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BDCS > CONCRETE > Flashcards

CONCRETE Flashcards

0
Q

What are form ties?

A

Metal wires or rods used to hold opposite sides of the form together and to prevent their collapse

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1
Q

What is the most common material for formwork?

A

Plywood (… With oil, plastic coating, or other non resistant)

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2
Q

What is slip forming?

A

When the form moves as the concrete cures… Forming continuous surfaces such as tunnels and high-rise building cores

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3
Q

How fast does a slip form move?

A

6-12 inches per hr

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4
Q

What are flying forms?

A

Large fabricated sections of formwork that are removed and re-used to form an identical section somewhere else … In big repetitive buildings

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5
Q

Concrete work isn’t perfect… What is the tolerance for columns piers and walls?

A

1/4 inch in 10 ft

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6
Q

Concrete work isn’t perfect… What is the tolerance for slabs on grade vs finish concrete floors?

A

Slab on grade: 1/2 inch in 10
Ft
FF: 1/8 inch in 10 ft

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7
Q

Concrete work isn’t perfect… What is the tolerance for The total height of interior versus exterior columns?

A

Interior : one inch in 100 feet

Corner columns: 1/2 inch in 100 feet

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8
Q

In addition to providing a vapor barrier water problems inside a concrete building can be minimized with…

A

A low water – cement ratio … Plenty of time to cure before interior finishes applied

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9
Q

What is a perm?

A

Passage of 1 grain of vapor per hour through 1 sf of material

… At a pressure differential of 1 inch of mercury between the two sides of the material

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10
Q

What are the two common spacings for welded wire fabric?

A

4 inches or 6 inches

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11
Q

What do rebars sit on?

A

Chairs

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12
Q

There are 5 types of cement. Tell me what they are.

A

Type I - Standard or normal

Type II - modified cement, for a massive structures where heat of hydration needs to be controlled…

Type III - high early strength cement … Quick set

Type IV - Low heat cement… Used in massive structures to minimize cracking

Type V - sulfate – resisting cement… For structure as opposed to water or high alkaline

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13
Q

What is hydration?

A

The chemical hardening of concrete

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14
Q

Why does concrete water need to be potable?

A

Concrete can only drink water without impurities to make sure foreign matter doesn’t interfere with adhesion to the cement paste

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15
Q

Hydration requires what water-cement ratio? Workability requires how much extra?

A

25%… An additional 10% to 15%

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16
Q

What is laitance and why?

A

Chalky substance on the mix… Too much water

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17
Q

What is the common percentage of water to cement by weight?

A

0.35 to 0.40

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18
Q

Aggregates make up what percentage of concrete by volume?

A

70% to 75%

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19
Q

What does an air – entraining agent do?

A

Tiny bubbles increase workability and durability… Also resistance to freezing and thawing

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20
Q

What do accelerators do?

A

Speed up hydration

21
Q

What do plasticizers do?

A

Reduce need for water while maintaining consistency … I.e higher strength concrete

22
Q

What do retarders do?

A

Slow down hydration to lower heat of hydration

23
Q

What does fly ash do?

A

Increases strength, decreases permeability, reduces temperature rise, increases sulfate resistant, and improves workability!

24
Q

What is autoclaved aerated concrete?

A

Precast with added aluminum powder in molds… Less density and therefore cuttable with woodworking tools … Limited structural abilities

25
Q

What is self-consolidating concrete?

A

A super plasticizer takes away need for vibration which means less labor

26
Q

What is carbon fiber concrete?

A

Instead of steel mesh… Epoxy coated carbon fiber is non corrosive and needs less conc coverage. .. Requires smaller foundations and support structures

27
Q

Poured gypsum decks are used for…

A

A very fire-resistant roof

Similar to concrete in that liquid is poured over reinforcing (wire mesh)

You can also buy precast

28
Q

What does the cylinder test measure? … What about core cylinder test?

A

Compressive strength. Tested in lab after different periods of curing time

Core cylinder test is when structure is in place… Core take out then tested

29
Q

Kelly ball test

A

Like the slump test – you see how far a stl ball drops into freshly laid concrete

30
Q

Why is the impact hammer test The only non-destructive way to test concrete strength after hardening?

A

A spring-loaded plunger is snapped against concrete surface and amount of rebound measured

31
Q

K slump test

A

Syringe on concrete – comparable to slump test

32
Q

What does the calcium chloride test measure?

A

Also called the moisture dome test… It measures moisture in concrete… Inexpensive and easy!

33
Q

How does the hygrometer test work?

A

Measures the relative humidity of the atmosphere adjacent to the slab

34
Q

What is the polyethylene sheet test?

A

Seal a sheet of plastic to floor … In 16 hours is there visible moisture?

35
Q

The electrical impedance test measures moisture in concrete by

A

Measuring conductance and capacitance

36
Q

Alkali-silica reaction

A

When high alkalinity dissolves sand and rock in the concrete

37
Q

What does a titration test measure?

A

Alkalinity

38
Q

What is honeycombing?

A

Formation of air pockets within concrete and next to forms

39
Q

Describe scrubbed concrete

A

Aggregate exposed

40
Q

Describe an acid wash finish

A

Brings out full color of the aggregate

41
Q

Describe water jet finish

A

Exposes aggregate

42
Q

How do you strike off concrete?

A

Pull a straight edge over the freshly

Finished concrete slab

43
Q

What does it mean to float a slab?

A

Smoothing a finer cement paste over the coarse aggregate … Giving it a “float finish”

44
Q

How is a bull float different than a standard hand held float?

A

Longer, with longer handle – worker can stand away

45
Q

Hard steel troweled finish creates…

A

A very smooth surface

46
Q

Broom finish creates

A

A rough-textured non-slip surface for outdoor

47
Q

Control joints…

A

Tell the crack where to be

48
Q

Construction joints … How to

Prevent leaks

A

Between two successive pours … You can use a water stop

49
Q

Difference between expansion and isolation joints

A

Both allow entire sections of a concrete structure to move independently. Isolation joints are less complex

BDCS (18 decks)

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