DUST PEEVENTION AND EOAD PRESERVATION^, 1914. 7 



EXPERIMENTS AT WEST PALM BEACH, FLA. 



OIL, TAR, OIL-ASPHALT, CORALLINE ROCK. 



These experiments, located on the Miami-Quebec highway, about 

 2 miles south of West Palm Beach, were constructed in April and 

 May, 1914, by Palm Beach County, under the direction of the Office 

 of Public Roads. The purpose was to develop a more economical 

 and durable road surface than is obtainable by the use of coralline 

 rock under ordinary methods of construction. 



There are in this county about 150 miles of hard-surface roads. 

 The material used exclusively for this surfacing is a soft, oolitic 

 limestone known as coralline rock, or locally as simply "rock." 

 It is obtained from two pits in Dade County, which borders Palm 

 Beach County on the south. One of these pits, located at Fort 

 Lauderdale, furnishes a coralline rock which is softer than the average 

 and contains a considerable proportion of sand. For ordinary con- 

 struction, it has given apparently satisfactory results. The rock 

 quarried from the other pit, located at Ojus, is blasted and excavated 

 from under water. It is comparatively hard and contains a relatively 

 small amount of fine material. It was therefore chosen as the more 

 suitable of the two for bituminous construction, and used in the 

 experiments. 



The experience gained from the construction of the experiments 

 at Miami 1 and from their inspection after long usage by traffic 

 showed conclusively that the best method of treatment involved 

 the use of rock from which the finer particles had been removed to 

 provide for uniform penetration of the bitumen. The experiments 

 at West Palm Beach were therefore all constructed on this basic 

 principle. The general method of construction preparatory to the 

 application of the bitumen was, in brief, as follows: 



The preparation of a thoroughly compacted subgrade parallel 

 to the finished surface and composed of the rock originally in the 

 roadbed; upon this, a course of screened rock with a uniform loose 

 depth of 3 inches, lightly compacted to allow a maximum penetration 

 of bituminous material. 



The screened rock used was produced at great disadvantage and 

 consequently high cost. Furthermore, in addition to screening out 

 the material below one-half inch in size, it would have been desirable, 

 if practicable, to screen out all above 1\ inches. These larger sizes 

 bad to Ix: picked out by band by the rakeman on the screen and by 

 the spreaders on the road. In any large-scale future work, a small 

 crushing plant, elevator, revolving screens, and bins should be 

 installed, preferably at thequarry. All rock was spread byshoveling 

 back from piles dumped u little in advance of (lie work. 



i Bulletin of 1 i I D< partmi at ol \.p Iculture No. 105. 

 Bull. 257 -15 2 



