Challenge

Project on Concrete Mix Design for various grades of Concrete

MManoj K6 Jun 2022

5# Project on Concrete Mix Design for various grades of Concrete

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

M35 GRADE CONCRETE WITH FLYASH:

Stipulations for proportioniong:

Grade designation: M35
Type of cement: OPC 33 grade conforming to IS 8112
Type of mineral admixture: Flyash conforming to IS 3812( Part 1)
nominal size of aggregate :20mm
Minimum cement content :320kg/m3

(From table 5 of IS 456:2000) – Exposure Condition

Maximum w/c ratio :0.45

(From table 5 of IS 456:2000) –Exposure Condition)

g) Workability:100mm(Slump value for pumpable concrete)
h) Exposure Condition : Severe (for reinforced concrete).
i) Method of concrete placing: Pumping
j) Degree of supervision: Good
k) Type of aggregate : Crushed angular aggregate
l) Maximum cement content : 450kg/m3
m) Chemical admixture type : Superplasticizer

Test data for materials:

Cement used: OPC 33 grade conforming to IS 8112
Specific gravity of cement : 3.15
Flyash : Conforming to IS 3812(Part 1)
Specific gravity of flyash: 2.2
Chemical admixture : Superplasticizer Conforming to IS 9103
Specific gravity of

Coarse aggregate :2.74
Fine aggregate :2.74

g) Water absorption:

Coarse aggregate : 0.5%
Fine aggregate :1.0%

h)Free surface moisture:

Coarse aggregate: Nil
Fine aggregate : Nil

i)Sieve analysis:

Coarse aggregate:
Fine aggregate : Conforming to grading zone I of table 4 of IS 383

Target strength for mix proportioning:

Fck= fck + 1.65S

Where, fck = Target average compressive strength at 28 days.

Fck= Characteristics Compressive strength at 28 days.

S = Standard deviation.

From Table 1 of IS 10262:2009, standard deviation, S= 5N/mm2

Therefore, Target strength = 35 + 1.65S

= 43.25N/mm2

Selection of water – cement ratio:

From Table 5 of IS 456:2000 for severe exposure, max w/c ratio=0.45

Based on experience , adopt w/c ratio as 0.40

0.40<0.45, Hence o.k

Selection of water content:

From Table 2 of IS 10262:2009, max.w/c for 20mm aggregate (for 25mm to 50mm slump range)

Estimated Water content for 10mm slump = 186+(6/100)*186

=197 litre

As superplasticizer is used , the water content can be reduced upto 30%

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

Hence the arrived water content = 197*0.71

=140litre

Calculation of cement content:

Water- cement ratio = 0.40

Cementitious material ( cement + flyash) content = 140/0.4=350Kg/m3

From Table 5 of IS456 minimum cement content for ‘severe’ exposure condition =320Kg/m3

350kg/m3>320kg/m3 , Hence ok

Now to proportion a mix containing flyash the following steps are suggested.

The percentage of flyash needs to be decided based on project requirement and quality of materials.

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 (This example is with increase of 10% cementitious material content).

Cementitious material content = 350x1.10 =385kg/m3

Water content = 140kg/m3

So, W/C ratio = 140/385=0.364

Flyash @30% total cementitious =385 x 30%

Material content = 115kg/m3

Cement (opc) = 385-115

=270Kg/m3

Saving of cement while using flyash = 350-270

=80kg/m3

Flyash being utilized = 115kg/m3

Proportion of volume of coarse aggregate and fine aggregate content:

From Table 3 of IS 10262:2009, Volume of coarse aggregate corresponding to 20mm size aggregate and fine aggregate (zone I) for Water cement ratio of 0.5=0.6

In the present case the water cement ratio is 0.40

Therefore , the volume of coardse aggregate needs to be increased to decrease the fine aggregate content.

As Water cement ratio is lower by 0.10, the proportion of volume of coarse aggregate is increased by 0.02( at the rate of-/+ 0.01 for every +-0.05 change in w/c ratio).

Therefore, corrected volume of coarse aggregate for the w/c ratio of 0.40 = 0.62

(Note : If coarse aggregate is not of angular type, then also the volume of coarse aggregate may be required to be increased suitably, based on experience)

For,pumpable concrete these values are reduced by10%

Therfore, Volume of coarse aggregate =0.62*0.9

=0.56

Volume of fine aggregate content= 1-0.56=0.44

MIX CALCULATIONS:

The mix calculation per unit volume of concrete shall be as follows:

Volume of concrete =1m3
Volume of cement= Mass of cement/Specific gravity of cement X1/1000

=270/3.15 X1/1000

=0.0857m3

Volume of flyash= mass of flyash/sp.garvity of flyash x 1/1000

=115/2.2 x 1/1000

=0.052m3

c)Volume of Water = Mass of water/Specific gravity of water X1/1000

=140/1 X 1/1000

=0.140m3

d)Volume of aggregates (FA&CA)=(a-(b+c+d))

=(1-(0.0857+0.140+0.052))

=0.722m3

e)Mass of Coarse aggregate = e X Volume of coarse aggregate X Specific gravity of coarse aggregate X 1000

=0.722*0.56*2.74*1000

=1108Kg/m3

f)Mass of fine aggregate = e X Volume of coarse aggregate X Specific gravity of coarse aggregate x 1000.

=0.722 x 0.44 x 2.74 x 1000

=870 Kg/m3

Mix proportions:

Cement =270Kg/m3

Flyash=115kg/m3

Water =140Kg/m3

Fine aggregate = 870kg/m3

Coarse aggregate= 1108 Kg/m3

Water- cement ratio= 0.45

MIX RATIO FOR M35 WITH FLYASH = 1:2.26:2.88

M50 GRADE CONCRETE WITHOUT FLYASH: