Project on Concrete Mix Design for various grades of Concrete

PROJECT I

Mix Design of Concrete

Task no. 1: Calculate the Concrete Mix Design for M35 grade concrete with fly ash.

Solution:

• Aim & Introduction:

• The aim of the task in project I is the calculation of mix design for M35 grade concrete with fly ash as per Indian Standard code IS10262:2009(Guidelines for concrete mix proportioning.
• The mix design calculation procedure is same as mix design without flyash. The only difference would be the specific gravity of the admixtures.
• The specific gravity of fly ash ranges from 2.1 to 3.

• Procedure:

• Step 1-Data Collection:

• Grade Designation : M35.
• Type of cement : OPC 53 grade of cement.
• Type of admixture : Fly ash
• Maximum nominal size of aggregate : 20 mm
• Minimum cement content : 340 Kg. (from Table 5 of IS 456:2000)
• Maximum water/ cement ratio : 0.45
• Workability : 100mm slump.
• Chemical Admixture : Super Plasticizer.
• Specific Gravity:

1. Cement : 3.15
2. Fly Ash : 2.9
3. Coarse aggregate : 2.74
4. Fine aggregate : 2.74

• Water Absorption:

1. Coarse aggregate : 0.5%
2. Fine aggregate : 1%

• Sieve Analysis:

1. Coarse aggregate :Confirming to Table 2- IS383.
2. Fine aggregate : Zone II Confirming to Table 4 of IS383.

• STEP 2 - Target Strength for proportion of M35 Grade concrete:

Target Strength (Fck) = fck + 1.65S

• The strength of concrete may get deviated based on the quality of the material, method of mixing and construction practices.
• Hence Target strength of concrete (Fck) should be higher than the required strength of the concrete(fck).
• The valure of standard deviation (S) for different grades of concrete is taken from Table 1 of IS 456:2000.
• Hence the calculation is,

Fck = fck + 1.65S

where, fck = 35 N/mm^2.( as grade of concrete M35 has compressive strength = 35N/mm^2).

S = 5 ( from Table 1 of IS 10262:2009)

CALC: Fck= 35 + 1.65x5

Fck= 43.25N/mm^2.

• STEP 3 - Selection OF Water - Cement Ratio:

• The maximum water content ratio for different grades of concrete is taken from Table 5 of IS 456:2000.
• The water-cement ratio can be reduces as per the requirement.
• The water-cement ratio directly affects the strength of the concrete.

Hence the w/c ratio is taken from Table 5 of IS 456:2000 considering exposure condition as severe.

Maximum water/cement = 0.45(from Table 5 of IS456:2000)

• STEP 4 - Selection OF Water Content:

• The maximum water content is considered from Table 2 of IS10262:2009
• For 20mm aggregate the water content is considered as

Maximum water content = 186 lit. (from Table 2 of IS10262:2009)

• Above found water content is for 25mm to 50mm slump. As the information given for the design is 100mm slump.
• So we need to increase the water content to get the required slump(clause 4.2 of IS10262) suggests to increase 3% of water content to get an extra 25mm slump.
• Hence we need to increase water content by 6% as there is 5mm increase in slump of concrete.

So the water content for 100mm slump = 186 + [(6/100)x186]

= 197.16L.

• Since we are using superplasticizers, the water content can be reduced inorder to egt strength in concrete. The amount of water - content to be reduced depends on the type of superplasticizer.

Percentage of reduction in water content = 20%

Water content obtained is =197.16- (0.20x198)

=157.73

Adopted Water content = 160L.

• STEP 5 - Calculation of Cement and Fly Ash Content:

Adopted water cement ratio = 0.45

Total cementitious (cement + Flys ash ) requirement = (Water content/ Water cement ratio)

= 160/0.45

= 355.55kg.

• Since Fly ash is used the amount of cementitious content (cement + Fly ash) shall be increased to get good workability and strength.
• The percentage of cementitious content to be increased depends on the experience and research.
• Here we have increased the cementitious content by 10%.

Final Cementitious content (Cement +Fly ash) = 356x1.0

= 391.6 kg

Minimum cement content required for sever exposure = 340kg (from Table 5 of IS 456)

Adopted cementitious content = 391.6kg > 340kg , Hence OK

Fly ash content requirement = 391.6 x 0.30 30% replacement.

= 117.48 =118 kg

Cement content requiremnet = Cementitious content - Fly ash

= 391.6 - 117.48

= 274.12.

• Calculation of super plasticizer at 0.6% to the mass of cementitious content = 391.6x(0.6/100) = 2.35kg.

• STEP 6 - Calculation of Coarse and Fine aggregate:

Coarse aggregate ratio = 0.62 (from Table 3 of IS10262:2009 for W/C =0.5)

Coarse aggregate ratio = 0.63(adding 0.01 for every decrease 0.05 or decreasing 0.01 for every increase 0.05).

Final Fine aggregate ratio = 0.37 (1-0.63) = 0.37.

• STEP 7 - Mix calculation of M35 Grade concrete:

• Volume of concrete = 1m^3.
• Toltal volme of cement = mass of cement/ (specific gravity of cementx1000)

= 275/(3.15x1000) = 0.087 m^3.

• Total volume fly ash = mass of Fly ash/ (specific gravity of fly ash x1000)

= 118/(2.5x1000) = 0.041m^3

• Volume of water = mass water/(specific gravity of water x 1000)

= 160/(1x1000) = 0.160m^3

• Volume of superplasticizer = mass of super plasticizer/ (specific gravity of superplasticizer x 1000)

= 2.35/(1.12x1000) = 0.002m^3

• Total aggregate requirement = A-(B+C+D+E)

= 1-(0.087+ 0.041+0.160+0.002) = 0.71m^3.

• Mass of coarse aggregate = e(total aggregate requirement) x Coarse aggregate volume x specific gravity of coarse aggreggate x 1000

= 0.71x0.63x2.74x1000 = 1225.6kg/m^3

• Mass of fine aggregate = e x volume of fine aggregate x specific gravity of fine aggregate x 1000

= 0.71 x 0.37x 2.74 x 1000 = 719.8 kg/m^3

Hence the mix design of M35 grade of concrete with Fly ash is

1. Cement : 391.6 kg/m^3
2. Fly ash : 118 kg/m^3
3. Fine aggregate : 720 kg/m^3
4. Coarse aggregate : 1226 kg/m^3
5. Water : 160kg/m^3

• Result:

• Hence the obatined mix ratio for the above calculated mix design of M35 grade of concrete with Fly ash is

1:1.83:3.13

Cementitious contect : Fine Aggregate : Coarse aggregate.

• Still the slump shall be measured and water content and dosage of admixture shall be adjusted for achieveing the required slump on trial. The mix proportion shall be adjusted for achieving the required slump on trial. The mix proportion shall be reworked for actual water content and checked for durability requirement.
• Two more trials having variation of 10% of water cement ratio in clause x shall be carried out and a graph between three water - cement ratio and corresponding strength shall be plotted to work out the mix proportions for given target strength for field trails. However durability shall be met.

Task no. 2: Calculate the Concrete Mix Design for M50 grade concrete without fly ash.

Solution:

• Aim & Introduction:

• The aim of the task in project I is the calculation of mix design for M50 grade concrete with admixture as per Indian Standard code IS10262:2009(Guidelines for concrete mix proportioning.
• Here we will use superplasticizer as admixtures.
• We will be refering several Indian Standard codes for this mix design , the main codes used are IS10262:2009, IS456:2000

• Procedure:

• Step 1-Data Collection:

• Grade Designation : M50.
• Type of cement : OPC 53 grade of cement.(Confirming IS12269)
• Maximum nominal size of aggregate : 20 mm
• Minimum cement content : 320 Kg. (from Table 5 of IS 456:2000)
• Maximum water/ cement ratio : 0.45
• Workability : 100mm slump.
• Exposure Condition : Severe.
• Chemical Admixture : Super Plasticizer.
• Specific Gravity:

1. Cement : 3.15
2. Coarse aggregate : 2.74
3. Fine aggregate : 2.64

• Water Absorption:

1. Coarse aggregate : 0.5%
2. Fine aggregate : 1%

• Sieve Analysis:

1. Coarse aggregate :Confirming to Table 2- IS383.
2. Fine aggregate : Zone II Confirming to Table 4 of IS383.

• STEP 2 - Target Strength for proportion of M35 Grade concrete:

Target Strength (Fck) = fck + 1.65S

• The strength of concrete may get deviated based on the quality of the material, method of mixing and construction practices.
• Hence Target strength of concrete (Fck) should be higher than the required strength of the concrete(fck).
• The valure of standard deviation (S) for different grades of concrete is taken from Table 1 of IS 456:2000.
• Hence the calculation is,

Fck = fck + 1.65S

where, fck = 50 N/mm^2.( as grade of concrete M50 has compressive strength = 50N/mm^2).

S = 5 ( from Table 1 of IS 10262:2009)

CALC: Fck= 50 + 1.65x5

Fck= 58.25N/mm^2.

• STEP 3 - Selection OF Water - Cement Ratio:

• The maximum water content ratio for different grades of concrete is taken from Table 5 of IS 456:2000.
• The water-cement ratio can be reduces as per the requirement.
• The water-cement ratio directly affects the strength of the concrete.

Hence the w/c ratio is taken from Table 5 of IS 456:2000 considering exposure condition as severe for M50.

Maximum water/cement = 0.45(from Table 5 of IS456:2000)

• STEP 4 - Selection OF Water Content:

• The maximum water content is considered from Table 2 of IS10262:2009
• For 20mm aggregate the water content is considered as

Maximum water content = 186 lit. (from Table 2 of IS10262:2009)

• Above found water content is for 25mm to 50mm slump. As the information given for the design is 100mm slump.
• So we need to increase the water content to get the required slump(clause 4.2 of IS10262) suggests to increase 3% of water content to get an extra 25mm slump.
• Hence we need to increase water content by 6% as there is 5mm increase in slump of concrete.

So the water content for 100mm slump = 186 + [(6/100)x186]

= 197.16L.

• Since we are using superplasticizers, the water content can be reduced inorder to egt strength in concrete. The amount of water - content to be reduced depends on the type of superplasticizer.

Percentage of reduction in water content = 20%

Water content obtained is =197.16- (0.20x198)

=157.73

Adopted Water content = 158L.

• STEP 5 - Calculation of Cement Content:

Adopted water cement ratio = 0.45

Total cementitious cement requirement = (Water content/ Water cement ratio)

= 158/0.45

= 320kg.

359kg/m^3 > 320kg/m^3 , hence ok

• STEP 6 - Calculation of Coarse and Fine aggregate:

Coarse aggregate ratio = 0.62 (from Table 3 of IS10262:2009 for W/C =0.5)

Coarse aggregate ratio = 0.63(adding 0.01 for every decrease 0.05 or decreasing 0.01 for every increase 0.05).

For pumpablr concrete these values must be reduced by 10%, hence = 0.632x0.9 =0.568

Final Fine aggregate ratio = 1-0.576 = 0.431

• STEP 7 - Mix calculation of M35 Grade concrete:

• Volume of concrete = 1m^3.
• Toltal volme of cement = mass of cement/ (specific gravity of cementx1000)

= 359/(3.15x1000) = 0.114 m^3.

• Volume of water = mass water/(specific gravity of water x 1000)

= 158/(1x1000) = 0.158m^3

• Volume of superplasticizer = mass of super plasticizer/ (specific gravity of superplasticizer x 1000)

= 7.6/(1.145x1000) = 0.006m^3

• Total aggregate requirement = A-(B+C+D+E)

= 1-(0.114+ 0.158+0.006) = 0.722m^3.

• Mass of coarse aggregate = e(total aggregate requirement) x Coarse aggregate volume x specific gravity of coarse aggreggate x 1000

= 0.722x0.568x2.74x1000 = 1123kg/m^3

• Mass of fine aggregate = e x volume of fine aggregate x specific gravity of fine aggregate x 1000

= 0.722 x 0.431x 2.64 x 1000 = 821 kg/m^3

Hence the mix design of M50 grade concrete is

1. Cement : 359 kg/m^3
2. Fine aggregate : 821 kg/m^3
3. Coarse aggregate : 1123 kg/m^3
4. Water : 158kg/m^3

• Result:

• Hence the obatined mix ratio for the above calculated mix design of M50 is

1:2.28:3.12

Cementitious contect : Fine Aggregate : Coarse aggregate.

• Still the slump shall be measured and water content and dosage of admixture shall be adjusted for achieveing the required slump on trial. The mix proportion shall be adjusted for achieving the required slump on trial. The mix proportion shall be reworked for actual water content and checked for durability requirement.
• Two more trials having variation of 10% of water cement ratio in clause x shall be carried out and a graph between three water - cement ratio and corresponding strength shall be plotted to work out the mix proportions for given target strength for field trails. However durability shall be met.