Ingredients and Mixing Concrete

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Ingredients and Mixing Concrete
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Definitions of Terms Associated with the
Materials used in Concrete

• A. Portland Cement a dry powder made by burning
  limestone and clay, and then grinding and mixing
  to an even consistency.
• B. Concrete a mixture of stone aggregates, sand,
  portland cement, and water that hardens as it
  dries.
• C. Masonry refers to anything constructed of
  brick, stone, tile or concrete units set or held
  in place with portland cement.
• D. Mortar a mixture of sand, portland cement,
  water and finishing lime.
• E. Finishing Lime a powder made by grinding and
  treating limestone.
• F. Fine Aggregate sand and other small particle
  of stone.
• G. Coarse Aggregate gravel large particles of
  stone used in concrete.
• H. Clay the smallest group of soil particles.
• I. Sand small particles of stone.
• J. Silt a substance composed of intermediate
  size soil particles.
• K. Gravel particles of stone larger than sand
  also called coarse aggregate.
• L. Washed sand sand flushed with water to remove
  clay and silt.
• M. Air-entrained concrete ready mix concrete
  with tiny bubbles of air trapped throughout the
  mixture to strengthen it.

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How does the bonding of aggregates form concrete?

• A. A cement and water mixture produces a paste
  that coats the surface of each of the pieces of
  aggregates.
• B. After a few hours after mixing, a chemical
  reaction starts between the cement and water
  called hydration.
• C. When this chemical reaction begins, the cement
  paste hardens gradually and the concrete sets.
• D. Upon the completion of the chemical reaction,
  the cement and water paste will harden much like
  glue and binds the aggregates together to form
  the solid mass of concrete.

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How do you select the ingredients for concrete?

• A. Portland Cement
•        Chemical combination of calcium, silicon,
  aluminum, iron, gypsum and small amounts of
  other ingredients.
•        Portland cement is not a trade name, but
  is used to distinguish this group of cement from
  other kinds.
•        Most cement will pass through a sieve of
  40,000 openings per square inch.
•        The cement manufacturing process includes
  several chemical reactions.
•        The result is a hydraulic product which
  sets and hardens after reacting with water.

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How do you select the ingredients for concrete?

• B. Types of Portland Cement are manufactured to
  meet physical and chemical requirements for
  special application.
•        Type I General Purpose Cement
•        Type II Modified Portland Cement has a
  lower heat of hydration than Type I.
•        Type III High/Early Strength Cement
•        Type IV Low Heat Cement
•        Type V Sulfate Resistant Cement
•        Air entraining Cement designated as
  Type Ia, IIa, and IIIa and basically correspond
  to Types I, Type II, and Type III.
•       lowers the water and sand requirements per
  cubic yard.
• can be worked more easily
• tends to reduce the segregation of the
  aggregates from the mix and improves uniformity
• may be finished earlier than the non-air
  entrained
• improves the resistance to freeze/thaw
  action
• it is effective in preventing serious
  surface scaling caused by the preventing the use
  of chemicals to melt snow and ice
• it is more watertight than air entrained

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How do you select the ingredients for concrete?

• C. Uses of each type.
•        Type I       Pavements
•         Sidewalks
•         Bridges
•        Type II
•       Used in structures of
  considerable size, such as large piers, heavy
  retaining walls.
•      Used where sulfate may attack concrete
•        Type III
•     Used when strengtheners are desired
•     Used in cold weather construction
•        Type IV
•     Development of strength is at a slower
  rate
•     Used in mass concrete such as large
  gravity dams where temperature rise
• resulting from the heat generated during
  hardening is a critical factor
•        Type V
•     Used only in construction exposed to
  severe sulfate action
•     Slower rate of strength gain than normal
  portland cement
•        Air entrained Cement used for the same
  type construction as Type I, Type II, and
  Type III.

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How do you select the ingredients for concrete?

• D. Aggregates
•        Fine aggregates
• Sand and other small particles of stone that
  will pass through a 1/4 inch mesh screen
• Clean and free of clay, silt and chaff
•        Coarse aggregates
• Gravel, pebbles or crushed rock ranging in size
  from 1/4 inch up.
• Size of coarse aggregate to use depends on the
  thickness of concrete slab being poured.
• In thin slabs or walls the coarse aggregate
  should not exceed 1/3 inch the thickness of the
  concrete being placed.
• To make good concrete, aggregates of various
  size should fit together to form a fairly solid
  mass.
• Stone particles must be clean and free of clay,
  silt, chaff or any other material.
•        Light weight aggregate (clay, slag or
  shale) Light weight insulating materials
  may be used to produce concrete which weigh 15
  to 90 lbs. per cubic foot.

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How do you select the ingredients for concrete?

• E. Test for aggregates
•        Organic matter test
• Fill a 12 ounce prescription bottle with sand
  up to the 1 2 ounce mark.
• A 3 solution of caustic soda (sodium
  hydroxide) is added to fill the bottle to the 7
  ounce mark.
• Shake the bottle thoroughly and let stand for
  24 hours.
• If the liquid is darker than a straw color, too
  much organic matter is present.
•        Silt test
• Fill a one quart glass jar to a depth of 2
  inches with the sand to be tested.
• Add water until the jar is 3/4 full
• Screw on a lid and shake the mixture vigorously
  for one minute to mix all particles with the
  water
• Shake the jar sideways several times to level
  the sand
• Place the jar where it will not be disturbed
  for one hour for a silt test or 12 hours for a
  clay and silt test
• After one hour measure the thickness of the
  silt layer on top of the sand
• If the layer is more than 1/8 inch thick, the
  sand is not suitable for use in concrete unless
  the silt is removed by washing
• If the layer is not 1/8 inch thick in 1 hour,
  let the mixture stand for 12 hours. Then,
  remeasure the layers that have settled on the
  sand.
• If the silt plus clay layer exceeds 1/8 inch,
  wash the sand before using it in concrete

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How do you select the ingredients for concrete?

• F. Water
•        Water should be
• Clean
• Free of oil
• Free of acid
• Free of alkali
• Free from harmful amounts of dirts
•        Should be free of excessive impurities
  which might effect
• Setting time
• Concrete strength
• Volume stability
• Surface discoloration
• Corrosion of steel
• Drinking water generally is suitable for mixing
  with concrete

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Cement

• Finely Ground
•  
• A Mixture Of 
• Lime
• Silica
• Alumina
• Iron Oxide
• Gypsum

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Concrete

• A Mixture of 
•  
• Portland Cement
•  
• Water
•  
• Aggregates

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Concrete

• Plastic or Pliable
• When Freshly Mixed
•  
•  
• Hardened or
• Rock-like When Set

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Properties of Concrete

• Plastic Hardened
•  
• Workable Strong
•  
• Uniform Durable
•  
• Consistent Economical
•  
• Non-segregating Water Tight
•  
• Resistant to Abrasion

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MANUFACTURE OF PORTLAND CEMENT

• Limestone Silica Sand
• 
  Cement Rock
  Iron Ore
• 
  Oxides
• Clay and Shale
•  
• (2600oF)
• \
•  
• Clinker
• Gypsum
• \
• Portland Cement

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Types Of Portland Cement

• Normal Portland Cement 
• Modified Portland Cement 
• High/Early Strength 
• Low Heat 
• Sulfate-Resisting
•  
• Other Types
•  
• Air-entrained
• Plastic
• White
• Oil Well
• Masonry
• Waterproof

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Air-Entrained

• Air is intentionally added
•  
• YUse air-entrained (Type 1A) Cement
•  
• YAdd air-entraining agent at mixer

1 CUBIC YARD
400- 600 Billion
Air Bubbles
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Advantages of Air Entrained Concrete

• Mixing concrete may reduce water and sand
•  
• Plastic concrete
• Reduced segregation and
• surface bleeding
• Improved workability
• May be finished sooner

• Hardened concrete
• Increased water tightness
• Resists freezing and thawing
• Resists surface scaling
• due to deicers

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Uses of Types of Portland Cement

• Type Use
• I General
• No special
  application
•  
• II Large structures
• Acid resistant
•  
• III Cold weather
• 
  Early form removal
•  
• IV Large structures
• 
  Reduced temperature rise
•  
• V High alkali soils
• 
  Severe sulfate action

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Aggregate
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Aggregate Sizes
Gravel Y Coarse ? 4  
Sand Y Fine ? 4     A Number 4 Sieve
Has   Mesh of 1/4" X 1/4"  
OR   16 Openings Per Square Inch
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Aggregate For Concrete

• Should be
•  
• Clean
•  
• Strong
•  
• Hard
•  
• Cubical

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Tests of Aggregate

• Organic Matter
•  
• Silt
•  
• Voids
•  
• Moisture
•  
• Graduation
•  
• Bulking

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Water For Concrete

• Is Suitable If It Is
•  
•  
• Clean Enough to Drink