Challenge

Project on Concrete Mix Design for various grades of Concrete

PPrachit Milmile3 Jan 2022

DESIGN

MIX DESIGN FOR M35 GRADE CONCRETE WITH FLY ASH

1. Stipulation for proportioning

a) Grade designation : M35
b) Type of cement : OPC 43 Grade conforming IS 8112-1989
c) Maximum nominal size of aggregate : 20mm
d) Minimum cement content : 360 kg/m3 (IS 456:2000) Exposure Condition
e) Maximum water-cement ratio : 0.4 (Table 5 of IS 456:2000)
f) Workability : 100 (Slump Value for pumpablr concrete)
g) Exposure condition : Extreme (For Reinforced Concrete)
h) Method of concrete placing : Pumping
i) Degree of supervision : Good
j) Type of aggregate : Crushed Angular Aggregates
k) Maximum cement content : 450 kg/m3
l) Chemical admixture type : Super Plasticizer conforming to IS 9103

Test data for material

Cement used : OPC 43 Grade conforming IS 8112-1989
Specific gravity of cement : 3.15
Fly ash: Conforming to IS 3812(Part 1)
Specific Gravity of fly ash= 2.2
Chemical admixture : Super Plasticizer conforming to IS 9103
Specific gravity of

1) Coarse aggregate 20mm : 2.74

2) Fine aggregate : 2.56

e) Water absorption:

1) Coarse aggregate : 0.5 %

2) Fine aggregate : 1.0

f) Free (surface) moisture:

1) Coarse aggregate : Nil

2) Fine aggregate : Nil

g) Sieve analysis:

1) Coarse aggregate: Conforming to all in aggregates of Table 2 of IS 383

2) Fine aggregate : Conforming to Grading Zone I of Table 4 of IS 383

Target Strength for Mix proportion

f’ck =fck + 1.65 s

where

ft = target average compressive strength at 28 days,

fck = characteristics compressive strength at 28 days, and

s = standard deviation.

From Table I of IS 10262:2009, Standard Deviation, s = 5 N/mm2. Therefore, target

ft = 35 + 1.65 x 5 = 43.25 N/mm2.

Selection of water-cement ratio

From the Table 5 of IS 456 for extreme exposure maximum Water Cement Ratio is 0.4

Based on experience adopted maximum water-cement ratio = 0.35.

0.35< 0.4, hence O.K

Selection of Water Content

From Table 2 of IS 10262:2009, maximum water content for 20 mm aggregate = 186 litre (for 25 to 50 mm slump range)

Estimated water content for 100 mm slump = 186+ (0.06x186) = 197 litre

Based on trials with Super plasticizer water content reduction of 29% has been achieved, Hence the arrived water content = 197x0.71= 140 litre.

Calculation of cement content

Adopted w/c Ratio = 0.35

Cement Content = 140/0.35 = 400 kg/m3

From Table 5 of IS 456, Minimum cement content for severe exposure conditions 320kg/m3

= 400 kg/m3 > 360 kg/m3 hence ok.

Now, to proportion to mix containing flyash the following steps are suggested

a) The percentage of fly ash needs to be decided based on project requirement and quality of materials.

b) In some cases increase in cementitious material can be warranted increase in cementitious material content and its percentage may be based on experiences may be based on expirence and trail. Here we will take increase of 10% cementitious material content.

Cementitious material content = 400 x 1.10= 440 kg/m^3

Water Content = 140 kg/m^3

So water-cement ratio = 140/440=0.31

Fly ash @ 30% of cementitious material = 440 x 30%=132 kg/m^3

Cement(OPC) = 440-132= 308 kg/m^3

Saving of cement while using fly as = 400-308= 92 kg/m^3

Fly ash utilized = 132 kg/m^3

Proportion of volume of coarse aggregate and fine aggregate content

From Table 3 of (IS 10262:2009) Volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (Zone I) for water-cement ratio of 0.6.

In the present case water-cement ratio is 0.35

Therefore, volume of coarse aggregate is required to be increased to decrease the fine aggregate content.

As the water-cement ratio is lower by 0.10. The proportion of volume of coarse aggregate is increased by 0.02 (at the rate of -/+ 0.01 for every ± 0.05 change in water-cement ratio).

Therefore, corrected proportion of volume of coarse aggregate for the water-cement ratio of 0.35 = 0.65

NOTE – In case the coarse aggregate is not angular one, then also volume of coarse aggregate may be required to be increased suitably based on experience & Site conditions.

For pumpable concrete these values should be reduced up to 10%.

Therefore, volume of coarse aggregate =0.65 x 0.9 =0.585.

Volume of fine aggregate content = 1 – 0.585= 0.415.

Mix Calculations

The mix calculations per unit volume of concrete shall be as follows:

a) Volume of concrete = 1 m^3
b) Volume of cement = [Mass of cement] / {[Specific Gravity of Cement] x 1000}

= 308/{3.15 x 1000}

= 0.097 m^3

c) Volume of cement = [Mass of cement] / {[Specific Gravity of Cement] x 1000}

= 132/{2.2 x 1000}

= 0.06 m^3

d) Volume of water = [Mass of water] / {[Specific Gravity of water] x 1000}

= 140/{1 x 1000}

= 0.140 m^3

e) Volume of chemical admixture = [Mass of chemical admixtures] / {[Specific Gravity of admixtures] x 1000}

= 7/{1.145 x 1/1000}

= 0.006 m^3

f) Volume of all in aggregate = [a-(b+c+d+e)]

= [1-(0.97+0.06+0.140+0.006)]

= 0.697 m^3

g) Mass of coarse aggregate= f x Volume of Coarse Aggregate x Specific Gravity of Fine Aggregate x 1000

= 0.697x 0.585 x 2.74 x 1000

= 1120 kg/m3

h) Mass of fine aggregate= f x Volume of Fine Aggregate x Specific Gravity of Fine Aggregate x 1000

= 0.697x 0.415x 2.56 x 1000

= 740 kg/m3

Mix proportions for trial 1

Cement = 308 kg/m3

Fly Ash = 132 kg/m3

Water = 140 kg/m3

Fine aggregate = 740 kg/m3

Coarse aggregate 20mm = 1120 kg/m3

Chemical admixture = 7 kg/m^3

Water-cement ratio = 0.31

Mix Proportion By weight = C:FA:CA = 1:1.68:2.54

MIX DESIGN FOR M50 WITHOUT FLY ASH