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Flashcards in 10 Concrete Construction Deck (37)
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1

Heat of hydration

During concrete hardening heat is given off by chemical process of hydration.

2

Concrete requires what to properly harden

Hydration with water

3

Concrete can be cured using several techniques

Pounding, sprinkling with water, covering with plastic film, sealing to reduce evaporation

4

Admixture

Ingredients or chemicals added to concrete to change its characteristics

5

Concrete must be cured at certain temperatures:

Between 50-70 degrees, over 100 will not be strong and near freezing with take a while.

6

Concrete can shrink while curing and can harden indefinitely slowly. Optimum time for design strength hardening is how many days

28

7

Types of concrete

Ordinary stone
High early strength
Expansive
Water permeable
Structural light weight
Insulating light weight
Gypsum

8

Concrete is compressive lay strong but weak in tensile strength. Compression strength can vary from

2,500-6,000 psi

9

When tensile strength is needed concrete must be

Reinforced with rebar

10

Mechanical vibrators are used when pouring concrete to ensure

It adheres fully with rebar and there are no air pockets.

11

Instead of an I beam, concrete is often shaped

As a T with rebar at the bottom

12

Pretensioned reinforcing.

Pretensioned concrete. Steel strands are stretched between anchors causing tensile force, concrete poured around it. Tension in steel is released, compressing concrete horizontally- Creates an upward bow in concrete that is flattened when compression forces are applied.

13

Post tensioning

Steel on concrete is tensioned after concrete hardens. Steel covered with grease or tubing to allow them to slide around concrete. Once hard the steel is tightened, compressing the concrete horizontally.

14

Cutting of tensioned concrete is not recommended because

Steel is under tension and may snap back like rubber band. Also cause structural failure

15

Cast in place concrete

Use of forms and wet concrete to form concrete shapes, done at sight

16

The single most important factor determining concrete strength

Water to cement ratio

17

If too much water is used in the concrete mix what happens

It won't be strong enough
Excess moisture will cause spalling during freeze or fire conditions

18

Because large construction can't be cast at on time, concrete needs to be formed in stages. To eliminate structural issues what is done

Rebar overlaps joints to be poured in stages.

19

Common cast in place systems

Flat slab
Slab and beam
Waffle construction

20

Flat slab system

Concrete slab supported by columns. Slab varied form 6-12" columns reinforced with drop panels or mushroom capitals

21

Flat plate

No reinforcements for concrete columns supporting slabs

22

Concrete Slab and beam framing

Slab supported by concrete beam. Lightweight, looks like wood framing on therms of spacing.

23

Waffle construction concrete.

Waffle pattern on bottom of slab. Steel reinforced at bottom of slabs.

24

Precast concrete.

Poured formed, and hardened at off site manufacturing facility, under controlled conditions to be shipped out for use.

25

advantage to precast concrete

Quality control,
Can be sheltered prior to use,
Efficient uniform and consistent

26

Precast concrete can be produced using polystyrene core causing

Improved insulation

27

Disadvantage to precast concrete

Transportation of members limits size and shape and is expensive.

28

Tilt up construction

Concrete wall sections cast laying down then tilted up into position.

29

Precast slabs can be solid or hollow, singe t, or double t. They can span

Solid Appx 30 ft
Tee slabs up to 120 ft

30

Roof integrity and strength is important for tilt up wall sections because

Failure of the roof can cause outward force causing wall collapse.