Project on Concrete Mix Design for various grades of Concrete

Q) Calculate the Concrete Mix Design for M35 grade concrete with fly ash & M50 grade concrete without Fly ash ?

Ans: AIM: To calculate the Concrete Mix Design for M35 grade concrete with fly ash & M50 grade concrete without fly ash.

INTRODUCTION:

Concrete is a very complex material. It's properties as fresh as well hardened concrete is a function of right mix of constituents of concrete, which if not done properly and will have adverse effect on the properties of concrete. Hence right proportion of all the constituents is more important. Concrete Mix Design is therefore scientific and systematic process of choosing economical relative proportion of various ingredients from available material which gives cohessive concrete of desired workability in fresh state and after that desired strength and durability in hardened state. So, it is step by step procedure for selection of water-cement ratio, water content and estimation of coarse aggregate content and fine aggregate content done in a laboratory with actual material which is going to be used. The process of selecting suitable ingredients for producing concrete of required strength, durability and workability as economical as possible is known as Concrete Mix Design.

OBJECTIVES:

• The objective of concrete mix design is to achieve the predetermined minimum strength and durability in most economical manner. The cost of concrete mainly depends on the two main factors that is the cost of material and cost of labour. Therefore, it is very important to keep in mind the cost of materials for concrete mix design and produce concrete as economically as possible.
• The objective of this project is to produce a mix design for M35 grade concrete containing fly ash and M50 grade concrete. The mix will be prepared as per IS method: Concrete mix proportioning guidelines from IS 10262:2009 and recommended guidelines from IS 10262:1982.

EQUATIONS: The values are listed down which needs to be follow for calculating the concrete mix design

(1)Target Mean Strength : This is calculated by using the formula f'ck = fck + 1.65 s

where, f'ck is the target mean strength of concrete

fck is the characteristic compressive strength at 28 days

S is the standard deviation that can be obtained from IS 10262:2009 , table-1

(2)Cement content : This is calculated by using the formula Cement content = water content / water-cement ratio

(3)Volume Calculations :

• (a)Volume of concrete = 1 m^3
• (b)Volume of cement = Mass of cement / Specific gravity of cement * 1 / 1000
• (c)Volume of water = Mass of water / Specific gravity of water * 1 / 1000
• (d)Volume of chemical admixtures = Mass of chemical admixture / Specific gravity of chemical admixture * 1 / 1000
• (e)Volume of total aggregate (Fine aggregate + Coarse aggregate) in the cement = Volume of concrete - (Volume of cement + Volume of water + Volume of chemical admixture + Volume of fly ash) = [a-(b+c+d)]
• (f)Volume of fly ash = Mass of fly ash / Specific gravity of fly ash * 1 / 1000
• (g)Mass of coarse aggregate = Volume of total aggregate * Volume of coarse aggregate * Specific gravity of coarse aggregate * 1000
• (h)Mass of fine aggregate = Volume of total aggregate * Volume of fine aggregate * Specific gravity of fine aggregate * 1000

CODES USED FOR CONCRETE MIX DESIGN:

1. IS 456:2000
2. IS 10262:2009
3. IS 3812 (PART 1)
4. IS 8112
5. IS 9103

PROCEDURE AND CALCULATION:

PART 1 : To calculate the Concrete Mix Design for M35 grade concrete with fly ash:

STEP 1: Stipulations for proportioning : The datas required for calculating the concrete mix design are ;

1. Grade designation : The grade of concrete used here is M35
2. Type of cement : OPC 43 grade conforming to IS 8112. This is the code for 43 grade cement
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/m^3 (From Table 5 of IS 456:2000 - Exposure condition)
6. Maximum water-cement ratio : 0.45 (From Table 5 of IS 456:2000 - Exposure condition)
7. Workability : 100mm (slump value for 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 aggregates
12. Maximum cement content : 450 kg/m^3
13. Chemical admixture type : Super plasticizer

STEP 2: Test data for materials : This is obtained from the manufacturer or vendor of the materials which we are using i.e.,

1. Cement used : OPC 43 Grade conforming to IS 8112
2. Specific gravity of cement : 3.15
3. Chemical admixture : Super plasticizer conforming to IS 9103
4. Specific gravity of fly ash : 2.2
5. Specific gravity of coarse aggregate : 2.74
6. Specific gravity of fine aggregate : 2.74
7. Water absorption of coarse aggregate : 0.5%
8. Water absorption of fine aggregate : 1.0%
9. Free surface moisture of coarse aggregate : Nil (The aggregate should be in dry condition and doesn't use wet condition)
10. Free surface moisture of fine aggregate : Nil
11. Sieve Analysis : Test for coarse aggregate should conforming to Table-2 of IS 383
12. Sieve Analysis : Test for fine aggregate should conforming to Grading of Zone-II of table-4 of IS 383

STEP 3: Target Strength for mix proportioning : This is calculated by using the formula f'ck = fck + 1.65 S

Where,

• f'ck = Target average compressive strength at 28 days
• fck = Characteristic compressive strength at 28 days and
• S = Standard deviation

So, from Table 1 of IS 10262:2009 the standard deviation is calculated for M35 grade concrete as, S = 5 N/mm^2

Target Strength f'ck = 35 + 1.65 * 5

Therefore, f'ck = 43.25 N/mm^2

Target mean strength = 43.25 N/mm^2

STEP 4 : Selection of water-cement ratio : This is obtained from Table-5 of IS 456:2000 and it can be taken depending upon the exposure condition.

The maximum water-cement ratio to design M35 grade concrete with fly ash can be found from Table 5 of IS 456-2000.

Here, Exposure condition : Severe (for reinforced concrete)

So, Maximum water-cement ratio : 0.45

Based on the experience, we have adopted water-cement ratio : 0.44

0.44<0.45, hence OK

Adopted water-cement ratio = 0.44

STEP 5 : Selection of water content : This water content value is also taken up from the Table-2 of IS 10262:2009.

Assume, Nominal size of aggregates = 20 mm

The maximum water content for 20mm aggregate is 186 litres (for 25 mm to 50 mm slump range) for this slump range it is 186 litres.

As per Clause 4.2 suggests increasing of 3% of water content for every extra 25 mm slump from 50 mm slump. So, here i have increased 50 mm slump (25+50) that value 186 is for 25 to 50 mm slump. Here it is 100 mm slump so, i have added 6% to this value.

Hence, Estimated water content = 186 + 6/100 * 186 = 197 litres.

(NOTE: As super plasticizer is used, the water content can be reduced upto 20% and above). Based on the trials with super plasticizer water content reduction of 20% has been achieved. So, the value should be should be 100 - 20 = 80

Hence the arrived water content = 197 * 80/100 = 197 * 0.8 = 158 litres

Therefore, the arrived water content = 158 litres

STEP 6 : Calculation of cementious content (cement + fly ash) :

Water-cement ratio (w-c) = 0.44

Water content (W) = 158 kg

Cementitious content (c) = W/w-c = 158/0.44 = 359 kg/m^3

The value of cementitious content is greater than the table value of 320 kg/m^3 which is from table 5 of IS 456:2000. So, from Severe exposure condition which equals to 320 kg/m^3.We can follow up with 359 kg/m^3 > 320 kg/m^3.Hence O.K

Hence, the new cementitious material content = 359 * 10% of cementitious material content = 359 * 1.10 = 394.9 kg/m^3

New water-cement ratio = 158/394.9 = 0.40

Fly ash content is taken as 30% of the total cementitious content = 0.3 * 394.9 = 118.47 kg/m^3

Cement required = 394.9 - 118.47 = 276.43 kg/m^3

Cement quantity saved using fly ash addition = 394.9 - 276.43 = 118.47 kg/m^3

STEP 7 : Calculation of volume of coarse aggregate and fine aggregate content :

This is calculated from Table 3 of I.S : 10262-2009 that is for 20mm size aggregateand for fine aggregate (zone 1) water cement ratio = 0.6. See in the Table -3 for maximum size of aggregate 20mm for zone 1 it is 0.60

So, in the present case the water-cement ratio whatever we have calculated is 0.40

Therefore, the volume of coarse aggregate needs to be increased since the water-cement ratio for that coarse aggregate is 0.6. We have to increase the coarse aggregate to decrease the fine aggregate content. So, for that the water-cement ratio should be added (that is +- 0.1for every +- 0.05 change in water-cement ratio) has to be added. Hence the value should be 0.632

We have increase the proportion of volume of coarse aggregate by 0.02. Here the corrected volume of coarse aggregate for water-cement ratio of 0.40 = 0.62 and mainly remember that the coarse aggregate is not of angular type, and the volume of coarse aggregate may required to be increased suitably based on the experience.

For pumpable concrete these values should be reduced up to 10%.

Therefore volume of coarse aggregate = 0.632 * 0.9 = 0.568

So, the volume of fine aggregate content = 1-0.568 = 0.431

Volume of Coarse aggregate content and Fine aggregate content is 0.568 and 0.431

STEP 8 : Mix Calculations :

In this calculation we will be finding out the volume of cement, water, fly ash, chemical admixture everything for per unit volume of concrete.

a)Volume of concrete = 1m^3

b)Volume of cement = Mass of cement(cement content)/Specific gravity * 1/1000 = 359/3.15 * 1/1000 = 0.113m^3

c)Volume of water = Mass of water(arrived water content)/Specific gravity of water * 1/1000 = 158/1 * 1/1000 = 0.158m^3

d)Volume of chemical admixture = Mass of chemical admixture/Specific gravity of admixture * 1/1000

Mass of chemical admixture = 2% of cementitious material = 359 * 2 / 100 = 7.18

= 7.18/1.145 * 1/1000 = 0.006m^3

e)Volume of aggregate (F.A & C.A) = (a-(b+c+d) = (1-(0.113 + 0.158 + 0.006) = 1-0.277 = 0.723m^3

f)Mass of Coarse aggregate = e * Volume of Coarse aggregate * Specific gravity of coarse aggregate * 1000 = 0.723 * 0.568 * 2.74 * 1000 = 1125.1 kg/m^3

g)Mass of Fine aggregate = e * Volume of fine aggregate * Specific gravity of fine aggregate * 1000 = 0.723 * 0.431 * 2.74 * 1000 = 747.87 kg/m^3

STEP 9 : RESULTS AND CONCLUSION : Trial Mix

Cement = 359 kg/m^3

Water = 158 litres

Fine aggregate = 747.87 kg/m^3

Coarse aggregate = 1125.1 kg/m^3

Chemical admixture = 7 KG/m^3

water-cement ratio = 0.40 (lowest W/C ratio is selected)

Trial Mix Ratio : 1: 2.08 : 3.13

i.e., Cement : Fine Aggregate : Coarse Aggregate

STEP 10 : Conditions for Concrete Mix Design :

• The slump value which is calculated by slump cone test for the concrete can be water content and dosage of admixture can be adjusted to achieve the required slump on trial that is required for the mix proportion.
• Two or more trials of variation of 10% water-cement ratio should be carried out and their value should be plotted in as per the graph what we have seen in the calculation of water-cement ratio for the given target strength of the concrete. So, the final aim is the durability of the concrete should be met. We should not compromise on the durability. So, this is how to calculate the Concrete Mix Design for M40 grade of concrete.

PART 2 : To calculate the Concrete Mix Design for M50 grade concrete without Fly ash :

STEP 1 : Stipulations for proportioning : The datas required for calculating the concrete mix design are ;

a. Grade of concrete = M50

b. Type of cement = OPC 43 grade conforming to IS 8112

c. Maximum nominal size of aggregate = 20 mm

d. Minimum cement content = 320 kg/m^3 (from Table-5 of I.S 456-2000 depending upon the exposure condition)

e. Workability = 100 mm (slump value for pumpable concrete)

f. Exposure condition = Severe (for reinforced concrete)

g. Method of concrete placing = Pumping

h. Degree of supervision = Good

i. Type of aggregate = Crushed angular aggregate

j. Maximum cement content = 450 kg/m^3

k. Chemical admixture type = Super plasticizer

STEP 2 : Test data for materials : That is required same data

1. Cement used = OPC 43 grade conforming to I.S 8112

2. Specific gravity of cement = 3.15

3. Chemical admixture = Super Plasticizer conforming to I.S 9103

4. Specific gravity of coarse aggregate = 2.74

5. Specific gravity of fine aggregate = 2.64

6. Water absorption value for Coarse aggregate = 0.5%

7. Water absorption value for Fine aggregate = 1.0%

8. Free surface moisture for Coarse aggregate = Nil

9. Free surface moisture for Fine aggregate = Nil

Because both aggregates should be of dry condition.

Sieve Analysis Test: In this values of Coarse Aggregate should conformed to table-2 of I.S 383 and the values of Fine Aggregate should conformed to grading zone 1 of Table 4 of I.S 383 with all these we have arrived at with the data required for concrete mix design.

STEP 3 : Target Strength for Mix Proportioning : That is calculated by using the formula f'ck = fck + 1.65 * S

Where f'ck = Target average compressive strength at 28 days

fck = Characteristic compressive strength at 28 days and

s = Standard deviation for M50 grade from Table-1 of I.S 10262:2009, Standard deviation value S = 5 N/mm^2

f'ck = 50 + 1.65 * 5 = 58.25 N/mm^2

Therefore the calculated Target mean strength = 58.25 N/mm^2

STEP 4 : Selection of Water-Cement ratio : This is calculated from Table-5 of I.S 456:2000 for Severe exposure condition

Maximum Water-Cement ratio = 0.45

But based on experience adopted water-cement ratio = 0.44

So, it can be considered 0.44 < 0.45, Hence OK.

Therefore the adopted water-cement(W/C) ratio = 0.44

STEP 5 : Selection of water-content : This is calculated from Table-2 of I.S 10262:2009, the maximum water content for 20mm aggregate is 186 litres and it is for the slump value of 25 to 50mm slump range.

As per clause 4.2 suggests increasing of 3% of water content for every extra 25mm slump. So a 6% is to be added to it.

So, next is the Estimated water content for 100mm slump and it should be 186 + (6/100) * 186 = 197 litre.

(NOTE : As super plasticizer is used, the water content can be reduced up to 20% and above.)

Achieve the water content reduction of 20%. So, this should be calculated for estimated water content. Hence the arrived water content is equal to we are reducing 20% from the estimated water content = 197 * (100 - 20%) = 197 * 0.8 = 158 litre.

Therefore Water required = 158 litre.

STEP 6 : Calculation of cement required :

Adopted water-cement ratio (w-c) = 0.44

Water content (W) = 158 kg

Cement content = W/w-c = 158/0.44 = 359 kg/m^3

From Table 5 of I.S 456, minimum cement content for "Severe" exposure conditions is 320 kg/m^3. So, as per calculation it is 359 which is greater than 320 (359 kg/m^3 > 320 kg/m^3) for that it should be followed hence OK.

Therefore Cement required = 359 kg/m^3.

STEP 7 : Volume of Coarse aggregate and Fine aggregate content : From Table-3 of I.S 10262:2009, Volume of Coarse aggregate corresponding to 20mm size aggregate and Fine aggregate (Zone II) for water-cement ratio of 0.50 is 0.62.

In the present case water-cement ratio is 0.44. Therefore, volume of coarse aggregate is required to be increased to decrease the fine aggregate content. As the water-cement ratio is lower by 0.06. 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 0.44

For 0.632 the pumpable concrete these values should be reduced up to 10%.

Therefore, volume of coarse aggregate = 0.632 * 0.9 = 0.568

Volume of fine aggregate content = 1 - 0.576 = 0.431.

Volume of Coarse aggregate and Fine aggregate is 0.568 and 0.431 respectively.

STEP 8 : Mix Calculations : The mix calculation per unit volume of concrete shall be as follows:

a) Volume of concrete = 1m^3

b) Volume of cement = (Mass of cement/Specific gravity of cement) * 1/1000 = 359/3.15 * 1/1000 = 0.114m^3.

c) Volume of water = (Mass of water/Specific gravity of water) * 1/1000 = 158/1 * 1/1000 = 0.1158m^3.

d) Volume of chemical admixture = Mass of admixture/Specific gravity of admixture * 1/1000 = 7.6/1.145 * 1/1000 = 0.006m^3.

e) Volume of all in aggregate = [a-(b+c+d)] = [1-(0.114+0.158+0.006)] = 0.722m^3

f) Mass of coarse aqggregate = e * volume of coarse aggregate * specific gravity of coarse aggregate * 1000 = 0.722 * 0.568 * 2.74 * 1000 = 1123 kg/m^3

g) Mass of fine aggregate = e * volume of fine aggregate * specific gravity of fine aggregate * 1000 = 0.722 * 0.431 * 2.64 * 1000 = 821 kg/m^3

STEP 9 : Mix Proportions : From the values that we have to calculate the mix proportions of the ingredients. So, thus we have arrived the mix proportions of the ingredients used for concrete.

1. Cement = 359 kg/m^3
2. Water = 158 kg/m^3
3. Fine aggregate = 821 kg/m^3
4. Coarse aggregate(20mm size) = 1123 kg/m^3
5. Chemical admixture = 7.18 kg/m^3
6. Water-Cement ratio = 0.44 (lowest value is considered)
7. Mix Proportions by weight is the values of trial mix ratio for Cement:Fine aggregate:Coarse aggregate = 1:2.28:3.12

So, this is how we have to calculate the Concrete Mix Design for M50 grade concrete without Fly ash

STEP 10 : Conditions for Concrete Mix Design :

• The slump cone value can be achieved by adjusting the water content and dosage of admixture to the trial mix. So, the mix proportions shall be reworked for the actual water content and checked for durability requirements should be achieved.
• Two or more trials having variation of 10% water-cement ratio and these values shall be plotted in the graph which we have seen to calculate the water-cement ratio that two or more with variation of 10% should be calculated and kept for the given target strength for field test. Even though if you make these charges that durability should be met and it cannot be compromised for under any circumstances. If you compromise on durability then the strength of the structure will not be achieved.

RESULTS :

• Mix proportion by weight of M35 grade of concrete with fly ash is 1:2.08:3.13 and its water-cement ratio was found to be 0.40.
• Mix proportion by weight of M50 grade of concrete without fly ash is 1:2.28:3.12 and its water-cement ratio was found to be 0.44