Challenge

Project on Concrete Mix Design for various grades of Concrete

BBhavana K Y15 Aug 2022

Concrete mix proportion

Stipulation for proportioning

Grade designation :35
Type of cement : OPC 43 grade confirming to IS8112
Type of mineral admixture : fly ash confirming to
Maximum nominal size of aggregate :20mm
Minimum cement content :320 kg/m³(from table 5 of IS456:2000 –depending upon exposure condition )
Maximum water cement ratio : 0.45(from table 5 of IS456:2000 – depending upon exposure condition )
Workability :100mm (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 aggregate
Maximum cement content :450kg/m³
Chemical admixture : super plasticizers

II.Test data for materials

a)Cement used :OPC 43grade confirming to IS 8112

b)Specific gravity of cement :3.15

c)Chemical admixture : Super plasticizers confirming to IS 9103

d)Fly ash confirming to IS 3812 (part – 1)

e)Specific gravity of fly ash : 2.2

f)Specific gravity of

*Coarse aggregate : 2.74

*Fine aggregate : 2.74

g)Water absorption

*Coarse aggregate : 0.5%

*Fine aggregate : 1%

h)Free surface moisture

*Coarse aggregate : Nil

*Fine aggregate : Nil

I)Sieve analysis

Coarse aggregate : confirming to grading zone 1 table 2 of IS 383

Fine aggregate : confirming to grading zone 1 table 4 of IS 383

3.Target strength of mix proportioning

f’_{ck =}f_{ck +}1.65S

where f’_{ck –}Target average compressive strength at 28days

f_ck – characteristic compressive strength at 28days

S – standard deviation

From table 1 of IS10262 : 2009 ,standard deviation , S = 5 N/mm²

Therefore target strength =35 + 1.65*5 = 43.25 N/mm²

Selection of water cement ratio

From table 5 of IS456:2000 for severe exposure , maximum water cement ratio = 0.45

Based on experience , adopted water – cement ratio is 0.40

0.40 < 0.45 hence OK

Selection of water content

From table 2 of IS10262 : 2009 ,maximum water content for 20mm aggregate = 186 liter (for 25mm to 50mm slump range )

Estimated water content for 100mm slump = 186 +6/100 *186 = 197 liter

As superplasticizers is used , the water content can be reduced up to 30% above

Based on the trail water , content reduction of 29% is achieved with plasticizers

Hence the arrived water content = 197*0.71 = 140liter

Calculation of cement content

Water – cement ratio = 0.40

Cementitious material (cement + fly ash) content = 140/0.4 = 350kg/m³

From table 5 of IS456 minimum cement content for severe exposure condition = 320 kg/m³

350kg/m³> 320kg/m³, hence ok

Now , to proportion a mix containing fly ash the following steps are suggested :

a)the percentage of fly ash needs to be decided based on project requirement and quality of materials

b)in some extent increases in cementitious material can be warranted increases in cementitious material content and its percentage may be based on experience and trail ( this example is with increases of 10% cementitious material content)

cementitious material content = 350*1.10 = 385kg/m³

water content = 140 kg/m³

so, water cement ratio = 140/385 = 0.364

fly ash at 30% total cementitious material content 385*30% = 115 kg/m³

cement (OPC) = 385 – 115 = 270 kg/m³

saving of cement using fly ash = 350-270 = 80 kg/m³

fly ash being utilized = 115 kg/m³

proportion of volume of coarse aggregate and fine aggregate content

from table 3 of IS 10262 : 2009 , volume of coarse aggregate corresponding to 20mm size aggregate and fine aggregate (Zone 1) for water cement ratio of 0.5 = 0.6

in the present case water cement ratio is 0.40

therefore , the volume of coarse aggregate needs to be increased to decrease the fine aggregate content

as water cement ratio is lower by 0.10 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 volume of coarse aggregate for the water cement ratio of 0.40 = 0.62

note : if 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

Mix calculation

Volume of concrete = 1 m³
Volume of cement = mass of cement/specific gravity of cement * 1/1000

= 270/3.15 *1/1000

= 0.086 kg /m³

c)volume of fly ash = mass of fly ash / specific gravity of fly ash * 1/1000

115/2.2* 1/1000

= 0.052m³

d)Volume of water = mass of water / specific gravity of water * 1/1000

= 140/1 * 1/1000

=0.140 kg/m³

e)volume of chemical admixture = mass of chemical admixture/specific gravity of admixture *1/1000

= 7.6/1.145 * 1/1000

= 0.006 m³

f) volume of aggregate ( FA and CA ) = ( a – (b+c+d+e))

= (1-(0.086+0.052+0.140+0.006)

= 0.716 m³

g) mass of coarse aggregate = f*volume of coarse aggregate*specific gravity of coarse aggregate*1000

= 0.716 * 0.56 *2.74 *1000 = 1098 kg/m³

h)mass of fine aggregate = f * volume of fine aggregate *specific gravity of fine aggregate *1000

= 0.716 * 0.44 *2.74 *1000 = 863 kg/m³

Cement = 270kg/m³

Fly ash = 115 kg/m³

Water = 140 kg/m³

Fine aggregate = 863 kg/m³

Coarse aggregate = 1098 kg/m³

Chemical admixture = 7 kg/m³

Water – cement ratio = 0.364

Trial mix ratio = 1:2.24:2.85

Concrete mix proportion

Stipulation for proportioning

a)Grade designation :50

b)Type of cement : OPC 43 grade confirming to IS8112

c)Type of mineral admixture : fly ash confirming to

d)Maximum nominal size of aggregate :20mm-

e)Minimum cement content :320 kg/m³(from table 5 of IS456:2000 –depending upon exposure condition )

f)Maximum water cement ratio : 0.45 (from table 5 of IS456:2000 – depending upon exposure condition )

g)Workability :100mm (slump value for 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/m³

m)qChemical admixture : super plasticizers