16 BULLETIN 220, U. S. DEPARTMENT OF AGRICULTURE. 



mixture of stone and bituminous material. The stone may be the 

 product of the crusher ranging in size from that which will be retained 

 on a screen having circular openings one-half inch in diameter to that 

 which will pass a screen having circular openings 1^ mches in diameter. 

 Stone of this size will require from 18 to 20 gallons of bituminous 

 material per cubic yard of stone. 



The wearing course is laid to a depth of 3 J inches loose, which will 

 compact to a thickness of about 2 inches by rolling. Section D shows 

 the application of a seal coat of hot bituminous material and clean 

 stone chips, and section E shows the finished surface after final 

 rolling. 



SURFACE TREATMENT. 



The surface treatment of an old macadam road with bituminous 

 material is shown in Plate IX, figure 1 . 



Section A shows a disintegrated macadam surface; section B, the 

 surface after sweeping; section C, the application of bituminous ma- 

 terial at the rate of about one-half gallon per square yard; and section 

 D, the application of pea gravel or stone chips to the treated surface, 

 completing the treatment. 



Before any application of bituminous material is made all loose 

 material should be removed and the road surface should be free from 

 dust, clean and dry. The bituminous material is applied either hot 

 Or cold, depending upon the consistency of the material. It may be 

 poured by hand, or by means of a mechanical distributor, and in the 

 former case should be thoroughly broomed into the surface, in order 

 to secure perfect adhesion. Enough stone chips or pea gravel 

 should then be applied to take up any excess bitummous material 

 that may be left on the surface. 



RESURFACING MACADAM ROADS. 



Plate IX, figure 2, illustrates the reconstruction of a macadam road 

 after it has become badly worn. The macadam width as shown is 16 

 feet, and the crown is one-half hich to the foot. 



Section A represents the worn macadam surface; section B, the 

 surface after spiking; section C, the road after it has been recrowned; 

 section D, the application of new stone of No. 2 size, compacted to 3 

 inches after rolling; section E, the application of bituminous material 

 by the penetration method at the rate of about 1^ gallons per square 

 yard; section F, a coating of stone chips which has been rolled; sec- 

 tion G, a seal coat of bituminous material averaging about one-half 

 gallon per square yard; and section H, the finished surface covered 

 with stone chips or pea gravel. 



This model illustrates the usual custom of restoring a macadam 

 road which has become badly worn and rutted, owing to excessive 

 travel and lack of maintenance. 



