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BASIC CONCRETE PRINCIPLES

ESTIMATING THE MATERIALS NEEDED FOR CONCRETE

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FOUR RULES FOR A QUALITY PRODUCT

• Use proper ingredients

• Correctly proportion & measure ingredients

• Thoroughly mix the ingredients

• Properly finish and cure the poured concrete

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ADVANTAGES OF USING CONCRETE

• Fire proof• Durable and permanent• Watertight• Economical• Sanitary• Low maintenance• Attractive• Termite & rodent proof• Storm resistant• Can be “homemade”

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AGRICULTURAL USES

• Fence posts• Driveways• Walls & foundations• Septic tanks• Walks• Water troughs• Feeding floors• Steps• Cattle guards• etc

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COMPOSITION OF CONCRETE

• Portland cement• Water• Aggregates (sand and

gravel)

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WHAT IS PORTLAND CEMENT

• Manufactured from lime, iron oxide, silica, and alumna.

• It is mixed in proper proportion and heated in a kiln to approximately 3000 degrees F.

• Resulting material is called clinker• Clinker is than pulverized and mixed with

gypsum into a fine powder.

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ORIGIN OF PORTLAND CEMENT

• Joseph Aspdin, in the early 19th century and the founder of the process that is still used today used the term because the cement he produced was the color of stone taken from the quarries on the island of Portland off the coast of England.

• Portland cement is packaged in sacks containing 1 cubic foot which weighs 94 lbs.

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AGGREGATES

• Basic filler of sand, crushed stone, & gravel

• Sand is a fine aggregate less than ¼ inch.• Gravel is a coarse aggregate more than ¼

inch.• Coarse aggregate add strength.• Aggregates are cheaper than cement and

considered a cost reducing material.

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WATER

• Should be clean and free from impurities.

• Impurities affects strength, coloration, corrosion of reinforcement steel and wire.

• It also affect setting time

• When all ingredients are properly mixed, the combined weight of a one cubic foot of concrete is 150-160 lbs.

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QUALITY OF CONCRETE

• Consistency or slump refers to the “wetness” or “dryness of the mix.

• Excessive slump can be corrected by the addition of aggregate.

• Plastic consistency is the best.

• Never exceed 6 inches of slump

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CONCRETE SLUMP RANGES

• Reinforced foundation walls –Min 2” Max 4”• Reinforced slabs, beams -Min 5” Max 2”• Building columns -Min 5” Max 3”• Pavements -Min 2” Max 1”• Sidewalks, driveways -Min 4” Max 2”

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UNIFORMITY & WORKABILITY

• Uniformity refers to the thorough mixing of all ingredients

• Workability refers to the ease which concrete can be placed and shaped.

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QUALITIES OF HARDENED CONCRETE

• Durability refers to resistance to chemical actions, freezing, and thawing. Good workmanship and proper mixing improves durability.

• Strength is measured as compressive and tensile. Compressive strength is usually 10 times the tensile strength of unreinforced concrete. Additional reinforcement will equalize the strength.

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Other Conditions

• Water-cement ratio, curing time, & curing methods are just as important as reinforcement.

• Rule of thumb: Use a 5-7 gallons of water per sack of cement. Exceeding this will weaken the mix.

• Concrete cured for 7 days is only 2/3 as strong as concrete cured for 28 days.

• Damp curing can increase as much as 50% for the first 7 days.

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WATERTIGHTNESS

• The ability to prevent water passage through the mass. The water-cement ratio and curing time affect watertightness.

• Less water in the mix increases watertightness.

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WEAR RESISTANCE

• The ability to resist abrasive action of vehicles, feet, flowing water, etc.

• Aggregates should be hard and tough to resist wear.

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READY MIXED CONCRETE

• Sold by cubic yard

• Two methods of mixing—transit mixer & shrink-mixed

• Transit mixer is when mixing is done on the truck

• Shrink-mixed begins in a stationary mixer and ends up in a truck mixer.

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ADVANTAGES OF READY-MIX

• Thoroughly mixed

• Ingredients are not handled on the job site.

• Less labor is required.

• Exact quantity needed can be ordered.

• Actual price can be calculated easily.

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ADMIXTURES

• Air-entraining –hundreds of microscopic air cell are dispersed in the mix to protect during freezing and thawing actions.

• Water-reducing –increases strength.• Retarding –slows down the setting time during

high temperature.• Accelerating –calcium chloride is added to mix to

shortened the set up time.• Pozzolans –controls expansion during heat.

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ESTIMATING READY-MIX CONCRETE

• Allows a 10% waste.

• When ordering mixtures by numbers: a 6-6-6 stands for 6 sacks of cement per cubic yard, 6 gallons of water per sack of cement, and 6 % entrained air.

• To determine surface area (length x width)

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CALCULATING READY-MIX CONRETE

• Determine surface area.• Determine the concrete thickness• Refer to chart to determine the number of cubic yards

of concrete needed.• Concrete thickness Divide Area by:

1 inch 3003 inches 1004 inches 756 inches 50

12 inches 25

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RECOMMENDED MIXES

• 5-Gallon mix –for acid or alkaline resistant walks, fence posts, flower boxes, & etc.

• 6-Gallon mix –for watertight floors, tanks, walls and all reinforced concrete.

• 7-Gallon mix –for foundation walls, retaining walls, underground concrete and concrete not under water pressure.

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MOISTURE IN SAND

• Damp sand – ¼ gal/cu.ft (falls apart when hand is opened.)

• Wet sand – ½ gal/cu.ft (ball of sand holds shape when hand is opened.)

• Very wet sand – (3/4 gal/cu.ft (ball is formed and leaves hand wet when opened.

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“FULLER’S” RULE

• Rule states – mixing of a total of 42 volumes of cement, sand, and gravel will produce 27 volumes of concrete.

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FULLER’S RULE

• Use a 1 – 2-1/4 – 3 mix to build 4”thick, 6’ wide, and 100’ long sidewalk.

– Determine the amount of concrete required.

6’ x 100’ x 4” or 6’ x 100’ x 1/3’ 12 1 =200 cubic feet of concrete

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FULLER’S RULE

• Determine the amount of raw materials needed.

200 X 42 =

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311 cu ft of raw materials

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FULLER’S RULE

• Determine the volume of mix needed.

1 + 2-1/4 + 3 = 6-1/4 (6.25) volumes of mix

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FULLER’S RULE

• Determine the sacks of cement needed.

311 cuft. raw materials = 49.76 sacks

6.25 volume of mix

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FULLER’S RULE

• Determine the cu. yds. of sand needed.

50 sacks x 2.25 = 4.17 cu yds of sand

27 cu.ft/yd

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FULLER’S RULE

• Determine the cu yds. Of gravel needed.

50 sacks x 3 = 5.55 cu yds of gravel

27 cu ft/yd

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FULLER’S RULE SUMMARY

• 1. 200 cu feet of concrete required

• 2. 311 cu ft of raw materials

• 3. 6-1/4 or 6.25 volumes of mix

• 4. 49.76 or 50 sacks of cement

• 5. 4.17 cu yds of sand

• 6. 5.55 cu yds of gravel

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MIXING CONCRETE

• Two common methods of mixing – machine and hand mixing.

• Steps in machine mixing

-add 10% water before adding in solids.

-add portion of gravel.

-add measured amount of cement

-add sand and remaining amts of gravel

-mix from 1 – 3 minutes

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MIXING CONCRETE

• Steps in hand mixing

-place sand in mixing container

-then add cement and mix thoroughly

-add gravel and continue to mix

-add measured amounts of water

-mix thoroughly