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Introduction to Concrete

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  • 1. Introduction to Concrete Prepared by: Marcia C. Belcher Construction Engineering Technology
  • 2. Concrete As A Material
    • Concrete, literally, forms the basis our modern life:
      • Roadways/transportation systems
      • Airstrips
      • Infrastructure (bridges, dams, buildings)
      • Harbor protection (breakwalls)
      • Water distribution (pipes & conduit)
  • 3. Concrete has deep roots in history: Wall at Palestrina, Italy, 1st Century BC
  • 4. Roman Aqueduct & Pantheon
  • 5. Concrete
    • The word “concrete” originates from the Latin verb “concretus”, which means to grow together.
  • 6. Advantage of Concrete
    • We have the ability to cast desired shapes
      • Arches, piers, columns, shells
    • Properties can be tailored according to need (strength, durability, etc.)
    • Ability to resist high temperatures
      • Will maintain structural integrity far longer than structural steel
    • Does not require protective coatings
    • Can be an architectural & structural member at the same time
  • 7. Sculptural Qualities of Concrete at Chapel at Ronchamp
  • 8. Concrete Structural Frame City of Arts and Sciences, Valencia Spain, Santiago Calatrava
  • 9. Properties of Quality Concrete
    • Workability
    • Durability
    • Strength
    • Chloride Penetration Resistance
    • Abrasion Resistance
  • 10. The Nature of Concrete
    • It is a composite material
    • Aggregates are 65% - 80% of the volume
      • Fine aggregate: sand
      • Coarse aggregate: stone
    • Cement: General term & applies to any binder
          • Portland cement
          • fly ash
          • ground slag
          • silica fume
    • Water
  • 11. Concrete Microstructure
  • 12. The Purpose Of The Aggregates
    • Large aggregates:
      • provide density (fill space)
      • provide strength
    • Fine aggregates:
      • fill small voids between large aggregates
      • Increases strength of the cement binder
  • 13. The Cement Matrix
    • Cement:
      • produces a crystalline structure
      • binds aggregates together
    • Water
      • causes chemical reaction to occur
      • water/cementitious “react”
      • produces workability
  • 14. What is Portland Cement?
    • Raw limestone, clay & gypsum minerals are ground into powder & heated in kiln
    • (1600 ° C)
    • Minerals interact at that temperature to form calcium silicates (clinker)
    • Available in five types, each with varying performance characteristics and uses
  • 15. Portland Cement Manufacturing Process
  • 16. Clinker
  • 17. Hydration
    • Portland cement becomes cementitious when mixed with water
    • This reaction is referred to as hydration.
    • During hydration, a crystalline structure grows to form bonds
    • Hydration begins as soon as water meets cement
    • Rate of hydration increases with increased cement fineness
  • 18. In Fact…….
    • Concrete does not gain strength by “drying out”
    • Concrete must have continuous free access to water to achieve its ultimate strength!!
  • 19. Air Entrainment Admixtures
    • All concrete containes “entrapped” air
        • Large bubbles
        • Large voids are undesirable for durability & permeability
    • Entrained air
        • Bubbles are microscopic in size & distributed through out concrete
        • Increases durability by providing “escape route” for freezing water as it expands
  • 20. When Do We Use Air Entrained Concrete?
    • Concrete to be placed in exterior locations requires air entraining (water/freeze/thaw)
  • 21. Water Reducers (Super-Plasticizers)
    • Increases viscosity
    • Water can be reduced
    • Results in higher strength and more durable concrete due to reduced water