Project on Concrete Mix Design for various grades of Concrete

(I) CONCRETE MIX DESIGN FOR M35 GRADE CONCRETE WITH FLYASH

AIM:

To calculate the concrete mix design for M35 grade concrete with flyash.

INTRODUCTION:

Concrete is a complex material which is made of mixing ingredients in right proportion. If concrete is not produced in the right mix proportion, it will not have the required properties. So, to know about the right mix proportion, mix design is used and concrete mix design can be defined as the systematic process of choosing the proportion of ingredients of concrete, so as to produce the concrete of desired properties and qualities, in the most economical way as possible.

Flyash is a pozzolana material which can be used for replacing cement in concrete, upto certain percentages. It is a by product from thermal power plants and using flyash in the construction industry can be an effective solution for the disposal of flyash itself and in reducing the rate of natural resources depleted for the production of concrete.

Following are the requirements for concrete mix design;

• Minimum compressive strength as per structural considerations.
• Adequate workability.
• Maximum water-cement ratio to achieve adequate durability.
• Maximum cement content to avoid shrinkage.

As per 10262, mix designation is represented as ratios of cement, fine aggregates, coarse aggregates, in terms of mass or volume. Water-cement ratio is expressed in mass.

Factors affecting mix proportion are as follows;

• Compressive strength.
• Workability.
• Durability.
• Maximum nominal size of aggregate.
• Grading and type of aggregate.
• Quality control.

Factors to be considered for mix proportion are as follows;

• Grade of concrete.
• Type of cement.
• Maximum nominal size of aggregate to be used as according to IS 456: 2000.
• Cement content.

PROCEDURE:

Grade of concrete = M35

Let, Maximum nominal size of aggregate = 20mm

Exposure condition = Severe

Degree of supervision = Good

Method of placing = Pumping

Admixture = Mineral admixture, flyash

(i) Stipulations for proportioning

• Concrete garde = M30
• Maximum nominal size of aggregate = 20mm
• Exposure condition = Severe
• Degree of supervison = Good
• Method of placing = Pumping
• Type of cement = OPC 43 grade confirming to IS 8112
• Type of aggregate = Crushed angular type
• Chemical admixture = Superplasticizer confirming to IS 9103
• Workability slump = 100(slump value for pumpable concrete)

(ii) Test data for materials

Specific gravity of;

• Cement = 3.15
• Fine aggregate = 2.74
• Coarse aggregate = 2.74
• Superplasticizer = 1.145
• Flyash = 2.2

Water absorbtion for;

• Fine aggregate = 1%
• Coarse aggregate = 0.5%

Free surface moisture for;

• Fine aggregate = Nil
• Coarse aggregate = Nil

Sieve analyis;

After sieve analysis, it is determined that fine aggregate confirms to grading zone 1 of table 4 of IS 383-1970.

(iii) Target mean strength for mix proportioning

f'ck = fck + 1.65S

where, f'ck = target average compressive strength at 28 days

fck = characteristics compressive strength at 28 days

S = standard deviation

As per IS 10262-2009 table 1, for M35 grade concrete, S = 5N/mm^2

therefore, f'ck = 35 + (1.65 x 5) = 43.25 N/mm^2

(iv) Selection of water-cement ratio

As per table 5 of IS 456:2000, for M35 grade concrete in severe exposure condition, the maximum w/c ratio is 0.45. Based on experience adopted w/c is 0.40.

(v) Selection of water content

As per table 2 of IS 10262-2009, the maximum water content for 20mm nominal size aggregate with slump 25-50mm range is 186 Kg.

For slump of 100mm, water content = 186 + ((3x2x186)/100) = 197Kg

But since superplasticizer is used, the water content can be reduced upto 30%. From trials, it is determined that, water content is reduced by 29%.

Now, reduced water content = 197 x 0.71 = 140 Kg

(vi) Calculation of cement content

w/c ratio = 0.40

Water content = 140Kg

Therefore, cement content = 140/0.4 = 350Kg/m^3. This is cementitious material.

Here, let us consider 10% increase in cementitious content.

Therefore, amount of cementitious material = 350 x 1.10 = 385 Kg/m^3.

Now, water-cement ratio = 140/385 = 0.364

Flyash at 30% total cementitious content = 0.30 x 385 = 115 Kg/m^3

Therefore, cement (OPC) = 385 - 115 = 270 Kg/m^3

Thus, saving of cement while using flyash = 350 - 270 = 80 Kg/m^3

Flyash being utilized = 115 Kg/m^3

(vii) Proportion of volume of coarse and fine aggregates

From table 3 of IS 10262-2009, volume of coarse aggregate corresponding to 20mm nominal size for zone 1 fine aggregate is 0.60, and this is for a w/c ratio of 0.50. But here, the calculated w/c ratio is 0.40.

Now, on correcting; 0.5-0.4 = 0.1

0.1/0.05= 2

2 x 0.01 = 0.02

Then, corrected volume for coarse aggregate with w/c ratio 0.40 = 0.6 +0.02 = 0.62

Again, for pumpable concrete, these values can be reduced by 10%.

Therefore, volume of coarse aggregate = 0.62 x 0.9 = 0.56

volume of coarse aggregate = 1 - 0.56 = 0.44

(viii) Mix calculation

(a) Volume of concrete = 1m^3

(b) Volume of cement = (Mass of cement/Specific gravity of cement) x (1/1000) = (270/3.15) x (1/1000) = 0.086m^3

(c) Volume of flyash = (Mass of flyash/Specific gravity of flyash) x (1/1000) = (115/2.2) x (1/1000) = 0.052m^3

(d) Volume of water = (Mass of water/Specific gravity of water ) x (1/1000) = (140/1) x (1/1000) = 0.140m^3

(e) Volume of admixture = (Mass of admixture/Specific gravity of admixture) x (1/1000)

Mass of chemical admixture = 2% of cemetitious material = 350 x 2% = 7Kg

Therefore, Volume of admixture = (7/1.145) x (1/1000) = 0.006m^3

(f) Volume of total aggregate = a- (b+c+d+e) = 1 - (0.086+0.052+0.140+0.006) = 0.716m^3

(g) Mass of coarse aggregate = (f) x volume of coarse aggregate x specific gravity x 1000

= 0.716 x 0.56 x 2.74 x 1000 = 1098Kg/m^3

(h) Mass of fine aggregate = (f) x volume of fine aggregate x specific gravity x 1000

= 0.716 x 0.44 x 2.74 x 1000 = 863Kg/m^3

(ix) Mix proportion

• Cement = 270Kg/m^3
• Flyash = 115 Kg/m^3
• Fine aggregate= 863Kg/m^3
• Coarse aggregate= 1098Kg/m^3
• Water= 140Kg/m^3
• Chemical admixture= 7Kg/m^3
• w/c ratio= 0.364

Therefore, mix proportion = 1 : 1.24 : 2.85, for a w/c ratio of 0.364

RESULT:

The calculated mix proportion for M35 grade concrete is 1 : 1.24 : 2.85, for a w/c ratio of 0.364.

(II) CONCRETE MIX DESIGN FOR M50 GRADE CONCRETE

AIM:

To calculate the concrete mix design for M50 grade concrete.

INTRODUCTION:

Concrete is a complex material which is made of mixing ingredients in right proportion. If concrete is not produced in the right mix proportion, it will not have the required properties. So, to know about the right mix proportion, mix design is used and concrete mix design can be defined as the systematic process of choosing the proportion of ingredients of concrete, so as to produce the concrete of desired properties and qualities, in the most economical way as possible.

Following are the requirements for concrete mix design;

• Minimum compressive strength as per structural considerations.
• Adequate workability.
• Maximum water-cement ratio to achieve adequate durability.
• Maximum cement content to avoid shrinkage.

As per 10262, mix designation is represented as ratios of cement, fine aggregates, coarse aggregates, in terms of mass or volume. Water-cement ratio is expressed in mass.

Factors affecting mix proportion are as follows;

• Compressive strength.
• Workability.
• Durability.
• Maximum nominal size of aggregate.
• Grading and type of aggregate.
• Quality control.

Factors to be considered for mix proportion are as follows;

• Grade of concrete.
• Type of cement.
• Maximum nominal size of aggregate to be used as according to IS 456: 2000.
• Cement content.

PROCEDURE:

Let, Maximum nominal size of aggregate = 20mm

Exposure condition = Severe

Degree of supervision = Good

Method of placing = Pumping

(i) Stipulation for proportioning

• Concrete garde = M50
• Maximum nominal size of aggregate = 20mm
• Exposure condition = Severe
• Degree of supervison = Good
• Method of placing = Pumping
• Type of cement = OPC 43 grade confirming to IS 8112
• Type of aggregate = Crushed angular type
• Chemical admixture = Superplasticizer confirming to IS 9103
• Workability slump = 100(slump value for pumpable concrete)

(ii) Test data for materials

Specific gravity of;

• Cement = 3.15
• Fine aggregate = 2.74
• Coarse aggregate = 2.74
• Superplasticizer = 1.145

Water absorbtion for;

• Fine aggregate = 1%
• Coarse aggregate = 0.5%

Free surface moisture for;

• Fine aggregate = Nil
• Coarse aggregate = Nil

Sieve analyis;

After sieve analysis, it is determined that fine aggregate confirms to grading zone 1 of table 4 of IS 383-1970.

(iii) Target mean strength for mix proportioning:

f'ck = fck + 1.65S

where, f'ck = target average compressive strength at 28 days

fck = characteristics compressive strength at 28 days

S = standard deviation

As per IS 10262-2009 table 1, for M50 grade concrete, S = 5N/mm^2

therefore, f'ck = 50 + (1.65 x 5) = 58.25 N/mm^2

(iv) Selection of water-cement ratio

As per table 5 of IS 456:2000, for M50 grade concrete in severe exposure condition, the maximum w/c ratio is 0.45. Based on experience adopted w/c is 0.40.

(v) Selection of water content

As per table 2 of IS 10262-2009, the maximum water content for 20mm nominal size aggregate with slump 25-50mm range is 186 Kg.

For slump of 100mm, water content = 186 + ((3x2x186)/100) = 197Kg

But since superplasticizer is used, the water content can be reduced upto 30%. From trials, it is determined that, water content is reduced by 29%.

Now, reduced water content = 197 x 0.71 = 140 Kg

(vi) Calculation of cement content

w/c ratio = 0.40

Water content = 140Kg

Therefore, cement content = 140/0.4 = 350Kg/m^3, which is greater than the minimum cement content of 320Kg/m^3 for severe exposure condition as per table 5 of IS 456:2000.

(vii) Proportion of volume of coarse and fine aggregates

From table 3 of IS 10262-2009, volume of coarse aggregate corresponding to 20mm nominal size for zone 1 fine aggregate is 0.60, and this is for a w/c ratio of 0.50. But here, the calculated w/c ratio is 0.40.

Now, on correcting; 0.5-0.4 = 0.1

0.1/0.05= 2

2 x 0.01 = 0.02

Then, corrected volume for coarse aggregate with w/c ratio 0.40 = 0.6 +0.02 = 0.62

Again, for pumpable concrete, these values can be reduced by 10%.

Therefore, volume of coarse aggregate = 0.62 x 0.9 = 0.56

volume of coarse aggregate = 1 - 0.56 = 0.44

(viii) Mix calculation

(a) Volume of concrete = 1m^3

(b) Volume of cement = (Mass of cement/Specific gravity of cement) x (1/1000) = (350/3.15) x (1/1000) = 0.111m^3

(c) Volume of water = (Mass of water/Specific gravity of water ) x (1/1000) = (140/1) x (1/1000) = 0.140m^3

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

Mass of chemical admixture = 2% of cemetitious material = 350 x 2% = 7Kg

Therefore, Volume of admixture = (7/1.145) x (1/1000) = 0.006m^3

(e) Volume of total aggregate = a- (b+c+d) = 1 - (0.111+0.140+0.006) = 0.743m^3

(f) Mass of coarse aggregate = (e) x volume of coarse aggregate x specific gravity x 1000

= 0.743 x 0.56 x 2.74 x 1000 = 1140Kg/m^3

(g) Mass of fine aggregate = (e) x volume of fine aggregate x specific gravity x 1000

= 0.743 x 0.44 x 2.74 x 1000 = 896Kg/m^3

(ix) Mix proportion

• Cement = 350Kg/m^3
• Fine aggregate= 896Kg/m^3
• Coarse aggregate= 1140Kg/m^3
• Water= 140Kg/m^3
• Chemical admixture= 7Kg/m^3
• w/c ratio= 0.40

Therefore, mix proportion = 1 : 2.56 : 3.26, for a w/c ratio of 0.40

RESULT:

The calculated mix proportion for M50 grade concrete is 1 : 2.56 : 3.26, for a w/c ratio of 0.40.