The Scandinavian Portland cement manufacturers have in hand
tests on cubes of cement mortar and cement concrete, which were
started in 1896, and are to extend over a period of twenty
years. A report upon the tests of the first ten years was
submitted at the end of 1909 to the International Association
of Testing Materials at Copenhagen, and particulars of them are
published in "Cement and Sea-Water," by A. Poulsen (chairman of
the committee), J. Jorsen and Co., Copenhagen, 1909, price 3s.

[Illustration: FIG. 32.--Tests of the Tensile Strength of
Cement and Sand Briquettes, Showing the Effect of Sea Water.]

Cements from representative firms in different countries were
obtained for use in making the blocks, which had coloured glass
beads and coloured crushed glass incorporated to facilitate
identification. 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