CETN III-47
(3/92)
that cementitious material containing aggregate achieved a more
satisfactory final product for sealing a section than did a
sodium silicate-cement sealant, provided the aggregate was small
enough not to impede pumping, and did not seal off the openings
between the voids. Sodium silicate-cement sealants flowed
readily from the injection pipe, but formed only a weak gel on
the floor of the test basin.
A sodium silicate-diocetin used to
stabilize voids filled with sand did not completely solidify
(harden) the sediment.
Long-term field exposure tests have been conducted to determine
how various sealants endured under actual field conditions when
exposed to the effects of waves, currents, freezing and thawing
cycles, wetting and drying cycles, abrasion, biological
influences,
and chemical reactions.
Three locations (Treat
Island, ME, Duck, NC, and Miami, FL), representing cold,
moderate,
and warm water environments, were selected.
The
ongoing tests are providing data to ascertain the strength,
durability,
and longevity of various cementitious sealants.
Sodium silicate-cement and sodium silicate-diacetin specimens,
however, experienced significant erosion and deterioration,
particularly at the mean water line where wave effects are
greatest.
This situation may be more extreme than that existing
within a rubble-mound structure, however, and may not be truly
representative of actual conditions to which placed sealants
would be subjected.
Considering the low compressive strengths of
the sodium silicate chemical gels and the observed rapid erosion
and deterioration rate in the field, their durability and
longevity are questioned, and long-term monitoring of the sand-
tightened Florida jetties should be undertaken to evaluate the
actual useful life of these sealing efforts.
Asphaltic sealants are durable, waterproof, flexible, and
chemically inert, which make bitumen a favorable choice as a
sealing material.
Asphaltic sealants set hard and bond well,
although no means of placing it in production quantities have
been developed.
Voids in coastal structures are currently filled
with asphaltic sealants by gravity flow and the use of vibrators.
Experience with these stabilization/sealing materials appear
promising, but methods to achieve deep penetration within a
coastal structure have not been developed.
Abundant literature
is available on successful marine applications of asphalt, but
there are no known cases of an asphaltic mixture being injected
into jetty voids.
When equipment and placement techniques for
pressure-injecting hot sand-asphaltic concrete are developed,
then tests should be conducted in the field to evaluate its
durability and effectiveness.
ADDITIONAL
INFORMATION:
Contact Mr. Robert R. Bottin, Jr., at 601-634-3827, CERC, Wave
Processes Branch, or Ms. Carolyn M. Holmes, CERC Program Manager
at 601-634-2025.
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