18 
BULLETIN 555, U. S. DEPARTMENT OF AGRICULTURE. 
Grading. 
Methods of 
sampling and 
grading. 
The gravel aggregate, when tested by means of laboratory 
screens, shall meet the following requirements : Per cent. 
Passing inch screen 100 
Passing inch screen and retained on 
^4-inch screen to 
Passing 1/4-inch screen not more than 
The gravel shall be sampled for quality and grading in accordance 
with the method described on page , paragraphs , of 
these specifications ; and the grading shall be determined in ac- 
cordance with the method described or referred to on page 
of these specifications, test No. 
SPECIFICATION FOR SEMIGRAVEL, TOP-SOIL, OR SAND-CLAY AGGREGATE 
ROAD SURFACING. 
FOR 
Definitions. 
Physical prop- 
erties, coarse ma- 
terial. 
Mechanical an- 
alysis of mate- 
rial passing 10- 
mesh sieve. 
Methods of 
sampl i n g and 
testing. 
The terms clay, silt, sand, and coarse material, used in this 
specification, are defined as follows :* 
Clay: Material separated by subsidence through water and 
possessing plastic or adhesive properties, generally below 
0.01 mm. diameter. 
Silt: Fine material, other than clay, which passes -a 200-mesh 
sieve, generally from 0.07 to 0.01 mm. diameter. 
Sand: Hard material, usually siliceous, which passes a 10- 
mesh sieve and is retained on a 200-mesh sieve, generally 
from 1.85 to 0.07 mm. diameter. 
Coarse material: Hard material of gravelly nature, retained 
on a 10-mesh sieve, i. e., more than 1.S5 mm. diameter. 
The coarse material, if any, of the aggregate, shall consist of 
hard, siliceous material, free from feldspar, mica, schist, hardpan, 
or other soft, friable material, in excess of 5 per cent. 
The material which will pass a 10-mesh sieve, when subjected 
to mechanical analysis, shall meet the following requirements: 
Per cent. 
Clay to 
Silt to 
Total sand to 
Sand retained on 60-mesh sieve to 
The material shall be sampled in accordance with the method 
described on pages , paragraphs of these specifica- 
tions ; and the mechanical analysis shall be made in accordance 
with the methods described or referred to on page of these 
specifications, tests Nos. 
Note. — To cover the range of materials adaptable for road con- 
struction, it is recommended that roads of these types be divided 
into three classes, designated, Hard or Class A, Medium or Class 
B, and Soft or Class C, according to the mechanical analysis of 
the material which is to be specified for use. The limiting per- 
centages of the constituents suggested for the three classes are 
as follows : 
Hard or 
Class A. 
Medium 
or 
Class B. 
Soft or 
Class C. 
Clav 
Per cent. 
9 to 15 
5 to 15 
65 to 80 
45 to 60 
Per cent. 
15 to 25 
10 to 20 
60 to 70 
30 to 45 
Per cent. 
10 to 25 
Silt 
10 to 20 
Total sand 
55 to 80 
15 to 30 
* The definitions here given are intended to apply to these terms only 
when used in connection with roads of these types. 
