Project on Concrete Mix Design for various grades of Concrete

Answer:- Mix Design for M35 grade concrete

Concrete is designed or does mix design as per our requirement to achieve the desired compressive strength.

Here, In this question, I have to do a mix design for M35 grade concrete.

Here, 'M' refers to the Design mix & the number '35' refers 35Mpa compressive strength that has to be achieved in 28 days after casting of concrete.

• Mixed designs are designed by the structural engineer and the mix proportion is determined by the concrete producer.
• Mix design is the most intellectual & rational approach for the selection of specific materials with their proportion & more or less for their unique characteristics.
• In the design mix, I have to give the details about how much & in which quantity of concrete ingredients like coarse aggregate, fine aggregate, cement, fly ash, & water are required for the M35 grade of concrete.

1. STIPULATION FOR PROPORTIONING

• a) Grade designation : M35
• b) Type of concrete : OPC 43 grade
• c) Type of mineral Admixture : Fly ash (conforming to IS 3812 Part-1)
• d) Maximum Nominal Size of aggregate : 20 mm
• e) Minimum cement content : 320 kg/m^3 ( From Table-5 of IS 456:200 as a severe condition)
• f) Maximum water cement ratio : 0.45 ( From Table-5 of IS 456:200 as a severe condition)
• g) Workability (slump) : 100 mm ( slump value for Pumpable condition)
• h)Exposure condition : Severe ( for RCC )
• i) Method of concrete placing : Pumping
• j) Type of aggregate : Crushed angular aggregate
• k) Degree of Supervision : Good
• l) Maximum cement content : 450 kg/m^3 ( as per clause 8.2.4.2 of IS 456:2000)
• m) Chemical admixture type : superplasticizer

2. Test date for materials

• a) Cement used : OPC 43 grade conforming IS 8112
• b) Specific Gravity of Cement : 3.15
• c) Fly ash : conforming IS 3812 part-1
• d) Specific Gravity of Fly ash : 2.2
• e) Specific Gravity of C.A & F.A : 2.74 & 2.74
• f) Water- absorption of C.A & F.A : 0.5% & 10%

Step 1 - Determination Of Target Strength of M35
formula,
f ' ck = fck + 1.65 x S

here,

fck = 35 N/mm^2

S ( standard deviation in N/mm^2 ) = 5 N/mm^2 ( from table -1 of IS 10262- 2009)

Now,

The Target strength = 35 + 1.65 x 5 = 43.25 N/mm^2

From Table 5 of IS 456:2000,

Maximum water-cement ratio for Sever exposure condition = 0.45

Based on experience, adopt a water-cement ratio as 0.4.

0.4<0.45,

Hence ok.

From Table 2 of IS 10262- 2009,

Maximum water content for 20 mm (Nominal maximum size of aggregate) = 186 Kg = 186 litre

(for slump 25mm to 50 mm range)

But we have to reach a slump of 100 mm then as per codel provision, we can increase/decrease water content by 3% for a change in a slump of 25mm

Therefore,

Estimated water content for 100mm slump = 186 + 6 x 186 / 100 = 197 liter.

As superplasticizer is used, the water content has to be reduced up to 30%

Based on experience water content reduction of 29% is achieved with a plasticizer.

Hence,

The arrived water content = 197 x 0.71 = 140 liter

Step 4 - Selection of Cement Content
Water-cement ratio = 0.4

Cementitious material content = 140 / 0.4 = 350 kg/m^3

From Table 5 of IS 456:2000,

Minimum cement Content for severe exposure condition = 320 kg/m^3

350 kg/m^3 > 320 kg/m^3,

hence, OK.

As per clause 8.2.4.2 of IS: 456:2000, Maximum cement content = 450 kg/m^3.

Now,

To proportion a mix containing fly ash the following steps are suggested

a) The percentage of fly ash needs to be decided based on the project requirement & Quality of materials.

b) In some cases increase in cementation material can be warranted. increase in cementation material content & its percentage may be based on experience & Trial.

(This mix design is with an increase of 10% cementation material Content )

cementation material content = 350 x 1.10 = 385 kg/m^3

Water content = 140 kg/m^3

so, corrected water-cement ratio = 140/385 = 0.364

Fly ash @ 30% of total cementation material = 385 x 30 / 100 = 115 kg /m^3

Hence,

cement content (OPC 43) = 385 - 115 = 270 kg/m^3

Fly ash = 115 kg/m^3

( we are saving 350-270= 80 kg/m^3 of cement)

From Table 3 of IS 10262- 2009,

The volume of C.A corresponding to 20mm size aggregate and F.A ( Zone 1) for water-cement = 0.6

in the present case, the water-cement ratio is 0.4

then, The volume of C.A needs to be increased or decreased F.A content.

(For every ±0.05 change in w/c, the coarse aggregate proportion is to be changed by 0.01. If the w/c is less than 0.5 (standard value), the volume of coarse aggregate is required to be increased to reduce the fine aggregate content. If the w/c is more than 0.5, the volume of coarse aggregate is to be reduced to increase the fine aggregate content.)

corrected volume of C.A for w/c of 0.4 = 0.6 + 0.02 = 0.62

(for pumpable concrete values are reduced by 10%)

Volume of C.A = 0.62 x 0.9 = 0.56

Volume of F.A = 1 - 0.56 = 0.44

a) Volume of concrete = 1 m^3

b) Volume of cement = (Mass of cement / Specific gravity of cement) x (1/100)

= (270 / 3.15) x (1/1000)

= 0.086 m^3

c) Volume of fly ash = (Mass of fly ash / Specific gravity of fly ash ) x (1/100)

= (115 / 2.2) x (1/1000)

= 0.052 m^3

d) Volume of water = (Mass of water / Specific gravity of water) x (1/1000)

= (140/1) x (1/1000)

= 0.14 m^3

e) Volume of Chemical admixture = (Mass of Chemical admixture / Specific gravity of Chemical admixture ) x (1/1000)

= (7/1.145) x (1/1000)

= 0.006 m^3

f) Volume of total aggregates (C.A + F.A ) = a – (b + c + d + e )

= 1 – ( 0.086 + 0.052 + 0.14 + 0.006)

= 0.716 m^3

g) Mass of coarse aggregates = f x Vol. of C.A x Specify gravity of C.A x 1000

= 0.716 x 0.56 x 2.74 x 1000

= 1098 kg/m^3

f) Mass of fine aggregates = f x Vol. of F.A x Specify gravity of F.A x 1000

=0.716 x 0.44 x 2.74 x 1000

= 863 kg/m^3

Hence,

Result

Mix proportion for M35 grade concrete is

Cement = 270 Kg/m^3

Fly ash = 150 Kg/m^3

Water = 140 Kg/m^3

Fine aggregate = 863 Kg/m^3

Coarse aggregate = 1098 Kg/m^3

Chemical Admixture = 7 Kg/m^3

water-cement ratio = 0.364

M35 mix ratio = 1 : 2.24 : 2.85

Step 6 - Estimation of the mix ingredients