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MAT1600 > Concrete and Cement > Flashcards

Concrete and Cement Flashcards

1
Q

Portland cements are used to make…

A

Concrete + motar, buildings, infrastructures, roads

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2
Q

Special cements (such as low-co2 and rapid hardening) are used for…

A

Immobilisation of toxic/ radioactive waste

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3
Q

Medical cements are used for…

A

Tooth and bone placements

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4
Q

ASTM…

A

Consists of calcium and calcium sulfates

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5
Q

Basis of most concrete reactions is…

A

A hydraulic reaction whereby the cement reacts with water and hardens

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6
Q

Definition of a paste and its use =

A

Cement + water

Rarely used by itself and so is combined with aggregates

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7
Q

Definition of mortar and its use =

A

Paste + sand

Used to join bricks together or used as a coating

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8
Q

Definition of concrete and its use =

A

Paste + sand + coarse aggregate

which is gravel or crushed rock

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9
Q

Aggregates are…

A

Sand, gravel, rocks ( much cheaper than cements)

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10
Q

Aggregates are bound together by…

A

Cement as it acts as a glue

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11
Q

Best to use aggregates that do not react with cement such as..

A

Granite, quartz and basalt

or a slightly reactive rock such as limestone

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12
Q

What happens when using a reactive material with cement (such as glass aggregate or sulfide)

A

They expand and cause the concrete to fail

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13
Q

Fine vs coarse aggregate =

A 
Fine = sand or crushed rocks
Coarse = larger rocks
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14
Q

Why should we not use glass aggregates or sulfide?

A

Aggregate does not normally react with the cement so this does and causes concrete failure

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15
Q

Two reasons we use aggregates

A
  • Strength; the concrete will be as strong as the aggregate

- Reduces thermal cracking (dilution of cement)

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16
Q

Shear-thinning is..

A

Concrete flows better if a force is applied to it otherwise it will set and harden

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17
Q

How to measure the flow of concrete:

A

-slump test; fill a cone with concrete then lift off and measure the distance in height

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18
Q

Role of water in cement:

A

Required for the hydration reaction and allows concrete to flow.

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19
Q

Too much water causes =

A
  • Forms extra pores
  • reduced durability and strength
  • delay the setting process.
20
Q

What is the normal water-cement ratio?

A

0.5 + - 0.2

21
Q

What does adding polymeric molecules to concrete do? (superplasticisers)

A

Increase the plastic molecules making more brittle so more durable.

22
Q

What happens when sulphate reacts with concrete?

A

The concrete reacts with the sulphate causing it to shrink

23
Q

What are the four main minerals in portland cement clinker?

A
  • Tricalcium silicate
  • Dicalcium silicate
  • Tetracalcium Aluminoferrite
  • Tricalcium aluminate
24
Q

What are the four main minerals in portland cement clinker in chemical symbols?

A
  • C3s
  • C2s
  • C3A
  • C4AF
25
Q

Hydration reaction =

A

Mixing with water; dissolves minerals

26
Q

Why is drying bad for fresh cement?

A

Stops the reaction process by evaporating water needed for reaction

27
Q

Important hydrate phases “Calcium silicate hydrate”

A
  • Formed by C3s and C2s
  • Non-crystallin (amorphous)
  • Main strength giving phase
28
Q

Important hydrate phases “Calcium hydroxide”

A
  • Formed by C3s and C2s
  • large crystallites
  • Protects from corrosion
29
Q

Important hydrate phases “Ettringite”

A
  • formed by c3a with water and gypsum
  • Needle like crystals
  • Initial setting of cement
30
Q

Important hydrate phases “Aluminoterite or AFm”

A

m for monosulphate

-Important as sink for al but also cause durability

31
Q

Importance of gypsum

A
  • gypsum plays a role in the setting of cement; controls setting
  • Without the cement would set straight away
32
Q

Heat of hydration graph

A

-Steep gradient is an acceleration period

33
Q

Three main types of cementitious materials:

A
  • Pozzolans
  • Ground granulated blast furnace slag
  • Limestone
34
Q

Pozzolanic reaction

A

Can blend portland cement with other forms of silicate

This is generally slower and can reduce early strength but contributes to long-term properties

35
Q

Pozzolanic additives:

A
  • Fly ash
  • Natural pozzolans
  • silica fume
  • Calcined caly
  • other waste silicate glass materials
36
Q

How is fly ash produced?

A
  • By product of coal combustion processes

- Helps fluidity of concrete

37
Q

Calcines clay

A
  • gives disordered reactive phase
  • highly reactive
  • Pozzolanic
  • Takes up alot of water
38
Q

Silica fume

A
  • by product of simiconductor
  • pozzolanic reaction
  • high early strength development
  • improves durability
39
Q

Slag

A
  • Reactives to form C-S-H or C-A-S-H

- Better than pozzolanic reaction

40
Q

Limestone

A

Calcium carbonate
Good for reactivity
-Improved properties such as strength

41
Q

5 key categories of portland cement:

A
  • Portland cement
  • Portland-composite cement
  • Blastfurnace cement
  • Pozzolanic cement
  • Composite cement
42
Q

Calcium aluminate cement =

A

High strength and rapid setting; strength loss under wrong conditions

43
Q

Geopolymer

A

Much lower emissions than portland cement

44
Q

Steel reinforcing=

A

Concrete is strong in compression but weaker in tension so increases tensile strength.
Steel is good in tension
chemistry of cement prevent steel from rusting

45
Q

Main cause of concrete failure =

A

Steel failure as steel rusts so it expands and crack the concrete

46
Q

How to prevent concrete failure =

A

Reduce permeability and water/cement ratio

47
Q

Causes of degredation =

A

Corrosive substances
Freeze thaw or frost-salt cycling
poor workmanship
seawater has sulphate and chloride

MAT1600 (4 decks)

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