STATE GEOLOGIST. 211 
For the construction of the proposed concrete dam in the Scioto river 
for the water supply system of Columbus, Ohio, the following specifica- 
tions were prepared by the City Engineer, Mr. Julian Griggs. 
SPECIFICATIONS FOR THE SCIOTO RIVER DAM. 
37, Concrete.—This will be composed of one part by measure of cement, 
loose measure, two parts loose sand, not compacted, and four parts of broken 
stone. All concrete shall be made only in mechanical mixers, either cubical 
steel or iron boxes, sometimes called malaxators, measuring five feet on 
the edge, and capable of mixing two-barrel batches of concrete at one 
time, or continuous rotary mixers of approved design. These mixers will 
‘be supplied with independent friction clutches for each mixer, giving inde- 
pendent action. A sufficient number of these must be provided to turn out the 
average quantity of 200 cubic yards daily, with an engine capable of turning 
them simultaneously when loaded. The equipment for manufacture of concrete 
wiil comprise all that is necessary for storing a sufficient quantity of material 
and for handling and accurately measuring the same when placed in the mixers. 
Material will be placed in the mixers in the order directed by the engineer 
which will in his judgment give best results, the proportion of water being 
so regulated that the concrete can be thoroughly compacted and will then 
show merely a film of moisture upon the surface. Each batch of concrete 
will be given 28 revolutions, or aS many as may be required to produce the 
most thorough mixing, at a rate not exceeding 7 revolutions per minute, 
not more than two barrels of cement, with the proper proportions of sand and 
stone, being mixed at one time. Provision for rapid transportation of the 
concrete must be made so that it shall be in place in the finished work before 
the initial set commences. For distributing and ramming the concrete in 
place after delivery, a sufficient force of rammers and shovelers shall be 
maintained for each mixer in operation to handle the concrete rapidly and 
-ram-it thoroughly. All concrete must be thoroughly compacted by ramming 
in layers not exceeding six inches in thickness before ramming. The rammers 
will be of iron or steel, with a flat rectangular face six inches square and 
weighing not less than twenty pounds. 
38.  Facings.—The exposed surfaces of concrete work shall be faced 
with a mortar composed of one part of standard Silica cement which shall 
comply with these specifications in every particular, and two parts of sand, 
to which shall be added one per cent. by weight each of pulverized alum and 
potash soap, the soap to be weighed before being dissolved in water and the 
alum to be thoroughly mixed dry with the cement and sand. The amount of 
water to be used shall be barely sufficient to flush slightly to the surface 
after hard ramming. 
The facings of this material shall be not less than three inches thick 
and shall be incorporated with the body concrete in the following manner: 
As each batch of concrete is placed next the forms a loose plank shall be 
put next the form of requisite thickness, so that when removed as soon as 
concrete is placed and lightly tamped the space left may be filled with the 
facing material, and the whole thoroughly rammed together at one and the 
same time. This ramming shall be done with such extreme care as to insure 
the absence of all holes or the bridging of the material, leaving the surface 
absolutely smooth and uniform when the forms are removed. Necessary devi- 
ations from this method may be adopted on the approval of the Chief Engi- 
neer. 
