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Carpentry > G7 > Flashcards

G7 Flashcards

(57 cards)

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1
Q

When is a conveyor used to transport concrete

A

When transporting concrete from an on site batch plant to the point of placement

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2
Q

How soon after the mix water is added to the concrete mixture must the concrete be placed

A

120 mins

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3
Q

Explain tailgate delivery

A

When the concrete is delivered directly to the form work

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4
Q

When is a concrete bucket used to place concrete

A

When moving concrete with a crane

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5
Q

What are two basic types of concrete pumps

A

Line pump

Crane mounted pump

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6
Q

How should concrete be placed on a sloped surface

A

Starting at the bottom of the slope and proceeding upwards

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7
Q

What is the maximum spacing of vibrator insertion points when vibrating a wall

A

1 1/2 times radius of influence…if unknown - 600mm

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8
Q

How can you tell when consolidation is adequate

A

When air bubbles stop rising

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9
Q

When are external vibrators used

A

When steel forms are used

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10
Q

At what stages of finishing is an edger used and why

A

After floating, troweling and broom finish to move aggregate away from the edge of the forms and for decorative purposes

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11
Q

What is the purpose of hand floating/bull floating

A

Pushes aggregate below the surface

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12
Q

Why is a divider tool not used to make control joints

A

Does not cut deep enough

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13
Q

When is the placing of concrete complete

A

When concrete has been placed up to the screed level

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14
Q

Why should bleed water be allowed to evaporate

A

Because it is not needed

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15
Q

Explain how a broom finish is created

A

With a smooth stiff bristle broom

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16
Q

When are screeds removed from the concrete

A

After strike off

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17
Q

What is the purpose of a screed

A

Concrete placement guide and guide for strike off bar

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18
Q

How is the top of a concrete wall finished

A

Float finish

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19
Q

What is the purpose of knee boards

A

Supports workers weight properly

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20
Q

What tool is used to transfer flexible patterns

A

Tamping/stamping tool

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21
Q

What are the two required conditions for proper concrete curing

A

Temperature and hydration

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22
Q

What is considered a favourable air temperature for concrete curing

A

15 - 20 degrees C

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23
Q

Explain the hydration process

Study These Flashcards
A

Chemical reaction that takes place when the water reacts with the cement

24
Q

4 methods of curing concrete

Study These Flashcards
A
  • Water curing
  • Water retaining
  • Mechanical barriers (plastic, paper)
  • Chemical membranes
25
How are chemical hardeners used
Sprayed/rolled onto the surface
26
Why are some curing compounds coloured
So full coverage can be seen
27
If two coats of curing compound are used, how is the second one applied
At right angles to the first application
28
Minimum curing time required to allow the concrete to gain 70% of its 28-day strength
3 days (70%) Not cured (50%) 7 days (90%) Kept moist continually (will continue to gain strength indefinitely)
29
Two purposes of chemical sealants
Durable and waterproof finish
30
How are powdered hardeners applied to concrete
Sprinkled onto the surface
31
Why should additional water not be added to the concrete when placing concrete in hot weather
Weakens concrete - increases the water cement ratio Evaporation rates are extreme in it weather
32
How is concrete cooled in hot weather
Cool aggregate by spraying with water Cool mix with refrigeration
33
Minimum temperature for curing concrete
10 degrees Celsius
34
What pre cautions should be taken when using hot water in the concrete mixture
It will set very fast (flash set)
35
What is the effect on concrete when using fossil-fuel- burning heaters un-ventilated enclosures
Carbon monoxide - can cause the concrete surface to become weak and dusty
36
How long should form work be left in place during cold weather
Once compressive strength reaches 3.5MPa
37
Four problems that can cause the form work to fail
Improper stripping and form removal Inadequate bracing Improper vibration Unstable soil under mudsills Shoring not plumb
38
What can cause a concrete slab on grade to sag and crack
Settling, and or, heaving Improper fill material
39
What causes spalling
Premature removal of forms (around rustication strips and windows bucks especially)
40
How can spalling be prevented
Using quality concrete that is placed and finished correctly
41
What is a white crystalline growth on the surface of concrete called
Efflorescence
42
Describe the procedure used to place concrete around bucks in a wall form
Vibrating well around bucks and or drilling holes to allow air to escape
43
What causes efflorescence
Crystals of dissolved salts that were in the water used to make the concrete
44
What is the maximum aggregate size that should be used when repairing concrete
Half depth of the patch
45
What are the advantages of using pre mixed grout
Can be mixed to liquid consistency and still provide strength
46
Why must you wet the area to be patched
To ensure the old concrete doesn't absorb water from the latching material
47
What surface repairs situation require using forms
Concrete patches
48
What is the minimum slump of repair concrete
50mm
49
How long should a patched area be allowed to cure
3 days
50
Why are metallic aggregates used in some grout
Offsets shrinkage if cementious materials
51
Why would non metallic grouts be used
Does not use iron compounds and does not rust the concrete
52
How are liquid grouts used
For small gaps - mixed thin enough to be pumped or poured - requires formwork
53
What are the disadvantages of using liquid grouts
Small gaps in the form work need to be caulked to keep the grout from escaping
54
What is cementation
The use of liquid grout
55
What safety precautions must be taken with concrete treatments
Some of the chemicals used are dangerous - always refer to the MSDS
56
What are the environmental concerns associated with concrete treatments
Can be hard on the ecology of a stream or the ground water
57
How is a suspended concrete slab water proofed
Torch on

Carpentry (8 decks)

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