3
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 V-pulley.
If using a 6 to 1 speed reduction 3 H.P. gasoline engine, use a 6 ¼” diameter “A”
section V-pulley.
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 W eight to Make 1 Cu. Ft. of Concrete
Air-entrained concrete
Concrete without air
Course
Course
C e m e n t
S a n d
aggregate W ater
C e m e n t
S a n d
aggregate W ater
lb
lb
lb
lb
lb
lb
lb
lb
29
53
46
10
29
59
46
11
27
46
55
10
27
53
55
11
25
42
65
10
25
47
65
10
24
39
70
9
24
45
70
10
23
38
75
9
23
43
75
9
*If crushed stone is used, decrease coarse aggregate by 3 lbs and increase sand by 3 lbs.
Metric conversion: 1 lb = 0.121 kg
10 lbs = 4.54 kg
1 i n . = 2 5 m m
1 C u . F t . = 0 . 0 2 8 m
3
Table 2. Proportions by Volume*
Air-entrained concrete
Concrete without air
Course
Course
C e m e n t
S a n d
aggregate W ater
C e m e n t
S a n d
aggregate W ater
lb
lb
lb
lb
lb
lb
lb
lb
1
2 1/4
1 1/2
1/2
1
2 1/2
1 1/2
1/2
1
2 1/4
2
1/2
1
2 1/2
2
1/2
1
2 1/4
2 1/2
1/2
1
2 1/2
2 1/2
1/2
1
2 1/4
2 3/4
1/2
1
2 1/2
2 3/4
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.
M a x i m u m -
size course
aggregate in.
1 1/2
3/8
1/2
3/4
1
1 1/2
M a x i m u m -
size course
aggregate in.
3/8
1/2
3/4
1
Portland Cement Association 1980
