Each block of concrete was provided with a
number plate and a lifting bolt, and was kept moist for one
month before being placed in position. The sand and gravel were
obtained from the beach on the west coast of Jutland. The
mortar blocks were mixed in the proportion of 1 to 1, 1 to 2,
and 1 to 3, and were placed in various positions, some between
high and low water, so as to be exposed twice in every twenty-
four hours, and others below low water, so as to be always
submerged. The blocks were also deposited under these
conditions in various localities, the mortar ones being placed
at Esbjerb at the south of Denmark, at Vardo in the Arctic
Ocean, and at Degerhamm on the Baltic, where the water is only
one-seventh as salt as the North Sea, while the concrete blocks
were built up in the form of a breakwater or groyne at Thyboron
on the west coast of Jutland. At intervals of three, six, and
twelve months, and two, four, six, ten, and twenty years, some
of the blocks have, or will be, taken up and subjected to
chemical tests, the material being also examined to ascertain
the effect of exposure upon them. The blocks tested at
intervals of less than one year after being placed in position
gave very variable results, and the tests were not of much
value.
The mortar blocks between high and low water mark of the Arctic
Ocean at Vardo suffered the worst, and only those made with the
strongest mixture of cement, 1 to 1, withstood the severe frost
experienced.
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