Ingredients of Concrete

8/9/2019 .Ingredients of 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, andwater that hardens as it dries.

C. Masonry: refers to anything constructed of brick, stone, tile or concreteunits 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 trappedthroughout 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 thesurface 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 andwater paste will harden much like glue and binds the aggregatestogether 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, gypsumand small amounts of other ingredients.

$ Portland cement is not a trade name, but is used to distinguishthis group of cement from other kinds.

$ Most cement will pass through a sieve of 40,000 openings persquare inch.

$ The cement manufacturing process includes several chemicalreactions.

$ The result is a hydraulic product which sets and hardens afterreacting with water.


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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 thanType 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 basicallycorrespond 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 ofchemicals to melt snow and ice

it is more watertight than air entrained


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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, andType III.


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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 beingpoured.

In thin slabs or walls the coarse aggregate should not exceed 1/3 inch the thicknessof the concrete being placed.

To make good concrete, aggregates of various size should fit together to form a fairlysolid 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 whichweigh 15 to 90 lbs. per cubic foot.


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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 7ounce 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 ful l

Screw on a lid and shake the mixture vigorously for one minute to mix all particleswith 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 aclay and silt test

After one hour measure the thickness of the sil t 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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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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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

Use air-entrained (Type 1A)Cement

Add air-entraining agent at

mixer

400- 600

Billion

Air Bubbles

1 CUBIC YARD


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Advantages of Air Entrained

Concrete

Mixing concrete mayreduce water and sand

Plastic concrete

Reduced segregation and

surface bleeding

Improved workability

May be finished sooner

Hardened concrete

Increased water tightness

Resists freezing andthawing

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 SizesGravel Coarse 4

Sand 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

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Ingredients of Concrete