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Challenge

Project on Concrete Mix Design for various grades of Concrete

AAnees Ansari Mohammed2 Aug 2022
DESIGN

AIM: To calculate the Concrete Mix Design for M35 grade concrete with fly ash and M50 grade concrete without Fly ash.

INTRODUCTION: Concrete is a vital building material. A concrete mix is a combination of five major elements in various proportions: cement, water, coarse aggregates, fine aggregate, and air. Additional elements such as cementitious materials(fly ash) and chemical admixtures can be incorporated into the mix to give it certain desirable properties. Some of the important properties of a good concrete mixture are workability, durability, desired strength, mix transportation, easy compaction, and impact resistance. This kind of mix is designed by considering the assumptions of Code books like Indian standard codes(IS method), British codes(BS method), American codes(ACI method), etc according to the conditions required.

A good concrete mixture should save the life of concrete as well as our money.

Mix design of concrete is designed step by step i.e, stipulations for proportioning, test data for material, target mean strength, selection of water-cement ratio, selection of water content, calculation of cement content, proportion volume of coarse and fine aggregates, mix calculation, mix proportion for the trail.

OBJECTIVES:

  • To achieve the desired workability in the plastic stage.
  • To achieve desired minimum strength in the hardened stage.
  • To achieve the desired durability in given environmental conditions.
  • To produce concrete as economically as possible.
  • The main object of this project is to calculate the mix design for the M35 grade concrete with fly ash and M50 grade concrete without fly ash as above desired properties.

EQUATIONS: The equations which are needed to follow for designing concrete mix are listed below:

  1. Target mean strength of concrete f'ck=fck+1.65 s. Where
    • f'ck=Target mean strength
    • fck= characteristic compressive strength of concrete after 28 days.
    • S=Standard deviation which can be obtained from table 8 IS 10262:2009
  2. Cement content: From the formula of water-cement ratio, cement content can be calculated i.e.,
    • Cement content=Water content/water-cement ratio
  3. Volume calculation of Mix:
    1. Volume of concrete= 1m^3
    2. Volume of cement=(Mass of cement/specific gravity of cement)*(1/1000)
    3. Volume of fly ash=(Mass of fly ash/Specific gravity of fly ash)*(1/1000)
    4. Volume of water=(Mass of water/Specific gravity of water)*(1/1000)
    5. Volume of Admixtures=(Mass of admixtures/Specific gravity of admixture)*(1/1000)
    6. Volume of aggregates=(a-(b+c+d+e))
    7. Mass of coarse aggregates=f*volume of coarse aggregates*specific gravity of coarse aggregates*1000
    8. Mass of fine aggregates=f*volume of fine aggregates*specific gravity of fine aggregates*1000
    9. Mass of admixtures=2*of mass of cementitious materials

GUIDELINES USED FOR CONCRETE MIX DESIGN: The following Indian Standard code books are used to design concrete mix:

  1. IS 456:2000
  2. IS 10262:2009
  3. IS 8112
  4. IS 9103
  5. IS 383
  6. IS 3812 (PART 1)

PROCEDURE AND CALCULATION:

PART 1: Calculation of concrete mix design for M35 concrete using OPC and fly ash

STEP 1: STIPULATIONS FOR PROPORTIONING

  1. Grade designation= M35
  2. Type of cement= OPC 43 grade conforming to IS 8112
  3. Type of mineral admixtures= Fly ash conforming to IS 3812 (PART 1)
  4. Maximum nominal size of aggregate= 20mm
  5. Minimum cement content= 320kg/mm^3 (from table 5 IS 456 2000 depending on exposure condition)
  6. Maximum water-cement ratio= 0.45 (from table 5 IS 456 2000 depending on exposure condition)
  7. Workability= 100mm(Slump)
  8. Exposure condition= Severe (for reinforced concrete)
  9. Method of concrete placing= Pumping
  10. Degree of supervision= Good
  11. Type of aggregate= Crushed angular aggregate
  12. Maximum Cement(OPC) content= 450 kg/m^3
  13. Chemical admixture type= Superplasticizers

STEP 2: TEST DATA FOR MATERIALS

  1. Cement used= OPC 43 grade conforming to IS 8112
  2. Specific gravity of cement= 3.15
  3. Fly ash= Conforming to IS 3812 (Part 1)
  4. Specific Gravity of Fly ash= 2.2
  5. Chemical admixture= Superplasticizer conforming to IS 9103
  6. Specific gravity of admixture= 1.145
  7. Specific gravity of:
    1. Coarse aggregate= 2.74
    2. Fine aggregate= 2.74
  8. Water absorption:
    1. Coarse aggregate= 0.5%
    2. Fine aggregate=1.0%
  9. Free surface moisture:
    1. Coarse aggregate= NIL (Absorbed moisture also NIL)
    2. Fine aggregate= NIL
  10. 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 PROPORTIONING

It is calculated by the formula f'ck=fck+1.65 s

where,

f'ck= Target mean compressive strength at 28 days,

fck= Characteristic compressive strength at 28 days, and

s= Standard deviation.

From table 1, IS 10262:2009, the Standard deviation for M35 is, s=5N/mm^2, and compressive strength fck= 35N/mm^2.

Target strength f'ck=35+(1.65*5)

Therefore, f'ck=43.25N/mm^2

Target mean strength=43.25 N/mm^2

STEP 4: SELECTION OF WATER-CEMENT RATIO

From table 5 IS 456 2000, the maximum water-cement ratio with exposure condition SEVERE is 0.45

Based on experience, we adopted a water-cement ratio=0.42

0.42<0.45, hence it is OK.

Therefore, the Adopted water-cement ratio=0.42

STEP 5 SELECTION OF WATER CONTENT

Based on the nominal size of aggregates, water content is taken from table 2 IS 10262 2000.

From stipulations, the Nominal size of aggregates= 20mm

So, from table 2 IS 10262 Maximum water content= 186kgs for slump value 25-50mm.

From clause 4.2 IS 10262, 3% of water content will be increased for every 25mm increase in slump value. In this case, we want water content for a slump value of 100mm. So, 6% of water content needs to be increased.

Estimated water content=186+(186*0.06)=197.16kgs.

NOTE: Because of using superplasticizers, up to 20% of water content can be decreased.

From the trails on superplasticizers, We have achieved a reduction of 20% in water content.

Obtained water-content= 197.16-(197.17*0.2)=157.72

Therefore, Water content≈158kgs

STEP 6 CALCULATION OF CEMENT CONTENT

Water cement ratio, W-C= 0.42

Water content, W= 158 kgs

Therefore, Cementitious content, C=W/(W-C)=158/0.42=376.10kg/m^3≈376kg/m^3

From Table 5 IS 456 2009, the Minimum cementitious content for the Exposure condition severe is 320kg/m^3

Hence,376kg/m^3 > 320kg/m^3. So it is OK

Hence, New cementitious content is 10% greater than that obtained one i.e., 376+(376*0.1)=413.6kg/m^3≈414kg/m^3

Water content=158 kgs.

So Water cement ratio=158/414=0.382

In this cementitious material, Fly ash content is 30%.

Therefore, fly ash content= 414*0.3=124.2kg/m^3

Final cement content= 414-124.2=289.8kg/m^3

So, The cement content that we saved by using fly ash is = 376-289.8=86.2kg/m^3

STEP 7 PROPORTION OF VOLUME OF COARSE AGGREGATES AND FINE AGGREGATES

From Table 3 Zone 1 IS 10262 2009, the Volume of Coarse aggregates for 20 mm size of water cement ratio of 0.5 is 0.6

But in the present case water-cement ratio that has been obtained for us is 0.38.

Therefore, the volume of coarse aggregates is required to be increased to decrease the fine aggregate content. As the water-cement ratio is lower by 0.12, the proportion of the volume of coarse aggregate is increased by 0.024 ( at the rate of -/+ 0.01 for every ± 0.05 change in water-cement ratio).

Therefore, the corrected proportion of the volume of coarse aggregate for the water-cement ratio of 0.38=0.624.

For pumpable concrete, these values should be reduced by 10%.

Therefore, volume of coarse aggregate=0.624-(0.624*0.1)=0.562

Volume of fine aggregate content=1-0.562=0.438

STEP 8 MIX CALCULATIONS

In this mix calculation, we are going to find out volumes of cement, water, fly ash, admixtures everything per unit volume of concrete.

  1. Volume of concrete= 1m^3
  2. Volume of cement=(Cement content/specific gravity of cement)*(1/1000)=(289.8/3.15)*(1/1000)=0.092m^3
  3. Volume of fly ash=(Fly ash content/Specific gravity of fly ash)*(1/1000)=(124.2/2.2)*(1/1000)=0.056m^3
    • Therefore the volume of cementitious materials=0.092+0.056=0.148m^3
  4. Volume of water=(Weight of water/Specific gravity of water)*(1/1000)=(158/1)*(1/1000)=0.158m^3
  5. The volume of admixtures=(Weight of admixtures/ Specific gravity of admixtures)*(1/1000)=((414*0.02)/1.145)*(1/1000)=0.00723m^3
    • Weight of admixtures=2% weight of cementitious materials=414*0.02=8.28 kg/m^3
  6. Volume of aggregates=(a-(b+c+d+e))=(1-(0.092+0.056+0.158+0.00732))=0.687m^3
  7. Mass of coarse aggregates=f*Volume of coarse aggregates*Specific gravity of coarse aggregates*1000=0.687*0.562*2.74*1000=1057.9kg/m^3
  8. Mass of fine aggregates=f*volume of fine aggregates*specific gravity of fine aggregates*1000=0.687*0.438*2.74*1000=824.48kg/m^3

STEP 9 MIX PROPORTION Trail mix

  • Cement=289.8 kg/m^3
  • Fly ash= 124.2 kg/m^3
  • Water= 158 litres
  • Fine aggregates= 824.48 kg/m^3
  • Coarse aggregates= 1057.9 kg/m^3
  • Superplasticizers (admixtures)= 8.28 kg/m^2
  • Water-cement ratio= 0.38 (Lowest W/C ratio is selected)
  • Trail Mix ratio= 289.8:824.48:1057.9=1 : 2.85 : 3.65

STEP 10 The slump shall be measured and the water content and dosage of admixtures shall be adjusted for achieving the required slump based on trial if required. The mix proportion shall be reworked for the actual water content and checked for durability requirements.

STEP 11 Two more trials having variation of +/-10 % of water cement ratio in STEP 10 shall be carried out and a graph between three water-cement ratios and their corresponding strengths shall be plotted to work out the mix proportions for the given target strength for field trails. However, durability requirements shall be met.

PART 2: Calculation of concrete mix design for M50 grade concrete using OPC without Fly ash

STEP 1: STIPULATIONS FOR PROPORTIONING

  1. Grade designation= M50
  2. Type of cement= OPC 43 grade conforming to IS 8112
  3. Maximum nominal size of aggregate= 20mm
  4. Minimum cement content= 340kg/m^3 (from table 5 IS 456 2000 depending on the exposure condition)
  5. Maximum water-cement ratio=0.45 (from table 5 IS 456 2000 depending on the exposure condition)
  6. Workability= 75mm(Slump)
  7. Exposure condition= Very severe(For reinforced concrete)
  8. Method of concrete placing= Pumping
  9. Degree of supervision= Good
  10. Types of aggregate= Crushed angular aggregate
  11. Maximum cement (OPC) content= 450 kg/m^3
  12. Chemical admixture type= Superplasticizers

STEP 2: TEST DATA FOR MATERIALS

  1. Cement used= OPC grade conforming to IS 8112
  2. Specific gravity of cement= 3.15
  3. Chemical admixture= Superplasticizer conforming to IS 9103
  4. Specific gravity of admixture= 1.145
  5. Specific gravity of:
    1. Coarse aggregate= 2.74
    2. Fine aggregate= 2.74
  6. Water absorption:
    1. Coarse aggregate= 0.5%
    2. Fine aggregate= 1.0%
  7. Free surface moisture:
    1. Coarse aggregate= NIL ( Absorbed moisture also NIL )
    2. Fine aggregate= NIL
  8. Sieve analysis:
    1. Coarse aggregate= Conforming to Table 2 of IS 383
    2. Fine aggregate= Conforming to grading Zone 1 of Table 4 of IS 383

STEP 3: TARGET STRENGTH FOR MIX PROPORTIONING

It is calculated by the formula f'ck=fck+1.65 s

Where,

f'ck= Target mean compressive strength at 28 days.

fck= Characteristic compressive strength at 28 days, and

s= Standard deviation

From table 1, IS 10262, the standard deviation for M50 is, s= 5 N/mm^2,and

compressive strength fck= 50 N/mm^2

Target strength f'ck=50+(1.65*5)

Therefore, f'ck=58.25n/mm^2

Target mean strength= 58.25 N/mm^2

STEP 4: SELECTION OF WATER-CEMENT RATIO

From table 5 IS 456 2000, the maximum water-cement ratio with exposure condition VERY SEVERE is 0.45

Based on experience, we adopted a water-cement ratio = 0.42

0.42<0.45, hence it is OK.

Therefore, the adopted water-cement ratio=0.42

STEP 5 SELECTION OF WATER CONTENT

Based on the nominal size of aggregates, water content is taken from table 2 IS 10262 2000.

From stipulations, the Nominal size of aggregates=20mm

So, from table 2 IS 10262 Maximum water content= 186kgs for slump value 25-50mm

From clause 4.2 IS 10262, 3% of water content will be increased for every 25mm increase in slump value. In this case, we want water content for a slump value of 75mm. So, 3% of water content needs to be increased.

Estimated water content=186+(186*0.03)=191.58

NOTE: Because of using superplasticizers, up to 20% and above of water content can be decreased.

From the trails on superplasticizers, We have achieved a reduction of 25% in water content.

Obtained water-content=191.58-(191.58*0.25)=143.69

Therefore, a Water content≈144 litres

STEP 6 CALCULATION OF CEMENT CONTENT

Water cement ratio, W-C= 0.42

Water content, W= 144 litres

Therefore, cement content,C=W/W-C= 144/0.42=343kg/m^3

From table 5 of IS 456 2000, In very severe exposure conditions minimum cement content for reinforced concrete is= 340kg/m^3

343kg/m^3>340kg/m^3, hence it is OK

Therefore, cement content=343kg/m^3

STEP 7 PROPORTION OF VOLUME OF COARSE AGGREGATES AND FINE AGGREGATES

From Table 3 Zone 1 IS 10262 2008, the Volume of Coarse aggregates for 20 mm size of water cement ratio of 0.5 is 0.6

But in the present case, the Water-cement ratio that has been obtained for us is 0.42.

Therefore, the volume of coarse aggregates is required to be increased to decrease the fine aggregate content. As the water-cement ratio is lower by 0.08, the proportion of the volume of coarse aggregate is increased by 0.016( at the rate of -/+0.01 for every ± 0.05 change in water-cement ratio).

Therefore, the corrected proportion of the volume of coarse aggregate for the water-cement ratio of 0.42=0.616.

For pumpable concrete, these values should be reduced by 10%.

Therefore, volume of coarse aggregate=0.616-(0.616*0.1)=0.5544

The volume of the fine aggregate=1-0.5544=0.4456

STEP 8 MIX CALCULATIONS

In this mix calculation, we are going to find out volumes of cement, water, fly ash, admixtures everything per unit volume of concrete.

  1. Volume of concrete= 1m^3
  2. Volume of cement= (mass of cement/specific gravity of cement)*(1/1000)=(343/3.15)*(1/1000)=0.109m^3
  3. Volume of water= (mass of water/specific gravity of water)*(1/1000)=(144/1)*(1/1000)=0.144m^3
  4. Volume of admixtures= (mass of admixtures/specific gravity of admixtures)*(1/1000)
    =(2% of the weight of cement/ specific gravity of admixtures)*(1/1000)
    =((343*0.02)/1.145)*(1/1000)=0.006m^3
    • Mass of admixtures= 2% of the mass of cement content=353*0.02=7.06kg/m^3
  5. Volume of aggregates=(a-(b+c+d))= (1-(0.109+0.144+0.006))=0.741m^3
  6. Mass of coarse aggregates=e*Volume of coarse aggregates*specific gravity of coarse aggregates*1000=0.741*0.5544*2.74*1000=1124.62kg/m^3
  7. Mass of fine aggregates=e*volume of fine aggregates*specific gravity of fine aggregates*1000=0.741*0.4456*2.74*1000=904.72kg/m^3

STEP 9 MIX PROPORTION Trail mix

  • Cement=343 kg/m^3
  • Water= 144 litres
  • Fine aggregates= 904.72 kg/m^3
  • Coarse aggregates= 1124.62 kg/m^3
  • Superplasticizers( admixtures)= 7.06kg/m^3
  • Water-cement ratio=0.42(Lowest W/C ratio is selected)
  • Trail Mix ratio= 343 : 904.72 : 1124.62= 1 : 2.64 : 3.28

STEP 10 The slump shall be measured and the water content and dosage of admixtures shall be adjusted for achieving the required slump based on trial if required. The mix proportion shall be reworked for the actual water content and checked for durability requirements.

STEP 11 Two more trials having variation of +/-10% water cement ratio in STEP 10 shall be carried out and a graph between three water-cement ratios and their corresponding strengths shall be plotted to work on the mix proportions for the given target strength for field trails. However, Durability requirements shall be met.

RESULTS:

  1. The mix proportion for the Design mix of M35 grade concrete using fly ash as partial replacement of OPC is 1 : 2.85 : 3.65 and the water-cement ratio is 0.38.
  2. The mix proportion for the Design mix of M50 using only OPC is 1 : 2.64 : 3.28 and the water-cement ratio is 0.42.
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