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CIVI 321 > SCMs > Flashcards

Flashcards in SCMs Deck (23):
1

What are SCMs?

A material that, when used with portland cement contributes to the properties of the hardened concrete through: Hydraulic Activity, Pozzolanic Activity or both.

2

Describe what pozzolans are?

A siliceous or alumino-silliceous material that, in a finely divided form and in the presence of moisture, chemically reacts with a hydration product of portland cement to form compounds possessing cementing properties.

3

Describe what natural pozzolans are?

A natural material which may also be calcined and/or processed.

4

What is CSH?

Calcium Silicate Hydrate: is the binder (glue) responsible for strength.

5

What is CH?

Calcium Hydroxide: does not have an important contribution to strength

6

What are the hydration products?

- CSH
- CH

7

What does SCMs do?

- Enhancement to mechanical properties and durability
- Refinement of porosity
- Densification of aggregate-cement paste interface

8

What is Transition Zone?

Is a thin layer between the bulk hydrated cement paste and the aggregate particles in concrete. This zone is the weakest component in concrete, and its also the most permeable area.

9

What are the different SCMs?

- Silica Fumes
- Fly Ash
- Slag
- Natural Pozzolans

10

What are silica fumes?

- Smoke by-product from furnaces used in the production of ferrosilicon and silicon metals
- Very Fine non crystalline silica: high silica content, extreme small particle size, large surface area and highly reactive pozzolan

11

Forms of silica fumes?

- As-produced powder
- Silica fume slurry (50-52% solids)
- Densified Silica Fume

12

Silica Fume...?

- Increases Strength (S+CH = CSH)
- Reduces Permeability thus enhances durability
- Increases concrete cohesiveness
- Good Curing

13

What are Fly Ashes?

By-product of coal burned power plants.

14

What are the two types of fly ash?

- Class F Fly Ash
- Class C Fly Ash

15

Describe Class F Fly Ash

- low calcium oxide fly ash
- produced by calcination of bituminous coal
- has pozzolanic properties
- Moderate Heat
- High concrete
- Sulfate resistance

16

Describe Class C Fly Ash

- High calcium oxide fly ash
- Produced by calcination of subbituminous coal or lignite.
- Has pozzolanic + cementitious properties
- Performance
- Higher early strength
- Soil Stabilization

17

What is the effect of fly ash on setting time?

- Fly ash usually hydrates slowly
- Setting time is moderately or severely extended depending upon the properties of fly ash, temperature and mixture proportions
- Finer fly ash results in shorter setting time (C)
- Higher CaO content results in shorter setting time (C)

18

Fly Ash...

- Increases later strength
- Reduces permeability thus enhances durability
- Increase workability
- Reduce heat of hydration
- Increase concrete ASR resistance
- Increase concrete sulfates resistance
- Good curing

19

What is slag?

By-product of the metallurgical industry. The most used in cement is iron blast furnace slag.

20

What are the uses of slag?

- Used as aggregate or disposed as waste
- Hydraulic Binder
- Hydraulic slags give similar hydration products to OPC but react slowly with water.

21

What are the effect of slag on fresh properties?

- At low temperatures, setting time is increased (slower hydration of GBFS)

22

Mechanical properties?

- Strength development of slag cement is slower at early stage than that of OPC but faster at later ages.
- At one year slag cement achieves significantly higher strength
- comparable strength to OPC at 28 days
- Improve the concrete resistance to fire damage
- penetration resistance
- Reduces AAR

23

The rate of strength of slag depends on...?

- Type of slag
- Cement placement rate
- temperature
- activation technique used