10 
General. 
Size. 
General. 
Size. 
General. 
Fineness. 
General. 
Grading. 
BULLETIN 704, U. S. DEPARTMENT OF AGRICULTURE. 
so as to produce, after rolling, a wearing course 2 inches in depth. 
A seal coat of bituminous material should then be applied and coy- 
ered with chips in sufficient quantity to take up all excess of bitu- 
men. Such roads may be maintained with surface treatments of 
bituminous material, covered with material conforming to Speci- 
fication RS-2. 
SPECIFICATION RBC-3. 
Broken Stone, Sand, and Filler for Fine Aggregate Bituminous Concrete 
Wearing Course. 
BROKEN STONE. 
The broken stone shall consist of angular fragments of rock, excluding 
schist, shale, and slate, free from thin or elongated pieces, soft or dis- 
integrated stone, dirt, or other objectionable matter, occurring either free 
or as a coating on the stone. 
It shall be that product of the crusher which, when tested by means 
‘of laboratory screens, will meet the following requirements: 
Per cent.. 
Passing.2-ineh) sereen: net Jess than2*2 == eee 95 
Retainedion, 4-inchiscreen, NO teleSSe phe eee eee ee eee = 20 
SAND. 
The sand shall be composed of sound durable-stone particles, free 
from a coating of clay or loam. 
When tested by means of laboratory screens mee sand shall meet the 
following requirements: 
Per cent. 
iRassine: “t-inch “Screens 22s s. ee a ee eee 100 
Retained on 200-mesh sieve, not less than______________________ 90 
MINERAL FILLER. 
The mineral filler shall consist of limestone, dust, dolomite dust, 
Portland cement, or natural cement. It shall be free from foreign or 
other objectionable material. 
When tested by means of laboratory sieves, the mineral filler shall 
meet the following requirements: 
Per cent. 
Passing (30-mMesShUsi@ ven 2 = a ea ee ee 100 
Total passing 200-mesh sieve, not Jess than] == 65 
TOTAL MINERAL AGGREGATE. 
The total mineral aggregate shali consist of a uniform mixture of 
the broken stone, sand, and mineral filler, the required grading of each 
being such as to produce, when properly proportioned, a mixture con- 
forming to the following limitations for grading. The exact propor- 
tion of each constituent producing a total mineral aggregate within 
these limitations shall be as directed by the engineer. 
When tested by means of laboratory screens and sieves the total 
mineral aggregate shall meet the following requirements: 
Per cent. 
Passing 4-inch and retained on 3-inch screen_=-—__-_=_+=_ == 5 to 10 
Passing 43-inch screen and retained on 10-mesh sieve________ 14 ton25 
Passing 10-mesh and retained on 40-mesh sieve_____________ (otOee 
Passing 40-mesh and retained on 80-mesh sieve_____________ 11 to 36 
Passing 80-mesh and retained on 200-mesh sieve___________- 10 to 25 
Passing )200-meshjisievesas eee a se USS se eee oo 5 to il 
