METHODS OF SAMPLING AXD TESTING HIGHWAY MATERIALS 73 
of which shall be from 0.14 to 0.16 millimeters in diameter. The finished 
needle shall be hardened and highly polished. A Roberts No. 2 parabola needle 
checked against the standard needlt may be used.* 2 
4. The water bath shall be maintained at a temperature not varying more 
than 0.1° C. from 25° C. (77° F.). The volume of water shall be not less than 
10 liters and the sample shall be immersed to a depth of not less than 10 centi- 
meters (4 inches) and shall be supported on a perforated shelf not less than 5 
centimeters (2 inches) from the bottom of the bath. 
5. Any apparatus which will allow the needle to penetrate without appreciable 
friction, and which is accurately calibrated to yield results in accordance with 
the definition of penetration, will be acceptable. 
6. The transfer dish for container shall be a small dish or tray of such 
capacity as will insure complete immersion of the container during the test. It 
shall be provided with some means which will insure a firm bearing and prevent 
rocking of the container. 
PREPARATION OF SAMPLE 
7. The sample shall be completely melted at the lowest possible temperature 
and stirred thoroughly until it is homogeneous and free from air bubbles. It 
shall then be poured into the sample container to a depth of not less than 15 
millimeters (five-eighths inch). The sample shall be protected from dust and 
allowed to cool in an atmosphere not lower than 18° C. (65° F.) for one hour. 
{1.00 to 1. 02 mm. 8°40'fo 9°40'. __ 0.14 to 0.16 mrn^ 
i t -+->- 
,>=! 
opprox. 
. , , \<— 6.3 5m. .77.- 
approximarely 
50.8 mm. (2") >j 
Fig. 27. — Needle for penetration test 
It shall then be placed in the water bath along with the transfer dish and 
allowed to remain one hour. 
PROCEDURE 
8. (a) In making the test the sample shall be placed in the transfer dish filled 
with water from the water bath of sufficient depth to completely cover the 
container. The transfer dish containing the sample shall then be placed upon 
the stand of the penetration machine. The needle loaded with specified weight 
shall be adjusted to make contact with the surface of the sample. This may be 
accomplished by making contact of the actual needle point with its image re- 
flected by the surface of the sample from a properly placed source of light. 
Either the reading of the dial shall then be noted or the needle brought to zero. 
The needle is then released for the specified period of time, after which the 
penetration machine is adjusted to measure the distance penetrated. 
At least three tests shall be made at points on the surface of the sample not 
less than 1 centimeter (three-eighths inch) from the side of the container and 
not less than 1 centimeter (three-eighths inch) apart. After each test the 
sample and transfer dish shall be returned to the water bath and the needle 
shall be carefully wiped toward its point with a clean, dry cloth to remove 
all adhering bitumen. The reported penetration shall be the average of at least 
three tests whose values shall not differ more than four points between maximum 
and minimum. 
(b) When desirable to vary the temperature, time and weight, and, in order 
to provide for a uniform method of reporting results when variations are made, 
the samples shall be melted and cooled in air as above directed. They shall 
then be immersed in water or brine, as the case may require, for one hour at 
the temperature desired. The following combinations are suggested : 
At 0° C. (32° F.) 200-gram weight, 60 seconds. 
At 46.1° C, (115° F.) 50-gram weight. 5 seconds. 
42 The TJ. S. Bureau of Standards will measure and certify the accuracy of penetration 
needles in accordance with the tolerances given. 
