84 



HIGHWAY CONSTRUCTION 



TABLE 12. 



Specific Gravity, Weight, Resistance to Crushing, and 

 Absorption Power of Stones. 



Cobblestone Pavement. Cobblestones bedded in sand possess 

 the merit of cheapness, and afford an excellent foothold for horses; 

 but the roughness of such pavements requires the expenditure of a 

 large amount of tractive energy to move a load over them. Aside from 

 this, cobblestones are entirely wanting in the essential requisites of a 

 good pavement. The stones being of irregular size, it is almost impos- 

 sible to form a bond or to hold them in place. Under the action of the 

 traffic and frost, the roadway soon becomes a mass of loose stones. 

 Moreover, cobblestone pavements are difficult to keep clean, and very 

 unpleasant to travel over. 



Belgian Block Pavement. Cobblestones were displaced by pave- 

 ments formed of small cubical blocks of stone. This type of 

 pavement was first laid in Brussels, thence imported to Paris, and from 

 there taken to the United States, where it has been widely known as 

 the "Belgian block" pavement. It has been largely used in New York 

 City, Brooklyn, and neighboring towns, the material being trap-rock 

 obtained from the Palisades on the Hudson River. 



The stones, being of regular shape, remain in place better than 

 cobblestones ; but the cubical form (usually five inches in each dimen- 

 sion) is a mistake. The foothold is bad; the stones wear round; and 

 the number of joints is so great that ruts and hollows are quickly 

 formed. This pavement offers less resistance to traction than cobble- 

 stones, but it is almost equally rough and noisy. 



Granite Block Pavement. The Belgian block has been gradually 



