SAMPLING AND TESTING HIGHWAY MATERIALS. 
15 
2. Mortars made of natural sand shall be compared to mortars 
made with the same cement and standard Ottawa sand mixed in 
the sa.me proportioD and of the same consistency. 
I. TENSION TEST. 
Che briquets for the tension test shall be molded in the Tension test 
standard mold as used for testing Portland cement. Single or specimens. 
molds may be used. They shall be Wiped with an oily 
cloth before using. 
4. Immediate mixing, the mortar shall be placed in the 
molds, pressed in firmly With the thumbs, and smoothed oft with 
a trowel without ramming. Additional 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 moderate 
pressure on the material. The mold Shall then be turned over 
and the operation of heaping, thumbing, and smoothing off 
repeated. 
5. Tests shall be made with any standard machine. The Method of test 
briquets shall be tested as soon as they are removed from the 
water. The bearing surfaces of the clips and briquets shall be 
free from grains of sand or dirt. The briquets shall be care- 
fully centered and the load applied continuously at the rate of 
600 pounds per minute* 
6. Testing machines s-hall be calibrated frequently in order to 
determine their accuracy. 
7. Briquets that are manifestly faulty, or which give strengths 
differing more than 15 per cent from the average value of all test 
pieces made from the sample and broken at the same period, 
shall not be considered in determining the tensile strength. 
II. COMPRESSION TEST. 
8. A cylindrical test piece 2 inches in diameter and 4 inches in Compression 
length shall be used in making the compression test. The molds test specimens. 
(single or gang molds) shall be made of noncorroding metal. 
The ends of the mold shall be parallel. They shall be oiled before 
using. During the molding of 'the test piece, the mold shall rest 
on a clean, plane surface (preferably a piece of plate glass which 
is allowed to remain in place until the mold is removed). 
0. The mortar shall be placed in the molds in four layer? about 
1 inch in thickness, each layer being thoroughly compacted, but 
not rammed by n -<teei tamper. The steel tamper shall have a 
total length of about 6£ inches. It shall be 1 inch in diameter 
for 11 inches with the handle o± inches long and five-eighths inch 
in diameter. It. shall weigh approximately three-quarters of a 
pound. The surface of each layer shall be roughened before the 
addition of the next layer. In compacting the test pieces no mix- 
ing water shall be forced out of the mortar. In finishing the test 
piece, mortar shall be heaped above the mold and smoothed off 
with a trowel. As soon as the test pieces from one sample are 
molded, the top of each mold shall be covered with a piece of 
glass which shall be brought to a firm bearing on the fresh mor- 
tar. The cover glasses shall remain in place until the molds 
are removed. 
1<». Test< of mortar cylinders shall be made in any testing ma- Method of test. 
chine which is adapted to meet the specified requirements. The 
test pieces shall be broken as soon as they are removed from the 
water. The ends of the test cylinders shall be smooth, plane sur- 
faces. The metal bearing plates of the testing machine shall be 
placed in direct contact with the ends of the test piece. Dur- 
ing the test a spherical bearing block shall be used on top of 
the cylinder. In order to secure a uniform distribution of the 
lcted over the test cylinder, the spherical block must be accurately 
centered. The diameter of the spherical bearing block should be 
only a little greater than that of the test piece. The test piece 
