Project on Concrete Mix Design for various grades of Concrete

AIM: To Calculate the Concrete Mix Design for M35 grade concrete without Fly-ash and M50 grade concrete without Fly-ash

INTRODUCTION:

Concrete mix design is the method of finding the precise proportion of cement, sand and aggregates for concrete to achieve the target strength in structures, therefore concrete mix design can be stated as concrete mix in terms of cement: sand: aggregates. The design is done according to the requirements of concrete strength. So, we can achieve the desirable properties of concrete either it is in fresh stage or in hardened stage. 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. other than basic ingredients are used to improve the properties of mix. This project consist of two parts, the first part deals with the design of M35 grade cement with fly ash as a part of it and second part is the design of M50 grade concrete without fly ash.

PART I. OBJECTIVE :

The objective of this project is to produce a M35 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.

mix design calculation of M 35 grade concrete following the IS 10262:2009 code procedure.

The mix design for M35 Grade Of Concrete for actual site conditions vary and thus this should be adjusted as per the location and other factors.

Grade of Concrete : M35
Characteristic Strength (Fck) : 35 Mpa
Standard Deviation : 1.91 Mpa*
Target Mean Strength : T.M.S.= Fck +1.65 x S.D.
(from I.S 456-2000) = 35+ 1.65×1.91
= 38.15 Mpa

Test Data For Material:
Aggregate Type : Crushed
Specific Gravity
Cement : 3.15
Coarse Aggregate : 2.67
Fine Aggregate : 2.62

Water Absorbtion test:

Coarse Aggregate : 0.5%
Fine Aggregate : 1.0 %

MIX DESIGN

Take Sand content as percentage of total aggregates = 36%

Select Water Cement Ratio = 0.43 for concrete grade M35

(From Fig 2. of I.S. 10262- 1982)

Select Water Content = 172 Kg

(From IS: 10262 for 20 mm nominal size of aggregates Maximum Water Content = 186 Kg/ M³ )

Hence, Cement Content= 172 / 0.43 = 400 Kg / M³

Formula for Mix Proportion of Fine and Coarse Aggregate:

1000(1-a₀) = {(Cement Content / Sp. Gr. Of Cement) + Water Content +(F_a / Sp. Gr.* P_f )}

1000(1-a₀) = {(Cement Content / Sp. Gr. Of Cement) + Water Content +C_a / Sp. Gr.* Pc )}

Where C_a = Coarse Aggregate Content

F_a = Fine Aggregate Content

P_f = Sand Content as percentage of total Aggregates

= 0.36

Pc = Coarse Aggregate Content as percentage of total Aggregates.

= 0.64

a₀ = Percentage air content in concrete (As per IS :10262 for 20 mm nominal size of

aggregates air content is 2 %) = 0.02

Hence,

1000(1-0.02) = {(400 /3.15) + 172 +(F_a / 2.62 x 0.36)}

Fa = 642 Kg/ Cum

As the sand is of Zone II no adjustment is required for sand.

Sand Content = 642 Kg/ Cum

1000(1-0.02) = {(400 /3.15) + 172 +(C_a / 2.67 x 0.64)}

Hence,

Ca = 1165 Kg/ Cum

From combined gradation of Coarse aggregates it has been found out that the proportion of 53:47 of 20 mm & 10 mm aggregates produces the best gradation as per IS: 383.

Hence, 20 mm Aggregates = 619 Kg

And 10 mm Aggregates = 546 Kg

To obtain slump in the range of 150-190 mm water reducing admixture brand SP430 from Fosroc with a dose of 0.3 % by weight of Cement shall be used.

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Hence the Mix Proportion becomes:

Cem	W/C	Water	Sand	20mm	10mm	Admix
400	0.43	172	635	619	564	1.2
1		0.43	1.6	1.547	1.36	0.003

Units – Kg/ M³

Cement : Sand: Coarse Aggregates = 1 : 1.6 : 2.907

Part II.PART I. OBJECTIVE :

The objective of this project is to produce a 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.

Stipulations for Concrete Mix Design

• Grade designation : M 50
• Type of cement : OPC 53 grade confirming to IS 8112
• Maximum nominal size of aggregate : 20 mm
• Minimum cement content : 360 kg/m³
• Maximum water-cement ratio : 0.35
• Workability : 50-75 mm (slump)
• Exposure condition : Extreme
• Method of concrete placing : Pumping
• Degree of supervision : Good
• Type of aggregate : Crushed angular aggregate
• Maximum cement content : 450 kg/m³
• Chemical admixture type : Super Plasticizer

Test Data for Materials

The following data are collected by performing standard tests in a laboratory.

Specific gravity of cement : 3.12

Specific gravity of Coarse Aggregate : 2.74

Specific gravity of Fine Aggregate : 2.56

Procedure for Concrete Mix Design of M 50 Concrete

i. Target Strength for Mix Proportioning

f_target = f_ck + 1.65 x s

f_target denotes the Target Average Compressive Strength at 28 days,

f_ck denotes the Characteristic Compressive Strength at 28 days,

‘s’ stands for Standard Deviation

According to the table 1 of IS 10262:2009,

standard deviation, s = 5.0 N/mm²

Therefore, target strength = 50 + 1.65 x 5.0 = 58.25 N/mm²

ii. Selection of Water/Cement Ratio

From Table 5 of IS 456:2000,

Maximum water-cement ratio = 0.35

iii. Selection of Water Content

From Table 2 of IS 456 , maximum water content =186 litres (for 25 to 50 mm slump range) for 20 mm aggregate.

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

If Super plasticizer is used, the water content can be reduced up to 20% and above.

Based on trials with Super plasticizer water content reduction of 27% has been achieved, Hence the arrived water content = 197 – [197 x (27/100)] = 143 litres.

iv. Calculation of Cement Content

Water-cement ratio = 0.35

Cement content = 143/0.35 = 410 kg/m³

From Table 5 of IS 456, minimum cement content for ‘Extreme exposure’ condition = 360 kg/m³

410 kg/m³ > 360 kg/m³, hence, O.K.

v. Proportion of Volume of Coarse Aggregate and Fine Aggregate Content

From Table 3 of IS 10262; volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (Zone II) for a water-cement ratio of 0.50 =0.62.

In the present case, the water-cement ratio is 0.35. Therefore. the 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 the volume of coarse aggregate is increased by 0.02 (at the rate of -/+ 0.01 for every ± 0.05 change in the water-cement ratio).

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

For pumpable concrete, these values should be reduced by 10 percent.

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

Volume of fine aggregate content =1 – 0.585 =0.415

vi. Mix Calculations

a) Volume of concrete = 1m³

b) Volume of cement = (Mass of Cement/ Its Specific Gravity ) X (1/1000)

= (410/3.12) X (1/1000)

= 0.131 m³

c) Volume of Water = (Mass of water/specific gravity of water) X (1/1000)

= (143/1) X (1/1000)

= 0.143 m³

d) Volume of Superplasticizer = (Mass of Superplasticizer / Specific gravity of admixture) X (1/1000)

= (8.2/1.145) X (1/1000)

= 0.007 m³

e) Volume of all aggregate = (a – (b + c + d))

= 1 – (0.131 + 0.143+0.007)

= 0.719 m³

e) Mass of coarse aggregate = Volume of All Aggregate X Volume of Coarse Aggregate X Specific Gravity of Coarse Aggregate X 1000

= 0.719 x 0.585 x 2.74 x 1000

= 1152.48 kg

f) Mass of fine aggregate = Volume of all aggregate X volume of fine aggregate X Specific gravity of fine aggregate X 1000

= 0.719 x 0.415 x 2.56 x 1000

= 763.86 kg

vii. Concrete Mix Proportions

• Cement = 410 kg/m³
• Water = 143 kg/m³
• Super plasticizer = 7 kg/m³
• Fine aggregates = 763.86 kg/m³
• Coarse aggregate = 1152.48 kg/m³
• W/c = 0.35