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Construction Materials > Week 1: Introduction & Concrete Constituents > Flashcards

Week 1: Introduction & Concrete Constituents Flashcards

1
Q

Generalities about concrete

A
  1. Porous material
  2. Ageing material
    • Strength increases
    • Porosity decreases
      -
  3. High compression strength: 20-120 mPa
    • Ordinary concrete (20-45 MPa)
    • High performance concrete (45-120 mPa)
  4. Low tensile strength
    - Concrete compresses a lot
    - Steel is used to reinforce concrete’s tension
    - /10 to measure compression strength
  5. Density = 2.3 tons/m3
  6. Deteriorates with time when exposed to aggressive environment
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2
Q

Difference between cement & concrete

A

Cement is a constituent of concrete. Whereas concrete is the final product

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3
Q

Basic concrete mix constituents

A
  1. Water + Cement= Glue
  2. Sand + Rocks/gravel= Aggregates
  3. Glue + Aggregates + Chemical admixtures= Concrete
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4
Q

Concrete Mix Proportions

A
  1. Cement. 7-14% volume
  2. Aggregates. 60-70% volume
  3. Water. 14-22%
  4. Chemical admixtures. >2%
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5
Q

Why are chemical admixtures used?

A
  1. Cold climates have slow hydration reaction

2. Add chemicals to speed up process

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6
Q

Portland Cement Basic Info

A
  1. Most common type of cement in the world

2. Referred to as OPC (Ordinary Portland Cement)

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7
Q

Cement Production- 2 main processess

A
  1. Clinker- main constituent
    - Limestone & Clay are burnt together
  2. Portland Cement
    - Grinding clinker & small amount of gypsum
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8
Q

Summarise the manufacture process

A
  1. Limestone is crushed
  2. Other raw materials, clay, limestone are stored
  3. Sent to preheaters
  4. Burning Kiln
  5. Gypsum added
  6. Final grinding
  7. Distribution/ Storage
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9
Q

Why is limestone grind into powder?

A

In order to increase the SA, thus speed up reaction

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10
Q

Raw material for Clinker

A
  1. Lime, CaO, Limestone, C, 91%
  2. Silica, SiO2, Clay, S, 4%
  3. Alumina, Al203, Clay, A, 4%
  4. Iron Oxide, Fe2O3, Clay, F, 1%
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11
Q

Clinker Burning Process: 750 degrees

A

Just need to know

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12
Q

Clinker Burning Process: 950 degrees

A
  1. Decarbonation of limestone (release of carbon)

2. CaCo3= CaO + CO2

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13
Q

Clinker Burning Process: 1350 degrees

A

Reaction between CaO:

  1. Calcium Silicate (Si)
  2. Calcium Aluminate (Al)
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14
Q

Clinker Burning Process: Max 1450 degrees

A
  1. Liquid formation with C3A & C4AF (iron oxide)

2. Formation of C3S resulting from the reaction between C2S and Ca0 still available

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15
Q

Cooling Process of Clinker

A
  1. Few minutes
  2. Temperature drops from 1300/1400- 80
  3. Cool down required to stabilise C3S
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16
Q

Cement Chemistry

A
  1. Tricalcium Silicate- C3S (Alite). Stabilisation of clinker
  2. Dicalcium Silicate- C2S (Belite)
  3. Tricalcium aluminate- C3A (Aluminate)
  4. Tetracalcium Aluminoferrite- C4AF (Ferrite)
17
Q

Silicates & Aluminates Proportion

A
  1. Silicates- 80%

2. Aluminates- 20%

18
Q

Oxide Composition of Clinker

A
  1. CaO- 60-67% weight
  2. SiO2- 17-25%
  3. Al2O3- 3-8%

Minor Constituents:

  1. Fe203- 0.5-6%
  2. MgO - 0.1-4%
19
Q

Purpose of Gypsum

A
  1. To prevent flash set
  2. Workability
  3. Time necessary to delay concrete
20
Q

Sustainability of Portland Cement

A
  1. Limestone sampling:
  • Landscape deterioration
  • Consumption of natural resources
  1. Transportation
  2. Decarbonation of Limestone: High release of CO2 in the atmosphere
  3. Burning process up to 1450 degrees: require a huge quantity of energy releasing more CO2 in the atmosphere
    - Bad carbon footprint
21
Q

Green Cements: Blended Cements Purpose

A

Replace a part of the clinker with SCMs

22
Q

Green Cements: Ecological advantages

A
  1. Waste from power plants
  2. By-products cause serious environmental pollution
  3. Reduce the production of Clinker
23
Q

Green Cements: Structural advantages

A
  1. Can improve concrete properties
24
Q

SCMs- Fly Ash

A
  1. Industrial waste from black coal fired power stations
  2. Pozzolanic reaction with cement and water
  3. 20-40% of cement is replaced by fly ash
  4. Spherical particles
25
Q

SCMs- GGBFS Slag

A
  1. Formed at high temperature in iron blast furnace
  2. Quenched with water spray forming granulated slag
  3. Ground to fine particles with semi-hydraulic reaction with water
  4. 60% of cement can be replaced
26
Q

Amorphous Silica

A
  1. Silica Fume: Industrial waste from silicon or ferrosilicon production
  2. Very fine material with highly pozzolanic reaction
  3. 5-10% of cement can be replaced
27
Q

Pozzolans:

A
  • Broad class of siliceous or siliceous/aluminous material
  • Possess little or no cementitious value by themselves
  • In finely divided form, will react with water
  • Form compounds possessing cementitious properties
28
Q

Australian Standards: General Purpose Cement

A
  1. GP
  2. GB
  3. GL
29
Q

Special Purpose Cement

A
  1. HE- High Early
  2. LH- Low Heat
  3. SR- Sulfate Resistance
  4. SL- Shrinkage Limited
30
Q

AS 3972-2010 Constituents

A
  1. Add up to 7.5% of mineral additions
    - Limestone
    - Fly ash
    - GGBFS
31
Q

Minor additions for GP:

A
  1. Add up to 5%
    • Selected inorganic natural materials
    • Organic mineral materials derived from clinker
    • e.g. Cement kiln dust
32
Q

Type GL cement

A
  1. Type GP + Limestone (8-20%)

2. Smaller carbon footprint

33
Q

Type GB cement

A
  1. Type GP
  2. Fly ash and/or slag
  3. Amorphous Silica
  4. Better strength & durability

Construction Materials (1 decks)

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