Challenge

Project on Concrete Mix Design for various grades of Concrete

CChaitanya Athava20 Jul 2022

Aim: To determine the mix design for M35 concrete with fly ash consisting of the following properties:

Grade designation: M35
Type of cement: OPC 43 grade confirming IS 12269
Type of mineral admixture: Fly ash
Maximum nominal size of aggregate: 20
Minimum water-cement ratio: 0.45 (Table 5 of IS 456:2000)
Workability: 100-120mm Slump
Exposure condition: moderate
Method of concrete placing: Pumping
Degree of supervision: Good
Type of aggregate: Crushed Angular aggregate
maximum cement content : 360 kg/cum
chemical admixture type: Super Plasticizer

Data obtained:

Cement used: OPC 43 grade (IS 12269)

The specific gravity of cement: 3.15

Fly ash – specific gravity: 2.2
Coarse aggregate- Specific gravity: 2.74
Fine aggregate – specific gravity: 2.74
water absorption of coarse aggregate: 0.5%
water absorption of fine aggregate: 1%
Coarse aggregate- Sieve analysis as per Table 2 of IS 383
Fine aggregate- Sieve analysis as per Grading zone I of Table 4 of IS 383

Procedure:

Target Strength for mix proportion is obtained from

f’ck = fck + 1.65s (Table I : IS 10262:2009)

Considering s = 5N/sq-mm.

Thus f’ck = 35+1.65(5) = 43.25 N/sq-mm.

Water-cement Ratio:

Considering maximum water-cement ratio = 0.4 (Table 5: IS 456:2000)

Water content

Maximum water content for 20 mm aggregate = 186 litres ( Table 2 : IS 10262:2009)

Estimated water content for 100mm slump = 186+(6/186) = 197 litres.

However, if super plasticizer is used, the water content can be reduced upto 20% to 30%.

Thus the water content obtained is 197-(30% of 197) = 132 litres.

Adopt 140 litres.

Cement Content

Adopted w/c ratio = 0.4

Cement content = 140/0.4 = 350 kg/cum.

Minimum cement content for moderate exposure = 320 kg/cum. (Table 5 : IS 456:2000)

350 kg/cum > 320 kg/cum.

Hence OK

Fly ash content:

Considering 10% increase in cementitious material

Thus, Cementitious content = 350x1.1 = 385 kg/cum.

Fly ash = 30% of total cementitious content = 385 x 0.3 = 115 kg/cum.

The proportion of the volume of coarse aggregate and fine aggregate:

Volume of coarse aggregate and fine aggregate for w/c ratio 0.5 = 0.6 (Table 3 : IS 10262:2009)

In this case, the w/c ratio is 0.4. Therefore, the volume of coarse aggregate is required to be increased to decrease the fine aggregate content. As the w/c ratio is reduced by 0.1, the proportion of the volume of coarse aggregate is increased by 0.02 ( at the rate of -/+ 0.01 for every ± 0.05 change in the w/c ratio).

Thus, the corrected proportion of the volume of coarse aggregate for w/c ratio of 0.4 = 0.62.

For pumpable concrete, it can be reduced upto 10%. Hence, volume of coarse aggregate = 0.62x0.9 = 0.56.

Volume of fine aggregate = 1-0.56 = 0.44.

MIX CALCULATIONS

The following mix calculations are carried out:

Volume of concrete = 1 cum.
Volume of cement = Mass of cement / (Sp. gravity x 1000) = 270/(3.15x1000) = 0.086 cum.
Volume of Fly ash = Mass of fly ash /(Sp. gravity x 1000) = 115/(2.2x1000) = 0.052 cum.
Volume of water = mass of water /(Sp. gravity x 1000) = 140/(1x1000)= 0.14 cum.
Volume of chemical admixture = Mass of chemical admixture /(Sp. gravity x 1000) = 7.6/(1.145x1000) = 0.006cum.
Volume of all in aggregate = [1-(0.086+0.052+0.14+0.006)] = 0.716 cum.
Mass of coarse aggregate = Vol. of all aggregates x Vol. of coarse aggregate x Sp. gravity of coarse aggregates x 1000 = 0.716x0.56x2.74x1000 = 1098 kg/cum.
Mass of fine aggregates = Vol. of all aggregates x Vol. of fine aggregate x Sp. gravity of fine aggregates x 1000 = 0.716x0.44x2.74x1000 = 863 kg/cum.

RESULT:

Mix Proportion Obtained:

Cement = 270 kg/cum.

Fly ash = 115 kg/cum

Water = 140 litres

Fine aggregates = 863 kg/cum.

Coarse aggregate = 1098 kg/cum.

Chemical admixture = 7kg/cum.

w/c ratio = 0.4

Mix proportion by weight = 1:2.24:2.85

CONCLUSION:

The slump should be measured and the water content and admixture can be adjusted to obtain the required slump. The mix proportion can be adjusted and reworked as per requirement.

Aim: To determine the mix design for M50 concrete as per the following properties:

Grade designation: M50
Type of cement: OPC 43 grade confirming IS 12269
Maximum nominal size of aggregate: 20
Minimum water-cement ratio: 0.45 (Table 5 of IS 456:2000)
Workability: 100-120mm Slump
Exposure condition: moderate
Method of concrete placing: Pumping
Degree of supervision: Good
Type of aggregate: Crushed Angular aggregate
maximum cement content : 360 kg/cum
chemical admixture type: Super Plasticizer