The Park Governments of Chicago 163 



might be suitable for park and boulevard drives. The result of 

 the combined experimentation of the three Boards has been the 

 adoption by each of an asphaltic concrete pavement. This re- 

 sult has perhaps been hastened by reason of the perfecting by 

 the South Park engineers of a portable plant for mixing bitu- 

 minous concrete. The machine was developed by Assistant Gen- 

 eral Superintendent Richards and Chief Engineer White since 

 entering the service of the South Park Board. Several of the 

 machines, which are built by the Link Belt Company, have been 

 sold to other municipalities, including the West and Lincoln 

 Park Boards. 



A large yardage of bituminous concrete pavement is being 

 laid each year. In 1910 approximately 25 miles of boulevards 

 were thus improved. Within a few years the park drives and 

 boulevards will be completely paved therewith. The Bureau's 

 study and inspection of paving operations has, therefore, been 

 confined to this type of construction. 



The bituminous concrete referred to consists of a mixture 

 of broken stone, sand, and bituminous cement, thoroughly mixed 

 before being laid and laid immediately after mixing, while in a 

 plastic condition. A thin layer of granite screenings is thrown 

 on the surface and rolled in before it becomes solidified. This 

 gives a gritty coating. The colored granite is pleasing in ap- 

 pearance. The South and Lincoln Park Boards use Wisconsin 

 red granite screenings, while the West Park Board uses black 

 granite. The last named claims that the black granite has a 

 greater resistance to abrasion. As the granite screenings form 

 an important element in the wearing surface, this feature is 

 worth consideration by the other two boards. 



The South Park Board used some inferior grades of as- 

 phaltic oil in 1910, but a better grade was used during 1911. 

 With the increase in automobile traffic the tendency should be 

 toward the use of asphalts which have proven successful. The 

 South and Lincoln Park Boards get their asphalt in barrels and 

 it has to be broken up before being introduced into the mixer. 

 The West Park Board has had some of their asphalt delivered 

 in tank wagons, kept heated and forced by air pressure to the 



