METHODS OF SAMPLING AND TESTING HIGHWAY MATERIALS 31 
specimen shall be measured in inches and hundredths ; two diameters shall be 
measured at right angles near the midlength. The test specimen shall be 
weighed immediately before testing. 
19. In general, only the ultimate compressive strength of the cylinders need 
be observed. The metal bearing plates of the testing machine shall be placed 
in contact with the ends of the test specimen ; cushioning materials shall not 
be used. An adjustable bearing block shall be used to transmit the load to the 
test specimen. The bearing block shall be used on top' of the specimen in 
vertical testing machines. The diameter of the bearing block shall be the same 
or slightly larger than that of the test specimen. The upper or lower section 
of the bearing block shall be kept in motion as the head of the testing machine 
is brought to a bearing on the test specimen. 
20. The load shall be applied uniformly and without shock. The moving 
head of the testing machine should travel at the rate of about 0.05 inch per 
minute when the machine is running idle. 
21. The total load indicated by the testing machine at failure of the test 
specimen shall be recorded and the unit compressive strength calculated in 
pounds per square inch, the area computed from the average diameter of the 
cylinder being used. The type of failure and appearance of the concrete shall 
be noted. 
22. The weight of the concrete in pounds per cubic foot shall be determined 
from the weight of the specimens and their dimensions. 
23. Density and yield of concrete when required shall be calculated from the 
unit volumes of the constituent materials and the volume of the fresh or set 
concrete as desired. Density is here understood to be the ratio of solids in the 
concrete to the total volume of the mass. Yield is the volume of concrete 
resulting from the volume of aggregate mixed as used. 
24. The report shall include the following : 
(a) The kind and origin of concrete materials. 
(&) Complete data on all tests of cement and aggregates. 
(c) A description of methods of making and testing the concrete, where 
methods deviate from the proposed standards. 
(d) The quantities of cement, aggregates, and water in each batch. 
(e) The method of measuring workability or plasticity with "slump" or 
" flow " of concrete. 
(f) The quantity of water expressed as a ratio to volume of cement. 
(g) The age at test. 
(h) The size of test specimens. 
(i) The date of molding and testing each cylinder. 
(;') The compressive strength in pounds per square inch of each test speci- 
men and the average of tests in a set. 
(k) A description of failure and appearance of concrete on each test specimen. 
(/) The unit weight, density, and yield of the concrete. 
23. METHOD OF MAKING AND STORING COMPRESSION 
SPECIMENS OF CONCRETE IN THE FIELD 
(A. S. T. M. standard method U), serial designation C 31-27, except as indicated. See 
p. 1) 
1. This method is intended to apply to the molding and storing of test speci- 
mens of concrete sampled from concrete being used in construction. 
2. The test specimens shall be cylindrical in form with the length twice the 
diameter. The standard shall be 6 by 12 inch cylinders where the coarse aggre- 
gate does not exceed 2 inches in size ; for aggregates larger than 2 inches, 8 by 
16 inch cylinders shall be used ; 2 by 4 inch cylinders may be used for mixtures 
without coarse aggregate. 
3. (a) The molds shall be cylindrical in form, made of nonabsorbent material, 
and shall be substantial enough to hold their form during the molding of the 
test specimens. They shall not vary in diameter more than one-sixteenth inch 
in any direction, nor shall they vary in height more than one-sixteenth inch 
from the height required. They shall be substantially water-tight so that there 
will be no leakage of water from the test specimen during molding. 18 
18 See footnote 17. 
