METHODS OF SAMPLING AND TESTING HIGHWAY MATERIALS 55 
for the weighings required in the freezing and thawing test. The same pro- 
cedure in weighings and reweighing as specified in section 23 shall be used. 
29. The specimens shall be immersed for 72 hours in water having a tempera- 
ture of 18° to 24° C. (65° to 75° F.) and then weighed as specified in sec- 
tion 23. 
30. When the specimens (either from the absorption test or from a specially 
prepared series | have been weighed after saturation with water, they shall 
be returned to the water and kept immersed till the freezing test is begun. For 
freezing they shall be placed with their concave faces upward in water-tight 
metal trays, suitably mounted in a rigid metal crate, 35 and immersed in ice 
water until the specimens have attained substantially the temperature of the 
water, after which the water shall be drawn down to a depth of one-half inch 
in each tray. The crate shall then be lifted as a whole, without disturbing the 
specimen?, and placed in the freezing apparatus. 
Freezing shall be performed in a quiet atmosphere, free from perceptible 
natural or artificial currents. If artificial freezing apparatus is employed 36 the 
apparatus shall have sufficient heat-absorbent capacity to enable the tempera- 
ture of the freezing chamber to be brought to — 10° C. (+14° F.) or below 
within 30 minutes after the introduction of the specimens. The temperature Hi 
the freezing apparatus shall not fall lower than —20° C. (—4° F.). The freez- 
ing shall be continued until the water in the trays is frozen solid. Exposure 
to freezing conditions in excess of this requirement shall be considered as 
without significance. 
At the conclusion of freezing under the specified conditions the crate of 
specimens shall be withdrawn and at once immersed in water at a temperature 
of 18° to 24° C. (65° to 75° F.) in a special receptacle of proper size. Heating 
shall be continued so that the water will regain the required temperature as 
soon as practicable after the specimens are immersed. A temperature of 18° 
to 24° C. (65° to 75° F.) shall then be maintained for not less than two hours. 
At the conclusion of the thawing treatment the crate of specimens shall be 
inspected and the condition of each sample after each thawing shall be noted 
in the records. 
35. METHODS OF MAKING COMPRESSION AND TENSION 
TESTS OF FINE AGGREGATE FOR CONCRETE 
1. Fine aggregate shall be tested for strength either by tension or compres- 
sion in a mortar proportioned either by volume or by weight, using a 1 : 3 mix. 
2. Mortars made of natural sand shall be compared to mortars made with 
the same cement and standard Ottawa sand mixed in the same proportion and 
of the same consistency. 
(A) TENSION TEST 
3. The briquets for the tension test, shall be molded in the standard mold as 
used for testing Portland cement. Single or gang molds may be used. They 
shall be wiped with an oily cloth before using. 
4. Immediately after mixing, the mortar shall be placed in the molds, pressed 
in firmly with the thumbs, and smoothed off 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 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 carefully centered and the load applied continuously at the rate of 600 
pounds per minute. 
33 Figure 22 shows a crate and trays suitable for use in the box for artificial freezing 
illustrated in Figure 23. 
38 Artificial freezing will generally be necessary. It may be conducted in a commercial 
0° F. refrigerating room or in an artificial freezing box similar to the one shown in 
Figure 23, in which 0° F. temperature can readily be produced by the use of salt and ice. 
