Cement

Question 1

How much of the C02 produced in the production of concrete comes from cement?

Answer 1

> 60% from modern concrete mixes
~25% comes from clinker substitution
80% for ordinary portland cement concrete

Question 2

What reaction takes place in the production of early forms of cement?

Answer 2

Lime reactions:
Calcinning calcium carbonate at ~700-900 C
(there is more info on slide 10 lecure 6)

Question 3

What are the 3 main stages of lime reactions

Answer 3

1. Calcium carbonate -> Lime
2. Quicklime + water –> portlandite
3. Portlandite hardens with CO2

Question 4

Name the main types of Hydraulic Inorganic Calcareous cements

Answer 4

Portland, Calcium aluminate, Pozzolaic, hydrophobic, Natural, expanding

Question 5

Name the main types of non-hydraulic inorganic calcareous cements

Answer 5

Limes, Gypsum cements and plasters

Question 6

What is the process for the production of odinary Portaland cement (OPC, ‘CEM 1’)

Answer 6

~75% limestone or chalk +
~25% clay or shale
--> Heat to 1450 C
--> Forms clinker 
--> Grind to powder
--> add ~4% gypsum

Question 7

What are the 3 main types of cement for packaging and transport?

Answer 7

• Ready-mix 47% of the market (6.2Mt)
• Precast 22% (2.8Mt)
• Retail 13% (2.4Mt)

Question 8

How is ready-mix concrete used?

Answer 8

Concrete is mixed and poured on site

Question 9

How is precast concrete used?

Answer 9

Product is manufactured off-site and tranported to site

Question 10

How is retail cement used?

Answer 10

must be mixed and poured on site, comes in a dry bag, small scale uses

Question 11

What is a Supplementary cementitous material (SCM)

Answer 11

Any reactive non-clinkered solid material used in cement (not including admixtures with special functions such as gypsum)

Question 12

What is cement clinker blended with?

Answer 12

A source of calcium sulphate (e.g. gypsum) and SCMs

Question 13

Give a few examples of SCMs

Answer 13

• finely ground limestone
• coal fly ash
• granulated blast furnace slag
• calcined clay
  (pictures on slide 25 lecture 6)

Question 14

When are SCMs added?

Answer 14

Either at the cement plant when limestone is added or at the concrete batching plant, this is dependent on cost

Question 15

What is capillary porosity?

Answer 15

• The space not filled by hydration pores
• 0.05 - 10 um in diammeter
• Influence strength and durability
• Determine transport properties in cement paste

Question 16

What pore humidity is needed to ensure hydration

Answer 16

> 80%, but it is slow blow 90% relative humidity

Question 17

What ratio of cement to hydration products occurs

Answer 17

1 unit of cement goes to 2.2 units of hydration products

Question 18

What does C-S-H stand for

Answer 18

Calcium Silicate hydrates

Question 19

What is the water to cement ratio (w/c) for high performance concrete

Answer 19

0.3

Question 20

What is the water to cement ratio (w/c) for structural concrete

Answer 20

0.45

Question 21

What is the water to cement ratio (w/c) for low performance (e.g. garden path) concrete

Answer 21

0.6

Question 22

What are the main phases of portland cement

Answer 22

Alite (C3S), Belite (C2S), aluminate (C3A), and ferrite (C4AF)

Question 23

Name some cement binder types

Answer 23

• Portland cement binder (CEM I)
• Blended (Portland) cement binders (CEM II-V LC^3)
• Reactive belite Portland cement binder (RBPC)
• Belite y’elemite - ferrite cement binder
• Calcium sulfoaluminate cement binder (CSA(B))
• Supersulfated Cement binder
  (more on slide 52 lecture 6