CONCRETE MIX DESIGN M40 GRADE

WHAT IS CONCRTE MIX DESIGN ?

The process of selecting suitable ingredients of concrete and determining their relative amounts with the objective of producing a concrete of the required, strength, durability, and workability as economically as possible, is termed the concrete mix design.

POINT TO BE REMEMBER WHILE MAKING MIX DESIGN

• The grade designation giving the characteristics strength required of concrete.

• The type of cement influences the rate of development of compressive strength of concrete.

• Maximum nominal size of aggregate to be used in concrete may be as large as possible within the limits prescribed by the IS : 456-2000.

• The cement content is to be limited from shrinkage, crack, and creep.

• The workability of concrete for satisfactory placing and compacting is related to the size and shape of the section,quantity and spacing of reinforcement and technique used for transportation, placing and compaction.

CONCRETE MIX DESIGN-M40 GARDE EXAMPLE

1.Design Stipulation For Proportioning

Grade Designation = M-40

Type of cement = O.P.C-43 grade confarming to IS 8112

Maximum nominal size of aggregate = 20 mm

Maximum Cement content =450 kg / m³

Minimum Cement content = 320  kg / m³

Maximum water cement ratio = 0.45

Workability = 100 mm (slump)

Exposure condition = Severe (for reinforced concrete)

Method of placing = Pumping 

Degree of supervision = Good

Type of aggregate = Crushed angular aggregate

Chemical admixture type = Superplasticiser

2. Test Data For Material

Cement used = OPC 43 grade confirming IS 8112

Sp. Gravity Cement = 3.15

Sp. Gravity Fine Aggregate = 2.61

Sp. Gravity Coarse Aggregate (20mm) = 2.65

Sp. Gravity Coarse Aggregate (10mm) = 2.66

Chemical admixture = Superplasticiser confirming IS 9103

Water absorption of coarser aggregate = 0.5%

Water absorption of coarser aggregate = 1%

Free surface moisture = Nil

3. Target Mean Strength

Target Mean Strength = 40 + ( 5 X 1.65 ) = 48.25 Mpa

Selection of water cement ratio

Assume water cement ratio = .40 - 0.45

4. Selection Of Water Content

Approximate water content for 20mm max. Size of aggregate = 180 kg /m³ (As per Table No. 2 , IS : 10262 ). As plasticizer is proposed we can reduce water content by 20%.

Now water content = 180 X 0.8 = 140kg /m³

5. Cement Content Calculation

Water cement ratio = 0.40

Water content per m³ of concrete = 144 kg

Cement content = 144/0.35 = 411.4 kg / m³

Say cement content = 412 kg / m³ (As per contract

Minimum cement content 350 kg / m³ )

Hence O.K.

6. Calculation of sand and coarse aggregate 

V = [ W + (C/S_c) + (1/p) . (f_a/S_fa) ] x (1/1000)

V = [ W + (C/S_c) + {1/(1-p)} . (ca/S_ca) ] 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 ) per m³ of concrete ,

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

S_c = specific gravity of cement,

(p) = Ratio of fine aggregate to total aggregate by absolute volume ,

(fa) , (ca) = total mass of fine aggregate and coarse aggregate (kg) per m³ of
Concrete respectively, and

Sfa , Sca = specific gravities of saturated surface dry fine aggregate and Coarse aggregate respectively.

As per Table No. 3 , IS-10262, for 20mm maximum size entrapped air is 2% .

Assume F.A. by % of volume of total aggregate = 36.5 %

0.98 = [ 160 + ( 400 / 3.15 ) + ( 1 / 0.365 ) ( Fa / 2.61 )] ( 1 /1000 )

=> Fa = 660.2 kg

Say Fa = 660 kg.

0.98 = [ 160 + ( 400 / 3.15 ) + ( 1 / 0.635 ) ( Ca / 2.655 )] ( 1 /1000 )

=> Ca = 1168.37 kg.

Say Ca = 1168 kg.

Considering 20 mm : 10mm = 0.6 : 0.4

20mm = 701 kg .
10mm = 467 kg .

Hence Mix details per m³

Cement = 400 kg
Water = 160 kg
Fine aggregate = 660 kg
Coarse aggregate 20 mm = 701 kg
Coarse aggregate 10 mm = 467 kg
Admixture = 0.6 % by weight of cement = 2.4 kg.
Recron 3S = 900 gm

Water: cement: F.A.: C.A. = 0.4: 1: 1.65: 2.92

7. Observation for concrete mix design

% Strength of concrete : The strength of concrete increases with

age.

Table for strength of concrete at various age

Age	Strength per cent
1 day	16%
3 days	40%
7 days	65%
14 days	90%
28 days	99%

A. Mix was cohesive and homogeneous.

B. Slump value = 120 mm

C. No. of cube casted = 9 

7 days average compressive strength = 42.07 N/mm2

28 days average compressive strength = 52.52 N/mm2

which is greater than 48.25 N/mm2

Hence the mix accepted.