A mix of M-80 Grade suitable for pumped concrete is to be designed with the following materials and detail.
- OPC 53 Grade, 7-day strength 52.5 N/mm2, Spgr 3.15
- Silica Fume Specific Gravity 2.20
- Standard deviation for the mix 5.0 N/mm2
- Grading and properties of river sand and 12.5 mm crushed aggregate are given in Table-1
- Superplasticizer based on modified Polycarboxylate, specific gravity 1.06, liquid pH 6.0. With the given set of materials, it was found that at a dosages of 2.5 % bwc it gives a reduction of 30% of water for the required slump of 100 mm after one hour at the average day site temperature of 37 degree C.
- As per grading of aggregates given in the Table-1, it is found that, if sand and aggregate are combined in the ratio of 45% and 55% they will give most suitable combined grading for pumped concrete.
- Air in the mix assumed 1.5%.
DESIGN CALCULATIONS
1. M-80 Grade of concrete design for a mean target strength of:
80 + 1.65 x 5 = 88.3 N/mm2 at 28 day age
2. With the given set of materials from various trials it was found that with OPC 450 Kg/m3, Silica Fume 45 Kg/m3 and W/C+SF ratio of 0.283 gives 28-day average cube compressive strength of 90.4 N/mm2.
3. Calculated density of the mix, worked out from reference 1.
 |
| Concrete Mix Design M80 Grade Pumpable Concrete |
4. Aggregates = 2440 – 140 – 450 – 45 = 1805 kg/m3
5. Sand = 1805 x 0.45 = 810 kg/m3 (say)
6. 12.5 mm Aggregate = 1805 x 0.55 = 995 kg/m3 (say)
Thus for M-80 Grade of concrete, quantity of materials per cu.m of concrete on the basis of saturated and surface dry aggregates.
|
Water
|
140 kg/m3
|
|
OPC 53 Grade
|
450 kg/m3
|
|
Silica fume
|
45 kg/m3
|
|
River sand
|
810 kg/m3
|
|
12.5 mm crushed aggregate
|
995 kg/m3
|
|
Superplasticizer
|
11.250 kg/m3
|
|
W/(C+SF) Ratio
|
0.283
|
|
Slump mm
|
102
|
|
7-day cube strength N/mm2
|
67.3
|
|
28-day cube strength N/mm2
|
89.5
|
| Table-1 Properties of Aggregates | |||
| I.S. Sieve size | Percentage passing by mass | ||
| River sand | 12.5 mm Crushed Agg | Combined aggregates grading of the mix | |
| 45% | 55% | ||
| 20 mm | 100 | 100 | 100 |
| 12.5 mm | 100 | 95 | x |
| 10 mm | 100 | 60 | 78 |
| 4.75 mm | 95 | 5 | 46 |
| 2.36 mm | 87 | 0 | 39 |
| 1.18 mm | 72 | - | 32 |
| 600 Micron | 40 | - | 18 |
| 300 Micron | 22 | - | 10 |
| 150,Micron | 5 | - | 2 |
| Specific gravity | 2.65 | 2.65 | - |
| Water absorption % | 0.8 | 0.5 | - |
| Organic impurities % | Nil | - | - |
| Coal & lignite % | Nil | Nil | - |
| Clay lumps % | Nil | Nil | - |
| Materials finer than 75 micron I.S. Sieve % | 0.2 | Nil | - |
| Flakiness index | - | 7.3 | - |
| Crushing value % | - | 10.5 | - |
