G-7 place and finish concrete Flashcards
at what stages of finishing is an edger used and why
after bull floating , push large aggr away from surface and form and rounds over
why is a divider tool not used to make control joints
not deep enough
what is the purpose of hand floating or bull floating
push aggregate down
when is the placing of concrete completed
after floating
why should the bleed water be allowed to evaporate
ruin water cement ratio if not causes dusting or crazing
explain how a broom finish is created
floated ,broomed horizontally edged , edged and troweled
when are screeds removed from the concrete
after striking off
what is the purpose of a screed
guide for striking off
how is the top of concrete wall finished
cleats removed and floated
what is the purpose of kneeboards
disperse weight
what tool is used to transfer flexible patterns
tamper
what are 5 precautions when finishing concrete with a power trowel
concrete is flat/level
can bear foot pressure
cover area uniformly
bleed water evaporated
allow concrete to harden between passes
how is the movement of a power trowel controlled
push down = right
push up= left
what is a burnished surface
mirror like finish
created by steep angled trowels
what are 2 different types of blades for a power trowels
float and trowel
what are the environmental concerns associated with concrete treatments
streams and ground water
describe how sealers and hardens also act as curing compounds
prevents moisture loss
how is a exposed aggregate wall surface created
chemicals on forms
then washed off
what is the difference between damp proofing and water proofing
moisture resistant
resist hydrostatic pressure
how is a suspended slab water proofed
roofing membrane
what are pigments used for
color
what are the 2 required conditions for proper curing
moisture /temp
what is a favorable temp for placing concrete
15-20
explain the hydration proccess
chemical reaction of water and cement
list 4 methods of curing concrete
water coat
wet covering
curing compound
mechanical barriers
how are chemical hardeners used
sprayed or sprinkled
why are some curing compounds colored
show coverage
If 2 coats of curing compound are used , how is the second one applied
Perpendicular /90 degrees
What is the minimum curing time required to allow the concrete to gain 70% of its 28 day strength
3 days
What are 2 purposes of chemical sealants
Waterproof and improve looks
How are powdered hardeners applied to concrete
after floating and troweling
How is the concrete mixture cooled in hot weather
Superplasticizer or cool water
What causes “plastic shrinking cracking “
Waterloss
What is the effect on concrete of using fossil fuel burning heaters and unvented enclosures?
Dusting /weak layer of concrete
List four problems that can cause a form to fail
Poor bracing, poor placement, poor vibrating bad stripping
How could vibration cause a form failure?
Over vibe equals stress on ties
What causes spalling?
Stripping before 3 1/2 MPA and bad stripping
What is a white crystalline growth on surface of concrete called?
EFFlorences
How can scaling be prevented
Low water, cement ratio, proper placement, quality of concrete
Describe the procedure used to place concrete around bucks in a wall form
Have we poles, if large have access hole for vibe and place on just one side
What is the maximum aggregate size that should be used when repairing con
Half the patch size
What are the advantages of using premixed grout?
Contains chemical bonding agents just add water
Why are the edges of the area to be patched sloped inward
Tequila patch
Why must you wet the area to be patched?
Some moisture won’t be sucked out of the patching mix before hydration is complete
What service repair situations required using forms
Walls and overhead
What is the minimum slump of repair concrete?
50 mm
How long should a patched area be allowed to cure?
Three days
Explain the sack rubbing process
Wet area, rub on stacking dry and let stand rub on dry sacking
