Supplementary Cementing Materials (SCM's) Flashcards
What is SCM’s?
Material when used with portland cement contributes to the properties of the hardened concrete through:
Hydraulic Activity
or
Pozzolanic Activity
or
BOTH
What are the 2 types of SCM’s?
Pozzolans and natural Pozzolans
What is a pozzolanic reaction?
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)
What are the 3 benefits of adding SCM’s?
Pozzolanic reaction –> higher strength
Physicall filler effect –> Less voids, higher strenght
Densification of agg.- Cement Paste transition Zone (BOTH)–> Denser transition zone (more impermeable)
What is the interfacial transition zone (ITZ)?
It is a thin layer between the agg. and cement of concrete caused by the wall effect
Where is the weakest component in the concrete?
ITZ
Where is the most permeable area in the concrete?
ITZ
What is silica fume?
A SCM
Smoke by product from the production of ferrosilicon and silicon metals
Very fine non-crystalline silica
Amorphous Silica
What is an amorphous silica?
High Silica content
Unstable
Surface can react
What is a crystal silica?
Like glass
No reaction
What are the 3 silica fume product forms?
As produced powder
Silica Fume slurry
Densified Silica Fume
What is particle size of SF?
<1micrometre
What is the strength activity index?
= (A/B)*100
A: average compressive strength of blended cement mixture cubes
B: average compressive strength of pure cement mixture cubes
What is responsible in the strength of cement (hydration product)
CSH
How can SF enhance durability to corrosion?
SF reduces permeability of concrete and diffusion of chlorides, which enhance durability to corrosion
What does adding SF will result in the cement?
higher strength
less permeability (enhance durability)
less segregation (Increase concrete cohesiveness)
How much days for moist curing to prevent water evaporation of SF concrete (Shrinkage cracks)?
7
What is FA?
By product of coal burned power plants
Spherical particles
What are the 2 type of FA?
Type C (high calcium oxyde)
Type F (low calcium oxyde)
Does FA have a filler effect?
Yes, less effective than SF
What is the particle size of FA?
Between 1micro meter to 100 micro meters
SA of FA?
200 to 700 m^2/kg
SA of SF?
13000 to 30000 m2/kg
Does SF has a higher pozzolanic activity than FA? (NOT SURE)
No, FA has higher pozzolanic activity (NOT SURE)
What does FA brings to concrete?
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
What influences the setting time of FA?
FA hydrates slowly (setting time extended)
Finer fly ash –> shorter setting time
high CaO content –> shorter setting time
FA concrete tends to gain strength at quicker rate or slower rate then concrete without FA?
Slower (long term gains are higher with FA)
When will the long term strength of OPC+FA be higher than OPC
90 days and after
which type of FA reduces sulfate attacks?
Type F (low calcium)
What is slag?
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)
What are the properties of slag?
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
How does the strength of concrete’s affected with slag?
Low early strength, High later strength (significant after 1 year)
Comparable strength to OPC after 28 days
What does slag bring to concrete?
Increases later strength
Reduces permeability (enhance durability/less corrosion)
Increases workability
Reduce Heat of hydration
Increase ASR resistance (less expansion)
Fire resistance
What are the 2 types of natural pozzolans?
Raw (ash from volcanic) and calcined natural pozzolans (calcined clays)
Which SCM’ could be used for ASR resistance?
FA
Slag
SF
Nat pozzolans
Which SCM’s could be used to reduce permeability?
FA
Slag
SF
Nat pozzolans
(ALL OF THEM)
Which SCM’s could be used to increase workability?
FA
Slag
Nat pozzolans
Which SCM’s could be used to reduce heat of hydration?
FA
Slag
Nat pozzolans
SF VARIES
Why does SF has high water requirements?
Because water evaporates and results in drying shrinkage
