46 BULLETIN" 407, U. S. DEPAETMEISTT OF AGEICULTTJBE. 



depression 55 feet from the soutli end of section 5, reported in Bulletin 

 No. 257, was still noticeable, but had not increased in size appreciably. 

 A few minor repairs had been made by using a mixture of sand and 

 oU and the surface was in very good condition. 



SUPPLEMENTARY REPORT OF EXPERIMENTS AT WEST PALM BEACH, 



FLA., 1914. 



OIL, TAR, OIL-ASPHALT, CORALLINE ROCK. 



These experimental sections were constructed on the Miami-Quebec 

 Highway, about 2 miles south of West Palm Beach, in May, 1914, 

 The original report giving the details of materials and methods is 

 pubhshed in U, S. Department of Agriculture Bulletin No. 257. As 

 shown in Table 9 in that report, the traffic over this road is heavy 

 suburban and the test of the various sections is therefore rather 

 severe. 



The work was inspected December 10, 1915, and the condition of 

 the sections at that time was as foUows: 



Experiment No. 1. (Residual aspJialtic petroleum, 2.3 gallons. Pen- 

 etration method.) — This section is in very satisfactory condition. The 

 bituminous material is still viscous, but the exudation and flow of 

 the excess has ceased and the inequahties in the surface resulting 

 from this flow are not sufficient to cause discomfort to traffic. There 

 is no evidence of weakness developing at any point. 



Experiment No. 2. {Refined coal tars, 1.3 gallons. Penetration 

 metliod.) — ^The bituminous material has continued to harden and the 

 surface is becoming pitted, owing to the fact that individual rocks 

 have been broken and worked out of their setting. These pits are 

 small and uniformly distributed and do not cause noticeable vibra- 

 tion in passing vehicles. About 25 feet from the south end of the 

 section a shallow depression has formed. It is due apparently to 

 settling of the pavement and not to wear. 



Experiment No. 3. (Refined coal tars, 1.2 gallons. Penetration 

 method.) — The proportion of rock exposed in the surface by the re- 

 moval of the binder under traffic has increased visibly in the past 

 year. These exposed rocks have worn lower than the surrounding 

 areas still coated with tar and the surface is full of small shallow 

 pits. The tar has become very hard and brittle. 



Experiment No. 4- (Residual asphaltic petroleum, 1.4 gallons. 

 Penetration method.) — ^The surface is in good condition, but is becom- 

 ing sHghtly rough, due to pits where the rock is exposed. The differ- 

 ence in appearance between the part of the section treated with sand 

 and that treated with stone chips is becoming more pronounced. 



Experiment No. 5. (Oil-asphalt, 1 .8 gallons. Penetration method.) — 

 This section has changed little in appearance or condition and has 

 resisted the action of traffic very satisfactorily. 



