Project on Concrete Mix Design for various grades of Concrete

Aim:-

To determine the mix proportions of all ingredients of concrete for M35 grade of concrete with fly ash and M50 grade concrete with OPC cement following the specifications given in IS code 10262:2009 and IS code 456:2000.

Introduction to concrete mix design:-

concrete mix design is the process of selection of all ingredients of concrete like cement, fine aggregate, coarse aggregate, water, admixtures(if used) and finding their approximate proportions to fulfill the desired qualities.

the properties of the concrete like compressive strength, durability, workability, etc depend on the proportions and the properties of the ingredients, grading, and type of aggregate, nominal size of the aggregate,w-c ratio.

the quality of concrete also depends on many factors like batching of ingredients, mixing, and curing.

data required for the concrete mix design:-

• grade of the concrete
• size of the aggregate
• max cement content
• w-c ratio
• workability in terms of slump
• exposure conditions
• grading zone of fine aggregate
• type of aggregate
• the specific gravity of all materials.

Objectives of concrete mix design:-

• to achieve the desired strength as required
• to maintain the durability of the structure throughout its design life for a given environmental conditions
• to attain the desired workability of the fresh concrete
• to produce the concrete economically minimizing the wastage of materials.

calculation of concrete mix design of M35 grade concrete using fly ash.

Assumed data:-

• grade designation:- M35
• type of cement:- OPC 43
• nominal size of aggregate:- 20mm
• type of aggregate:- crushed angular aggregate
• minimum cement content:- 320 kg/m^3
• maximum cement content :- 450 kg/m^3(as per IS 456)
• maximum w-c ratio:- 0.45
• workability:- 100mm
• exposure condition:-severe
• type of mineral admixture:- fly ash
• the specific gravity of fly ash:- 2.2
• the specific gravity of cement:- 3.15
• the specific gravity of fine aggregate:- 2.6
• the specific gravity of coarse aggregate:- 2.75
• super plasticize
• pumpable concrete

DESIGN MIX

• target mean strength:-

target mean strength can be determined by the equation:- fm = fck + 1.65(standard deviation)

fck =35 N/mm^2

standard deviation= 5 (as per Is 10262)

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

• selection of w-c ratio:-

based on exposure conditions from is 456 max w-c ratio is 0.45

from the graph (target mean strength and w-c ratio) the plotted w-c atio is 0.36

adopt the lesser value from the above i.e., take w-c ratio as 0.36

but the min w-c ratio is taken as 0.4 as per the Is codal specifications.

• selection of water content:-

from Is code 10262:2009 max water content for 20mm nominal size of aggregate is taken as 186 liters

the above value of 186 liters is taken for a slump of 25-50mm, so for every increase in 25mm slump water content should be increased by 3%

for 100mm slump value the max water content is 186+0.06(186)=197 lts

as superplasticizer is used water content can be reduced by 26%

so water content = 197*0.74= 145.78

• calculation of cement content:-

water content / cement content= 0.4

cement content= 145.78/0.4= 364.45 kg(cement + fly ash)

increasing the cement content by 10% for 30% of fly ash

total cement content = 1.10*364.45= 400.895( satisfies the condition of min and max cement content as per Is code 456)

now, the w-c ratio= is 145.78/400.895= 0.36

as we considered 30% of fly ash

weight of fly ash = 0.3*400.895= 120.26 kg/m^3

weight of cement= 400.895-120.26=280.62 kg/m^3

• calculation of the proportion of coarse aggregate and fine aggregate:-

from table 3 of Is 10262 for 20mm aggregate and fine aggregate conforming to zone 2

volume of coarse aggregate/ volume of total aggregate= 0.64 for w-c ratio of 0.5

volume of coarse aggregate is required for the w-c ratio is 0.4

the proportion of the volume of aggregate varies by 0.01 by every decrease or increase by 0.05

the corrected volume of coarse aggregate is 0.62

for pumpable concrete, the above value may be reduced by 10%

assuming 1 unit of total aggregates

proportion of coarse aggregate= 0.62*0.9=0.56

proportion of fine aggregate=1-0.56=0.44

• Mix calculation:-

taking the volume of concrete as 1m^3

volume of cement= (280.62/3.15)*1/1000=0.089

volume of fly ash= (120.26/2.2)*1/1000=0.054

volume of water= (145.78/1)*1/1000=0.145

volume of chemical admixtue= (7.6/1.145)*1/1000=0.006

volume of total aggregate= 1-(0.089+0.054+0.145+0.006)=0.706

mass of coarse aggregate= volume* proportion* sp gravity* 1000= 0.706*0.56*2.75*1000=1087.24 kg/m^3

mass of fine aggregate= volume* proportion* sp gravity* 1000= 0.706*0.44*2.6*1000=807.644 kg/m^3

• FINAL RESULTS:-

1. cement= 280.62 kg/m^3
2. fly ash=120.26 kg/m^3
3. water=145.78 kg/m^3
4. coarse aggregate=1087.24 kg/m^3
5. fine aggregate=807.644 kg/m^3

• MIX PROPORTION:- 1: 2.87: 4.33

CONCRETE MIX DESIGN OF M50 GRADE CONCRETE:-

Data assumed:-

• grade of concrete:- M50
• nominal size of aggregate:- 20mm
• type of aggregate:- crushed angular aggregates
• slump workability:- 75mm
• exposure condition:- severe
• max cement content :- 450 kg/m^3
• admixture:- superplasticizer
• sp gravity of cement:- 3.15
• sp gravity of coarse aggregate:- 2.74
• sp gravity of fine aggregate:- 2.65
• sp gravity of superplasticizer:- 1.145

DESIGN MIX

• target mean strength:-

fm= fck+1.65(standard deviation)

fm= 50+1.65*5=58.25 N/mm^2

• selection of the w-c ratio:-

max w-c ratio for severe exposure condition as per Is 456 is 0.45

from graph 1 the value of the w-c ratio is 0.33

the w-c ratio is taken as the lesser value of the above 2 values, but the min w-c ratio is taken as 0.4

so, adopt the w-c ratio as 0.4

• water content:-

from the code, the water content for the 20mm nominal size of aggregate is taken as 186 liters

the above value is suitable for the slump of 25-50mm

so for every increase in 25mm slump water content should be increased by 3%

now, the water content = 186+3%=191.58 liters

the use of a superplasticizer reduces the water content and increase the workability

the amount of water content reduced by the water content = 25%

water content = 191.58*0.75=143.6 kg/m^3

• cement content:-

cement content= water content/ w-c ratio

cement content= 143.6/0.4= 358.9 kg/m^3 (satisfies both conditions of max and min cement content)

• calculation of the proportion of coarse aggregate and fine aggregate:-

from table 3 of Is 10262 for 20mm aggregate and fine aggregate conforming to zone 2

volume of coarse aggregate/ volume of total aggregate= 0.64 for w-c ratio of 0.5

volume of coarse aggregate is required for w-c ratio is 0.4

the proportion of the volume of aggregate varies by 0.01 by every decrease or increase by 0.05

the corrected volume of coarse aggregate is 0.62

assuming 1 unit of total aggregates

proportion of coarse aggregate= 0.62

proportion of fine aggregate=0.38

• Mix calculation:-

taking the volume of concrete as 1m^3

volume of cement= (359/3.15)*1/1000=0.114

volume of water= (143/1)*1/1000=0.143

volume of chemical admixtue= (7.6/1.145)*1/1000=0.006

volume of total aggregate= 1-(0.114+0.143+0.006)=0.737

mass of coarse aggregate= volume* proportion* sp gravity* 1000= 0.737*0.62*2.74*1000=1252.01 kg/m^3

mass of fine aggregate= volume* proportion* sp gravity* 1000= 0.737*0.38*2.65*1000=742.159 kg/m^3

• FINAL RESULTS:-

1. cement= 359 kg/m^3
2. water=143 kg/m^3
3. coarse aggregate=1252 kg/m^3
4. fine aggregate=742.159 kg/m^3

• MIX PROPORTION:- 1: 2.06: 3.48