Project on Concrete Mix Design for various grades of Concrete
AIM:
Calculate the Concrete Mix Design for M35 grade concrete with fly ash & M50 grade concrete without Fly ash
INTRODUCTION:
Concrete mix design is a procedure of selecting the suitable ingredients of concrete and their relative proportions with an objective to prepare concrete of certain minimum strength, desired workability and durability as economically (value engineered) as possible.
Fly-ash is the most economical and easily available mineral admixture that can partially replace cement in a concrete mix ,the resultant concrete will have excellent fresh, hardened and durable properties.
As per IS:456, the maximum replacement of cement with fly-ash have a capping of 35%.
As we decide to go for a concrete mix design, collect the following data beforehand as few design stipulation are freezed on the basis of these data.
OBJECTIVE:
To determine the most economical & practical combination of readily available materials to produce a concrete that will satisfy the performance requirements under particular conditions of use.
Also, to determine the proportion of ingredients that would produce a workable concrete mix that is durable, and of required strength and at a minimum cost.
This objective is to prepare by using Concrete mix proportioning guidelines from IS:10262-2009 & IS:46-2000.
PRELIMINARY DATA REQUIRED FOR MIX DESIGN:
Purely governed on the local conditions, were the concrete need to be applied
- Exposure Conditions of the structure: The general environment to which the concrete will be exposed during its service life, is categorized into five class to severity, as per IS 456.
The exposure condition limit the minimum cement content content (with flyash it is total cementitious content – “cement + flyash”), maximum water – cement ratio content (with flyash it is total water – cementitious content) and minimum grade of concrete.
As per exposure condition, you have the above data for working the first trial and arriving its mix proportion.
If you are getting desired result at lower cement content (with flyash it is total cementitious content), you need to put extra as freezed by IS 456.
- Minimum thickness of member:Size of aggregate should not be more t han one-fourth of the minimum thickness of member, mostly 20 mm nominal size aggregate is suitable for most works. It is always suggested to go the maximum nominal size of aggregate to save on quantity of cement per unit of concrete.
- Cement Grade:Cement type/grade locally available that can be made available throughout construction period
- Workability:Placing condition of concrete governs its workability, low – slump of 25-75 mm (lightly reinforced sections in slab, beam, column) to high – slump of 100-150 mm (slip form, pumped concrete)
PART-1: Mix Design FOR M35 Concrete with Fly ash Data.
Step 1: Stipulations for Concrete mix Design
Grade Designation : M35
Type of Cement : OPC 53 grade confirming to IS 8112
Type of Flyash : Class F
Maximum nominal size of aggregate: 20 mm
Minimum cement content: 340 kg/m3
Maximum water-cement ratio: 0.45
Workability: 100 mm (slump)
Exposure condition : Moderate (for reinforced concrete)
Method of concrete placing : Pumping
Degree of supervision : Good
Type of aggregate : Crushed angular aggregate
Maximum cement content : 450 kg/m3
Chemical admixture type : Super Plasticizer
Step 2: Test Data for Materials (to be determined in the laboratory):
Specific gravity of cement: 3.15
Specific gravity of flyash : 2.2
Specific gravity of Coarse aggregate: 2.74
Specific gravity of Fine aggregate: 2.74
Step 3: Procedure for Concrete Mix Design of M35 Concrete with Fly ash:
ftarget = fck + 1.65 x s
Therefore the terms;
‘ftarget‘ is the Target Average Compressive Strength at 28 days,
‘fck’ is the Characteristic Compressive Strength at 28 days, and
‘s’ is the Standard Deviation
as per the table I of IS: 10262-2009 , the standard deviation, s is 5.0 N/mm²
Therefore, target strength = 35 + 1.65 x 5.0 = 43.25 N/mm²
Note : Under control conditions if Target average compressive strength is achieved then at field ,the probability of getting compressive strength of 30 MPa is very high
Step 4: Selection of Water/Cement Ratio:
From Table 5 of IS 456:2000,
Maximum water-cement ratio = 0.45
Note : Do not start with w/cm ratio above 0.50,even though the other desired results like Strength, workability could be achieved.
Step 5: Selection of Water Content:
From Table 2 of IS 10262-2009, maximum water content =186 liters (for 25 to 50 mm slump range) for 20 mm aggregate.
Estimated water content for 100 mm slump =186+(6/100) x 186 =197 liters. Therefore Adopted water content is = 197 L
Based on trials with Super plasticizer, water content reduction of 20% has been achieved. Hence the arrived water content = 197-[197 x (20/100)] = 158 liters.
Step 6: Calculation of Cement Content & Fly ash:
Water-cement ratio =0.45
Cement content = 158/0.45 = 351 kg/m3
The Cementitious content must be increased in order to attain good workability & strength. Here we are increasing cementitious content by 10%.
Final Cement content = 351 x 1.1 = 386 kg/m3
From Table 5 of IS 456:2000, minimum cement content for ‘MODERATE’ exposure condition
386 kg/m3 > 340 kg/m3, hence, O.K.
Cement material content = 386 kg/m3
New Water cement ratio = 158-386 = 0.4
Fly ash content is taken as 30% of total cement content = 386 x 0.3 = 115.8 kg/m3
Cement required = 386 – 115.8 = 270.2 kg/m3
Cement Content & Fly ash required is 386 kg/m3 and 115.8 kg/m3 & New w/c ratio is 0.4.
Step 7: The Proportion of the Volume of Coarse Aggregate and Fine Aggregate Content
From Table 3 of IS 10262:2009, the volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (Zone II) for a water-cement ratio of 0.50 =0.62.
In the present case, the water-cement ratio is 0.45. Therefore. the volume of coarse aggregate is required to be increased to decrease the fine aggregate content. As the water-cement ratio is lower by 0.10. the proportion of the volume of coarse aggregate is increased by 0.02 (at the rate of -/+ 0.01 for every ± 0.05 change in the water-cement ratio). Therefore. the corrected proportion of the volume of coarse aggregate for the water-cement ratio of 0.45 = 0.64.
For pumpable concrete, these values should be reduced by 10 percent.
Therefore, volume of coarse aggregate = 0.64 x 0.9 = 0.576.
Volume of fine aggregate content =1 – 0.576 =0.424
Step 8: Mix Calculations:
- a) Volume of concrete = 1m3
- b) Volume of cement = (Mass of Cement/Specific Gravity of Cement) X (1/1000)
= (270.2/3.15) x (1/1000)
= 0.085 m³
- c) Volume of flyash = (Mass of flyash/Specific Gravity of flyash) X (1/1000)
= (115.8/2.2) x (1/1000)
= 0.052 m³
- d) Volume of water = (Mass of Water/Specific Gravity of Water) X (1/1000)
= (158/1) x (1/1000) = 0.158 m³
- e) Volume of super plasticizer = (Mass of Super plasticizer / Specific Gravity of Admixture) x (1/1000)
= (8.2/1.145) x (1/1000)
= 0.007 m³
- f) Volume of all aggregate = (a-(b+c+d+e))
= 1 – (0.085 + 0.052+0.158+0.007)
= 0.698 m³
- g) Mass of coarse aggregate = Volume of all Aggregate X Volume of coarse Aggregate X Specific Gravity of Coarse Aggregate X 1000
= 0.698 x 0.576 x 2.74 x 1000
= 1101.6 kg
- g) Mass of fine aggregate = Volume of all Aggregate X Volume of Fine Aggregate X Specific Gravity of Fine Aggregate X 1000
= 0.698 x 0.424 x 2.74 x 1000
= 810.9 kg
Step 9: Concrete Mix Proportions:
Cement = 270.2 kg/m³
Fly ash = 115.8 kg/m³
Water = 158 kg/m³
Super plasticizer = 7 kg/m³
Fine aggregates = 810.9 kg/m³
Coarse aggregate = 1101.6 kg/m³
W/c = 0.40 (Lowest w/c is selected)
Final Concrete Mix Ratio
Mix ratio of M35 is 1: 2.1: 2.85 (Cement: Fine aggregate: Coarse aggregate)
(OR)
Mix ratio of M35 is 1: 0.42: 3.0: 4.07 (Cement: Fly ash: Fine aggregate: Coarse aggregate)
Step 10: This trail mix ratio should match the workability, durability, minimum strength of M35 grade concrete.
Step 11: If it does not satisfy the above criteria two or more trails for increase of 10% should be done.
PART-2: Mix Design For M50 Concrete.
Step 1: Stipulations for Concrete mix Design
Grade Designation : M50
Type of Cement : OPC 53 grade confirming to IS 8112
Maximum nominal size of aggregate: 20 mm
Minimum cement content: 320 kg/m3
Maximum water-cement ratio: 0.45
Workability: 100 mm (slump)
Exposure condition : Severe (for reinforced concrete)
Method of concrete placing : Pumping
Degree of supervision : Good
Type of aggregate : Crushed angular aggregate
Maximum cement content : 450 kg/m3
Chemical admixture type : Super Plasticizer
Step 2: Test Data for Materials (to be determined in the laboratory):
Specific gravity of cement: 3.15
Specific gravity of Coarse aggregate: 2.74
Specific gravity of Fine aggregate: 2.74
Step 3: Procedure for Concrete Mix Design of M50 Concrete:
ftarget = fck + 1.65 x s
Therefore the terms;
‘ftarget‘ is the Target Average Compressive Strength at 28 days,
‘fck’ is the Characteristic Compressive Strength at 28 days, and
‘s’ is the Standard Deviation
as per the table I of IS: 10262-2009 , the standard deviation, s is 5.0 N/mm²
Therefore, target strength = 50 + 1.65 x 5.0 = 58.25 N/mm²
Note : Under control conditions if Target average compressive strength is achieved then at field ,the probability of getting compressive strength of 30 MPa is very high
Step 4: Selection of Water/Cement Ratio:
From Table 5 of IS 456:2000,
Maximum water-cement ratio = 0.45
Note : Do not start with w/cm ratio above 0.50,even though the other desired results like Strength, workability could be achieved.
Step 5: Selection of Water Content:
From Table 2 of IS 10262-2009, maximum water content =186 liters (for 25 to 50 mm slump range) for 20 mm aggregate.
Estimated water content for 100 mm slump =186+(6/100) x 186 =197 liters. Therefore Adopted water content is = 197 L
Based on trials with Super plasticizer, water content reduction of 20% has been achieved. Hence the arrived water content = 197-[197 x (20/100)] = 158 liters.
Step 6: Calculation of Cement Content:
Water-cement ratio =0.45
Cement content = 158/0.45 = 351 kg/m3
From Table 5 of IS 456:2000, minimum cement content for ‘MODERATE’ exposure condition
351 kg/m3 > 320 kg/m3, hence, O.K.
Cement Content required is 351 kg/m3 & w/c ratio is 0.45.
Step 7: The Proportion of the Volume of Coarse Aggregate and Fine Aggregate Content
From Table 3 of IS 10262:2009, the volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (Zone II) for a water-cement ratio of 0.50 =0.62.
In the present case, the water-cement ratio is 0.45. Therefore. the volume of coarse aggregate is required to be increased to decrease the fine aggregate content. As the water-cement ratio is lower by 0.10. the proportion of the volume of coarse aggregate is increased by 0.02 (at the rate of -/+ 0.01 for every ± 0.05 change in the water-cement ratio). Therefore. the corrected proportion of the volume of coarse aggregate for the water-cement ratio of 0.45 = 0.64.
For pumpable concrete, these values should be reduced by 10 percent.
Therefore, volume of coarse aggregate = 0.64 x 0.9 = 0.576.
Volume of fine aggregate content =1 – 0.576 =0.424
Step 8: Mix Calculations:
- a) Volume of concrete = 1m3
- b) Volume of cement = (Mass of Cement/Specific Gravity of Cement) X (1/1000)
= (351/3.15) x (1/1000)
= 0.1114 m³
- c) Volume of water = (Mass of Water/Specific Gravity of Water) X (1/1000)
= (158/1) x (1/1000) = 0.158 m³
- d) Volume of super plasticizer = (Mass of Super plasticizer / Specific Gravity of Admixture) x (1/1000)
= (8.2/1.145) x (1/1000)
= 0.007 m³
- e) Volume of all aggregate = (a-(b+ c+ d ))
= 1 – (0.1114+0.158+0.007)
= 0.723 m³
- f) Mass of coarse aggregate = Volume of all Aggregate X Volume of coarse Aggregate X Specific Gravity of Coarse Aggregate X 1000
= 0.723 x 0.576 x 2.74 x 1000
= 1141.0 kg
- g) Mass of fine aggregate = Volume of all Aggregate X Volume of Fine Aggregate X Specific Gravity of Fine Aggregate X 1000
= 0.723 x 0.424 x 2.74 x 1000
= 839.9 kg
Step 9: Concrete Mix Proportions:
Cement = 351 kg/m³
Water = 158 kg/m³
Super plasticizer = 7 kg/m³
Fine aggregates = 839.9 kg/m³
Coarse aggregate = 1141.0 kg/m³
W/c = 0.45
Final Concrete Mix Ratio
Mix ratio of M50 is 1: 2.39: 3.25 (Cement: Fine aggregate: Coarse aggregate)
Step 10: This trail mix ratio should match the workability, durability, minimum strength of M50 grade concrete.
Step 11: If it does not satisfy the above criteria two or more trails for increase of 10% should be done.
RESULTS:
PART 1: Mix Proportion by weight of M35 grade of Concrete is 1: 2.1: 2.85 (Cement: Fine aggregate: Coarse aggregate) and its water-cement ratio was found to be 0.40.
(OR)
Mix Proportion by weight of M35 grade of Concrete is 1: 0.42: 3.0: 4.07 (Cement: Fly ash: Fine aggregate: Coarse aggregate) and its water-cement ratio was found to be 0.40.
PART 2: Mix Proportion by weight of M50 grade of Concrete is 1:2.39:3.25 and its water-cement ratio was found to be 0.45.
CONCLUSION
As a conclusion for our concrete mix, we were able to properly mix the water, Portland cement, sand, and stone aggregates following the proper steps and procedures. We also found during the mixing that water makes the concrete more workable.