Project on Concrete Mix Design for various grades of Concrete

CHALLENGE-5

PROJECT ON CONCRETE MIX DESIGN FOR VARIOUS GRADE OF CONCRETE

PREPARED BY- MEGHA GUPTA

Calculate the concrete mix design for M35 grade concrete with Fly ash & M50 grade concrete without Fly ash.

Aim: Aim of the project is to create mix design for M35 grade of concrete using fly ash in the mix and M50 grade of concrete without fly ash. The main objective is to obtain the proportion of ingredients of concrete so as to obtain required grades i.e. M35 and M50.

Introduction: Concrete is a mixture of cement, fine aggregate and coarse aggregate mixed in proper proportion so as to obtain required properties of concrete. For every grade of concrete, the requirement of material is always different. The amount of material changes with for every concrete mix with change in properties of material. In this project concrete mix design has been prepared for two different grades i.e. M35 and M50. M35 grade means the concrete will have compressive strength of 35MPa after 28 days of curing period. To obtain this desired strength how much quantity of cement, fine aggregate, coarse aggregate must be mixed with water depends upon design mix. Properties of all the ingredients must be checked before working on design mix as they have huge impact on design mix and the ultimate mix proportion required to attain desired properties from concrete. Basic properties like specific gravity, fineness of ingredients, moisture content, zone & shape of aggregate must be checked beforehand. In present project, the basic properties of ingredients have been assumed within the range specified in various codes.

Design Mix preparation and final proportion for first trail:

1. Design of M35 grade of concrete using fly ash.

Grade Designation: M35

• Data collection:

• Type of cement: OPC 43 conforming to IS:8112-1989
• nominal Size Aggregate: 20 mm
• cement content: 320kg/m³
• water content ratio: 0.45
• Workability: 100mm slump
• Exposure condition: Severe
• Chemical Admixture: Superplasticizer
• Mineral Admixture: Fly Ash confirming to IS 3812 (part 1)
• Degree of supervision: Good
• Type of aggregate: Crushed Angular
• cement content: 450 kg/m³

• Preparation of design mix:

• Cement used: OPC Grade 43 conforming to IS: 8112-1989
• Gravity of cement = 3.13
• Sand: Conforming to zone III
• gravity of CA: 2.71
• Gravity of sand: 2.727
• Gravity of fly ash: 2.2
• Gravity of super plasticizer: 1.145
• Free surface moisture:
• Coarse Aggregate: Nil
• Sand: Nil
• Fine Aggregate: Nil
• Target strength (f_t) = f_ck +1.65*S (S=5 from Table no. 8, IS 456: 2000)

f_t = 35 +(1.65 x 5) = 43.25 N/mm²

• Selection of water cement ratio:

From table 5 of IS 456:2000,

max W/C ratio =0.45

Considering w/c ratio = 0.4

From table 2 of IS 10262:2009, (max. size if coarse aggregate is 20mm) max. water content =186 Lt (for 25 to 50 mm slump range).

Estimated water content for 100 mm slump = 186 + (6/100) x 186 =197 Lt

Superplasticizer is used. 20% reduction in water content due to superplasticizer

Water content = 197- (197*0.2) = 157.6 Lt

• Calculation of cement & fly ash content:

W/C ratio = 0.4

Cementitious material (cement + fly ash) content = 157.6/0.4 = 393.5 kg/m³

393.5 kg/m³ > 320 kg/m³. Hence OK

To proportion a mix containing fly ash the following steps are suggested:

1. a) Decide the percentage fly ash to be used based on project requirement and quality of fly ash.
2. b) In certain situations, increase in cementitious material content may be warranted. The decision on increase in cementitious material content and its percentage may be based on experience and trials.

Cementitious material content = 393.5 X 1.1 = 432.85 kg/m³

Water content = 157.6 Lt

So, water-cement ratio = 157.6/432.85 = 0.364

Fly ash @ 25% of total cementitious material content= 432.85 X 25% = 108.21 kg/m³

Cement content = 432.85 - 108.21 = 324.64 kg/m³

324.64 kg/m³ > 320 kg/m³. Hence OK

• Proportion of volume of coarse aggregate and fine aggregate:

Volume of coarse aggregate is required to be increased to decrease the fine aggregate content. As the water-cement ratio is lower by 0.05, the proportion of volume of coarse aggregate is to be increased by 0.01 (at the rate of -/+ 0.01 for every ± 0.05 change in water-cement ratio).

Table 3 (10262:2009), Volume of C.A. corresponding to 20mm size aggregates and F.A. confirming to zone III.

For W/C of 0.5 = 64% C.A

For W/C of 0.364 = 64+2.72 = 66.72% C.A

Therefore, Proportion of volume of C.A & F.A

Volume of C.A = 66.72%

Volume of F.A = 1 – 0.6672 = 33.28%

• Mix calculations:

• Volume of concrete in m³ = 1 m³
• Volume of cement (m³) = mass of cement/ Specific gravity of cement x 1000

= 324.64 / (3.13 x 1000) = 0.1257 m³

• Volume of fly ash (m³) = mass of fly ash / Specific gravity of fly ash x 1000

= 108.21/(2.2 x 1000) = 0.0492 m³

• Volume of water (m³) = mass of water / Specific gravity of water x 1000

= 157.6 / 1 x 1000 = 0.1576 m³

• Volume of chemical admixture = mass of chemical admixture / Specific gravity of chemical admixture x 1000 = 7.6/ (1.145* 1000) = 0.006 m³
• Volume of all in aggregate (m³) = Volume of concrete – (Volume of cement + Volume of fly ash + Volume of water + volume of admixture)

= 1 – (0.1257 + 0.0492 + 0.1576 + 0.006) = 0.6615 m³

• Volume of C.A (m³) = 0.6615 x 0.6672 = 0.4414 m³
• Volume of F.A (m³) = 0. 6615 x 0. 3328 = 0.2201 m³

• Mix proportions for one cumec of concrete (for first trial):

• Mass of cement (kg/m³) = 324.64 kg/m³
• Mass of fly ash (kg/m³) = 108.21 kg/m³
• Mass of water (kg/m³) = 157.6 kg/m³
• Mass of F.A (kg/m³) = 1000 x 2.727 x 0.2201 = 600.213 kg/m³
• Mass of C.A (kg/m³) = 2.71 x 1000 x 0.4414 = 1196.194 kg/m³
• Mass of admixture = 6.87 kg/m³
• W/C ratio = 0.364

Final Proportion for M35 for first trial calculated with respect to Cementitious material = 1: 1.387 : 2.764

Final Proportion for M35 for first trial calculated with respect to Cement = 1: 0.333 : 1.85 : 3.685

2. Design of M50 grade of concrete without fly ash.

Grade Designation: M50

• Data collection:

• Type of cement: OPC 43 conforming to IS:8112-1989
• nominal Size Aggregate: 20 mm
• cement content: 320kg/m³
• water content ratio: 0.45
• Workability: 100mm slump
• Exposure condition: Severe
• Chemical Admixture: Superplasticizer
• Mineral Admixture: GGBS confirming to IS 16714
• Degree of supervision: Good
• Type of aggregate: Crushed Angular
• cement content: 450 kg/m³

• Preparation of design mix:

• Cement used: OPC Grade 43 conforming to IS: 8112-1989
• Gravity of cement = 3.15
• Sand: Conforming to zone II
• gravity of CA: 2.74
• Gravity of sand: 2.65
• Gravity of GGBS: 3
• Gravity of super plasticizer: 1.145
• Free surface moisture:
• Coarse Aggregate: Nil
• Sand: Nil
• Fine Aggregate: Nil
• Target strength (f_t) = f_ck +1.65*S (S=5 from Table no. 8, IS 456: 2000)

f_t = 50 +(1.65 x 5) = 58.25 N/mm²

• Selection of water cement ratio:

From table 5 of IS 456:2000,

max W/C ratio =0.45

Considering w/c ratio = 0.38

From table 2 of IS 10262:2009, (max. size if coarse aggregate is 20mm) max. water content =186 Lt (for 25 to 50 mm slump range).

Estimated water content for 100 mm slump = 186 + (6/100) x 186 =197 Lt

Superplasticizer is used. 20% reduction in water content due to superplasticizer

Water content = 197- (197*0.2) = 157.6 Lt

• Calculation of cement & GGBS content:

W/C ratio = 0.38

Cementitious material (cement + GGBS) content = 157.6/0.38 = 414.74 kg/m³

414.74 kg/m³ > 320 kg/m³. Hence OK

To proportion a mix containing GGBS the following steps are suggested:

1. a) Decide the percentage GGBS to be used based on project requirement and quality of fly ash.
2. b) In certain situations, increase in cementitious material content may be warranted. The decision on increase in cementitious material content and its percentage may be based on experience and trials.

Cementitious material content = 414.74 X 1.1 = 456.214 kg/m³

Water content = 157.6 Lt

So, water-cement ratio = 157.6/456.214 = 0.346

GGBS @ 25% of total cementitious material content = 456.214 X 25%

= 114.054 kg/m³

Cement content = 456.214 - 114.054 = 342.161 kg/m³

342.161 kg/m³ > 320 kg/m³. Hence OK

• Proportion of volume of coarse aggregate and fine aggregate:

Volume of coarse aggregate is required to be increased to decrease the fine aggregate content. As the water-cement ratio is lower by 0.05, the proportion of volume of coarse aggregate is to be increased by 0.01 (at the rate of -/+ 0.01 for every ± 0.05 change in water-cement ratio).

Table 3 (10262:2009), Volume of C.A. corresponding to 20mm size aggregates and F.A. confirming to zone II.

For W/C of 0.5 = 62% C.A

For W/C of 0.364 = 62 + 3.08 = 65.08% C.A

Therefore, Proportion of volume of C.A & F.A

Volume of C.A = 65.08%

Volume of F.A = 1 – 0.6508 = 34.92%

• Mix calculations:

• Volume of concrete in m³ = 1 m³
• Volume of cement (m³) = mass of cement / Specific gravity of cement x 1000

= 342.161 / (3.15 x 1000) = 0.1086 m³

• Volume of GGBS (m³) = mass of GGBS / Specific gravity of GGBS x 1000

= 114.054 / (3 x 1000) = 0.038 m³

• Volume of water (m³) = mass of water / Specific gravity of water x 1000

= 157.6 / 1 x 1000 = 0.1576 m³

• Volume of chemical admixture = mass of chemical admixture / Specific gravity of chemical admixture x 1000 = 7.6/ (1.145* 1000) = 0.006 m³
• Volume of all in aggregate (m³) = Volume of concrete – (Volume of cement + Volume of fly ash + Volume of water + volume of admixture) = 1 – (0.1086 + 0.038 + 0.1576 + 0.006) = 0.6898 m³
• Volume of C.A (m³) = 0.6898 x 0.6508 = 0.4489 m³
• Volume of F.A (m³) = 0. 6898 x 0. 3492 = 0.2409 m³

• Mix proportions for one cumec of concrete (for first trial):

• Mass of cement (kg/m³) = 342.161 kg/m³
• Mass of GGBS (kg/m³) = 114.054 kg/m³
• Mass of water (kg/m³) = 157.6 kg/m³
• Mass of F.A (kg/m³) = 1000 x 2.74 x 0.2409 = 660.066 kg/m³
• Mass of C.A (kg/m³) = 2.65 x 1000 x 0.4489 = 1189.585 kg/m³
• Mass of admixture = 6.87 kg/m³
• W/C ratio =0.346

Final Proportion for M50 for first trial calculated with respect to Cementitious material = 1: 1.447 : 2.608

Final Proportion for M50 for first trial calculated with respect to Cement = 1: 0.333 : 1.929 : 3.477

Using above proportions concrete should be prepared and then workability of concrete is checked. If the required workability is attained then we must check the compressive strength requirement of concrete by casting a cube of 150 mm X 150 mm X 150 mm. The cube should be checked after 28 days of curing for compressive strength using CTM or UTM. If the concrete cube attains required strength, then that proportion can be finalized. If any of the requirement (i.e. workability or compressive strength) is not attained then changes are to be done in the mix proportion so as to obtain and fulfil the requirement.