Cement

Question 1

Name 5 additions which can be used In combination with PC .

Answer 1

1. Fly Ash (FA) –
2. Ground Granulated Blastfurnace Slag (GGBS)
3. Condensed Silica Fume (CSF)
4. Metakaolin (MK)
5. Limestone

Question 2

How is fly ash (FA) produced?

Answer 2

1. Coal, consisting of a mixture of carbonaceous matter and other minerals is pulverised to a fine material before being injected into the power station furnace.
2. Combustion of coal produces fine ash which is precipitated from flue gases either mechanically or electrostatically.
3. Particles fuse to form tiny glass spheres of complex silicates
4. FA is collected and stored.

Question 3

What does characteristics of FA depend on?

Answer 3

Coal composition
Combustion temperature
Precipitation method

Question 4

How is GGBS produced?

Answer 4

1. Iron ore, coke and limestone are added to the blast-furnace at a temperature of around 1500C.
2. Iron ore is chemically reduced to form molten iron and a fusion of lime from limestone and siliceous and aluminous residues from iron ore and coke produces slag.
3. Molten slag is periodically tapped off and rapidly quenched using sprayed water to produce a granular material similar in size to coarse sand.
4. ‘Granulated’ slag is then dried and ground to a fine powder in conventional grinding mills to form GGBS.

Question 5

characteristics of GGBS.

Answer 5

Chemical composition of raw materials,

Degree of grinding

Question 6

How is Silica fume (CSF) produced

Answer 6

1. High purity quartz and coal are fired in submerged-arc electric furnaces.
2. The escaping gaseous silicon monoxide (SiO) oxidises and condensates in the form of extremely fine spherical particles of amorphous silica (SiO2).
3. Coarser particles are removed from flue gases by cyclone and finer particles (CSF) collected by baghouse filters.
4. CSF is stored in either powder form or more commonly slurry form.

Question 7

Characteristics of silica fume:

Answer 7

Chemical composition of raw materials,

Efficiency of heat recovery of furnace

Question 8

how is Metakolin (MK) produced?

Answer 8

1. Large quantities of coarse kaolin discarded as they are not fine enough for china and paper production.
2. The raw material kaolin is thermally activated and the most common constituent, kaolinite (Al2Si2O5(OH)4) is dehydroxilised at 700-800C.
3. The resulting calcined kaolinite clay is a very fine powder which is highly pozzolanic - MK.

Question 9

Characteristics of Metakolin:

Answer 9

Chemical composition of raw materials,

Temperature of thermal activation

Question 10

Influence of FA/GGBS/CSF/MK on fresh concrete properties:

Answer 10

FA / GGBS reduce water demand,
CSF / MK increase water demand,
They improve cohesion of the mix

Question 11

Influence of FA/GGBS/CSF/MK on hydrating concrete properties:

Answer 11

Rate of hydration,
Setting times,
Development of early strength,
Development of long-term strength,

Question 12

In what ways can limestone beneficially effect concrete?

Answer 12

workability,
stability,
density
permeation properties