Project on Concrete Mix Design for various grades of Concrete
Aim –
As concrete is a heterogeneous material that has various ingredients like coarse aggregates, fine aggregates, water, admixtures, etc. for mixing. For concrete to achieve the desired strength these ingredients have to be included in the specific amount. This specific amount is decided based on the mix design as per the IS code 10262:2019. The specific amount is selected such that concrete gives desired workability in the plastic state, desired durability in the given environmental state, desired strength in the hardened state, and economical concrete as possible.
Introduction –
This project contains two types of concrete mix design
1. Concrete mix design of M35
The concrete mix design of M35 is done by taking fly ash, superplasticizer, and wet aggregates.
2. Concrete mix design of M50
The concrete mix design of M50 is done by taking superplasticizer and partially dry aggregates.
Concrete Mix Design of M35
DATA FOR CONCRETE MIX DESIGN OF M35 GRADE CONCRETE WITH FLY ASH
Grade of Concrete 35 N/mm^2
Maximum Size of Aggregate 20 mm
Type of aggregates
Crushed Angular Aggregates
Slump Workability 120 mm
Degree of Quality Control Good
Exposure Severe (For Reinforced Concrete)
Method of concrete placing Pumping
Maximum cement content As per IS 456:2000
Chemical Admixture (confirming to IS 9103-1999 Superplasticizers - Normal
Zone of Fine Aggregates Zone III
Type of Mineral Admixture Fly ash confirming to IS 3812 (Part-1)
Test Data for Material Cement OPC 53 N/mm^2
Confirming to IS 12269-2013 Specific Gravity
Cement 3.15 As per IS code
Coarse Aggregate at Surface Saturated Condition 2.74
Fine Aggregate at Surface Saturated Condition 2.65
Chemical Admixture (Super Plasticizer) 1.145 Fly Ash
2.2 Water Absorption
Coarse Aggregate 0.87
Fine Aggregate 1.26
Moisture Content of aggregates as per IS 2386 (Part -3) : 1967
Coarse Aggregate 2.15 %
Fine Aggregate 4.68 %
Free Moisture Content
Free surface moisture of coarse aggregates = Moisture content - water absorption
Coarse Aggregate 1.28 %
Free surface moisture of Fine aggregates = Moisture content - water absorption
Fine Aggregate 3.42 %
Fineness Modulus 2.41
Aggregate Impact Value 18.76 %
Combined Flakiness and Elongation Index 28.56 %
Admixture Superplasticizer 1 Percent by Cement Wt
Water Reduction by Superplasticizer
23 Percent of Water Quantity
Pozzolanic Material
Amount of Fly ash Material being used 30 %
Increase in the cement content 10 %
Pumpable Concrete
Reduction for Pumpable concrete 10 %
Design Mix
1. Target Strength for Mix F(ck) =f(ck)+1.65*σ
5 (As per Table 2 of IS 10262:2019)
Also, as per Table 1 of IS 10262:2019, value of X (=1.65*σ ) for M35 σ 6.5
F(ck) =35+1.65*5
Target Mean Strength from standard deviation 43.25 MPa
Target Mean Strength from value of X 41.5 MPa
The higher value of adopted. Therefore taking target mean strength 43.25 MPa
2. Air Entrapped
(As per Table 3 of IS 10262:2019) For 20mm nominal maximum size of aggregates 1 Percent 3. W/C Ratio
As Per Table 5 of IS 456:2000
Maximum Water Cement ratio for severe exposure 0.45
Minimum Grade of Concrete in severe exposure M30
From Fig 1 of IS 10262:2019, for target mean strength of 43.25 MPa and OPC cement grade of 53 MPa 0.36 Value of W/C ratio came out of Fig 1 is less than the maximum limit for severe exposure of concrete to the environment Therefore taking value of W/C ratio 0.36
4. Water Content Calculation
From Table 4 of IS 10232:2019, water content for 20mm nominal maximum size of aggregates
Water for 50 mm slump value as per table 4 186 Kg/m^3
Slump required at the site for workability 120 mm
Estimated water content for site slump
Water content for 75 mm slump 201.624 Kg/m^3
The effect of Superplasticizer is to reduce water content and increase workability. Generally superplasticizers giver reduction in water content by more than 20%
Taking Plasticizer by percentage of weight of cement 1 Percent
Amount of water reduced by superplasticizer (Assuming) 23 Percent
Water Content =
Hence the water content 155.25 Kg/m^3
5.Calculation of Cement
W/C ratio 0.36
Cement Content Calculation =
Cement amount as calculated 431.25 Kg/m^3
As IS 456 has recommended the value of cement for M 35 grade of concrete
Minimum value of Cement 320 Kg/m^3
Maximum value of Cement 450 Kg/m^3
Nowadays as the economy is one of the main concerns of the projects.
Cement is one material that is costly and a small substitution of cement with fly ash also serves the structural purpose of the project. So, fly ash is being used as a substitute material which has a certain advantage over conventional advantage like less permeability, less heat of hydration, reduction of cracks, bleeding etc.
Use of pozzolanic material, sometimes a requirement of increment of the cement content is warranted. It is decided based on the trials and experience.
Taking the content of fly ash as 30 % and increment of cement content as 10 %
Cement content after incrementing for fly ash 474.38 Kg/m^3
Weight of fly ash 142.31 Kg/m^3
Cement content taken 332.06 Kg/m^3
Finally Cement Taken 332.06 Kg/m^3
Finally Taken Cement must be more than 320 Kg/m^3 for severe exposure
No of bags for Cement (Assuming 1 Bag = 50 Kgs) 6.64 Bags
Correction for water content 119.54 Kg/m^3
Finally Taken Water Content 155.25 Kg/m^3
Total plasticizer required 3.32 Kg/m^3
6. Calculation of proportion of Coarse Aggregate to Total Aggregate
From Table 5 of IS 10232:2019, for 20 mm size of aggregate and Zone III of Sand (FA). This table gives value of ration of CA/TA for W/C ratio 0.5
For W/C ratio 0.5, Proportion of CA/TA 0.64
Required W/C ratio 0.36
The proportion of volume of coarse aggregates to that of total aggregates is increased at the rate of 0.01 for every decrease in the water-cement ratio by 0.05 and decreased at the rate of 0.01 for every increase in the water-cement ratio by 0.05
Correction for W/C ratio as per Clause 5.5.1 of IS 10232:2019 0.668
Assuming 1 unit as total aggregate then
For Pumpable concrete, general reduction of 10 % of aggregates is done for ease of doing work.
The proportion of Coarse Aggregates 0.6012
The proportion of Fine Aggregates 0.3988
Proportion of Fine Aggregates = 1-Proportion of Coarse Aggregates
7. Mix Calculation
Taking volume of concrete 1.000 Cum (Assumption)
Volume of Air Entrapped = As per table 3 of IS 10262
Volume of Air Entrapped 0.010 Cum
Volume of Cement =
Volume of cement 0.105 Cum
Volume of Water =
Volume of Water 0.155 Cum
Volume of Chemical Admixture =
Volume of Chemical admixture 0.003 Cum
Volume of Fly Ash =
Volume of Fly Ash 0.065 Cum
Volume of Aggregates = Total Volume - Volume of Air Entrapped - Volume of Cement - Volume of Water - Volume of Admixture - Volume of Fly Ash
Volume of Aggregate in 1 Cum 0.662 Cum
Quantity of Coarse Aggregate 1090.084 Kg/m^3
Quantity of Coarse Aggregates = Volume of Total Aggregates X Proportion of Coarse Aggregates X Specific Gravity of Coarse Aggregates X 1000
Quantity of Fine Aggregate 699.345 Kg/m^3
Quantity of Fine Aggregates = Volume of Total Aggregates X Proportion of Fine Aggregates X Specific Gravity of Fine Aggregates X 1000
8. Correction for wet aggregate
As the above calculation is done for the saturated surface dry condition. If the condition is otherwise then while calculating the water content, we have to make allowance for either free surface moisture or dry aggregates
Wet Coarse Aggregates =
Wet Coarse Aggregates 1104.0372 Kg/m^3
Wet Fine Aggregates =
Wet Fine Aggregates 723.263 Kg/m^3
This increment in the value of aggregates is accounted for the decrease in water quantity as excess water is available with aggregates in addition to being supplied by the W/C ratio required water content
Increase in water content
For Coarse Aggregates
Increase in water due to coarse aggregates = Mass of coarse aggregate in SSD condition - mass of coarse aggregate in wet condition = -13.953 Kg/m^3
Increase in water due to fine aggregates = Mass of fine aggregate in SSD condition - mass of fine aggregate in wet condition = -23.918 Kg/m^3
Increase in water content = -37.871 Kg/m^3
9. Final Quantities
For Surface Saturated Dry Condition
Only (In Kg/m^3) For Wet Condition (In Kg/m^3)
| For 1 Cum | For 1 Cum | ||
| Cement | 332.064 | Cement | 332.064 |
| Water | 155.250 | Water | 117.380 |
| Admixture | 3.321 | Admixture | 3.321 |
| Coarse | 1090.084 | Coarse | 1104.037 |
| Fine | 699.345 | Fine | 723.263 |
| Fly Ash | 142.313 | Fly Ash | 142.313 |
| Final W/C | 0.468 | Final W/C | 0.353 |
This decrease in W/C ratio is due to the wet aggregates as these aggregates also have free some water over and above required for absorption to saturated surface dry condition. This additional water supplements the W/C ratio water requirement.
Concrete Mix design of M50
DATA FOR CONCRETE MIX DESIGN OF M50 GRADE CONCRETE WITHOUT FLY ASH
Grade of Concrete
50
N/mm^2
Maximum Size of Aggregate
20
mm
Type of aggregates
Crushed Angular Aggregates
Slump Workability
75
mm
Degree of Quality Control
Good
Exposure
Severe
(For Reinforced Concrete)
Method of concrete placing
Chute
(Non-Pumpable)
Maximum cement content without fly ash
450
Kg/m^3
Chemical Admixture (confirming to IS 9103-1999
Superplasticizers - Normal
Zone of Fine Aggregates
Zone III
Test Data for Material
Cement
OPC
53
N/mm^2
Confirming to IS 12269-2013
Specific Gravity
Cement
3.15
As per IS code
Coarse Aggregate at Surface Saturated Condition
2.74
Fine Aggregate at Surface Saturated Condition
2.65
Chemical Admixture (Super Plasticizer)
1.145
Water Absorption
Coarse Aggregate
0.87
Fine Aggregate
1.26
Fineness Modulus
2.41
Aggregate Impact Value
18.76
%
Combined Flakiness and Elongation Index
28.56
%
Admixture
Superplasticizer
1
Percent by Cement Wt
Water Reduction by Superplasticizer
23
Percent of Water Quantity
Design Mix
1. Target Strength for Mix
F(ck)
=f(ck)+1.65*σ σ 5
(As per Table 2 of IS 10262:2019)
Also, as per Table 1 of IS 10262:2019, value of X (=1.65*σ) for M50
6.5
F(ck)
=50+1.65*5
Target Mean Strength from the standard deviation
58.25
MPa
Target Mean Strength from value of X
56.5
MPa
The higher value of adopted. Therefore taking target mean strength
58.25
MPa
2. Air Entrapped
(As per Table 3 of IS 10262:2019)
For 20mm nominal maximum size of aggregates
1
Percent
3. W/C Ratio
As Per Table 5 of IS 456:2000
Maximum Water Cement ratio for severe exposure
0.45
Minimum Grade of Concrete in severe exposure
M30
From Fig 1 of IS 10262:2019, for target mean strength of 58.25 MPa and OPC cement grade of 53 Mpa
0.33
Value of W/C ratio came out of Fig 1 is less than the maximum limit for severe exposure of concrete to environment
Therefore taking value of W/C ratio
0.33
4. Water Content Calculation
From Table 4 of IS 10232:2019, water content for 20mm nominal maximum size of aggregates
Water for 50 mm slump value as per table 4
186
Kg/m^3
Slump required at site for workability
75
mm
Estimated water content for site slump =Water content for 75 mm slump
191.58
Kg/m^3
The effect of Superplasticizer is to reduce water content and increase workability. Generally superplasticizers giver reduction in water content by more than 20%
Taking Plasticizer by the percentage of the weight of cement
1
Percent
Amount of water reduced by superplasticizer (Assuming)
23
Percent
Water Content =
Hence the water content
147.52
Kg/m^3
5.Calculation of Cement
W/C ratio
0.33
Cement Content Calculation =
Cement amount as calculated
447.02
Kg/m^3
As IS 456 has recommended the value of cement for M
50
grade of concrete
Minimum value of Cement
320
Kg/m^3
Maximum value of Cement
450
Kg/m^3
Finally Cement Taken
447.02
Kg/m^3
No of bags for Cement
(Assuming 1 Bag = 50 Kgs)
8.94
Bags
Correction for water content
147.52
Kg/m^3
Finally Taken Water Content
147.52
Kg/m^3
Total plasticizer required
4.47
Kg/m^3
6. Calculation of proportion of Coarse Aggregate to Total Aggregate
From Table 5 of IS 10232:2019, for 20 mm size of aggregate and Zone III of Sand (FA). This table gives the value of ratio of CA/TA for W/C ratio 0.5
For W/C ratio 0.5, the Proportion of CA/TA
0.64
Required W/C ratio
0.33
The proportion of the volume of coarse aggregates to that of total aggregates is increased at the rate of 0.01 for every decrease in the water-cement ratio by 0.05 and decreased at the rate of 0.01 for every increase in the water-cement ratio by 0.05
Correction for W/C ratio as per Clause 5.5.1 of IS 10232:2019
0.674
Assuming 1 unit as total aggregate then
The proportion of Coarse Aggregates
0.674
The proportion of Fine Aggregates
0.326
Proprtion of Fine Aggregates = 1-Proportion of Coarse Aggregates
7. Mix Calculation
Taking the volume of concrete
1.000
Cum
(Assumption)
The volume of Air Entrapped = As per table 3 of IS 10262
The volume of Air Entrapped
0.010
Cum
The volume of Cement =
Volume of cement0.142
Cum
The volume of Water =
Volume of Water0.148
Cum
The volume of Chemical Admixture =
The volume of Chemical admixture
0.004
Cum
The volume of Aggregates = Total Volume - Volume of Air Entrapped - Volume of Cement - Volume of Water - Volume of Admixture
The volume of Aggregate in 1 Cum
0.697
Cum
Quantity of Coarse Aggregate
1286.579
Kg/m^3
Quantity of Coarse Aggregates = Volume of Total Aggregates X Proportion of Coarse Aggregates X Specific Gravity of Coarse Aggregates X 1000
Quantity of Fine Aggregate
601.852
Kg/m^3
Quantity of Fine Aggregates = Volume of Total Aggregates X Proportion of Fine Aggregates X Specific Gravity of Fine Aggregates X 1000
8. Correction for Water Absorption by aggregate
As the above calculation is done for the saturated surface dry condition. If the condition is otherwise then while calculating the water content, we have to make allowance for either free surface moisture or dry aggregates
Partially Saturated Coarse Aggregates
1275.482
Kg/m^3
Corrected Partially Fine Aggregates
594.363
Kg/m^3
This reduction in the value of aggregates is accounted for the increase in water quantity as excess water above W/C ratio is being absorbed by the aggregates to make surface saturated dry
Increase in water content
For Coarse Aggregates
Increase in water due to coarse aggregates =
Mass of coarse aggregate in SSD condition - mass of coarse aggregate in dry condition
=
11.097
Kg/m^3
Increase in water due to fine aggregates =
Mass of fine aggregate in SSD condition - mass of fine aggregate in dry condition
=
7.489
Kg/m^3
Increase in water content
=
18.586
Kg/m^3
9. Final Quantities
For Surface Saturated Dry condition Only (In Kg/m^3)
For Dry or Partially Dry Condition (In Kg/m^3)
| For 1 Cum | For 1 Cum | ||
|
Cement |
447.020 | Cement | 447.020 |
| Water | 147.517 |
Water |
166.102 |
| Admixture | 4.470 | Admixture | 4.470 |
|
Coarse |
1286.579 | Coarse | 1275.482 |
|
Fine |
601.852 |
Fine |
594.363 |
| Final W/C | 0.330 | Final W/C | 0.372 |
This Increase in W/C ratio is due to the dry or partially saturated aggregates as these aggregates also absorb some water. This absorption of water decreases water required for proper chemical reaction and leads to undeveloped strength due to a shortage of water
Results:
From both concrete mix designs, we got to know the all the concrete ingredients required to make concrete of required grade which gives desired properties as required in both plastic and hardened state of concrete. Concrete ingredients required for 1 cum of concrete and 1 bag (50 Kgs) of cement are shown in the final quantities subsection (Serial No 9).