1. What Is concrete?
    1. Definition: Concrete is a mixture of portland cement, aggregate and water that is mixed wet, formed, and dries to a permanently hard and strong material.
  2. History
    1. Thought to have been used in 3000 B.C. in core of pyramids
    2. Supposedly invented by the Romans in 200 B.C.
    3. Not used extensively until the late 19th century.
    4. Reinforced concrete (using steel reinforcing bars) invented in 20th century.
    5. Frank Lloyd Wright was one of first architects to use reinforced concrete in Untiy Temple, Oak Park, built in 1908.
  3. Uses of concrete in buildings
    1. Footings
    2. Foundation Walls
    3. Slab-on-grade
      1. Basement floor slabs
      2. First floor slabs
      3. Garage floor slabs
    4. Columns
    5. Beams
    6. Retaining walls to hold back earth embankments to keep from eroding or washing away the soil
    7. Structural slabs
    8. Structural walls
    9. Stairs
    10. Paving (sidewalks, driveways, or roads)
    11. Floor fill over concrete structural slabs to bury piping or electrical conduit or to level floors, usually made of light weight concrete
    12. Roof fill over concrete structural slabs to provide a slight slope for flat roofs to drain usually made of light weight or insulating concrete
    13. Swimming pools
    14. Precast concrete slabs, walls, etc.
    15. Concrete masonry units
    16. Finish flooring (terrazzo)
    17. Ornamental uses
    18. Stoops
    19. Chimney caps
  4. Concrete structural condition types
    1. Plain (no reinforcement)
    2. Reinforced (includes steel "re-bars")
    3. Prestressed (tensile stress is imposed on reinforcing prior to concrete setting up)
    4. Post-tensioned (tensile stress is imposed on reinforcing after concrete has set up)
  5. Concrete Strength
    1. Factors which determine strength
      1. Water-cement ratio, measured in gallons of water per sack of cement - the less water used per sack the stronger the mix
      2. one sack of cement weighs 94 pounds
      3. minimum water required for "hydration" (the chemical reaction which solidifies cement) is 3 ½ gallons per sack, but more water is required to produce "workability" of the mix.
      4. Super-plasticizers can be added to increase workability without affecting the water-cement ratio
      5. Curing
      6. Age
        1. ½ strength in 3 days
        2. Initial set after 2 to 3 hours
        3. full strength at 28 days
    2. Importance of strength
      1. Structural elements (columns, beams and slabs) are sized based on their expected strength - the stronger the concrete, the smaller the structural element can be.
    3. Testing
      1. Performed by an independent testing agency for every "batch" of concrete
      2. Compression tests - three 6" diameter x 12" long "cylinders" of concrete are taken at time of delivery of concrete for each batch
      3. Slump tests are also made at time of delivery - this tests how "stiff" the mix is and can be compared against other batches to be used in the same building to monitor consistency of the mixes.
  6. Materials which make up concrete
    1. Portland cement
    2. Aggregate
      1. Fine - sand
      2. Coarse - gravel
      3. Light weight aggregates - expanded slag or shale
    3. Water - potable
    4. Admixtures
      1. Air-entraining
      2. Super-plasticizers
      3. Accelerators (for use in winter)
      4. Retarders (for use in summer)
  7. Density
    1. Normal weight: 150 pounds per cubic foot
    2. Light weight: 110 pounds per cubic foot
  8. Mixing Concrete
    1. Types of mixing plants
      1. Batch plant at site
      2. Ready-mix plant - concrete delivered to job site in agitator trucks
    2. Measurement of materials
      1. Water measured by volume
      2. Cement measured by weight
      3. Aggregate measured by weight
      4. "Well proportioned" mix
  9. Formwork
    1. Types
      1. Constructed formwork
      2. Slip forming
      3. "In situ"
    2. Materials
      1. Wood
        1. Boards
        2. Plywood
      2. Metal
      3. Fiberglass
      4. Earth
    3. Form-release agents
    4. Bracing
    5. Form ties
    6. Shoring and re-shoring
    7. Reuse of formwork
  10. Placing Concrete
    1. Clean and level subgrade
    2. Weather precautions
      1. Do not pour flatwork in rain
      2. Do not pour concrete on frozen substrates
      3. Do not pour in exceptionally hot weather
    3. Place reinforcing bars and secure to formwork
    4. Place concrete in "lifts" of 6" to 20" high
    5. Continuously pour, do not leave off work without providing a bulkhead
    6. Spading and vibration - do not over-vibrate to prevent segregation
    7. Construction joints - key in joints where pour is finished for the day
    8. Control joints in slabs to control shrinkage about every 8 feet (rule of
    thumb is 2 x the slab thickness (in feet), thus a 4" thickl slab needs control joints every 8 feet in both directions.
  11. Finishing concrete slabs
    1. Screeding
    2. Darbying or "Floating"
    3. Edging
    4. Wood floating
    5. Troweling
      1. steel trowel for normal concrete
      2. Aluminum or magnesium trowel for air-entrained concrete
    6. Specialty finishes
      1. Brooming for sidewalks and driveways
      2. Exposed aggregate
      3. Staining
      4. Impressing
    7. Curing
      1. Continuous fine water spray
      2. Soaked burlap
      3. Soaked straw
      4. Coating with cure and seal spray-on chemical
    8. Sealing