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concrete lecture by 8gY3UTk


									       MAGM 200
Introduction to Mechanical

           Mr. Conrado
• Concrete is strong, durable,
  economical, versatile, and
• Is a mixture of Portland
  Cement, fine aggregate,
  course aggregate, and water.
•   Portland Cement
     –   A mixture of minerals that are fire
         kilned and mixed with gypsum.
     –   Manufactured to fine standards set by
         the American Society for Testing
         Materials (ASTM).
     –   Is sold in one cubic foot bags weighing
     –   When mixed with water forms a paste
         that binds aggregates together and
         solidifies into a rock hard mass.
     –   Is colorable and stampable for
•   Aggregates
     –   A combination of fine and course
         aggregates account for 60 percent of
         the total mass
     –   Sold by the cubic foot or cubic yard
     –   Fine Aggregate
           •   Sand that will fit through a1/4” screen
           •   Should be clean and free of silt or
           •   Use the jar test to check for silt content
                  –   Place 2” of sand in a jar, fill three
                      quarters full with water, shake well, let
                      stand for 1 hour. If more than 1/8” of silt
                      settles on top – reject the load.
           •   Wetness
                  –   Affects how much water is to be added
                      to the mix
                  –   To determine squeeze a handful and
                      compare to the illustration.
•   Aggregates
     –   Course aggregates
          •   Usually gravel and crushed stone
              between ¼” – 1 ½” in diameter
          •   Rule of thumb – do not use aggregate
              larger than ¼ the thickness of the
              thickness of the concrete.
•   Water
     –   Generally if the water is fit to drink it is
         ok to use in the concrete.
     –   Do not use seawater, water containing
         debris, acid, or oil.

•   Proportion Properly
     –   1:2:3: - Cement : Sand : Gravel
     –   Water varied from 5 to 7 gals. of water
         per sack or cubic foot.
•   To work with concrete you need a
    variety of special tools.
•   Caution – Wet concrete can be caustic
    so be sure to wear a long sleeve shirt,
    long pants, and gloves when working
    with it.
•   When working with concrete the tools
    need to be kept clean at all times.
    Unkept tools that have dry cement
    caked on it become heavy and don’t
    work properly.
    Estimating Area and Quantity
•   To determine the amount of concrete needed the project area must first be
     –   First find the Square footage of the area to be covered.
     –   Now multiply by the desired thickness in feet.
     –   Divide by 27
     –   Your answer will be the amount of concrete needed in cubic yards.
•   Below are examples on how to find square footage of different shapes.
    Sidewalk 4”thick x 3’wide x 30’Length
•   Solution
     –   Volume = 4/12” (.33’) x 3’ x 30’ ÷ 27
           •   Answer = 1.1 yd³
     Testing the mix –Slump Test
•   Concrete should not be too soupy or
    too stiff. To determine the proper
    solution perform a slump test.
     –   Slump test
           •   Fill the slump cone with concrete
               tamping with a rod about 25 times for
               each of three layers.
           •   Level the concrete at the top of the
           •   Remove the cone
           •   Measure the difference
     –   The difference should be 3-4 inches
Finishing Concrete
Finishing Concrete
Finishing Concrete
Finishing Concrete
Finishing Concrete
Finishing Concrete

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