Estimating Concrete Construction

and Material Cost

Concrete weights and measures.

• A. One sack of cement = 94 pounds or one cubic foot

• B. One gallon of water = 8.3 pound• C. 7.5 gallons of water = 1 cubic foot• D. One cubic yard = 27 cubic feet• E. One cubic foot of sand weights about 100

pounds• F. One cubic foot of gravel weights about 100

pounds

Estimating concrete for a job.

• A. The unit of measure for concrete is the cubic yard, which contains 27 cubic feet.

• B. To determine the needed amount of concrete, find the volume in cubic feet of the area to be concreted and

divide this figure by 27.• C. Formula for determining the amount of concrete needed

for any square or rectangle area:• Cubic yards of concrete =•  • Width in feet x length in feet x thickness in feet• 27

Estimating concrete for a job.

• Example: a 4" thick floor for a 30 x 60 ft. building would require:

• 30' x 60' x 1/3' = 600 cu. ft. = 22.22 cu. yards• 27 cu. ft. 27 cu. ft.

Estimating concrete for a job.

• D. The determined amount of concrete must allow for waste or slight

variation in concrete thickness. An additional five to 10 percent will be needed to cover waste and other unforseen facts.

Estimating concrete for a job.

• E. Fuller method:• It takes 42 parts of materials to make 27 parts of cement.• $       Volume = 200 cu. ft.• $       Cu. ft. of raw materials needed 42/27 ( 200 cu ft.) = 311 cu. ft. • $       Cu. ft. of raw materials per batch: 1+2 2 +4 = 7 2 cu. ft.• $       Number of batches = 311 cu. ft. = 41.467

• 7 2 cu. ft.• $       Sacks of cement = 1 (41.467) = 41.467 or 42 sacks• $       Cu. ft. of fine aggregate (41.467) (2 2) = 103.66 or 104 cu. ft.• $       Cu. ft. of coarse aggregate (41.467) (4) = 165.86 or 166 cu. ft.• $       Water to add per batch 7-5/8 = 6 3/8 gals.

Estimating concrete for a job.

• F. Absolute volume method. • $                                           Formula:• Absolute Volume = Weight of loose materials• Specific gravity x unit wt. of water

• $                                           Cement:• Absolute Volume = 1 cu. ft. x 94 lbs./cu. ft. = 94 = 0.478 cu.ft.• 3.15 x 62.4 196.56• • $                                           Fine Aggregate:• Absolute Volume = 2 2 cu. ft. x 100#/cu. ft. = 250 = 1.540 cu.ft.

2.6 x 62.4 162.24•

Estimating concrete for a job.

• F. Absolute volume method.• $                       Coarse aggregate:

• Absolute Volume = 4 cu. ft. x 100#/cu. ft. = 400 = 2.480 cu.ft.

• 2.65 x 62.4 165.3

• $                         Water:

• Absolute Volume= 7/7 2 x 62.4 = 7/7 2 = 0.933 cu. ft.

• 1 x 62.4

Estimating concrete for a job.

• F. Absolute volume method.• $       Total volume of concrete per sack cement = 5.431 cu. ft.• $       Cement = 1 (200/5.43) = 36.8 or 37 sacks• $       Fine aggregate = 2 2 (200/5.43) = 92.1 or 93 cu. ft.• $       Coarse aggregate = 4 (200/5.43) = 147.2 or 148 cu. ft.

Water to add = 7-5/8=6 3/8 gallons per batch

Estimating concrete for a job.

• Changing the thickness in inches to fractions and decimal parts of a foot. For calculating quantities of concrete use the following table.

• Inches Fractional Part of Foot Decimal Part of Foot

– 4 4 2 or 1/3 .33

– 5 5/12 .42

– 6 6/12 or 2 .50

– 7 7/12 .58

– 8 8 12 or 2/3 .67

– 10 10/12 or 5/6 .83

– 12 1 1.00

CONCRETE WEIGHTS AND

MEASURES • 1 Sack of Cement = 94 pounds

» = 1 Cubic Foot

•  

• 1 Gallon of Water = 8.3 pounds

 

• 7.5 Gallons of Water = 1 Cubic Foot

•  

• 1 Cubic Yard = 27 Cubic Feet

• 1 Cubic Foot of Sand Weighs About 100 Pounds

PROBLEM:How many square feet will a cubic yard of concrete cover if it is placed 4 inches thick?

There are 27 Cubic Feet in 1 Cubic Yard 

Each Cubic Foot May Be Divided Into Three Volumes 4 Inches Deep and 1

Foot Square  

 

THE CONCRETE MIX YIELDS OF CONCRETE

• 1. Rule of Thumb:

Yield Equals 60 Percent of Volume

• 2. Absolute Volume

• Cement 47% Solids

• Sand 60% Solids

• Gravel 55% Solids

• Water 100% Solids

WHAT WILL A 1 : 2 : 3 - 6 GALLON MIX YIELD?

• -ABSOLUTE VOLUME

• FT3 X % SOLIDS = FT3

• Cement ______ 47 ______• Sand ______ 60 ______• Gravel ______ 55 ______• Water ______ 100 ______•  • TOTAL YIELD (FT3) ______

• (YARD3) ______•  

• MIXES ______• YARD3

HOW MANY BAGS OF CEMENT ARE NEEDED TO MIX 1 CUBIC YARD OF CONCRETE USING A 1 : 2 : 3 - 6 GALLON MIX?

(Rule of thumb)•  • Yield =_______ YD3 = FT3/MIX• 27 FT3/YARD3

•  • 1 CUBIC YARD = _______1 BAG MIXES• YARD3/MIX•  • USE________BAGS OF CEMENT

WHAT WILL A 1 : 2 : 3 - 6 GAL. MIX YIELD?

FT3

• Cement ________• Sand ________• Gravel ________• Water ________• Total ________ FT3

• x 60% ________ FT3

•  • Yard3 ________• Mix

•  • Mixes ________• Yard3

•  • CALCULATED BY THE RULE OF THUMB