OFFICE OF PUBLIC ROADS AND RURAL ENGINEERING. 339 



The following subjects are under investigation : The effect of vari- 

 ous solvents upon extracted bitumen ; the study of asphalts by means 

 of the penetration test; the relative binding value of various bitu- 

 mens with different types of rock; bituminous materials suitable for 

 use in the construction of top-soil roads ; the thickness of films upon 

 bituminous aggregates; a study of fluid bitumens by means of the 

 viscosity test; a study of heavy refined tars by means of the float 

 test; the effect of colloids on bituminous materials; the effect of oils 

 in oil-cement concrete. 



EXPERIMENTAL BITUMINOUS ROAD CONSTRUCTION AND MAINTENANCE. 



Supervision or inspection has been conducted in the construction 

 and maintenance of a number of experimental sections of roads in 

 the vicinity of Washington and other places throughout the United 

 States. New lines of experiment include the use of Florida coralline 

 rock with various types of bituminous materials, the use of pit-run 

 gravel in bituminous concrete, the investigation of the comparative 

 value of different types of rock with various bituminous materials 

 in the construction of bituminous macadam and bituminous concrete 

 roads, and the use of screened gravel in penetration macadam. Plans 

 have been completed to investigate the use of bituminous materials. 

 As a result of laboratory investigations an experimental section of 

 natural soil and asphalt road was built at Arlington Farm in co- 

 operation with the Division of Construction. 



NONBITUMINOUS ROAD-MATERIAL INVESTIGATIONS. 



Investigations were continued on the toughness of cement mortars 

 carrying various percentages of sand and cement, the relation be- 

 tween the physical properties and service results of road-building 

 gravel, and waterproofing silos with oil-cement concrete. The fol- 

 lowing investigations were started : The effect of freezing and thaw- 

 ing on argillaceous rocks; the relative effect of mortar and sand 

 cushions for brick pavements; and the relation between the tensile 

 strength of mortars and the mechanical analysis of sand. 



The following papers and bulletins were also published during 

 the year : " Relation Between the Properties of Hardness and Tough- 

 ness of Road-Building Rock," in the Journal of Agricultural Re- 

 search ; Department Bulletin 348, " Relation of Mineral Composition 

 and Rock Structure to the Physical Properties of Road Materials," 

 and " The Section of Rocks According to the Results of Physical 

 Tests as Related to their Use in Different Types of Roads," pub- 

 lished as a part of Department Bulletin 370, " Results of Physical 

 Tests of Road-Building Rocks." 



STANDARDIZATION OF METHODS OF TESTING BITUMINOUS ROAD MATERIALS. 



Department Bulletin 314, " Methods for the Examination of 

 Bituminous Road Materials," was prepared and published ; also two 

 papers in the Journal of Agricultural Research : "A New Penetra- 

 tion Needle for Use in Testing Bituminous Materials," and " The 

 Effect of Controllable Variables Upon the Penetration Test for 

 Asphalts and Asphalt Cements." Other investigations have been 

 conducted, having the following purposes in view : The development 

 of a new method for determining paraffin scale; improvements in 

 the fixed carbon determination; the use of ether as a solvent for 

 bituminous materials instead of naphtha; a toughness test for 

 bituminous materials; a standard method of counting ultra-micro- 



