Saele, of the Public Works Laboratory of the City of Paris.
The principal difference in M. Deval's method consists in the use of
hot water for the period of hardening. The briquettes are made in the
usual way, and of the ordinary size; and the cement to be tested is
gauged with three times its weight of normal sand, and the smallest
quantity of water possible. After preparation, the briquettes are
allowed to harden in air for a period ranging from 24 hours for
Portland cement to 30 days for certain slow-setting hydraulic limes.
After this period, the samples are immersed in water kept at a
temperature of 80 deg. C., in which they remain for from two to seven
days. The briquettes are then broken in the ordinary way. After
careful comparisons of many varieties of cement hardened hot and cold,
M. Deval finds that cold tests are fallacious, inasmuch as they may
fail to detect bad material. Portland cement of good quality will not
only stand water at 80 deg. C., but will attain in seven days about the
same strength as is reached in the cold after 28 days. The hot test
therefore saves time. The hot test is an unfailing proof for free
lime; cements containing this constituent betraying weakness, and
cracking, swelling, and disintegrating in a very significant manner.
This last result is regarded as a valuable quality of the new method
of testing cement, the general effect of which appears to be to
enhance the test value of really good cements, while depreciating
those of an inferior character.
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