Project on Concrete Mix Design for various grades of Concrete

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.

Objective:-

[03:06, 5/30/2022] indrajeet: 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

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

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

(g) Mass of fine aggregate= ex Volume of Fine Aggregate x Specific Gravity of Fine Aggregate x 1000

STEP 4: SELECTION OF WATER-CEMENT RATIO
The maximum water-cement ratio to design M50 grade concrete can be found from Table 5
of IS 456-2000. Maximum W/C ratio =0.45
Based on experience adopted water cement ratio is .44
0.44<0.45, hence ok
Adopted W/C ratio=0.44

STEP 5: 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)
Clause 4.2 suggests increasing of 3% of water content for every extra 25mm slump from
50mm slump. So a 6% is to be added to it
Estimated water content for 100 mm slump
186+ (6/100)*186 = 197 litre.
(Note: 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 20% has been achieved,
Hence the arrived water content
197*0.8 = 158 litre
Water required 158 litres

EP 6: CALCULATION OF CEMENT AND FLY ASH REQUIRED
Adopted w/c Ratio 0.44
Total cementitious (Cement + fly ash)requirement =
Water content/ Water Cement ratio
158/0.44 = 359 kg/m

The cementitious content has to be increased in order to attain good workability and strength. The increment required is determined on the basis
of experience and research. Here we are increasing cementitious content by 10%
Final cementitious content 359 X 1.10 = 395 kg
From Table 5 of IS 456, Minimum cement content for ‘Severe’ exposure conditions 320 kg
395 kg/m > 320 kg/m hence ok.
Cementitious material content 395
New water cement ratio 158/395 =0.4
Fly ash content is taken as 30% of the total cementitious content 395 X .3 = 118.5 kg/m
Cement required 395 – 118 = 277 kg/m
Cement quantity saved due to fly ash addition 350-277 = 73 kg/m
Cementitious material, cement and fly ash required is 395 kg/m , 277 kg/m and 118 kg/m and the new water-cement ratio is 0.4 respectively

STEP 7: 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 II) for water-cement ratio of 0.50 is 0.62.
In the present case water-cement ratio is 0.44. Therefore, volume of coarse aggregate is required to be increased to decrease the fine aggregate
content. As the water-cement ratio is lower by 0.06. 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
0.44 0.632
For pumpable concrete these values should be reduced up to 10%. Therefore, volume of
coarse aggregate
0.632 x 0.9 =0.568.
Volume of fine aggregate content 1 – 0.568 =0.431
Volume of fine aggregate and coarse aggregate is 0.431 and .568

STEP 10: The slump shall be measured, the water content and dosage of admixture shall be adjusted for achieving the required slump on trial. The
mix proportion shall be reworked for the actual water content and checked for durability requirements
STEP 11: Two more trials having variation of 10% of water-cement ratio shall be carried out and a graph between three water- cement ratios and
corresponding strengths shall be plotted to work out the mix proportions for the given target for field trials.

PART 2:To Calculate the Concrete Mix Design for M50 grade concrete without fly ash:-

(Note: 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 20% has been achieved,
Hence the arrived water content
197 X 0.8 = 158 litre
Water required 158 litres

RESULTS:
Mix Proportion by weight of M35 grade of concrete with fly ash is 1:2.08:2.72 and its water-cement ratio was found to be 0.4.
Mix Proportion by weight of M50 grade of concrete without fly ash is 1:2.28:3.12 and its water-cement ratio was found to be 0.44.

2) Table – 5 Minimum Cement Content, Maximum Water-Cement Ratio and Minimum Grade of Concrete for Different Exposures with
Normal Weight Aggregate of 20 mm Nominal Maximum Size IS: 456-2000

3) Table 2 of IS 383: Grade size distribution for different nominal sizes of coarse aggregate:-

4) Table 4 of IS 383: Grading of fine aggregate:-

5) Table I of IS 10262:2009: Assumed standard deviations:-

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