40 BULLETIN 40*7^ U. S. DEPARTMENT OP AGRICULTURE. 



Since the work was done with convicts and the conditions were favor- 

 able, the cost is probably considerably lower than it would have been 

 under ordinary conditions. 



EXPERIMENT AT WEST PALM BEACH, FLA. 



In May, 1914, a series of seven experimental sections involving the 

 use of coralline rock and bituminous materials was constructed on 

 the Miami-Quebec Highway, about 2 miles south of West Palm Beach. 

 The details of construction are given in U. S. Department of Agri- 

 culture Bulletin No, 257. In order to determine the wearing quaU- 

 ties of a sand-asphalt or bituminous-sand surface in comparison with 

 the seven experimental surfaces, a section of this material was added 

 to the series in January, 1915. It is continuous with the other experi- 

 ments and adjoins section 7. 



Experiment No. 8.— Bituminous Sand Mixing Method. 



The original coralline rock road was scarified and reshaped for the 

 foundation. The cross section of the fomidation was parallel to the 

 finished surface and 2 inches below it. During the time which 

 elapsed between the preparation of the foundation and the laying of 

 the wearing course, the former was thoroughly compacted by traffic 

 and had become shghtly dusty. 



In order to secure a sand which was fairly well graded, it was nec- 

 essary to mix two sands in approximately equal proportions. This 

 was done while they were being screened to remove twigs and other 

 undesirable matter. The mechanical analyses of the original sands 

 and the graded combination are given in Table 42, and the analysis 

 of the fluxed native asphalt, B, is the same as given in Table 41. 



The bitimiinous sand was prepared by mixing heated 'sand and 

 asphalt on a mixing board with rakes and shovels. A heater having 

 about 90 square feet of heating surface was improvised to bring the 

 temperature of the sand up to from 350° F. to 400° F. and two 1-barrel 

 asphalt kettles were used to heat the bitumen to 300° F. 



Beginning at the south end of the section for the first 52 hnear feet 

 the sand and asphalt are mixed in the proportions of 10 cubic feet of 

 sand to 10 gallons of asphalt; in the next 27 hnear feet the propor- 

 tions are 10 cubic feet of sand to 11 gallons of asphalt; and in the 

 remaining 3 linear feet the surface consists of a mixture of 10 cubic 

 feet of sand No. 1 to 11 gallons of asphalt. The sand-asphalt mixture 

 was spread 2 J inches thick and was held in place with 2 by 4 inch 

 timber while it was being roUed with a 6-ton tandem roller. 



The work was interrupted by a succession of showers. The section 

 was so short that an organization of competent labor could not be 

 perfected and the equipment was of the crudest kind. 



