BIS METHOD OF CONCRETE DESIGN

Indian standard institution has recommended guidelines for concrete mix design based on available materials. Use of silica fumes, admixture pozzolana etc. is beyond the scope of IS 10262-2009. Steps for design as per IS 10262-2009 are enlisted below.

1. The target average compressive strength (f’_ck) at 28 days is given by using equation

f’_ck = f_ck + ks

Where,

f’_{ck =}target mean strength

f_ck= characteristic compressive strength at 28 days,

s = standard deviation of compressive strength,

k= a constant, depending upon the accepted proportion of low results and the number of tests.

2. The water cement (w/c) ratio is chosen from an empirical relationship (a graph) for the given 28-daytarget mean strength. The w/c ratio is checked against the limiting w/c ratio to satisfy the durabilityrequirements.

3. Initially, water content, as mass (kg) per unit volume (m³) of concrete, is selected from TABLE 2 of IS 10262-2009 for nominal maximum size of coarse aggregate and given slump range.

4. The cement content is calculated from the w/c ratio and the water content. The cement content, thus calculated, is then checked against the minimum cement content to satisfy the durability requirement.

5. Volume of coarse aggregate per unit volume of total aggregates is calculated from TABLE 3 of IS 10262 -2009 for a given grading zone of fine aggregates.

6. Fine aggregates volume per unit of total aggregates volume calculated by subtracting the coarse aggregates volume obtained in previous step from 1.

7. Coarse and fine aggregates per kg of concrete are calculated from equation given below.

C_{a = [1000V-W+ ]} S_{ca (1-p)}

f_{a = [1000V-W+ ] p} S_ca

C_{a =} total mass of coarse aggregate, [kg per m³ of concrete],

f_a= total mass of fine aggregate, [kg per m³ of concrete],

V = absolute volume of fresh concrete m³.

W = mass of water (kg) per m³ of concrete,

C = mass of cement (kg) per m³ of concrete,

 S = specific gravity of cement

p = ratio of fine aggregate to total aggregate by absolute volume,

S_fa= specific gravity of saturated surface dry fine aggregate,

S_ca= specific gravity of saturated surface dry coarse aggregate.

8. Water content is adjusted based on the absorption and the current moisture content to generate equivalent of saturated surface dry condition of the aggregates.