32 BULLETIN 249, IT. S. DEPARTMENT OF AGRICULTURE. 
alignment, and cross section, and shall be rolled until firm and hard with a 
roller of the macadam type weighing not less than ten (10) tons and not more 
than fifteen (15) tons. Should earth be encountered which will not compact 
by rolling so as to be firm and hard, it shall be removed and replaced with suit- 
able material, and that portion of the subgrade shall be again rolled. When 
the rolling is completed, the surface of the subgrade shall conform to the cross 
section shown on the plans and shall have the proper elevation and alignment, 
and shall be so maintained until the concrete surface is in place. 
SHOULDERS. 
The shoulders shall be partially built up at the time the subgrade is being pre- 
pared, and before the pavement is opened to general traffic they shall be care- 
fully graded to the required cross section and shall be thoroughly compacted by 
rolling with a roller weighing not less than ten (10) tons and not more than 
fifteen (15) tons. 
The contract price for shaping subgrade and shoulders shall be compensation 
in full for all work required of the contractor under the headings " Subgrade" 
and " Shoulders." 
MATERIALS. 
Cement.— The cement for use in this work shall meet the requirements of the 
United States Government specification for Portland cement, as published in 
Circular No. 33, United States Bureau of Standards, issued May 1, 1912. 
All cement shall be held at least ten (10) days after sampling, before it is 
used in any part of the work. If the cement satisfactorily passes all tests that 
may be made within that time, it may be used, and the 28-day test will not be 
insisted upon, but if it should fail to pass satisfactorily any test made within 
that time, then the cement shall not be used until it has passed satisfactorily 
all tests, including the 28-day test. All cement shall be delivered on the work 
in cloth or paper bags containing ninety-four (94) pounds net weight, and this 
amount of cement shall be considered as having a volume of one (1) cubic foot. 
In order to allow ample time for inspecting and testing, the cement shall be 
stored in a suitable weather-tight building having the floor blocked or raised 
from the ground, and shall be stored so as to permit of easy access for proper 
inspection and so that each carload shipment may be readily identified. 
Sand. — The sand for use in the concrete shall be composed of particles of 
hard, durable stone, and not more than three (3) per cent, by weight, of clay, 
loam, or silt. No clay, however, will be permitted if it occurs as a coating on 
the sand grains. The grains shall be of such sizes that all will pass a one- 
fourth (I) inch mesh screen; that not more than twenty (20) per cent will 
pass a No. 50 sieve; and that not more than sixty (60) per cent nor less than 
twenty (20) per cent will be retained on a No. 20 sieve. The sand shall be of 
such quality that a mortar made in the proportion of one (1) part of cement 
to three (3) parts of the sand, according to standard methods, when tested at 
any age not exceeding twenty-eight (28) days, will have a tensile strength of 
at least one hundred (100) per cent of that developed in mortar of the same 
proportions made of the same cement and standard Ottawa sand. The cement 
used in these tests shall be from an accepted shipment of that proposed for use 
with the sand. 
Gravel. — The gravel for use in the concrete shall be composed of hard, sound, 
durable particles of stone, and not more than one (1) per cent, by weight, of 
clay, loam, or silt. No clay, however, will be permitted if it occurs as a 
