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CIVE40007 – Materials > Cement > Flashcards

Cement Flashcards

1
Q

What’s the technical reason for caring about cement?

A

Its the key binding agent in mortar and concrete

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2
Q

What is the environmental reason for caring about cement?

A

Cement is responsible for >60% of the CO2 emissions arising from the production of modern concrete mixes

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3
Q

What is the socio-economic reason for caring about cement?

A

We depend on concrete and thus cement to provide essential building and infrastructure services

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4
Q

How was cement used in 5600BC?

A
  • Concrete floors of huts in Lepenski Vir, Yugoslavia
  • Material uncertain but probably lime
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5
Q

How was cement used in 2500 BC?

A
  • Great Pyramid, Giza, Egypt
  • Cementing material lime (from limestone, CaCO3) or burnt gypsum
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6
Q

How did greeks create mortars?

A

Used lime and sand

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7
Q

How is lime produced?

A

By calcining (heating) natural calcium carbonate
(limestone, chalk, marble, etc.) at approximately 700-900°C

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8
Q

How is portlandite formed?

A

Using quicklime and water

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9
Q

What is slaked lime?

A

Hydrated lime also called slaked lime is produced when water is added to calcium oxide -> raise pH

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10
Q

Why does slaked lime not harden in water?

A

Water is a product

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11
Q

How did romans create stronger mortar and concretes?

A

Mixed lime with fine volcanic ash containing silica and alumina

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12
Q

When was Portland cement patented and who by?

A

1824 - Joseph Aspdin

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13
Q

What is ‘Portland cement’ made from?

A

Limestone + fine clay heated to 1200°C

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14
Q

What’s the dominate phase in Portland cement clinker?

A

alite (C3S)

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15
Q

What’s the difference between alite and belite?

A

Alite is more reactive

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16
Q

What are the two types of inorganic calcareous cements?

A

Hydraulic and Non-hydraulic

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17
Q

What are some hydraulic cements?

A
  • PC
  • Natural cements
  • Calcium aluminate cements
  • Pozzolanic cement
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18
Q

What are types of Portland cement?

A
  • Ordinary PC
  • Rapid hardening PC
  • Low heat PC
  • White PC
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19
Q

What are non-hydraulic cements?

A
  • Lime
  • Gypsum cements and plasters
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20
Q

How are the different Portland cements differentiated?

A

Using British/European Standard designation

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21
Q

What are cements currently standardised in terms of?

A

Raw materials

22
Q

What are the typical ratios for Portland cement?

A
  • 75% limestone/chalk
  • 25% clay or shale
  • 4% gypsum
23
Q

What temp is rotary kiln usually at?

A

1450 degrees

24
Q

What happens during calcination?

A

Calcium carbonate is converted into calcium oxide, which reacts with raw material constituents to form clinker minerals.

25
Q

What’s an example of a cement plant?

A

Dunbar in Scotland

26
Q

Why are raw materials crushed and ground prior to being fed into a cement kiln?

A
  • To homogenise the feedstock
  • To provide more surface area for reactions in the kiln
27
Q

What are the different types of packing of cement?

A
  1. Ready-mix - onsite
  2. Precast - off site
  3. Retail
  4. Other/ not specified
28
Q

What are SCMs?

A

SCMs are materials used as a partial replacement of portland cement to improve both fresh and hardened concrete properties

29
Q

What are some common SCMs?

A
  • Coal fly ash
  • Calcined clay
  • Limestone (+gypsum)
  • Granulated blast furnace slag
30
Q

How long does it take for the phases along a heat exchanger to form in a rotary kiln?

A

30 min

31
Q

What is a phase?

A

A phase is a form of matter that is uniform throughout in chemical composition and physical state

32
Q

How can phase composition of Portland cement clinker be estimated?

A

From the ‘Bogue composition’

33
Q

Why is seawater not good for concrete?

A

Seawater which contains a high chloride concentration (not good for chloride- induced steel corrosion)

34
Q

How does hydration occur?

A

Continues in the presence of sufficient amounts of water

35
Q

How are hydration products 1 unit volume of cement?

A

They are less dense than clinker

35
Q

What are the process of hydration products?

A

Setting and hardening

36
Q

What is PC like in the initial setting?

A

Plastic workable paste

37
Q

What is the PC like in the final set?

A

Stiff unworkable

38
Q

What is the PC like during hardening?

A

Rigid solid gaining strength with time

39
Q

What is the hydration of cement?

A

Hydration is the process by which Portland cement becomes a firm, hardened mass after the addition of water

40
Q

What does unhydrated cement look like?

A

White

41
Q

What is C-S-H?

A

Calcium-silicate hydrate (C-S-H) is the main binder in cement and concrete. It starts forming from the early stages of cement hydration and it progressively densifies as cement sets.

42
Q

What are capillary pores?

A
  • Space not filled by hydration products
43
Q

What size are capillary pores usually?

A

0.05-10 micrometers

44
Q

What are features of C-S-H?

A
  • Enormous specific surface
  • High porosity
  • Low permeability
45
Q

What is the Interfacial transition
zone?

A
  • The interfacial transition zone (ITZ), which is known as the most important interface in concrete, is located between cement paste and aggregate in traditional concrete
  • Weakness zone
46
Q

What does it mean if the w/c = 0.3?

A

High performance

47
Q

What if the w/c = 0.45

A

Structural purposes

48
Q

How does porosity change?

A

With increasing degree of cement hydration

49
Q

What are some binder types?

A
  • Portland cement binder (CEM I)
  • Reactive belite Portland cement binder (RBPC)
  • Calcium sulfoaluminate cement binder (CSA(B))
  • Blended (Portland) cement binders (CEM II-V, LC3)
50
Q

What are pros of alkali -activated materials?

A
  • Heat and fire resistant
  • Superior thermal expansion properties
  • Much faster setting process and strength development
51
Q

What are cons of alkali -activated materials?

A
  • May be prone to shrinkage and cracking
  • Steel corrosion chemistry is different
  • Health and safety (handling high pH solutions)
  • Activator adds expense and environmental impacts

CIVE40007 – Materials (16 decks)

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