Introduction to Concrete

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Introduction to Concrete

  1. 1. Introduction to Concrete Prepared by: Marcia C. Belcher Construction Engineering Technology
  2. 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. 3. Concrete has deep roots in history: Wall at Palestrina, Italy, 1st Century BC
  4. 4. Roman Aqueduct & Pantheon
  5. 5. Concrete • The word “concrete” originates from the Latin verb “concretus”, which means to grow together.
  6. 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. 7. Sculptural Qualities of Concrete at Chapel at Ronchamp
  8. 8. Concrete Structural Frame City of Arts and Sciences, Valencia Spain, Santiago Calatrava
  9. 9. Properties of Quality Concrete • Workability • Durability • Strength • Chloride Penetration Resistance • Abrasion Resistance
  10. 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. 11. Concrete Microstructure
  12. 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. 13. The Cement Matrix • Cement: – produces a crystalline structure – binds aggregates together • Water – causes chemical reaction to occur – water/cementitious “react” – produces workability
  14. 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. 15. Portland Cement Manufacturing Process
  16. 16. Clinker
  17. 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. 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. 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. 20. When Do We Use Air Entrained Concrete? • Concrete to be placed in exterior locations requires air entraining (water/freeze/thaw)
  21. 21. Water Reducers (Super-Plasticizers) • Increases viscosity • Water can be reduced • Results in higher strength and more durable concrete due to reduced water

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