Project on Concrete Mix Design for various grades of Concrete

Aim:

To determine the concrete mix design for M35 grade concrete with fly ash and M50 grade concrete without fly ash

Introduction:

Concrete mix design is a procedure of selecting the suitable ingredients of concrete and their relative proportions with an objective to prepare concrete of certain minimum strength, desired workability and durability as economically as possible.

The method of concrete mix design consists of selection of optimum proportions of ingredients, i.e., water, cement, fine aggregate, Coarse aggregate and admixture if needed to produce Concrete of specified properties such as strength, workability, durability, etc., The Compressive strength of hardened concrete which is generally considered to be as index of it's other properties, depends upon many factors, e.g. quality and quantity of cement, water and aggregates; batching and mixing; placing, compaction and curing. The cost of Concrete is made up of the cost of materials, plant and labour. The variations in the cost of materials arise from the fact that the cement is several times costly than the aggregate, thus the aim is to produce as lean mix

Objective Of Mix Design :

• To achieve the designed/desired workability in the plastic stage
• To achieve the desired minimum strength in the hardened stage
• To achieve the desired durability in the given environmental conditions
• To produce Concrete as economically as possible
• The main objective of this project is to determine the mix design for M35 garde Concrete with fly ash and M50 grade concrete without fly ash as per IS method.

Codes Used: IS 10262: 2009, IS 456: 2000

Step By Step Procedure:

PART 1: TO CALCULATE THE MIX DESIGN FOR M35 GRADE CONCRETE WITH FLY ASH

Step 1: Stipulations for Concrete Design Mix

• Grade Designation: M35
• Type of cement: OPC 53 Grade confirming to IS 8112
• Maximum nominal size of aggregate: 20 mm
• Minimum cement content: 320kg/m
• Maximum W/C ratio: 0.45 (Table 5- IS 456:2000 Exposure condition)
• Workability:100mm (Slump value for pumpable concrete)
• Exposure Condition: Severe (For reinforced concrete)
• Degree of supervision: Good
• Type of aggregate: Crushed Angular Aggregates
• Maximum Cement Content: 450kg/m^3
• Chemical admixture type: Super plasticizer

Step 2: Test Data for Materials

• Cement used: OPC 53 Grade conforming to IS 8112
• Specific gravity of cement: 15 Test IS 2720
• Fly ash: Confirming to IS 12089
• Specific gravity of fly ash: 90
• Chemical admixture: Super plasticizer 0.6% conforming to IS 9103
• Specific gravity of coarse aggregate: 74
• Specific gravity of fine aggregate: 74
• Water absorption of Coarse aggregate: 5%
• Water absorption of fine aggregate: 0%
• Free surface moisture of coarse aggregate: Nil
• Free surface moisture of fine aggregate: Nil
• Sieve analysis for Coarse aggregate: Conforming to Table 2- IS 383
• Sieve analysis for Fine aggregate: Conforming to Grading Zone 2 of Table 4- IS 383

Step 3: Target Strength for Mix Proportioning

Target strength for M35 grade concrete can be found from the formula given in the codebook.

F'ck = fck +1.65×S

Where,

F'ck = Target average compressive strength at 28 days

fck = Characteristics Compressive strength at 28 days

S = Standard deviation

The Standard deviation (S) value for the M35 grade concrete is given in table 8 of IS456.

Therefore, Target Strength = 35+ (1.65×5)

= 43.25 N/mm^2

Target mean strength = 43.25 N/mm^2

Step 4: Selection of Water-Cement Ratio

The maximum water-cement ratio to design M35 grade concrete can be found from Table 5-IS456 given below

Maximum W/C ratio = 0.45

Based on Experience, Adopted W/C ratio = 0.4

Adopted W/C ratio = 0.45

Step 5: Selection of Water Content

From table 4 of IS 10262: 2009, maximum water content for 20mm aggregate is 186 litre (for 25 to 50mm slump range)

Clause 4.2 suggest that increasing the 3% of water content for every extra 25mm slump

For 50mm slump, We have to add 6% to it

= 186+(6/100)×186

= 197 litres.

(Note: If super plasticizer is used, the water content can be reduced upto 20% and above)

Based on the trials with super plasticizer water content reduction of 20% has been achieved,

Hence the arrived water content = 197×0.8 = 158 litre

Adopted Water Content Required = 160 litres

Step 6: Calculation of cement and fly ash required

Adopted W/C ratio = 0.45

Total Cementious (cement + fly ash) Required

= Water Content/ Water-Cement ratio

= 160/0.45

= 355.55 Kg/m^3

From Table 5 of IS 456, Minimum cement content for severe exposure Conditions = 320 Kg

356 Kg/m^3 > 320 Kg/m^3 hence ok

Cementing material content = 356

Since Fly ash is used, the amount of Cementitious content (Cement + Fly ash) shall be increased to get good workability and strength.

The percentage of cementitious content to be increased depends on the experience and research. Here we have increased the cementitious content by 10%.

Final Cementitious Content (Cement + Fly ash)

= 356×1.10

= 391.6 kg

Minimum Cement Content required for severe exposure = 340 kg (Table 5- IS 456)

Adopted Cementious content = 391.6 kg > 320 kg

Fly ash content required = 391.6 × 0.30 (30% replacement)

= 117.48 ~ 118 kg

Cement content required = Cementious content - fly ash

= 391.6 - 117.48

= 274.12

So, Cementious material required = 391.6 kg/m^3

Cement required = 274.12 kg/m^3

Fly ash required = 118 kg/m^3

Water/Cement ratio = 0.45

Step 7: Volume of Coarse Aggregate and Fine Aggregate Content

From table 3 of IS 10262: 2009, Volume of coarse aggregate corresponding to 20mm size aggregate (Zone 2) for water-cement ratio of 0.5 = 0.62

In the present case, water cement ratio is 0.45.

Coarse aggregate ratio for 0.45 W/C ratio,

= 0.62 + 0.01

= 0.63

(Adding 0.01 for every decrease and 0.05 and vice versa)

Final Fine aggregate ratio = 1- 0.63

= 0.37

Therefore,

Volume of Coarse aggregate ratio = 0.549

Volume of Fine aggregate ratio = 0.451

Step 8: Mix Calculations

The mix calculations as per unit volume of concrete shall be as follows:

1. A) Volume of Concrete = 1m^3
2. B) Volume of Cement = mass of cement/specific gravity of cement × 1/1000 = (275/3.15) × 1/1000

= 0.087 cu.m

2. C) Volume of Fly Ash = mass of fly ash/ specific gravity of fly ash × 1/1000 = (118/2.5) × 1/1000

= 0.041 cu.m

1. D) Volume of water = mass of water/specific gravity of water × 1/1000 = (160/1) × 1/1000

= 0.160 cu.m

1. E) Volume of Chemical Admixture = Mass of admixture/specific gravity of admixture × 1/1000

= (2.35/1.12) × 1/1000

= 0.002 cu.m

1. F) Volume of aggregate (fine and coarse aggregate) = [A- (B+C+D+E)]

= [1 (0.087+0.041+0.160+0.002)]

= 0.71 cu.m

1. G) Mas of Coarse aggregate = F × Volume of Coarse aggregate× Specific gravity of coarse aggregate × 1000

= 0.71 × 0.63 × 2.74 × 1000

= 1225.6 kg/m^3

1. H) Mass of fine aggregate = F × Volume of fine aggregate × specific gravity of fine aggregate × 1000

= 0.71 × 0.37 × 2.74 × 1000

= 719.8 kg/m^3

Step 9: Mix Proportions

Sr. No	Materials	Quantity
1	Cement	275 kg/m3
2	Fly Ash	118 kg/m3
3	Water	158 kg/m3 or Liter/ m3
4	Fine Aggregate	720 kg/m3
5	Coarse Aggregate	1226 kg/m3
6	Chemical Admixture	2 kg/m3
7	W/C ratio	0.45

To find the design mix ratio, divide the calculated value of all materials by the weight of cement.

Therefore, Mix Ratio of M35 Grade concrete by weight

= Cement: Fly ash: F.A: C.A: Water

= 1: 0.4: 2.6: 4.46: 0.58

Note:

The slump shall be measured, the water content and dosage of admixture shall be adjusted for achieving the required slumps on trial, the mix proportion shall be reworked for the actual water content and checked for durability requirements.

Two more trails 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 proportion for the given for field trails.

PART 2: TO CALCULATE THE CONCRETE MIX DESIGN FOR M50 GRADE CONCRETE WITHOUT FLY ASH

Step 1: Stipulations for Concrete Mix Design

• Grade of designation: M50
• Type of cement: OPC 53 grade conforming to IS 8112
• Maximum Nominal size of aggregate: 20mm
• Minimum Cement content: 320 kg/cu.m (from table 5 of IS 456:2000 Exposure condition)
• Maximum W/C ratio: 45 (table 5 of IS 456:2000)
• Workability: 100 mm
• Exposure Condition : Severe(For Reinforced concrete)
• Method of Concrete placing : Pumping
• Degree of supervision : Good
• Type of aggregate : Crushed Angular Aggregates
• Maximum Cement Content : 450 kg/cu.m
• Chemical admixture type : Super plasticizer

Step 2: Test Data for Materials

• Cement used: OPC 53 conforming to IS 8112
• Specific gravity of cement: 15 (test - IS 2720)
• Chemical admixture: Super plasticizer conforming to IS 9103
• Specific gravity of Coarse aggregate: 74
• The specific gravity of fine aggregate: 74
• Water absorption (Test IS 2386):
• for Coarse aggregate: 5%
• for Fine aggregate: 0%
• Free Surface moisture of coarse aggregate: Nil
• Free surface moisture of fine aggregate: Nil
• Sieve analysis for Coarse aggregate: conforming to table 2 IS 383
• Sieve analysis for Fine aggregate: conforming to grading Zone 2 of table 4 - IS 383

Step 3: Target Strength for Mix Proportioning

F'ck = fck + 1.65 × S

Where,

F'ck = Target average compressive strength at 28 days

fck = Characteristics Compressive strength at 28 days

S = Standard deviation

From table 1 of IS 10262:2009, Standard deviation, S = 5N/mm^2

Therefore, Target Strength = 50+ (1.65×5)

= 58.25 N/mm^2

Target mean strength = 58.25 N/mm^2

Step 4: Selection of Water-Cement Ratio

The maximum water-cement ratio to design M50 grade concrete can be found from

Table 5 of IS 456:2000 for sever exposure, W/C ratio = 0.45,

Based on experience, adopted W/C ratio = 0.44

0.44 > 0.45 hence, Ok

Adopted W/C ratio = 0.44

Step 5: Selection of Water Content

From table 2 of IS 10262:2009, maximum water content for 20mm aggregate

= 186 litres (for 25mm to 50mm slump range)

Clause 4.2 suggests increasing 3% of water content for every extra 25mm slump

For 50mm slump, we have to add 6% to it

= 186 + (6/100) × 186

= 197 litre.

(If super plasticizer is used, the water content can be reduced upto 20% and above)

Based on trails with super plasticizer water content reduction of 20% has been achieved,

Hence the arrived water content = 197× 0.8

= 158 litres

Water Required = 158 litres

Step 6: Calculation of Cement Required

Adopted W/C ratio = 0.44

Cement Content = 158/0.44

= 359 kg/cu.m

From table 5 of IS 456, minimum cement content for severe exposure conditions = 320 kg/cu.m

359 kg/cu.m > 320 kg/cu.m, hence ok

Cement required = 359 kg/cu.m

Step 7: Volume of Coarse Aggregate And Fine Aggregate

From table 3 of IS 10262:2009, Volume of coarse aggregate corresponding to 20mm size aggregate and fine aggregate (Zone 2) for water-cement ratio of 0.5 = 0.62

In the present case, W/C ratio = 0.44.

Therefore, the volume of coarse aggregate is required to be increased to decrease the fine aggregate content. As the water-cement ratio is lower by 0.06.

The proportion of volume of coarse aggregate is increased by 0.02 (at the rate of +/- 0.01 for every +/- 0.05 change in W/C ratio)

Therefore, Corrected proportion of volume of coarse aggregate for the water-cement ratio of 0.44 = 0.632

For pumpable concrete, these values should be reduced upto 10%.

Therefore, Volume of coarse aggregate

= 0.632 × 0.9

= 0.568

Volume of fine aggregate ratio = 1 - 0.568 = 0.432

Volume of coarse aggregate ratio = 0.568

Volume of fine aggregate ratio = 0.432

Step 8: Mix Calculations

The mix calculations per unit volume of concrete shall be as follows :

1. A) Volume of concrete = 1 cu.m
2. B) Volume of cement = mass of cement/specific gravity of cement × 1/1000

= 359/3.15 × 1/1000

= 0.114 cu.m

1. C) Volume of water = mass of water/specific gravity of water × 1/1000

= 158/1 × 1/1000

= 0.158 cu.m

1. D) Volume of Chemical Admixture = Mass of admixture/Specific gravity of admixture × 1/1000

= 7.6/1.145 × 1/1000

= 0.006 cu.m

1. E) Total Volume of aggregate (fine aggregate and Coarse aggregate)

= [A - (B+C+D)]

= [1- (0.114 + 0.158 + 0.006)]

= 0.722 cu.m

1. F) Mass of Coarse aggregate = E × Volume of coarse aggregate × Specific gravity of Coarse aggregate× 1000

= 0.722 × 0.568 × 2.74× 1000

= 1123 kg/cu.m

1. G) Mass of Fine aggregate = E × Volume of fine aggregate × Specific gravity of fine aggregate × 1000

= 0.722 × 0.431 × 2.74 ×1000

= 821 kg/cu.m

Step 9: Mix Proportion

Sr. No	Materials	Quantity
1	Cement	359 kg/m3
2	Water	158 kg/m3
3	Fine Aggregate	821 kg/m3
4	Coarse Aggregate	1123 kg/m3
5	Chemical Admixture	7.18 kg/m3
6	W/C ratio	0.44

Therefore, the mix ratio for the M50 grade of concrete by weight

= Cement : F.A : C.A : water

= 1 : 2.28 : 3.12 : 0.44

Mix Proportion by Weight = 1 : 2.28 : 3.12 : 0.44

Note:

The slump shall be measured, the water content and dosage of admixture shall be adjusted for achieving the required slumps on trial, the mix proportion shall be reworked for the actual water content and checked for durability requirements.

Two more trails 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 proportion for the given for field trails.

Result:

From both concrete mix designs, we got to know that all the concrete ingredients required to make concrete of required grade give desired properties as required in both plastic and hardened state of concrete. The concrete mix design ratios for M35 and M50 are as follows

• Mix Proportion by weight of M35 Grade Concrete with Fly ash:

Cement: Fly Ash: Fine Aggregate: Coarse Aggregate = 1:0.4:2.6:4.46

• Mix Proportion by weight of M50 Grade Concrete without Fly ash:

Cement: Fine Aggregate: Coarse Aggregate = 1:2.28:3.12