STATE GEOLOGIST. 209 
ience, and must be varied from time to time to suit the conditions of the 
weather and the ingredients. lt is very important that Portland cement shall 
have sufficient water for its complete hydration. Natural cement requires 
less water for hydration than Portland. 
17. The contents of the charging box shall be dumped immediately into 
the cubical mixer, which shall be revolved for not less than two minutes 
at a rate not exceeding nine revolutions per minute. The product is im- 
proved by longer mixing, and all the time less than period required for 
initial set, available between deliveries required at the forms should be 
utilized for extra turns to the mixer. The facing material shall be mixed 
by hand, and a very small gang will be able to keep the forms supplied, as 
for a facing of a uniform thickness of two inches, about 70 cubic yards only 
will be required for a lock, or about 3% cubic yards to each section. A 
close watch must be kept of the quantity used, and the above limit must not 
be exceeded. 
Ill. DEPOSITING AND RAMMING CONCRETE. 
18. Each lock wall shall be built in sections, averaging about 20 feet in 
length, making 10 sections to each wall. The planes of division between 
sections shall be at right angles to the axis of the lock, and are indicated 
on drawings furnished from this office. 
19. Each section shall be a monolithic mass of concrete built contin. 
uously from the bottom to completion without horizontal joints. The sections 
Shall be filled with horizontal layers about six inches thick, each layer to be 
deposited before the “initial” set of the previously deposited layer. 
20. The vertical planes of division between sections shall be made by 
_transverse bulkheads built in the forms and at each bulkhead a dovetail or 
recess shall be made for the interlocking of adjacent sections, the dovetails 
reaching from foundation to one foot below the coping of the sections. 
21. Alternate sections shall be built first, then the bulkheads shall be 
removed and the remaining sections filled with concrete. 
22. Before beginning a section, its foundation shall be swept clean with 
wire brooms and covered with a wet layer one inch thick of 1 to 1 cement 
mortar to make a close joint between the wall and the foundation. 
23. The walls of the wooden forms shall be kept well wet during the 
progress of the concrete work to prevent their absorption of water from the 
newly placed concrete. 
24. The lowest step or thickest part of the lock walls shall consist of not 
less than two (2) feet of Portland cement concrete next to the face of 
the wall and a backing of Natural cement concrete. All other walls or parts 
of walls shall be of Portland cement concrete. 
25. The exposed faces and copings of all walls shall consist of Portland 
cement and torpedo sand 1 to 3. The thickness of facings shall not exceed 
1% inches, nor be less than % inch. 
96. The facing and backing must go on simultaneously in the same 
horizontal layers. In order to gauge the thickness of the facing accurately, 
a light board or diaphragm of thin metal with convenient handles shall be 
set on edge parallel to and 1% inches from the front wall of the forms. 
The facing material shall be deposited in the space between this board and 
the form. The concrete of the backing shall then be deposited and spread 
against the back of this board, which may then be withdrawn and the whole 
mass thoroughly rammed so as to bond the facing and backing by destroying 
the surface of demarcation between them, but no stone must be forced 
14—S. G. 
