Project on Concrete Mix Design for various grades of Concrete
A. Grade Designation: M35
- Target mean strength of concrete f’ck=fck+1.65S
Where, fck = Characteristics compressive strength at 28 days
S= Standard Deviation (IS 10262:2009 , table 1)
= 35+ 1.65*5= 43.25 N/mm2.
From the below graph, w/c ratio = 0.33
2.Selection of water cement ratio (w/c ratio):
From Table 5 of IS 456:2000, depending upon the exposure condition.
M35 grade of concrete , RCC the condition is very severe and w/c ratio= 0.33
Assume water cement ratio as 0.45 , as it greater than 0.33 , adopted w/c ratio is 0.33
3.Selection of water content :
Consider aggregates under dry condition.
From table -2 of IS 10262:2009, the maximum water content for 25mm to 50mm slump=186 litre ( additional 3% slump may be added for every 25mm slump)
4.Selection of cement content:
It can be calculated from w/c ratio
Minimum cement content is taken from table-5 of IS 456:2000
Therefore C=W/w/c = 186/0.45=413.33 kg
5.Volume of Coarse aggregate and fine aggregate content:
The proportion of volume of coarse aggregate and fine aggregate can be determined from table 3of IS 10262 :2009 (selected depend upon the F.A zone)
Type of cement : OPC 33 grade confirming to IS 269
Maximum nominal size of aggregate :20mm
Minimum cement content : 340 kg /m3 ( from table -5 of IS 456 :2000-exposure condition)
Maximum water cement ratio : 0.45 (from table -5of IS 456:2000-exposure condition)
Workablity:100 mm (slump to pumpable value)
Exposure condition : Very severe( for rcc)
Method of concrete placing : pumping
Degree of supervision : good
Type of aggregate: crushed angular aggregate
Chemical admixture type: super plasticizers to IS 9103
Specific gravity of cement = 3.15
Fly ash : confirming to IS 3812
Specific gravity of fly ash=2.2
Estimated water content for 100 mm = 186+6/100*186=197 litre
( 6% of slump is added as increase of slump value)
As superplatizicers is used the water content content can be reduced upto 30%
Based on trails water content reduction of 29% , hence arrived water content =197 * (100-29%)0.71=140 lit.
Calculation of cement content:
w/c ratio=0.33
cementitious material(cement+fly ash)=140/0.33=424 kg/m3
From table -5 of IS 456 mimimum cement for very severe exposure condition =340 kg/m3 , 424kg/m3 > 340kg/m3 hence ok .
In proportion mix with fly ash following steps are considered
- The percentage of fly ash needed to be decided based on requirement and quality of materials
- In some cases increase in cementitious material can be warranted .Increase in cementitious material content and its percentage based on trial and experience ( consider 10% cementitious material content).
Cementitious material content=424*1.10=466kg/m3
Water content =140 kg/m3
W/c ratio=140/466=0.300
Fly ash @30% =466*30%=139kg/m3
Cement (OPC)=466-139=327kg/m3
Saving of cement using fly ash= 424-327=97
Fly ash utilizied=139 kg/m3
Proportion of volume of coarse aggregate and fine aggregate content :
From table 3 of IS 10262:2009 , volume of coarse aggregate =20mm , FA (zone 1) for w/c ratio of 0.5 =0.6
In present case w/c ratio is 0.45
Volume of coarse aggregate need to be increased to decrease FA content , as w/c ratio is lower by 0.10, the proportion of volume of CA is increased by 0.02 , corrected volume of CA for w/c ratio of 0.45=0.67( note: if coarse aggregate is not of angular type , then also volume of coarse aggregate may be required to be increased suited ) For pumpable concrete these values are reduced by 10%
Hence volume of CA =0.67*0.9=0.603
Volume of FA= 1-0.603=0.39
Mix calculation
The mix calculation per unit volume of concrete
a)Volume of concrete =1m3
b)Volume of cement = mass of cement/ specific gravity of cement *1/1000 =327/3.15*1/1000=0.103 m3
c)Volume of fly ash=mass of fly ash /specific gravity of fly ash *1/1000=139/2.2*1/1000=0.06m3.
d)Volume of water =mass of water /specific gravity of water*1/1000 =140/1*1/1000=0.140m3
e)Volume of chemical admixture= mass of chemical admixture/specific gravity of chemical admixture *1/1000=7.6/1.145*1/1000=0.006m3.
f)Volume of aggregate (FA&CA)= (a-(b+c+d+e))=0.691m3
g)Mass of coarse aggregate = f*volume of CA *specific gravity of CA *1000=0.691*0.603*2.74*1000=1141.6 Kg/m3
h)Mass of FA=f*volume of FA*specific gravity of FA *1000 =0.691*0.39*2.74*1000=738.4 kg/m3
Mix proportion for trial number 1:
Cement =327 kg/m3
Fly ash = 139 kg/m3
Water =140 kg /m3
Fine aggregate = 1141.6kg/m3
CA=738kg/m3
Chemical admixture=7 kg/m3
w/c ratio=0.33
trial mix ratio =
Note: the slump shall be measured and water content and dosage of admixture shall be adjusted. Two or more trials having variation of 10 % of w/c ratio is carried out .
B. Grade designation :M50
Target mean strength of concrete (f’ck):
f’ck= fck+1.65S= 50+1.65*5=58.25N/mm2
Where fck = characteristics compressive strength at 28 days
S= Standard deviation (IS 10262:2009, table 1)
From graph w/c ratio =0.35
2.Selection of water cement ratio (w/c):
From table -5 of IS 456:2000 , it can be taken depending upon exposure condition
3.Selection of water content :
From table -2 of IS 10262 :2009,
The maximum water content for 25mm to 50mm slump =186 lit
(additional slump 3% may be added for every 25 mm slump)
Note : Aggregate should be in dry condition
4.Selection of water cement ratio
Its calculated from w/c ratio
Minimum cement content is taken frm table -5 of IS 456:2000
C=W/w/c
5.Volume of CA&FA content:
The proportion of volume of CA and FA can be determined from table -3 of IS 10262:2009.
Type of cement :OPC 53 grade confirming to IS 12269
Maximum nominal size of aggregate :20mm
Minimum cement content : 360 kg/m3 ( from table -5 of IS 456:2000)
Maximum water content :0.4 ( from table -5 of IS 456:2000)
Workability : 100mm ( slump value for pumpable concrete)
Exposure condition: extreme (for rcc)
Method of concrete placing : pumping
Degree of supervision :good
Type of aggregate :crushed angular aggregate
Maximum cement content: 450 kg/m3
Chemical admixture: superplasticizer confirming to IS 9103
Specific gravity of cement: 3.15
Specific gravity of CA &FA : 2.74
Water absorption of CA:0.5%, FA : 1.0%.
Sieve analysis of CA : Conforming to IS 383 Table-2
Sieve analysis of FA : Conforming to IS 383 Table-4
Selection of w/c ratio : from table 5 of IS 456:2000 for extreme condition w/c ratio is 0.4 , assume w/c as 0.4
Selection of water content : from table 2 of IS 10262 :2009 , maximum water content for 20mm aggregate =186 lit (25mm to 50mm slump range)
C=W/w/c=186/0.4=465 lit
Estimated water content for 100 mm slump = 186 + 6/100*186=197lit
As super plasticizers is used , water content can be reduced up to 20% & above
Based on trials water content reduction of 29% is achieved , hence arrived water content =197*(100-29%)0.71=140lit
Calculation of cement content:
w/c ratio : 0.4
cement content =140/0.4=350 kg/m3
from table 5 of IS 456 :2000 minimum cement ratio for extreme condition= 360 kg/m3,
Proportion of volume of CA and FA content :
From table 3 of IS 10262: 2009 , volume of CA =20mm ,FA zone 1 for w/c ratio=0.6
In present w/c ratio is 0.4
Hence volume of CA needs to be increased to decrease FA content
Volume of coarse aggregate need to be increased to decrease FA content , as w/c ratio is lower by 0.10, the proportion of volume of CA is increased by 0.02 , corrected volume of CA for w/c ratio of 0.4=0.62( note: if coarse aggregate is not of angular type , then also volume of coarse aggregate may be required to be increased suited )
For pumpable concrete these values are reduced by 10%
Hence volume of CA =0.62*0.9=0.56
Volume of FA= 1-0.56=0.44
Mix calculation
The mix calculation per unit volume of concrete
a)Volume of concrete =1m3
b)Volume of cement = mass of cement/ specific gravity of cement *1/1000 =350/3.15*1/1000=0.111 m3.
c)Volume of water =mass of water /specific gravity of water*1/1000 =140/1*1/1000=0.140m3
d)Volume of chemical admixture= mass of chemical admixture/specific gravity of chemical admixture *1/1000= 7/1.145*1/1000=0.006m3.
e)Volume of aggregate (FA&CA)= (a-(b+c+d+e))=0.743m3
f)Mass of coarse aggregate = e*volume of CA *specific gravity of CA *1000
=0.743*0.56*2.74*1000=1140 Kg/m3
g)Mass of FA=e*volume of FA*specific gravity of FA *1000 =0.743*0.44*2.74*1000=896kg/m3
Mix proportion for trial number 1:
Cement =350 kg/m3
Water =140 kg /m3
Fine aggregate = 896kg/m3
CA= 1140 kg/m3
Chemical admixture=7 kg/m3
w/c ratio=0.4
trial mix ratio =1: 2.56: 3.26
Note: The slump shall be measured and water content and dosage of admixture shall be adjusted.
Two or more trials having variation of 10 % of w/c ratio is carried out and graph between 3 w/c ratios and corresponding strength are plotted to work out mix proportion for given target strength . However durability shall be met