Supplementary Cementing Materials (SCM's)

Question 1

What is SCM’s?

Answer 1

Material when used with portland cement contributes to the properties of the hardened concrete through:
Hydraulic Activity
or
Pozzolanic Activity
or
BOTH

Question 2

What are the 2 types of SCM’s?

Answer 2

Pozzolans and natural Pozzolans

Question 3

What is a pozzolanic reaction?

Answer 3

When SCM’s is added, it provide a reactive amorphous silica (S) in the hydration products in order to have more Calcium Silica Hydroxyde (CH–>CSH). (this addition of S leads to a pozzolanic reaction)

Question 4

What are the 3 benefits of adding SCM’s?

Answer 4

Pozzolanic reaction –> higher strength
Physicall filler effect –> Less voids, higher strenght
Densification of agg.- Cement Paste transition Zone (BOTH)–> Denser transition zone (more impermeable)

Question 5

What is the interfacial transition zone (ITZ)?

Answer 5

It is a thin layer between the agg. and cement of concrete caused by the wall effect

Question 6

Where is the weakest component in the concrete?

Answer 6

ITZ

Question 7

Where is the most permeable area in the concrete?

Answer 7

ITZ

Question 8

What is silica fume?

Answer 8

A SCM
Smoke by product from the production of ferrosilicon and silicon metals
Very fine non-crystalline silica
Amorphous Silica

Question 9

What is an amorphous silica?

Answer 9

High Silica content
Unstable
Surface can react

Question 10

What is a crystal silica?

Answer 10

Like glass
No reaction

Question 11

What are the 3 silica fume product forms?

Answer 11

As produced powder
Silica Fume slurry
Densified Silica Fume

Question 12

What is particle size of SF?

Answer 12

<1micrometre

Question 13

What is the strength activity index?

Answer 13

= (A/B)*100
A: average compressive strength of blended cement mixture cubes
B: average compressive strength of pure cement mixture cubes

Question 14

What is responsible in the strength of cement (hydration product)

Answer 14

CSH

Question 15

How can SF enhance durability to corrosion?

Answer 15

SF reduces permeability of concrete and diffusion of chlorides, which enhance durability to corrosion

Question 16

What does adding SF will result in the cement?

Answer 16

higher strength
less permeability (enhance durability)
less segregation (Increase concrete cohesiveness)

Question 17

How much days for moist curing to prevent water evaporation of SF concrete (Shrinkage cracks)?

Answer 17

7

Question 18

What is FA?

Answer 18

By product of coal burned power plants
Spherical particles

Question 19

What are the 2 type of FA?

Answer 19

Type C (high calcium oxyde)
Type F (low calcium oxyde)

Question 20

Does FA have a filler effect?

Answer 20

Yes, less effective than SF

Question 21

What is the particle size of FA?

Answer 21

Between 1micro meter to 100 micro meters

Question 22

SA of FA?

Answer 22

200 to 700 m^2/kg

Question 23

SA of SF?

Answer 23

13000 to 30000 m2/kg

Question 24

Does SF has a higher pozzolanic activity than FA? (NOT SURE)

Answer 24

No, FA has higher pozzolanic activity (NOT SURE)

Question 25

What does FA brings to concrete?

Answer 25

Increases late strength (S+CH=CSH) Reduces permeability (enhance durability) Increase workability Reduce heat of hydration Increase concrete Alkali-Silica reaction resistance Increate concrete sulfate resistance

Question 26

What influences the setting time of FA?

Answer 26

FA hydrates slowly (setting time extended) Finer fly ash --> shorter setting time high CaO content --> shorter setting time

Question 27

FA concrete tends to gain strength at quicker rate or slower rate then concrete without FA?

Answer 27

Slower (long term gains are higher with FA)

Question 28

When will the long term strength of OPC+FA be higher than OPC

Answer 28

90 days and after

Question 29

which type of FA reduces sulfate attacks?

Answer 29

Type F (low calcium)

Question 30

What is slag?

Answer 30

by product of metallurgical industry Crystalline (used as agg.) Can be used hydraulic binders (GBFS; Granulated Blast Furnace Slag) React slowly with water (low heat of hydration)

Question 31

What are the properties of slag?

Answer 31

Smoother than cement particles density is lower than cement Replacement by weight leads to a higher paste volume and better workability At low T, setting time is increased Low heat of hydration

Question 32

How does the strength of concrete's affected with slag?

Answer 32

Low early strength, High later strength (significant after 1 year) Comparable strength to OPC after 28 days

Question 33

What does slag bring to concrete?

Answer 33

Increases later strength Reduces permeability (enhance durability/less corrosion) Increases workability Reduce Heat of hydration Increase ASR resistance (less expansion) Fire resistance

Question 34

What are the 2 types of natural pozzolans?

Answer 34

Raw (ash from volcanic) and calcined natural pozzolans (calcined clays)

Question 35

Which SCM' could be used for ASR resistance?

Answer 35

FA Slag SF Nat pozzolans

Question 36

Which SCM's could be used to reduce permeability?

Answer 36

FA Slag SF Nat pozzolans (ALL OF THEM)

Question 37

Which SCM's could be used to increase workability?

Answer 37

FA Slag Nat pozzolans

Question 38

Which SCM's could be used to reduce heat of hydration?

Answer 38

FA Slag Nat pozzolans SF VARIES

Question 39

Why does SF has high water requirements?

Answer 39

Because water evaporates and results in drying shrinkage