Project on Concrete Mix Design for various grades of Concrete
Calculate the Concrete Mix Design for M35 grade concrete with fly ash & M50 grade concrete without Fly ash
Ans :
INTRODUCTION : Concrete mix design is the process of finding right proportions of cement, sand and aggregates for concrete to achieve target strength in structures. So, concrete mix design can be stated as Concrete Mix = Cement:Sand:Aggregates.
Concrete mix design involves a process of preparation in which a mix of ingredients creates the required strength and durability for the concrete structure. Because every ingredient in the mix consists of different properties, it's not an easy task to create a great concrete mix.
The object of mix design is to decide the proportions of materials which will produce concrete of required properties. The mix proportions should be selected in such a way that the resulting concrete is of desired workability while fresh and it could be placed and compacted easily for the intended purpose.
The design of concrete mix is not a simple task on account of the widely varying properties of the constituent materials, the conditions that prevail at the site of work, in particular the exposure condition, and the conditions that are demanded for a particular work for which the mix is designed.
The best concrete mix design is the one which satisfies all the aspects for which it was designed
Strength- The strength of 95% cube casted after 28 days of Curing should be greater than the characteristic strength for which concrete has been designed.
Workability & placing- As working condition changes so does the properties desired from concrete also changes, the concrete which can be easily placed without segregation and with least compaction required.
Durability- The concrete must be durable enough to face harsh conditions of atmosphere for which it has been designed.
AIM :
1. To calculate the Concrete Mix Design for M35 grade concrete with fly ash
Means the calculation is done for knowing the exact amount of ingradients (i.e. Water , cement , sand , aggregate) required to make M35 grade concrete with fly ash having good strength , workability , etc.
2. To calculate the Concrete Mix Design for M50 grade concrete without Fly ash
Means the calculation is done for knowing the exact amount of ingradients (i.e. Water , cement , sand , aggregate) required to make M50 grade concrete without fly ash having good strength , workability , etc.
Calculations / Procedure :
1. Concrete Mix Design for M35 grade concrete with fly ash
Step :1
Stipulations for proportioning
a. Grade designation : M35
b. Type of cement : OPC 43 grade conforming to IS 8112
c. Type of mineral admixture: Fly ash confirming to IS 3812 ( Part 1)
d. Maximum nominal size of aggregates : 20mm
e. Minimum 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 : 450 kg/m^3.
m. Chemical admixture type : Superplaticizer.
Step :2
Test data for materials
a. Cement used : OPC 43 grade confirming to IS 8112
b. Specific gravity of cement : 3.15
c. Fly ash : Conforming to IS 3812 part 1
d. Specific gravity of flyash : 2.2
e. Chemical admixture : Superplaticizer conforming to IS 9103
f. Specific gravity of :
Coarse aggregate (CA) : 2.74
Fine aggregate (FA) : 2.74
g. Water absorption :
Coarse aggregate : 0.5%
Fine aggregate : 1%
h. Free surface moisture
Coarse aggregate : Nil
Fine aggregate : Nil
i. Seive analysis
Coarse aggregates:
| IS seive size (mm) | Analysis of coarse aggregate fraction | % of different fraction | Remarks | |||
| I | II | I | II | Combined | ||
| 20 | 100 | 100 | 60 | 40 | 100 | Confirming to |
| 10 | 0 | 71.2 | 0 | 28.5 | 28.5 | Table 2 |
| 4.75 | 9.4 | 3.7 | 3.7 | of | ||
| 2.36 | 0 | IS 383 |
Fine aggregate : Conforming to grading Zone 1 of table 4 IS 383.
Step :3
To find target mean strength for mix proportioning
Target mean strength f'ck = fck +1.65s
= 35 +1.65*5 =43.25 N/mm2
fck- Characteristic compressive strength
s- Standard deviation
Step:4
Selection of water-cement ratio
Maximum water-cement ratio =0.45 (for severe condition ,from table 5 of IS 456-2000)
On experience water- cement ratio =0.4
0.4 <0.45, Hence OK.
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 100 mm slump ,= 186+(6/100)*186 =197 litres
As superplaticizer is used, the water content is reduced upto 30%
Based on trials water content reduction of 29% is achieved with plasticizer
Hence arrived water content = 197*0.71 = 140 litres
Step :6
Calculation of cement content
Water - cement ratio = 0.4
Cementatious material ( Cement +flyash ) = 140/0.4 =350 Kg/m3
In table 5 of IS 456-2000, the cement content for severe exposure =320 kg/m3
350 Kg/m3 > 320 Kg/m3
Hence OK.
To proportion the mix containing flyash the following steps are suggested :
a. The percentage of flyash need to be decided based on project requirement and qualityof materials.
b. In some cases increase in cementatious materials can be warrned . Increase in cementatious material content and its percentage may be based on experience and trial
In this increase of 10% cementatious material content is considered.
Cementatious material content = 350*1.1 =385 kg/m3
Water content = 140 kg/m3
So, water- cement ratio = 140/385 =0.364
Fly ash at 30% total cementatious material content = 35-30% =115 kg/m3
Cement (OPC) =385-115 =270 kg/m3
Saving of cement while using flyash = 350-270=80 kg/m3
Fly ash beign utilized = 115 kg/m3
Step: 7
Proportion of volume of coarse aggregate and fine aggregate content
From table 3 of IS 1026:2009 ,volume of coarse aggregate corresponding to 20 mm 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 water- cement ratio is lowered by 0.1 ,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)
Hence the corrected value ofcoarse aggregate for the water-cemnt ratio = 0.64
( 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 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 cement ) *1/1000
= (270/3.15 )*1/1000 =0.086 m3
c. Volume of flyash = (Mass of flyash / Specific gravity of flyash )*1/1000
= (115/2.2) *1/1000 = 0.052 m3
d. Volume of water = ( Mass of water / Specific gravity of water)*1/1000
= (140/1)*1/1000 =0.140 m3
e. Volume of chemical admixture = ( Mass of admixture / specific gravity of admixture)*1/1000
=( 7.6/1.14)*1/1000 =0.006 m3
f. Volume of aggregate ( Fine and coarse) = 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*0.576*2.74*1000 =1130 kg/m3
h. Mass of fine aggregate = f* Volume of fine aggregate* Specific gravity of fine aggreate*1000
= 0.716*0.424*2.74*1000= 831 kg/m3
Step :9
Mix proportion
Cement = 270 kg/m3
Fly ash = 115 kg/m3
Water = 140 kg/m3
Fine aggregate = 831 kg/m3
Coarse aggregate = 1130 kg/m3
Chemical admixture = 7 kg/m3
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 admixyure shall be adjusted for achieving the required slump on trial . The mix proportion shall be reworked for the actual water content and checkedd for durability requirements.
Step :11
Two or more trials having variation of 10 % of water-cement ratio in Clause 10( Step 10) 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 strength for feild trials .However durability shall be met.
2. Concrete Mix Design for M50 grade concrete without Fly ash
Step :1
Stipulation for proportioning
a. Grade designation : M50
b. Type of cement : OPC grade 43 conforming to IS 8112
c. Maximum nominal sizeof aggregate: 20mm
d. Minimum cement content : 320 kg/m3
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 : 450 kg/m3.
l. Chemical admixture type : Superplaticizer.
Step:2
Test data for materials
a. Cement used : OPC 43 grade confirming to IS 8112
b. Specific gravity of cement : 3.15
c. Chemical admixture : Superplaticizer conforming to IS 9103
d. Specific gravity of :
Coarse aggregate : 2.74
Fine aggregate : 2.74
e. Water absorption :
Coarse aggregate : 0.5%
Fine aggregate : 1%
f. Free surface moisture
Coarse aggregate : Nil
Fine aggregate : Nil
g. Seive analysis
Coarse aggregates:
| IS seive size (mm) | Analysis of coarse aggregate fraction | % of different fraction | Remarks | |||
| I | II | I | II | Combined | ||
| 20 | 100 | 100 | 60 | 40 | 100 | Confirming to |
| 10 | 0 | 71.2 | 0 | 28.5 | 28.5 | Table 2 |
| 4.75 | 9.4 | 3.7 | 3.7 | of | ||
| 2.36 | 0 | IS 383 |
Fine aggregate : Conforming to grading Zone 1 of table 4 IS 383.
Step:3
To find target mean strength for proportioning
Target mean strength , f'ck =fck +1.65 s
= 50+1.65*5 =58.25 N/mm2
fck = Characteristic strength
s=standard deviation
Step:4
Selection of water cement ratio
From Table :5 of IS 456-2000, by exposure condition
Here severe condition is considered , Maximum water-cement ratio=0.45
Based on experience water- cement ratio =0.4
0.4 <0.45 ,Hence OK.
Step :5
Selection of water content
Maximum water content for 20mm aggregate =186 litres ( Table 2 of IS 1026:2009) for 25mm to 50mm slump range
For 100 mm slump ,= 186+(6/100)*186 =197 litres
As superplaticizer is used, the water content is reduced upto 30%
Based on trials water content reduction of 29% is achieved with plasticizer
Hence arrived water content = 197*0.71 = 140 litres
Step :6
Calculation of cement content
Water - cement ratio = 0.4
Cement content = 140/0.4 =350 kg/m3
In table 5 of IS 456-2000, the cement content for severe exposure =320 kg/m3
350 kg/m3 > 320 kg/m3
Hence OK.
Step: 7
Proportion of volume of coarse aggregate and fine aggregate content
From table 3 of IS 1026:2009 ,volume of coarse aggregate corresponding to 20 mm 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 water- cement ratio is lowered by 0.1 ,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)
Hence the corrected value of coarse aggregate for the water-cemnt ratio = 0.64
( 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 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 calculation
For unit volume of concrete
a. Volume of concrete = 1 m3
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 =0.140 m3
d. Volume of chemical admixture = (Mass of admixture/Specific gravity of admixture)*1/1000
= (7.6/1.145)*1/1000 =0.006 m3
e. Volume of agggregate (fine adn coarse) = a-(b+c+d)
=1-( 0.111+0.140+0.006) =0.743 m3
f. Mass of coarse aggregate = ex Volume of coarse aggregate x Specific gravity of coarse aggregate x 1000
=0.743*0.576*2.74*1000= 1173 kg/m3
g. Mass of fine aggregate =e* Volume of fine aggregate* Specific gravity of fine aggregate *1000
= 0.743*0.424*2.74*1000 =863 kg/m3
Step :9
Mix proportion
Cement = 350 kg/m3
Water = 140 kg/m3
Fine aggregate= 863 kg/m3
Coarse aggregate = 1173 kg/m3
Chemical admixture = 7 kg/m3
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 admixyure shall be adjusted for achieving the required slump on trial . The mix proportion shall be reworked for the actual water content and checkedd for durability requirements.
Step :11
Two or more trials having variation of 10 % of water-cement ratio in Clause 10( Step 10) 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 strength for feild trials .However durability shall be met.
Result : 1. The mix design for M 35 grade of concrete with flyash is 1: 2.15:2.94
2. The mix ratio for M 50 grade concrete without flyash is 1:2.46:3.35
References : IS 10262 :2009 , IS 8112 , IS 9103, IS 456:2000