Bureau of Indian Standards (BIS) Method of Mix Design

Bureau of Indian Standards (BIS) has recommended a Mix Design Concept mainly based on the research works performed in national laboratories. This method can be applied for both medium-strength and high-strength concretes. The step-by-step approach of the BIS mix design is given below.

1. The target mean compressive  strength at 28 days is given by = f_ck + tSwhere f_ck = characteristic compressive strengtht = a statistical valueS = the standard deviation
2. It is desirable to establish a relationship between concrete strength and water–cement ratio at the site. If such a relationship is not available the water–cement ratio corresponding to the target strength may be determined from the relationship given in Table 8.6. It is possible to design in an effective way if the strength of the cement is incorporated in the concrete mix. This is done in the BIS design. Thus, if the 28-days strength is known, the water–cement ratio can be obtained from Fig. 8.1.Table 8.6 Strength and water–cement ratioSource: ACI 211.1–91.Reproduced with permission from the American Concrete Institute, Farmington Hills, MI (www.concrete.org)
3. The air content can be obtained from Table 8.7 for the normal size of the aggregate used.Table 8.7 Approximate air content Figure 8.1 Relationship between free water–cement ratio and concrete strength for different cement strengthsTable 8.8 Approximate sand and water content per m³Source: IS: 10262–82.
4. The water content and percentage of sand are determined from Table 8.8 for medium-strength (less than M 35 grade) and high-strength (greater than M 35 grade) concrete.
5. The cement content per unit volume of concrete is obtained asMass of cement = The cement calculated from the above relationship has to be checked against the minimum cement content requirement for durability from Table 8.9, and the greater of the two has to be taken.Table 8.9 Details for different exposures of concreteSource: IS: 456–2000.
6. The quantity of aggregate can be calculated from the following relationship:(8.1)(8.2)where V = absolute volume of fresh concrete= (gross volume) – (volume of entrapped air) m³W = mass of water per m³ of concrete, kgC = mass of cement per m³ of concrete, kgS_c = specific gravity of cementP = ratio of fine aggregate to total aggregate by absolute volumef_a, c_a = total masses of fine and coarse aggregates per m³ of concrete, respectively, kgS_fa, S_ca = specific quantities of saturated, surface-dry fine aggregate and coarse aggregate, respectively.
7. The mix proportions have been calculated based on the assumption that the aggregates are saturated and surface dry. When there is any deviation, necessary correction has to be incorporated.
8. The above calculated mix properties have to be checked by means of trial batches.
9. First the workability is checked, this forms Mix No. 1. If the measured workability is different from the assumed one, then the water content is changed (Table 8.10), and the whole mix design is modified keeping the new water–cement ratio constant.(b) A minor adjustment in the aggregate quantity may be made to improve the finishing quality or freedom from bleeding and segregation. This forms Mix. No. 2.(c) Now the water–cement ratio is changed by ±10% and the mix proportion is recalculated. This will form trial Mix Nos. 3 and 4.(d) Testing for trial Mix Nos. 2, 3 and 4 are done simultaneously.(f) These test results will provide adequate information including the relationship between compressive strength and water–cement ratio from which the correct mix proportion can be arrived at.

Table 8.10 Adjustment of value in water content and sand percentage for other conditions

Source: IS: 10262–82.