Project on Concrete Mix Design for various grades of Concrete

1.Calculate the Concrete Mix Design for M35 grade concrete with fly ash & M50 grade concrete without Fly ash

AIM: To Calculate the Concrete Mix Design for M35 grade concrete with fly ash & M50 grade concrete without Fly ash.

INTRODUCTION:

Mix Design of Concrete can be defined as the method of calculating a suitable quantity of materials of concrete and finding out the required proportions with the object of producing concrete of certain minimum strength and durability as economically as possible.Here we are doing Project on concrete mix design of M35 and M50 grade by adding various types of admixtures and get morestrength as well as it’s become economical mix design as far as cost is concern.The fresh concrete properties like workability, setting time and hardened concrete properties like compressive strength, durability etc. are attained surely by this method. Use of additives like admixtures,retarders etc.

OBJECTIVE:

The objective of this project is to produce a mix design for M35 grade concrete containing fly ash and M50 grade concrete. The mix will be prepared as per IS METHOD: Concrete mix proportioning guidelines from IS 10262:2009 and recommented guide lines from IS 10262:1982.

EQUATIONS USED:

1)Target mean strength

f’ck =fck + 1.65s

Where

• f’ck = target average compressive strength at 28 days
• fck = characteristics compressive strength at 28 days, and
• s = standard deviation

2)Cement content

Cement content = water content / water-cement ratio

3) Volume Calculations

• (a) Volume of concrete
• (b) Volume of cement = [Mass of cement] / [Specific Gravity of Cement] x 1/1000
• (c) Volume of water = [Mass of water] / [Specific Gravity of water] x 1/1000
• (d)Volume of chemical admixture = [Mass of admixture] / [Specific Gravity of admixture] x 1/1000
• (e) Volume of all in aggregate =[a-(b+c+d)]
• (f) Mass of coarse aggregate= e x Volume of Coarse Aggregate x Specific Gravity of Fine Aggregate x 1000
• (g) Mass of fine aggregate= e x Volume of Fine Aggregate x Specific Gravity of Fine Aggregate x 1000

Mix Design For M35 Grade Concrete With Fly Ash

• 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)
• 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.

• Proportion of 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, w/c ratio is 0.4. Therefore, 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 volume of coarse aggregate is increased by 0.02 ( at the rate of -/+ 0.01 for every ± 0.05 change in w/c ratio).

Thus, the corrected proportion of 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.

• The Concrete Mix Design for M50 grade concrete without fly ash:

Grade Designation = M-50
Type of cement = O.P.C-43 grade
Brand of cement = Ramco
Admixture = Sika [Sikament 170 ( H ) ]
Fine Aggregate = Zone-II

Sp. Gravity

Cement = 3.15
Fine Aggregate = 2.61
Coarse Aggregate (20mm) = 2.65
Coarse Aggregate (10mm) = 2.66

Minimum Cement (As per contract) =400 kg / m³
Maximum water cement ratio (As per contract) = 0.45

Mix Calculation: –

1. Target Mean Strength = 50 + ( 5 X 1.65 ) = 58.25 Mpa

2. Selection of water cement ratio:-
Assume water cement ratio = 0.35

3. Calculation of water: –
Approximate water content for 20mm max. Size of aggregate = 180 kg /m³ (As per Table No. 5 , IS : 10262 ). As plasticizer is proposed we can reduce water content by 20%.

Now water content = 180 X 0.8 = 144 kg /m³

4. Calculation of cement content:-
Water cement ratio = 0.35
Water content per cum 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 400 kg / m³ )

Hence O.K.

5. Calculation for C.A. & F.A.: [ Formula’s can be seen in earlier posts]-

Volume of concrete = 1 m³
Volume of cement = 412 / ( 3.15 X 1000 ) = 0.1308 m³
Volume of water = 144 / ( 1 X 1000 ) = 0.1440 m³
Volume of Admixture = 4.994 / (1.145 X 1000 ) = 0.0043 m³
Total weight of other materials except coarse aggregate = 0.1308 + 0.1440 +0.0043 = 0.2791 m³

Volume of coarse and fine aggregate = 1 – 0.2791 = 0.7209 m³
Volume of F.A. = 0.7209 X 0.33 = 0.2379 m³ (Assuming 33% by volume of total aggregate )

Volume of C.A. = 0.7209 – 0.2379 = 0.4830 m³

Therefore weight of F.A. = 0.2379 X 2.61 X 1000 = 620.919 kg/ m³

Say weight of F.A. = 621 kg/ m³

Therefore weight of C.A. = 0.4830 X 2.655 X 1000 = 1282.365 kg/ m³

Say weight of C.A. = 1284 kg/ m³

Considering 20 mm: 10mm = 0.55: 0.45
20mm = 706 kg .
10mm = 578 kg .
Hence Mix details per m³
Increasing cement, water, admixture by 2.5% for this trial

Cement = 412 X 1.025 = 422 kg
Water = 144 X 1.025 = 147.6 kg
Fine aggregate = 621 kg

Coarse aggregate 20 mm = 706 kg
Coarse aggregate 10 mm = 578 kg
Admixture = 1.2 % by weight of cement = 5.064 kg.

Water: cement: F.A.: C.A. = 0.35: 1: 1.472: 3.043

Conclusion:

. Mix was cohesive and homogeneous.
. Slump = 120 mm
. No. of cube casted = 9 Nos.
7 days average compressive strength = 52.07 MPa.
28 days average compressive strength = 62.52 MPa which is greater than 58.25MPa
Hence the mix accepted.

Table I of IS 10262:2009: Assumed standard deviations

Table 2 of IS 10262:2009: maximum water content for 20 mm aggregate