Project on Concrete Mix Design for various grades of Concrete
Que. Calculate the Concrete Mix Design for M35 grade concrete with fly ash
Mix design for M35 grade concrete with fly ash
Aim : Mix design for M 35 grade concrete with fly ash
Procedure :-
1. Stipulations for proportioning
a. Grade designation : M35
b. Type of cement : OPC 43 grade conforming to IS 8112
c. Type of mineral admixture: Fly ash confirming to IS 3812 ( Part 1)
d. Maximum nominal size of aggregates : 20mm
e. Minimum cement content : 320 kg/m^3 (Table :5 IS 456-2000,based on exposure condition)
f. Maximum water-cement ratio : 0.45 (Table :5 IS 456-2000,based on exposure condition)
g. Workability :100mm slump value of pumpable concrete
h. Exposure condition : Severe ( for reinforced concrete)
i. Method of concrete placing : Pumping
j. Degree of supervision : Good
k. Type of aggregate: Crushed angular aggregate
l. Maximum cement content : 450 kg/m^3.
m. Chemical admixture type : Superplaticizer.
2. Test data for materials
a. Cement used : OPC 43 grade confirming to IS 8112
b. Specific gravity of cement : 3.15
c. Fly ash : Conforming to IS 3812 part 1
d. Specific gravity of flyash : 2.2
e. Chemical admixture : Superplaticizer conforming to IS 9103
f. Specific gravity of :
Coarse aggregate : 2.74
Fine aggregate : 2.74
g. Water absorption :
Coarse aggregate : 0.5%
Fine aggregate : 1%
h. Free surface moisture
Coarse aggregate : Nil
Fine aggregate : Nil
i. Seive analysis
Coarse aggregates:
| IS seive size (mm) | Analysis of coarse aggregate fraction | Percentage of different fraction | Remarks | |||
| I | II | I | II | Combined | ||
| 20 | 100 | 100 | 60 | 40 | 100 | Confirming to |
| 10 | 0 | 71.2 | 0 | 28.5 | 28.5 | Table 2 |
| 4.75 | 0 | 9.4 | 0 | 3.7 | 3.7 | |
| 2.36 | 0 | 0 | 0 | 0 | 0 | IS 383 |
Fine aggregate : Conforming to grading Zone 1 of table 4 IS383.
3. To find target mean strength for mix proportioning
Target mean strength f'ck = fck +1.65s
= 35 +1.65*5 =43.25N/mm2
fck- Characteristic compressive strength
s- Standard deviation
4. Selection of water-cement ratio
Maximum water-cement ratio =0.45 (for severe condition ,from table 5 of IS 456-2000)
On experience water- cement ratio =0.4
0.4 <0.45, Hence OK.
5. Calculation of water content
Maximum water content for 20mm aggregate =186 litres ( Table 2 of IS 1026:2009) for 25mm to 50mm slump range
For 100 mm slump = 186+(6/100)*186 =197 litres
As superplaticizer is used, the water content is reduced upto 30%
Based on trials water content reduction of 29% is achieved with plasticizer
Hence arrived water content = 197*0.71 = 140 litres
6. Calculation of cement content
Water - cement ratio = 0.4
Cementatious material( Cement +flyash ) = 140/0.4 =350kg/m3
In table 5 of IS 456-2000, the cement content for severe exposure = 320kg/m3
350kg/m3>320kg/m3
Hence OK.
a. The percentage of flyash need to be decided based on project requirement and qualityof materials.
b. In some cases increase in cementatious materials can be warrned . Increase in cementatious material content and its percentage may be based on experience and trial
In this increase of 10% cementatious material content is considered.
Cementatious material content = 350*1.1 = 385kg/m3
Water content = 140kg/m3
So, water- cement ratio = 140/385 =0.364
Fly ash at 30% total cementatious material content = 35-30% = 115 kg/m3
Cement (OPC) =385-115 = 270kg/m3
Saving of cement while using flyash = 350-270 = 80kg/m3
Fly ash beign utilized = 115 kg/m3
7. Proportion of volume of coarse aggregate and fine aggregate content
From table 3 of IS 1026:2009 ,volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (Zone 1 ) for water- cement ratio =0.6
In present case the water - cement ratio is 0.4
Therefore the volume of coarse aggregate needs to be increased to decrease the fine aggregate content .
As the water- cement ratio is lowered 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 water-cement ratio)
Hence the corrected value ofcoarse aggregate for the water-cemnt ratio = 0.64
(If coarse aggregate is not of angular type, then also the volume of coarse aggregate may be required to be increased suitably ,based on experience)
For pumpable concrete, these are reduced by 10 %
Volume of coarse aggregate = 0.64*0.9 = 0.576
Volume of fine aggregate = 1-0.576 =0.424
8. Mix calculations
Mix calculation per unit volume of concrete:
1) Volume of concrete = 1 m^3.
2) Volume of cement = (Mass of cement / Specific gravity of cement ) *1/1000
= (270/3.15 )*1/1000 =0.086 mm3
3) Volume of flyash = (Mass of flyash / Specific gravity of flyash )*1/1000
= (115/2.2) *1/1000 = 0.052m3
4) Volume of water = ( Mass of water / Specific gravity of water)*1/1000
= (140/1)*1/1000 =0.140mm3
5) Volume of chemical admixture = ( Mass of admixture / specific gravity of admixture)*1/1000
=( 7.6/1.14)*1/1000 =0.006m3
6) Volume of aggregate ( Fine and coarse) = a- (b+c+d+e)
= 1-(0.086+0.052+0.140+0.006) =0.716m3
7) Mass of coarse aggregate = f* Volume of coarse aggregate * Specific gravity of coarse aggregate *1000
= 0.716*0.576*2.74*1000 =1130kg/m3
8) Mass of fine aggregate = f* Volume of fine aggregate* Specific gravity of fine aggreate*1000
= 0.716*0.424*2.74*1000= 831kg/m3
9. Mix proportion
Cement = 270kg/m3
Fly ash = 115kg/m3
Water =140kg/m3
Fine aggregate = 831kg/m3
Coarse aggregate = 1130kg/m3
Chemical admixture =7kg/m3
Water- cement ratio = 0.364
Mix ratio 1: 2.15: 2.94
10. The slump shall be measured and the water content and dosage of admixyure shall be adjusted for achieving the required slump on trial . The mix proportion shall be reworked for the actual water content and checkedd for durability requirements.
11. Two or more trials having variation of 10 % of water-cement ratio in Clause 10( Step 10) shall be carried out and a graph between three water -cement ratios and corresponding strengths shall be plotted to work out the mix proportions for the given target strength for feild trials .However durability shall be met.
Result : The mix design for M 35 grade of concrete with flyash is 1:2.15:2.94
Ques.2 M50 grade concrete without Fly ash
RESULTS:
Mix Proportion by weight of M35 grade of concrete with fly ash is 1:2.08:2.72 and its water-cement ratio was found to be 0.4.
Mix Proportion by weight of M50 grade of concrete without fly ash is 1:2.28:3.12 and its water-cement ratio was found to be 0.44.
APPENDIX
1) PHYSICAL CHARACTERSTICS OF DIFFERENT TYPES OF OPC CEMENT
2) Table – 5 Minimum Cement Content, Maximum Water-Cement Ratio and Minimum Grade of Concrete for Different Exposures with Normal Weight Aggregate of 20 mm Nominal Maximum Size IS: 456-2000
3) Table 2 of IS 383: Grade size distribution for different nominal sizes of coarse aggregate
4) Table 4 of IS 383: Grading of fine aggregate
5) Table I of IS 10262:2009: Assumed standard deviations
6) Table 2 of IS 10262:2009: maximum water content for 20 mm aggregate
