18 BULLETIN" 220, U. S. DEPARTMENT OF AGRICULTURE. 



ing; section D shows various types of expansion joints, namely, 

 wood, felt, and bituminous filler; section E, the bituminous carpet 

 coat consisting of one-third to one-half gallon of bituminous material 

 per square yard and sufficient '"torpedo" sand or stone chips to pro- 

 vide a satisfactory wearing surface. 



BITUMINOUS CONCRETE ROADS— " TOPEKA SPECIFICATION." 



Plate X, figure 2, represents a type of bituminous concrete con- 

 struction. It is preferably laid over a concrete base to the depth 

 shown, but is frequently constructed over a well-consolidated mac- 

 adam or crushed-stone base. 



Section A shows the subgrade; section B, the concrete foundation 

 composed of broken stone or gravel concrete mixed in the propor- 

 tion 1:3:7 and having a finished thickness of 6 inches. Section C 

 demonstrates the manner of constructing the curbs. It also shows 

 the joint left at the end of each day's work. Section D. shows the 

 layer of bituminous concrete before and after rolling. The compo- 

 sition of this concrete is commonly as follows: 



Per cent. 



Bitumen soluble in carbon bisulphide 7-11 



Mineral aggregate passing a 2-mesli sieve 100 



Passing 2-rnesli sieve and retained on 4-mesh sieve 5-10 



Passing 4-mesh sieve and retained on 10-mesh sieve 8-22 



Passing 10-mesh sieve and retained on 40-mesh sieve 25-55 



Passing 40-mesh sieve and retained on 200-mesh sieve 18-30 



Passing 200-mesh sieve 5-11 



Section E shows the application of a seal coat with stone chip 

 dressing. The amount of bituminous material applied should not 

 exceed one-half gallon to the square yard, and the seal coat is fre- 

 quently omitted when the bituminous concrete is sufficiently dense to 

 warrant the omission. 



Section F shows the finished surface. 



PAVED ROADS OTHER THAN CONCRETE. 



Paved roads are sometimes advisable where there is heavy traffic. 

 The materials which have been adapted to country roads during the 

 past years are brick, asphalt block, granite block, and a small stone 

 block extensively used in Germany and known as "kleinpflaster." 



A good paving brick laid on a sand cushion with a substantial con- 

 crete foundation makes a road well adapted to both horse-drawn and 

 motor traffic. The first cost of such a road is generally high, but 

 this is largely offset by its durability and low maintenance cost. 



Asphalt blocks are molded from sand, broken stone, and asphalt 

 under pressure into rectangular blocks, which are laid on a concrete 

 foundation somewhat in the same manner as brick. The asphalt 

 blocks are more resilient than the brick and consequently more free 



