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ACI Method of Mix Design

Start

If slump is not given, decide the slump:

Use Table 3.1

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Table 3.1 Recommended Slumps For Various Types of Construction

Slump (in)Types of Construction Max Min

Reinforced Footings 3 1Plain Footings 3 1Beams 4 1Building Columns 4 1Pavement and Slab 3 1Mass Concrete 2 1

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Decide the maximum size of aggregate; choose the maximum possible size using the following guidelines:Maximum size not > 1/5 narrower dimension between forms

not > 1/3 depth of slab not > ¾ of clear spacing between reinforcing bars

Decide the amount of water and air (Table 3.2)

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Table 3.2 Approximate Mixing Water and Air Content Requirements for Different Slumps and Nominal Maximum Sizes of Aggregates

Water (Ib/yd3 of concrete for indicated nominal maximum sizes of aggregate)

Nonair-Entrained ConcreteSlump (in) 3/8 in. 1/2 in. 3/4 in. 1 in 11/2 in. 2in. 3 in. 6in. 1 to 2 350 335 315 300 275 260 220 1903 to 4 385 365 340 325 300 285 245 2106 to 7 410 385 360 340 315 300 270 ----

Amount of 3 2.5 2 1.5 1 0.5 0.3 0.2 Entrapped Air (%)

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Table 3.2 Approximate Mixing Water and Air Content Requirements for Different Slumps and Nominal Maximum Sizes of Aggregates

Water (Ib/yd3 of concrete for indicated nominal maximum sizes of aggregate) Air-Entrained Concrete

Slump (in) 3/8 in. 1/2 in. 3/4 in. 1 in 11/2 in. 2in. 3 in. 6in. 1 to 2 305 295 280 270 250 240 205 1803 to 4 340 325 305 295 275 265 225 2006 to 7 365 345 325 310 290 280 260 ----

(Air Content %)Mild Exposure 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 Moderate Exp. 6.0 5.5 5.0 4.5 4. 5 4.0 3.5 3.0Extreme Exp. 7.5 7.0 6.0 6.0 5.5 5.0 4.5 4.0

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Select the W/C ratio (Table 3.3)

Calculate Cement Content (=C/W * wt of water)

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Table 3.3 Relationship Between Water/Cement Ratio and

Compressive Strength of Concrete

Water/Cement Ratio by WeightCompressive Strength Nonair-entrained Air-entrainedAt 28 days (psi) Concrete Concrete

6000 0.41 -----5000 0.48 0.44000 0.57 0.483000 0.68 0.592000 0.82 0.74

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Choose the amount of coarse aggregate Table 3.4

Calculate the amount of fine aggregate using estimated weight of fresh concrete (Table 3.5) and the known weights of water, cement, and coarse aggregate

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Table 3.4 Volume of Coarse Aggregate per Unit of Volume of Concrete

Volume of Coarse Aggregate per unit Volume of Concrete for different Fineness Moduli of Sand

Max Size ofAggregate 2.40 2.60 2.80 3.003/8 in. 0.50 0.48 0.46 0.44

1/2 in. 0.59 0.57 0.55 0.533/4 in. 0.66 0.64 0.62 0.60 1 in 0.71 0.69 0.67 0.6511/2 in. 0.75 0.73 0.71 0.69 2in. 0.78 0.76 0.74 0.72 3 in. 0.82 0.80 0.78 0.76 6in. 0.87 0.85 0.83 0.81

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Table 3.5 First Estimate of Weight of Fresh Concrete (Ib/yd3)

Max Size of Nonair-Entrained Air-EntrainedAggregate Concrete Concrete3/8 in. 3844 36901/2 in. 3890 37603/4 in. 3960 3840 1 in 4010 390011/2 in. 4070 3960 2 in. 4120 4000 3 in. 4160 4040 6 in. 4230 4120

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Adjust for moisture content in coarse and fine aggregate

Trial Mix

End

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Example: Mix Design of Normal- Weight Concrete

Design a concrete mix using the following details

Required strength: 4000 psi

Type of structure: Beam

Max size of aggregate: ¾ in.

Fineness modulus of sand: 2.6

Coarse Aggregate Weight: 100 Ib/ft3

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Moisture absorption for coarse aggregate 3 %

Moisture absorption for fine aggregate 2 %

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Solution

Required slump for beams (Table 3.1) = 3 in.

Maximum aggregate size (given) = ¾ in.

For a slump between 3 and 4 in. and a maximum aggregate

size of ¾ in.

Weight of water required per cubic yard of concrete (Table 3.2)

= 340 Ib/yd3

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Compression strength f’c = 4000 psi

W/C ratio (Table 3.3) = 0.57

Amount of cement = 340/.57 = 596.5 Ib/yd3

Using a sand fineness value of 2.6 and Table3.4

Volume of coarse aggregate = 0.64 yd3

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Weight of coarse aggregate = (0.64)*(27 ft3/yd3)*100

=1728 Ib/yd3

Estimated weight of fresh concrete for aggregate of ¾ in. maximum size

(Table 3.5) = 3960 Ib/yd3

Weight of sand = [weight of fresh concrete – weight of (water +

cement + coarse aggregate) =3960-340-596.5-1728 =1295.5 Ib

Net weight of sand = 1.02* 1295.5 =1321.41 Ib

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Net weight of gravel = 1.03*1728

= 1779.84 Ib

Net weight of water = 340- 0.02*1295.5- 0.03*1728

= 262.25 Ib

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For one yd3 of Concrete

Cement = 596.50 IbSand = 1321.41 IbGravel = 1779.84 IbWater = 262.25 Ib