PORTLAND CEMENT CONCRETE PAVEMENTS. - 21" 
were worked out by a contractor of considerable experience. Labor- 
ers for preparing the subgrade, setting the forms, and for covering 
the concrete with earth should be provided in addition to those 
called for in the diagrams. 
HANDLING MATERIALS. 
One of the most difficult problems which has to be solved in con- 
nection with concrete road construction is that of determining the 
proper methods to employ in handling and delivering the materials 
for the concrete. The different kinds of material required must be 
delivered to the mixer in definite proportions at the same time, and 
it is evident that the location of the several sources from which the 
materials are obtained, with respect to each other and to the road, 
will have a very great influence in determining the most economical 
transportation methods. 
Consider, for example, a project on which is used a concrete 
mixer of the street-paving type which mixes a batch containing 
three sacks of cement. If the work is to progress normally, the 
quantities of the different materials required each day will be 
approximately as follows: 
Cement barrels— 320 
Sand cubic yards 70 
Coarse aggregate , do 140 
Water _gallons__ 8, 800 
In addition to the above, if the mixer runs continuously, about 
10,000 gallons of water will be required each day for keeping wet 
that part of the pavement which will have been laid during the two 
preceding weeks, and for sprinkling the subgrade before the con- 
crete is placed. This makes the total weight of water which may 
be required each day about 75 tons, and the total weight of all the 
materials combined about 420 tons per day. 
The importance of the water supply is not always appreciated by 
contractors and engineers, and the provision made for delivering 
water on the work has sometimes been entirely inadequate. Another 
frequent error is that of overestimating the amount of water which a 
chosen stream is capable of supplying. In general, the most practi- 
cable method of delivering the water is to pump it through a pipe line 
laid along the road. The pipe should be at least 2 inches in diameter, 
and for the mixer under consideration the pump should be capable 
of furnishing about 25,000 gallons of water in 10 hours to any point 
on the pipe line. Ordinarily at least 10,000 feet of pipe will be 
required if the concrete is to be sprinkled for two weeks after it is 
laid. 
