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Materials > Non Metals > Flashcards

Non Metals Flashcards

1
Q

Definition of masonry

A

A construction of building units or materials (e.g. clay, concrete, glass, gypsum, stone) bonded together with or without an accepted method of joing (e.g. mortar or grout)

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2
Q

What is veneer?

A

A masonry front with steel/concrete/wood structural elements

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3
Q

Advantages of masonry

A

Can use local materials (stone and clay)
Gives high thermal mass
Durable (>500 years)
High fire resistance

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4
Q

Disadvantages of masonry

A

Requires manual labour (hard to mechanise)
Difficult to make really tall structures
–Heavy- need thick and strong foundations
–Tensile strength is limiyed
–Bricks have a lower tensile strength than concrete, therefore a limitatiom
Little shearing resistance in an earthquake
(low seismic resistance)

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5
Q

Dry stone

Advantages and disadvantages

A 
Very simple
Very durable
Interlocking stone
Skilled crafting to fit stones together
Filled with soil to block wind an insulate
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6
Q

How are bricks made?

A

Clay is mixed with sand and pressed into moulds
Clay is baked at about 900-1000°c
Sand is needed for stability
Water is needed for effective moulding
Some organic matter and lime is needed to accelerate firing and make more equal
Dry pressing can be used for better equality product, but is more expensive
Extruded bricks (12% water) are cut by wires from a column of clay (cheaper)

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7
Q

What gives bricks their reddish colour?

A

Iron and it depends on the firing (yellow, red, pink, grey

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8
Q

Uk standard brick size

A

215 x 102.5 x 65mm

Little International trade

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9
Q

Compressive strength of bricks

And the limitations of this

A

20-40 MPa
Can be up to 100MPa
Combined with the high weight of bricks, this limits the height of buildings that can be built
Gd quality concrete =40Mpa

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10
Q

Brick types in the UK

A

Engineering
Facings (thin)
Commons (internal–have been replaced with concrete masonry bricks)

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11
Q

What was historically used instead of cement in mortar?

A

Lime

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12
Q

What three components make up mortar?

A

Cement
Sand
Water

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13
Q

What is mortar used for?

A

To bind bricks together

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14
Q

What is a disadvantage of mortar?

A

It is often the weakest point under shear load

It’s is less strong than bricks, so you don’t want much of it

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15
Q

Standard mortar thickness

A

~5-10mm

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16
Q

How are bricks laid?

A

In courses, over lapping to spread load, joined by mortar

If there are vertical lines you can tell it is not real masonry

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17
Q

Advantages of multiple brick thickness

A

Adds shear strength and spreads load

A cavity wall can be used for insulation

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18
Q

How are multiple brick walls joined together

A

With tie rods, that preferably do not conduct heat

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19
Q

What are concrete blocks(CMU, concrete masonry unit) that contain fly ash called

A

Cinder blocks or breeze blocks

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20
Q

What properties does fly ahs add to concrete blocks?

A

Light weight
Aerated concrete will make then v light weight(~8 MPa)
Thermal insulation

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21
Q

What do concrete blocks look like?

A

Mostly hollow core ~20MPa compression
Usually larger than a brick
(440x215x100mm in UK)

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22
Q

Aggregates in concrete blocks

A

Fine (and are often precast)

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23
Q

What is the difference between soft mud bricks and dry press bricks?

A

Soft mud have more water–25-30%
Dry press have less- 8%
More water means more variability

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24
Q

Compressive strength of bricks
their maximum
And a problem to do with this

A

Higher is better
15-35MPa
Class A engineerinh Brick 125MPa
There is a high variability in bricks, therefore you can’t work to a high wuility unless you have high quality engineering bricks

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25
Q

Water absorption of bricks

A

Lower is better
Normal 20-30%
Class A engineering brick <4.5%

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26
Q

Frost resistance of bricks

A

Measured by mass loss during standard tests

Measured as high medium low

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27
Q

What is efflorescence?

A

Moisture travels through masonry and evaporates, depositing salt componants from mortar or within the bricks (sulfate or carbonate salts) on surfaces
Avoid this by keeping moisture out form masonry with a damp course
Not aturturally a problem just ugly
Shows bricks aren’t great quality

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28
Q

Definition of glass

A

Solid material lacking long-range chemical order, usually made by supercooling a liwuid
Fast cooling= non equilibrium

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29
Q

What is the structure of glass like?

A

Cooling or compressing a liquid can give a glassy material that looks like a solid on observable timeframes.
But has a trapped disordered liquid like local structure
(kinetic ally trapped)

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30
Q

What does annealing of glass do?

A

Longer term heating
You heat the material to a temp. below melting to allow it to soften and therefore to move a little to a more ordered state.

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31
Q

What is Tg?

And what can happen?

A

Glass transition
Some properties e.g. Cp thermal expansion show a distinct change at a given temperature
~500-600°C for soda lime silicate glass
~1200 for SiO2
Don’t know the physics about how this works

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32
Q

What is viscosity?

A

The resistance to flowing

High viscosity= acts more like a solid

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33
Q

What is significant about a viscosity temperature graph for Glass?

A

There is no step chabge/jump between liquid and solid
This is because it is distorted at the atomic level.
And so every is stored
As you heat it up you gradually release this and allow it to move around more and more

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34
Q

What type of glass is most commonly used in structures?

A

Soda lime silicate (Na2O-CaO-SiO2) or borosilicate for thermal resistance

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35
Q

What is soda lime silicate glass used for?

A

Almost always use din structures
Common window glass
Bottles
Jars

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36
Q

What is float glass process?

A

Used to produce glass, where the glass floats on liquid tin
Processed at 1050-1200°C
Gives very flat surface

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37
Q

Mechanical properties of glass

A

Extremely brittle - due to defects
(Engineering glass isn’t within 1% of predicted strength
Theoretical bending strength 14,000MPa
Actual 20-200MPa)

Very weak Iin tension

Static fatigue - H2O attack chemical bonds in cracks making it weaker under long-term loading

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38
Q

What is tempering of glass?

A

Heating a sheet of glass to above Tg, then quenching surfaces rapidly

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39
Q

How does tempering work?

A

Quenching puts surfaces in conpression
And the centre/core in tension
(glass is weak in tension)
You have to overcome the compression force before you create a crack
To break toughened glass you need to crack through the surface region into the core
Fracture leaves cubic fragments due to stored strain energy

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40
Q

What is gorilla glass?

A

That that has been toughened chemically
By reolaceing sodium, Na, with potassium, K.
K is bigger than Na therefore a force increased and the first layer of glass on the surface is put under compression

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41
Q

What is laminated glass?

A

A glass polymer composite for enhanced toughness and fracture resistance.
A polymer film is sandwiched between two glass sheets

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42
Q

What polymer film is often used in laminated glass?

And how is it applied?

A

Polyvinyl-butyral

It is rolled on and heated to remove air and bond polymer to glass

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43
Q

Benifits of laminated glass

And uses

A

Protects the surface
Holds in the broken fragments if fracture occurs

Car windscreens
Windows
Phone screen protectors

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44
Q

What is bulletproof glass?

A

Composite material of tempered glass and polycarbonate laminate
(ie multiple layers of laminated glass)
~20-75mm thick

You have to match the optical properties of the two materials so you can see through

Laminate layers are much more elastic, therefore, glass breaks and laminate deforms elastically.
Glass underneath is still intact

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45
Q

What is multiple glazing?

A

2 or 3 sheets of glass, in a sealed, unit with gas or a vacuum in between
dessicant can also be used in the gas space, to keep the gas environment dry (stops fogging)

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46
Q

Why do we use multiple glazing?

A

Each interface gives resistance to heat transfer

Therfore gives enhanced thermal insulation properties.

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47
Q

What do we need to be careful about with multiple glazing?

A

Need similar thicknesses of glass inside and outside to prevent shearing and popping the glass, from vertical loading

Temperature differences between inside and outside can cause cracking

Dimensional changes in units can break seals around unit edges–moisture gets in, window gets fog or mold

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48
Q

Cement clinker in portland cement

A

Altite - tricalcium silicate
Belite - dicalcium silicate
Aluminate - tricalcium aluminate
Tetracalcium aluminiferrite

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49
Q

What is portland cement

A

A hydraulic cement (capable of setting hardening and remaining stable under water).
It consists essentially of hydraulic calcium silicates

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50
Q

General process of making cement

A

Limestone and clay are heated to high temperatures in a kiln
Water is added to harden and incorporate the water into a hardened structure.
Come out of kiln as clinker
Cooled quickly
Clinker is mixed with gypsum
Grind into a powder

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51
Q

What is cement

A

Gypsum + clinker

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52
Q

What is gypsum

A

CaSO4. 2H2O

Hydrated calcium sulphate

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53
Q

What is C an abbreviation for?

A

CaO

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54
Q

What is S an abbreviation for?

A

SiO2

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55
Q

What is A an abbreviation for?

A

Al2O3

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56
Q

What is F an abbreviation for?

A

Fe2O3

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57
Q

What is H an abbreviation for?

A

H2O

58
Q

What is -S an abbreviation for?

S with a line on top

A

SO3

59
Q

What is the abbreviation for alite?

A

C3S

3CaO.SiO2

60
Q

What is the abbreviation for blite?

A

C2S

2CaO.SiO2

61
Q

What is the abbreviation for Tricalcium aluminate

A

C3A

3CaO.Al2O3

62
Q

What is the abbreviation for Tetracalcium aluminoferrite

A

C4AF

4CaO.Al2O3.Fe2O3

63
Q

What is the abbreviation for Gypsum?

A

C-SH2

CaSO4. 2H2O

64
Q

What does limestone supply when making cement?

A

Ca

65
Q

What does clay/shale/ sand supply when making cement?

A

Al2O3(A) , SiO2(S) , Fe2O3(F)

66
Q

What temperature do you need to heat the rotary kiln to when making cement?

A

~1400°C

67
Q

Normal clinker composition of alite

A

About 65%

68
Q

Normal clinker composition of blite

A

About 20%

69
Q

Normal clinker composition of tricalcium aluminate

A

About 8%

70
Q

Normal clinker composition of tetracalcium aluminoferrite

A

About 8%

71
Q

Perpose of alite

A

Gives early (<7 days) strength development

72
Q

Perpose of blite

A

Gives longer term gain of strength

73
Q

Perpose of tricalcium aluminate

A

Controls initial setting

74
Q

Perpose of tetracalcium aluminoferrite

A

Controls the melting in the kiln
Gives grey colour
Similar hydration products to tricalcium aluminate
but reacts slower and doesn’t contribute as much strength

75
Q

How much Co2 is produce dper kg of cement

A

0.8kg of cement

50% from fuel, 50% from chemistry

76
Q

What percent of global human-derived Co2 is produced from making cement?

A

~8%

77
Q

What does limestone breakdown into in the kiln?

A

CaCO3= CaO + CO2

Heat to 1400 °C

78
Q

What type of reaction takes place when cement mixes with water?

A

Hydratiom
Particles dissolve
Ions rearrange in solution phase
Solid hydrate pahsas solidify and give strenhth

79
Q

Why is drying bad for fresh cement?

A

Water forms an essential part of the solid phases in hardened cement
Drying slows or stops reactions, causes cracking and loss of strength

80
Q

Calcium silicate hydrate (C-S-H) is formed by the hydration of what?

A

C3S and C2S

81
Q

What is another word for non-crystalline?

A

Amorphous

82
Q

Is C-S-H porous?

A

Calcium silicate hydrate is porous on nanometer length scale

83
Q

What is the chemical composition of calcium silicate hydrate (C-S-H)?

A

There is no fixed chemical composition
But approximately
1.6CaO . SiO2 . 1.8H2O

84
Q

What is calcium silicate hydrates use in hardened binders?

A

It fills a lot of space
The glue that holds the cement together
Chemically and physically disordered

85
Q

What is Ca(OH) 2?

A

Calcium hydroxide

Portlandite

86
Q

What is portlandite?

A

Calcium hydroxide

Ca(OH) 2

87
Q

How is calcium hydroxide produced

A

Portlandite is produced as a by-product of C3S and C2S hydration
As they have more Ca than can be accommodated in C-S-H
Makes large crystallites

88
Q

What is the use of portalndite/calcium hydroxide?

A

Helps durability by holding internal PH high
And do protects the steel and stops rusting
Doesn’t contribute to strength

Grows around aggregate particles
‘interfacial transition zone’

89
Q

What is Aft?

A

Ettringite
C3A. 3C-S.32H
t is tri-sulphate
Needles interlockin

90
Q

How is Aft formed?

A

By fast reaction of C3A with water and gypsum

It is the first hydrate phase that forms

91
Q

What does Aft formation do?

A

It is naturally occurring during fast reaction of C3A, water and gypsum
The Interlocking needles causes initial setting of cement
Mostly converted to AFm at longer ages
You can reshape it if you push it hard enough
-reshape the surface, move and break the needles

92
Q

What is AFm?

A

m stands for mono) calcium sulphate
C3A. C-S. nH
n= 11-19

93
Q

How is AFm formed?

A

Eventually you run out of sulphite, when ettringite (Aft) is being formed,
B4 C3A
Ettringite is then dissolved and reformed as AFm

94
Q

What is AFm for?

A

Contributes to a bit of strength

Fills in some space

95
Q

What are SCMs?

A

Supplementary cementitious materials

Any mineral compound that blends with cement and reacts to alter the properties of the binder

NOT aggregates
NOT organic admixtures

Most scms are pozzolans
A waste source of cheap silica
SiO2 with or without Al203

(note: limestone (CaCO3) is a SCM but not a pozzolan as it contains no Si or Al)

96
Q

What is the pozzolanic reaction?

A

When the Si02 (and Al2O3) in SCMs (supplementary cementitious materials)
react with CH in the portlandite to form more C-S-H

CH + S + xA - - > C-(A)-S-H

97
Q

Why do we use SCMs?

A 
We react SiO2 ( and Al2O3) with CH
To make C-S-H, which fill pore spaces at a longer age and refine pores
This improves strength and durability
Also improves sustainability (low C02)
And can reduce cost
98
Q

Examples of pozzolanic SCM

A

Fly Ash (by-product from coal fired power generation)

Natural pozzolans (volcanic earth)

Heat-treated (‘calined’) clays

Silica fume (by-product from semiconductor Si manufacture)

Rice husk Ash (by-product from burning agricultural waste)

Other waste silicate glass materials

99
Q

SCMs not classified as pozzolans

A

Limestone - CaCO3

Blast furnace slag (by-product from iron making)
also hydraulic - performs alot better

100
Q

Why is pozzolanic reaction slower than cement hydration?

A

Takes about a week to start

You have to make portlandite first so that CH is available to react

101
Q

Influence of SCMs

A

Cement substitution with pozzolans usually reduces early strength (except with silica fume)

Better long term properties
Extra C-(A)-S-H fills ins pace and gives strength
Chemical durability–chloride/sulphate resistance generally improved
(therefore marine concreting is done with slag bended portland cements)

102
Q

Definition of paste

A

Cement + water

Rarely used alone, usually with aggregates

103
Q

Definition of mortar

A

Paste + sand (‘fine’ aggregate <5mm)

Paste= cement + water

104
Q

Use of mortar

A

Join bricks together or as a coating

105
Q

Composition of concrete

A

Paste + sand + coarse aggregate

Paste= cement + sand
Sand= 'fine' aggregate <5mm

Coarse aggregate= gravel, crushed rock, usually up to a few cm
Unreactive and strong, to avoid harming durability and petformamce

Aggregate dilutes the paste- cheap, reduces heat release
Well graded aggregate size- helps cohesion and reduces bleed

106
Q

Why is water important in concrete?

A

Required in cement hydration reactions

Makes concrete flow

107
Q

How do you test concrete flow?

A

Cone test
How much a cone of concrete drops in height

0%= no change in height
1/2= normal
108
Q

Why is too much water in concrete bad?

A

It forms extra pores

  • reduces durability– more permeable –> less resistance to chlorine penetration, carbonation, sulphate ingress
  • reduction in strength (more holes)

Can delay setting/hardening

Causes bleeding, segregation, plastic settlement

Increases drying shrinkage

109
Q

Normal ratio of water/cement

A

0.5 +- 0.2

110
Q

Effect of water on the strength of cement

A

More water = less strength
Less water = stronger, faster, sooner

Water content measured as water/cement mass ratio (w/c)
If blended w/binder

111
Q

How can you reduce the water content of cement?

A

With (super)plasticisers

Polmer additives that improve flow

112
Q

What causes segregation of cement?

And how to avoid it

A

To much water

Keep water content low (with plasticisers)
Fine aggregates help avoid

Need a cohesive mix
Need mix to stay together
To allow pumping
Make more viscous

113
Q

What is plastic shrinkage cracking in concrete?

And how do you avoid it

A

Rapid water evaporation from the surface straight after you pour it
Early, therefore paste still has some fluidity and us plastic (can still change its shape)
Top surface shrinks and cracks (shallow cracks
Aggragates stop the bulk from shrinking
Water bleeds up to the surface and evaporates

Avoid drying
Control rate of water travelling through material (bleed)

114
Q

What is drying shrinkage cracks

A

Similar to plastic shrinkage cracking

but happens after the material has hardened

115
Q

What is plastic settlement?
Problems it causes
How to avoid this

A

If you get the aggregates or balance between aggregates and paste wrong
Aggregate particles sink through the paste,
water travels up
leaving water pockets under aggregates and reinforcing bars
Cracks on surface (sags either side and pulls apart)

Cracks extend down to the first reinforcing bars
Steel corrodes
This is fatal ft or duribility

Vibrate concrete properly
Use less water
Use right additives to make concrete cohesive
Protect surface after casting

116
Q

What is alkali-activated (geoploymer) cements

A

Aluminisilicate materials + alkaline solution(‘activator’)

Alkaline solution–blast furnace slag or pozzolans

(Blended cement + no portland + chemicals)
Concrete based on supplementary materials

117
Q

What aluminisilicate materials can be used in alkali-activated cement

A

Blast furnace slag or pozzolans

118
Q

Benifits of alkali-activated cements

A

~69-90% less CO2 emissions than portland cement

119
Q

Draw back of alkali-activated cements

A

Need for an alkaline solution

No convenient alkaline solution (irritant or corrosive)

120
Q

What is calcium aluminate cement (CAC)

A

Also known as high-alumina cement (HAC) or SECAR
special type of clinker produced by a melting process instead of solid state clinkerisation process

CA and CA2

121
Q

Benifits of calcium aluminate cement (CAC)

A

Reacts with water for high early strength
~90% of final strength after 24 hrs
Therefore used in prestressing

Acid resistant

122
Q

Disadvantage of calcium aluminate cement

A

Can have catastrophic strength loss if you use >0.45% water
After 10 urs solid hydrate phase change shape and take up less place
Up to 80% of strength is lost
Collapses

Very sensitive to water content

Expensive retrofitting or demolition has been required

123
Q 
What is magnesium oxychloride
Benifits
Disadvantages
Uses
Varient types
A

MgO + MgCl2 and H20
5Mg(OH)2MgCl2.8H20

Very high early strength >70MPa after 3-7 days
White cement
Very low CO2
Inexpensive

Very sensitive to water (not hydraulic)
dissolves in the rain

Indoor uses- floors, tiles, artificial ivory billiar balls

Swap chloride for sulphate instead
Or zinc instead of magnesium
To enhance resistance

124
Q

What is bitumen

A

(asphalt)
A mixture of heavy organic molecule, solid at room temperature
Naturally occurring or synthetic

Not technically a cement but is a binder
And the material made with it is a concrete

Non hydraulic

125
Q

Use of bitumen in concrete

A

Is a binder
Used to bind stones/gravel together into a solid hardened material (concrete)

Us wheat or chemical solvents to soften bitumen and make flowable%workable as desired

126
Q

Why reinforce concrete with steel?

A

Concrete is good in compression but not in tension

Steel is good in tension but not in compression

127
Q

What type of steel is used in reinforcement and why?

A

Mild steel
That are often ribbed to bond better to the concrete (ribbed reinforcing bar - rebar)

Cheeper than stainless
Passivation chemistry(resistance to corrosion) works better for mild steel
128
Q

How is steel reinforcement usually used? (shape)

And connected?

A

Meshes
Cages
For effective distribution

Can be prefabricated or constructed on site

Connected by
welding
Tying steel wire
Interwoven

Can be spiral, square, cylindrical

129
Q

What percent of the cross-sectional area is steel reinforcement in concrete?

A

~3-5%

Beware of congestion as concrete must flow through the gaps to properly compact

130
Q

Why do we prestressed concrete?

A

To strengthen it against predetermined tensile forces which will exist when in service
This helps prevent cracking in the concrete as there is a greater compressive force to overcome before the concrete is in tension

131
Q

How is steel pretensioned?

A

Steel tendons (cable, bar or wire/group of wires) are tensioned to introduce a pre-conoression and counteract tensile stresses that it will undergo. Therefore prevent cracking

  1. tendons stretched
  2. concrete poured
  3. tension released

It relys on developing an effective interfacial bond between the steel and concrete

132
Q

What are two ways of pre-stressing concrete?

A

Pre-tensioning

  1. Tendons strectched
  2. Concrete poured
  3. Tension released

Post-tensioning

  1. Concrete poured with a duct
  2. Tendons inserted and tensioned
133
Q

How do you post-tension concrete?
Benifits
Disadvantages

A
  1. concrete poured with a duct
  2. Tendons inserted and tension

It is easier to conduct on site than pre-tensioning

Can have severe problems if the steel corrodes and stress application is lost

134
Q

What is passive film in reinforced concrete?

A

When steel is embedded in concrete a protective double layered passive film is formed.
Iron oxides forming the passive film

Inner layer- FeO and Fe3O4
Outer layer- Fe2O3

135
Q

What happens if the passive film in reinforced concrete breaks down?

A

The Fe corrodes

136
Q

What causes the passive film on reinforced concrete to form?

A

Fe oxidses
This is enabled by the alkaline conditions of
12

137
Q

What are the two layers in the passive film in reinforced concrete?

A

Inner layer–FeO and Fe3O4

Outerlayer–Fe2O3

138
Q

What is the main cause of concrete failure?

A

Steel failure!
When steel rusts it expands and cracks the concrete
The durability of concrete is fundamentally controlled by permeability of concrete
-rate of flow of fluid into concrete
Porous concrete allows ingress of corrosive species (may allready be present)

139
Q

How corrosion occurs in reinforced concrete

A

Water and oxygen is able to access the steel

Anode
The Fe releases electrons
Fe(0) - - > Fe2+ + 2e-

Cathode
Oxygen reacts with water
H20 + 02 + 4e- - - > 4OH-

Fe2+ + 2OH- - - - > Fe(OH) 2

Rust is formed and the volume is 4x greater than Fe

140
Q

What are the two main causes of corrosion in reinforced concrete?

A

Chloride ingress

Carbonation of concrete (PH drops)

141
Q

Are are mild steel rebar protected from corrosion in portland cement based concrete?

A

Because of the high PH

142
Q

How does chloride exacerbate corrosion?

A

Cl- H20 02 enter

Cl- reacts with Fe to make FeCl2

H20 0H and FeCl2 react to make
H+ Fe(OH) 2 + Cl-

Materials (2 decks)

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