DUST PBEVENTTON" AND ROAD PRESERVATION, 1914. 17 



The following report covers the condition of the existing experi- 

 ments on January 16, 1915: 



Experiment No. 3 (Penetration Method— Hot, Heavy Oil). 



This experiment remains in fairly good condition, although it has 

 worn to a somewhat rough and uneven cross section. No breaks have 

 occurred, however, and only one worn depression was noted. 



Experiment No. 4 (Penetration Method — Cold, Light Oil). 



This experiment continues in fair condition, although it does not 

 present as good an appearance as No. 3. A group of small worn 

 places were noted just north of the middle of the section. 



Experiment No. 5 (Penetration Method — Hot, Heavy Oil). 



This is decidedly the poorest of the remaining sections, and appar- 

 ently demonstrates the lack of economy in reducing the wearing 

 course of rock to less than 2\ inches of uncompacted material. Sev- 

 enteen worn depressions, ranging from one-half square foot to 2 scpiare 

 feet in area were distributed throughout the section, and it was appar- 

 ent that they had been brought to grade by filling with coralline rock. 

 These will be patched with bituminous material and rock. 



Experiment No. 6 (Penetration Method — Hot, Heavy Oil). 



This experiment continues in excellent condition after having been 

 under rather heavy traffic for over 18 months, and is a successful 

 demonstration of what can be accomplished in this form of construc- 

 tion. The bitumen has flowed in a couple of places and is still lively, 

 but the cross section is well preserved, and there is no evidence of ex- 

 cessive wear. 



SUPPLEMENTARY REPORT OF EXPERIMENTS ON ROCKVILLE PIKE, 



MARYLAND, 1913. 



The original report of these experiments was given in U. S. Depart- 

 ment of Agriculture Bulletin No. 105, and the following information 

 covers their history to and including an inspection on February 9, 1915. 



Experiment No. 1 (Refined Coal Tar — Hot Application). 



This experiment has shown somewhat marked fraying along the 

 edge , and a rery noticeable deterioration of a strip along one edge 

 for about 400 feet where trees overhang the road. The underlying 

 macadam is fast becoming exposed over fairly large areas, and at the 

 time of inspection il appeared probable that the restoration <>f the ni;i t 

 will be necessary early in the spring of L915. One single-track trolley 



