Project on Concrete Mix Design for various grades of Concrete

MIX DESIGN FOR M35 GRADE CONCRETE WITH FLY ASH

AIM:

Mix design for M35 grade concrete with fly ash.

INTRODUCTION:

• The mix are designed by the structural engineer and the mix proportions are determined by the concrete procedure.
• These are the requirements for the basis of selection and proportioning of mix ingredients.
• Minimum compressive strength required for structural considerations.
• Adequate workability.
• Maximum water cement ratio to attain adequate durability.
• Maximum cement content to avoid shrinkage.

PROCEDURE:

Step 1:- Stipulations for proportioning

1. grade designation: M35
2. Type of cement: OPC 43 grade conforming 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 IS 456-2000, based on exposure condition)
6. Maximum water-cement ratio: 0.45 (Table 5 IS 456-2000, based on 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 confirming to IS 8112
2. Specific gravity of cement: 3.15
3. Fly ash: Conforming to IS 3812 part 1
4. Specific gravity of flyash: 2.2
5. Chemical admixture: Superplasticizer conforming to IS 9103
6. Specific gravity of: i) Coarse aggregate: 2.74 ii) Fine aggregates: 2.74
7. Water absorption: i) Coarse aggregate: o.5% ii) Fine aggregates: 1%
8. Free surface moisture: i) Coarse aggregate: Nil ii) Fine aggregates: Nil

Step 3:- To find target mean strength for mix proportioning

Target mean strength f'ck = fck + 1.65 s

= 35+1.65*5

= 43.25 N/mm^2

fck= Characteristic compressive strength

s= Standard deviation

Step 4:- Selection of water-cement ratio

Maximum water-cement ratio= 0.5 (for severe condition from table 5 of IS 456-2000)

On experience water-cement ratio= 0.4

0.4<0.45, Hence ok.

Step 5:- Calculation of water content

Maximum water content for 20mm aggregatre = 186 litres ( Table 2 of IS 1026:2009) for 25mm to 50mm slump range

For 100mm slump = 186+ (6/100)*186 = 197 litres

As superplasticizer is used, the water content is reduced upto 30%

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

Hence arrived water content = 197*0.71 = 140 litres

Step 6:- Calculation of cement content

Water-cement ratio = 0.4

Cementatious material (cememt + 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 flyash need to be decided based on project reqirement and quality of materials.
2. In some cases increase in cementatious materials can be warrned. Incerase in cementatious material content and its percentage may be based on experience and trial.

In this 10% increase of cementatiuos material content is considered.

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

water content= 140 kg/m^3

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

Fly ash @ 30% total cementatious material content = 385* 30% = 115kg/m^3

Cement(OPC) = 385-115= 270

Saving of cement while using flyash = 350-270 = 80 kg/m^3

Fly ash being utilized = 115

Step 7:- Proportioning of volume of coarse aggregate and fine aggregate content

From table 3 of IS 1026:2009, volumw of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate(zone 1) for water cement ratio= 0.6

In present case the w/c ratio is 0.4

Therefore the volume of coarse aggregate needs to be increased to decrease the fine aggregate content.

As the w/c ratio is lowered by 0.1 , the proportion of volume of coarse aggregate is increased by 0.02 ( at the rate of +/- 0.0. for every +/- 0.05 change in water-cement ratio)

Hence corrected value of coarse aggregate for the w/c ratio of 0.4 = 0.62

( If coarse aggregate is not of angular type, then also the volume of coarse aggregate may be required to increased suitabily based on experience )

For pumpable concrete, these are reduced by 10%.

Volume of coarse aggregate = 0.64*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 flyash) * 1/1000 =(270/3.15)*1/1000 = 0.086 m^3
3. volume of flyash= (Mass of flyash/specific gravity of flyash)*1/1000 = (115/2.2)*1/1000 = 0.052 m^3
4. volume of water = (Mass of water/specific gravityof water)*1/1000 = (140/1)*1/1000 = 0.140 m^3
5. volume of chemical admixture = (Mass of admixture/specific gravity of admixturer)*1/1000 = = (7.6/1.14)*1/1000 = 0.006 m^3
6. volume of aggregate (Fine & coarse) = a-(b+c+d+e) = 1-(0.086+0.052+0.140+0.006) = 0.716 m^3
7. Mass of coarse aggregate = f* volume of coarse aggregate * specific gravity of coarse aggregate*1000 = 0.716*0.576*2.74*1000 = 1130 kg/m^3
8. Mass of fine aggregate = f* volume of fine aggregate*specific gravity of fine aggregate*1000 = 0.716*0.424*2.74*1000 = 831 kg/m^3

Step 9:- Mix proportion

Cement = 270 kg/m^3

Fly ash = 115 kg/m^3

Water = 140 kg/m^3

Fine aggregate = 831 kg/m^3

Coarse aggregate = 1130 kg/m^3

Chemical admixture = 7 kg/m^3

Water cement ratio = 0.364

MIX RATIO 1: 2.15 : 2.94

Step 10:-

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

Step 11:-

Two or more trials having variation of 10% of w/c ratio in step 10 shall be carried out and a graph between three w/c ratios and corresponding strength shall be plotted to work out the mix proportions for the given target strength for field trials. However durability shall be met.

Result:-

The design mix for M35 grade of concrete with fly ash is 1 : 2.15 : 2.94

MIX DESIGN FOR M50 GRADE CONCRETE

AIM:

Mix design for M50 grade concrete

PROCEDURE:

Step 1:- Stipulations for proportioning

1. grade designation: M50
2. Type of cement: OPC 43 grade conforming to IS 8112
3. Maximum nominal size of aggregates: 20mm
4. Minimum cement content: 320 kg/m^3 (Table 5 IS 456-2000, based on exposure condition)
5. Maximum water-cement ratio: 0.45 (Table 5 IS 456-2000, based on 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 confirming to IS 8112
2. Specific gravity of cement:3.15
3. Chemical admixture: Superplasticizer conforming to IS 9103
4. Specific gravity of: i) Coarse aggregate: 2.74 ii) Fine aggregates: 2.74
5. Water absorption: i) Coarse aggregate: o.5% ii) Fine aggregates: 1%
6. Free surface moisture: i) Coarse aggregate: Nil ii) Fine aggregates: Nil

Step 3:- To find target mean strength for mix proportioning

Target mean strength f'ck = fck + 1.65 s

= 50+1.65*5

= 58.25 N/mm^2

fck= Characteristic compressive strength

s= Standard deviation

Step 4:- Selection of water-cement ratio

Maximum water-cement ratio= 0.5 (for severe condition from table 5 of IS 456-2000)

On experience water-cement ratio= 0.4

0.4<0.45, Hence ok.

Step 5:- Calculation of water content

Maximum water content for 20mm aggregatre = 186 litres ( Table 2 of IS 1026:2009) for 25mm to 50mm slump range

For 100mm slump = 186+ (6/100)*186 = 197 litres

As superplasticizer is used, the water content is reduced upto 30%

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

Hence arrived water content = 197*0.71 = 140 litres

Step 6:- Calculation of cement content

Water-cement ratio = 0.4

Cement content = 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:- Proportioning of volume of coarse aggregate and fine aggregate content

From table 3 of IS 1026:2009, volumw of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate(zone 1) for water cement ratio= 0.6

In present case the w/c ratio is 0.4

Therefore the volume of coarse aggregate needs to be increased to decrease the fine aggregate content.

As the w/c ratio is lowered by 0.1 , the proportion of volume of coarse aggregate is increased by 0.02 ( at the rate of +/- 0.0. for every +/- 0.05 change in water-cement ratio)

Hence corrected value of coarse aggregate for the w/c ratio of 0.4 = 0.62

( If coarse aggregate is not of angular type, then also the volume of coarse aggregate may be required to increased suitabily based on experience )

For pumpable concrete, these are reduced by 10%.

Volume of coarse aggregate = 0.64*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 flyash) * 1/1000 =(350/3.15)*1/1000 = 0.111 m^3
3. volume of water = (Mass of water/specific gravityof water)*1/1000 = (140/1)*1/1000 = 0.140 m^3
4. volume of chemical admixture = (Mass of admixture/specific gravity of admixturer)*1/1000 = = (7.6/1.14)*1/1000 = 0.006 m^3
5. volume of aggregate (Fine & coarse) = a-(b+c+d+e) = 1-(0.111+0.052+0.140+0.006) = 0.743 m^3
6. Mass of coarse aggregate = f* volume of coarse aggregate * specific gravity of coarse aggregate*1000 = 0.743*0.576*2.74*1000 = 1173 kg/m^3
7. Mass of fine aggregate = f* volume of fine aggregate*specific gravity of fine aggregate*1000 = 0.743*0.424*2.74*1000 = 863 kg/m^3

Step 9:- Mix proportion

Cement = 350 kg/m^3

Water = 140 kg/m^3

Fine aggregate = 863 kg/m^3

Coarse aggregate = 1173 kg/m^3

Chemical admixture = 7 kg/m^3

Water cement ratio = 0.4

MIX RATIO 1: 2.46 : 3.35

Step 10:-

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

Step 11:-

Two or more trials having variation of 10% of w/c ratio in step 10 shall be carried out and a graph between three w/c ratios and corresponding strength shall be plotted to work out the mix proportions for the given target strength for field trials. However durability shall be met.

Result:-

The design mix for M35 grade of concrete is 1 : 2.46 : 3.35

Tables used as per IS code:-

1. Table 8 of IS 10262

Grade	standard deviation(s) N/mm^2
M10	3.5
M15	3.5
M20	4
M25	4
M30	5
M35	5
M40	5
M45	5
M50	5

2.Table 5 of IS 456:2000 Based on exposure condition

S.no	Exposure	Min cement content (kg/m^3)	Max. w/c ratio	Min. grade of concrete	Min cement content (kg/m^3)	Max free w/c ratio	Min. grade of concrete
1.	Mild	220	0.6	-	300	0.55	M20
2.	Moderate	240	0.6	M15	300	0.5	M25
3.	Severe	250	0.5	M20	320	0.45	M30
4.	Very severe	260	0.45	M20	340	0.45	M35
5.	Extreme	280	0.4	M25	360	0.4	M40

3. Table 2 of IS 10262:2009

S.no	Nominal max. size of aggragate (mm)	Maximum water content(kg)
1.	10	208
2.	20	186
3.	40	165

4.Table 3 of IS 1026:2009

S.no	Nominal max size of aggregate	zone iv	zone iii	zone ii	zone i
1.	10	0.5	0.48	0.46	0.44
2.	20	0.66	0.64	0.62	0.6
3.	40	0.75	0.73	0.71	0.69