DUST PREVENTION AND ROAD PRESERVATION, 1915. 7 



The guard rail was built of red-cedar posts with two rails of yellow 

 pine. The posts, which had been dipped in asphaltic material, were 

 set 4 feet in the ground and sawed off 3 feet 3 inches above the sur- 

 face. The 2-inch by 6-inch rails were given two coats of white lead 

 and oil. The guard rail is set in each instance 3 feet outside the 

 edge of the surfaced road. 



Materials. — The materials used in all surface experiments were 

 tested in the laboratories of the office and the results are given in 

 Tables 4 to 9, mclusive. 



Table 4. — Physical properties of stone used in surface construction. 



Test. 



Sandstone. 



Gneiss. 



Trap. 



2.50 



2.80 



3.00 



156 



175 



187 



.132 



.28 



.43 



4.8 



3.0 



2.6 



8.3 



13.2 



15.5 



16.5 



18.8 



18.3 



5 



5 



13 



Granite. 



Specific gravity 



Weigiit per cubic foot pounds. . 



Water absorbed per cubic foot pounds. . 



Per cent of wear 



French eoeflficient of wear 



Hardness 



Toughness 



2.70 



168 

 .328 



3.0 

 13.3 

 18.7 



Table 5. 



-Mechanical analyses of stone used in the bituminous-macadam by the penetration 

 methods. 





Sandstone. 



Gneiss. 



Trap. 



Granite. 





12.0 

 55.1 

 22.3 

 10.6 



9.3 



59.9 



22.0 



7.0 



1.7 



2').1 



47.2 



17.5 



9.6 



.5 



.1 



19.8 





57.7 



Passing l^inch, retained on l-}-ineh screen 



16.7 





5.8 







Passing |-inch, retained on ^inch screen 

















100.0 



99.9 



100.0 



100.0 



Table 6. — Mechanical analyzes cf stone and gravel used in the bituminous macadam by 

 the mixing method, and the bituminous-concrete. 



Paasing 

 Passing 

 Pas.'iing 

 Passing 

 Passing 

 Passing 



Passing 

 Passirg 

 Passing 

 Passing 

 Passing 

 Passing 

 Passing 



2-lnch, retained on 1 |-inch screen 



1 J-incn, retained on l{-inch screen 



1 J^-incti, retained on 1-inch screen 



1-inch, retained on 3-inch screen 



J-inch, retained on l-inch screen 



J-inch, retained on {-inch screen 



I -inch screen 



lO-mesh, retained on 20-niesh screen . . . 

 20-niesh, retained on 30-mesh screen . . . 

 30-niesh, retained on 4f)-mesh screen . . . 

 40-niesh, retained on SO-mesh screen . . . 

 .50-mesh, retained on SO-mcsh screen . . . 

 ^'j-mesh, retained on lfX)-mesh screen. . 

 l')f>-nie.sh, retained on 2fX)-mesh screen. 

 200-me8h screen 



Sandstone. 



Per cent. 



6.4 



12.1 



38.0 



29.5 



13.2 



.6 



.2 



Gneiss. 



Trap. 



Per cent. 



Per cent. 





22.4 



6.9 



35.4 



32.8 



24.0 



29.5 



15.0 



25.3 



3.2 



5.1 





.4 





100.0 



100,0 



Granite. 



Per cent. 



1.8 



24.4 



44.5 



13.5 



8.3 



6.3 



1.2 



100.0 



Gravel. 



Per cent. 



1.3 



8.9 



11.3 



17.2 



U3.3 



4.8 



5.8 



8.3 



7.3 



5.4 



0.5 



2.8 



13.1 



100.0 



I Retained on 10- mesh screen. 



