Ingredients and mixing concrete

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  • 1. Ingredients and Mixing Concrete
  • 2. 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.
  • 3. 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.
  • 4. 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.
  • 5. 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
  • 6. 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.
  • 7. 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.
  • 8. 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
  • 9. 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
  • 10. Cement • Finely Ground • • A Mixture Of: • Lime • Silica • Alumina • Iron Oxide • Gypsum
  • 11. Concrete • A Mixture of: • • Portland Cement • • Water • • Aggregates
  • 12. Concrete ÷ Plastic or Pliable • When Freshly Mixed • • • Hardened or • Rock-like When Set
  • 13. Properties of Concrete • Plastic Hardened • • Workable Strong • • Uniform Durable • • Consistent Economical • • Non-segregating Water Tight • • Resistant to Abrasion
  • 14. MANUFACTURE OF PORTLAND CEMENT • Limestone + Silica Sand Cement Rock Iron Ore » Oxides • + • Clay and Shale • • (2600oF) • • • Clinker • + • Gypsum • • Portland Cement
  • 15. 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
  • 16. Air-Entrained • Air is intentionally added •  YUse air-entrained (Type 1A) Cement •  YAdd air-entraining agent at mixer 400- 600 Billion Air Bubbles 1 CUBIC YARD
  • 17. 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
  • 18. 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
  • 19. Aggregate
  • 20. 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
  • 21. Aggregate For Concrete • Should be: • • Clean • • Strong • • Hard • • Cubical
  • 22. Tests of Aggregate • Organic Matter • • Silt • • Voids • • Moisture • • Graduation • • Bulking
  • 23. Water For Concrete • Is Suitable If It Is: • • • Clean Enough to Drink