Although the specimens were
exposed to several months of winter frost as well as to the
heat of the summer, no change was visible in any part of the
concrete at the end of six months.
Mons. R. Feret, Chief of the Laboratory of Bridges and Roads,
Boulogne-sur-Mer, France, has given expression to the following
opinions:--
1. No cement or other hydraulic product has yet been found
which presents absolute security against the decomposing action
of sea-water.
2. The most injurious compound of sea-water is the acid of the
dissolved sulphates, sulphuric acid being the principal agent
in the decomposition of cement.
3. Portland cement for sea-water should be low in aluminium and
as low as possible in lime.
4. Puzzolanic material is a valuable addition to cement for
sea-water construction,
5. As little gypsum as possible should be added for regulating
the time of setting to cements which are to be used in sea-
water.
6. Sand containing a large proportion of fine grains must never
be used in concrete or mortar for sea-water construction.
7. The proportions of the cement and aggregate for sea-water
construction must be such as will produce a dense and
impervious concrete.
On the whole, sea-water has very little chemical effect on good
Portland cements, such as are now easily obtainable, and,
provided the proportion of aluminates is not too high, the
varying composition of the several well-known commercial
cements is of little moment.
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