SCM’s And Non-standard Portland Cements

Question 1

State 5 SCMs/additions

Answer 1

Granulated blast-furnace slag (GGBS)
Fly ashes (PFA)
Silica fume (SF)
Burnt shale
Pozzolanic (natural) materials

Question 2

From an environmental view why do we use SCM’s

Answer 2

By products-carbon footprint reduced

Avoids using raw materials and diverts material from landfill

Question 3

From a performance view, why do we use SCMs

Answer 3

They’re pozzolans-produce extra C-S-H when reacted with lime calcium hydroxide-reduce in porosity-less permeable-increased durability

Question 4

What is a pozzolanic material?

Answer 4

Finely divided materials which don’t have cementitious properties but react with lim in presence of water producing extra C-S-H

Question 5

Compare the reaction of SCMs with water against CEM 1 with water

Answer 5

SCM reaction is slow-strength development slower

C-S-H produced has lower C/S ratio

Question 6

How is GGBS different from other SCM’s in the way it interacts with water?

Answer 6

GGBS contains Ca-self hydraulic-would slowly hydrate and set in the presence of water

Question 7

Why do SCM’s form C-S-H in the presence of calcium

Answer 7

SCM’s are silica rich and contain some aluminium and iron. The Si and Al react with the calcium present in portlandite, producing C-S-H

Question 8

When are SCM’s unstable and why?

Answer 8

SCM’s are non-crystalline (glassy), and therefore unstable in high pH’s.
Cement hydrates-CH produced-pH 12.6-dissolution of glassy SCM-Si and Al ions released and react with Ca in portlandite-form C-S-H.

Question 9

What is GGBS and how is it made?

Answer 9

SCM-byproduct of iron production
Iron ore + limestone heated at 1800C-react leaving molten slag behind-cooled very quickly to make glassy-ground to cement fineness