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Flashcards in Concrete Deck (46):
1

What are Clinkers?

Cement raw materials finely ground and carefully proportioned before heated to temperatures from 2,000 to 3,000 degrees (F) to from hard pellets

2

What is the composition of concrete

Mixture of aggregates and often controlled amounts of entrained air and held together by a hardened paste made from cement and water

3

What is air entrainment

Air entrainment is the intentional creation of tiny air bubbles in concrete.

4

What are the 3 components of concrete

Water
Aggregate: Sand/gravel
(Portland) Cement

5

What is the most commonly used cement in the military

Portland Cement

6

What is the chemical reaction called when water and cement mix?

Hydration

7

What is the optimal temperature for cement hardening

73 degrees

8

What 2 functions does water play in concrete

• Effect hydration
• Improve workability

9

What determines the strength of concrete

ratio of cement to water

10

Does more water or less water strengthen concrete

less water

11

Aggregates make up what total volume of finished cement

60-80%

12

What is the primary purpose of aggregate in cement

To gain economy

13

What are the most common contaminating materials in concrete

dirt, clay, salt

14

What are the rules of thumb for the maximum size aggregates should be in concrete

- The maximum size should not exceed 1/5 the minimum diameter of a wall or similar structure
– Not to exceed 1/3 the slab thickness
– Not to exceed 3⁄4 of the clear space between reinforcing bars

15

What are the 5 types of Portland cement

– Type I (Normal Portland)
– Type II (Modified)
– Type III (High early)
– Type IV (Low heat)
– Type V (Sulfate resistant)

16

What are 3 other cements

• White Portland
• Air Entrained (Type I, II, III)
• Oil Well Cements
• Waterproofed Portland cements
• Plastic cement

17

What does a bag of Portland Cement weigh

– Bags-94 lbs (contains one cu ft of loose
measurement)

18

How many and what are the types of CONCRETE

• Reinforced
• Prestressed
• Precast
• Lightweight

19

What are the benefits of precast concrete

- In dead-loads making savings in
foundations and reinforcement
- Improved thermal properties
- Improved fire resistance
- Savings in transporting and handling pre- cast units on site
- Reduction in formwork and propping

20

What are the disadvantages of concrete

• Low tensile strength
• Expands and contracts
• Shrinks when dry
• Heavy

21

What do construction joints do?

join concrete that is paved at different times

22

Do construction joints allow for movement of concrete members

No

23

What do contraction joints do

control natural cracking from stresses caused by concrete shrinkage, thermal contraction, and moisture.

24

At what angel are transverse contraction joints cut

At a right angle to the pavement centerline and edges.

25

What do isolation joints do

separate the pavement from objects or structures, and allow independent movement of the pavement, object or structure without any connection that could cause damage.

26

Where are isolation joints used

where a pavement joins sidewalks and buildings, and intersects other pavements or bridges.

27

What do expansion joints do

Permit volume change movement of a concrete structure or member.

28

What is the minimum width of an expansion joint

1/4′′ wide

29

1 person can manually mix approximately how much concrete per hour

1 cubic yard

30

Describe the hand mixing sequence of concrete

Three part gravel, then Two part sand (mix dry 3x), then One part Portland cement, and add water

31

Project Volume (PV) = ?

length x width x height x number of pours

32

Loss Factor = ?

if PV 5400 cubic ft (or 200 cubic yards), add 5% to project

33

Loose Volume (LV) = ?

LF x 1.5 (and round up)

34

Equation for calculating cement from Loose Volume (LV)

1/6 x LV = number of bags of cement (rounded up)

35

Equation for calculating sand from Loose Volume (LV)

2/6 x LV = cubic feet (yards) of cement
OR
LV/3 = cubic feet (yards) of cement**

**This may be "funny" math

36

Equation for calculating gravel from Loose Volume (LV)

3/6 x LV = cubic feet (yards) of gravel
OR
LV/2 = cubic feet (yards) of gravel

37

Equation for calculating gallons of water from number of bags of cement

Water (in gals) = number of bags of cement x 8

38

Forms must be what in order to hold concrete properly until it sets

Tight, rigid, and strong

39

What materials are forms usually made of

Wood, metal, earth, fiber

40

What are the elements of wooden forms

Sheathing, batten, yoke, and bracing

41

What does the yoke do in a wooden form

ties the top of sheathing together in column form

42

What is the difference between a vertical keyway and a horizontal keyway

one is vertical and the other is horizontal

43

What is the maximum rate of filling concrete to avoid excessive pressure on form

4 ft per hour

44

How deep does the land under a slab need to be moistened (if plastic isn't being used as a barrier between the slab and the ground)

6 inches

45

Slabs which will support load bearing walls must be what?

Reinforced with rebar

46

True or False: Rebar in slabs must sit above the frost line

False. Must be below frost line