SAMPLING AND TESTING HIGHWAY .MATERIALS. 45 
the specification requirements, then a sample shall be taken from 
each hatch represented or from 1 out of each 20 barrels, samples 
to be taken from at least 3 inches below the surface and at least 
3 inches from the side of the barrel. A clean hatchet may be used 
if the material is hard enough to shatter and a broad, stiff putty 
knife if the material is soft. The samples so taken shall be 
melted and thoroughly mixed and an average sample taken from 
the combined material for examination. 
METHODS OF SAMPLING BITUMINOUS MIXTURES. 
A daily sample shall be taken by any of the following methods : 
(a) Samples shall be cut from the finished pavement about 6 
to 8 inches square and extending full depth of pavement before 
application of any sealing coat which may be used. 
(b) Samples shall be taken during preparation of the paving 
mixture from trucks or wagons at the asphalt plant and combined 
into composite samples of not less than 1 pound each. 
(c) Samples shall be taken either at the road or asphalt plant 
of any bituminous mixture which appears defective. 
METHOD OF SAMPLING MINERAL FILLER. 
Mineral filler shall bo sampled according to the method for 
sampling Portland cement received in carload lots. 
METHOD OF SAMPLING PREMOLDED JOINT FILLERS. 
One section at least 1 foot long and the full width of the joint 
shall be submitted from each consignment. 
DETERMINATION OF SPECIFIC GRAVITY OF BITUMINOUS 
MATERIALS. 
1. The specific gravity of bituminous materials shall be ex- 
pressed as the ratio of the weight of a given volume of the mate- 
rial at 25° C. (77° F. ) to that of an equal volume of water at 
the same temperature, and shall be expressed thus: 
A. Hydrometer Method (Used tor Thin Fluid Bitumens). Hydrometer 
method. 
2. The specific gravity of thin fluid bituminous road materials 
may be determined with the above-mentioned apparatus by first 
pouring a suih>ient quantity of the material into a tin cup which 
is then placed in a large dish containing cold or warm water, as 
occasion may require. The material in the cup should be stirred 
with the thermometer until it is brought to a temperature of 25° 
C, after which it should be immediately poured into the hydro- 
meter jar and its gravity determined by means of the proper 
hydrometer. In case the hydrometer sinks slowly, owing to the 
viscosity of the material, it should be given sufficient time to come 
to a definite resting point, and tin's point should be checked by 
raising the hydrometer and allowing it to sink a second time. 
The hydrometer should never be pushed below the point at which 
it naturally comes to rest until the last reading has been made. 
It may then bo pushed below the reading for a distance of three 
or four of the small divisions on the scale, whereupon it should 
immediately begin to rise. If it fails to do so. the material is 
too viscous for the hydrometer method, and the pycnometer 
method should be employed. 
3. The direct specific gravity reading obtained by the foregoing 
method is based upon water at 15.5 0% 0. taken as unity. For all 
practical purposes this reading may be corrected to water al 25 3 
C, considered as unity, by multiplying it by 1.002. Thus: Specific 
gravity 25° C./25° C.=specific gravity 25°/15.5° < '. I 
