Project on Concrete Mix Design for various grades of Concrete

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

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

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

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

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

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 cement

0.142

Cum

The volume of Water =

Volume of Water

0.148

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 =

Partially Saturated Coarse Aggregates

1275.482

Kg/m^3

Partially Saturated Fine Aggregates =

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