SAMPLING AND TESTING HIGHWAY MATERIALS. 25 
(&) Should a 7-day. test be required, the test specimens shall 
remain at the works as long as possible to harden and tben 
shall be shipped so as to arrive at the laboratory in time to make 
the test on tbe required date. 
METHOD OF SECURING SPECIMENS OF HARDENED 
CONCRETE FROM THE STRUCTURE. 
(A. S. T. M tentative method, serial designation, C 42-21 T.) 
1. The methods and precautions herein specified apply to secur- 
ing test specimens from hardened concrete in the structure. 
2. A specimen from hardened concrete to be tested for strength 
shall not be taken until the concrete has become hard enough so 
that the cutting of the specimen will not disturb the bond be- 
tween the mortar content and the coarse aggregate of the speci- 
men. 
3. The specimen from the structure can best be secured by use Securing 
of a core drill. For specimens taken perpendicular to a hori- samples. 
zontal surface a drill using chilled shot may be used, but when 
taken perpendicular to a vertical surface a diamond drill should 
be used. 
4. (a) The core specimen taken shall be as nearly as possible 
a cylinder whose length is twice the diameter. 
(&) In securing a specimen perpendicular to a horizontal sur- 
face care shall be taken to secure, if possible, a specimen whose 
beds shall be parallel to the horizontal bed of the concrete as 
originally placed. 
(c) In securing a specimen perpendicular to a vertical surface, 
or to a surface with a batter, care shall be taken as to the 
point of securing the specimen. The lower portion of any one 
unit of depositing in mass concrete is more dense than is the 
upper portion of the unit, therefore a specimen shall be taken 
from near the middle of such unit of deposit. 
5. A specimen to be taken from hardened concrete wdiich has 
been removed from a structure shall be cut out by a drill or 
shall be cut into a symmetrical test piece by tooling or by sawing. 
The method of sawing can seldom be used to advantage in the 
field. In selecting this test specimen care shall be used to see 
that the concrete selected has not been injured or shattered by 
the method of its removal from the structure. 
6. The specimen secured shall have ends, or beds, as nearly 
as possible perpendicular to its axis, and if the specimen has 
ends with uneven surfaces, these ends shall be made parallel 
plane surfaces with a mortar richer than the mortar of the 
specimen or with a mixture of cement and calcined gypsum 
(plaster of Paris). 
ABSORPTION TEST OF CONCRETE. 
1. Specimens for the absorption test shall be apparently sound, 
solid pieces of concrete and shall not show cracks or fissures. 
The specimens shall be so marked as to permit the identity of 
each one to be ascertained at any stage of the test. 
2. Preparatory to the absorption test all specimens shall first Method of test 
be weighed and then dried in a drier or oven at a temperature 
of not less than 110° 0. (230° F.) for not less than three hours. 
After removal from the drier, the specimens shall be allowed to 
cool to a temperature of 20° to 25° C. (68° to 77° F.) and re- 
weighed. If the specimens were apparently dry when taken, 
and the second weight closely checks the first, the specimens 
shall be considered dry. If the specimens were known to ho 
wet when taken, they shall be placed in the drier for a further 
drying treatment of two hours, and reweighed. If the third 
weight checks the second, the specimens shall be considered dry. 
In case of any doubt, the specimens must be redried (ov 2-hour 
periods until check weights are obtained. 
