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^ inches 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^ 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 
-tone 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 bituminous 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 inch 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. 
