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GCU - Construction Materials > Concrete Test 1 > Flashcards

Concrete Test 1 Flashcards

1
Q

Concrete is like a sponge in that…

A

Spaces absorb moisture

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2
Q

In freezing conditions water in pours could…

A

Freeze, increasing in volume and causing cracks

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3
Q

Greater connectivity of pours usually gives

A

Less durability

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4
Q

Only _____ pours affect durability

A

Open

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5
Q

Definition of porosity

A

Overall volume of pours (open and closed)

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6
Q

Definition of permeability

A

Measure of ease with which water / gas can flow through a material

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7
Q

More permeable / porous concretes are used in places like

A

Roads, runways, motorways to allow water to drain

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8
Q

Permeability is not the same as porosity, give exmaple…

A

You could have a high porosity (with closed pours) and low permeability

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9
Q

Usually with concrete the permeability will be…

A

Relative to the porosity

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10
Q

Definition of absorption

A

Ability to draw water into voids (open pours only)

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11
Q

Usually porosity is ____________________ to absorption (_____________________)

A

Not equal to

Due to closed pours not absorbing water

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12
Q

There are how many forms of density - give names

A

Two

Bulk density

Relative density

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13
Q

Definition of bulk density

A

Measure of compaction - tells how closely particles are packed - is defined as dry mass of unit volume

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14
Q

Definition of relative density

A

Same definition as bulk density only volume is only the volume of the solids, no spaces (pours)

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15
Q

Bulk density will have….

A

A greater volume

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16
Q

Relative density will have

A

Smaller volume due to solids being crushed

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17
Q

Definition of moisture content

A

Mass of water in concrete related to its dry mass

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18
Q

When determining mass, concrete samples will be…

A

Put in an oven to dry / remove moisture then weighed

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19
Q

In highly porous concrete relative density will always be __________ than bulk

A

Greater

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20
Q

Two types of porosity are

A

Open porosity

Closed porosity

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21
Q

In most cases, the higher the porosity…

A

The higher the permeability

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22
Q

Bulk density formula

A

P = mass / volume (solids + voids)

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23
Q

Relative density formula

A

P = mass / volume (solids only)

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24
Q

total water absorption is the…

A

Maximum value moisture content

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25
Q

Moisture content cannot exceed…

A

The total water absorption

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26
Q

Concrete is composed of (5)

A

1) cement
2) crushed rock or gravel
3) sand
4) water
5) sometimes chemical admixtures and other materials

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27
Q

Cement + water =

A

Cement paste

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28
Q

Cement + sand + water =

A

Cement mortar

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29
Q

Cement + sand + gravel + water =

A

Concrete

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30
Q

More water used = ______ pores & _________ concrete

A

More

Weaker

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31
Q

The first British standard for Portland cement was published in

A

1904

32
Q

Examples of non hydraulic cements are (2)

A

1) Gypsum (plaster of Paris)

2) Calcite (lime based cement)

33
Q

Disadvantage of gypsum and calcite (non hydraulic cement is…

A

It has high solubilities of calcium hydroxide and gypsum therefore rapid deterioration in moist / wet conditions

34
Q

Hydraulic cements are (2)

A

1) More durable

2) hydration products are insolvable - cements set under water

35
Q

A definition of Portland Cement is….

A

A hydraulic binder capable of setting, hardening and remaining stable under water

36
Q

Portland cement consists essentially of…

A

Hydraulic calcium silicates, usually containing calcium sulphate

37
Q

EN197-1: Portland cement clinker is a hydraulic material which shall consist of at least _____ by mass of calcium silicates, the remainder consisting of ______ and _______

A

2/3
TBC
TBC

38
Q

Raw materials of Portland Cement are (2)

A

1) 3/4 limestone (calcareous materials - lime bearing)

2) 1/4 clay (argillaceous materials - silica, alumina, iron)

39
Q

6 stages of production of Portland Cement are;

A

1) Limestone ground to fine powder and mixed with washed clays (ratio 2:1)
2) Mixture fed into top of rotary inclined kiln, fuel fed in at bottom, giving temperature gradient
3) Water is quickly driven off at top
4) Limestone decomposes to quicklime
5) Some materials (such us aluminium or iron) melt and bind the other materials to form lumps of clinker
6) Clinker is allowed to cool before adding some gypsum and grinding he two to form OPC

40
Q

Cement abbreviation

CaO = ?

A

TBC

41
Q

Cement abbreviation

SiO2 = ?

A

TBC

42
Q

Cement abbreviation

AI2O3 = ?

A

TBC

43
Q

Cement abbreviation

Fe2O3 = ?

A

TBC

44
Q

Cement abbreviation

H2O = ?

A

Water

45
Q

Cement abbreviation

CO2 = ?

A

Oxygen

46
Q

Cement abbreviation

SO3 = ?

A

TBC

47
Q

Chemical composition of OPC

1) Calcium oxide
2) Silica
3) Alumina
4) Iron Oxide
5) Sulphur Trioxide
6) Magnesia
7) Sodium @ Potassium Oxides

A

1) 60 - 70%
2) 17 - 25%
3) 3 - 8%
4) 0.5 - 6%
5) 1 - 3%
6) 0.1 - 4%
7) 0.5 - 1.3%

48
Q

Oxides form

A

Hydraulic compounds

49
Q

The 4 main hydraulic compounds that can be formed from oxides are

A

1) Di calcium Silicate
2) Tri calcium Silicate
3) Tri calcium Aluminate
4) Tetra Calcium Alumino Ferrite

50
Q

Abbreviation for Di calcium silicate is

A

C2S

51
Q

Abbreviation for Tri calcium silicate is

A

C3S

52
Q

Abbreviation for Tri Calcium Aluminate is

A

C3A

53
Q

Abbreviation for Tetra Calcium Alumino Ferrite is

A

C4AF

54
Q

The 2 main hydraulic compounds are (include abbreviation)

A

1) C2S Di-Calcium Silicate

2) C3S Tri-Calcium Silicate

55
Q

When water is added to hydraulic compounds to start the hydration process what are the 4 main hydration products

A

1) Calcium Silicate Hydrate (gel)
2) Calcium Hydroxide
3) Ettringite
4) Calcium Aluminate Hydrate

56
Q

Abbreviation for Calcium Silicate Hydrate is

A

CSH

57
Q

Abbreviation for Calcium Hydroxide is

A

CH

58
Q

Abbreviation for Calcium Aluminate Hydrate is

A

CAH

59
Q

C2S Di-Calcium Silicate reacts _____________ over _____________ with a _________ amount of heat released ______ kJ/kg

A

Very slowly
Many years
Small
260

60
Q

C2S Di-Calcium Silicate is a ______ responsible for ____________

A

Gel

Strength

61
Q

C3S Tri-Calcium Silicate reacts _________ over _________. Heat being released is _____ kJ/kg

A

More quickly than C2S
2-3 weeks
500

62
Q

C3A Tri-Calcium Aluminate reacts ___________ over ________. Heat produced is _____ kJ/kg

A

very rapidly (flash set)
Few hours
870

63
Q

To prevent flash set of C3A Tri-Calcium Aluminate _________ is added

A

Gypsum

64
Q

Initial phase of hydration process for C3A Tri-Calcium Aluminate produces the hydration product ___________. When it moves onto the normal phase the hydration product is _____________.

A

Tri-sulphoaluminate (Ettringite)

Mono-sulphoaluminate

65
Q

C3A Tri-Calcium Aluminate is responsible for _____ ______________

A

Early strength

66
Q

Negatives associated with C3A Tri-Calcium Aluminate (2)

A

1) Concrete is liable to sulphate attack

2) High heat of hydration (mass concreting)

67
Q

C4AF Tetra Calcium Alumino Ferrite produces _____ kJ/kg heat in hydration

A

420

68
Q

Flash set in C4AF Tetra Calcium Alumino Ferrite is controlled by

A

Adding gypsum

69
Q

C4AF Tetra Calcium Alumino Ferrite is ________ in its effects which are (2)

A

Neutral

1) small contribution to strength
2) gives typical grey colour (sole effect)

70
Q

Hydration rate has the following order

A

C3A (Tri-Calcium Aluminate) > C3S (Tri-Calcium Silicate) > C4AF (Tetra Calcium Alumino Ferrite) > C2S (Di-Calcium Silicate)

71
Q

During hydration process ________ forms first, followed by _________ and ___________ with a small change in the total ___________ of the paste

A

Ettringite
CH (Calcium Hydroxide)
CSH (Calcium Silicate Hydrate)
Volume

72
Q

The rate of hydration can be increased in the following ways (3)

A

1) Temperature - for each 10degC increased hydration rate doubles
2) Fineness of cement - more fineness of cement more surface area hydration can take place
3) Change proportion of cement components (e.g. increase C3S and CA)

73
Q

During the hydration process the following %ages of heat are liberated at different intervals (3)

A

1) 30% within first day
2) 50% within first three days
3) Remaining over time

74
Q

As thermal conductivity of concrete is low it acts as an insulator, containing the heat within the concrete and forcing the temperature to rise may cause

A

Cracking

75
Q

A way to lower the heat of hydration is to

A

Adjust the fineness and composition of cement (e.g. increasing C3S and C3A as in type IV cement)

GCU - Construction Materials (4 decks)

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