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Jays Carpentry Lvl 2 > G7 > Flashcards

G7 Flashcards

place finish and cure concrete

1
Q

explan when a conveyor is used to transport concrete?

A

onsite, large jobs, protect from weather.

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2
Q

how soon after the mix water is added to the concrete mixture must the concrete be placed in the forms ?

A

maximum 120 minutes

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3
Q

explain tailgate delivery

A

trucks chute to forms

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4
Q

when is a concrete bucket used to place concrete ?

A

when building is more than a few stories high and a cranes more feasible to use

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5
Q

what’re two basic types of concrete pumps?

A

boom ( crane) & line

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6
Q

how does the aggregate size affect concrete placement?

A

large aggregates limit pumping

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7
Q

list 5 guidelines for placing concrete

A

check forms & falsework, uniform lifts, place within 120 min of batching

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8
Q

how should concrete be placed on a sloping surface?

A

start from the bottem work your way up

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9
Q

describe how to reduce the segregation of the aggregate from the cement paste

A

don’t drop through, don’t over vibrate, don’t use wrong rake, don’t slide too far at wrong angle

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10
Q

what’s the max spacing of vibrator insertion points when vibrating a wall?

A

1/2 the radius of influence, 600mm if unknown

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11
Q

how far into a preceding layer of concrete should a vibrator penetrate?

A

6” or 150mm

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12
Q

how can you tell when consolidation is adequate ?

A

bubbles stop, sheen forms

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13
Q

when are external vibrators used?

A

metal forms for precast, 1200mm apart

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14
Q

what stages of finishing is an edger used and why?

A

after bull floating, pushes large aggregate away from surface and form rounds over

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15
Q

what’s the purpose of hand floating or bull floating ?

A

push aggregate down and allow bleed water to escape

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16
Q

why is a divider tool not used to make control joints?

A

the groove is not deep enough

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17
Q

when is the placing of concrete completed ?

A

after floating

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18
Q

why should the bleed water be allowed to evaporate ?

A

to not dilute surface concrete, causing dusting and crazing

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19
Q

explain how a broom finish is created?

A

float, edge, trowel, broom, edge

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20
Q

when are screeds removed from concrete?

A

after strike off

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21
Q

what’s the purpose of a screed

A

elevated guide for strike off

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22
Q

when placing concrete for a slab, what precaution should be taken with the reinforcing steel?

A

keep off ground using chairs or bricks

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23
Q

how is the top of the concrete wall finished

A

remove cleats and floats

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24
Q

what’s the purpose of kneeboards

A

distribute the finishers weight

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25
Q

what tools used to transfer flexible patters

A

tamper boards

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26
Q

what are 2 required conditions for proper concrete curing?

A

moisture and favourable temperature

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27
Q

what’s considered a favourable air temperature for concrete curing ?

A

15-20 degrees Celsius

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28
Q

explain the hydration process

A

chemical reaction of water and cement

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29
Q

list 4 methods of curing concrete

A

water coating, wet covering, curing compound, mechanical barrier

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30
Q

how are chemical hardeners used?

A

sprayed or sprinkled onto surface and floated In

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31
Q

why are some curing compounds coloured?

A

to show coverage

32
Q

if two coats of curing compound are used, how is the second one applied?

A

at 90 degrees or perpendicular to the first coat

33
Q

what’s the minimum curing time required to allow the concrete to gain 70% of its 28day strength ?

A

3 days

34
Q

what are 2 purposes of chemical sealants?

A

durable waterproof finish, improves looks, cleanable surface

35
Q

how are powdered hardeners applied to concrete ?

A

telecast on & floated or troweled In

36
Q

what type of tools should be used to pry forms loose when stripping?

A

wood wedges, wood bars

37
Q

why must rustication be removed very carefully ?

A

to not damage green concrete

38
Q

explain the stripping process for foundation forms.

A

orderly and safely, remove cleats, 2x4s, walers, ties, sheathing, de-nail, stack lumber

39
Q

explain how-to strip and lift slab tables

A

using fall protection, lower jacks onto dollies, attach lines to core, roll out 1/4 way, attach first pair of slings, roll out and attach second pair, detach line from core, hoist out

40
Q

explain how to strip and lift gang form panels

A

using fall protection, partially strip leaving top taper ties in but loose, attach tag lines and crane, tension crane, finish stripping take top taper ties off, clear area

41
Q

whats the ideal tempurature range for placing concrete ?

A

15-20 degrees Celsius

42
Q

why should additional water not be added to the concrete when placing concrete in hot weather ?

A

it weakens the concrete

43
Q

how is the concrete mixture cooled in hot weather

A

spray aggregate with cold water cool the mix with water

44
Q

what causes “plastic shrinkage cracking”?

A

rapid water evaporation

45
Q

what’s the minimum temperature for curing concrete?

A

10 degrees celcius internal

46
Q

what’s the minimum time that concrete should be cured?

A

3 days

47
Q

what precautions should be taken when using hot water in the concrete mixture ?

A

avoid flash set by adding cement last and after scheming mix temperature

48
Q

what is the effect on concrete of using fossil fuel burning heaters in an unventilated enclosure?

A

CO2 weakens concrete and causes dusting

49
Q

how long should formwork be left in place during cold weather ?

A

minimum 3 days or untill it reaches a strength of 3.5mpa or greater

50
Q

list 4 problems that can cause formwork to fail

A

improper stripping, improper rate of placement, improper vibrating, improper bracing

51
Q

how could vibration cause a form to fail?

A

over vibrating near a stressed tie

52
Q

what can cause a concrete slab on grade to sag and crack?

A

settling or heaving of sub grade

53
Q

what causes spallimg ?

A

chipping caused by stripping techniques or stripping too soon

54
Q

what is a white crystalline growth on the surface of concrete called ?

A

efflorescense

55
Q

how can scaling be prevented

A

quality concrete, placed and finished correctly, low w:c ratio

56
Q

describe the procedure used to place concrete around bucks in a wall form

A

place on one side only to prevent air entrapment/ vibrate and have holes drilled into buck

57
Q

what causes efflorescense

A

salts amd chemicals in water or aggregate

58
Q

what’s the maximum aggregate size that should be used when repairing concrete ?

A

1/2 depth of patch

59
Q

what are advantages of using pre mixed grouts?

A

contains chemical bonding agents, just add water

60
Q

why must your wet the area to be patched?

A

to key the patch

61
Q

what’s the minimum slump of repair concrete ?

A

50mm

62
Q

how long should a patched area be allowed to cure?

A

3 days minimum

63
Q

explain the sack rubbing process

A

wet the area, rub on sacking, let stand, rub on dry sacking

64
Q

why are metallic aggregates used in some grouts?

A

so that metal expansion makes up for concrete shrinkage

65
Q

why would non metallic grouts be used?

A

to avoid rust staining

66
Q

how are liquid grouts used ?

A

forms and poured in

67
Q

what are the disadvantages of using liquid grouts?

A

forms required

68
Q

what is cementation?

A

use of liquid grout In industrial/ commercial projects

69
Q

what safety precautions must be taken with concrete treatments?

A

read msds

70
Q

what are the environmental concerns associated with concrete treatments?

A

streams and ground water

71
Q

describe how sealers and hardeners also act as curing compounds

A

coat surface to stop moisture loss

72
Q

how is an exposed aggregate wall surface created?

A

uniform coat of retardent painted on the surface, don’t slide concrete on surface of treated form, strip after 24hours

73
Q

what’s the difference between dampproofing and waterproofing materials?

A

dampproofing meant to repel moisture and waterproofing is mean to repel hydrostatic pressure

74
Q

how is a suspended concrete slab waterproofed?

A

membrane roofing

75
Q

what are pigments used for?

A

colouring concrete or surface

Jays Carpentry Lvl 2 (7 decks)

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