Project on Concrete Mix Design for various grades of Concrete

AIM- Concrete mix design for M35 grade concrete with fly-ash.

INTRODUCTION- Design mix of concrete is done to attain the required strength, durability to resist the exposure condition, and workability when it is fresh, in an economical way. Any mix above the M25 grade of concrete is designed mix to sustain the minimum desired compressive load, exposure condition and scope of work.

All the properties of ingredients are checked and observed during the concrete mix design. Each ingredient of mix is properly scrutinized for the appropriate properties of the ingredients required for the mix. Design mix follows the weight batching system, attains desired strength as well as economical. Maximum water/cement ratio to attain adequet durability. Maximum Cement content to avoid shrinkage. Quantity of material used is rational it's neither overused nor underused. It is based on laboratory trial/error method. Admixtures can be used rationally to modify the properties of concrete. It is based on actual available material to be used in construction work. Locally available material can satisfy the standard criteria and can be used for making concrete mix design, and cost can be reduced.

Following guidelines are followed for Design Mix Concrete:-

1. IS method- Concrete mix proportioning guidelines (Bureau of Indian Standards IS- 10262-2009)& (IS- 456-2000), and Recommended guidelines for Concrete Mix Design IS - 10262-1982.
2. British Standard method- BS EN 206-1 and its complimentary standards BS 8500 part 1&2
3. ACI method- American Standard 211, 211-91, reapproved -2002

Required material properties of Concrete mix design for following materials:-

1. Cement-

• Grade of cement
• Consistency of cement
• Initial & Final setting time
• Specific gravity

2. Aggregate-

• Density of aggregate
• Bulking of aggregate
• Specific Gravity
• Fineness modulus
• Water absorption
• Silt content
• Unit weight
• Particle size

Procedure-

Stipulation for proportioning-

1. Grade designation : M35
2. Type of cement : OPC 43 grade conforming to IS 8112
3. Type of mineral admixture : Fly ash conforming to IS 3812 (Part 1)
4. Maximum nominal size of aggregate : 20 mm
5. Mininmum cement content: 320 kg/m^3 (from table 5 of IS 456:2000- Exposure condition)
6. Maximum water-cement ratio : 0.45 (from table 5 of IS 456:2000- Exposure condition)
7. Workability: 100 mm (slump value for pumpable concrete)
8. Exposure condition: Severe (for RCC)
9. Method of concrete placing : Pumping
10. Degree of supervision : Good
11. Type of aggregate : Crushed angular aggregate
12. Maximum cement content : 450 Kg/m^3
13. Chemical admixture type: Superplasticizer

Test Data for materials:

1. Cement used : OPC 43 grade confotming to IS 8112
2. Specific gravity of cement : 3.15
3. Fly ash : conforming to IS 3812 (Part 1)
4. Specific gravity of fly ash : 2.2
5. Chemical admixture : superplasticizer conforming to IS 9103
6. Specific gravity of: Coarse aggregate= 2.74, fine aggregate 2.74
7. Water absorption: Coarse aggregate= 0.5%, fine aggregate= 1%
8. Free surface moisture: Coarse aggregate: Nil , fine aggregate: Nil

Target strength for mix proportioning

step 1- Target mean strength of concrete.

f'ck = fck +1.65 S

[f'ck = Target mean compressive strength after 28 days in N/mm^2.

fck = characteristic compressive strength after 28 days in N/mm^2.

S=standard deviation, in N/mm^2 (table 2 IS 10262:2019)]

f'ck = 35 + 1.65*5 = 43.25 N/mm^2

Step 2- Selection W/C ratio from table 5 IS 456:2000 for severe condition

Max. w/c ratio = 0.45, adopt 0.40

Step 3- Selection of water content from table 4 IS 10262:2019

maximum water content for 20 mm aggregate = 186 litre

for slump value of 100 mm

maximum water content = 186 + 6%*186 = 197.16 , say 197 litre

As superplasticizers is used water content can be reduced to 20% - 30%.

Reduce water content 25%.

now water content = 197*0.75 = 147.75 say 148 litre.

Step 4- calculation of cement content

W= 148 litre

w/c = 0.40

(Cement+ Fly ash) content = 148/0.40 = 370 kg/m^3 > 320 Kg/m^3, hence OK. (from IS 456:2000 table 5 )(severe exposure condition)

Proportioning of fly ash and cement

Cementitious material = 370 Kg/m^3

Add 10% = 370*1.10 = 407 Kg/m^3

Water content = 148 Kg/m^3

Water/ Cement ratio = 0.36

Fly-ash @30% total cementitious material content = 407* 30% = 122 Kg/m^3

Cement (OPC) = 407-122 = 285 Kg/m^3

Saving of cement while using fly-ash = 85 Kg/m^3

Step 5 - Proportion of volume of coarse aggregate and fine aggregate.

from table 3 IS 10262:2009 volume of coarse aggregate corresponding to 20 mm size coarse aggregate and fine aggregate(zone I) for water/cement ratio 0.50= 0.60

in this case w/c = 0.40

so now, volume of coarse aggregate needs to be increased to decrease fine aggregate content.

Corrected volume of coarse aggregate for water cement ratio of 0.40 = 0.62

for pumpable concrete these values can be reduced by 10%

so volume of coarse aggregate= 0.62*0.90 = 0.558, say 0.56

so now volume of fine aggregate = 1 - 0.56 = 0.44

Step 6- Mix calculation

a) Volume of concrete 1m^3

b) Volume of cement = (285/3.15)*(1/1000) = 0.09 m^3

c) Volume of Fly-ash = (122/2.20)*(1/1000) = 0.055 m^3

d) volume of water = (148/1)*(1/1000) = 0.148 m^3

e) Volume of chemical admixture = 2%of cementious material/specific gravity * 1/1000

= (7.4/1.145)*1/1000

= 0.006 m^3

f) Volume of aggregate (CA &FA) = a-(b+c+d+e)

= 0.70m^3

g) Mass of coarse aggregate = 0.70*0.56*2.74*1000 = 1074 kg/m^3

h) Mass of fine aggregate = 0.70*0.44*2.74*1000 = 844 Kg/m^3

RESULT

Mix proportion for trial :

Cement = 285 kg/m^3

Fly-ash = 122 Kg/m^3

Water = 148 kg/m^3

Fine agg. = 844 kg/m^3

Coarse agg. = 1074 kg/m^3

Admixture = 7.4 kg/m^3

W/C = 0.36

Trial Mix ratio (1: 2.07 : 2.64)

Two or more trials has to be done with 10% variation in water cement ratio, durability requirements should be fulfilled.

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2.

AIM- Concrete mix design for M50 grade concrete.

INTRODUCTION- Design mix of concrete is done to attain the required strength, durability to resist the exposure condition, and workability when it is fresh, in an economical way. Any mix above the M25 grade of concrete is designed mix to sustain the minimum desired compressive load, exposure condition and scope of work.

All the properties of ingredients are checked and observed during the concrete mix design. Each ingredient of mix is properly scrutinized for the appropriate properties of the ingredients required for the mix. Design mix follows the weight batching system, attains desired strength as well as economical. Maximum water/cement ratio to attain adequet durability. Maximum Cement content to avoid shrinkage. Quantity of material used is rational it's neither overused nor underused. It is based on laboratory trial/error method. Admixtures can be used rationally to modify the properties of concrete. It is based on actual available material to be used in construction work. Locally available material can satisfy the standard criteria and can be used for making concrete mix design, and cost can be reduced.

Following guidelines are followed for Design Mix Concrete:-

1. IS method- Concrete mix proportioning guidelines (Bureau of Indian Standards IS- 10262-2009)& (IS- 456-2000), and Recommended guidelines for Concrete Mix Design IS - 10262-1982.
2. British Standard method- BS EN 206-1 and its complimentary standards BS 8500 part 1&2
3. ACI method- American Standard 211, 211-91, reapproved -2002

Required material properties of Concrete mix design for following materials:-

1. Cement-

• Grade of cement
• Consistency of cement
• Initial & Final setting time
• Specific gravity

2. Aggregate-

• Density of aggregate
• Bulking of aggregate
• Specific Gravity
• Fineness modulus
• Water absorption
• Silt content
• Unit weight
• Particle size

Procedure-

Stipulation for proportioning-

1. Grade designation : M50
2. Type of cement : OPC 43 grade conforming to IS 8112
3. Maximum nominal size of aggregate : 20 mm
4. Mininmum cement content: 320 kg/m^3 (from table 5 of IS 456:2000- Exposure condition)
5. Maximum water-cement ratio : 0.45 (from table 5 of IS 456:2000- Exposure condition)
6. Workability: 100 mm (slump value for pumpable concrete)
7. Exposure condition: Severe (for RCC)
8. Method of concrete placing : Pumping
9. Degree of supervision : Good
10. Type of aggregate : Crushed angular aggregate
11. Maximum cement content : 450 Kg/m^3
12. Chemical admixture type: Superplasticizer

Test Data for materials:

1. Cement used : OPC 43 grade confotming to IS 8112
2. Specific gravity of cement : 3.15
3. Specific gravity of fly ash : 2.2
4. Chemical admixture : superplasticizer conforming to IS 9103
5. Specific gravity of: Coarse aggregate= 2.74, fine aggregate 2.74
6. Water absorption: Coarse aggregate= 0.5%, fine aggregate= 1%
7. Free surface moisture: Coarse aggregate: Nil , fine aggregate: Nil

Target strength for mix proportioning

step 1- Target mean strength of concrete.

f'ck = fck +1.65 S

[f'ck = Target mean compressive strength after 28 days in N/mm^2.

fck = characteristic compressive strength after 28 days in N/mm^2.

S=standard deviation, in N/mm^2 (table 2 IS 10262:2019)]

f'ck = 50 + 1.65*5 = 58.25 N/mm^2

Step 2- Selection W/C ratio from table 5 IS 456:2000 for severe condition

Max. w/c ratio = 0.45, adopt 0.33 (From graph 1 IS 10262:2019)

Step 3- Selection of water content from table 4 IS 10262:2019

maximum water content for 20 mm aggregate = 186 litre

for slump value of 100 mm

maximum water content = 186 + 6%*186 = 197.16 , say 197 litre

As superplasticizers is used water content can be reduced to 20% - 30%.

Reduce water content 28%.

now water content = 197*0.72 = 141.84 say 142 litre.

Step 4- calculation of cement content

W= 142 litre

w/c = 0.33

Cement content = 142/0.33 = 430 kg/m^3 > 320 Kg/m^3, hence OK. (from IS 456:2000 table 5 )(severe exposure condition)

Step 5 - Proportion of volume of coarse aggregate and fine aggregate.

from table 3 IS 10262:2009 volume of coarse aggregate corresponding to 20 mm size coarse aggregate and fine aggregate(zone I) for water/cement ratio 0.50= 0.60

in this case w/c = 0.33

so now, volume of coarse aggregate needs to be increased to decrease fine aggregate content.

Corrected volume of coarse aggregate for water cement ratio of 0.33 = 0.63

for pumpable concrete these values can be reduced by 10%

so volume of coarse aggregate= 0.63*0.90 = 0.57

so now volume of fine aggregate = 1 - 0.56 = 0.43

Step 6- Mix calculation

a) Volume of concrete 1m^3

b) Volume of cement = (430/3.15)*(1/1000) = 0.137m^3

c) volume of water = (142/1)*(1/1000) = 0.142 m^3

d) Volume of chemical admixture = 2%of cementious material/specific gravity * 1/1000

= (7.4/1.145)*1/1000

= 0.006 m^3

e) Volume of aggregate (CA &FA) = a-(b+c+d)

= 0.715 m^3

f) Mass of coarse aggregate = 0.715*0.57*2.74*1000 = 1116 kg/m^3

g) Mass of fine aggregate = 0.715*0.43*2.74*1000 = 842 Kg/m^3

RESULT

Mix proportion for trial :

Cement = 430 kg/m^3

Water = 142 kg/m^3

Fine agg. = 842 kg/m^3

Coarse agg. = 1116 kg/m^3

Admixture = 7.4 kg/m^3

W/C = 0.33

Trial Mix ratio (1: 1.96 : 2.60)

Two or more trials has to be done with 10% variation in water cement ratio, durability requirements should be fulfilled.