Composites 2 Flashcards

1
Q

Is concrete a composite?

A

yes

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2
Q

What is filler is concrete made out of?

A

Aggregate- rock and sand

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3
Q

What matrix is concrete made out of

A

Cement

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4
Q

What percentage of concrete is aggregate?

A

70-80%

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5
Q

What is the purpose of sand in aggregate?

A

Fills voids to reduce porosity

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6
Q

How does concrete set

A

Cement undergoes a cementation reaction

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7
Q

What is the water used for in cement

A

incorporates into the structure

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8
Q

Main minerals (C)

A

CaO

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9
Q

Main minerals (A)

A

Al2O3

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10
Q

Main minerals (F)

A

Fe2O3

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11
Q

Main minerals (S)

A

SiO2

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12
Q

Density of concrete

A

2 gcm3 (dense)

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13
Q

(L/H) concrete fracture toughness

A

L

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14
Q

(L/H) concrete tensile strength

A

L

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15
Q

Why is concrete used?

A

Cheap and good compressive strength

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16
Q

Why does concrete get better with age

A

Cementation reaction still taking place

17
Q

What does the strength depend on in concrete?(2)

A

Minerals and amount of water

18
Q

Pro of adding more water to your concrete

A

Makes concrete more workable

19
Q

Con of adding more water

A

As it increases shrinkage it makes cracking more likely

20
Q

what is reinforced concrete

A

concrete with steel rods

21
Q

What is pre-stressed concrete?

A

Steel rods under tensile stress while concrete is pored

22
Q

Con of steel reinforced concrete

A

water rusts steel making it expand and create cracks

23
Q

Why is concrete so bad for the enviroment

A

Only cause so much produced, actual production is quite low co2

24
Q

Why would you use wood?(5)

A

Cheap, strong, lightweight, aesthetics, eco friendly

25
Q

Structure of wood - Fibre

A

Lignin holds cellouse fibres and hemicellulose together in same direction

26
Q

Structure of wood - cell structure

A

Made of cells with microfibril facing different ways in each layer

27
Q

structure of wood- macrostructure

A

Long unidirectional polymer cells

28
Q

Why is softwood less dense

A

Has more hollow cells for transporting water

29
Q

Can wood float on water

A

yes

30
Q

What effects wood strength

A

direction of cells

31
Q

Does wood have good compressive strength

A

no

32
Q

Which type of wood does wood densification use?

A

Soft wood

33
Q

How does wood densification work?

A

Uses chemicals and heat to remove lignin and hemicelluloses

34
Q

Why densify wood?

A

Outperforms in specific strength, energy to manufacture and cost