10 
BULLETIN 555, U. S. DEPARTMENT OF AGRICULTURE, 
Physical prop- 
erties. 
Grading. 
Method of sam- 
pling. 
Methods of 
testing. 
The stone shall meet the following requirement : 
Per cent of wear_: not more than 
(or French coefficient not less than ) 
The broken stone, when tested by means of laboratory screens, 
shall meet the following requirements : 
Per cent. 
Passing inch screen 100 
Passing * inch screen and retained 
on inch screen to 
Passing inch screen not more than 
Stone shall be sampled for quality and grading in accordance 
with the method described on page , paragraphs , 
of these specifications. 
Tests of the physical properties and grading of the stone shall 
be made in accordance with the methods described or referred to 
on pages of these specifications, tests Nos. 
SPECIFICATION FOR STONE OR GRAVEL SCREENINGS FOR FINE 
FOR PORTLAND-CEMENT CONCRETE BASE. 
AGGREGATE 
General. 
Thysical prop- 
erties. 
Grading. 
Mortar 
strength tests. 
Method of sam- 
pling. 
The screenings shall consist of material obtained by crushing 
hard, durable rock or gravel, all of which shall pass a revolving 
screen having circular openings three-eighths of an inch in diam- 
eter. They shall be free from lumps of clay and at the time of 
use from lumps or crusts of hardened material. 
If the screenings are produced from rock, the rock shall meet 
the following requirement : 
Per cent of wear not more than 
(or French coefficient not less than ) 
The screenings shall be well graded from coarse to fine and 
when tested by means of laboratory screens and sieves shall meet 
the following requirements: 
Per cent. 
Passing 1-inch screen not less than 
Passing 20-mesh and retained on 50-mesh 
sieve to 
Passing 100-mesh sieve not more than 
When that portion of the screenings which passes a one-quarter 
inch laboratory screen is mixed with Portland cement in the 
proportions of 1 part of cement to 3 parts of screenings, by weight, 
according to standard methods of making 1 :3 mortar briquets, 
the resulting mortar at the age of 7 and 28 days shall have a 
tensile strength of at least t per cent of the strength de- 
veloped in the same time by mortar of the same proportions 
made of the same cement and Ottawa sand. 
Preliminary acceptance samples shall be subjected to both 7 and 
28 day tests and acceptance based thereupon. Samples tested 
during the progress of the work will be accepted on the basis of 
the 7-day test. 
Stone shall be sampled for quality in accordance with the 
method described on page , paragraphs , of these 
* It is recommended that a %-inch screen be specified here, 
t It is recommended that the minimum strength ratio be 90 per cent 
for this purpose. 
