G-7 Place and Finish Concrete Flashcards
1
Q
Describe concrete finishing
A
top surfaces of cast in place concrete must be finished to a smooth, uniform surface for appearance and durability
2
Q
Wall finish
A
after concrete has been vibrated into place the surface of top of wall is finished level strip or chamfer strip set elevation of top of wall. then hand float is used to finish
3
Q
Architectural concrete finish
A
- that of which is left exposed to view
- this is final finish of building and must be finished with steel trowel
- wait for bleed water to evaporate and trowel with steel trowel
4
Q
Flatwork finishing
A
- can be finished with simple hand tools or power equipment
- starts when bleed water in evaporated
5
Q
Vibration
A
- slabs must be vibrated like walls or columns
- ## edges must be well vibed to reduce bug holes
6
Q
screeding or striking off
A
- levels the survace of concrete to elevation set by screeds
-
7
Q
floating
A
- after concrete has been placed and screeded level
- the surface is floated
- ## this pushes any large aggregate below the surface of concrete slab
8
Q
Bull float
A
used for large areas very large wooden or metal float with long handle attached
9
Q
Hand floats and kneeboards
A
tops of walls and small concrete slabs can be done with hand float
- if hand floating larger job kneeboards are used
10
Q
wooden hand floats must be made of?
A
- edge grain cedar with pine or furr handle
11
Q
Broom finish
A
- provides non-skid finish and should be used when slipping might be a hazard
- broom should have smooth stiff bristles
- steel trowel is done followed immediately by broom lightly dragged across surface
12
Q
edger
A
used to round corners of the surface of slab .
- done after concrete is floated to remove large aggregates away from forms.
13
Q
Steel trowel
A
12- 16 inches
- longer legnths needed when less pressure is required short is needed hen more pressure is required
14
Q
Fresno
A
15
Q
divider
A
used to create decretive divisions in walkways an patios
- used to create control joints joints
-
16
Q
Stamped concrete
A
uses manufactured stamps that are set into the partially set surface of concrete.
- done after bleed water is evaporated
- surface of slab is covered with fine powdered release agent that is designed to allow the stamps to be removed cleanly from the concrete
17
Q
Power trowel
A
used for finishing concrete slabs
- have four spinning concrete trowel blades that spin clockwise
18
Q
walk behind power trowels
A
- size determined by diameter of circle it makes
- ranges from 24inces to 48 inches in diameter
19
Q
riding power trowels
A
for large projects
- two or three separate trowels are assembled into one
- operator rides on top and is able to control movement and rake of blades
20
Q
Float blade
A
- used for final levelling of concrete surface
- usually 10” wide
- made from thick gauge steel
blades are kept flat for initial pass
second pass kept at 90° (crossover floating)
21
Q
Trowel blades
A
- typically 8” wide
- made from thin steel
- each pass will increase density of the slab surface
22
Q
Using power trowel
A
- make sure concrete is levelled properly
- should support foot pressure before power trowel
- make sure bleed water has evaporated
- move over entire surface evenly
- allow concrete to harden between passes with trowel
23
Q
Curing compounds
A
- membrane - curing compounds consist of chemicals and waxes that are sprayed, brushed or rolled on. protect surface of the concrete from early drying
24
Q
Sealers
A
chemicals that seal the surface of concrete and prevent the formation of dust on a worn concrete surface
25
chemical hardeners
provides a hard-wearing concrete surface and prevent dusting of the concrete
26
Metallic or aggregate hardeners
- used in ares where heavy wear is expected
- (steel mills and factories)
- applied dry to the top of the concrete as it is being finished
27
Bond breakers
- chemicals used to break bond between layers of concrete
| -
28
bonding agents
epoxies and adhesives are used to create a good bond between fresh concrete placed over old concrete
29
Damp proofing
concrete foundations that are below grade should be coated on the outside with a damp proofing agent
30
water proofing
waterproofing membrane applied to foundation walls to resist hydrostatic pressures
31
Pigment
coulering agents may be added during concrete mixing or may be shaken onto surface when slab is being finished
32
Hydration
the chemical reaction that takes place when water reacts with cement. this allows it to harden. must be kept wet so it can get hard.
33
Curing
process of keeping concrete moist.
- concrete not sured at all will only get 50% strength
- cured for three days will get 70%
- cured for 7 days will get to 90%
34
Temperature for curing
keeping concrete warm promotes curing.
prime curing temperature is overcast skies at 15-20°
35
Cold weather concrete
formwork left in place to help concrete cure.
| - once compressive strength reaches 3.5MPa damage caused by freezing is reduced.
36
Accelerators
speed up hydration, which releases more heat warming the concrete.
37
Prep for formwork in cold temperatures
- concrete must not be placed on frozen ground
- all formwork must be free of ice and snow
- cover formwork awaiting concrete
- insulated formwork will increase curing rate and strength
38
Heated enclosures
using heated enclosures concrete can continue as usual. fuel burning heaters must have exhaust vented outside because carbon monoxide causes surfaces of concrete to be weak and dusty
39
Hot weather conditions
when temperatures are above 25°C rapid evaporation of water in concrete occurs. water loss will accelerate setting times and create shrinkage cracks.
40
Preventing rapid evaporation
- moisten sub grade and all formwork
- place and finish smaller sections of concrete then normal
- use fine spray of water to keep surfaces moist during placement
- cover floated slabs with plastic sheeting while waiting to finish them
- apply curing components and membranes immediately after finishing
41
Retarding admixture
added to concrete for pumping and are particularly useful in hot weather. lengthens the setting time of concrete but does not have any effects on the strength gain of concrete
42
Super plasticizing
- developed for placing concrete in very hot temperatures
| - allow extreme slumps to be obtained without increasing the water/cement ratio
43
Curing concrete walls
- wall forming can be left in place for three days
| - spraying walls with curing compound after walls have been stripped will extend curing period
44
Curing flatwork
most efficient way to cure concrete slab is to use curing agent. this is sprayed onto slab after finishing it.b
45
Chemical sealers
- sprayed or rolled onto surfaces
- give concrete a durable waterproof finish
- exterior concrete surfaces sealants will increase freeze thaw resistance
46
Chemical Hardeners
- start a chemical reaction in concrete that hardens the surface and creates a durable finish that is highly resistant to wear, physical damage and some chemicals
- liquids powders or sprays
47
sodium silicate
common hardening agent that is applied to new or existing concrete surfaces to increase hardening
48
Mechanical Hardeners
- increase durability of concretes
- added at the troweling stage
- worked in and bonded to the surface to protect concrete
- metal shavings, plastic particles,
49
formwork failure
- improper stripping and form removal
- inadequate bracing
- improper vibration
- unstable mudsils
- shoring not plumb
- improper concrete placement
- lack of attention
50
Crazing
series of small cracks in surface of concrete. happens due to working the bleed water back into the slab during finishing
51
Dusting
when surface of concrete is weakened
- caused by early age freezing
- adding to much water while placing concrete
- using unvented heaters
- working bleed water back into the surface
52
Preventing dusting
1. maintained designated water/cement ratio
2. do not add water to finishing process. protect the fresh concrete from direct exposure to the sun, rain and freezing
3. vent heateres!!!!
53
Discolouration in concrete
Prevented by :
- clean formwork
- maintaining uniform consistency of the concrete mixture
- using uniform aggregate types and colour
- proper placement of concrete
- adequate vibration
54
Effloresence
white powdery crystal substance that seems to blooms out of cured concrete. dissolved salts in concrete mic
- unattractive but generally harmless
55
Scaling
small pieces of concrete flake off the surface of a concrete slab. scaling is dude to lowered concrete strength at the surface.
56
Spalling
pieces of concrete chipping off the surface around openings or edges
- spalling around rustication strips or window and door bucks is caused by removing forms before concrete s strong enough to resist stripping stresses
57
Honeycomb
occurs at the base of concrete columns when concrete is dropped through reenforcing steel and not vibrated adequately
- can result is rebar being exposed
- no not over vibrate
58
concrete voids
spaces caused by trapped air under window bucks and blockouts.
must vibrate properly around bucks
- drill holes in bottom of bucks to allow air to escape
59
Repair concrete Grout
- concrete mixture that uses only sand and aggregate
| - mixture high in cement content which allows strength to be maintained while being mixed to almost liquid consistency.
60
Mortar
same as grout but cement content is lower. consistency is much stiffer
mortar is used to bond bricks together
61
Concrete (patching)
- small batches of concrete can be used to fix large defects
- water used must be clean
- aggregates must be clean and chosen for size
62
Bonding compounds
used to ensure positive bond between patch and concrete being repaired.
woodglue can be used
63
sacking mix
sacking is a mixture of portland cement and fine aggregates and admixtures.
- used to patch minor defects in concrete like bug holes and honeycomb that can get water in and freeze causing spalling
64
patching procedure
make test batch and test run a patch, check for discolouration and strength
65
preparing patched surfaces
edges of area to be patched should be undercut (cut smooth) to provide a key where new patch concrete is being placed.
66
formwork and patching
sometimes formwork must be left in place when patching occurs to allow to harden properly
67
Overhead paches
patching material must be stiff and must be braced
68
wall patches
usually has opening in top to allow placement of patching material
69
Floor patches
more rebar could be drilled and place to allow patch to take better
70
Presoaking
once surfaces have been swept and vacuumed clean, it should be kept wet for at least two hours to ensure old concrete will not absorb water from patching material
71
Bonding
just prior to patching material, apply bonding material and patch before bonding has a chance to dry
