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CIVI 321 > SCMs > Flashcards

SCMs Flashcards

1
Q

What are SCMs?

A

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

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2
Q

Describe what pozzolans are?

A

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.

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3
Q

Describe what natural pozzolans are?

A

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

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4
Q

What is CSH?

A

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

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5
Q

What is CH?

A

Calcium Hydroxide: does not have an important contribution to strength

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6
Q

What are the hydration products?

A
  • CSH

- CH

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7
Q

What does SCMs do?

A
  • Enhancement to mechanical properties and durability
  • Refinement of porosity
  • Densification of aggregate-cement paste interface
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8
Q

What is Transition Zone?

A

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.

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9
Q

What are the different SCMs?

A
  • Silica Fumes
  • Fly Ash
  • Slag
  • Natural Pozzolans
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10
Q

What are silica fumes?

A
  • 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
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11
Q

Forms of silica fumes?

A
  • As-produced powder
  • Silica fume slurry (50-52% solids)
  • Densified Silica Fume
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12
Q

Silica Fume…?

A
  • Increases Strength (S+CH = CSH)
  • Reduces Permeability thus enhances durability
  • Increases concrete cohesiveness
  • Good Curing
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13
Q

What are Fly Ashes?

A

By-product of coal burned power plants.

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14
Q

What are the two types of fly ash?

A
  • Class F Fly Ash

- Class C Fly Ash

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15
Q

Describe Class F Fly Ash

A
  • low calcium oxide fly ash
  • produced by calcination of bituminous coal
  • has pozzolanic properties
  • Moderate Heat
  • High concrete
  • Sulfate resistance
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16
Q

Describe Class C Fly Ash

A
  • High calcium oxide fly ash
  • Produced by calcination of subbituminous coal or lignite.
  • Has pozzolanic + cementitious properties
  • Performance
  • Higher early strength
  • Soil Stabilization
17
Q

What is the effect of fly ash on setting time?

A
  • 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
Q

Fly Ash…

A
  • 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
Q

What is slag?

A

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

20
Q

What are the uses of slag?

A
  • Used as aggregate or disposed as waste
  • Hydraulic Binder
  • Hydraulic slags give similar hydration products to OPC but react slowly with water.
21
Q

What are the effect of slag on fresh properties?

A
  • At low temperatures, setting time is increased (slower hydration of GBFS)
22
Q

Mechanical properties?

A
  • 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
Q

The rate of strength of slag depends on…?

A
  • Type of slag
  • Cement placement rate
  • temperature
  • activation technique used

CIVI 321 (7 decks)

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