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Flashcards in Concrete Deck (79)
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1

What are concrete cylinders tests used for?

To estimate concrete strength at a given time

2

When you need concrete to set quickly, what type of concrete should be used to produce high early strength?

Type III

3

What chemical reaction takes place when Portland cement is hardening?

Hydration

4

What is the difference between fine and coarse aggregate?

The coarse stone will not pass through a 1/4" sieve

5

What should be added to concrete in cold weather?

Calcium chloride

6

Which of the following is not a reason to use an admixture?

To increase permeability

7

What is the most noticeable characteristic of air-entrained concrete?

Increased workability

8

What is the effect of adding too much water to a concrete mix?

Higher slump and lower strength

9

Can fly ash be introduced into a concrete mix specifying a minimum cement content?

Yes, if called for by the specifier

10

The maximum delivery time for ready mix concrete is:

90 minutes or 300 revolutions of the mixer drum

11

Mat, raft, or floating foundations are specified when:

The allowable bearing capacity of the soil is very low to great depths

12

What type of forms are used to place concrete by extrusion?

Slip-forms

13

What is the minimal quality plywood that can be used when building concrete forms?

BB

14

What is the best type of nail to use for nailing bracing and forms when the nails must be removed when the pour is completed?

Double headed or duplex nails

15

Which of the following is the most economical wood to use for formwork?

Kiln-dried pine

16

The usual safety factor for new form ties is:

2:1

17

The purpose for form liners is to provide:

Special textures

18

How much does concrete weigh per cubic foot?

150 lbs

19

What is the best way to reduce lateral pressure on concrete forms when placing concrete?

Slower placement

20

When an engineer's specifications for removal of concrete forms is not available, the ACI has recommendations for the length of time concrete should remain in the forms when the aire temperature is above:

50 degrees

21

What is the main reason for steel reinforcement in a concrete member?

To resist tensile forces

22

Placing drawings show details for fabrication and:

Placing of reinforcing steel

23

What are the characteristics of a #5 bar?

625" diameter, .31% area and 1.043 lbx. per LF

24

What do the markings on rebar represent?

Producers mill, bar size, steel type and grade

25

Lowering the top bars or raising the bottom bars by 1/2" more than specified in a 6" concrete slab could reduce it's load carrying capacity by:

Approximately 20%

26

What is the maximum variation of stirrup location in a floor slab?

+ or - 1"

27

Which of the following is not a type of rebar splice?

Bundled

28

What is the minimum length of lap in a lapped splice for reinforcing bars?

12"

29

The most effective waterstops are made of

PVC

30

To what depth should a contraction joint be cut into a concrete slab?

One-fourth the slab thickness