16 



BULLETIN 555, U. S. DEPARTMENT OF AGRICULTURE. 



SPECIFICATION FOR GRAVEL FOR PLAIN GRAVEL ROADS. 



General. The gravel shall be composed of hard, durable rock, of high 



resistance to abrasion,* together with sand and clay or other 

 binding material, and shall be free from thin or elongated pieces. 

 Grading. j # ^ or base course : 



(a) The gravel, when tested by means of 

 laboratory screens, shall meet the 

 following requirements : 



Passing a -inch screen 



Total retained on 1/4-inch, screen _ 

 (&) The material retained on the 1/4-inch 

 screen is known as coarse aggregate. 

 The coarse aggregate, when tested 

 by means of a laboratory screen, 

 shall meet the following require- 

 ment: 



Per cent. 

 100 



Total retained on -inch 



screen to 



(c) The material passing the 1/4-inch 

 screen is known as fine aggregate. 

 The fine aggregate, when tested by 

 means of a laboratory sieve, shall 

 meet the following requirement: 



Total passing 200-mesh sieve to 



2. For wearing course : 



(a) The gravel, when tested by means of 

 laboratory screens, shall meet the 

 following requirements : 



100 

 to 



to 



Passing a -inch screen 



Total retained on 1/4-inch screen_ 

 (6) The material retained on the 1/4-inch 

 screen is known as coarse aggregate. 

 The coarse aggregate, when tested 

 by means of a laboratory screen, 

 shall meet the following require- 

 ment: 



Total retained on -inch 



screen 



(c) The material passing the 1/4-inch 

 screen is known as fine aggregate. 

 The fine aggregate, when tested by 



* The conference believes it highly desirable to specify definite test 

 limits for the resistance of gravel to abrasion. The only State which 

 has so far extensively employed an abrasion test for gravel is Ohio. 

 Available test records, therefore, cover only gravels used in that State ; 

 and it is felt that sufficient data have not been obtained as yet to war- 

 rant the use of an abrasion test clause in the gravel specifications of 

 other States. The conference recommends that individual States make 

 use of the Ohio test for the purpose of establishing limits which may 

 be used later in specifying satisfactory graTels which are available for 

 their highway work. A description of this test will be found on page 30. 



