Concrete SCMs (6)

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Marciaho
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269860
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Concrete SCMs (6)
Updated:
2014-04-08 23:55:57
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Concrete SCMs
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Concrete SCMs (6)
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Concrete SCMs (6)
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  1. Cementitious materials (4)
    • Cement 
    • Flyash - waste from thermal power stations
    • Silica Fume - Wast from ferrosilicon industry
    • Blast furnace slag - Waste from steel manufacturing
  2. Reasons for using SCMs
    • Economic 
    • Technical (workability/durability) 
    • Environmental (waste materials)
  3. Technical benefits
    • Improved workability
    • Reduce Permeability
    • Improves durability
    • Reduce risk of cracking
  4. SCM types
    • Flyash
    • Slag
    • Microsilica
  5. Flyash performance
    • Pozzolanic material containing glassy phases
    • Moderate fineness and reactivity 300-500m^2/kg
    • Spherical shape and improves workability
    • Dosage 25-30%
  6. Slag Performance
    • Latent Hyrdaulic binder (needs hydroxides) 
    • Moderate fineness and reactivity 400-600 m^2/kg
    • Angular, crushed shape
    • Dosage 30-70%
  7. Microsilica
    • Pozzolanic material with reactive silica
    • Extremely fine, highly reactive 20000 m^2/kg
    • Chunky, round shape
    • Dosage 5-10%
  8. Microsilica used in concrete to enhance properties (4)
    • High chloride resistance (marine exposure)
    • High sulphate resistance (industrial exposure)
    • Reduce permeability (tunnels, resevoirs)
    • Improved abrasion resistance (slabs)
  9. A hydraulic cement sets and hardens by reacting chemically with ______ and doing so under ____
    • water.
    • e.g portlad cement, slag, class c fly ash
  10. Pozzolan a siliceous material in the presence of moisture reacts at ordinary temperatures with ________ to form compounds possessing cementitious properties
    Carbon Hydroxide
  11. Calcium Hydroxide
    • No cementing properties
    • Contributes little to strength
    • Easily leached
    • Vulnerable to chemical attack
  12. C-S-H 
    Calcium Silicate Hydrate
    • Main cementitious compount
    • Glue that holds concrete together
  13. Ternary Blended Concrete
    Three binder types used
    What does it produce?
    • Portland cement (50-60%)
    • Flyash or slag (25-45%)
    • Silica fume (5-10%) 
    • Produces concrete with high levels of workability strength and durability
  14. Effect of SCMs on properties of fresh concrete (5)
    • 1. Water demand and workability
    • 2. Bleeding
    • 3. Setting time
    • 4. Air content
    • 5. Heat of hydration
  15. Effect of Flyash on water demand
    • Decrease! 
    • 25% -> 6-10% less water
  16. Effect of Slag on water demand
    • Small reduction
    • up to 10%
  17. Silica Fume
    • Increase! 
    • This should be offset by the use of high range water reducer
  18. Effect of SCM on bleeding
    • Flyash decrease
    • Slag Decrease or increase
    • Silica Fume double decrease
  19. Effect of SCM on setting time
    Class F Fly ash
    Class C flyash
    Slag
    Silica Fume
    • Class F flyash = Increase
    • Class c flyash = Both
    • Slag = Increase
    • Silica Fume = little effect
  20. Effect of SCM on Temperature rise
    Low lime class f flyash effect
    May reduce temperatures in large pours
  21. What do properties do flyash depend on to have an effect on air content?
    Carbon content, Alkali, Fineness and impurties

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