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. ^ p or Dase 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 
to 
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 
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: 
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 gravels which are available for 
their highway work. A description of this test will be found on page 30. 
