Hawassa University, CEng Dep’t Mix Design Example

ACI –METHOD of MIX DESIGN

PROCEDURE

1. Data to be collected
 Fines modulus of selected F.A.
 Unit weight of dry-rodded C.A.
 Sp. gr. Of CA & FA.
 Absorption characteristics of both CA & FA.
 Sp. gr. Of cement (3.15)
 Maximum size of aggregate.
2. Choice of slump (table 1)
3. Estimating the mixing water and air content (table 2)
4. Selecting W/C ratio based on strength or maximum size of aggregate for non-air entrained
(table 3) and for air entrained (table 4)
5. Calculating the cement content
6. Estimating the bulk volume of dry-rodded as per unit volume of concrete
7. Calculate the weight of CA per m3 of concrete (table 5)
WCA = bulk vol. * bulk density
8. Calculate the solid volume of CA in one m3 of concrete
VCA = WCA /1000 sp. gr.
9. Similarly the solid volume of cement, water and volume of air is calculated in one m 3.
10. Solid volume of sand is then calculated by subtracting the solid volume of cement, CA, water &
the entraps air from the data volume of concrete (table 6) or if the wt. of concrete per unit
volume is assumed or can be estimated from experience, the rigged wt. of FA Is the difference
between the wt. of fresh one and the total wt. of the other ingredients.
11. Adjustments of aggregate moisture.

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Hawassa University, CEng Dep’t Mix Design Example

Table: 1 Recommended slumps for various types of construction

Maximum Slump Minimum Slump

Types of Construction
(mm) (mm)
Reinforced foundation walls and footings 75 25
Plain footings, caissons, and substructure
75 25
walls
Beams and reinforced walls 100 25
Building columns 100 25
Pavements and slabs 75 25
Mass concrete 75 25

Table: 6 First Estimate of Weight of Fresh Concrete

Maximum size of First estimate of concrete weight, kg/m 3

aggregate, mm Non-air entrained concrete Air-entrained concrete
10 2285 2190
12.5 2315 2235
20 2355 2280
25 2375 2315
40 2420 2355
50 2445 2375
70 2465 2400
150 2505 2435

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Hawassa University, CEng Dep’t Mix Design Example

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Hawassa University, CEng Dep’t Mix Design Example

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Hawassa University, CEng Dep’t Mix Design Example

Mix Design Example :

Concrete is required for a portion of a structure that will be below a ground level in a location where it
will not be exposed to severe weathering or sulfate attack. Structural considerations require it to have
an average 28- day compressive strength of 24MPa with slump of 75 to 100 mm. The coarse aggregate
has a nominal maximum size of 37.5 dry-rodded mass of 1600 kg/m3. Ordinary Portland cement will be
used and its specific gravity is assumed to be 3.15. The coarse aggregate has a bulk specific gravity of
2.68 and absorption of 0.5 percent. The fine aggregate has a bulk specific gravity of 2.64, absorption of
0.7% and a fineness modulus of 2.8.

Solution:

Step 1: The slump is required to be 75 to 100 mm.

Step 2: The aggregate to be used has a nominal max size of 37.5mm

Step 3: The concrete will be non-air entrained since the structure is not exposed to severe weathering.
From table 2 the estimated mixing water for a slump of 75 to 100 mm in non air entrained concrete
made with 37.5 aggregate is found to be 181 kg/m3.

Step 4: The water-cement ratio for non-air entrained concrete with strength of 24MPa is found from
table 3 to be 0.62.

Step 5: From the information developed in step 3 and 4. The required cement content is found to be
181/0.62 = 292 kg/m3.

Step 6: The quantity of coarse aggregate is estimated from 5. For a fine aggregate having a fineness
modulus of 2.8 and 37.5 mm nominal maximum size coarse aggregate, the table indicated that 0.71 m3
of coarse aggregate, on a dry-rodded basis, may be used in each cubic meter of concrete. The required
dry mass is therefore, 0.71 *1600 = 1136 kg.

Step 7: With the quantities of water, cement, and coarse aggregate established, the remaining material
comprising the cubic meter of concrete must consist of fine aggregate and whatever air will be
entrapped. The required fine aggregate may be determined on the basis of either mass or absolute
volume as shown below.

Step 7.1 Mass basis: The mass of a cubic meter of non-air-entrained concrete made with aggregate having
a nominal maximum size of 37.5 mm is estimated to be 2410kg.(Table 6)

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Hawassa University, CEng Dep’t Mix Design Example

Masses already known are

 Water (net mixing) 181 kg

 Cement 292 kg
 Coarse aggregate 1136 kg
 Total 1609 kg

The mass of fine aggregate, therefore, is estimated to be 2410-1609 = 801 kg

Step 7.2 Absolute volume basis: with the quantities of cement, water and coarse aggregate established,
and the approximate entrapped air content (as opposed to purposely entrained air) of 1 percent
determined from table 2 the sand content can be calculated as follows

181
Volume of water =  0.181m 3
1000

292
Solid volume of cement = = 0.093m3
3.15 * 1000

1136
Solid volume of coarse aggregate = = 0.424m3
2.68 * 1000

Volume of entrapped air = 0.01 * 1 = 0.010 m3

Total solid volume of ingredients 0.708 m3 except fine aggregate then volume of fine aggregate then is
=1-0.708=0.292m3

Step 8: Adjustments for Aggregate moisture

C.A. absorbs 0.5/100*1136 (wt. of C.A.) = 5.68 kg of mixing water.

F.A. absorbs 0.7/100*801 (wt. of F.A.) = 5.601 kg of mixing water.

Therefore, the estimated requirement for added water

= 181 + 5.68 + 5.601 = 192.287 lit.

Then, the estimated batch wt. for cubic meter of concrete are

Water 192 lit.

Cement 292 kg
C.A. 1136 kg
F.A. 801 kg

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