Project on Concrete Mix Design for various grades of Concrete

CONCRETE MIX DESIGN CALCULATION

AIM:

Aim of this project is to determine the concrete mix design for M35 grade concrete with fly-ash & M50 grade concrete without fly-ash.

INTRODUCTION:

Concrete is a complex material and has the right mix of constituents of concrete, which if not done properly and will have adverse effect on the properties of concrete. There are three types of concrete mixes among this design mix is the mostly reliable one since it can be done using skilled persons. Design mix is widely used for more extensive and important concrete works. Indian code books IS 456-2000 and IS 10262-2009 are required to achieve a design mix. Nominal and standard mix can be used for concrete with undemanding performance may be used only for very small jobs when the strength of concrete does not exceed 30 N/mm^2.

PROCEDURE:

Data:

Type of cement = OPC 33 grade conforming to IS 8112

Exposure condition = moderate

Concrete type = reinforced concrete

Consider workability = 100 mm

Nominal minimum size of aggregate = 20 mm

Consider aggregate in zone-1

Method of concrete placing = pumping

Degree of supervision = good

Type of aggregate = crushed angular aggregate

Chemical admixture type = superplasticizer

Specific gravity of cement = 3.15

Specific gravity of coarse aggregate = 2.74

Specific gravity of fine aggregate = 2.74

Specific gravity of chemical admixture = 1.145

Procedure for M35 grade concrete with fly-ash:

consider fly-ash is used as mineral admixture with a specific gravity = 2.2

• Target mean strength of concrete (fck’):

fck’ = fck + 1.65S

where, fck = characteristics compressive strength at 28 days

S = Standard deviation

Target mean strength of M35 grade of concrete:

fck’ = 35 + (1.65*5)

= 43.25 N/mm^2

• Selection of water cement ratio:

1. Using graph-1:

Using graph water cement ratio corresponding to fck’ = 43.25 N/mm^2,

w/c = 0.35

2. Using graph-2:

Using graph water cement ratio corresponding to fck’ = 43.25 N/mm^2,

w/c = 0.40

3. Using table-5 of IS-456:2000:

Using table for moderate exposure, max w/c = 0.50

Using 1, 2, 3, min w/c is taken for calculation, w/c = 0.35

• Selection of water content:

From table-2 of IS 10262:2009, water content is found

Using table water content for 20 mm nominal size of aggregate = 186 kg = 186 litres

This table is applicable for slump value between 25 and 50 mm, for additional slump 3% may be added for every 25 mm slump

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

As superplasticizer is used, the water content can be reduced up to 30% and above

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

Hence, water content = 197*0.71 = 140 litres

• Selection of cement content:

Cement content (cement + fly-ash) = water content / (w/c)

Cement content (cement + fly-ash) = 140/0.35 = 400 kg/m^3

Since fly-ash is used,

1. The percentage of fly-ash needs to be decided based on project requirement and quality of materials
2. In some cases, increase in cementitious material can be warranted, increase in cementitious material content and its percentage may be based on experience and trail (here it is with increase of 10% cementitious material content)

Cementitious material content = 400*1.1 = 440 kg/m^3

Water content = 140 kg/m^3

Water cement ratio = 0.318

Fly ash @ 30% total cementitious material content = 440*0.3 = 132 kg/m^3

Cement (OPC) = 440-132 = 308 kg/m^3

Saving of cement while using fly-ash = 400-308 = 92 kg/m^3

Fly ash being utilized = 132 kg/m^3

• Volume of coarse aggregate & fine aggregate content:

Using table-3 of IS 10262:2009, volume of coarse aggregate per unit volume of total aggregate for different zones of fine aggregate is found

Volume of coarse aggregate per unit volume of total aggregate (e)= 0.60

In the present case the water cement ratio = 0.35

So, the volume of coarse aggregate needs to be increased to decrease the fine aggregate content, the proportion of volume of coarse aggregate is increased at the rate of -/+ 0.01 for every -/+ 0.05 change in water cement ratio

Therefore, corrected volume of coarse aggregate for the water-cement ratio of 0.35 = 0.63

For pumpable concrete these values are reduced by 10%

Therefore, volume of coarse aggregate = 0.63*0.9 = 0.567

Volume of fine aggregate = 1-0.567 = 0.433

• Mix calculation:

1. Volume of concrete = 1 m^3
2. Volume of cement = (mass of cement/specific gravity of cement) * (1/1000)

= (308/3.15) * (1/1000)

= 0.097 m^3

3. Volume of fly-ash = (mass of fly-ash/specific gravity of fly-ash) * (1/1000)

= (132/2.2) * (1/1000)

= 0.06 m^3

4. Volume of water = (mass of water/specific gravity of water) * (1/1000)

= (140/1) * (1/1000)

= 0.14 m^3

5. Volume of chemical admixture = (mass of chemical admixture/specific gravity of chemical admixture) * (1/1000)

= ((2% of cement content)/1.145) * (1/1000)

= (8.8/1.145) * (1/1000)

= 0.007 m^3

6. Volume of aggregate (FA & CA) = 1-(2+3+4+5)

= 1-(0.097+0.06+0.14+0.007)

= 0.696

7. Mass of coarse aggregate = e*volume of CA*specific gravity of CA*1000

= 0.696*0.567*2.74*1000

= 1081.291 kg/m^3

8. Mass of fine aggregate = e*volume of FA*specific gravity of FA*1000

= 0.696*0.433*2.74*1000

= 825.748 kg/m^3

• MIX PROPORTION:

Cement = 308 kg/m^3

Fly-ash = 132 kg/m^3

Water = 140 kg/m^3

Fine aggregate = 825.748 kg/m^3

Coarse aggregate = 1081.291 kg/m^3

Chemical admixture = 8.8 kg/m^3

Water cement ratio = 0.35

• Mix ratio for trail number-1:

Cement : fine aggregate : coarse aggregate = 1 : 2.681 : 3.510

• 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.

• Two more trails having variation of 10% water-cement ratio in ‘i’ shall be carried out and a graph between three water-cement ratios and corresponding strengths shall be plotted to work out the mix proportions for the given target strength for field trails. However, durability shall be met.

Procedure for M50 grade concrete without fly-ash:

• Target mean strength of concrete (fck’):

fck’ = fck + 1.65S

where, fck = characteristics compressive strength at 28 days

S = Standard deviation

Target mean strength of M35 grade of concrete:

fck’ = 50 + (1.65*5)

= 58.25 N/mm^2

• Selection of water cement ratio:

1. Using graph-1:

Using graph water cement ratio corresponding to fck’ = 43.25 N/mm^2,

w/c = 0.30

2. Using graph-2:

Using graph water cement ratio corresponding to fck’ = 43.25 N/mm^2,

w/c = 0.35

3. Using table-5 of IS-456:2000:

Using table for moderate exposure, max w/c = 0.50

Using 1, 2, 3, min w/c is taken for calculation, w/c = 0.30

• Selection of water content:

From table-2 of IS 10262:2009, water content is found

Using table water content for 20 mm nominal size of aggregate = 186 kg = 186 litres

This table is applicable for slump value between 25 and 50 mm, for additional slump 3% may be added for every 25 mm slump

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

As superplasticizer is used, the water content can be reduced up to 30% and above

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

Hence, water content = 197*0.71 = 140 litres

• Selection of cement content:

Cement content = water content / (w/c)

C = 140/0.30

= 466.667 kg/m^3

• Volume of coarse aggregate & fine aggregate content:

Using table-3 of IS 10262:2009, volume of coarse aggregate per unit volume of total aggregate for different zones of fine aggregate is found

Volume of coarse aggregate per unit volume of total aggregate (e)= 0.60

In the present case the water cement ratio = 0.3

So, the volume of coarse aggregate needs to be increased to decrease the fine aggregate content, the proportion of volume of coarse aggregate is increased at the rate of -/+ 0.01 for every -/+ 0.05 change in water cement ratio

Therefore, corrected volume of coarse aggregate for the water-cement ratio of 0.30 = 0.64

For pumpable concrete these values are reduced by 10%

Therefore, volume of coarse aggregate = 0.64*0.9 = 0.576

Volume of fine aggregate = 1-0.576 = 0.424

• Mix calculation:

1. Volume of concrete = 1 m^3
2. Volume of cement = (mass of cement/specific gravity of cement) * (1/1000)

= (466.667/3.15) * (1/1000)

= 0.148 m^3

3. Volume of water = (mass of water/specific gravity of water) * (1/1000)

= (140/1) * (1/1000)

= 0.14 m^3

4. Volume of chemical admixture = (mass of chemical admixture/specific gravity of chemical admixture) * (1/1000)

= ((2% of cement content)/1.145) * (1/1000)

= (9.334/1.145) * (1/1000)

= 0.008 m^3

5. Volume of aggregate (FA & CA) = 1-(2+3+4)

= 1-(0.148+0.14+0.008)

= 0.704

6. Mass of coarse aggregate = e*volume of CA*specific gravity of CA*1000

= 0.704*0.576*2.74*1000

= 1111.08 kg/m^3

7. Mass of fine aggregate = e*volume of FA*specific gravity of FA*1000

= 0.704*0.424*2.74*1000

= 817.879 kg/m^3

• MIX PROPORTION:

Cement = 466.667 kg/m^3

Water = 140 kg/m^3

Fine aggregate = 817.879 kg/m^3

Coarse aggregate = 1111.08 kg/m^3

Chemical admixture = 9.334 kg/m^3

Water cement ratio = 0.4

• Mix ratio:

Cement : fine aggregate : coarse aggregate = 1 : 1.752 : 2.38

• 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.

• Two more trails having variation of 10% water-cement ratio in ‘i’ shall be carried out and a graph between three water-cement ratios and corresponding strengths shall be plotted to work out the mix proportions for the given target strength for field trails. However, durability shall be met.

RESULT:

This project was done to determine the concrete mix design for M35 grade concrete with fly-ash & M50 grade concrete without fly-ash. Using Indian codes IS 456:2000 and IS 10262:2009, concrete mix design obtained for M35 grade concrete with fly-ash is 1 : 2.681 : 3.510 and concrete mix design obtained for M50 grade concrete without fly-ash is 1 : 1.752 : 2.38. This result is based on the consideration we made and the test result of materials used. Many such trails are made and they are plotted in a graph with variation in water-cement ratio between water cement ratio and corresponding strengths shall be plotted to work out the mix proportions for the given target strength for field trails.