No single phase of concrete construction work confronts the builder with a wider range of choices than the problem of moving this versatile material on the construction site. Although to the uninitiated it might appear at first glance that there are nearly as many solutions as there are problems, the situations most frequently encountered can often be solved economically in two or more ways. As is so often the case, the critical problem is to correctly determine which two (or more) systems will in any particular instance result in acceptable handling costs. In choosing a handling system, these are several points to keep in mind. Concrete is normally designed to be placed within 15 to 30 minutes after it leaves a mixer or agitator. If site handling operations (from supply point until compaction in formwork begins) exceed this period the mix stiffens and becomes unworkable. Correct handling procedure is therefore important both for economic reasons and to ensure maximum durability of the concrete in service. Choice of the most suitable technique depends on a number of factors: job specification establish mix proportions, workability, quantities and rates of placing; prevailing site conditions, in terms of terrain, climate, elevations and supply difficulties, influence choice of equipment. Segregation of the coarse aggregate must be prevented at all stages of handling. Segregation has the greatest tendency to occur at points of discharge, such as at the ends of chutes and conveyor belts, and at hopper gates. Segregation cannot be corrected during subsequent handling and placing operations. Discharge should be as near to the final point of placing as possible. This saves labor and avoids segregation. Discharge should be as near vertical as can be achieved. Concrete should never be made to flow laterally by means of a vibrator.