Mix proportioning:

[IS 456- 2000, IS 1343 – 1980/ 2012, IS 10262- 2009, SP - 23]

Factor influencing the mix proportions:

i) Grade designation – M10, M15……... M50, M100 etc.

ii) Type and grade of cement – 33, 43, 53, high strength OPC

- Rapid hardening Portland Cement – early strength

- Low heat Cement – mass concreting

- PPC and PSC – prestressed concrete

iii) Maximum nominal size of aggregate – size of sieve on which 15 % retains (10-20 mm

preferable)

iv) Grading of combined aggregate

v) Water-cement ratio

vi) Workability

vii) Durability – exposure conditions

viii) Quality control

Mix proportion methods:

1. Trial and adjustment

2. British mix design

3. ACI mix design

4. IS design mix

5. Rapid method/ CRI of India (boil water curing of concrete specimens

Design M30 grade of concrete from the given data:

1. Combined coarse aggregate (CCA); 10 mm - 35 % & 20 mm –

65 %

Specific gravity (Sp. Gr.)– 2.95, Water Absorption (WA)– 0.68

Fineness modulus (FM) – 6.41, Free moisture – 0.48

2. Fine aggregate;

Sp. Gr. – 2.46, WA – 1.51, FM – 2.96, Free moisture – 0.62

3. Cement; - PSC

Sp. Gr. – 2.96

Compressive strength;

7 days maturity – 29.93 N/ mm2 (average of 3 specimens)

28 days strength – 44.90 = 45 N/mm2 (say)

4. Workability – Compacting Factor (CF) – 0.80 => Slump – 40

mm

5. Exposure condition – moderate

6. Degree of quality control – Good

Formulation procedure;

Standard deviation – 5.0 N/ mm2 [IS 456, T-8]

Aggregate – crushed angular

f’ck = fck + t x S = 30 + 1.65 x 5 = 38.25 N/ mm2

water/ cement ratio = 37.5

weight of water – 186 Kg/ m3 [for 20 mm nominal size (IS 10262, T-4)]

Fine Aggregate – 35 %

For mild exposure of M30 grade concrete [IS 456, T - 5]

Maximum, Water/ cement ratio – 0.45

Minimum Cement Content – 320 Kg/ m3

As per IS 10262, T-6;

Adjustment Water content (%) % age of sand in total aggregate

For sand of Zone-I 0.0 + 1.5

For decrease in CF (0.8 – 0.6) = 0.2

- 6.0 0.0

For decrease in W/ C (0.45 – 37.5) = 0.075

0.0 - 1.5

Total = - 6.0 0.0

So, required sand content = 35 + 0.0 = 35 %

And required water content = 186 – (186 x 6)/ 100 = 174.84 Kg/ m3

Calculation of cement content:

Cement content = 174.84/ 0.40 = 437.10 = 438.0 Kg (say)

Entrapped air = 2 % i.e. 0.02

Calculation of aggregate content:

V = [W + C/ Sc + (1/ p) x fa/ Sfa] x 1/ 1000, and

V = [W + C/ Sc + {1/ (1 - p)} x Ca/ Sca] x 1/ 1000

Where,

V = absolute volume of fresh concrete, which is equal to gross volume (m3) minus the

volume of entrapped air,

W = mass of water (Kg)/ m3 of concrete,

C = mass of cement (Kg)/ m3 of concrete,

Sc = specific gravity of cement,

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

fa ca = total masses of fine aggregate and coarse aggregate (Kg)/ m3 of concrete respectively,

and

Sfa, Sca = specific gravities of saturated surface dry fine and coarse aggregates respectively.

Fine aggregate;

(1 - 0.02) x 1000 = 174.84 + 438.0/ 2.98 + (1/ 0.35) x FA/ 2.46

FA/ 0.861 = 980 – 174.84 – 146.98 = 658.18

FA = 566.70 Kg/ m3

Coarse aggregate;

980 = 174.84 – 438.0/ 2.98 + {1/ (1 – 0.35)} x CA/ 2-95

CA/ 1.918 = 980 – 174.84 – 146.98 = 658.18

CA = 1262.40 Kg/ m3

Now, the mix proportion in SSD condition;

W/ 174.84 = C/ 438.0 = FA/ 566.70 = CA/ 1262.40

0.40: 1: 1.29: 2.88

For mix proportion in dry condition;

Extra water for CA = [(0.68 – 0.48)/ 100] x 1262.40 = 2.53

Extra water for FA = [(1.51 – 0.62)/ 100] x 566.70 = 5.044

The required water content = 174.84 + 2.53 + 5.044 = 182.414 Kg/ m3

The mix proportion;

W’/ 182.414 = C/ 438.0 = FA/ 566.70 = CA/ 1262.40

0.416: 1: 1.29: 2.88

Assignments Problems;

1. Design of M40 and M50 grades of concrete in presence of

plasticizer/ super-plasticizer and incorporation of fly-ash by

partial replacement of cement, as per IS 10262-2009.

2. Design M40 grade of concrete with and without plasticizer by

IS method from the following given data;

Maximum size of aggregate – 20 mm

Shape of CA – angular

Degree of workability – 0.85

Degree of quality control – fair

Degree of exposure – severe

Cement – 53 grade

Specific Gravity – 3.15

C C A – 20 and 12.5 mm in the ratio 60: 40

FA – conforming to zone II

Sp. Gr. of CA – 2.67

Sp. Gr. of FA – 2.60

FM of CA & FA – 6.68 & 2.68

Free surface moisture;

CA – Nil and that of FA – 0.5 %

Water absorption;

CA – 0.50 % and that of FA – 1.5 %

Entrapped air – 2 %

3. Use ACI method to design a concrete mix which is required to have a specified mean

strength of 30 MPa at 7 days. The slump requirement is 25 mm and a maximum size of 10

mm. The fineness modulus of all in aggregate (CA & FA) is 2.8. Assume negligible water

absorption and moisture content, bulk density of CA is 1600 Kg/ m3 and extreme exposure

condition.