Concrete and Cement

Question 1

Portland cements are used to make…

Answer 1

Concrete + motar, buildings, infrastructures, roads

Question 2

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

Answer 2

Immobilisation of toxic/ radioactive waste

Question 3

Medical cements are used for…

Answer 3

Tooth and bone placements

Question 4

ASTM…

Answer 4

Consists of calcium and calcium sulfates

Question 5

Basis of most concrete reactions is…

Answer 5

A hydraulic reaction whereby the cement reacts with water and hardens

Question 6

Definition of a paste and its use =

Answer 6

Cement + water

Rarely used by itself and so is combined with aggregates

Question 7

Definition of mortar and its use =

Answer 7

Paste + sand

Used to join bricks together or used as a coating

Question 8

Definition of concrete and its use =

Answer 8

Paste + sand + coarse aggregate

which is gravel or crushed rock

Question 9

Aggregates are…

Answer 9

Sand, gravel, rocks ( much cheaper than cements)

Question 10

Aggregates are bound together by…

Answer 10

Cement as it acts as a glue

Question 11

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

Answer 11

Granite, quartz and basalt

or a slightly reactive rock such as limestone

Question 12

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

Answer 12

They expand and cause the concrete to fail

Question 13

Fine vs coarse aggregate =

Answer 13

Fine = sand or crushed rocks
Coarse = larger rocks

Question 14

Why should we not use glass aggregates or sulfide?

Answer 14

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

Question 15

Two reasons we use aggregates

Answer 15

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

- Reduces thermal cracking (dilution of cement)

Question 16

Shear-thinning is..

Answer 16

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

Question 17

How to measure the flow of concrete:

Answer 17

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

Question 18

Role of water in cement:

Answer 18

Required for the hydration reaction and allows concrete to flow.

Question 19

Too much water causes =

Answer 19

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

Question 20

What is the normal water-cement ratio?

Answer 20

0.5 + - 0.2

Question 21

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

Answer 21

Increase the plastic molecules making more brittle so more durable.

Question 22

What happens when sulphate reacts with concrete?

Answer 22

The concrete reacts with the sulphate causing it to shrink

Question 23

What are the four main minerals in portland cement clinker?

Answer 23

• Tricalcium silicate
• Dicalcium silicate
• Tetracalcium Aluminoferrite
• Tricalcium aluminate

Question 24

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

Answer 24

• C3s
• C2s
• C3A
• C4AF

Question 25

Hydration reaction =

Answer 25

Mixing with water; dissolves minerals

Question 26

Why is drying bad for fresh cement?

Answer 26

Stops the reaction process by evaporating water needed for reaction

Question 27

Important hydrate phases "Calcium silicate hydrate"

Answer 27

- Formed by C3s and C2s - Non-crystallin (amorphous) - Main strength giving phase

Question 28

Important hydrate phases "Calcium hydroxide"

Answer 28

- Formed by C3s and C2s - large crystallites - Protects from corrosion

Question 29

Important hydrate phases "Ettringite"

Answer 29

- formed by c3a with water and gypsum - Needle like crystals - Initial setting of cement

Question 30

Important hydrate phases "Aluminoterite or AFm"

Answer 30

m for monosulphate | -Important as sink for al but also cause durability

Question 31

Importance of gypsum

Answer 31

- gypsum plays a role in the setting of cement; controls setting - Without the cement would set straight away

Question 32

Heat of hydration graph

Answer 32

-Steep gradient is an acceleration period

Question 33

Three main types of cementitious materials:

Answer 33

- Pozzolans - Ground granulated blast furnace slag - Limestone

Question 34

Pozzolanic reaction

Answer 34

Can blend portland cement with other forms of silicate | This is generally slower and can reduce early strength but contributes to long-term properties

Question 35

Pozzolanic additives:

Answer 35

- Fly ash - Natural pozzolans - silica fume - Calcined caly - other waste silicate glass materials

Question 36

How is fly ash produced?

Answer 36

- By product of coal combustion processes | - Helps fluidity of concrete

Question 37

Calcines clay

Answer 37

- gives disordered reactive phase - highly reactive - Pozzolanic - Takes up alot of water

Question 38

Silica fume

Answer 38

- by product of simiconductor - pozzolanic reaction - high early strength development - improves durability

Question 39

Slag

Answer 39

- Reactives to form C-S-H or C-A-S-H | - Better than pozzolanic reaction

Question 40

Limestone

Answer 40

Calcium carbonate Good for reactivity -Improved properties such as strength

Question 41

5 key categories of portland cement:

Answer 41

- Portland cement - Portland-composite cement - Blastfurnace cement - Pozzolanic cement - Composite cement

Question 42

Calcium aluminate cement =

Answer 42

High strength and rapid setting; strength loss under wrong conditions

Question 43

Geopolymer

Answer 43

Much lower emissions than portland cement

Question 44

Steel reinforcing=

Answer 44

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

Question 45

Main cause of concrete failure =

Answer 45

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

Question 46

How to prevent concrete failure =

Answer 46

Reduce permeability and water/cement ratio

Question 47

Causes of degredation =

Answer 47

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