34 DEPARTMENT BULLETIN 1216, U. S. DEPT. OF AGRICULTURE 
6. (a) Two to four hours after molding, the test specimens shall be capped 
with a thin layer of stiff neat-cement paste in order that the cylinder may 
present a smooth end for testing. The cap shall be formed by means of a 
piece of plate glass one-fourth inch in thickness or a machined metal plate 
one-half inch in thickness and of a diameter 2 or 3 inches larger than that of 
the mold. The plate shall be worked on the fresh cement paste until it rests 
on top of the mold. The cement for capping should be mixed to a stiff paste 
two to four hours before it is to be used in order to avoid the tendency of the 
cap to shrink. Adhesion of the concrete to the top and bottom plates may be 
avoided by oiling the plates or by inserting a sheet of paraffined paper. 
(b) When directed, specimens may be capped after having been received in 
the laboratory. 
7. (a) At the end of 48 hours the test specimens shall be removed from the 
molds and buried in damp sand except in case the molds shown in Figure 11 
are used, when they may be buried in damp sand without removal of the mold, 
thus permitting shipping in the molds. 
(&) When directed, specimens may be cured in a manner .similar to the 
structure. 
8. (a) The test specimens shall remain buried in damp sand until 10 days 
prior to the date of test. They shall then be well packed in damp sand or wet 
shavings and shipped to the testing laboratory, where they shall be stored 
either in a moist room or in damp sand until the date of test. 
(&) Should a seven-day test be required, the test specimens shall remain at 
the work as long as possible to harden and then shall be shipped so as to arrive 
at the laboratory in time for test on the required date. 
(c) Test specimens shall be protected from drying after removal from damp 
storage and before testing. 
24. METHODS OF SECURING SPECIMENS OF HARDENED 
CONCRETE FROM THE STRUCTURE 
(A. S. T. M. standard method U), serial designation C 42-27) 
1. These methods and precautions are intended to apply to securing 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 between the mortar and the coarse aggregate 
of the specimen. 
3. The specimen from the structure can best be secured by use of a core 
drill. For specimens taken perpendicular to a horizontal 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 surface 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 place 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 or deposit. 
5. A specimen to be taken from hardened concrete which has been removed 
from a structure shall be cut out by a drill or shall be cut into a symetrical 
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 per- 
pendicular to its axis, and, if the specimen has ends with uneven surfaces, these 
ends shall be made to parallel plane surfaces by capping with a thin layer of 
mortar richer than the mortar of the specimen or with a mixture of cement 
and calcined gypsum (plaster of Paris). 
7. In case the dimensions of a specimen are necessarily appreciably different 
from the recommended shape which requires a height twice the diameter, 
allowance for the ratio of height to diameter must be made in determining the 
