METHODS OF SAMPLING AND TESTING HIGHWAY MATERIALS 11 
40. This sand shall be considered standard when not more than 5 grains 
are retained on the No. 20 sieve, and not more than 5 grams pass the No. 30 
sieve, after one minute continuous sieving of a 100-gram sample, in the manner 
specified for sieving cement on the No. 200 sieve. (See section 31.) 
50. The Nos. 20 and 30 sieves shall conform to the requirements for these 
sieves as given in the standard specifications for sieves for testing purposes 
(serial designation E 11) of the American Society for Testing Materials (3). 
51. Immediately after mixing the standard mortar in accordance with the 
methods for mixing cement pastes and mortars the molds shall be filled heaping 
full without compacting. Then the mortar shall be pressed in firmly with the 
thumbs, applying pressure 12 times to each briquet, at points to include the 
entire surface. The pressure shall be such that the simultaneous application 
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Fig. 4. — Details for briquet 
Fig. 
-Gang mold 
of both thumbs will register a pressure of between 15 and 20 pounds. Each 
application of the thumbs shall be maintained not longer than sufficient to 
attain the specified pressure. Then the mortar shall be heaped above the mold 
and smoothed off with a trowel. The trowel shall be drawn over the mold in 
such a manner as to exert a pressure of not more than 4 pounds. The mold 
shall then be turned over upon a plane plate oiled with mineral oil. and the 
operation of heaping, thumbing, and smoothing off repeated. No ramming or 
tamping shall be used, nor any troweling in excess of that required to smooth off 
the specimen. 
52. The briquets shall be tested as soon as they are removed from the water. 
Tests may be made with any machine meeting the following requirements : 
The machine shall be capable of weighing the applied load within 0.5 per cent 
of the nominal value. The sensibility reciprocal (the weight required to be 
added to the load to move the beam from a horizontal position of equilibrium 
