Challenge

Project on Concrete Mix Design for various grades of Concrete

JJagadeep. M M22 Jan 2022

DESIGN

MIX DESIGN FOR M35 GRADE CONCRETE WITH FLY ASH

Aim: Mix design for M35 grade concrete with fly ash

Procedure:

Step:1

Stipulation for proportioning

Grade designation: M35
Type of cement:OPC 43 grade conforming to IS 8112
Type of mineral admixture: fly ash conforming to IS 3812(part1)
Maximum nominal size of aggregate: 20mm
Minimum cement content: 320kgm^3(from table of IS 456:2000)
Maximum water cement ratio: 0.45 (from table 5 of IS 456:2000)exposure condition
Workability:100mm (slum value for pumpable concrete)
Exposure condition: severe(for reinforced concrete)
Method of concrete placing: pumping
Degree of supervision: Good
Type of aggregate: Crushed angular aggregate
Maximum cement content: 450kg/m^3
Chemical admixture type: superplasticizer conforming to IS 9103

Step:2

Test data for materials

Cement used: OPC 43 grade conforming to IS 8112
Spacific gravity of cement: 3.15
Fly ash: conforming to IS 3812(part1)
Specific gravity of fly ash: 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%

h. Free surface moisture:

Coarse aggregate:nil

Fine aggregate:nil

i. Sieve analysis:

Coarse aggregate: conforming to table 2 of IS 383

Fine aggregate: conforming to grading zone 1 of table 4 of IS 383

Step:3

Target strength for mix proportion

f'ck=fck+1.65S

from table 1IS 10262:2009, standard diviation, S=5N/mm^2

=35+(1.65*5)=43.25N/mm^2

fck=characteristics of compressive strength

s=standard diviation

Step:4

Selection of water cement ratio

Maximum water cement ratio=0.45 (for severe condition, from table 5 of IS 456:2000)

Based on experience, adopt water-cement ratio as 0.4

0.4<0.45,hence ok

Step:5

Selection of water content

Maximum water content for 20mm aggregate=186liter (table 2 of IS 10262:2009)for 25mmto50mm slump rang

Estimated water content for 100mm slump=186+{(6/100)*186}

=197liters

As superplasticizer is used the water content can be reduce upto 30% based on trial water content reduction of 29% is achieved with plasticizer.

hence the arrived water content=197*0.71

=140liters

Step:6

Calculation of cement content

water cement ratio=0.4

cementitious material(cement + fly ash)content

=140/0.4=350kg/m^3

from table 5 0f IS 456:2000 minimum cement content for 'severe'exposure condition=320kg/m^3

350kg/m^3>320kg/m^3 .hence ok

Now, to proportion a mix containing fly ash the following steps are suggested.

a)The percentage of fly ash need to be decided based project requirment & quality of materials

b)In sum case increase in cementitious material can be warned. Increase in cementitious material content & its percentage may be based on experience & trial(this example is with increase of 10% cementitious material content)

Cementitious material content =350*1.10=385kg/m^3

Water content =140kg/m^3

so, water cement ratio =140/350=0.364

fly ash @30% total cementitious material content =385*30%=115kg/m^3

cement(OPC) =385-115=270kg/m^3

saving of cement while using fly ash =350-270=80kg/m^3

fly ash being utilized =115kg/m^3

Step:7

Proportion of volume of coarse aggregate & fine aggregate content

from table 3 of IS 10262:2009, volume of coarse aggregate corresponding to 20mm size aggregate & fine aggregate (zone 1)for water cement ratio=0.6

In the present case the water cement ratio is 0.4

Therefore the volume of coarse 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 +/- 0.01for every +/- 0.05 change in the water cement ratio)

Therefore corrected volume of coarse aggregate for the water cement ratio of 0.40=0.62

(if coarse aggregate is not of angular type then also the volume of coarse aggregate may be required to be increased suitably based on exprience)

for pumpable concrete these value are reduced by 10%

therefor volume of coarse aggregate=0.2*0.9=0.56

volume of fine aggregate concrete=1-0.56=0.44

Step:8

Mix calculation

The mix caculation per unit volume of concrete shall be as follows.

a)Volume of concrete=1m^3

b)volume of cement =[(mass of cement/specific gravity of cement)*(1/1000)]

=[(270/3.15)*(1/1000)]=0.086m^3

c)Volume of fly ash=[(mass of fly ash/specific gravity of fly ash)*(1/1000)]

=[(115/2.2)*(1/1000)]=0.052m^3

d)Volume of water =[(mass of water/specific gravity of water)*(1/1000)]

=[(140/1)*(1/1000)]=0.140m^3

e)Volume of chemical admixture=[(mass of chemical admixture/specific gravity of admixture)*(1/1000)]

=[(7.6/1.145)*(1/1000)]=0.006m^3

f)Volume of aggregate(FA&CA)=[a-(b+c+d+e)]

=[1-(0.086+0.052+0.140+0.006)]

=0.716m^3

g)Mass of coarse aggregate=f*Volume of coarse aggregate*Specific gravity of coarse aggregate*1000

=0.716*0.56*2.74*1000

=1098kg/m^3

h)Mass of fine aggregate=f*Volume of fine aggregate*specific graviry of fine aggregate*1000

=0.716*0.44*2.74*1000

=863kg/m^3

Step:9

Mix proportion for trial

Cement=270kg/m^3

Fly ash=115kg/m^3

Water=140kg/m^3

Fine aggregate=863kg/m^3

Coarse aggregate=1098kg/m^3

Chemial admixture=7kg/m^3

Water cement ratio=0.364

Trial mix=1:2.24:2.85

Step:10

The slump shall be measured & the water content & dosage of admixture shall be adjusted for achieving the slump on trial. The mix proportion shall be reworked for the actual water content & checked for durability requirements.

Step:11

Two more trials having variation of 10% of water cement ratio in clause 10 shall be carried out & a graph between three water cement ratios & corresponding strength shall be plotted to work out the mix proportions for the given target strength for field trials. However durabillty shall be met.

MIX DESIGN OF M50 GRADE CONCRETE

Aim: Mix design for M50 grade concrete