Project on Concrete Mix Design for various grades of Concrete

PROJECT – 1

Aim:- To calculate the concrete mix design for M₃₅ grade concrete with fly ash & M₅₀ grade concrete without fly ash

Introduction:-

Concrete mix design is the method of finding the precise proportion of cement, sand, and aggregates for concrete to achieve the target strength in structures, therefore concrete mix design can be stated as concrete mix in terms of cement: sand: aggregates. The design is done according to the requirements of concrete strength. So, we can achieve the desirable properties of concrete either it is in fresh stage or in hardened stage. The fresh concrete properties like workability, setting time and hardened concrete properties like compressive strength, durability etc. are attained surely by this method. Use of additives like admixtures, retarders etc. Other than basic ingredients are used to improve the properties of mix. This project consists of two parts, the first part deals with the design of M₃₅ grade cement with fly ash as a part of it and second part is the design of M₅₀ grade concrete without fly ash.

Fly ash or pulverized fuel ash is finely divided powder thrown out as a waste material at the thermal power plants using pulverized coal for raising steam in the boilers. In the building industry, the use of fly ash a part replacement of cement in mortar and concrete.

Objective:-

The objective of this project is to produce a mix design for M₃₅ grade concrete containing with fly ash and M₅₀ grade concrete. The mix will be preparing as per Indian Standard method. Concrete mix proportion guidelines from IS 10262: 2009.

M₃₅ grade concrete with fly ash

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 conforming to IS 3812 ( part 1 )
4. Maximum nominal size of aggregate : 20 mm
5. Minimum cement content : 320 kg/m³
6. Maximum water-cement-ratio : 45
7. Workability : 100 mm ( slump )
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 (opc) content : 450 kg/m³
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 : 15
3. Fly ash : confirming to IS 3812 (part 1)
4. Specific gravity of fly ash : 2
5. Chemical admixture : Superplasticizer confirming to IS 9103
6. Specific gravity of:

• Coarse aggregate : 74
• Fine aggregate : 74

1. Water absorption:

• Coarse aggregate : 5 %
• Fine aggregate : 0%

1. Free (surface) moisture:

• Coarse aggregate : Nill
• Fine aggregate : Nill

I ) Sieve analysis:

• Coarse aggregate : conforming to Table 2 of IS 383
• Fine aggregate : confirming to grading zone1 of Table 4

Of IS 383

Step-3:- TARGET STRENGTH FOR MIX PROPORTIONING

f’ _ck = f _ck + 1.65 s

Where ,

f‘ _ck = target average compressive strength at 28 days,

f _ck = characteristics compressive strength at 28 days, and

s = standard deviation.

From Table 1, Standard deviation, s = 5 N/mm².

Therefore, target strength = 35 + 1.65* 5 = 43.25 N/mm².

Step-4:- SELECTION OF WATER-CEMENT RATIO

From Table 5 of IS 456, maximum water-cement ratio = 0.45

Based on experience, adopt w/c ratio as 0.42

0.42 < 0.45, hence ok.

Step-5:- SELECTION OF WATER CONTENT

From Table 2, Maximum water content

For 20 mm aggregate = 186 litre ( for 25 or 50 mm slump range )

Clause 4.2 suggests increasing of 3% of water content for every extra 25 mm slump from 50 mm slump. So 6% is to be added to it.

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

Note:- As superplasticizer is used, the water content can be reduced up to 30%.

Based on trials with superplasticizer water content reduction of 25 % has been achieved. Hence, the arrived water content = 197*0.75 = 147 litres

Water required = 147 litres.

Step-6:- CALCULATION OF CEMENT AND FLY ASH CONTENT

Water-cement ratio = 0.42

Cementitious material ( cement + fly ash ) content = 147/0.42

(Water content/ water-cement ratio) = 350 kg/m³

From Table 5 of IS 456, minimum cement

Content for ‘ severe ‘ exposure conditions = 320 kg/m³

350 kg/m³ > 320 kg/m³ ,

Hence, ok.

The cementitious material content has to be increased in order to attain good workability and strength. The increment required is determined on the basis of experience and research. Here we are increasing cementitious content by 10%.

Cementitious material content = 350*1.10 = 385 kg/m³

Water content = 147 kg/m³

So, w/c ratio = 147/385

= 0.38

Fly ash @ 30% of total cementitious material content = 385*0.3

= 115 kg/m³

Cement (OPC) = 385-115 = 270 kg/m³

Saving of cement while using fly ash = 350-270 = 80 kg/m³, and

Fly ash being utilized = 115 kg/m³

Cementitious material, cement and fly ash required is 385 kg/m³, 270 kg/m³ and 115 kg/m³ and the new water-cement ratio is 0.38 respectively.

Step-7:- PROPORTION OF VOLUME OF COARSE AGGREGATE AND FINE AGGREGATE

From Table 3, volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (zone-1) for w/c ratio of 0.50 = 0.60.

In the present case water-cement ratio is 0.42. Therefore, 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 volume of coarse aggregate is increased by 0.02 ( at the rate of -/+ 0.01 for every _+ 0.05 change in water-cement ratio ).

Therefore, corrected proportion of volume of coarse aggregate for the water-cement ratio of 0.42 = 0.62

For pumpable concrete these values should be reduced by 10%.

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

Volume of fine aggregate content = 1- 0.56 = 0.44

Step-8:- MIX CALCULATIONS

1. Volume of concrete = 1 m³
2. Volume of cement = [ Mass of cement/ Specific gravity of

Cement] * 1/1000

= (270/3.15)*1/1000 = 0.086 m³

1. Volume of fly ash = [ Mass of fly ash/Specific gravity of fly

Ash]*1/1000

= (115/2.2)*1/1000 = 0.052 m³

1. Volume of water = [ Mass of water/Specific gravity of

Water]*1/1000

= 147/1*1/1000 = 0.147 m³

1. Volume of chemical admixture = [Mass of admixture/Specific gravity of

Admixture]*1/1000

= [7.6/1.145]*1/1000 = 0.006 m³

1. Volume of all in aggregate = [a-( b+c+d+e )]

= [1-(0.086+0.052+0.147+0.006)]

= 0.709 m³

1. Mass of coarse aggregate = f*volume of coarse aggregate*Specific

Gravity of coarse aggregate*1000

= 0.709*0.56*2.74*1000

= 1087 kg

1. Mass of fine aggregate = f*volume of fine aggregate*Specific

Gravity of fine aggregate*1000

= 0.709*0.44*2.74*1000

= 854 kg

Step-9:- MIX PROPORTIONS

Cement = 270 kg/m³

Fly ash = 115 kg/m³

Water = 147 kg/m³

Fine aggregate = 854 kg/m³

Coarse aggregate = 1087 kg/m³

Chemical admixture = 7.6 kg/m³

Water-cement ratio = 0.38

Trial mix ratio (C:F.A:C.A) = 270:854:1087

Mix proportion by weight = 1:3.16:4.02

Step-10:- The slump shall be measured and the water content and dosage of admixture shall be adjusted for achieving the required slump based on trial, if required. The mix proportions shall be reworked for the actual water content and checked for durability requirements.

Step-11:- Two more trials having variation of _+ 10% of water-cement ratio in step-10 shall be carried out and a graph between three water-cement ratios and their corresponding strengths shall be plotted to work out the mix proportions for the given target strength for field trials. However, durability requirement shall be met.

PART-2

Aim:- To calculate the concrete mix design for M₅₀ grade concrete without fly ash .

M₅₀ grade concrete without fly ash

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 aggregate : 20 mm
4. Minimum cement content : 320 kg/m³
5. Maximum water-cement-ratio : 45
6. Workability : 100 mm ( slump )
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 (opc) content : 450 kg/m³
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 : 15
3. Chemical admixture : Superplasticizer confirming to IS 9103
4. Specific gravity of:

1)Coarse aggregate : 2.74

2) Fine aggregate : 2.74

1. Water absorption:

1)Coarse aggregate : 0.5 %

2) Fine aggregate : 1.0%

1. Free (surface) moisture:

1)Coarse aggregate : Nill

2) Fine aggregate : Nill

I ) Sieve analysis:

1)Coarse aggregate : conforming to Table 2 of IS 383

2)Fine aggregate : confirming to grading zone1 of Table 4

Of IS 383

Step-3:- TARGET STRENGTH FOR MIX PROPORTIONING

f’ _ck = f _ck + 1.65 s

Where ,

f‘ _ck = target average compressive strength at 28 days,

f _ck = characteristics compressive strength at 28 days, and

s = standard deviation.

From Table 1, Standard deviation, s = 5 N/mm².

Therefore, target strength = 50 + 1.65* 5 = 58.25 N/mm²

Step-4:- SELECTION OF WATER-CEMENT RATIO

From Table 5 of IS 456, maximum water-cement ratio = 0.45

Based on experience, adopt w/c ratio as 0.42

0.42 < 0.45, hence ok.

Step-5:- SELECTION OF WATER CONTENT

From Table 2, Maximum water content

For 20 mm aggregate = 186 litre ( for 25 or 50 mm slump range )

Clause 4.2 suggests increasing of 3% of water content for every extra 25 mm slump from 50 mm slump. So 6% is to be added to it.

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

Note:- As superplasticizer is used, the water content can be reduced up to 20% and above.

Based on trials with superplasticizer water content reduction of 25 % has been achieved. Hence, the arrived water content = 197*0.75= 147 litres

Water required = 147 litres.

Step-6:- CALCULATION OF CEMENT AND FLY ASH CONTENT

Water-cement ratio = 0.42

cement content = 147/0.42

(Water content/ water-cement ratio) = 350 kg/m³

From Table 5 of IS 456, minimum cement

Content for ‘ severe ‘ exposure conditions = 320 kg/m³

350 kg/m³ > 320 kg/m³ ,

Hence, ok.

Cement required = 350 kg/m³

Step-7:- PROPORTION OF VOLUME OF COARSE AGGREGATE AND FINE AGGREGATE

From Table 3, volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (zone-1) for w/c ratio of 0.50 = 0.60.

In the present case water-cement ratio is 0.42. Therefore, 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 volume of coarse aggregate is increased by 0.02 ( at the rate of -/+ 0.01 for every _+ 0.05 change in water-cement ratio ).

Therefore, corrected proportion of volume of coarse aggregate for the water-cement ratio of 0.42 = 0.62

For pumpable concrete these values should be reduced by 10%.

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

Volume of fine aggregate content = 1- 0.56 = 0.44

Step-8:- MIX CALCULATIONS

1. Volume of concrete = 1 m³

1. Volume of cement = [ Mass of cement/ Specific gravity of

Cement] * 1/1000

= [350/3.15]*1/1000 = 0.111 m³

1. Volume of water = [ Mass of water/Specific gravity of

Water]*1/1000

= 147/1*1/1000 = 0.147 m³

1. Volume of chemical admixture = [Mass of admixture/Specific gravity of

Admixture]*1/1000

= [7.6/1.145]*1/1000 = 0.006 m³

1. Volume of all in aggregate = [a-( b+c+d )]

= [1-(0.111+0.147+0.006)]

= 0.736 m³

1. Mass of coarse aggregate = e*volume of coarse aggregate*Specific

Gravity of coarse aggregate*1000

= 0.736*0.56*2.74*1000

= 1129 kg

1. Mass of fine aggregate = e*volume of fine aggregate*Specific

Gravity of fine aggregate*1000

= 887 kg

Step-9:- MIX PROPORTIONS

Cement = 350 kg/m³

Water = 147 kg/m³

Fine aggregate = 887 kg/m³

Coarse aggregate = 1129 kg/m³

Chemical admixture = 7.6 kg/m³

Water-cement ratio = 0.42

Trial mix ratio (C:F.A:C.A) = 350:887:1129

Mix proportion by weight = 1:2.53:3.22

Step-10:- The slump shall be measured and the water content and dosage of admixture shall be adjusted for achieving the required slump based on trial, if required. The mix proportions shall be reworked for the actual water content and checked for durability requirements.

Step-11:- Two more trials having variation of _+ 10% of water-cement ratio in step-10 shall be carried out and a graph between three water-cement ratios and their corresponding strengths shall be plotted to work out the mix proportions for the given target strength for field trials. However, durability requirement shall be met.