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11
Q

How does one reduce the chance of cold joints occurring during wet screening?

A

Limit the size of the pour

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12
Q

Where is an extremely high tolerances expected?

A

Movie studios or ice arenas

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13
Q

What is the name of the type of truck that is loaded with individual ingredients and mixes the concrete while travelling to the job site?

A

Ready mix truck

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14
Q

What is the name of the type of truck that carries all of the ingredients of concrete separately until arrival at the job site where the ingredients are mixed?

A

Mobile batch mixing trucks

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15
Q

Concrete should be placed within ____ hrs after the water is added.

A

2 hours

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16
Q

Moving concrete horizontally can cause segregation. T or F

A

T.

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17
Q

Concrete should always be case against previously cast portions of fresh concrete and consolidated together in order to prevent a cold joint from forming. T or F

A

T

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18
Q

What is a cold joint?

A

A cold joint is formed when fresh concrete is placed against previously placed concrete that has begun to set and the two are not properly combined together.

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19
Q

The placement of concrete for walls should be done in shallow, horizontal layers or lifts. T or F

A

T

20
Q

Where should the placement of concrete start for stairs or step footings?

A

At the bottom and work upwards.

21
Q

Why is a drop chute recommended for concrete placement in columns?

A

To prevent concrete from splattering high on the formwork and drying our resulting in a shitty architectural quality.

To reduce segregation of the plastic concrete.

22
Q

If concrete is allowed to free fall more than 1.5 metres, especially through layers of rebar, what may happen?

A

The aggregate can segregate resulting in increased lateral pressure on the forms.

23
Q

Should columns and the supported slab be poured at the same time?

A

No. Due to shrinkage of the column.

24
Q

For underwater placement of concrete what should be used?

A

A tremie system of pipes which are fitted with a hopper at the top and a valve at the bottom that allows the flow to be stopped

25
Q

What is consolidation in regards to concrete?

A

Consolidation is to allow the concrete to flow to all spaces within the formwork while releasing entrapped air (voids or air pockets) in the concrete that have resulted from placement.

26
Q

Rodding or spading are considered acceptable methods of consolidating concrete for most construction projects. T or F

A

T

27
Q

Should an immersion vibrator be lowered Quickly or Slowly?

A

Quickly. At least 150 mm into the previously placed lift and withdrawn slowly in an up and down motion.

28
Q

In an immersion vibrator is lowered slowly. What could happen?

A

The upper surface is consolidated and forms a crust that does not allow entrapped air to rise to the surface.

29
Q

When are external vibrators used?

A

When immersion vibrator will not fit or when a high-quality face is desired. Formwork must be attached firmly.

30
Q

Why should excessive vibration be avoided?

A

Causes the heavy coarse aggregates to sink and leaves a weak, paste-rich layer near the top and the coarse aggregate with no cement paste at the bottom.

Also increase lateral pressures on formwork.

31
Q

What may happen if vibration is inadequate?

A

Can result in trapped air pockets or voids at the surface which are called honeycomb.

Large rock pockets could occur which will seriously weaken the structure.

Could form ugly bug holes on the surface of concrete formed by air bubbles.

32
Q

The lower the water/cement ratio, the ______ the concrete strength and durability. This also decreases the hydrostatic pressure.

A

Greater

33
Q

What does a plasticizer do?

A

Increase place ability with a resulting increase in formwork pressure.

34
Q

Expansion joints are usually made from what material?

A

Asphalt-impregnated fibreboard.

35
Q

What are some ways to reduce shrinkage in concrete?

A

Temperature bars, welded wire fabric or expansive cement.

36
Q

Portland cement only accounts for ____ to ____ percent of the volume of concrete.

A

7-15 %

37
Q

What are some raw materials that Portland cement is made from?

A

Limestone, iron, silica, alumina, gypsum.

38
Q

The rule of thumb is to use ___ “ slump for slabs and ____ “ slump for columns or walls.

A

3, 4

39
Q

Why should columns and the supported Slav be poured at different times?

A

Due to the potential shrinkage of the column

40
Q

What is the main purpose of consolidation?

A

Allow the concrete to flow to all spaces with the formwork while releasing entrapped air.

41
Q

What can be caused by excessive consolidation?

A

Cause the heavy coarse aggregates to sink and leaves a weak, paste-rich layer near the top and the coarse aggregate with no cement paste at the bottom (segregation).

Can increase lateral pressure on the formwork.

Loss of entrained air.

Sand streaks.

42
Q

What can be caused by inadequate vibration?

A

Trapped air pockets or voids at the surface (honeycomb).

Rock pockets can be formed.

Won’t coat the formwork completely. (Bug holes)

43
Q

What affects slump?

A

Water/cement ratio and the addition of admixtures such as plasticizers and retarders.

44
Q

What are some methods of controlling shrinkage in concrete slabs?

A

Temperature bars, welded wire fabric or expansive cement.

45
Q

What is the primary cause of concrete shrinkage?

A

The access water added will evaporate and the the shrinking is a result of drying.

020301 (11 decks)

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