SAMPLING AND TESTING HIGHWAY MATERIALS. 23 
18. Compression tests shall be made immediately upon removal Method of test. 
of the concrete test pieces from the curing room : that is, the test 
pieces shall be loaded in a damp condition. The length and aver- 
age diameter of the test piece shall be measured in inches and 
hundredths; two diameters shall be measured at right angles 
near the mid length. The test piece shall be weighed immediately 
before testing. 
19. In general, only the ultimate compression strength of the 
cylinders need be observed. The metal bearing plates of the rear- 
ing machine shall be placed in contact with the ends of the test 
piece: cushioning materials shall not be used. An adjustable 
bearing block shall be used to transmit the load to the test piece. 
The bearing block shall be placed on top of the test piece in ver- 
tical testing machines. The diameter of the bearing block shall be 
approximately the same as that of the test piece. The upper 
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 piece. 
20. The load shall be applied uniformly and without shock. The 
moving head of the testing machine should travel at the rate of 
about 0.1 inch per minute when the machine is running idle. 
21. The total load indicated by the testing machine at failure 
of the test piece 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 di- Weight. 
mensions. 
23. Density and yield of concrete when required shall be cal- Density. 
culated from the unit volumes of the constituent materials and 
the volume of the concrete. 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 one volume of ag- 
gregate mixed as used. 
24. The report of tests shall include the following: Report of test, 
(a) The kind and origin of concrete materials; 
(6) Complete data on all tests of cement and aggregates; 
u) A description of methods of making and testing the con- 
crete ; 
( d) The quantities of cement, aggregates, and water in each 
batch ; 
(e) The method of measuring workability or plasticity with 
M slump " or " flow " of concrete : 
{f) The quantity of water expressed as a ratio to volume of 
cement ; 
( <i i The age at test ; 
I A i The size of test pieces ; 
(i) The date of molding and testing each cylinder: 
(/) The compression strength in pounds per square inch of each 
test piece and average of tests in a set : 
(fc) A description of the failure and appearance of the con- 
crete in each test piece; 
(/> The unit weight, density and yield of the concrete, 
METHOD OF MAKING AND STORING SPECIMENS OF 
CONCRETE IN THE FIELD. 
(A. S. T. M. standard method, serial designation. C 31—21, slightly 
modified.) 
1. The methods herein specified apply to molding and storing of 
test specimens made from samples of concrete being used in con- 
struction. 
2. The test specimens shall be cylindrical in form with the length 
twice the diameter. In general, a mold whose diameter is not less 
than four times the diameter of the largest size aggregate shall 
