Portland cement

Question 1

Describe three properties of cement.

Answer 1

-Binds solid aggregates together by hardening from a plastic state
-Has both adhesive and cohesive properties
-Functions by forming a plastic paste when mixed with water, which develops rigidity and then steadily increases in compressive strength by chemical reactions with water

Question 2

What is Portland cement?

Answer 2

A hydraulic cement produced by pulverising clinker, consisting of crystalline hydraulic calcium silicates, usually containing one or more of the following: water, calcium sulphate, up to 5% limestone, processing additions

Question 3

How much of the worlds concrete uses Portland cement?

Answer 3

> 95%

Question 4

Give the following compounds abbreviations: Calcium oxide (CaO), Silicon Dioxide (SiO2), Aluminium Oxide (Al2O3), Iron Oxide (Fe2O3), Water (H2O), Sulphur Trioxide (SO3), Carbon Dioxide (CO2), Sodium Oxide (Na2O), Potassium Oxide (K2O)

Answer 4

CaO - C
SiO2 - S
Al2O3 - A
Fe2O3 - F
H2O - H
SO3 - S(bar)
CO2 - c
Na2O - N
K2O - K

Question 5

Describe Alite clinker.

Answer 5

(C3S) Hardens rapidly, develops high strength

Question 6

Describe Belite clinker.

Answer 6

(Beta-C2S) Hardens slowly, develops high strength

Question 7

Describe Aluminate clinker.

Answer 7

(C3A) Reacts with gypsum, products are of low solubility

Question 8

Describe Ferrite clinker.

Answer 8

(C4AF) Similar of C3A Aluminate but not as rapid

Question 9

Describe Calcium Silicate Hydrate (C-S-H).

Answer 9

-Formed by the hydration of Alite and Belite
-Makes up to 70 wt% of fully hydrated phase
-The major strength contributing phase

Question 10

Describe Calcium Hydroxide/Portlandite (C-H).

Answer 10

-By product of Alite and Belite hydration (they have more Ca than can be accommodated for in C-S-H)
-Makes up to 20 wt% of fully hydrated phase
-Does not contribute to strength

Question 11

Describe Ettringite.

Answer 11

-Direct reaction of Aluminate with water leads to flash set (stiffening without strength development) forming aluminate hydrates
-By adding gypsum, aluminate reacts moderately an forms ettringite (Alumina ferric oxide tri-sulphate)

Question 12

Why is mineral component tat added to cement?

Answer 12

To improve performance and reduce cost

Question 13

What are supplementary cementitious materials (SCMs)?

Answer 13

Mineral component tat (NOT AGGREGATES)

Question 14

What is a Pozzolanic reaction?

Answer 14

Silica and alumina component reacts with portlandite to produce more C-S-H

Question 15

What is the point of carrying out pozzolanic reactions?

Answer 15

C-S-H fills pore spaces at longer age, improving strength and durability

Question 16

How fast is a pozzolanic reaction?

Answer 16

Generally slower than cement hydration

Question 17

What happens when cement is substituted for pozzolans?

Answer 17

Early strength is reduced

Question 18

What physical properties change when the cement is blended?

Answer 18

-Extra C-S-H fills in space, which gives extra strength
-Chemical durability improves

Question 19

Give some examples of Pozzolanic SCMs.

Answer 19

-Fly ash
-Volcanic earth
-Calcines clays
-Silica fumes
-Rice husk ash
-Waste silicate glass

Question 20

Give two examples of non-pozzolanic SCMs.

Answer 20

-Limestone
-Blast furnace slag