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020301 > 020301e Finishinh And Curing Of Concrete > Flashcards

020301e Finishinh And Curing Of Concrete Flashcards

1
Q

Bronze and magnesium tools are used to bring moisture and fine aggregates to the surface. T or F

A

T

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2
Q

Steel tools are used to bring moisture and fine aggregates to the surface. T or F

A

F. Steel tools are used in the final finish operation when a smooth polished surface is desired.

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3
Q

What is a disadvantage to using wooden floats?

A

Tend to stick to air-entrained concrete.

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4
Q

Do not allow the placement of concrete to precede the screening operation by more than ___ m to ___ m.

A

1.8, 2.4

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5
Q

A slab should be bull floated perpendicular to the direction that it was screeded. T or F

A

T

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6
Q

When must bull floating be completed?

A

Before the accumulation of bleed water on the surface begins.

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7
Q

What may be caused by bull floating a concrete surface with bleed water on it?

A

Dusting or scaling of the surface

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8
Q

Why should you never add cement or fine aggregate to absorb excess bleed water?

A

It will affect the strength and durability of the surface finish.

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9
Q

What is needed to prevent the surface of exterior slabs from forming a crust on hot windy days?

A

Windscreen

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10
Q

Your footprint should leave an indentation ____ mm deep and stiff enough that the rotating blades of the machine will not throw cement paste when attaching float pads to power trowels before floating.

A

3 mm

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11
Q

Each successive trowelling produces a more dense and polished surface. T or F

A

T

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12
Q

Residential concrete floors, garage slabs and slabs covered with resilient flooring or carpeting usually only require two trowelling. T or F

A

T

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13
Q

___ trowellings are recommended for light industrial uses.

A

3

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14
Q

When is concrete usually ready for trowelling?

A

Once the sheen from the moisture brought to the surface during floating has disappeared.

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15
Q

What may be caused by impulsive or excessive trowelling?

A

Unsound, non-durable surface with defects that may cause dusting, scaling or crazing.

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16
Q

Never trowel concrete before the surface moisture has evaporated. T or F

A

T

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17
Q

What may be caused by sprinkling the concrete surface with water when power trowelling?

A

Burn marks on the surface.

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18
Q

How should a garden take be used to level concrete and what will happen if it is used incorrectly?

A

Tines up. If used incorrectly, the long times will segregate the concrete aggregates.

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19
Q

What is a strike-off board used for?

A

To level and bring the concrete surface to the correct elevation.

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20
Q

What tools are used to embed the large aggregates and bring mortar to the surface?

A

Bullfloats and darbies

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21
Q

What type of floats are used on air-entrained concrete and why?

A

Magnesium or aluminum because wood floats may adhere to air-entrained concrete.

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22
Q

How can you identify whether a tool is a magnesium float or s steel trowel by comparing their handles?

A 
Floats = Closed handles 
Trowel = Open handles
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23
Q

What tool is used to cut grooves into fresh concrete to help control where cracking will occur?

A

Jointer/divider

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24
Q

Describe a power trowel.

A

A gas powered machine with 4 adjustable blades.

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25
Q

What type of concrete broom is used to put a light texture on concrete surfaces?

A

Horsehair

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26
Q

What are the 3 steps used to level concrete when placing it

A
  1. Screed
  2. Bull float
  3. Floating
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27
Q

Why and when is bull floating done?

A

Immediately after screeding, before bleed water collects on surface.

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28
Q

Should be bullfloated perpendicular to the direction it was screeded. T or F

A

T

29
Q

What are the 4 reasons for floating concrete slabs?

A
  1. Embed larger aggregates
  2. Cut high spots, fill low spots.
  3. Compact the mortar at the surface, sealing it for troweling
  4. Work in hardeners.
30
Q

How can you tell that concrete has set enough to be floated?

A

When bleed water has evaporated leaving a dull surface colour and the concrete has developed sufficient strength that a footprint will leave an imprint about 6 mm deep.

31
Q

What is used to reduce the amount of time needed to float a large slab?

A

Power trowels equipped with float pads.

32
Q

What effect does troweling have on the concrete finish?

A

Trowelling compacts, densifies and hardens the concrete surface making it smoother and stronger.

33
Q

In what direction should concrete be broomed to produce a non-slip surface?

A

Perpendicular to traffic flow.

34
Q

List five types of hardeners.

A
  1. Non-metallic hardeners
  2. Metallic hardeners
  3. Coloured hardeners
  4. Natural aggregates
  5. Aluminium oxide non-slip grains
35
Q

What is the main hardening ingredient in metallic hardeners?

A

Ferrous metal particles

36
Q

What are the three ingredients of natural aggregate hardeners?

A
  1. Hard, wear-resistant aggregate with a maximum size of 10 to 12 mm
  2. 3 mm finely crushed aggregate
  3. Type 10 Portland Cement
37
Q

When are aluminum oxide particles placed to produce a non-slip surface?

A

After the concrete has been troweled once.

38
Q

Why are concrete toppings used?

A

To give surface trueness and high-strength abrasive resistance.

39
Q

What are the advantages of applying sealer to concrete?

A

Reduce absorption and penetration of harmful substances into hardened concrete.
Reduce freeze-thaw damage of the concrete.
Reduce the corrosion of reinforcing steel caused by acids, water penetrations, de-overs and carbon dioxide and makes the surface easier to clean.
Protects from dusting.

40
Q

What prevents overlays and toppings from pulling away from existing concrete as they shrink?

A

Bonding agents

41
Q

Describe concrete stamps.

A

Produce interlocking patterns and are made of steel, aluminum or plastic. Consist of a small platform with bits (ridges) and an upright centre post.

42
Q

What is used with concrete stamps to give rounded edges to the pattern?

A

A polyethylene sheet between the concrete and the stamping pad.

43
Q

When are concrete stencils placed?

A

After the concrete has been placed, screeded and bullfloated

44
Q

When stencilling concrete, how should you keep from colouring the grout lines?

A

After the stencil has been embedded, colour the concrete with a dry shake coloured hardener that tints only the surface and leaves the natural concrete colour where the stencil has been embedded.

45
Q

The releasing agent prevents concrete from sticking to the texturing mats. What else can it be used for?

A

Introduce a contrasting colour to give a more authentic appearance.

46
Q

What kind of surface is produced by spreading and embedding rock salt?

A

A pitted one.

47
Q

List 4 methods of exposing concrete aggregates.

A
  1. Waterwashing and brushing
  2. Sandblasting
  3. Acid etching
  4. Grinding and polishing
48
Q

When should you start to water wash and brush concrete?

A

After the concrete has set up enough to bear the weight of a person on kneeboarding, with no indentation.

49
Q

When should concrete be sandblasted?

A

72 hours after placement

50
Q

What are used to create patterns and designs when sandblasting?

A

Templates

51
Q

Why is curing essential for good concrete?

A

The water-tightness, durability, strength and appearance of concrete depend on it.

52
Q

What is the primary purpose of curing?

A

To minimize loss of moisture

53
Q

Initial curing conditions require concrete to be maintained at ______ and kept ______ for a minimum of ______

A

20 Celsius (70 deg F)
Thoroughly moist
3 days

54
Q

In concrete is improperly cured, it’s strength may be reduced by up to _____ %.

A

50%

55
Q

When should curing begin?

A

Immediately following the final finishing step

56
Q

What are the two reasons of placing a polyethylene barrier on the ground before placing reinforcement?

A
  1. To prevent dry soils from absorbing moisture our if the concrete mix.
  2. To provide a slips her that reduces subgrade drag
57
Q

List 7 methods of curing concrete.

A

Wet curing, wet burlap, spray or fogging, ponding, waterproof paper cover, poly cover, liquid membrane curing

58
Q

Why are different coloured polyethylene sheets used?

A

White sheets are used in hot weather to reflect heat to help keep concrete temps cooler and black sheets are used in cool weather to absorb heat.

59
Q

Why does polyethylene sometimes leaves a blotchy or mottled surface?

A

Water vapour condenses under wrinkles in the film, forming puddles that cause discolouration of the concrete.

60
Q

What type of curing allows traffic and work to continue on the slab as it cures?

A

Liquid membrane cure

61
Q

What type of defect shows up on the surface of concrete slabs if they rapidly dry out?

A

Plastic cracks caused by shrinkage.

62
Q

What is done to prevent the concrete surface from drying out too quickly in hot windy conditions?

A

Apply moisture by fog ponding without letting water puddle as finishing continues.

63
Q

What is the best type of curing to use in hot weather?

A

A water type, where the surface is kept wet to prevent evaporation and to cool the concrete.

64
Q

When the temp goes below ______ special measures must be taken to ensure that _____ does not slow down or stop.

A

5 degrees C

Hydration

65
Q

What type of heater will cause the surface to dust?

A

An open flame (direct fires) heater

66
Q

Heaters should be used when air temps are below 0 C (32F) t or f

A

T

67
Q

In cold weather besides using a heater to keep the concrete warm, what should be done for proper curing?

A

Moisten the surface of the concrete. Heated air is low in humidity

68
Q

Tests show that improper curing of cement can reduce the expected strength by up to __?

A

50 percent woah

020301 (11 decks)

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