Project on Concrete Mix Design for various grades of Concrete

Aim:

To calculate the concrete mix design for M35 grade concrete with fly ash and M50 grade concrete without fly ash.

Introduction:

Concrete mix design involves a process of preparation in which a mix of ingredients creates the required strength and durability for the concrete structure and Mix design can be defined as the process of selecting suitable ingredients of concrete and determining their relative proportions with the object of producing concrete of certain minimum strength and durability as economically as possible.The design is done according to the requirements of concrete strength.This project deals with the design mix of M35 grade concrete with fly ash and M50 grade concrete without fly ash.

Objective:

The main objective of this project is to produce a design mix of M35 grade concrete that containing fly ash and M50 grade concrete without fly ash.This concrete mix will be prepared as per Concrete Mix Proportioning guidelines from IS 10262:2009 and recommended guidelines from IS 10262:1982.

Concrete Mix Design 1 : M35 grade concrete with fly ash.

Procedure:

Step 1 : STIPULATIONS FOR CONCRETE MIX DESIGN

a) Grade designation : M35
b) Type of cement : OPC 53 Grade conforming IS 12269
c) Type of mineral admixture : Fly Ash confirming to IS 8112
d) Maximum nominal size of aggregate : 20 mm
e) Minimum cement content : 320 kg/m³ ( Table 5 of IS 456:2000 - Exposure condition )
f) Minimum water-cement ratio : 0.45 (Table 5 of IS 456:2000 ( exposure condition )
g) Workability : 100-120mm slump
h) Exposure condition : Moderate (For Reinforced Concrete)
j) Method of concrete placing : Pumping
k) Type of aggregate : Crushed Angular Aggregates
m) Maximum cement content : 390 kg/m³
n) Chemical admixture type : Super Plasticizer ECMAS HP 890

Step 2 : TEST DATA FOR MATERIALS

a) Cement used: OPC 53 Grade

b) Specific gravity of cement: 3.15

c) Fly ash: confirming to IS 3812 (part 1 )

d)Specific gravity of fly ash : 2.2

e) Chemical admixture: Super Plasticizer

f) Specific gravity:

1) Coarse aggregate 20mm : 2.67
2) Fine aggregate: 2.65
3) GGBS: 2.84

g) Water absorption:

1) Coarse aggregate : 0.5 %
2) Fine aggregate (M.sand) : 2.5 %

h) Free moisture:

1) Coarse aggregate: Nil
2) Fine aggregate: Nil

i) Sieve analysis:

1) Coarse aggregate: All in aggregates of Table 2 of IS 383
2) Fine aggregate: Grading Zone II of Table 4 of IS 383.

Step 3 : TARGET STRENGTH FOR MIX PROPORTIONING
f’ck =fck + 1.65 s
where
a)f’ck = target average compressive strength at 28 days,
b)fck = characteristics compressive strength at 28 days, and
c)s = standard deviation.

From Table I of IS 10262:2009, Standard Deviation, s = 5 N/mm². Therefore, target strength = 35 + 1.65 x 5 = 43.25 N/mm².

Step 4 : SELECTION OF WATER-CEMENT RATIO
Adopted maximum water-cement ratio = 0.41.

From the Table 5 of IS 456:2000 for Very severe Exposure maximum Water Cement Ratio is 0.45
0.41 < 0.45 Hence ok

Step 5 : SELECTION OF WATER CONTENT
From Table 2 of IS 10262:2009, maximum water content for 20 mm aggregate = 186 litre (for 25 to 50 mm slump range) Estimated water content for 100 mm slump = 186+ (6/186) = 197 litre.

(Note: If Super plasticizer is used, the water content can be reduced upto 20% and above.)

Based on trials with Super plasticizer water content reduction of 20% has been achieved, Hence the arrived water content = 197-[197 x (20/100)] = 158 litre.

Step 6 : CALCULATION OF CEMENT AND FLY ASH CONTENT
Adopted w/c Ratio = 0.41
Cement Content = 158/0.41 = 385 kg/m³
From Table 5 of IS 456, Minimum cement content for ‘Very severe’ exposure conditions 340kg/m³
= 385 kg/m³ > 340 kg/m³ hence ok.

cementious material content = 385

New water cement ratio = 158/385= 0.4

Fly Ash content is taken as 30 % of the total cementious content = 385 x 0.3 = 115.5kg/m³

Cement required = 385 - 115 = 270 kg/m³

cement quantity saved due to fly ash addition = 350-270=80 kg/m³

Step 7 : VOLUME OF COARSE AGGREGATE AND FINE AGGREGATE CONTENT
From Table 3 of (IS 10262:2009) Volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (Zone II) for water-cement ratio of 0.50 =0.62 .

In the present case water-cement ratio is 0.41. 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 = 0.64

NOTE – In case the coarse aggregate is not angular one, then also volume of coarse aggregate may be required to be increased suitably based on experience & Site conditions.

For pumpable concrete these values should be reduced up to 10%. Therefore, volume of coarse aggregate =0.64 x 0.9 =0.576.

Volume of fine aggregate content = 1 – 0.576= 0.424.

Step 8 : MIX CALCULATIONS
The mix calculations per unit volume of concrete shall be as follows:
a) Volume of concrete = 1 m³

b) Volume of cement = [Mass of cement] / {[Specific Gravity of Cement] x 1/1000}
= 270/{3.15 x 1/1000}
= 0.085 m³

c) Volume of fly ash = [mass of fly ash]/ [specific gravity of water x 1/1000]

=[115/2.2)x(1/1000)

=0.052

d) Volume of water = [Mass of water] / {[Specific Gravity of water] x 1000}
= 158/{1 x 1000}
= 0.158m³

e) Volume of chemical admixture = 1.54 litres/ m³ (By Trial and Error Method used 0.4% by the weight cement)

f) Volume of all in aggregate = [a-(b+c+d)]
= [1-(0.122+0.158+0.004)]
= 0.716 m³

g) Mass of coarse aggregate= e x Volume of Coarse Aggregate x Specific Gravity of Fine Aggregate x 1000
= 0.716 x 0.576 x 2.67 x 1000
= 1102 kg/m³

h) Mass of fine aggregate= e x Volume of Fine Aggregate x Specific Gravity of Fine Aggregate x 1000
= 0.716 x 0.424 x 2.60 x 1000
= 789 kg/m³

Step 9 : MIX PROPORTIONS
Cement = 308 kg/m³
Fly ash = 115 kg / m³ Water = 158 l/m³
Fine aggregate = 789 kg/m³ Coarse aggregate 20mm = 1102 kg/m³
Chemical admixture = 1.54 kg/m³ (0.4% by the weight of cement)
Density of concrete = 2512 kg/m³
Water-cement ratio = 0.41
Mix Proportion By weight = 1:2.04:2.86.

Step 10 :

The slump shall be measured,the water content and dosage of admixture shall be adjusted for achieving the required slump on trial. The mix roportion shall be reworked and checked for durability requirements.

Step 11 :

Two more trials having variation of ± 10 percent of water-cement ratio in A-10 shall be carried out and a graph between three water-cement ratios and their corresponding strengths shall he plotted to work out the mix proportions for the given target strength for field trials. However, durability requirement shall be met.

Concrete Mix Design 2 : M50 grade concrete without fly ash

Step 1:Stipulations for Concrete Mix Design

• Grade designation : M 50
• Type of cement : OPC 53 grade confirming to IS 8112
• Maximum nominal size of aggregate : 20 mm
• Minimum cement content : 360 kg/m³
• Maximum water-cement ratio : 0.35
• Workability : 50-75 mm (slump)
• Exposure condition : Extreme (for reinforced concrete)
• Method of concrete placing : Pumping
• Degree of supervision : Good
• Type of aggregate : Crushed angular aggregate
• Maximum cement content : 450 kg/m³
• Chemical admixture type : Super Plasticizer

Step 2 : Test Data for Materials