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Building Materials > Introduction to Concrete > Flashcards

Introduction to Concrete Flashcards

0
Q

List the four main components of concrete.

A
  1. Fine Aggregates
  2. Coarse Aggregates
  3. Cement Paste (Portland cement)
  4. Water
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1
Q

Concrete has a very high tensile strength.

A) True
B) False

A

False

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2
Q

Concrete sets as the chemical process ________ begins.

A

Hydration.

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3
Q

High early strength Portland cement is known as type __________ cement.

A

3A-air-entraining

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4
Q

The __________ possible size of coarse aggregate should always be used.

A

Largest

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5
Q

A simple test for the mixing water when creating concrete is that the water should be ___________.

A

Potable (drinkable)

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6
Q

In mixing concrete, the ratio of _______ to _______ is the most critical.

A

Water (1) to Concrete (2)

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7
Q

What are the five strengths of concrete?

A
  1. High compressive strength
  2. Good wear resistance
  3. Low porosity
  4. Low Maintenance
  5. Ability to be moulded into any shape
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8
Q

What are the four weaknesses of concrete as a building material?

A
  1. Low tensile strength
  2. Tendency to shrink upon curing
  3. Brittleness
  4. High weight
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9
Q

What is concrete?

A

Concrete is a mix of cement paste and natural rock aggregates.

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10
Q

What is cement paste?

A

Cement pasts is a mix of cement and water that fills the void between every aggregate material and acts as a glue that bonds the ingredients together.

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11
Q

What are the possible legal outcomes if a concrete truck driver is asked to add water to the mix at the site?

A

The driver will record the request for additional water on the delivery ticket and the concrete supplier will not be responsible for any reduced quality.

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12
Q

Concrete is designed to attain its full strength in _____ days.

A

28

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13
Q

The compressive strength of concrete is denoted in ______ in the imperial system and _____ in the metric system.

A

Psi

MPa

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14
Q

The test for consistency of concrete is called the ______ test.

A

Slump

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15
Q

What is Porosity?

A

The ratio of voids in the concrete to the total concrete volume.

16
Q

What is the mix of aggregate by volume in 1:2:3?

A

1 part cement
2 parts sand
3 parts gravel

17
Q

Concrete gains _____ of its strength in the first 3 to 7 days.

A

50%

18
Q

The amount of air-entrained air is usually between ____ and ____ of the volume of the concrete.

A

5% and 8%

19
Q

The test for the consistency of concrete is called the ______ test.

A

Slump

20
Q

In cold climates, the additive ________ must be ordered for all concrete that will be exposed to freeze-thaw cycles.

A

Air-entrainment

21
Q

Concrete that is to be pumped should have _______ coarse aggregate and ______ sand content.

A

Smaller

Higher

22
Q

The maximum time allowed for placement of the concrete from time the water is added is _________.

A

2 hours

23
Q

What personal protective devices should a worker wear when working with concrete?

A

Safety glasses and long pants, rubber boots and gloves.

24
Q

To properly vibrate concrete the vibrator should be:
A) lowered quickly and raised slowly
B) lowered slowly and raised quickly

A

A) lowered quickly and raised slowly

25
Q

What is the major cause of honeycomb?

A

Inadequate vibration can result in trapped air pockets or voids at the surface, called honey combing.

26
Q

What can happen if concrete is vibrated excessively?

A

Excess vibration can cause increased lateral pressure. Can also cause heavy coarse aggregates to sink and leaves a weak, paste-rich layer near the top.

27
Q

To properly cure, fresh concrete needs _______ and _______.

A

Moisture

Heat

28
Q

What can moving concrete horizontally cause when placing?

A

Segregation, separation of the cement paste from the coarse aggregates.

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