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Mix design is using specific proportions of ingredients such as aggregates, water, admixtures and cement to produce a concrete suited for a particular job or project. Here you will find the concept of mix design as per IS456:2000.Characteristic strength

This means that value of the strength of concrete below which, not more than 5 percent of the test results are expected to fall.

Target mean strength

ft = fck + K.s

where

ft = target mean strength

fck = characteristic strength

K = a statistical constant, depending on the definition of fck and is derived from the mathematics of Normal Distribution

s = standard deviation

The value of K is equal to 1.65 where not more than 5% of test results are expected to fall below the characteristic strength

=>ft = fck + 1.65 s

Acceptance Criteria (IS 456 : 2000)

Compressive strength

Both the following conditions must be met :

a) The mean strength of any four consecutive test results compiles with the appropriate limits in Table 3.

For M15 grade

Mean of 4 consecutive results in N/mm2 must be greater than or equal to

fck + 0.825 x SD or

fck + 3 N/mm2 , whichever is greater

For M20 or above grade

Mean of the group of 4 consecutive results in N/mm2 must be greater than or equal to

fck + 0.825 x SD or

fck + 4 N/mm2 , whichever is greater

Acceptance Criteria

b) Any individual test result complies with the appropriate limits in Table 3.

For M15 grade

Individual test results in N/mm2 must be greater than or equal to

( fck â€“ 3 ) N/mm2

For M20 or above grade

Individual test results in N/mm2 must be greater than or equal to

( fck â€“ 4 ) N/mm2

Acceptance Criteria

Flexural strength

Both the following conditions must be met :

a) The mean strength of any four consecutive test results exceeds the specified characteristic compressive strength by at least 0.3 N/mm2

b) The strength determined from any test result is not less than the specified characteristic strength less 0.3 N/mm2