020301e Finishinh And Curing Of Concrete

Question 1

Bronze and magnesium tools are used to bring moisture and fine aggregates to the surface. T or F

Answer 1

T

Question 2

Steel tools are used to bring moisture and fine aggregates to the surface. T or F

Answer 2

F. Steel tools are used in the final finish operation when a smooth polished surface is desired.

Question 3

What is a disadvantage to using wooden floats?

Answer 3

Tend to stick to air-entrained concrete.

Question 4

Do not allow the placement of concrete to precede the screening operation by more than ___ m to ___ m.

Answer 4

1.8, 2.4

Question 5

A slab should be bull floated perpendicular to the direction that it was screeded. T or F

Answer 5

T

Question 6

When must bull floating be completed?

Answer 6

Before the accumulation of bleed water on the surface begins.

Question 7

What may be caused by bull floating a concrete surface with bleed water on it?

Answer 7

Dusting or scaling of the surface

Question 8

Why should you never add cement or fine aggregate to absorb excess bleed water?

Answer 8

It will affect the strength and durability of the surface finish.

Question 9

What is needed to prevent the surface of exterior slabs from forming a crust on hot windy days?

Answer 9

Windscreen

Question 10

Your footprint should leave an indentation ____ mm deep and stiff enough that the rotating blades of the machine will not throw cement paste when attaching float pads to power trowels before floating.

Answer 10

3 mm

Question 11

Each successive trowelling produces a more dense and polished surface. T or F

Answer 11

T

Question 12

Residential concrete floors, garage slabs and slabs covered with resilient flooring or carpeting usually only require two trowelling. T or F

Answer 12

T

Question 13

___ trowellings are recommended for light industrial uses.

Answer 13

3

Question 14

When is concrete usually ready for trowelling?

Answer 14

Once the sheen from the moisture brought to the surface during floating has disappeared.

Question 15

What may be caused by impulsive or excessive trowelling?

Answer 15

Unsound, non-durable surface with defects that may cause dusting, scaling or crazing.

Question 16

Never trowel concrete before the surface moisture has evaporated. T or F

Answer 16

T

Question 17

What may be caused by sprinkling the concrete surface with water when power trowelling?

Answer 17

Burn marks on the surface.

Question 18

How should a garden take be used to level concrete and what will happen if it is used incorrectly?

Answer 18

Tines up. If used incorrectly, the long times will segregate the concrete aggregates.

Question 19

What is a strike-off board used for?

Answer 19

To level and bring the concrete surface to the correct elevation.

Question 20

What tools are used to embed the large aggregates and bring mortar to the surface?

Answer 20

Bullfloats and darbies

Question 21

What type of floats are used on air-entrained concrete and why?

Answer 21

Magnesium or aluminum because wood floats may adhere to air-entrained concrete.

Question 22

How can you identify whether a tool is a magnesium float or s steel trowel by comparing their handles?

Answer 22

Floats = Closed handles 
Trowel = Open handles

Question 23

What tool is used to cut grooves into fresh concrete to help control where cracking will occur?

Answer 23

Jointer/divider

Question 24

Describe a power trowel.

Answer 24

A gas powered machine with 4 adjustable blades.

Question 25

What type of concrete broom is used to put a light texture on concrete surfaces?

Answer 25

Horsehair

Question 26

What are the 3 steps used to level concrete when placing it

Answer 26

1. Screed 2. Bull float 3. Floating

Question 27

Why and when is bull floating done?

Answer 27

Immediately after screeding, before bleed water collects on surface.

Question 28

Should be bullfloated perpendicular to the direction it was screeded. T or F

Answer 28

T

Question 29

What are the 4 reasons for floating concrete slabs?

Answer 29

1. Embed larger aggregates 2. Cut high spots, fill low spots. 3. Compact the mortar at the surface, sealing it for troweling 4. Work in hardeners.

Question 30

How can you tell that concrete has set enough to be floated?

Answer 30

When bleed water has evaporated leaving a dull surface colour and the concrete has developed sufficient strength that a footprint will leave an imprint about 6 mm deep.

Question 31

What is used to reduce the amount of time needed to float a large slab?

Answer 31

Power trowels equipped with float pads.

Question 32

What effect does troweling have on the concrete finish?

Answer 32

Trowelling compacts, densifies and hardens the concrete surface making it smoother and stronger.

Question 33

In what direction should concrete be broomed to produce a non-slip surface?

Answer 33

Perpendicular to traffic flow.

Question 34

List five types of hardeners.

Answer 34

1. Non-metallic hardeners 2. Metallic hardeners 3. Coloured hardeners 4. Natural aggregates 5. Aluminium oxide non-slip grains

Question 35

What is the main hardening ingredient in metallic hardeners?

Answer 35

Ferrous metal particles

Question 36

What are the three ingredients of natural aggregate hardeners?

Answer 36

1. Hard, wear-resistant aggregate with a maximum size of 10 to 12 mm 2. 3 mm finely crushed aggregate 3. Type 10 Portland Cement

Question 37

When are aluminum oxide particles placed to produce a non-slip surface?

Answer 37

After the concrete has been troweled once.

Question 38

Why are concrete toppings used?

Answer 38

To give surface trueness and high-strength abrasive resistance.

Question 39

What are the advantages of applying sealer to concrete?

Answer 39

Reduce absorption and penetration of harmful substances into hardened concrete. Reduce freeze-thaw damage of the concrete. Reduce the corrosion of reinforcing steel caused by acids, water penetrations, de-overs and carbon dioxide and makes the surface easier to clean. Protects from dusting.

Question 40

What prevents overlays and toppings from pulling away from existing concrete as they shrink?

Answer 40

Bonding agents

Question 41

Describe concrete stamps.

Answer 41

Produce interlocking patterns and are made of steel, aluminum or plastic. Consist of a small platform with bits (ridges) and an upright centre post.

Question 42

What is used with concrete stamps to give rounded edges to the pattern?

Answer 42

A polyethylene sheet between the concrete and the stamping pad.

Question 43

When are concrete stencils placed?

Answer 43

After the concrete has been placed, screeded and bullfloated

Question 44

When stencilling concrete, how should you keep from colouring the grout lines?

Answer 44

After the stencil has been embedded, colour the concrete with a dry shake coloured hardener that tints only the surface and leaves the natural concrete colour where the stencil has been embedded.

Question 45

The releasing agent prevents concrete from sticking to the texturing mats. What else can it be used for?

Answer 45

Introduce a contrasting colour to give a more authentic appearance.

Question 46

What kind of surface is produced by spreading and embedding rock salt?

Answer 46

A pitted one.

Question 47

List 4 methods of exposing concrete aggregates.

Answer 47

1. Waterwashing and brushing 2. Sandblasting 3. Acid etching 4. Grinding and polishing

Question 48

When should you start to water wash and brush concrete?

Answer 48

After the concrete has set up enough to bear the weight of a person on kneeboarding, with no indentation.

Question 49

When should concrete be sandblasted?

Answer 49

72 hours after placement

Question 50

What are used to create patterns and designs when sandblasting?

Answer 50

Templates

Question 51

Why is curing essential for good concrete?

Answer 51

The water-tightness, durability, strength and appearance of concrete depend on it.

Question 52

What is the primary purpose of curing?

Answer 52

To minimize loss of moisture

Question 53

Initial curing conditions require concrete to be maintained at ______ and kept ______ for a minimum of ______

Answer 53

20 Celsius (70 deg F) Thoroughly moist 3 days

Question 54

In concrete is improperly cured, it's strength may be reduced by up to _____ %.

Answer 54

50%

Question 55

When should curing begin?

Answer 55

Immediately following the final finishing step

Question 56

What are the two reasons of placing a polyethylene barrier on the ground before placing reinforcement?

Answer 56

1. To prevent dry soils from absorbing moisture our if the concrete mix. 2. To provide a slips her that reduces subgrade drag

Question 57

List 7 methods of curing concrete.

Answer 57

Wet curing, wet burlap, spray or fogging, ponding, waterproof paper cover, poly cover, liquid membrane curing

Question 58

Why are different coloured polyethylene sheets used?

Answer 58

White sheets are used in hot weather to reflect heat to help keep concrete temps cooler and black sheets are used in cool weather to absorb heat.

Question 59

Why does polyethylene sometimes leaves a blotchy or mottled surface?

Answer 59

Water vapour condenses under wrinkles in the film, forming puddles that cause discolouration of the concrete.

Question 60

What type of curing allows traffic and work to continue on the slab as it cures?

Answer 60

Liquid membrane cure

Question 61

What type of defect shows up on the surface of concrete slabs if they rapidly dry out?

Answer 61

Plastic cracks caused by shrinkage.

Question 62

What is done to prevent the concrete surface from drying out too quickly in hot windy conditions?

Answer 62

Apply moisture by fog ponding without letting water puddle as finishing continues.

Question 63

What is the best type of curing to use in hot weather?

Answer 63

A water type, where the surface is kept wet to prevent evaporation and to cool the concrete.

Question 64

When the temp goes below ______ special measures must be taken to ensure that _____ does not slow down or stop.

Answer 64

5 degrees C | Hydration

Question 65

What type of heater will cause the surface to dust?

Answer 65

An open flame (direct fires) heater

Question 66

Heaters should be used when air temps are below 0 C (32F) t or f

Answer 66

T

Question 67

In cold weather besides using a heater to keep the concrete warm, what should be done for proper curing?

Answer 67

Moisten the surface of the concrete. Heated air is low in humidity

Question 68

Tests show that improper curing of cement can reduce the expected strength by up to __?

Answer 68

50 percent woah