STATE GEOLOGIST. 191 
SPECIFICATIONS FOR STONE. 
The aggregate shall consist of crushed trap rock, granite, hard lime- 
stone, or other material equally hard and durable which shall meet the 
approval of the engineer. The broken stone shall be free from vegetable 
or organic matter in any shape and free from mud and dust or from lumps 
of clay or clay covered fragments. When sand is to be used in the con- 
crete, the stone shall be screened to pass through a (——) inch ring and 
retained by a screen of 4 inch rings. The stone should be thoroughly 
wet before mixing with the mortar. When it is desired to use screenings 
with the crushed stone, the proper proportion of sand to be used shall be 
determined by analysis. 
SPECIFICATIONS FOR CONCRETE. 
Proportions.—/he concrete shall consist of one part cement, 2 to 
4 parts of sand, and 4 to Io parts of crushed stone measured by loose vol- 
ume, (The proportions must vary to suit the character of the work and 
the requirements which the concrete must meet.) 
Mixing,—The sand and cement shall be thoroughly mixed dry, then 
sufficient water added to make a plastic or wet mortar and the whole thor- 
oughly mixed again. The stone, having been previously wet down, shall 
then be added and the whole mass thoroughly mixed until every particle 
of stone is coated with mortar’ The concrete thus mixed should-be imme- 
diately placed in position and rammed until excess mortar shows over the 
entire surface. (Where surfaces are to be exposed, either a facing of I 
cement to 2 sand shall be used and placed in position as the mass of con- 
crete advances, or else the stone should be forced back by thrusting down 
flat bladed shovels along the face of the form, thus allowing the richer 
mortar to run in next the form which makes a smooth impervious surface. ) 
No concrete which has attained partial set shall be used. The engineer 
will be guided by the tests in establishing a limit of time beyond which 
any concrete once mixed shall not be used in the work. 
