18 



BULLETIN 555, TJ. S. DEPARTMENT OP AGRICULTURE. 



Grading. 



M e t h e & s of 

 sanipl in g and 

 grading. 



SPECIFICATION 



Definition!. 



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 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. 



FOR SEMIGRAVEL, TOP-SOIL, OR SAND-CLAY AGGREGATE FOR 

 ROAD SURFACING. 



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 1.85 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: 



Clav. 

 Silt. 



Total sand 



Sand retained on 60-mesh sieve. 



Hard or 

 Class A. 



Per cent. 



9 to 15 



5 to 15 



65 to 80 



45 to 60 



Medium 



or 

 Class B. 



Per cent. 

 15 to 25 

 10 to 20 

 60 to 70 

 30 to 45 



Soft or 

 Class C. 



Per cent. 

 10 to 25 

 10 to 20 

 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. 



