Project on Concrete Mix Design for various grades of Concrete

AIM:

To determine the mix design for M35 grade of concrete with fly ash.

OBJECTIVES:

• 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 environment conditions.
• To produce concrete as economically as possible.

Introduction:

Data for the mix design of M35 grade of concrete

- Grade of cement = 35 N/mm^2

- Maximum size of aggregates = 20 mm

- Type of aggregates = cruhed angular aggregates

- Slump workability = 100 mm

- Degree of supervision = Good

- Exposure condition = Severe (for Reinforced concrete)

- Method of concrete placing = Pumping

- Maximum cement content = As per 456: 2000

- Chemical admixture = superplastizers- Normal

- Zone of aggregates = Zone lll

- Type of mineral admixture = Fly ash ( IS 3812; part-1)

Test Data for Materials:

- Cement = OPC 53 N/mm^2

- Specific gravity of

* Cement = 3.15

* Coarse aggregate = 2.74

* Fine aggregate = 2.65 As per IS code

* Chemical admixture = 1.145 (super plastizer)

* Fly ash = 2.2

- Water Absorption

* Coarse aggregate = 0.87

* Fine aggregate = 1.26

- Moisture Content

* Coarse aggregate = 2.15%

* Fine aggregate = 4.68%

Procedure:

1.Target Mean Strength:

f_t= f_ck + 1.65 x S

Where,

‘f_t‘ is the target average compressive strength at 28 days,

‘f_ck‘ is the characteristic compressive strength at 28 days, and

‘s’ is the standard deviation

As per the table I of IS: 10262-2009 , standard deviation, s = 5.0 N/mm²

Therefore, target strength = 35 + 1.65 x 5.0 = 43.25 N/mm^2

2. Water Cement Ratio:

From Table 5 of IS 456: 2000

Maximum water-cement ratio = 0.433

3. Maximum water content:

From Table 2 of IS 456, maximum water content = 186 litre (for 25 to 50 mm slump range) for 20 mm aggregate.

Estimated water content for 100 mm slump =186+(6/100) x 186 =197 liter.

(Note: If Super plasticizer is used, the water content can be reduced upto 20% to 30%.)

Hence the arrived water content = 197-[ 30% of 197 ] = 132 litre

4. Cement Content:

Water-cement ratio =0.4

Cement content = 132/0.4 = 330 kg/m³

From Table 5 of IS 456, minimum cement content for exposure condition = 320 Kg/m^3

330 kg/m³ > 320 kg/m³, hence, O.K.

5. Fly Ash Content:

Considering 10% increase in the cementious material

Thus, Cementious content = 330*1.1= 363 Kg/m^3

Fly ash = 30% of total cementious material = 363*0.3= 109 Kg/m^3.

6. Proportion of volume of coarse aggregate and fine aggregates:

From Table 3 of IS 10262, volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate for a water-cement ratio of 0.50 = 0.62.

In the present case, the water-cement ratio is 0.4. Therefore, the volume of coarse aggregate is required to be increased to reduce the fine aggregate content.

As the water-cement ratio is lower by 0.10, the proportion of the volume of coarse aggregate is increased by 0.02 (at the rate of -/+ 0.01 for every ± 0.05 change in the water-cement ratio). Therefore. the corrected proportion of the volume of coarse aggregate for the water-cement ratio of 0.4 = 0.62.

For pumpable concrete, these values should be reduced by 10 percent.

Therefore, volume of coarse aggregate = 0.62 x 0.9 = 0.558.

Volume of fine aggregate content =1 – 0.558 = 0.442.

7. Mix Calculations:

a) Volume of concrete = 1 m^3

b) Volume of cement = (Mass of cement/Specific Gravity of Cement) X (1/1000)

= (330/3.12) X (1/1000)

= 0.105 m^3

c) Volume of water = (Mass of water/specific gravity of water) X (1/1000)

= (132/1) X (1/1000)

= 0.132 m^3

d) Volume of Fly ash = (Mass of fly ash / Specific gravity of admixture) X (1/1000)

= (109/2.2) X (1/1000)

= 0.049 m³

e) Volume of all aggregate = (a-(b+c+d))

= 1 – (0.105+0.132+0.049)

= 0.714 m³

f) Mass of coarse aggregate = Volume of all aggregate X volume of coarse aggregate X Specific gravity of coarse aggregate X 1000

= 0.714 x 0.558 x 2.74 x 1000

= 1091.64 kg

g)Mass of fine aggregate = Volume of all aggregate X volume of fine aggregate X Specific gravity of fine aggregate X 1000

= 0.714 x 0.442 x 2.56 x 1000

= 807.90 kg

Result:

• Cement = 350 kg/m³
• Water = 147 kg/m³
• Super plasticizer = 7 kg/m³
• Fine aggregates = 814.73 kg/m³
• Coarse aggregate = 1141.88 kg/m³
• W/c = 0.45

Mix proportion by weight is = 1:2.08:2.72

8. 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 actual water content and checked for durability requirements.

9. Two more trials having variatrions of 10% of w/c ratio in clause 8 shall be carried out and a graph b/w three w/c ratios and corresponding strengths shall be ploted to work out the mix proportions for the given target strength for field trials. However, durability should be met.

Conclusion:

The slump should be measured and the water content and admixture can be adjusted to obtain the required slump. The mix proportion can be adjusted as per requirment.

AIM:

To determine the mix design of M50 grade of concrete without fly ash.

OBJECTIVES:

• 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 environment conditions.
• To produce concrete as economically as possible.

Procedure:

Data for Mix design of M50 grade of concrete

- Grade of cement = 50 N/mm^2

- Maximum size of aggregates = 20 mm

- Type of aggregates = cruhed angular aggregates

- Slump workability = 100 mm

- Degree of supervision = Good

- Exposure condition = moderate

- Method of concrete placing = Pumping

- Maximum cement content = 360 Kg/cum As per 456: 2000

- Chemical admixture = super plasticizers- Normal

- Minimum water-cement ratio = 0.45 (As per table 5 of IS 456: 2000)

Test Data for Materials:

Cement = OPC 43 N/mm^2

- Specific gravity of

* Cement = 3.15

* Coarse aggregate = 2.74

* Fine aggregate = 2.65 As per IS code

* Chemical admixture = 1.145 (super plasticizer)

- Water Absorption

* Coarse aggregate = 0.87

* Fine aggregate = 1.26

Procedure:

1. Target Mean Strength:

Target Mean Strength f'ck = fck + 1.65s

Considering s= 5 N/mm^2 ( Table 1 of IS 10262: 2009)

Thus, f'ck= 50+1.65(5)

= 58.25 N/mm^2

2. Water Cement Ratio:

Considering maximum water cement ratio = 0.40 from table 2 of IS 456: 2000

3. Water content:

From Table 2 of IS 456, maximum water content =186 litres (for 25 to 50 mm slump range) for 20 mm aggregate.

Estimated water content for 100 mm slump =186+(6/100) x 186 =197 litres.

(Note: If Super plasticizer is used, the water content can be reduced up to 20% to 30%.)

Hence the arrived water content = 197 – [197 x (30/100)] = 140 litres.

4.Cement Content:

Water cement ratio = 0.4

Cement content = 140/0.4= 350 Kg/cum.

minimum cement content for moderate exposure = 320 kg/cum ( table 5 of IS 456: 2000)

350 kg/cum> 320 cum,

Hence, O.K.

5. Proportion of volume of coarse aggregte and fine aggregate:

From Table 3 of Is 10262: 2009. volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate for a water-cement ratio of 0.50 =0.62.

In the present case, the water-cement ratio is 0.35. 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 0.10. the proportion of the volume of coarse aggregate is increased by 0.02 (at the rate of -/+ 0.01 for every ± 0.05 change in the water-cement ratio).

Therefore. the corrected proportion of the volume of coarse aggregate for the water-cement ratio of 0.4 = 0.62

For pumpable concrete, these values should be reduced by 10 percent.

Therefore, volume of coarse aggregate = 0.65 x 0.9 = 0.56

Volume of fine aggregate content =1 – 0.56= 0.44.

6.Mix Calculations:

a) Volume of concrete = 1m³

b) Volume of cement = (Mass of Cement/ Specific Gravity of cement ) X (1/1000)

= (350/3.12) X (1/1000)

= 0.111 cum.

c) Volume of Water = (Mass of water/specific gravity of water) X (1/1000)

= (140/1) X (1/1000)

= 0.14 cum.

d) Volume of Superplasticizer = (Mass of Superplasticizer / Specific gravity of admixture) X (1/1000)

= (7.6/1.145) X (1/1000)

= 0.006 cum

e) Volume of all aggregate = (a – (b + c + d))

= 1 – (0.111 + 0.14+0.006)

= 0.743 cum.

e) Mass of coarse aggregate = Volume of All Aggregate X Volume of Coarse Aggregate X Specific Gravity of Coarse Aggregate X 1000

= 0.743 x 0.56 x 2.74 x 1000

= 1140 kg

f) Mass of fine aggregate = Volume of all aggregate X volume of fine aggregate X Specific gravity of fine aggregate X 1000

= 0.743 x 0.44 x 2.74 x 1000

= 896 kg.

Result:

Mix proportion obtained:

• Cement = 350 kg/cum
• Water = 140 kg/cum
• Fine aggregates = 896 kg/cum
• Coarse aggregate = 1140 kg/cum
• W/c = 0.4
• Chemical admixture= 7 Kg/cum.

Mix proportion by weight is = 1:2.56:3.26

7. 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 actual water content and checked for durability requirements.

8. Two more trials having variatrions of 10% of w/c ratio in clause 8 shall be carried out and a graph b/w three w/c ratios and corresponding strengths shall be ploted to work out the mix proportions for the given target strength for field trials. However, durability should be met.

Conclusion:

The slump should be measured and the water content and admixture can be adjusted to obtain the required slump. The mix proportion can be adjusted as per requirment.