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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
what tools used to transfer flexible patters
tamper boards
26
what are 2 required conditions for proper concrete curing?
moisture and favourable temperature
27
what's considered a favourable air temperature for concrete curing ?
15-20 degrees Celsius
28
explain the hydration process
chemical reaction of water and cement
29
list 4 methods of curing concrete
water coating, wet covering, curing compound, mechanical barrier
30
how are chemical hardeners used?
sprayed or sprinkled onto surface and floated In
31
why are some curing compounds coloured?
to show coverage
32
if two coats of curing compound are used, how is the second one applied?
at 90 degrees or perpendicular to the first coat
33
what's the minimum curing time required to allow the concrete to gain 70% of its 28day strength ?
3 days
34
what are 2 purposes of chemical sealants?
durable waterproof finish, improves looks, cleanable surface
35
how are powdered hardeners applied to concrete ?
telecast on & floated or troweled In
36
what type of tools should be used to pry forms loose when stripping?
wood wedges, wood bars
37
why must rustication be removed very carefully ?
to not damage green concrete
38
explain the stripping process for foundation forms.
orderly and safely, remove cleats, 2x4s, walers, ties, sheathing, de-nail, stack lumber
39
explain how-to strip and lift slab tables
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
explain how to strip and lift gang form panels
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
whats the ideal tempurature range for placing concrete ?
15-20 degrees Celsius
42
why should additional water not be added to the concrete when placing concrete in hot weather ?
it weakens the concrete
43
how is the concrete mixture cooled in hot weather
spray aggregate with cold water cool the mix with water
44
what causes "plastic shrinkage cracking"?
rapid water evaporation
45
what's the minimum temperature for curing concrete?
10 degrees celcius internal
46
what's the minimum time that concrete should be cured?
3 days
47
what precautions should be taken when using hot water in the concrete mixture ?
avoid flash set by adding cement last and after scheming mix temperature
48
what is the effect on concrete of using fossil fuel burning heaters in an unventilated enclosure?
CO2 weakens concrete and causes dusting
49
how long should formwork be left in place during cold weather ?
minimum 3 days or untill it reaches a strength of 3.5mpa or greater
50
list 4 problems that can cause formwork to fail
improper stripping, improper rate of placement, improper vibrating, improper bracing
51
how could vibration cause a form to fail?
over vibrating near a stressed tie
52
what can cause a concrete slab on grade to sag and crack?
settling or heaving of sub grade
53
what causes spallimg ?
chipping caused by stripping techniques or stripping too soon
54
what is a white crystalline growth on the surface of concrete called ?
efflorescense
55
how can scaling be prevented
quality concrete, placed and finished correctly, low w:c ratio
56
describe the procedure used to place concrete around bucks in a wall form
place on one side only to prevent air entrapment/ vibrate and have holes drilled into buck
57
what causes efflorescense
salts amd chemicals in water or aggregate
58
what's the maximum aggregate size that should be used when repairing concrete ?
1/2 depth of patch
59
what are advantages of using pre mixed grouts?
contains chemical bonding agents, just add water
60
why must your wet the area to be patched?
to key the patch
61
what's the minimum slump of repair concrete ?
50mm
62
how long should a patched area be allowed to cure?
3 days minimum
63
explain the sack rubbing process
wet the area, rub on sacking, let stand, rub on dry sacking
64
why are metallic aggregates used in some grouts?
so that metal expansion makes up for concrete shrinkage
65
why would non metallic grouts be used?
to avoid rust staining
66
how are liquid grouts used ?
forms and poured in
67
what are the disadvantages of using liquid grouts?
forms required
68
what is cementation?
use of liquid grout In industrial/ commercial projects
69
what safety precautions must be taken with concrete treatments?
read msds
70
what are the environmental concerns associated with concrete treatments?
streams and ground water
71
describe how sealers and hardeners also act as curing compounds
coat surface to stop moisture loss
72
how is an exposed aggregate wall surface created?
uniform coat of retardent painted on the surface, don't slide concrete on surface of treated form, strip after 24hours
73
what's the difference between dampproofing and waterproofing materials?
dampproofing meant to repel moisture and waterproofing is mean to repel hydrostatic pressure
74
how is a suspended concrete slab waterproofed?
membrane roofing
75
what are pigments used for?
colouring concrete or surface

Jays Carpentry Lvl 2 (7 decks)

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