METHODS OF SAMPLING AND TESTING HIGHWAY MATERIALS 21 
11. METHOD OF TEST FOR QUANTITY OF CLAY AND SILT 
IN GRAVEL [FOR HIGHWAY CONSTRUCTION] 
(A S T M standard method (/). serial destination D 72-21, except as indicated. 
See p. 1) 
1. This test 'overs the determination of the quantity of clay and silt in 
[natural] gravel to be used in highway construction. 
2. The sample as received shall be moistened and thoroughly mixed, then 
dried to constant weight at a temperature between 100° and 110° C. (212° and 
230° F.) 
3. The pan or vessel to be used in the determination shall be 12 inches (30.5 
centimeters) in diameter by not less than 4 inches (10.2 centimeters) deep, 
as nearly as may be obtained. 
4. (a) A representative portion of the dry material weighing not less than 
50 times the weight of the largest stone in the sample shall be selected from 
the sample and placed in the pan [which has been dried and accurately 
weighed.] 
(b) Sufficient water shall be poured into the pan to cover the gravel. The 
gravel shall be agitated vigorously for 15 seconds with a trowel or stirring rod. 
After it has settled for 15 seconds the water shall be poured off into a tared 
evaporating dish, care being taken not to pour oft any gravel. This is repeated 
until the wash water is clear. The washed material shall be dried to constant 
weight in an oven at a temperature between 100° and 110° C. (212° and 230° F.), 
weighed, and the net weight of gravel determined. 
5. The percentage of clay and silt shall be calculated from the formula : 
- , , .,. Original weight — weight after washing vinn 
Percentage of clay and silt=- — ". . — = — . ., -X100 
Original weight 
6. For a check on the results, the wash water shall be evaporated to dryness 
and the residue weighed : 
t* *. * - i -i„ Weight of residue. .„__ 
Percentage of ciay and silt= ^ . . — = . _, X100 
Original weight 
12. METHOD OF DECANTATION TEST FOR SAND AND 
OTHER FINE AGGREGATES 
(A. S. T. M. tentative standard method (a), serial designation D 136-22 T) 
1. This method of test covers the determination of the total quantity of silt, 
loam, clay, etc., in sand and other fine aggregates.' 3 
2. The pan or vessel to be used in the determination shall be approximately 
9 inches (230 millimeters) in diameter and not less than 4 inches (102 milli- 
meters) in depth. 
3. The sample must contain sufficient moisture to prevent segregation and 
shall be thoroughly mixed. A representative portion of the sample sufficient to 
yield approximately 500 grams of dried material shall then be dried to a con- 
stant weight at a temperature not exceeding 110° C. (230° F.). 
4. The dried material shall be placed in the pan and sufficient water added to 
cover the sample (about 225 cubic centimeters). The contents of the pan shall 
be agitated vigorously for 15 seconds, and then be allowed to settle for 15 sec- 
onds, after which the water shall be poured off, care being taken not to pour off 
any sand. This operation shall be repeated until the wash water is clear. As 
a precaution, the wash water shall be poured through a No. 200 sieve and any 
material retained thereon returned to the washed sample. The washed sand 
shall be dried to a constant weight at a temperature not exceeding 110° C. 
(230° F.) and weighed. 
5. The results shall be calculated from the formula : 
t, „ ., , Original dry weight — weight after washing w -,,,,. 
PeroentaL'eofsilr.elav. loam, etc. = 1 ■ . , -, — - • ^ — X100 
Original dry weight 
13 This determination of the percentage of silt, clay, loam, etc., will include all water- 
soluble material present, the percentage of which may be determined separately if desired. 
