12 BULLETIN 249, U. S. DEPARTMENT OF AGRICULTURE. 



Before any concrete is placed the subgrade should be thoroughly^ 

 sprinkled with water or a part of the water contained in the concrete 

 will be absorbed by the subgrade, which may interfere with the 

 process of setting. 



For one-course work the concrete should be deposited between the 

 forms in such quantity that when it is struck off and compacted it 

 will present a uniform surface and have the depth required for the 

 finished pavement. Each batch of concrete should be dumped as 

 nearly in place as is practicable and should preferably be spread by 

 means of mortar hoes. The men who do the spreading should avoid 

 walking in the concrete, because each time the foot sinks into it the 

 coarse aggregate is shoved down, and when the foot is withdrawn the 

 space thus left tends to fill with mortar, which causes a lack of uni- 

 formity in the concrete. 



After the concrete has been spread approximately to the required 

 cross section it should be struck off with a strike board having slightly 

 more crown than the cross section of the road. This allows for a 

 slight amount of settlement when the concrete is compacted. The 

 compacting should be done with a tamper shaped to conform with 

 the cross section of the road and operated by two men, one standing 

 on each side of the pavement. Suitable designs for strike boards are 

 shown in Plate X, figures 2 and 3. The heavier design (PL X, fig. 3), 

 on account of its durability, is especially adapted for use where a 

 considerable amount of work is to be done. It is also in general 

 somewhat more satisfactory than the light design on account of its 

 greater rigidity. Plate X, figure 4 shows a design for a tamper 

 made of steel which has been used very satisfactorily for compacting 

 concrete after it has been struck off, and which is very rigid and 

 durable. 



Sometimes the tamping and striking off are done with the same 

 template, but this is not altogether satisfactory, because when this is 

 done it is impracticable for the template to have a greater crown than 

 is required for the finished pavement, and it is difficult to strike off 

 the concrete with such a template and at the same time make pro- 

 vision for compacting. 



In the case of two-course pavements it is important that the top 

 course be placed before the concrete in the bottom course has taken 

 its initial set. The bottom course should be well compacted and 

 struck off, but the striking off need not be as carefully done as in the 

 case of the top course. The top course should be constructed in a 

 manner similar to that described for one-course pavements. 



FINISHING THE SUr.FACE. 



The surface of a concrete pavement may be given either a rough or 

 a smooth finish. A slightly roughened surface has the advantage of 



