PORTLAND CEMENT CONCRETE ROADS. 31 



chased. If the pavement is to be machine-finished, heavy forms 

 are desirable and usually are more economical than light ones, as 

 they hold their shape much better under the vibrations set up by the 

 finishing machine. The forms should always be set true to line 

 and grade before the subgrade is finished, in order to serve as a guide 

 for the finishing. It is very essential that the forms be firmly sup- 

 ported and bear uniformly upon the subgrade, as any sag produces 

 an irregular surface in the pavement. The ends of the different 

 sections of forms should be fastened together so that no relative dis- 

 placement occurs. The joints between the sections on the two sides 

 of the road should not be opposite each other, but should be stag- 

 gered. The height of the forms should preferably be equal to the 

 thickness of the pavement at the edge. Forms 1 inch less in height 

 than the edge of the pavement can be used satisfactorily, however, 

 by bolting under them a 1-inch strip of wood. These wood strips 

 should be somewhat wider than the base of the forms, so that addi- 

 tional bearing can be secured. In States that use a variable thick- 

 ness of pavement at the edge this arrangement reduces the amount 

 of forms required for different classes of work. 



Forms for concrete pavements should always be oiled before the 

 concrete is placed against them. This oiling prevents the concrete 

 from sticking to them, makes cleaning easy, and prolongs the life 

 of the forms. Any crude oil can be used for this purpose and 

 approximately 1 barrel per mile will be required. 



The use of bent forms should be prohibited. It is usually specified 

 that variations in the surface of the pavement of over one- fourth 

 of an inch in 10 feet will not be permitted. These variations in the 

 surface of the pavement are caused to a large extent by the forms, 

 so it would appear that no greater variation should be permitted in 

 the forms than is permitted in the pavement. Forms, therefore, 

 should not be used if their top surfaces vary more than one-fourth 

 inch when tested with a 10-foot straightedge. A sufficient number of 

 forms should be provided so that it will not be necessary to remove 

 them within 12 hours after the concrete is placed. 



HANDLING AND HAULING MATERIALS. 



For handling and hauling the materials used in concrete pave- 

 ment construction a number of different methods may be used. The 

 most economical method to employ will, of course, depend upon the 

 particular problems of the work in question. The discussion of 

 this subject will be confined to the general methods which may be 

 employed and the advantages and disadvantages of each. 



Nearly all of the materials used in concrete pavements are shipped 

 by rail. The method of unloading the materials from railroad cars 

 will depend to a large extent upon the method of handling the re- 



