Concrete Mix Design Calculations

CONCRTE MIX DESIGN (IS METHOD)

1 Characteristic compressive cube strength at 28 days = 20 Mpa

Maximum size of course aggregate = 20 mm

Type of aggregate = Crushed rock

Degree of work ability = 0.9 CF (slump:30-60mm)

Degree of quality control = weigh batching but occasional supervision and test

Type of exposure = Moderate

2 Characteristics of materials

i Cement

a Type of cement used (OPC)

b Specific gravity of cement 3.15

c Bulk density of cement 1500 kg/m3

ii Aggregates

a Specific gravity

Coarse aggregate 2.6

Fine aggregate 2.6

b Bulk density

Coarse aggregate 1600 kg/m3

Fine aggregate 1700 kg/m3

c Fineness modulus

Coarse aggregate 6.5

Fine aggregate 2.2

d Water absorption

Coarse aggregate 0.5 per cent

Fine aggregate Nil

e Free surface moisture

Coarse aggregate Nil

Fine aggregate 0.2 per cent

f Grading of aggregate

3 Target mean strength

Target mean compressive strength 28 Mpa

4 Maximum water-cement ratio

Water-cement ratio for durability under moderate exposure conditions 0.55

IS METHOD OF MIX DESIGN

Water Content 186 Kgs/Cum

Percentage of Fine aggregate T-10.14 35 %

Adjustments in water T-10.14 3 %

Adjustments in Sand T-10.14 -3.5 %

Water Content 191.58 Kgs

Sand Content 31.5 %

Air Content 2 %

W/C Ratio 0.5

Concrete Volume 0.98

Cement Content 383 Kgs

Total Volume of Aggregate 0.67

Total Mass of Aggregate 1734

Mass of Fine Aggregate 546

Mass of Course Aggregate 1188

Estimation of Mix Design Ratio

Mass of Course Aggregate 1188 Kgs

Mass of Fine Aggregate 546 Kgs

Mass of Cement 383.2 Kgs

Mass of Water 186 Kgs

Mix Design Ratio 0.49 :1 :1.43 :3.1

Steps of Mix Design as per IS Method

Step 1: From the known degree of control and the require characteristic strength, determine the SD*

Step 2: Fix the Target Strength from the equation

Target Strength = fck + 1.65 x SD*

Step 3: For the required target strength determine the free water – cement ratio from the curves**

Step 4: The value obtained should be checked with the maximum water – cement ratio*

Step 5: Determine water content in kg per cum of concrete and percentage of sand in total aggregate by absolute weight. Apply correction*** for water content and sand content

Step 6: After determining the water content, go back to step 3 and taking that water – cement ratio, determine the weight of cement.

Step 7: Check the cement content obtained above with that required from the point of durability* and apply correction, if required. Adopt greater of two values.

Step 8: Estimate the % of entrapped air****. The percentage depends upon the degree of compaction. Even after good compaction, there will be some entrapped air in concrete.

Table 8 : IS 456 – 2000

IS 10262

SP 23, Table 36 and Table 6 of IS 10262

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