Project on Concrete Mix Design for various grades of Concrete

Concrete mix design for M35 grade concrete with fly ash and M50 grade concrete without fly ash:

Aim of project:

• Aim of the project is to find the appropriate proportions of the ingredients of M35 grade concrete(with fly ash) and M50 grade concrete (without fly ash) which are cement,sand, course aggregate,water and chemical admixture.

Introduction of project:

• The process of selecting suitable ingredients of concrete and determining their relative amounts with the objective of producing concrete of the required strength, workabiliy and  durability as economical as possible is known as design mix of concrete.
• Proportions of concrete are depends on characteristic of material used.
• Depends on required properties of the concrete,w/c ratio in cement paste, cement paste and aggregate ratio in the concrete mixture,sand and coarse aggregate ratio in aggregate mixture are decided.
• Overall objective of mix design is the selection of suitable ingredients among the available material and determining the most economical combination that will produce concrete with the required properties.

Step by step procedure for mix design of M35 grade concrete with fly ash:

Step1:

• Grade designation:M35
• Type of cement:M43
• Maximum nominal size of aggregate=20mm
• Exposure condition is severe
• Workability is 100mm
• Method of concrete placing is pumping
• Degree of supervision is good
• Type of aggregate is crushed angular aggregate
• Chemical admixture type is superplasticizer

Step2:Test data for material

• Specific gravity of course aggregate is 2.74
• Specific gravity of fine aggregate is 2.74
• Water absorption of course aggregate is 0.5%
• Water absorption of fine aggregate is 1%
• Free surface moisture is Nill for both coarse and fine aggregate.

Step3: calculation of target mean strength.

Ft=Fck+(1.65×standard deviation)

Standard deviation is taken from table1 of IS10262:2009.For M35 grade of concrete standard deviation is 5N/mm2.

Ft=35+(1.65×5)=35+8.25=43.25N/mm2.

Step4: Determination of water-cement ratio:

w/c(assume severe environment exposure condition)=0.45

Above w/c ratio is taken from table 5 of IS 456:2000

Based on experience adopted w/c is 0.4.

0.4 is less than 0.45 so it is ok.

w/c=0.4

Step5: Selection of water content

water content is taken based on nominal size of aggregate and slump size from table 2 of Is 10262:2009.

For 20mm nominal size of aggregate water content is 186 litre.

Above water content is for 25 to 50mm slump size but for 100mm slump size estimated water content is (186+6%of186) that is 197 litre.

Note:for every 25mm increase in slump water content is increases by 3%.

As super plasticisers used water content is reduced by 20 to 30%.

Based on trials with super plasticisers,water content reduction of 29% is achieved.

Water content=0.71×197=140 litre.

Step6:Calculation of cement content

w/c=0.4

Cementious material={140/0.4}=350 kg/m3.

Based on severe environment exposure condition(table 5 of Is456:2000) minimum cement content is 320 kg/m3.

350>320 ,so ok.

Cementious material is increases based on experience and trial,now in this project cementious material is increases by 10%

Cementious material content=350×1.10=385 kg/m3.

Water content=140kg/m3.

New w/c ratio is (140/385),that is 0.364.

Fly ash content is 30%of total cementious material,that is (385×30%)=115 kg/m3.

Cement content=385-115=270kf/m3.

Fly ash content=115 kg/m3.

Saved cement by use of fly ash=350-270=80kg/m3

Step7: proportion of volume of course aggregate and fine aggregate

Volume of course aggregate per unit volume of total aggregate is based on the nominal size of aggregate and zone of fine aggregate,it is taken from table3 of Is10262:2009

For 20mm nominal size of aggregate and zone1 sand volume of course aggregate per unit volume of total aggregate is 0.6

As w/c ratio is lowers by 0.1,the proportion of of course aggregate is increases by 0.02

Corrected volume of course aggregate is {0.6+0.02} that is 0.62.

Note:If course aggregate are not of angular type,then also volume of course aggregate is increases suitably.In this project course aggregate are of angular type.

For pumpable concrete volume of course aggregate is reduced by 10%.

Volume of course aggregate=0.9×0.62=0.56

Volume of fine aggregate=1-0.56=0.44

Step8:Mix calculations

Volume of concrete=1m3

Volume of cement=(mass of cement/specific gravity of cement)×(1/1000)

Vc=(270/3.15)×(1/1000)=0.086m3

Vol of fly ash=(115/2.2)×(1/1000)=0.052m3

Vol of water=(140/1)×(1/1000)=0.140m3

Vol of chemical admixture=(7.6/1.145)×(1/1000)=0.006m3

Vol of total aggregate={1-(0.086+0.052+0.140+0.006)}=0.716m3.

Mass of coarse aggregate=0.716×0.56×2.74×1000=1098 kg/m3.

Mass of fine aggregate=0.716×0.44×2.74×1000=863 kg/m3.

Step9:Mix proportion

• Cement=270kg/m3
• Fly ash=115bkg/m3
• Water=140 kg/m3
• Fine aggregate=863kg/m3
• Coarse aggregate=1098kg/m3.
• Chemical admixture=7.6kg/m3
• w/c=0.364

Trial mix ratio=270:863:1098=(270/270):(863/270):(1098/270)=1:2.24:2.85

Step10:

Water content and dosage of admixture is adjusted for achieving required slump.

Step11:

2 trials having variation of 10%of water content is carried out and graph between corresponding compressive strength & w/c ratio is drawn.

Explanation of the result of M30 grade concrete mix design:

Trial mix ratio=1:2.24:2.85

• 50 kg of cement
• (50×2.24) kg of sand that is 112 kg 
• (50×2.85) kg of coarse aggregate that is 142.5 kg

Step by step procedure for mix design of M50 grade concrete with out fly ash:

Step1:

• Grade designation:M35
• Type of cement:M43
• Maximum nominal size of aggregate=20mm
• Exposure condition is severe
• Workability is 100mm
• Method of concrete placing is pumping
• Degree of supervision is good
• Type of aggregate is crushed angular aggregate
• Chemical admixture type is superplasticizer

Step2:Test data for material

• Specific gravity of course aggregate is 2.74
• Specific gravity of fine aggregate is 2.74
• Water absorption of course aggregate is 0.5%
• Water absorption of fine aggregate is 1%
• Free surface moisture is Nill for both coarse and fine aggregate.

Step3: calculation of target mean strength.

Ft=Fck+(1.65×standard deviation)

Standard deviation is taken from table1 of IS10262:2009.For M50 grade of concrete standard deviation is 5N/mm2.

Ft=50+(1.65×5)=50+8.25=58.25N/mm2.

Step4: Determination of water-cement ratio:

w/c(assume severe environment exposure condition)=0.45

Above w/c ratio is taken from table 5 of IS 456:2000

Based on experience adopted w/c is 0.4.

0.4 is less than 0.45 so it is ok.

w/c=0.4

Step5: Selection of water content

water content is taken based on nominal size of aggregate and slump size from table 2 of Is 10262:2009.

For 20mm nominal size of aggregate water content is 186 litre.

Above water content is for 25 to 50mm slump size but for 100mm slump size estimated water content is (186+6%of186) that is 197 litre.

Note:for every 25mm increase in slump water content is increases by 3%.

As super plasticisers used water content is reduced by 20 to 30%.

Based on trials with super plasticisers,water content reduction of 29% is achieved.

Water content=0.71×197=140 litre.

Step6:Calculation of cement content

w/c=0.4

Cement content={140/0.4}=350 kg/m3.

Based on severe environment exposure condition(table 5 of Is456:2000) minimum cement content is 320 kg/m3.

350>320 ,so ok.

Cement content=maximum {320,350}=350kg/m3

Step7: proportion of volume of course aggregate and fine aggregate

Volume of course aggregate per unit volume of total aggregate is based on the nominal size of aggregate and zone of fine aggregate,it is taken from table3 of Is10262:2009

For 20mm nominal size of aggregate and zone1 sand volume of course aggregate per unit volume of total aggregate is 0.6

As w/c ratio is lowers by 0.1,the proportion of of course aggregate is increases by 0.02

Corrected volume of course aggregate is {0.6+0.02} that is 0.62.

Note:If course aggregate are not of angular type,then also volume of course aggregate is increases suitably.In this project course aggregate are of angular type.

For pumpable concrete volume of course aggregate is reduced by 10%.

Volume of course aggregate=0.9×0.62=0.56

Volume of fine aggregate=1-0.56=0.44

Step8:Mix calculations

Volume of concrete=1m3

Volume of cement=(mass of cement/specific gravity of cement)×(1/1000)

Vol of cement=(350/3.15)×(1/1000)=0.111m3

Vol of water=(140/1)×(1/1000)=0.140m3

Vol of chemical admixture=(7.6/1.145)×(1/1000)=0.006m3

Vol of total aggregate={1-(0.086+0.052+0.140+0.006)}=0.743m3.

Mass of coarse aggregate=0.743×0.56×2.74×1000=1140 kg/m3.

Mass of fine aggregate=0.746×0.44×2.74×1000=896 kg/m3.

Step9:Mix proportion

• Cement=350kg/m3
• Water=140 kg/m3
• Fine aggregate=896kg/m3
• Coarse aggregate=1140kg/m3.
• Chemical admixture=7.6kg/m3
• w/c=0.4

Trial mix ratio=350:896:1140=(350/350):(896/350):(1140/350)=1:2.56:3.257

Step10:

Water content and dosage of admixture is adjusted for achieving required slump.

Step11:

2 trials having variation of 10%of water content is carried out and graph between corresponding compressive strength & w/c ratio is drawn.

 Explanation of the result of M50 grade concrete mix design:

Trial mix ratio=1:2.56:3.257

• 50 kg of cement
• (50×2.56) kg of sand that is 128kg
• (50×3.257) kg of coarse aggregate that is 162.85 kg.