Project on Concrete Mix Design for various grades of Concrete
PROJECT ON CONCRETE MIX DESIGN FOR VARIOUS GRADES OF CONCRETE
AIM
To calculate concrete mix design for M35 grade concrete with fly ash and M50 grade concrete without fly ash.
INTRODUCTION
Concrete is a very complex material and has the right mix of constituents of concrete, which if not done properly and will have an adverse effect on the properties of concrete. Concrete mix design is a systematic process of choosing an economical relative proportion of various ingredients from available material that gives concrete the desired workability in the fresh state and desired strength and durability in the hardened stage. The objective of concrete mix design is to achieve the predetermined minimum strength and durability in the most economical manner. It also depends on mixing, batching, placing, compaction and curing.
MATERIALS REQUIRED
- Cement
- Fine aggregate
- Coarse aggregate
- Admixture
- Fly ash
- Water
DATA PROVIDED FOR M50 GRADE CONCRETE
Grade of concrete M50
Type of cement 43
Maximum nominal size of aggregate 20 mm
Minimum cement content 320 Kg/m^3
Maximum water-cement ratio 0.45
Workability True slump at 100mm
Environmental exposure Severe
Method of concrete placing Pumping
Degree of supervision Good
Type of aggregate Crushed and angular
Maximum cement content 450 kg/m^3
Chemical admixtures Superplasticizers
The specific gravity of cement 3.15
The specific gravity of coarse aggregate 2.74
The specific gravity of fine aggregate 2.74
Sieve analysis of fine aggregate Zone 1 (table 4, IS 383)
Sieve analysis of coarse aggregate Table 2, IS 383
PROCEDURE AND CALCULATIONS FOR M50 GRADE DESIGN MIX WITHOUT USING FLY ASH
Step 1 - Determination of Target strength
The first step in our design mix is to find the target mean strength as target mean strength to act as a benchmark to our design mix. The target mean strength can be calculated as per IS 10262-2009,
f'ck=fck+1.65*S
Where fck= characteristic compressive strength of concrete in 28 days
S= standard deviation (taken from table 1)
From table 1, take S=5,
Therefore, f'ck= 50+1.65*5= 58.25 N/mm^2
Step 2 - Selection of water-cement ratio
From table 5 of IS 456:2000, the water-cement ratio is taken as per the exposure condition.
For severe condition w/c ratio= 0.45 ~ 0.4
Minimum cement content= 320 Kg/mm^3
Step 3 - Selection of water content
From table 2 of IS 10262:2009, maximum water content for 20mm dry aggregate = 186 L
( For 25 mm to 50 mm slump range)
Estimated w/c for 100mm slump= 186+6%*186= 197 litre
As superplasticizer is used, the w/c can be reduced up to 30%
Based on trials w/c reduction of 29% is achieved with plasticizer
Hence the arrived w/c = 197* (100-29)%= 140 litre
Step 4 - Calculation of cement content
Water-cement ratio=0.4
Cementitious material (cement+fly ash) content = 140/0.4 =350Kg/m^3
From table 5 of IS 456, minimum cement content for severe exposure condition = 320 Kg/m^3
320 Kg/m^3 < 350 Kg/m^3, Hence ok
Step 5 - Proportion of volume of coarse aggregate and fine aggregate content
From table 3, of IS 10262-2009, the volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (zone 1) of water-cement ratio=0.6
In the present case, the water cement ratio is 0.40
Therefore, the volume of coarse aggregate needs to be increased to decrease the fine aggregate content.
As the water-cement ratio is lowered 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 water-cement ratio)
Therefore, the corrected volume of coarse aggregate for the water-cement ratio of 0.40=0.62
(Note: if the coarse aggregate is not of angular type, then also the volume of coarse aggregate may be required to be increased suitably based on experience)
For pumpable concrete these values are reduced by 10%
Therefore, volume of coarse aggregate = 0.62*0.9 = 0.56
Volume of fine aggregate content= 1- 0.56= 0.44
Step 6 - Mix calculations
The mix calculation per unit volume of concrete shall be as follows:
- Volume of concrete= 1m^3
- volume of cement = (mass of cement/specific gravity of cement) * 1/1000
= (350/3.15) * 1/1000 = 0.111m^3 - Volume of water= (mass of water/ specific gravity of water) * 1/1000
= (140/1)* 1/1000= 0.140m^3 - Volume of chemical admixture= (mass of chemical admixture/ specific gravity of admixture) *1/1000
= (7.6/1.145) * 1/1000 = 0.006 m^3 - Volume of aggregate (FA &CA) = (a-(b+c+d+e)) = (1-(0.111+0.052+0.140+0.006) = 0.743 m^3
- Mass of CA = e * volume of CA * Sp. gravity of CA *1000
= 0.743 * 0.56 * 2.74 * 1000 = 1140 Kg/m^3 - Mass of FA = e * volume of FA * Sp. gravity of FA *1000
= 0.743*0.44*2.74*1000= 896 Kg/m^3
Step 7 - State all the proportions calculated
- Cement - 350 Kg/m^3
- Water - 140 Kg/m^3
- Fine aggregate - 896 Kg/m^3
- Coarse aggregate- 1140 Kg/m^3
- Chemical admixtures- 7 Kg/m^3
- Water-cement ratio-0.4
Therefore, trial mix ratio = 1:2.56:3.26
Two more trials having variation of 10% of water-cement ratio in clause 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 strength for field trials. However, durability shall be met.
DATA PROVIDED FOR M35 GRADE CONCRETE
Grade of concrete M35
Type of cement 43
Maximum nominal size of aggregate 20 mm
Minimum cement content 320 Kg/m^3
Maximum water-cement ratio 0.45
Workability True slump at 100mm
Environmental exposure Severe
Method of concrete placing Pumping
Degree of supervision Good
Type of aggregate Crushed and angular
Maximum cement content 450 kg/m^3
Chemical admixtures Superplasticizers, Fly ash
The specific gravity of cement 3.15
The specific gravity of fly ash 2.2
The specific gravity of coarse aggregate 2.74
The specific gravity of fine aggregate 2.74
Sieve analysis of fine aggregate Zone 1 (table 4, IS 383)
Sieve analysis of coarse aggregate Table 2, IS 383
PROCEDURE AND CALCULATIONS FOR M35 GRADE DESIGN MIX USING FLY ASH
Step 1 - Determination of Target strength
The first step in our design mix is to find the target mean strength as target mean strength to act as a benchmark to our design mix. The target mean strength can be calculated as per IS 10262-2009,
f'ck=fck+1.65*S
Where fck= characteristic compressive strength of concrete in 28 days
S= standard deviation (taken from table 1)
From table 1, take S=5,
Therefore, f'ck= 35+1.65*5= 43.25 N/mm^2
Step 2 - Selection of water-cement ratio
From table 5 of IS 456:2000, the water-cement ratio is taken as per the exposure condition.
For severe condition w/c ratio= 0.45 ~ 0.4
Minimum cement content= 320 Kg/mm^3
Step 3 - Selection of water content
From table 2 of IS 10262:2009, maximum water content for 20mm dry aggregate = 186 L
( For 25 mm to 50 mm slump range)
Estimated w/c for 100mm slump= 186+6%*186= 197 litre
As superplasticizer is used, the w/c can be reduced up to 30%
Based on trials w/c reduction of 29% is achieved with plasticizer
Hence the arrived w/c = 197* (100-29)%= 140 litre
Step 4 - Calculation of cement content
Water-cement ratio=0.4
Cementitious material content = 140/0.4 =350Kg/m^3
From table 5 of IS 456, minimum cement content for severe exposure condition = 320 Kg/m^3
320 Kg/m^3 < 350 Kg/m^3, Hence ok
Now total cementitious material (cement+fly ash)=350
There's an increase of 10% of cementitious material due to the addition of fly ash= 350*1.1= 385 Kg/m^3
Water content= 140 Kg/m^3
so, water-cement ratio= 140/385 =0.364
Fly ash at 30% cementitious materials,
fly ash=385*0.3= 115Kg/m^3
Hence, cement= 385-115= 270 Kg/m^3
`implies` cement saved= 80 Kg/m^3
Step 5 - Proportion of volume of coarse aggregate and fine aggregate content
From table 3, of IS 10262-2009, the volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (zone 1) of water-cement ratio=0.6
In the present case, the water-cement ratio is 0.40
Therefore, the volume of coarse aggregate needs to be increased to decrease the fine aggregate content.
As the water-cement ratio is lowered 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 water-cement ratio)
Therefore, the corrected volume of coarse aggregate for the water-cement ratio of 0.40=0.62
(Note: if the coarse aggregate is not of angular type, then also the volume of coarse aggregate may be required to be increased suitably based on experience)
For pumpable concrete these values are reduced by 10%
Therefore, volume of coarse aggregate = 0.62*0.9 = 0.56
Volume of fine aggregate content= 1- 0.56= 0.44
Step 6 - Mix calculations
The mix calculation per unit volume of concrete shall be as follows:
- Volume of concrete= 1m^3
- volume of cement = (mass of cement/specific gravity of cement) * 1/1000
= (350/3.15) * 1/1000 = 0.086 m^3 - Volume of fly ash = (mass of fly ash/sp gravity of fly ash) * 1/1000
=(155/2.2) * 1/1000 = 0.052 m^3 - Volume of water= (mass of water/ specific gravity of water) * 1/1000
= (140/1)* 1/1000= 0.140m^3 - Volume of chemical admixture= (mass of chemical admixture/ specific gravity of admixture) *1/1000
= (7.6/1.145) * 1/1000 = 0.006 m^3 - Volume of aggregate (FA &CA) = (a-(b+c+d+e)) = (1-(0.086+0.052+0.140+0.006) = 0.716 m^3
- Mass of CA = f * volume of CA * Sp. gravity of CA *1000
= 0.716 * 0.56 * 2.74 * 1000 = 1098 Kg/m^3 - Mass of FA = f * volume of FA * Sp. gravity of FA *1000
= 0.716 *0.44*2.74*1000= 863 Kg/m^3
Step 7 - State all the proportions calculated
- Cement - 270 Kg/m^3
- Fly ash- 115 Kg/m^3
- Water - 140 Kg/m^3
- Fine aggregate - 863 Kg/m^3
- Coarse aggregate- 1098 Kg/m^3
- Chemical admixtures- 7 Kg/m^3
- Water-cement ratio-0.364
Therefore, trial mix ratio = 1:2.24:2.85
Two more trials having variation of 10% of water-cement ratio in clause 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 strength for field trials. However, durability shall be met.
RESULT
Calculated concrete mix design for M35 grade concrete with fly ash and M50 grade concrete without fly ash is as follows:
Trial mix ratio for M50 grade concrete without fly ash = 1:2.56:3.26
Trial mix ratio for M35 grade concrete with fly ash = 1:2.24:2.85
CONCLUSION
To wrap off my project, I'd want to point out that each design mix is unique, based on the state of the aggregates utilised and a variety of other aspects. Experiment with this mix ratio to see if the concrete reaches the target mean strength; if it does, go ahead and use this design mix. If not, change a few values and calculate a fresh design mix until you reach the intended mean strength.
REFERENCES
- IS 383
- IS 10262-2009
- IS 456:2000