Project on Concrete Mix Design for various grades of Concrete
CHALLENGE 5
- Calculate the Concrete Mix Design for M35 grade concrete with fly ash and M50 grade concrete without fly ash.
Aim: The main aim of this project is to determine mix proportion of two different grade of concrete with and without the presence of fly ash.
Introduction: Concrete Mix Design is the concept of determining the correct proportion of the ingredients that are required for the preparation of the concrete i.e., the proportion of cement, coarse aggregates, fine aggregates and water content to achieve the good strength, durability, workability of concrete used for the construction. The proportioning of the ingredients of the concrete governs in 2 states namely in plastic and hardened state. If the concrete in the plastic state is not workable, the concrete cannot be placed and compacted properly but the initial strength will be at a higher rate. The concrete with high workability uses more concrete to fill in the narrow gaps and ensures that the gap is completely filled. The compressive strength of the concrete which is one of the important characteristics of the concrete is determined by the mix design. The increase in the compressive strength of the concrete the more is the load carrying capacity of the structure. This compressive strength is influenced by the water – cement ratio because of the hydration process.
Mix Design for M35 grade concrete with Fly Ash:
Ans: Grade of concrete = M35
Type of cement = 53 grade (OPC)
Type of Mineral admixture=Fly ash
Maximum nominal size of aggregate = 20mm
Minimum cement content = 340kg (From Table 5 of IS 456)
Maximum cement content = 450kg
Replacement of cement with fly ash = 30%
Maximum W/C ratio = 0.45 (From Table 5 of IS 456)
Workability = 100mm (Assumed) (Done for critical condition)
Exposure condition = Very Severe
Chemical admixture type: Superplasticizer
Specific gravity of cement = 3.15
Specific gravity of fly ash = 2.9
Specific gravity of coarse aggregate = 2.74
Specific gravity of fine aggregate = 2.74
Water absorption of coarse aggregate = 0.5%
Water absorption of fine aggregates = 1%
Fine aggregate is confirmed to zone 2
Target strength = fck+1.65S (S=Standard Deviation. For M35 grade S=5 (From Table 1 of IS10262))
=35+1.65*5
=43.25N/mm2
Maximum water cement ratio for M35 grade of concrete from table 5 of IS 456 is 0.45. The water – cement ration of very severe exposure condition for M35 grade concrete is 0.45. Hence the same water – cement ratio is adopted.
Maximum water content for 50mm slump is 186L as per Table 2 of IS1026
For 100mm slump the water content is increased by 3% as per the code IS1026 to obtain an additional slump of 25mm. Therefore, in order to get slump value of 100mm, in total the water – cement ratio as to be increased by 6%.
Thus, the water content is 186+0.06*186=197.16L
Since the superplasticizer is used the water – cement ration can be reduced between 20-30%. Here the adopted reduction in water – cement ratio is 20%.
Therefore, the water content adopted after using the superplasticizer = 197.16-0.2*197.16
=157.72
Adopted water content = 160L
Cement required = water content/W – C ratio
=160/0.45
=355.55kg
Since the fly ash is used the amount of cementitious content can be increased to achieve good concrete strength. The percentage of cementitious content is increased by 10%.
The cementitious content after increasing it by 10% = 356*1.1
=391.6
The minimum cement content for very severe exposure condition for M35 grade concrete is 340kg. The cementitious content adopted is 391.6 which is more than the minimum cement content thus it is OK.
Fly ash content = 30% of cement content
=391.6*0.3
= 117.48
Say = 118kg
Cement content = 391.6 – 118
=274.12kg
From the table 3 of IS 10262 for fine aggregates of zone II and water cement ratio = 0.5 we have coarse aggregate ratio = 0.62
Coarse aggregate ratio for W-C ratio of 0.45 = 0.63
Fine aggregate ratio = 1-0.63 = 0.37
Volume of concrete = 1m3
Volume of cement = 275 / (3.15*1000) = 0.087m3
Volume of fly ash = 118/ (2.5*1000) = 0.041m3
Volume of water = 160 / (1*1000) = 0.16m3
Total aggregate required = 1 – (0.087+0.16+0.041) = 0.71m3
Coarse aggregate content = 0.71*0.63*2.74*1000 = 1225.6kg
Fine aggregate content = 0.71*0.37*2.74*1000 = 719.8 kg
- Cement content = 275kg
- Fly ash = 118kg
- Fine aggregate content = 722kg
- Coarse aggregate content = 1226kg
- Water content = 160L
The mix proportion for M35 grade of concrete with fly ash is given as 1:0.4:2.6:4.45:0.58
Mix Design for M50 grade concrete without Fly Ash:
Grade of concrete = M50
Type of cement = 53 grade (OPC)
Maximum nominal size of aggregate = 20mm
Minimum cement content = 360kg
Maximum cement content = 450kg
Maximum W/C ratio = 0.4
Exposure condition: Extreme
Workability = 100mm
Specific gravity of cement = 3.15
Specific gravity of coarse aggregate = 2.74
Specific gravity of fine aggregate = 2.74
Water absorption of coarse aggregate = 0.5%
Water absorption of fine aggregates = 1%
Fine aggregate is confirmed to zone 2
Target strength = fck+1.65S
=50+1.65*5
=58.25N/mm2
Maximum water cement ratio for M50 grade of concrete for extreme condition from table 5 of IS 456 is 0.4
Maximum water content for 50mm slump is 186L
For 100mm slump the water content is increased by 6%. Thus, the water content is 186+0.06*186=197L
Adopted water content = 197L
Cement required = water content/W – C ratio
=197/0.4
=492.5kg
Adopted cement content = 493kg
From the table 3 of IS 10262 for fine aggregates of zone II and water cement ratio = 0.5 we have coarse aggregate ratio = 0.62
Coarse aggregate ratio for W-C ratio of 0.45 = 0.63
Fine aggregate ratio = 1-0.63 = 0.37
Volume of concrete = 1m3
Volume of cement = 493 / (3.15*1000) = 0.156m3
Volume of water = 197/ (1*1000) = 0.197m3
Total aggregate required = 1 – (0.156+0.197) = 0.647m3
Coarse aggregate content = 0.647*0.63*2.74*1000 = 1116.85kg
Fine aggregate content = 0.647*0.37*2.74*1000 = 655.9 kg
- Cement content = 495 kg
- Fine aggregate content = 660kg
- Coarse aggregate content = 1120kg
- Water content = 190L
The mix proportion for M50 grade of concrete is given as 1:1.33:2.26:0.38
Conclusion:
From the project carried out it can be concluded that the mix design for various grades of concrete with or without the presence of the fly ash has slight effect in the amount of the water content used in the preparation of the concrete. The mix design of any grade of concrete plays a major role in the compressive strength of the concrete. Thus the mix design as to be done to determine the correct proportion of the ingredients that are required for the preparation of the concrete.
Vijayalakshmi S H