2-OPERATION
DRUM SPEED
The mixer drum should revolve between 20 and 25 R.P.M.’s for best results in mixing concrete. To obtain this speed using a 1725/1800 R.P.M. electric motor, use a 2” diameter “A” section
If using a 6 to 1 speed reduction 3 H.P. gasoline engine, use a 6 ¼” diameter “A” section
GETTING READY FOR MIXING
Lay out forms for your concrete floor, patio, driveway, sidewalk, etc.
The quality of concrete is directly related to the quality of the cement paste. The quality of the paste, in turn, is directly related to the amount of water mixed with the cement. For a given amount of cement, as the amount of mixing water is reduced, the strength of the paste increases, making the concrete stronger and more durable.
The proportions by weight given in Table 1 can be used as a starting point to make 1 cu. Ft. (0.028 m3) of strong, durable concrete. The proportions given in Table 2 are volumetric; 1 bag of cement is equal to 1 cu. ft. (0.28 m3) and weighs 94 lbs.
(42.6 kg). The Canadian bag of cement has a net mass of 40 kg.
The proportions are only a guide and may need adjustments to give a workable mix with locally available aggregates.
Table 1. Proportions by Weight to Make 1 Cu. Ft. of Concrete
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| Concrete without air |
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M a x i m u m - |
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| Course |
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| Course |
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size course |
| Cement | S a n d | aggregate W a t e r | Cement | S a n d | aggregate | W a t e r | |||
aggregate in. |
| l b |
| l b | l b | l b | l b |
| l b | l b | l b |
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3/8 |
| 2 9 |
| 5 3 | 4 6 | 1 0 | 2 9 |
| 5 9 | 4 6 | 1 1 |
1/2 |
| 2 7 |
| 4 6 | 5 5 | 1 0 | 2 7 |
| 5 3 | 5 5 | 1 1 |
3/4 |
| 2 5 |
| 4 2 | 6 5 | 1 0 | 2 5 |
| 4 7 | 6 5 | 1 0 |
1 |
| 2 4 |
| 3 9 | 7 0 | 9 | 2 4 |
| 4 5 | 7 0 | 1 0 |
1 1/2 |
| 2 3 |
| 3 8 | 7 5 | 9 | 2 3 |
| 4 3 | 7 5 | 9 |
*If crushed stone is used, decrease coarse aggregate by 3 lbs and increase sand by 3 lbs. |
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Metric conversion: | 1 lb = 0 .121 kg |
| 10 lbs = 4 . 54 kg |
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1 in . = 25mm |
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| 1 Cu. Ft. = 0.028 m 3 |
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Table 2. Proportions by Volume* |
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| Concrete without air |
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M a x i m u m - |
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| Course |
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| Course |
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size course |
| Cement | S a n d | aggregate W a t e r | Cement | S a n d | aggregate | W a t e r | |||
aggregate in. |
| l b |
| l b | l b | l b | l b |
| l b | l b | l b |
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3/8 |
| 1 | 2 | 1/4 | 1 1/2 | 1/2 | 1 | 2 | 1/2 | 1 1/2 | 1/2 |
1/2 |
| 1 | 2 | 1/4 | 2 | 1/2 | 1 | 2 | 1/2 | 2 | 1/2 |
3/4 |
| 1 | 2 | 1/4 | 2 1/2 | 1/2 | 1 | 2 | 1/2 | 2 1/2 | 1/2 |
1 |
| 1 | 2 | 1/4 | 2 3/4 | 1/2 | 1 | 2 | 1/2 | 2 3/4 | 1/2 |
1 1/2 |
| 1 | 2 | 1/4 | 3 | 1/2 | 1 | 2 | 1/2 | 3 | 1/2 |
*The combined volume is approximately 2/3 of the sum of the original bulk volumes.
ãPortland Cement Association 1980
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