Project on Concrete Mix Design for various grades of Concrete
AIM: To calculate the concrete mix design for M35 grade of concrete with flyash.
INTRODUCTION: Concrete mix design is the process of finding the proportion of cement, sand, aggregate and water to achieve desired strength required for the structure.
The mix design is done according to structural requirement ,site condition, topography as well as the distance between concrete mixing site and the construction site
In mix design concrete workability and slump is taken into consideration.
Objective:The objective of the project to mix design M35 grade concrete with fly ash to make the concrete economical with the help of IS codes.
STEP 1: Stipulations for Concrete design mix
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Grade designation |
M35 |
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Type of cement |
OPC 43 Grade confirming to IS 8112 |
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Type of mineral admixture |
Fly ash confirming to IS 3812 (Part 1) |
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Maximum nominal size of aggregate |
20 mm |
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Minimum cement content |
320 kg/m3 (Table 5 of IS 456:2000- Exposure condition) |
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Maximum water-cement ratio |
0.45 (Table 5 of IS 456:2000 Exposure condition) |
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Workability |
100 mm (slump value for pumpable concrete) |
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Exposure condition |
Severe (For Reinforced Concrete) |
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Method of concrete placing |
Pumping |
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Degree of supervision |
Good |
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Type of aggregate |
Crushed Angular Aggregates |
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Maximum cement content |
450 kg/m3 |
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Chemical admixture type |
Super Plasticizer |
Step 2: Target strength for mix proportioning
f'ck=fck+1.65s
where,
f'ck=target average compressive strength after 28days
fck=characteristic compressive strength after 28days
s=standard deviation
f'ck=35+1.65*5=43.25N/mm2
From Table I of IS 10262:2009, Standard Deviation, s = 5 N/mm2.
Step 3:Selection of water-cement ratio
The free water cement ratio required for target strength of 43.25N/mm2 is 0.44 for OPC 43 grade curve.
This is lower than the maximum value 0.45 prescribed for severe exposure for reinforced concreteas per table 5 of IS456 2000.
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STEP 4: Selection of water content |
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From Table 2 of IS 10262:2009, maximum water content for 20 mm aggregate |
186 litre (for 25 to 50 mm slump range) |
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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. |
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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
STEP 5: Calculation of Cement and Flyash requirement
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Adopted w/c Ratio |
0.44 |
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Total cementitious (Cement + fly ash)requirement = Water content/ Water Cement ratio |
158/0.44 = 359 kg/m3 |
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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% |
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Final cementitious content |
359 X 1.10 = 395 kg |
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From Table 5 of IS 456, Minimum cement content for ‘Severe’ exposure conditions |
320 kg |
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395 kg/m3 > 320 kg/m3 hence ok. |
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Cementitious material content |
395 |
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New water cement ratio |
158/395 =0.4 |
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Fly ash content is taken as 30% of the total cementitious content |
395 X .3 = 118.5 kg/m3 |
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Cement required |
395 – 118 = 277 kg/m3 |
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Cement quantity saved due to fly ash addition |
350-277 = 73 kg/m3 |
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Cementitious material, cement and fly ash required is 395 kg/m3 , 277 kg/m3and 118 kg/m3 and the new water-cement ratio is 0.4 respectively |
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STEP 6: Volume of coarse aggregate & fine aggregate content |
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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. |
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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). |
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Therefore, corrected proportion of volume of coarse aggregate for the water-cement ratio of 0.44 |
0.632 |
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For pumpable concrete these values should be reduced up to 10%. Therefore, volume of coarse aggregate |
0.632 x 0.9 =0.568. |
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Volume of fine aggregate content |
1 – 0.568 =0.431 |
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Volume of fine aggregate and coarse aggregate is 0.431 and 0.568 |
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STEP 8: Mix calculation |
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The mix calculations as per unit volume of concrete shall be as follows: |
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a) Volume of concrete |
1 m3 |
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b) Volume of cement = [Mass of cement] / [Specific Gravity of Cement] x 1/1000 |
(277/3.15) X (1/1000) =0.087m3 |
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c) Volume of fly ash = [Mass of fly ash] / [Specific Gravity of fly ash] x 1/1000 |
(118/2.2) X (1/1000) =0.053m3 |
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d) Volume of water = [Mass of water] / [Specific Gravity of water] x 1/1000 |
(158/1) X (1/1000) = 0.158m3 |
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e) Volume of chemical admixture = [Mass of admixture] / [Specific Gravity of admixture] x 1/1000 |
(7.6/1.145) X (1/1000) =0.006 m3 |
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f) Volume of all in aggregate = [a-(b+c+d+e)] |
[1-(0.087+0.053+0.158+0.006)] = 0.696m3 |
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g) Mass of coarse aggregate= f x Volume of Coarse Aggregate x Specific Gravity of Fine Aggregate x 1000 |
0.696x 0.568 x 2.74 x 1000 = 1077 kg/m3 |
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h) Mass of fine aggregate= f x Volume of Fine Aggregate x Specific Gravity of Fine Aggregate x 1000 |
0.696x 0.431x 2.74 x 1000 = 822 kg/m |
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STEP 9: Mix proportion |
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Cement |
277 kg/m3 |
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Fly ash |
118 kg/m3 |
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Water |
158 l/m3 |
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Fine aggregate |
822 kg/m3 |
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Coarse aggregate 20mm |
1077 kg/m3 |
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Chemical admixture |
7.18 kg/m3 |
STEP 10:The slump should be checked and water content and admixture should be adjusted to achieve required slump on trail.
More than two trail should be done and water content should be adjusted.
AIM:To calculate the concrete mix design for M50 grade of concrete.
Objective: The objective of mix design to design high strength concrete
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STEP 1: Stipulations for Concrete design mix |
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Grade designation |
M50 |
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Type of cement |
OPC 53 Grade confirming to IS BIS 12269 - 1987 |
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Maximum nominal size of aggregate |
20 mm |
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Minimum cement content |
320 kg/m3 (Table 5 of IS 456:2000- Exposure condition) |
|
Maximum water-cement ratio |
0.45 (Table 5 of IS 456:2000 Exposure condition) |
|
Workability |
100 mm (slump value for pumpable concrete) |
|
Exposure condition |
Severe (For Reinforced Concrete) |
|
Method of concrete placing |
Pumping |
|
Degree of supervision |
Good |
|
Type of aggregate |
Crushed Angular Aggregates |
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Maximum cement content |
450 kg/m3 |
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Chemical admixture type |
Super Plasticizer |
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STEP 2: TEST DATA FOR MATERIALS |
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Cement used |
OPC 53 Grade conforming IS 12269-1987 |
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Specific gravity of cement |
3.15 |
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Chemical admixture |
Super Plasticizer conforming to IS 9103 |
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Specific gravity of coarse aggregate |
2.74 |
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Specific gravity of fine aggregate |
2.64 |
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Water absorption of coarse aggregate |
0.5% |
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Water absorption of fine aggregate |
1.0% |
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Free surface moisture of Coarse aggregate |
Nil |
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Free surface moisture of Coarse aggregate |
Nil |
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Sieve analysis: Coarse aggregate |
Conforming to Table 2 of IS 383 |
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Sieve analysis: Fine aggregate |
Conforming to Grading Zone II of Table 4 of IS 383 |
Step 3- Target strength for mix proportion
f'ck=fck+1.65s
where,
f'ck=target average compressive strength after 28days
fck=characteristic compressive strength after 28days
s=standard deviation
f'ck=50+1.65*5=58.25N/mm2
From Table I of IS 10262:2009, Standard Deviation, s = 5 N/mm2.
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STEP 4: Selection of water cement ratio |
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The maximum water-cement ratio to design M50 grade concrete can be found from Table 5 of IS 456-2000 for severe exposure. |
Maximum W/C ratio =0.45 |
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Based on experience adopted water cement ratio is 0.44 0.44<0.45, hence ok |
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Adopted W/C ratio=0.44 |
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STEP 5: SELECTION OF WATER CONTENT |
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From Table 2 of IS 10262:2009, maximum water content for 20 mm aggregate |
186 litre (for 25 to 50 mm slump range) |
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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. |
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(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 |
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Water required 158 litres |
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STEP 6: Calculation for cement required |
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Adopted w/c Ratio |
0.44 |
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Cement Content |
158/0.44 = 359 kg/m3 |
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From Table 5 of IS 456, Minimum cement content for ‘Severe’ exposure conditions |
320kg/m3 |
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359 kg/m3 > 320 kg/m3 hence ok. |
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Cement required is 359 kg/m3 |
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STEP 7: Volume of coarse and fone aggregate |
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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). |
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Therefore, corrected proportion of volume of coarse aggregate for the water-cement ratio of 0.44 |
0.632 |
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For pumpable concrete these values should be reduced up to 10%. Therefore, volume of coarse aggregate |
0.632 x 0.9 =0.568. |
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Volume of fine aggregate content |
1 – 0.576 =0.431 |
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Volume of fine aggregate and coarse aggregate is 0.431 and .568 respectively |
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STEP 8: Mix calculation |
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The mix calculations per unit volume of concrete shall be as follows: |
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a) Volume of concrete |
1 m3 |
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b) Volume of cement = [Mass of cement] / [Specific Gravity of Cement] x 1/1000 |
(359/3.15) X (1/1000) =0.114m3 |
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c) Volume of water = [Mass of water] / [Specific Gravity of water] x 1/1000 |
(158/1) X (1/1000) = 0.158m3 |
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d) Volume of chemical admixture = [Mass of admixture] / [Specific Gravity of admixture] x 1/1000 |
(7.6/1.145) X (1/1000) =0.006 m3 |
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e) Volume of all in aggregate = [a-(b+c+d)] |
[1-(0.114+0.158+0.006)] = 0.722m3 |
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f) Mass of coarse aggregate= e x Volume of Coarse Aggregate x Specific Gravity of Fine Aggregate x 1000 |
0.722x 0.568 x 2.74 x 1000 = 1123 kg/m3 |
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g) Mass of fine aggregate= e x Volume of Fine Aggregate x Specific Gravity of Fine Aggregate x 1000 |
0.722x 0.431x 2.64 x 1000 = 821 kg/m3 |
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STEP 9: Mix proportion |
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Cement |
359 kg/m3 |
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Water |
158 l/m3 |
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Fine aggregate |
821 kg/m3 |
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Coarse aggregate 20mm |
1123 kg/m3 |
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Chemical admixture |
7.18kg/m3 |
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Water-cement ratio |
0.44 |
Step 10: The slump shall be measured, the water content and dosage of admixture shall be adjusted for achieving the required slump on trial.
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.
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.