Cement

Question 1

What’s the technical reason for caring about cement?

Answer 1

Its the key binding agent in mortar and concrete

Question 2

What is the environmental reason for caring about cement?

Answer 2

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

Question 3

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

Answer 3

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

Question 4

How was cement used in 5600BC?

Answer 4

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

Question 5

How was cement used in 2500 BC?

Answer 5

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

Question 6

How did greeks create mortars?

Answer 6

Used lime and sand

Question 7

How is lime produced?

Answer 7

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

Question 8

How is portlandite formed?

Answer 8

Using quicklime and water

Question 9

What is slaked lime?

Answer 9

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

Question 10

Why does slaked lime not harden in water?

Answer 10

Water is a product

Question 11

How did romans create stronger mortar and concretes?

Answer 11

Mixed lime with fine volcanic ash containing silica and alumina

Question 12

When was Portland cement patented and who by?

Answer 12

1824 - Joseph Aspdin

Question 13

What is ‘Portland cement’ made from?

Answer 13

Limestone + fine clay heated to 1200°C

Question 14

What’s the dominate phase in Portland cement clinker?

Answer 14

alite (C3S)

Question 15

What’s the difference between alite and belite?

Answer 15

Alite is more reactive

Question 16

What are the two types of inorganic calcareous cements?

Answer 16

Hydraulic and Non-hydraulic

Question 17

What are some hydraulic cements?

Answer 17

• PC
• Natural cements
• Calcium aluminate cements
• Pozzolanic cement

Question 18

What are types of Portland cement?

Answer 18

• Ordinary PC
• Rapid hardening PC
• Low heat PC
• White PC

Question 19

What are non-hydraulic cements?

Answer 19

• Lime
• Gypsum cements and plasters

Question 20

How are the different Portland cements differentiated?

Answer 20

Using British/European Standard designation

Question 21

What are cements currently standardised in terms of?

Answer 21

Raw materials

Question 22

What are the typical ratios for Portland cement?

Answer 22

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

Question 23

What temp is rotary kiln usually at?

Answer 23

1450 degrees

Question 24

What happens during calcination?

Answer 24

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

Question 25

What's an example of a cement plant?

Answer 25

Dunbar in Scotland

Question 26

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

Answer 26

- To homogenise the feedstock - To provide more surface area for reactions in the kiln

Question 27

What are the different types of packing of cement?

Answer 27

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

Question 28

What are SCMs?

Answer 28

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

Question 29

What are some common SCMs?

Answer 29

- Coal fly ash - Calcined clay - Limestone (+gypsum) - Granulated blast furnace slag

Question 30

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

Answer 30

30 min

Question 31

What is a phase?

Answer 31

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

Question 32

How can phase composition of Portland cement clinker be estimated?

Answer 32

From the 'Bogue composition'

Question 33

Why is seawater not good for concrete?

Answer 33

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

Question 34

How does hydration occur?

Answer 34

Continues in the presence of sufficient amounts of water

Question 35

How are hydration products 1 unit volume of cement?

Answer 35

They are less dense than clinker

Question 35

What are the process of hydration products?

Answer 35

Setting and hardening

Question 36

What is PC like in the initial setting?

Answer 36

Plastic workable paste

Question 37

What is the PC like in the final set?

Answer 37

Stiff unworkable

Question 38

What is the PC like during hardening?

Answer 38

Rigid solid gaining strength with time

Question 39

What is the hydration of cement?

Answer 39

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

Question 40

What does unhydrated cement look like?

Answer 40

White

Question 41

What is C-S-H?

Answer 41

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.

Question 42

What are capillary pores?

Answer 42

- Space not filled by hydration products

Question 43

What size are capillary pores usually?

Answer 43

0.05-10 micrometers

Question 44

What are features of C-S-H?

Answer 44

- Enormous specific surface - High porosity - Low permeability

Question 45

What is the Interfacial transition zone?

Answer 45

- 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

Question 46

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

Answer 46

High performance

Question 47

What if the w/c = 0.45

Answer 47

Structural purposes

Question 48

How does porosity change?

Answer 48

With increasing degree of cement hydration

Question 49

What are some binder types?

Answer 49

- 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)

Question 50

What are pros of alkali -activated materials?

Answer 50

- Heat and fire resistant - Superior thermal expansion properties - Much faster setting process and strength development

Question 51

What are cons of alkali -activated materials?

Answer 51

- 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**