22 
Bl'LU.TIX 1216, U. S. DEPARTMENT OF AGRICULTURE. 
(d) Sufficient water shall be added to produce concrete of the 
required workability. 
Note. — Concrete testa should be made on plastic mixtures. It 
is of the utmost Importance thai a uniform degree <>f workability i>e 
secured in testa involving comparisons of different materials and 
methods. 
(c) The whole shall he mixed thoroughly until the entire mass 
is homogeneous in appearance. 
11. The workability or plasticity Of each hatch of concrete shall 
he measured immediately alter mixing by one of the following 
methods : 
Slump test. {,n Slump test, made in accordance with the test for con- 
sistency of Portland cement concrete (A. S. T. M. tentative 
method, serial designation 1) 138-22 T). 
Flow test. (&) Flow test, made by placing a metal form in the shape of 
a frustum Of a cone 6| inches in top diameter, 1<» indies in bottom 
diameter, and 5 inches deep, od the table of the How apparatus. 
The fresh concrete shall be placed in the mold in two layers. 
Kach layer shall be puddled and finished as described in section 
i:>. Immediately after molding, the form shall be removed by a 
steady upward pull; the specimen raised one-half inch and 
dropped 15 times in about six seconds by means of a suitable cam 
and crank. The spread of the fresh concrete due to this treat- 
ment as compared with the original bottom diameter of the cone, 
expressed as a percentage, is the "How." 
Forms. 12. The forms shall preferably be of metal. Each form shall 
be provided with a machined metal base plate, and shall he oiled 
with a heavy mineral oil before using. Particular care shall be 
taken to obtain tight forms so that the mixing water will not 
escape during molding. 
Notk :_Satisfnctory forms c;m bo made from lengths of cold-drawn 
steel tubing, split along one element and closed by means of a cir- 
cumferential band and bolt, Lengths of steel water pipe machined on 
the inside, from rolled metal plans, from galvanized steel, machined 
iron oi Steel castings. Paraffined cardboard molds will give good 
result.-; under expert supervision. 
13. Concrete test pieces shall be molded by placing the fresh 
concrete in the form in Layers 8 to 4 Inches in thickness. Bach 
layer shall be puddled with 25 strokes of a live-eighths inch round 
steel bar of a length 1) inches greater than the length of the moid, 
pointed at the lower end. After the top layer has been puddled, 
the surplus concrete shall be cleaned off with a trowel, and the 
mold covered with a machined metal plate or a piece of plate glass 
at least one-quarter inch thick, winch will be used later in capping 
the test piece. 
Capping. 14. Two to four hours after molding, the test pieces shall be 
rapped with a thin layer of stiff, neat, cement paste in order that 
the cylinders may present a smooth end for loading. The cap shall 
be formed by means of a machined metal plate or a piece of plate 
g;lass of suitable size, at least one-quarter inch thick, worked down 
on i he fresh cement paste until it rests on the top of the cylinder 
form. The cement for capping shall he mixed to a stiff paste be- 
fore beginning to mix the concrete; in this way the tendency of the 
cap to Shrink will be largely eliminated. The adhesion of the 
concrete to the metal base plate and the glass can be largely 
eliminated by oiling the cover plate or by inserting a sheet of 
paraffined 1 issue paper. 
In. Concrete test pieces shall be removed from the forms 20 to 
48 hours after molding, marked, weighed, and Stored in damp 
sand, under damp cloths, or in a moist chamber until the date of 
test. The temperature of tin' curing room should not fall outside 
the range of 60° to 7.~i° F. 
16. Tests shall he made at the age of 7 and 2S days; ages of 3 
months and 1 year are recommended, if longer time tests are 
required. 
17. Three to live test pieces should he made in investigations in 
which accurate comparisons are desired. 
