Project on Concrete Mix Design for various grades of Concrete
calculate the concrete mix design for M35 grade concrete with fly ash and M50 grade concrete without fly ash'
INTRODUCTION : concrete mix design is the process of selecting suitable ingredients for producing concrete of required strength, durability and workability as economcal as possible. this process is usually adopted for structure which requires higher grade of concrete and large construction projects.
AIM : calculate the concrete mix design for M35 grade concrete with fly ash and M50 grade concrete without fly ash
PROCEDURE :
PART-1 : to calculate concrete mix design for M35 grade concrete with fly ash.
step-1 : stipulation for proportioning -
a) grade designation- M35
b) type of cement- OPC 43 grade conforming to IS 8112
c) type of mineral admixture- fly ash conforming to IS 3812 ( part-1)
d) maximum nominal size aggregate- 20mm
e) minimum cement content- 320kg/m^3 ( from table 5 of IS 456:2000- Exposure condition)
f) workability- 100mm (slump value for pumpable concrete)
g) exposure condition- Severe condition( for reinforced concrete)
h) method of concrete placing - Pumping
i) max w/c ratio- 0.45 ( from table 5 of IS 456:2000- exposure condition)
j) type of aggregate0- crushed angular aggregate
k) max cement content-kg/m^3
l) chemical admixture type- superplasticizer
step-2 : test data for materials -
a) chemical used- OPC 43 grade conforming to IS 8112
b) specific gravity of cement- 3.15
c) fly ash- conforming to IS 3812 ( part-1)
d) specific gravity of fly ash- 2.2
e) chemical admixture- superplasticizer conforming to IS 9103
f) specific gravity of- coarse aggregate: 2.74
- fine aggregate: 2.74
g) water absorption - coarse aggregate: 0.5%
- fine aggregate : 1.0%
h) free surface moisture- coarse aggregate : nil
- fine aggregate : nil
i) sieve analysis- coarse aggregate: table 2 of IS 383
- fine aggregate : conforming to grading zone-1 of table of IS 383
step-3 : target strength for mix proportioning -
target mean strength of concrete (f'ck)= fck + 1.65 S
fck= charecteristics compressive strength of concretein 28 days.
S = standard deviation obtained from table 1 of IS 10262:2009
standard deviation (S) for M35 grade of concrete from above table is 5.0 n/mm^2
hence, f'ck= fck + 1.65 S
=35 + 1.65 x 5.0
= 43.25 n/mm^2
so the target mean strength for M35 grade of concrete is 43.25 n/mm^2.
step-4 : selection of water cement ratio -
from table 5 of IS 456:2000 for severe exposure water cement ratio = 0.45
based on experiene adopt water cement ratio as 0.40
0.40 < 0.45, hence ok.
adopted w/c ratio is 0.40.
step-5 : selection of water content -
- the maximum water content for 20mm aggregate( for 25mm to 50mm slump) is 186kg or 186 litre
-clause 4.2 of IS 10262:2009 suggest that for additional slump 3% may be added for every 25mm slump
estimated water content for 100 mm slump = 186 + 6/100
= 197litre
- if superplasticizer is used the water content can be reduced upto 20%
based on trial water content reduction of 29% is achieved with plasticizer,
hence, arrived water content= 197 x 0.71
= 140 litre
step-6: calculation of cement content and fly ash -
adopted w/c ratio= 0.40
water content= 140
cementitious material (cement + flyash) content = 140/0.40
= 350 kg/m^3
from table 5 of IS 456-2000 minimum cement content for severe exposure condition = 320 kg/m^3
350 kg/m^3 > 320kg/m^3, hence ok.
- 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 cases increase in cementitious material can be warranted. increased in cemetitious material content and its percnetage may be based on experience and trial.
-here we have to increased the cementitious material by 10%
cementitious material content = 350 x 1.10
= 385 kg/m^3
minimum cement content required for severe exposure condition as per IS 456-2000 = 340 kg/m^3
therefore, 385 kg/m^3 >340 kg/m^3, hence ok.
water content = 140 kg/m^3
water cement ratio= 140/385
= 0.364
total cementious material content fly ash 30% = 385 x 30%
= 115kg/m^3
cement content opc= 385 - 115
= 270 kg/m^3
cement required = 270 kg/m^3
fly ash required = 115 kg/m^3
step-7 : proportion volume of coarse aggregate and fine aggregate content
from table 3 of IS 10262-2009, volume of coarse aggregate correponding to 20mm size aggregate and fine aggregate (zone-1) for w/c ratio of 0.5 is 0.6.
in the present case the w/c ratio = 0.4
therfore, the volume of coarse aggregate needs to be increased to decrease the fine aggregate content.
as w/c ratio is lower by 0.10, the proportion of volume of coarse aggregate is increased by 0.02
( at rate of +/- 0.01 for every +/- 0.05 change in w/c ratio )
therefore, corrected volume of coarse aggregate fo w/c ratio of 0.40 = 0.6 + 0.02
= 0.62
for pumpable concrete the values are reduced by 10%
volume of coarse aggregate= 0.62 x 0.9= 0.56
volume of fine aggregate = 1 - 0.56 = 0.44
step-8 : mix calculations
a) volume of concrete = 1m^3
b) volume of cement = mass of cement / specific gravity of cement X 1/1000
= 270/3.15 X 1/1000
= 0.086 M^3
c) vol.of fly ash = mass of fly ash/specific gravity of fly ash X 1/1000
= 115/2.2 X 1/1000
= 0.052 m^3
d)volume of water = mass of water/specific gravity of water x 1/1000
= 140/1 x 1/1000
= 0.140 m^3
e) volume of chemical admixture = mass of admixture/ specific gravity of admixture x 1/1000
= 7.6/1.145 x 1/1000
= 0.006 m^3
f) volume of aggregate(FA AND CA)= (a-(b+c+d+e))
= (1-(0.086+0.052+0.140+0.006))
= 0.716M^3
g) mass of coarse aggregate = f X volume of coarse aggregate X specific gravity of coarse aggregate X 1000
= 0.716 X 0.56 X 2.74 X 1000
= 1098 kg/m^3
h) mass of fine aggregate = f X volume of fine aggregate X sp. gravity of fine aggregate X 1000
= 0.716 X 0.44 X 2.74 X 1000
= 863 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 = 863 kg/m^3
coarse aggregate = 1098 kg/m^3
water cement ratio = 0.364
chemical admixture = 7 kg/m^3
therefore, the mix ratio for M35 grade of concrete= cement ( cement +flyash) : FA : CA : water
= 1: 2.24 : 2.85 : 0.42
NOTE :
1. 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 proportion shall be rewarded for the actual water content and checked for durability requirement.
2. two more trial having variation of 10% of w/c ratio in clause 10 shall be carried out and graph between three w/c ratio and correspondong strength shall be plotted to workout the mix proportion for the given target strength for field trials. however durability shall be met.
PART-2 : to calculate concrete mix design for M50 grade concrete without fly ash.
Step-1 : stipulation of proportioning -
a) grade designation = M50
b) type of cement = OPC 43 grade conforming IS 8112
c) max nominal size of aggregate = 20mm
d) minimum cement content = 320 kg/m^3 ( from table 5 of IS 456:2000- exposure condition)
e) max w/c ratio = 0.45 ( from table 5 of IS 456:2000- exposure condition)
f) workability = 100mm ( slump value for 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 = 450 kg/m^3
l) chemical admixture type = super plasticizer
Step-2 : test data for materials -
a) cement used = opc 43 grade conforming to IS 9103
b) chemical admixture =superplasticizer conforming to IS 8112
c) specific gravity of cement = 3.15
d) sp. gravity - coarse aggregate = 2.74
- fine aggregate = 2.74
e) water absorption - coarse aggregate= 0.5%
- fine aggregate = 1.0%
f) free surface moisture - coarse aggregate= nil
- fine aggregate = nil
g) sieve analysis - coarse aggregate conforming to table 2 of IS 383 and fine aggregate conforming to grading zone-1 oftable 4 of is383.
Step-3 : target mean strength for mix proportioning.
f'ck = fck + 1.65 S
f'ck= target mean strength of 28 days
fck= charecteristics compressive strength of 28 days
S = standard deviation
from table 1 of IS 10262:2009 std deviation S= 5.0 N/mm^2
f'ck= 50 + 1.65 X 5.0
= 58.25 N/mm^2
target mean strength(f'ck) = 58.25 N/mm2
Step-4 : selection of water cement ratio -
from table 5 of IS 456:2000 for severe exposure
maximum w/c ratio = 0.45
based on experience, adopted w/c ratio 0.40.
Step-5 : selection of water content -
from table-2 IS 10262-2009,
maximum water content for 20mm aggregate= 186 litre ( for 25mm to 50mm slump)
estimated water content for 100mm slump = 186 +( 6/100 x 186)
= 197.16= 196 litre
-as superplasticizer is used the water content can be reduced upto 20% and above
-based on trial water content reduction of 29% is achieved with plasticizer
hence the arrived water content = 197 x 0.71
= 140 litre.
water content= 140 litre.
Step-6: calculation of cement content -
w/c ratio = 0.4
cement content = 140/0.4
= 350kg/m^3
from table 5 of IS 456-2000 minimum cement content for severe exposure condition = 320 kg/m^3
so, 350kg/m^3 > 320 kg/m^3, hence ok
Step-7 : proportion of volume of coarse aggregate and fine aggregate content -
from table 3 of IS 10262-2009, volume of coarse aggregate correponding to 20mm size aggregate and fine aggregate (zone-1) for w/c ratio of 0.5 is 0.6.
in the present case the w/c ratio = 0.4
therfore, the volume of coarse aggregate needs to be increased to decrease the fine aggregate content.
as w/c ratio is lower by 0.10, the proportion of volume of coarse aggregate is increased by 0.02
( at rate of +/- 0.01 for every +/- 0.05 change in w/c ratio )
therefore, corrected volume of coarse aggregate fo w/c ratio of 0.40 = 0.6 + 0.02
= 0.62
for pumpable concrete the values are reduced by 10%
volume of coarse aggregate= 0.62 x 0.9= 0.56
volume of fine aggregate = 1 - 0.56 = 0.44
Step-8 : mix calculation -
a) volume of concrete = 1m^3
b) volume of cement = mass of cement / sp. gravity of cement X 1/1000
= 350 / 3.15 x 1/1000
= 0.111 kg/m^3
c) volume of water = mass of water/ sp.gravity of water x 1/1000
= 140/1 x 1/1000
= 0.140 kg/m^3
d) volume of chemical admixture = mass of chemcal admixture/ sp. gravity of admixturre x 1/1000
= 7/1.145 x 1/1000
= 0.006 m^3
e) volume of aggregate ( FA nad CA) = ( a - (b+c+d))
= ( 1-(0.111+0.140+0.006)
= 0.743 m^3
f) mass of coarse aggregate = e x volume of coarse aggregate x spe. gravity of aggregate x 1000
= 0.743 x 0.56 x 2.74 x 1000
= 1140 kg/m^3
g) mass of fine aggregate = e x volume of fine aggregate x sp. gravity of fine aggregate x 1000
= 0.743 x 0.44 x 2.74 x 1000
= 896 kg/m^3
Step-9 : mix proportion -
cement = 350 kg/m^3
water = 140 kg/m^3
fine aggregate = 896 kg/m^3
coarse aggregate = 1140 kg/m^3
chemical admixture = 7 kg/m^3
w/c ratio = 0.4
therefore, the mix ratio for M50 grade of concrete without fly ash= cement : FA : CA : water
= 1 : 2.56 : 3.26 : 0.4
NOTE :
1. 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 proportion shall be rewarded for the actual water content and checked for durability requirement.
2. two more trial having variation of 10% of w/c ratio in clause 10 shall be carried out and graph between three w/c ratio and correspondong strength shall be plotted to workout the mix proportion for the given target strength for field trials. however durability shall be met.
RESULT :
Concrete mix design for M30 and M50 are as follows :
a) mix proportion for M30 grade concrete with fly ash = cement : FA : CA
= 1 : 2.24 : 2.85
b) mix proportion for M50 grade concrete without fly ash = cement : FA : CA
= 1: 2.56 : 3.26