The number of men required is determined by the amount of concrete to be placed in a given time, the method of mixing, and the size of the batch; that is, the number of bags of cement mixed at one time. The amount of concrete one man can mix by hand in a day depends upon the experience of the man, the layout of the work, and other duties required of him. One man should average 11/2 to 13/4 cubic yards of concrete in eight hours, including mixing and wheeling not more than 50 feet.
The gang for a one-bag batch may consist of 3 men, but a larger number make a more efficient force, for when the concrete is mixed by hand the men can take turns at the various tasks and will not tire so easily. The assigning of tasks so that each man's time fits into that of the others requires considerable study and is one of the chief factors making for loss or profit.
MACHINE MIXING.
Good concrete can be mixed by hand or machine. The quantity of concrete work in prospect is the factor that determines the more economical method. A small amount (say 100 to 200 cubic yards) does not warrant the purchase of a machine, but it is often feasible and economical to hire a machine from a neighbor or contractor if the quantity of concrete to be placed is more than 15 cubic yards.
A mixer should be purchased only after careful consideration of the amount and character of the work to be done and the conditions affecting its use.
The two types of mixers most used are the batch mixer, which mixes and dumps a definite quantity, and the continuous, which discharges a constant stream of concrete. The continuous type is not adapted to farm work unless the concrete can be handled as fast as it is mixed, thus permitting the machine to work continuously.
