STATE GEOLOGIST. 31 - 
They regained one-half of the lost water after five days under water. If 
so much water is lost under such conditions, it is readily seen what a 
serious loss must occur in actual practice unless unusual care is taken to 
protect the mortar surface. There is no question but that this loss of 
water seriously impairs the strength of the mortar. 
The three sets of tests with fine sand in table number 5 illustrate 
the effect obtained by using varying percentages of water. ‘The table 
shows that from 7 to Io per cent. of tensile strength is lost by using too 
much water, and from 30 to 40 per cent. by using too little. This illu- 
strates the necessity of properly proportioning the water to the cement 
and sand used. ‘The water used was proportioned by weight to the com- 
bined weight of sand and cement. 
PERMEABILITY OF CEMENT MORTAR. 
Work of Melick and Shepherd.—In 1899 and 1900, * Messrs. N. A. 
Melick and C. W. Shepherd, students in the Ohio State University, carried 
on, under the direction of the late Prof. C. N. Brown, a series of tests to 
determine the permeability of cement mortar. The question they sought ~ 
to answer in reference to permeability, propounded by Mr. Julian Griggs, 
M. Am. Soc. C. E., Chief Engineer of the City of Columbus, Ohio, was 
this: “Is it necessary to use soap and alum and Silica Portland cement, or 
can a cheaper mixture be made impermeable.” 
The experiments were carried on with three kinds of sand; standard 
sand or crushed quartz passing a No. 20 sieve and being held upon a No. 
30 sieve, lake sand, and a mixture of equal parts of lake sand and quartz. 
Medusa, Dyckerhoff and Silica Portland cement were used. The water 
pressure was applied to the cement mortar by means of a 34 inch pipe 
threaded into the back of a metal disc, 15 inches in diameter. Bolted to 
the face of this disc was a flanged metal collar, 10 inches in diameter. 
Within the collar was rammed from 2 to 3 inches of the mortar, the 
permeability of which was to be tested. A neat cement filler 4% inch 
to %4 inch thick was troweled around the ring to prevent water leaking 
between the collar and the concrete. Figure 2 shows a section of collar 
filled with mortar ready to bolt on to the disc. The mortar was mixed 
so dry that water would just flush to the surface upon thorough ram- 
ming. Great care was taken to get uniform ramming over each portion 
of the disc; the rammer being constructed in the form of a double sector 
just fitting within the metal collar. | 
After investigation of actual work being done in Columbus, O., the 
young men estimated that in ramming, 8 foot-pounds\of work were done 
upon each square inch of surface of the concrete which the city was 
laying. Hence they designed the rammer so that they could easily do a 
similar amount of work upon the ramming of the mortar into these collars. 
*Taken from the thesis of Messrs. N A. Melick and C. W. Shepherd, civil engineering grad- 
uates from the Ohio State University in 1900. The work was done at the suggestion and expense 
of the Engineers’ Club, of Columbus, Ohio. 
