Project on Concrete Mix Design for various grades of Concrete

PROJECT ON CONCRETE MIX DESIGN FOR VARIOUS GRADES OF CONCRETE

INTRODUCTION: To design a concrete mix of M35 grade with the addition of fly ash to meet the requirements of strength and durability.

MIX DESIGN FOR M35 GRADE CONCRTE WITH FLY ASH

AIM: Mix design for M35 grade concrete with fly ash.

PROCEDURE:

Step 1: Stipulations for proportioning:-

1. Grade designation: M35
2. Type of cement: OPC 43 confirming to IS 8112
3. Type of mineral admixture: Fly ash confirming to IS 3812 (Part 1)
4. Maximum nominal size of aggregates: 20mm
5. Minimum cement content: 320 kg/m^3 (Table 5 of IS 456 - 2000, for exposure condition)
6. Maximum water - cement ratio: 0.45 (Table 5 of IS 456 - 2000, for exposure condition)
7. Workability: 100mm slump value of pumpable concrete
8. Exposure condition: Severe (for reinforced concrete)
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

Step 2: Test data for materials:-

1. Cement used: OPC 43 grade conforming 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
7. Specific gravity of fine aggregate: 2.74
8. Water absorption of coarse aggregate: 0.5%
9. Water absorption of fine aggregate: 1%
10. Free surface moisture of coarse aggregate:NIL
11. Free surface moisture of coarse aggregate: NIL
12. Sieve analysis:

Coarse aggregate : Confirming to Table 2 of IS 383

Fine aggregate: Confirming to grading zone 1 of table 4 IS 383.

Step 3: Calculation of target mean strength for mix proportioning:-

The strength of concrete may deviate based on the quality of the material, method of mixing and construction practices. Hence target mean strength(f'ck) should be higher than the required strength of the concrete(fck). The value of standard deviation (s) for different grades of concrete is given in Table 1 of IS 456.

Standard deviation for M35 grade of concrete is 5.0N/mm^2

Target mean strength f'ck = fck + 1.65s

= 35 + 1.6 x 5

= 43.25 N/mm^2

fck = characteristic compressive strength

s = standard deviation

Step 4: Selection of water - cement ratio:-

The maximum water - cement ratio for different grades of concrete is given in Table 5 of IS 456. You can reduce the water cement ratio based on your requirements.

Maximum water cement ratio = 0.45 (for severe condition from table 5 of IS 456 - 2000)

Adopted water - cement ratio = 0.40 (on experience based)

0.4<0.45 hence, ok.

Step 5: Calculation of water content:-

Maximum water content for 20mm aggregate = 186 litres (Table 2 of IS 10262:2009) for 25mm to 50mm slump value.

So we need to increase the water - content to get the required slump value. clause 4.2 of IS 10262 suggests to increase 3% of water content to get an extra 25mm slump. Hence we increase water content by 6% to get the additional 50mm slump for our concrete.

For 100mm slump = 186 + (0.06 x 186) = 197.16lts

Since we are using superplasticizers water content can be reduced upto 30%

Based on trials water content reduction of 29% is achieved with superplasticizers

Hence arrived water content = 197.16 x 0.71 = 140 lts

Step 6: Calculation of cement content:-

Water cement ratio = 0.4

Cementatious material(cement+flyash) = 140/0.4 = 350 kg/m^3

in table 5 of IS 456 - 2000, the cement content for severe exposure = 320 kg/m^3

350 kg/m^3 > 320 kg/m^3 hence, ok.

To proportion the mix containing flyash the following steps are suggested:

1. The percentage of fly ash need to be decided based on project requirement and quality of materials.
2. In some cases increase in cementatious materials can be warned. increase in cementatious material content and its percentage may be based on the experience and trial.

In this increase of 10% cementatious material is considered.

Cementatious material content = 350 x 1.1 = 385 kg/m^3

Water content = 140 kg/m^3

so water cement ratio = 140/385 = 0.364

Fly ash at 30% total cementatious material content = 35 - 30% = 115 kg/m^3

cement (OPC) = 385-115=270 kg/m^3

saving of cement while using fly ash = 350-270 = 80 kg/m^3

fly ash being utilized = 115 kg/m^3

Step 7: Proportion of 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 1) for water cement ratio = 0.6

In present case the water cement ratio = 0.4

.'. 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 water cement 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)

for pumpable concrete, these are reduced by 10%

volume of coarse aggregate = 0.64 x 0.9 = 0.576

volume of fine aggregate = 1 - 0.576 = 0.424

Step 8: Mix calculations:-

Mix calculation per unit volume of concrete:

1. Volume of concrete = 1m^3

2. Volume of cement = (mass of cement/ specific gravity of cement) x 1/1000

= (270/3015) x 1/1000

= 0.086m^3

3. Volume of fly ash = (mass of fly ash/ specific gravity of fly ash) x 1/1000

= (115/2.2) x 1/1000

= 0.052m^3

4. Volume of water = (mass of water/specific gravity of water) x 1/1000

= (140/1) x 1/1000

= 0.140m^3

5. Volume of chemical admixture = (mass of admixture/specific gravity of admixture) x 1/1000

= (7.6/1.14) x 1/1000

= 0.006m^3

6. Volume of aggregate (Fine and Coarse) = 1-(2+3+4+5)

= 1-(0.0086+0.052+0.140+0.006) = 0.716m^3

7. Mass of coarse aggregate = 6 x volume of coarse aggregate x specific gravity of coarse aggregate x 1000

= 0.716 x 0.576 x 2.74 x 1000

= 1130 kg/m^3

8. Mass of fine aggregate = 6 x volume of fine aggregate x specific gravity of fine aggregate x 1000

= 0.716 x 0.424 x 2.74 x 1000

= 831 kg/m^3

Step 9: Mix proportion:-

1. Cement = 270 kg/m^3

2. Fly ash = 115 kg/m^3

3. Water = 140 kg/m^3

4. Fine aggregate = 831 kg/m^3

5. Coarse aggregate = 1130 kg/m^3

6. Chemical admixture = 7 kg/m^3

7. Water cement ratio = 0.364

MIX PROPORTION = 1:2.15:2.94

Step 10:-

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

Step 11:-

Two more trials having variation of 10% of water cement ratio in clause x shall be carried out and a graph between three water cement ratios and corresponding strengths shall be plotted as work out the mix proportions for the given target strength for field trials. however, durability shall be met.

RESULT:

The mix design for M35 grade concrete with flyash for trial 1 is 1:2.15:2.94

INTRODUCTION: To design a concrete mix of M50 grade to meet the requirements of strength and durability.

MIX DESIGN FOR M50 GRADE CONCRTE

AIM: Mix design for M50 grade concrete.

PROCEDURE:

Step 1: Stipulations for proportioning:-

1. Grade designation: M50
2. Type of cement: OPC 43 grade confirming to IS 8112
3. Maximum nominal size of aggregates: 20mm
4. Minimum cement content: 320 kg/m^3 (Table 5 of IS 456 - 2000, for exposure condition)
5. Maximum water - cement ratio: 0.45 (Table 5 of IS 456 - 2000, for exposure condition)
6. Workability: 100mm slump value of pumpable concrete
7. Exposure condition: Severe (for reinforced concrete)
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

Step 2: Test data for materials:-

1. Cement used: OPC 43 grade conforming to IS 8112
2. Specific gravity of cement: 3.15
3. Chemical admixture: Superplasticizer conforming to IS 9103
4. Specific gravity of coarse aggregate: 2.74
5. Specific gravity of fine aggregate: 2.74
6. Water absorption of coarse aggregate: 0.5%
7. Water absorption of fine aggregate: 1%
8. Free surface moisture of coarse aggregate:NIL
9. Free surface moisture of coarse aggregate: NIL
10. Sieve analysis:

Coarse aggregate : Confirming to Table 2 of IS 383

Fine aggregate: Confirming to grading zone 1 of table 4 IS 383.

Step 3: Calculation of target mean strength for mix proportioning:-

The strength of concrete may deviate based on the quality of the material, method of mixing and construction practices. Hence target mean strength(f'ck) should be higher than the required strength of the concrete(fck). The value of standard deviation (s) for different grades of concrete is given in Table 1 of IS 456.

Standard deviation for M35 grade of concrete is 5.0N/mm^2

Target mean strength f'ck = fck + 1.65s

= 50 + 1.6 x 5

= 58.25 N/mm^2

fck = characteristic compressive strength

s = standard deviation

Step 4: Selection of water - cement ratio:-

The maximum water - cement ratio for different grades of concrete is given in Table 5 of IS 456. You can reduce the water cement ratio based on your requirements.

Maximum water cement ratio = 0.45 (for severe condition from table 5 of IS 456 - 2000)

Adopted water - cement ratio = 0.40 (on experience based)

0.4<0.45 hence, ok.

Step 5: Calculation of water content:-

Maximum water content for 20mm aggregate = 186 litres (Table 2 of IS 10262:2009) for 25mm to 50mm slump value.

So we need to increase the water - content to get the required slump value. clause 4.2 of IS 10262 suggests to increase 3% of water content to get an extra 25mm slump. Hence we increase water content by 6% to get the additional 50mm slump for our concrete.

For 100mm slump = 186 + (0.06 x 186) = 197.16lts

Since we are using superplasticizers water content can be reduced upto 30%

Based on trials water content reduction of 29% is achieved with superplasticizers

Hence arrived water content = 197.16 x 0.71 = 140 lts

Step 6: Calculation of cement content:-

Water cement ratio = 0.4

Cementatious material(cement+flyash) = 140/0.4 = 350 kg/m^3

in table 5 of IS 456 - 2000, the cement content for severe exposure = 320 kg/m^3

350 kg/m^3 > 320 kg/m^3 hence, ok.

Step 7: Proportion of 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 1) for water cement ratio = 0.6

In present case the water cement ratio = 0.4

.'. 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 water cement 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)

for pumpable concrete, these are reduced by 10%

volume of coarse aggregate = 0.64 x 0.9 = 0.576

volume of fine aggregate = 1 - 0.576 = 0.424

Step 8: Mix calculations:-

Mix calculation per unit volume of concrete:

1. Volume of concrete = 1m^3

2. Volume of cement = (mass of cement/ specific gravity of cement) x 1/1000

= (350/3015) x 1/1000

= 0.111m^3

3. Volume of water = (mass of water/specific gravity of water) x 1/1000

= (140/1) x 1/1000

= 0.140m^3

4. Volume of chemical admixture = (mass of admixture/specific gravity of admixture) x 1/1000

= (7.6/1.14) x 1/1000

= 0.006m^3

5. Volume of aggregate (Fine and Coarse) = 1-(2+3+4)

= 1-(0.111+0.140+0.006) = 0.743m^3

6. Mass of coarse aggregate = 5 x volume of coarse aggregate x specific gravity of coarse aggregate x 1000

= 0.743 x 0.576 x 2.74 x 1000

= 1173 kg/m^3

7. Mass of fine aggregate = 5 x volume of fine aggregate x specific gravity of fine aggregate x 1000

= 0.743x 0.424 x 2.74 x 1000

= 863 kg/m^3

Step 9: Mix proportion:-

1. Cement = 350 kg/m^3

2. Water = 140 kg/m^3

3. Fine aggregate = 863 kg/m^3

4. Coarse aggregate = 1173 kg/m^3

5. Chemical admixture = 7 kg/m^3

6. Water cement ratio = 0.4

MIX PROPORTION = 1:2.46:3.35

Step 10:-

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

Step 11:-

Two more trials having variation of 10% of water cement ratio in clause x shall be carried out and a graph between three water cement ratios and corresponding strengths shall be plotted as work out the mix proportions for the given target strength for field trials. however, durability shall be met.

RESULT:

The mix design for M35 grade concrete with flyash for trial 1 is 1:2.46:3.35

TABLES USED: