DUST PREVENTION AND ROAD PRESERVATION. 25 



EXPERIMENTS AT MIAMI, FLA. 



OILS-CORALLINE ROCK. 



These experiments are located on the Biscayne Drive about 2 miles 

 north of Miami, Fla. This road is the principal highway connecting 

 Miami with F.ort Lauderdale, Palm Beach, and other cities along the 

 Florida east coast and is subjected to a fairly heavy mixed traffic, 

 with numbers of automobiles during the winter season. Like most 

 of the roads in Dade County, it is surfaced with a soft oolitic limestone 

 formed from coral remains and known locally as marl or coralline 

 rock. Deposits of this material are found in abundance throughout 

 the county, and it comes from the pit in a soft, usually moist condi- 

 tion somewhat resembling coarse gravel with a large proportion of 

 fine material. It varies from pure white to rusty yellow in color. 

 Upon exposure to the atmosphere and traffic on the road, it shows 

 remarkable cementing qualities, becoming fairly hard, dense, and 

 impervious, and, when used in newly constructed roads, it yields a 

 smooth excellent surface at a comparatively low cost. These roads, 

 however, wear rapidly and very unevenly, and potholes develop to 

 such an extent and size as to make the surface rough and unsatisfac- 

 tory for travel. To avoid this condition persistent maintenance by 

 patching or the frequent resurfacing of the road is necessary and this 

 is accomplished by scarifying the surface, recrowning, and rolling. 

 The intense white color of the road surface also offers some objection 

 on account of its trying effect on the eyes, and several unsuccessful 

 efforts at surface treatment with bituminous materials have been 

 tried for the double purpose of preserving the road and producing a 

 more satisfactory color. A study of the general nature of the coral- 

 line rock led to the belief that a more satisfactory and permanent sur- 

 facing might be obtained in construction with a properly selected 

 bituminous binder, and the following experiments were instituted in 

 cooperation with the commissioners of Dade County, beginning with 

 station at the Miami end of the work. The experiments were begun 

 on June 9, 1913, and completed on June 28, 1913. 



The equipment consisted of a 10-ton gasoline roller, scarifier, grader, 

 two 1-barrel heating kettles, and hand-pouring pots. The oil was 

 in all cases applied by pouring pots. The sand used in finishing the 

 surface was a very fine, white siliceous pit sand, which was screened 

 for the purpose of removing twigs, leaves, and other foreign matter. 

 Two asphaltic oils, one light and the other heavy, were used, and the 

 characteristics of each are shown in the following table. The light 

 oil was used without heating and the heavy oil was applied at a tem- 

 perature of about 200° F. 



