Project on Concrete Mix Design for various grades of Concrete
AIM: To Calculate the Concrete Mix Design for M35 grade concrete with fly ash & M50 grade concrete without Fly ash
INTRODUCTION:
Concrete mix design is the method of finding the precise proportion of cement, sand and aggregates for concrete to achieve the target strength in structures, therefore concrete mix design can be stated as concrete mix in terms of cement: sand: aggregates. The design is done according to the requirements of concrete strength. So, we can achieve the desirable properties of concrete either it is in fresh stage or in hardened stage. The fresh concrete properties like workability, setting time and hardened concrete properties like compressive strength, durability etc. are attained surely by this method. Use of additives like admixtures, retarders etc. other than basic ingredients are used to improve the properties of mix. This project consist of two parts, the first part deals with the design of M35 grade cement with fly ash as a part of it and second part is the design of M50 grade concrete without fly ash.
OBJECTIVE:
The objective of this project is to produce a mix design for M35 grade concrete containing fly ash and M50 grade concrete. The mix will be prepared as per IS METHOD: Concrete mix proportioning guidelines from IS 10262:2009 and recommented guide lines from IS 10262:1982.
EQUATIONS USED:
1)Target mean strength
f’ck =fck + 1.65s
Where
- f’ck = target average compressive strength at 28 days
- fck = characteristics compressive strength at 28 days, and
- s = standard deviation
2)Cement content
Cement content = water content / water-cement ratio
3) Volume Calculations
- (a) Volume of concrete
- (b) Volume of cement = [Mass of cement] / [Specific Gravity of Cement] x 1/1000
- (c) Volume of water = [Mass of water] / [Specific Gravity of water] x 1/1000
- (d)Volume of chemical admixture = [Mass of admixture] / [Specific Gravity of admixture] x 1/1000
- (e) Volume of all in aggregate =[a-(b+c+d)]
- (f) Mass of coarse aggregate= e x Volume of Coarse Aggregate x Specific Gravity of Coarse Aggregate x 1000
- (g) Mass of fine aggregate= e x Volume of Fine Aggregate x Specific Gravity of Fine Aggregate x 1000
PART 1:To Calculate the Concrete Mix Design for M35 grade concrete with fly ash:
M35 grade concrete with Fly ash
Step 1:Stipulations for Concrete design mix
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 of aggregate : 20mm
e) minimum cement content : 320 kg/m3
f) maximum water cement ratio : 0.45 ( from table 5 of IS 456:2000)
g) workability : 100mm ( slump value for pumpable concrte )
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 : 450 kg/m3
m) chemical admixture type : superplasticizer
Step 2: test data for materials
a) cement used : OPC 43 grade conforming to 8112
b) SG of cement : 3.15
c) fly ash : conforming to IS 3812 ( part 1)
d) SG of fly ash : 2.2
e) chemical admixture :superplasticizer conforming to IS 9103
f) SG of
coarse aggregate : 2.74
fine aggregate : 2.74
g) water absorption for
coarse aggregate :0.5 %
fine aggregate : 1.0%
h) free surface moisture for
coarse aggregate : nil
fine aggregate : nil
i) Sieve analysis
coarse aggregate : conforming to IS 383 table 2
fine aggregate : conforming to grading Zone I of table 4 of IS 383
Step 3
EQUATIONS USED:
1)Target mean strength
f’ck =fck + 1.65s
Where
- f’ck = target average compressive strength at 28 days
- fck = characteristics compressive strength at 28 days, and
- s = standard deviation
From table 1 of IS 10262:2009 , standard deviation S= 5 N/mm2
therefore target strength :35 + 1.65 x 5 = 43.25 N/mm2
Step 4
selection of w/c ratio :
from table 5 of IS 456:2000 for severe exposure ,
maximum w/c ratio = 0.45
based on experience , adopt w/c ratio as 0.40
0.40 < 0.45 hence ok
step 5
selection of water content
from table 2 of IS 10262:2009, maximum water content for 20 mm aggregate = 186 litre ( for 25 mm to 50 mm slump range)
estimated water content for 100 mm slump 186 +(0.06*186) = 197 litre
as superplasticizer is used the water content can be reduced upto 30% . Based on trials water content reduction of 29 % is achieved with plasticizer
Hence, the arrived water content = 197 * 0.71 = 140
Step 6
calculation of cement content :
w/c ratio =0.4
cementitious material (cement +fly ash content) 140/0.4= 350 kg/m3
from table 5 IS 456:2000 minimum cement content for severe exposure condition =320 kg/m3
350 kg/m3 > 320 kg/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 cases increase in cementitious material can be warranted. Increase in cementitious material content and its percentage may be based on experience and trial (here is increase of 10% cementitious material content)
cementitious material content = 350*1.10 =385 kg/m3
water content = 140 kg/m3
so, w/c ratio = 140/385 = 0.364
fly ash @ 30% total cementitious material content = 385 *30%=115 kg/m3
cement(OPC) = 385-115 =270 kg/m3
saving of cement while using fly-ash =350-270 =80 kg/m3
fly ash being utilized = 115 kg/m3
step 7
proportion of volume of coarse aggregate and fine aggregate content =
From table 3 of IS 10262:2009, vol of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (zone I) for w/c ratio of 0.5=0.6
Here the w/c is 0.40 Therefore, volume of coarse aggregate is required to be increased to decrease the fine aggregate content. As the 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, the corrected vol of coarse aggregate for the w/c 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
step 8 :
a) Volume of concrete = 1 m3
b)Volume of cement = [Mass of cement] / [Specific Gravity of Cement] x 1/1000 = (270/3.15)*(1/1000)
= 0.086 m3
c) volume of fly ash = [Mass of fly ash] / [Specific Gravity of fly ash] x 1/1000 =(115/2.2) *(1/1000)
=0.052 m3
d) volume of water = [Mass of water] / [Specific Gravity of water] x 1/1000 =(140/1) *(1/1000) = 0.140 m3
e) volume of chemical admixture = [Mass of admixture] / [Specific Gravity of admixture] x 1/1000 = (7.6/1.145) *1/1000 ( 2 percent of cementious content)
=0.006 m3
f) volume of aggregate (FA & CA) = a-(b+c+d+e)
= (1-(0.086+0.052+0.140+0.006)
=0.716m3
g) mass of coarse aggregate = f x Volume of Coarse Aggregate x Specific Gravity of Coarse Aggregate x 1000
= 0.716 * 0.56*2.74*1000
= 1098 kg/m3
h)mass of fine aggregate = f x Volume of fine Aggregate x Specific Gravity of Fine Aggregate x 1000
= 0.716*0.44*2.74*1000
=863 kg/m3
step 9
mix proportion for trial number 1
cement = 270 kg/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
w/c ratio = 0.364 (considering the minimum value)
trial mix ratio = 1:2.24:2.85
STEP 10:The slump shall be measured, the water content and dosage of admixture shall be adjusted for achieving the required slump on trial. The mix proportion shall be reworked for the actual water content and checked for durability requirements
STEP 11:Two more trials having variation of 10% of water-cement ratio 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 for field trials.
PART 2:To Calculate the Concrete Mix Design for M50 grade concrete without fly ash:
M50 grade concrete without Fly ash
Step 1:Stipulations for Concrete design mix
a) Grade designation : M50
b) type of cement : OPC 53 grade conforming to IS BIS 12269 - 1987
c) maximum nominal size of aggregate : 20mm
d) minimum cement content : 320 kg/m3
e) maximum water cement ratio : 0.45 ( from table 5 of IS 456:2000)
f) workability : 100mm ( slump value for pumpable concrte )
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/m3
l) chemical admixture type : superplasticizer
Step 2: test data for materials
a) cement used : OPC 53 grade conforming to IS BIS 12269 - 1987
b) SG of cement : 3.15
c)chemical admixture :superplasticizer conforming to IS 9103
d) SG of fly ash : 2.2
e) SG of
coarse aggregate : 2.74
fine aggregate : 2.74
f) water absorption for
coarse aggregate :0.5 %
fine aggregate : 1.0%
g) free surface moisture for
coarse aggregate : nil
fine aggregate : nil
h) Sieve analysis
coarse aggregate : conforming to IS 383 table 2
fine aggregate : conforming to grading Zone I of table 4 of IS 383
Step 3
EQUATIONS USED:
1)Target mean strength
f’ck =fck + 1.65s
Where
- f’ck = target average compressive strength at 28 days
- fck = characteristics compressive strength at 28 days, and
- s = standard deviation
From table 1 of IS 10262:2009 , standard deviation S= 5 N/mm2
therefore target strength :50 + 1.65 x 5 = 58.25 N/mm2
Step 4
selection of w/c ratio :
from table 5 of IS 456:2000 for severe exposure ,
maximum w/c ratio = 0.45
based on experience , adopt w/c ratio as 0.40
0.40 < 0.45 hence ok
step 5
selection of water cantent
from table 2 of IS 10262:2009, maximum water content for 20 mm aggregate = 186 litre ( for 25 mm to 50 mm slump range)
estimated water content for 100 mm slump 186 +(0.06*186) = 197 litre
as superplasticizer is used the water content can be reduced upto 30% . Based on trials water content reduction of 29 % is achieved with plasticizer
Hence, the arrived water content = 197 * 0.71 = 140
Step 6
calculation of cement content :
w/c ratio =0.4
cementitious material (cement +fly ash content) 140/0.4= 350 kg/m3
from table 5 IS 456:2000 minimum cement content for severe exposure condition =320 kg/m3
350 kg/m3 > 320 kg/m3 , hence ok
Cement required is 350 kg/m3
step 7
proportion of volume of coarse aggregate and fine aggregate content =
From table 3 of IS 10262:2009, vol of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (zone I) for w/c ratio of 0.5=0.6
Here the w/c is 0.40 Therefore, volume of coarse aggregate is required to be increased to decrease the fine aggregate content. As the 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, the corrected vol of coarse aggregate for the w/c 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
Volume of fine aggregate and coarse aggregate is 0.44 and 0 .56 respectively
Step 8 :
MIX calculation
a) volume of concrete : 1m3
b) Volume of cement = [Mass of cement] / [Specific Gravity of Cement] x 1/1000= (350/3.15) X (1/1000) =0.111m3
c)Volume of water = [Mass of water] / [Specific Gravity of water] x 1/1000 = (140/1) X (1/1000) = 0.140m3
d) volume of chemical admixture = [Mass of admixture] / [Specific Gravity of admixture] x 1/1000 =(7/1.145) X (1/1000) =0.006 m3 ( 2 percent of cement content)
e) Volume of all in aggregate =
[a-(b+c+d)] =1-(0.111+0.140+0.006) =0.743 m3
f) Mass of coarse aggregate= e x Volume of Coarse Aggregate x Specific Gravity of coarse Aggregate x 1000
=0.743*0.56*2.74*1000
=1140kg/m3
g)Mass of fine aggregate= e x Volume of fine Aggregate x Specific Gravity of Fine Aggregate x 1000
= 0.743*0.44*2.74*1000
=896 kg/m3
step 9
mix proportion for trial no 1
|
cement = 350 kg/m3 water = 140 kg/m3 fine aggregate = 896 kg/m3 coarse aggregate = 1140 kg/m3 chemical admixture = 7 kg/m3 w/c ratio = 0.40 trial ratio = 1:2.56:3.26 |
STEP 10:The slump shall be measured, the water content and dosage of admixture shall be adjusted for achieving the required slump on trial. The mix proportion shall be reworked for the actual water content and checked for durability requirements
STEP 11:Two more trials having variation of 10% of water-cement ratio 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 for field trials
RESULTS:
Mix Proportion by weight of M35 grade of concrete with fly ash is 1:2.24:2.85 and its water-cement ratio was found to be 0.364 .
Mix Proportion by weight of M50 grade of concrete without fly ash is 1:2.56:3.26 and its water-cement ratio was found to be 0.4 .