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Non-Metals Flashcards

1
Q

What is masonry?

A

Blocks of brick held together with mortar

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2
Q

What are the advantages of using masonry?

A

-Usually locally available stones or clay
-Tends to give high thermal mass
-Usually durable (>500 yrs)
-Usually high fire resistance

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3
Q

What are the disadvantages of using masonry?

A

-Requires manual labour, hard to mechanise
-Difficult to make very tall structures
-Heavy, needs thick and strong foundation
-Tensile/flexural strength is very limited
-Compressive strength of bricks can also be a limitation
-Unreinforced masonry has low resistance to shearing forces in earthquakes

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4
Q

What material is brickwork?

A

Usually made from baked clay, iron clay gives a red colour

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5
Q

What is the compressive strength of brickwork?

A

Can be up to 100 MPa but usually around 20-40 MPa

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6
Q

What is the composition of mortar?

A

Cement + sand + water
Historically lime was used instead of cement, and is still sometimes used today

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7
Q

What is the strength of mortar under load?

A

Usually the weakest point under shear load

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8
Q

What is the standard thickness of mortar?

A

5-10 mm

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9
Q

What are concrete masonry units (CMU) made out of?

A

Fly ash cement, usually precast with fairly fine aggregates

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10
Q

What does CMU provide a structure?

A

Light weight and thermal insulation

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11
Q

What is the average compressive strength of CMU?

A

~20 MPa

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12
Q

What are the structural uses for the materials used to make brick?

A

-Sand is used for dimensional stability
-Water is needed for effective moulding
-Organic matter or lime accelerates firing

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13
Q

What is the water content of soft mud bricks?

A

25-30% water - meaning they have more variability

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14
Q

What is the water content of dry press bricks?

A

~8%, more expensive but give a better product

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15
Q

What is the water content of extruded bricks?

A

~12%, they are cut by wires from a column of clay, making them very cheap

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16
Q

What is the compressive strength of class A engineering brick BS EN 771?

A

125 MPa

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17
Q

What is the compressive strength of a normal brick?

A

15-35 MPa

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18
Q

What is the water absorption of class A engineering brick BS EN 771?

A

<4.5%

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19
Q

What is the water absorption of normal brick?

A

~20-30%

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20
Q

Describe efflorescence.

A

-Moisture travels through masonry and evaporates, leaving salt on surfaces or salt components are present from mortar or from within the clay/concrete
-Avoid this by keeping water out from masonry
-Not usually a problem but aesthetically an issue.

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21
Q

How is glass usually made?

A

By supercooling a liquid

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22
Q

Compare the theoretical and actual structural properties of glass.

A

Theoretical flaws could be very strong.
-Theoretical bending strength ~14 000 MPa
-Actual bending strength 20-200 MPa

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23
Q

How is the strength of glass determined?

A

By the size of the largest flaw

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24
Q

What is the process of tempering glass?

A

Heating a sheet of glass, then quenching surfaces rapidly

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25
Q

Describe how tempering glass works.

A

-Quenching puts the surface into compression and the centre in tension, strengthening the surface
-To break tempered glass, a crack must form between the surface region into the core region
-Fracture leaves cubic fragments due to stored strain energy

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26
Q

How is laminated glass made?

A

A polymer film is sandwiched between two glass sheets

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27
Q

Describe how laminated glass works.

A

-Polyvinyl-butyral is the most common film used which is rolled out and heated to exclude air and bond polymer to glass
-Protects surfaces and holds in the broken glass fragments is fracture occurs, cracks in a spider web pattern
-Used a lot in car windscreens and other places that are likely to break

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28
Q

How is bullet proof glass made?

A

Multi-layered tempered glass/polycarbonate laminate, or multiple layers of laminated glass ~20-75 mm thick

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29
Q

Describe how bullet proof glass works.

A

-Optical properties of materials must be matched
-Polymer layers are much more elastic than glass

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30
Q

How is multiple glazed glass made?

A

2 or 3 sheets of glass are sealed into a unit, with a gas layer in between

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31
Q

Describe how multiple glazing glass works?

A

-Sometimes a vacuum can be used if the temperature differential is not going to be too high
-Desiccants are sometimes used in the gas space
-Each interface gives resistance to heat transfer
-Need similar thickness of glass inside and outside to prevent shearing
-Temperature mismatch between inside and outside can cause cracking
-Dimensional changes in units can break seals around unit edges and let moisture in

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32
Q

Describe three properties of cement.

A

-Binds solid aggregates together by hardening from a plastic state
-Has both adhesive and cohesive properties
-Functions by forming a plastic paste when mixed with water, which develops rigidity and then steadily increases in compressive strength by chemical reactions with water

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33
Q

What is Portland cement?

A

A hydraulic cement produced by pulverising clinker, consisting of crystalline hydraulic calcium silicates, usually containing one or more of the following: water, calcium sulphate, up to 5% limestone, processing additions

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34
Q

How much of the worlds concrete uses Portland cement?

A

> 95%

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35
Q

Give the following compounds abbreviations: Calcium oxide (CaO), Silicon Dioxide (SiO2), Aluminium Oxide (Al2O3), Iron Oxide (Fe2O3), Water (H2O), Sulphur Trioxide (SO3), Carbon Dioxide (CO2), Sodium Oxide (Na2O), Potassium Oxide (K2O)

A

CaO - C
SiO2 - S
Al2O3 - A
Fe2O3 - F
H2O - H
SO3 - S(bar)
CO2 - c
Na2O - N
K2O - K

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36
Q

Describe Alite clinker.

A

(C3S) Hardens rapidly, develops high strength

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37
Q

Describe Belite clinker.

A

(Beta-C2S) Hardens slowly, develops high strength

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38
Q

Describe Aluminate clinker.

A

(C3A) Reacts with gypsum, products are of low solubility

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39
Q

Describe Ferrite clinker.

A

(C4AF) Similar of C3A Aluminate but not as rapid

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40
Q

Describe Calcium Silicate Hydrate (C-S-H).

A

-Formed by the hydration of Alite and Belite
-Makes up to 70 wt% of fully hydrated phase
-The major strength contributing phase

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41
Q

Describe Calcium Hydroxide/Portlandite (C-H).

A

-By product of Alite and Belite hydration (they have more Ca than can be accommodated for in C-S-H)
-Makes up to 20 wt% of fully hydrated phase
-Does not contribute to strength

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42
Q

Describe Ettringite.

A

-Direct reaction of Aluminate with water leads to flash set (stiffening without strength development) forming aluminate hydrates
-By adding gypsum, aluminate reacts moderately an forms ettringite (Alumina ferric oxide tri-sulphate)

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43
Q

Why is mineral component tat added to cement?

A

To improve performance and reduce cost

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44
Q

What are supplementary cementitious materials (SCMs)?

A

Mineral component tat (NOT AGGREGATES)

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45
Q

What is a Pozzolanic reaction?

A

Silica and alumina component reacts with portlandite to produce more C-S-H

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46
Q

What is the point of carrying out pozzolanic reactions?

A

C-S-H fills pore spaces at longer age, improving strength and durability

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47
Q

How fast is a pozzolanic reaction?

A

Generally slower than cement hydration

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48
Q

What happens when cement is substituted for pozzolans?

A

Early strength is reduced

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49
Q

What physical properties change when the cement is blended?

A

-Extra C-S-H fills in space, which gives extra strength
-Chemical durability improves

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50
Q

Give some examples of Pozzolanic SCMs.

A

-Fly ash
-Volcanic earth
-Calcines clays
-Silica fumes
-Rice husk ash
-Waste silicate glass

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51
Q

Give two examples of non-pozzolanic SCMs.

A

-Limestone
-Blast furnace slag

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52
Q

What are the components of cement paste?

A

cement + water

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53
Q

What are the components of mortar?

A

cement + fine aggregates (<5 mm) + water

54
Q

What are the components of concrete?

A

cement + fine aggregates + coarse aggregates + water

55
Q

What are aggregates?

A

Inert additives which can be bound together with cement to make concrete

56
Q

What are the three main roles of adding aggregates to a cement?

A

-Can increase strength
-Can reduce weight
-Higher integrity

57
Q

How do aggregates change a concretes strength?

A

-A concrete cannot be stronger than the aggregate, because it fails at its weakest point
-Need good quality, clean, strong aggregates
-Clay contamination tends to have bad effects

58
Q

How do aggregates change a concretes weight?

A

Lightweight aggregates for lightweight concretes

59
Q

How do aggregates change a concretes integrity?

A

Reduces thermal cracking (dilution of cement)

60
Q

Why is water important in concrete?

A

-Required to make cement hydration reactions
-Makes concrete flow (increased slump)

61
Q

What happens if too much water is added to a concrete?

A

-Delays setting/hardening
-Forms extra pores, which reduces durability and strength

62
Q

Describe the flow of concrete?

A

Shear-thinning, which means it flows more readily when a force is applied, this is why mixing trucks are kept rotating.
Self-compacting concrete flows like a liquid with no vibration, this is achieved by adding chemicals.

63
Q

What causes the shear-thinning nature of cement?

A

Needle shape of ettringite crystals

64
Q

What causes plastic shrinkage cracking?

A

-Rapid evaporation from the surface makes the paste shrink
-Evaporation also causes drying shrinkage cracks

65
Q

How can shrinkage and cracking be reduced?

A

Aggregate particles stay in place and prevent shrinkage that causes cracking/crazing

66
Q

What causes plastic settlement?

A

Solid aggregate particles can sink through the paste, leaving water pockets under aggregates and reinforcing bars and cracks on the surface

67
Q

What is an expected water/cement mass ratio for a regular concrete?

A

0.3-0.7

68
Q

Name the main 6 non-Portland cements.

A

-Calcium aluminate cement (CAC)
-Calcium sulpho-aluminate cement (CSA)
-Magnesium oxychloride cement
-Magnesium phosphate cement
-Alkali-activated (geopolymer) cement
-Bitumen/Tar

69
Q

What are the physical properties of Magnesium oxychloride cement?

A

-Very high early strength (>70 MPa after 3-7 days)
-Sensitive to water
-Useful for indoor floors, tiles, artificial ivory and billboard balls

70
Q

What are the main physical properties of Alkali-activated (geopolymer) cement?

A

-Can use blast furnace slag or pozzolans
-60-90% less carbon emissions than Portland cement
-Need an alkaline solution

71
Q

What is Bitumen?

A

A mixture of heavy organic molecules, solid at room temperature

72
Q

What are the main physical properties of Bitumen?

A

-Used to bind stones/gravel together into solid hardened material
-Is technically a binder not a cement
-Use heat to soften and make flowable

73
Q

Compare how good concrete and steel are in tension and compression.

A

Concrete is strong in compression but weak in tension, steel is very good in tension

74
Q

What kind of steel is used for reinforcements and why?

A

Usually mild (but not stainless) steel, as they tend to not only be cheaper but can be chemically altered to be corrosion resistant, they are often ribbed which creates a stronger bond to the concrete

75
Q

What are pre-tensioned cables?

A

Cables are installed, so when concrete is poured over the tension is released - this relies on interfacial bonding to steel

76
Q

What are post-tensioned cables?

A

Concrete is poured and then the cables are inserted and tensioned - this can have severe problems is the steel corrodes and the stress application is lost

77
Q

What is the equation for rusting?

A

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

78
Q

What causes iron corrosion?

A

Iron oxides form a passive film on the steel inside the concrete, which breaks down and leads to corrosion

79
Q

How can corrosion be prevented?

A

Reduce permeability of concrete

80
Q

How do you reduce the permeability of concrete?

A

Reduce the water/cement ratio, by using superplasticisers

81
Q

What are the specifications for testing in compression?

A

-Cubes (100-300 mm) or cylinders (100-300 mm diameter, with aspect ratio 2.0)
-Loaded faces must be flat
-Smaller specimens are stronger, because failure occurs at largest flaw
-Cylinders fail at lower loads due to the less restraint on faces

82
Q

What is an extrinsic property of concrete?

A

Strength (depends on sample size)

83
Q

What are the intrinsic properties of concrete?

A

Density, melting point, temperature

84
Q

Why are specimens not often tested in tension?

A

Tension tests are sensitive to specimen geometry, size and loading rate

85
Q

What is creep testing?

A

Stressing a material at a load well below failure for a long time

86
Q

What causes concrete creep?

A

C-S-H nanogranules in the microstructure sliding over each other and becoming compressed/deformed under load

87
Q

How should a creep tests samples be arranged?

A

-Test the samples for around 12 months
-Load samples at different ages (2-90d) to get better understanding of effects of binder maturity

88
Q

How does creep levels effect cracking?

A

Low tensile strength and low creep will crack more

89
Q

What is electrochemical testing used for?

A

To check the condition of reinforcing steel (detect corrosion currents)

90
Q

What are radiographic or radar-based methods used to determine?

A

To identify the location of reinforcement, the condition of the cover concrete, or large cracks

91
Q

What is the Schmidt (rebound) hammer test?

A

To see how much the hammer bounces off the surface

92
Q

What is the Windsor (penetration) prove used for?

A

To see how far into the surface can a projectile penetrate

93
Q

What is the pullout test used for?

A

A bolt is screwed into a drilled hole, and the difficulty to pull it out is measured

94
Q

What is the ultrasonic pulse velocity test used for?

A

To see how well the microstructure of the material transmits ultrasound

95
Q

How can Chloride corrosion be prevented in cold regions?

A

Salts are applied to concrete for de-icing

96
Q

What is the main ways to prevent Chloride attack?

A

-Reduce permeability
-Denser binder
-Pozzolanic reactions help in the long term (by producing more C-S-H from Portlandite)

97
Q

What effect does chloride have on steel?

A

Makes it rust

98
Q

Describe the ponding test for Chloride permeability.

A

-Concrete cylinder or slab, with a pool of chloride solution on top, and wait several months
-Measure how far chloride has travelled into the material, to calculate the diffusion coefficient

99
Q

What are the advantages and disadvantages of the ponding chloride permeability test?

A

-Simple and accurate
-Very slow and labour intensive

100
Q

Describe the rapid chloride permeability test.

A

Apply voltage and correlate the current passed by the specimen in 6 hours to chloride diffusion

101
Q

What parameters does the rapid chloride permeability test depend on?

A

-Chloride ions present
-Other dissolved ions in the pore solution

102
Q

What is a disadvantage of the rapid voltage permeability test?

A

Cannot be used to compare materials with different chemistry, but is useful for quality control of one material

103
Q

Describe the hybrid method to test chloride permeability.

A

Use electrical acceleration of chloride mitigation, but split the sample and measure actual chloride depth at the end of the test

104
Q

What are the advantages of the hybrid chloride permeability test?

A

-24 hour testing time, without dealing with the resistivity of the material
-Can compare different types of cement
-More reproducible

105
Q

What are the two reaction pathways for sulphate attack in concrete?

A

-Internal: Sulphates present within concrete, causing phase evolution after a long period
-External: Sulphates from the environment, entering the material and causing phase changes

106
Q

Describe a Thaumasite Sulphate attack.

A

-Needs cool, wet conditions, with both carbonates and sulphates present
-C-S-H is converted to thaumasite
-Concrete loses its strength and becomes soft and ‘mushy’
-Relatively rare worldwide, but important in UK conditions

107
Q

How do you test for Sulphate resistance in concrete?

A

-Immerse the concrete in a sulphate rich solution (usually 5 wt% Na2SO4)
-Measure specimen length regularly
-Testing for conversion of AFm to AFt phases
-Crystallisation of sulphate salts can cause additional (physical) damage

108
Q

What are the properties of Sulphate resistant concretes?

A

-Low Alite content, or high slag content
-Favours the formation of C-S-H rather than AFm phases during hydration, so does not expand
-High slag content also reduces permeability in the long-term

109
Q

What is an alkali-aggregate reaction?

A

When the aggregate contains reactive components, it can be attacked by the pore solution (Portland cement contains small amounts of Na and K that stay in the pore solution)

110
Q

What are the main Alkali guidelines put in place in the UK?

A

-Limits om alklai content of concrete based on aggregate reactivity classification
-Most cements sold in the UK are low-alkali
-Blending with slag or pozzolans helps protect from damage

111
Q

Describe the accelerated testing method (ASTM).

A

Mortar bars are places in 40 g/L NaOH at 80 degrees, and the expansion is measured after 16 days

112
Q

What are some advantages and disadvantages of the accelerated testing method?

A

-Adv: Fast and widely used
-Disadv: Known to give false results (because its an extremely aggressive test)

113
Q

What are the issues with carbonation?

A

-Atmospheric CO2 can act as an acid, which reduces the pH of cement which can induce corrosion of the steel reinforcements
-Happens fastest at intermediate humidity (~65%) or under wet-dry cycles
-The main limitation on concrete service life in warm climate areas without marine exposure

114
Q

How do you measure carbonation?

A

Measure the depth of CO2 ingress after exposure to CO2 (often at a higher concentration)

115
Q

Why could carbonation be a positive thing?

A

It is a possible route to global CO2 reduction, reversing some of the emissions from cement production

116
Q

What is freeze-thaw damage?

A

Degradation based on the ingress of water, when it freezes water expands ~9% and even more when higher salt levels are present

117
Q

What happens during a freeze-thaw test?

A

-Samples (usually cylinders or slabs) experience freeze-thaw cycles repeatedly
-Tens to hundreds of cycles used
-Measure changes in elastic modulus, dimensions, mass
-Sometimes just give a visual rating of damage

118
Q

How can freeze-thaw damage be prevented?

A

-Put appropriately sized bubbles into concrete
-Gives the water space to expand into as it freezes

119
Q

Name some of the activities covered by the material standards.

A

-Construction
-Nanotechnology
-Energy management
-Health and safety

120
Q

What forms can material standards come in?

A

-Guides
-Codes of practise
-Specifications
-Supporting documents

121
Q

What are prescriptive standards?

A

-Specify ingredients and recipes
-If a material is made as specified it is assumed to be okay
-Need to build in safety margins to be conservative

122
Q

What are performance-based standards?

A

-Define what a material needs to do, including how to test
-Allow the producer to design a material to meet these requirements
-More scope for innovation, but it takes a lot more work to prove the sufficient performance

123
Q

What speciality products tend to have purpose-written standards?

A

-Roof tiles
-Masonry blocks
-Paving slabs
-Tile grout

124
Q

What is the structure of European standards of concrete?

A

-Family tree of standards
-Strong cement/concrete industry influence in drafting
-Cascading set of requirements for materials to be used in concrete
-Many testing methods are integrated into material standards

125
Q

What is the composition of CEM I Portland cement?

A

> 95% Portland clinker

126
Q

What is the composition of CEM II Portland-composite cement?

A

65-94% Portland + 1 pozz./limestone

127
Q

What is the composition of CEM III Blast furnace cement?

A

5-64% Portland + slag

128
Q

What is the composition of CEM IV Pozzolanic cement?

A

45-89% Portland + 1 pozzolana

129
Q

What is the composition of CEM V Composite cement?

A

20-64% Portland + slag + 1 other SCM

130
Q

What is ASTM C150?

A

Portland cement

131
Q

What is ASTM C595?

A

Blended hydraulic cements

132
Q

What is ASTM C1157?

A

Standard performance specification for hydraulic cement

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