6 DEPARTMENT BULLETIN 1216, U. S. DEPT. OF AGRICULTURE 
for these tests on a standardized cement which gives a residue of about 20 per 
cent on the No. 200 sieve. 
31. The test shall be made with 50 grams of cement. The sieve shall I* 1 
thoroughly clean and dry. The cement shall be placed on the No. 200 sieve, 
with pan and cover attached, if desired, and shall be held in one hand in a 
slightly inclined position, so that the Sample will be well distributed over the 
sieve, at the same time gently striking the side about 150 times per minute 
against the palm of the other hand on the upstroke. The sieve shall be 
turned every 25 strokes about one-sixth of a revolution in the same direction 
The operation shall continue until not more than 0.05 gram passes through 
in one minute of continuous sieving. The fineness shall be determined from 
the weight of the residue on the sieve expressed as a percentage of the weight 
of the original sample, applying the sieve correction. 
Notes. — The essential points in the sieving operation may be summarized as follows : 
(1) Rotation of the sieve throughout the process. (2) Guarding against loss of materia! 
Sieve over white paper and always tap the sieve gently. (3i Use of a balance which 
will give results correct within 5 milligrams and sufficiently sensitive so that the rest poin' 
will be deflected at least two divisions of the scale for an added load of 5 milligrams 
(4 i Washers, shot, and slugs should never be used on the sieve. (5) Excessive humidit 
interferes with good sieving. It tends to> decrease the percentage of cement passing the 
sieve, and in general to produce irregular results. 
A plus ( + ) sieve correction indicates the amount to be added to and a minus ( — ) 
sieve correction the amount to be subtracted from the percentage passing the sieve to 
obtain the true fineness. The percentage passing is the amount obtained by subtracting 
the per cent residue from 100. The corrections are used in the reverse order when applied 
to the residues direct. 
32. Mechanical sieving devices may be used, but the cement shall not be 
rejected if it meets the fineness requirement when tested by the hand method 
described in section 31. 
MIXING CEMENT PASTES AND MORTARS 
33. The quantities of dry materials to be mixed at one time shall be 50O 
grams for neat cement mixtures and 1,000 grams for mortar mixtures. The 
proportions of cement or cement and sand shall be stated by weight in grams 
of the dry materials; the quantity of water shall be expressed in cubic centi- 
meters (1 cubic centimeter of water =1 gram). The dry materials shall be 
weighed, placed upon a nonabsorbent surface, thoroughly mixed dry if sand is 
used, and a crater formed in the center, into which the proper percentage ot* 
clean water shall be poured ; the material on the outer edge shall be turned 
into the crater by the aid of a trowel. After an interval of one-half minute 
for the absorption of the water the operation shall be completed by continuous, 
vigorous mixing, squeezing, and kneading with the hands for at least one 
minute. During the operation of mixing, the hands shall be protected by rubber 
gloves. 
Note. — In order to secure uniformity in the results of tests for the time of setting 
and tensile strength the manner of mixing above described shall be carefully followed. 
At least one minute is necessary to obtain the desired plasticity which is not appre- 
ciably affected by continuing the mixing for several minutes. The exact time necessary 
is dependent upon the personal equation of the operator. The error in mixing shall be 
on the side of overmixing. 
34. The temperature of the room, the materials, the mixing water, the moist 
closet, and storage-tank water shall be maintained as nearly as practicable at 
21° C. (70° F.) and the mixing water, moist closet, and the water in the 
storage tank shall not vary from this temperature more than 3° C. (5° F.). 
NORMAL CONSISTENCY 
35. The Vicat apparatus consists of a frame A (fig. 1) bearing a movable 
rod B, weighing 300 grams, one end C being 1 centimeter in diameter for a dis- 
tance of 6 centimeters, the other having a removable needle D, 1 millimeter hi 
diameter, 6 centimeters long. The rod is reversible, and can be held in any 
desired position by a screw E, and has midway between the ends a mark F 
which moves under a scale (graduated to millimeters) attached to the frame A. 
The paste is held in a rigid conical ring, resting on a glass plate about 10 centi- 
meters square. The ring shall be made of a noncorroding, nonabsorbent mate- 
rial, and shall have an inside diameter of 7 centimeters at the base, 6 centi- 
meters at the top, and a height of 4 centimeters. 
