Week 1: Introduction & Concrete Constituents

Question 1

Generalities about concrete

Answer 1

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

Question 2

Difference between cement & concrete

Answer 2

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

Question 3

Basic concrete mix constituents

Answer 3

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

Question 4

Concrete Mix Proportions

Answer 4

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

Question 5

Why are chemical admixtures used?

Answer 5

1. Cold climates have slow hydration reaction

2. Add chemicals to speed up process

Question 6

Portland Cement Basic Info

Answer 6

1. Most common type of cement in the world

2. Referred to as OPC (Ordinary Portland Cement)

Question 7

Cement Production- 2 main processess

Answer 7

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

Question 8

Summarise the manufacture process

Answer 8

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

Question 9

Why is limestone grind into powder?

Answer 9

In order to increase the SA, thus speed up reaction

Question 10

Raw material for Clinker

Answer 10

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%

Question 11

Clinker Burning Process: 750 degrees

Answer 11

Just need to know

Question 12

Clinker Burning Process: 950 degrees

Answer 12

1. Decarbonation of limestone (release of carbon)

2. CaCo3= CaO + CO2

Question 13

Clinker Burning Process: 1350 degrees

Answer 13

Reaction between CaO:

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

Question 14

Clinker Burning Process: Max 1450 degrees

Answer 14

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

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

Question 15

Cooling Process of Clinker

Answer 15

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

Question 16

Cement Chemistry

Answer 16

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

Question 17

Silicates & Aluminates Proportion

Answer 17

1. Silicates- 80%

2. Aluminates- 20%

Question 18

Oxide Composition of Clinker

Answer 18

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%

Question 19

Purpose of Gypsum

Answer 19

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

Question 20

Sustainability of Portland Cement

Answer 20

1. Limestone sampling:

• Landscape deterioration
• Consumption of natural resources

2. Transportation
3. Decarbonation of Limestone: High release of CO2 in the atmosphere
4. Burning process up to 1450 degrees: require a huge quantity of energy releasing more CO2 in the atmosphere
   - Bad carbon footprint

Question 21

Green Cements: Blended Cements Purpose

Answer 21

Replace a part of the clinker with SCMs

Question 22

Green Cements: Ecological advantages

Answer 22

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

Question 23

Green Cements: Structural advantages

Answer 23

1. Can improve concrete properties

Question 24

SCMs- Fly Ash

Answer 24

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

Question 25

SCMs- GGBFS Slag

Answer 25

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

Question 26

Amorphous Silica

Answer 26

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

Question 27

Pozzolans:

Answer 27

- 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

Question 28

Australian Standards: General Purpose Cement

Answer 28

1. GP 2. GB 3. GL

Question 29

Special Purpose Cement

Answer 29

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

Question 30

AS 3972-2010 Constituents

Answer 30

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

Question 31

Minor additions for GP:

Answer 31

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

Question 32

Type GL cement

Answer 32

1. Type GP + Limestone (8-20%) | 2. Smaller carbon footprint

Question 33

Type GB cement

Answer 33

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