Project on Concrete Mix Design for various grades of Concrete
TO DETERMINE THE MIX DESIGNFOR M35 CONCRETE WITH FLY ASH CONSISSTING OF THE FOLLOWING PROPERTIES:
- Grade of designation:M35
- Types of mineral admixturesFLY ASH
- Maximum nominal size of aggregate :20
- Minimum water-cement ratio:0.45
- Workability:100-120mm slump
- Exposure condition:moderate
- Method of concrete placing:pumping
- Degree of supervision:Good
- Type of aggregate:crushed angular aggregate
- Maximum cement content:360kg/cum
- Chemical admixture type:super plasticizer
DATA OBTAINED:
- Cement used:OPC43grade(IS 12269)
SPECIFIC GRAVITY OF CEMENT:3.15
- Fly ash - specific gravity:2.2
- Coarse aggregate - specifc gravity:2.74
- Fine aggregate - specific gravity:2.74
- Water absorption of coarse aggregate:0.5%
- Coarse aggregate - seive analysis as per Table 2 of IS 383
- Fine aggregate - seive analyasis as per grading zone 1 of Table 4 of IS 383
PROCEDURE:
- Target strength for mix proportion is obtained from
fck = fck+1.65(Table 1 : IS 10262-2009)
Considering s = 5N/sq-mm
Thus FCK = 35+1.65(5) = 43.25 N/sq-mm
- WATER - CEMENT RATIO:
Considering maximum water - cement ratio = 0.4(Table 5: IS 456 2000)
- WATER CONTENT
Maximum water content for 20mm aggregate = 186 liters(Table 2: IS 10262:2009)
Estimated water content for 100mm slump = 186+(6/186) = 197 liters
However,it super plasticizer is used,the water content can be reduced upto 20% to 30%
Thus the water content obtained is 197-(30% of 197) = 132 liters
Adopt 140 liters
- CEMENT CONTENT
Adopted w/c ratio = 0.4
Cement content = 140/0.4 = 350 kg/cum
Minimum cement content for moderate exposure = 320 kg/cum.(Table 5 : IS 456 2000)
350 kg/cum > 320 kg/cum
Hence ok
- FLY ASH CONTENT
Considering 10% increase in cementitious material
Thus,cementious content = 350x1.1 = 385 kg/cum
Fly ash = 30% of total cementious cement = 385 x 0.3 = 115 kg/cum
- PROPORTION OF VOLUME OF COARSE AGGREGATE AND FINAL AGGREGATE:
Volume of coarse aggregate and final aggregate for w/c ratio o.5 = 0.6 (Table 3: IS 10262:2009)
In this case,w/c ratio is 0.4.Therefore volume of coarse aggregate is required to be increased to decreased the fine aggregate content. As the w/c ratio is reduced by 0.1,the proportion of volume of coarse aggregate is increased by 0.02 (at the rate of -/+0.01 for every ±0.05 change in w/c ratio).
Thus ,the corrected proportion of volume of coarse aggregate for w/c ratio of 0.4 = 0.62
For pumpable concrete,it can be reduced upto 10%. Hence,volume of coarse aggregate = 0.62 x 0.9 = 0.56
volume of fine aggregate = 1-0.56 = 0.44
MIX CALCULATIONS
The following mix calculations are carried out:
- Volume of concrete = 1 cum
- Volume of cement = Mass of cement / (specific gravity x 1000) = 270/(3.15x1000) = 0.86 cum
- Volume of fly ash = Mass of fly ash/(specific gravity x 1000) = 115/(2.2x1000) = 0.52 cum
- Volume of water = mass of water/(specific gravity x 1000) = 140/(1x1000) = 0.14 cum
- Volume of chemical admixture = Mass of chemical admixture/(specific gravity x 1000) = 7.6/(1.145x1000) = 0.006 cum
- Volume of all in aggregate = (1-(0.086+0.052+0.14+0.006)) = 0.716 cum
- Mass of coarse aggregate = volume of all aggregate x volume of coarse aggregate x specific gravity of coarse aggregates x 1000 = 0.716x0.56x2.74x1000 = 1098 kg/cum
- Mass of fine aggregates = volume of all aggregate x volume of fine aggregate x specific gravity of fine aggregate x 1000 = 0.716x0.44x2.74x1000 = 863 kg/cum
RESULT
Mix proportion obtained:
Cement = 270 kg/cum
Fly ash = 115 kg/cum
Water = 140 liters
Fine aggregate = 863 kg/cum
Coarse aggregate = 1098 kg/cum
Chemical admixtures = 7 kg/cum
W/C ratio = 0.4
Mix proportion by weight = 1:2.24:2.85
CONCLUSION
The slump should be measured and the water content and admixture can be adjusted to obtain the required slump.
The mix proportion can be adjusted and reworked as per requirement.