G4 - LT #2 - Process of concrete curing

Question 1

What are two required conditions for proper concrete curing?

Answer 1

Moisture & favorable temp.

Question 2

What is considered a favorable air temperature for concrete curing?

Answer 2

15 to 20 degrees and over cast

Question 3

Explain the hydration process

Answer 3

Chemical reaction of water & cement

Question 4

List 4 methods of curing concrete:

Answer 4

1) Water coating
2) Water covering
3) Curing compound
4) Mechanical barrier

Question 5

How are chemical hardeners used?

Answer 5

Sprayed or sprinkled unto surface and floated in

Question 6

Why are some curing compounds colored?

Answer 6

Showing coverage

Question 7

If 2 coats of curing compound are used, how is the second one applied?

Answer 7

90 degrees to the first coat

Question 8

What is the minimum curing time required to allow the concrete to gain 70% of its 28 day strength

Answer 8

3 days

Question 9

What are two purposes of chemical sealants?

Answer 9

Durable water proof finish, improved looks & cleanable surface

Question 10

How are powdered hardeners applied to concrete?

Answer 10

Telecast on & floated or troweled in

Question 11

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

Answer 11

Weakens concrete

Question 12

How is the concrete mixture cooled in hot weather?

Answer 12

1) Refrigerate mix water
2) Spray aggregate w/ cold water

Question 13

What causes plastic shrinkage cracking?

Answer 13

rapid water loss

Question 14

What is the effect on the concrete of using fossil fuel-burning heaters in unvented enclosures?

Answer 14

Co2 weakens concrete & causes dusting

Question 15

What is hydration?

Answer 15

Chemical reaction that takes place when the water reacts with the cement in the concrete mixture

Question 16

What is the process of keeping concrete moist called?

Answer 16

Curing

Question 17

Concrete not cured at all will attain % of strength ?

Answer 17

50 % of 28 day str.

Question 18

Concrete cured 3 days will reach % of str?

Answer 18

70 %

Question 19

Concrete cured for 7 days reaches % of str?

Answer 19

90 %

Question 20

If concrete is moist continuously, it will continue to gain strength, T OR F?

Answer 20

T

Question 21

What happens to a slab that freezes?

Answer 21

It spalls, needs redo

Question 22

When is the damage reduced from freezing for concrete?

Answer 22

Once it reaches 3.5 MPA (500 PSI) damage reduced

Question 23

What form is suspect. to freeze?

Answer 23

Narrow concrete walls 8” or less

Question 24

What is done to warm a mixture when placing in cold temps?

Answer 24

1) Add hot water to the aggregate
2) Cement is added if aggregagte/water is below 38 degrees

Question 25

Cement added to very hot water causes what?

Answer 25

A flash set

Question 26

T or F - The heat from the hydration of the cement will keep massive concrete (more than 8 ft thick) warm enough to resist freezing

Answer 26

True

Question 27

What does an accelerator do in the hydration process?

Answer 27

Speeds up hydration, adding more heat, warming the cocnrete. Increased hydration speeds up the strength gain, reaching 3.5 MPA faster. Used for narrow and thin slabs

Question 28

Adding water to make concrete workable does what?

Answer 28

Makes it unworkable and discardable

Question 29

Excess exposure to carbon dioxide will cause the surface of the concrete to become:

Answer 29

Weak & dusty

Question 30

When the job site temp is over 25 degrees, what happens?

Answer 30

Rapid evaporation of the water in the concrete mixture and the surrounding materials. Water loss accelerates the settling & creates plastic shrinkage cracks

Question 31

What does retarding admixture do?

Answer 31

Lengthens setting time without long term effects on the strength gain of concrete

Question 32

What does super plasticizing admixture do?

Answer 32

Allow extreme slumps to be obtained without increasing the water/cement ratio or decreasing the strength

Question 33

How can you extend the curing process of a concrete form after stripping?

Answer 33

Spray the wall with a curing compound

Question 34

What is the difference between a sealer and a hardener?

Answer 34

Sealer aids in moisture retention and curing while, giving a durable water proof finish Hardener hardens the surface for a durable finish to wear, physical damage and some chemicals

Question 35

What can be added to a new or existing concrete surface to increase the hardness?

Answer 35

Sodium silicate reacts with the free lime in the concrete to form a hard, dustproof surface.