Project on Concrete Mix Design for various grades of Concrete
Aim: Mix design for M35 grade of concrete with fly ash
Introduction: The mix is designed by the structural engineer and the mix proportions are determined by the concrete procedure.Maximum water cement ratio to attain adequate durability.Maximim cement content to avoid shrinkage.Minimum compressive strength required for structural considerations.
Procedure:
Step 1: Stipulations for proportioning
a] Grade designation: M35
b] Type of cement: OPC 43 grade conforming to IS 3812(Part 1)
c] Type of admixture: Fly ash confirming to IS 3812(Part 1)
d] Maximum nominal size of aggregate: 20mm
e] Maximum cement content: 320 kg/m^3(Table 5 IS 456-2000,based on exposure condition)
f] Maximum water cement ratio: 0.45(Table 5 IS 456-2000,based on exposure condition)
g] Workability: 100mm slump value of pumpable concrete
h] Exposure condition: Severe(For reinforced concrete)
i] Method of concrete placing: Pumping
j] Degree of supervision: Good
k] Type of aggregate: Crushed angular aggregate
l] Maximum cement content: 450kg/m^3
m]Chemical admixture type: Superplasticizer
Step 2: Test data for materials
a] Cement used: OPC 43 grade conforming to IS 8112
b] Specific gravity of cement: 3.15
c] Fly ash: Confirming to IS 3812 part 1
d] Specific gravity of fly ash: 2.2
e] Chemical admixture: Superplasticizer conforming to IS 9103
f] Specific gravity: 1] Coarse aggregate: 2.74 2] Fine aggregate: 2.74
g] Wate absorption: 1] coarse aggregate: 0.5% 2] Fine aggregate: 1%
h] Free surface moisture: 1] Coarse aggregate: Nil 2] Fine aggregate: Nil
Step 3: To find mean strength for mix proportioning
Target mean strength f'ck = fck+1.65 s
= 35+1.65*5
= 43.25 N/mm^2
fck= Characteristic compressive strength
s= Standard deviation
tep 4: Selection of water cement ratio
Maximum water cement ratio= 0.5(for severe condtion from table 5 of IS 456-2000)
On experience water cement ratio= 0.4
0.4<0.45, Hence O.K.
Step 5: Calculation of water content
Maximum water content for 20mm aggregate= 186 litres (Table 2 of IS 1026:2009) for 25mm to 50mm slump range.
For 100mm slump= 186+(6/100)*186= 197 litres
As superplasticizer is used,the water content is reduced upto 30%
Based on trails water content reduction of 29% is achieved with pasticizer.
Hence arrived water content= 197*0.71= 140 litres.
Step 6: Calculation of cement content
Water cement ratio= 0.4
Cementatious material(cement+fly ash)= 140/0.4 = 350 kg/m^3
In table 5 of IS 456-2000,the cement content for severe exposure = 320 kg/m^3
350 kg/m^3 > 320 kg/m^3
Hence O.K.
To proportion the mix containing flyash the following steps are suggested:
1] The percentage of flyash need to be decided based on project requirement and quality of materials.
2] In some cases increase in cementatious materials can be warned.Increase in cementatious material content and its percentage may be based on experience and trail.
In this 10% increase of cementatious material content is considered.
Cementatious material content = 350*1.1= 385 kg/m^3
Water content= 140 kg/m^3
So,water cement ratio=140/385 = 0.364
Flyash at 30% total cementatious material content = 385*30% = 115 kg/m^3
Cement(OPC) = 385-115=270
Saving of cement while using fly ash= 350-270=80 kg/m^3
Fly ash being utilized = 115 kg/m^3
Step 7: Proportioning of volume of coarse aggregate and fine aggregate content
From table 3 of IS 1026:2009,Volume of coarse aggregate corresponding to 20mm size aggregate and fine aggregate(Zone 1) for water cement ratio = 0.6
In present case the water cement ratio is 0.4
Therefore,The volume of coarse aggregate needs to be increased to decrease the fine aggregate content.
As the W/C ratio is lowered by 0.1,the proportion of volume of coarse aggregate is increased by 0.02.
Hence corrected value of coarse aggregate for the w/c ratio of 0.4 = 0.62
For pumpable concrete,these are reduced by 10%
Volume of coarse aggregate = 0.64*0.9 = 0.576
Volume of fine aggregate = 1-0.576 = 0.424
Step 8: Mix calculations
Mix calculation per unit volume of concrete:
a] Volume of concrete = 1 m^3
b] Volume of cement = (Mass of cement/specific gravity of flyash)*1/1000= (270/3.15)*1/1000 = 0.086 m^3
c] Volume of flyash= (Mass of flyash/specific gravity of water)*1/1000 = (115/2.2)*1/1000= 0.052 m^3
d] Volume of water= (Mass of water/specific gravity of water)*1/1000 = (140/1)*1/1000 = 0.140 m^3
e]Volume of chemical admixture= (Mass of admixture/speific gravity admixture)*1/1000=(7.6/1.14)*1/1000= 0.006 m^3
f] Volume of aggregate(fine and coarse)= a-(b+c+d+e) = 1-(0.086+0.052+0.140+0.006)= 0.716 m^3
g] Mass of coarse aggregate = f*volume of coarse aggregate*specific gravity of coarse aggregate*1000 = 0.716*0.576*2.74*1000 = 1130 kg/m^3
h] Mass of fine aggregate= f* volume of fine aggregate*specific gravity of fine aggregate*1000 = 0.716*0.424*2.74*1000= 831 kg/m^3
Step 9: Mix proportion
Cement = 270 kg/m^3
Fly ash = 115 kg/m^3
Water = 140 kg/m^3
Fine aggregate = 831 kg/m^3
Coarse aggregate = 1130 kg/m^3
Chemical admixture = 7 kg/m^3
Water cement ratio = 0.364
MIX RATIO 1:2.15:2.94
Step 10:
The slump shall be measured and the water content and dosage of admixture shall be adjusted for achieving the required slump on trial.The mix prooportion shall be reworked for the actual water content and checked for durability requirements.
Step 11:
Two or more trials having variation of 10% of w/c ratio in step 10 shall be carried out and a graph between 3 w/c ratio and corresponding strength shall be plotted to work out the mix proportion for the given target strength for field trials.
Result:
The design mix for M35 grade of concrete with fly ash is 1:2.15:2.94
Aim: Mix design for M50 grade of concrete
Procedure:
Step 1: Stipulations for proportioning
a] Grade designation: M50
b] Type of cement: OPC 43 grade conforming to IS 8812
c] Maximum nominal size of aggregate: 20mm
d] Maximum cement content: 320 kg/m^3(Table 5 IS 456-2000,based on exposure condition)
e] Maximum water cement ratio: 0.45(Table 5 IS 456-2000,based on exposure condition)
f] Workability: 100mm slump value of pumpable concrete
g] Exposure condition: Severe(For reinforced concrete)
h] Method of concrete placing: Pumping
i] Degree of supervision: Good
j] Type of aggregate: Crushed angular aggregate
k] Maximum cement content: 450kg/m^3
l]Chemical admixture type: Superplasticizer
Step 2: Test data for materials
a] Cement used: OPC 43 grade conforming to IS 8112
b] Specific gravity of cement: 3.15
c] Chemical admixture: Superplasticizer conforming to IS 9103
d] Specific gravity: 1] Coarse aggregate: 2.74 2] Fine aggregate: 2.74
e] Wate absorption: 1] coarse aggregate: 0.5% 2] Fine aggregate: 1%
f] Free surface moisture: 1] Coarse aggregate: Nil 2] Fine aggregate: Nil
Step 3: To find mean strength for mix proportioning
Target mean strength f'ck = fck+1.65 s
= 50+1.65*5
= 58.25 N/mm^2
fck= Characteristic compressive strength
s= Standard deviation
tep 4: Selection of water cement ratio
Maximum water cement ratio= 0.5(for severe condtion from table 5 of IS 456-2000)
On experience water cement ratio= 0.4
0.4<0.45, Hence O.K.
Step 5: Calculation of water content
Maximum water content for 20mm aggregate= 186 litres (Table 2 of IS 1026:2009) for 25mm to 50mm slump range.
For 100mm slump= 186+(6/100)*186= 197 litres
As superplasticizer is used,the water content is reduced upto 30%
Based on trails water content reduction of 29% is achieved with pasticizer.
Hence arrived water content= 197*0.71= 140 litres.
Step 6: Calculation of cement content
Water cement ratio= 0.4
Cementatious material(cement+fly ash)= 140/0.4 = 350 kg/m^3
In table 5 of IS 456-2000,the cement content for severe exposure = 320 kg/m^3
350 kg/m^3 > 320 kg/m^3
Hence O.K.
Step 7: Proportioning of volume of coarse aggregate and fine aggregate content
From table 3 of IS 1026:2009,Volume of coarse aggregate corresponding to 20mm size aggregate and fine aggregate(Zone 1) for water cement ratio = 0.6
In present case the water cement ratio is 0.4
Therefore,The volume of coarse aggregate needs to be increased to decrease the fine aggregate content.
As the W/C ratio is lowered by 0.1,the proportion of volume of coarse aggregate is increased by 0.02.
Hence corrected value of coarse aggregate for the w/c ratio of 0.4 = 0.62
For pumpable concrete,these are reduced by 10%
Volume of coarse aggregate = 0.64*0.9 = 0.576
Volume of fine aggregate = 1-0.576 = 0.424
Step 8: Mix calculations
Mix calculation per unit volume of concrete:
a] Volume of concrete = 1 m^3
b] Volume of cement = (Mass of cement/specific gravity of flyash)*1/1000= (350/3.15)*1/1000 = 0.111 m^3
c] Volume of water= (Mass of water/specific gravity of water)*1/1000 = (140/1)*1/1000 = 0.140 m^3
d]Volume of chemical admixture= (Mass of admixture/speific gravity admixture)*1/1000=(7.6/1.14)*1/1000= 0.006 m^3
e] Volume of aggregate(fine and coarse)= a-(b+c+d+e) = 1-(0.111+0.052+0.140+0.006)= 0.743 m^3
f] Mass of coarse aggregate = f*volume of coarse aggregate*specific gravity of coarse aggregate*1000 = 0.743*0.576*2.74*1000 = 1173 kg/m^3
g] Mass of fine aggregate= f* volume of fine aggregate*specific gravity of fine aggregate*1000 = 0.743*0.424*2.74*1000= 863 kg/m^3
Step 9: Mix proportion
Cement = 350 kg/m^3
Water = 140 kg/m^3
Fine aggregate = 863 kg/m^3
Coarse aggregate = 1173 kg/m^3
Chemical admixture = 7 kg/m^3
Water cement ratio = 0.4
MIX RATIO 1:2.46:3.35
Step 10:
The slump shall be measured and the water content and dosage of admixture shall be adjusted for achieving the required slump on trial.The mix prooportion shall be reworked for the actual water content and checked for durability requirements.
Step 11:
Two or more trials having variation of 10% of w/c ratio in step 10 shall be carried out and a graph between 3 w/c ratio and corresponding strength shall be plotted to work out the mix proportion for the given target strength for field trials.
Result:
The design mix for M35 grade of concrete with fly ash is 1:2.46:3.35