POETLAND CEMENT CONCRETE ROADS. 45 



VII.) The machine is supplied with flanged wheels, which travel 

 on the side forms used for the pavement. Power for traction and op- 

 eration is generally furnished by an air-cooled gasoline engine. The 

 machine is provided with a striking template, a tamper, and a finish- 

 ing belt so arranged that each may be operated separately, or any 

 two, or all operated simultaneously. In practice, the striking tem- 

 plate and tamper, and the tamper and belt are usually operated at 

 the same time. After the concrete has been roughly spread it is 

 struck off by means of the striking template. On the second passage 

 of the machine, the strike board is still in place and the tamper is 

 placed in operation. The third time over usually only the tamper 

 is permitted to operate. For the fourth passage both the tamper 

 and the belt are used. For the final finishing operation either the 

 belt alone is employed, or the tamper and belt. A common fault 

 where machine finishing is used is the tendency to let the machine do 

 a large part of the spreading. The machine was never intended for 

 this purpose and will not operate satisfactorily if a large amount of 

 concrete must be pushed ahead of the striking template. For best 

 results not more than 2 inches of excess thickness should be ahead 

 of the striking template at any one time. 



The principal advantages of a finishing machine from the stand- 

 point of cost are derived from the striking template and the tamper. 

 These devices replace the usual heavy timber strike board and 

 tamper, which require from two to four men to operate them. From 

 an engineering standpoint the machine serves a useful purpose by 

 making it possible to use a drier and hence a stronger concrete than 

 it would be possible to use if hand finishing methods were employed. 

 Its principal disadvantage is that it is not adjustable to various 

 widths of pavement without providing new trusses, striking template, 

 and tamper. The objection is not serious, however, in States that 

 have their road widths well standardized. 



From the standpoint of the traveling public the finish of the sur- 

 face is the most important quality of the pavement. Kegardless of 

 its strength and wear, the traveler invariably judges a pavement by 

 its riding qualities. A smooth surface should, therefore, be the con- 

 stant aim. The surface should be frequently tested by means of a 

 straightedge laid parallel to the center line of the pavement. Va- 

 riations in the surface of over one- fourth inch in 10 feet should be 

 corrected before the final belting. The joints are the chief source 

 of trouble in securing a good surface. High joints can practically 

 be eliminated by the use of the straight-edge, and its use is particularly 

 recommended at joints between sections of concrete laid on different 

 days. The edges of the pavement and of all joints should be rounded 

 to about 1-inch radius with an edging tool. 



