Note: Descriptions are shown in the official language in which they were submitted.
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The invention relates to a lining for a conduit,particularly for a concrete water conduit.
Various kinds of industrial installations --
such as power plants using sea water for cooling, and
chemical plants using sea water as a source for some of
the materials naturally present in sea water -- transport
the water from the open sea to the inland location where
the water is to be used, in l-arge conduits most often
made of Portland cement concrete. Such conduits tend to
beco~e rapidly fouled with a variety of living organisms,
including both animals and plants of a considerable variety
of kinds whose habit of growth is to attach themselves to
a stationary surface and feed on the materials contained in
the water flowing past. Fouling by such organisms rather
rapidly reduces the capacity of the conduits and has required
periodic shutdown for the purpose of laborious scraping of
the accumulated growths from the surfaces. This is a very
expensive operation, not only because of the labor involved
but more importantly because of the interference with pro-
duction which results.
It has been known for many years that concreteconduits can be protected against corrosion by acids which
eat away the material of the`conduit, by casting the
concrete against a corrosion-resistant plastic lining
having projections interlocking with the concrete, such as
T-shaped ribs which become embedded in the surface of the
concrete, as shown in the expired U.S. Patent 2,816,323,
of Munger. However, such linings have not been shown
to be useful in preventing attachment and growth of living
organisms.
It has also been known that the attachment and
growth of barnacles, seaweeds, and other living creatures
which attach themselves to the exterior surfaces of boat
hulls, buoys, piling, and other structures exposed to
seawater, could be prevented by application of a poison,
~ such as metallic copper, or paints containing various
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compounds of copper or other poisonous metals, or most
advantageously sheets of flexible plastic or elastomer
material containing poisons. The materials of greatest
long term effectiveness appear to be elastomer materials
containing poisons that are very slightly soluble in
water but somewhat soluble in the elastomer, so that
they diffuse slowly to the surface, and therefore are
continuously present at the surface for many years in
minute but effective quantity because of the very low
solubility in water, as disclosed in Cardarelli U.S.
patents 3,417,181 and 3,426,473.
According to the present invention there is
provided a corrosion-resistant conduit lining, repellant
to living organisms, comprising a flexible corrosion-
resistant layer provided with projecting keys capable of
being key-bonded to a conduit, and united thereto another
layer of flexible material for exposure to the fluid in the
conduit, said another layer being characterized by the
presence of a compound which is slightly soluble in the
~20 material of said another layer and is very slightly water-
soluble and also is toxic~to organisms which tend to attach
themselves to surfaces and;grow on such surfaces.
In another aspect of the invention there is
provided the combination of a conduit lining of the
invention, and a concrete conduit cast around the
lining so that the lining is keyed to it.
The invention more particularly involves the
discovery that a surface material which will repel the
organisms which tend to attach themselves to conduit linings
can easily be provided on the inner surfaces of concrete
conduits and other concrete structures such as
reservoirs by preparing the known plastic lining material
with locking ribs on one surface, and applying to the
other surface of the plastic lining material a layer of
an elastomeric material containing a long term effective
poison. The composite lining is applied to the building
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forms for the conduit with the locking ribs outward, and
the concrete is poured so as to embed the locking ribs
and hold the lining firmly in place. The lining pre-
ferably covers the entire inner surface of the conduit,
with essentially none of the concrete ultimately exposed
to the seawater on the inside, when the building forms
are removed. :
In the construction of such lined concrete
conduits, it is preferred to preassem~le the plastic
sheets, having locking ribs on one side, with a sub-
stantial thickness, on the other side, of elastomer con-
taining a suitable poison. However the same excellent
results can be obtained by constructing the plastic
lined conduit first, and then applying a further lining
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of a material containing a slowly released poison, but
with a generally higher labor cost.
The backing or supporting layer i~ preferably
made from a suitable flexible inert material such as
5 plasticized polyvinyl chIoride, fabricated in extruded
strips provided with locking ribs of T-shaped cross
section. To this flexible, plastic lining is then
adhered material including an appropriate toxicant com-
pound. The composite sheet is wrapped around the inner
10 concrete form with the toxicant-containing material
against the form, and the concrete conduit material is
poured so as to surround and embed the locking ribs and
therefore to hold the lining immovably in place on all
or most of the exposed inner surface of the conduit when
15 it is built.
THE DRAWINGS
In the accompanying drawings:
Fig. 1 is a cross-section on a small scale of
a large diameter concrete conduit provided with a lining
20 in accordance with this invention.
Fig. 2 is a partial section on a larger scale
of one embodiment of the invention.
Fig. 3 is a similar partial section of another
embodiment.
DETAILED DESCRIPTION
The lining material of this invention is pre-
ferably made of at least two somewhat different kinds
of compositions because they perform somewhat different
functions which are most advantageously performed by
30 different compositions.
The base which is mechanically bonded to the
concrete structure should be a somewhat stretchable but
chemically unreactive material, so that it will not
suffer rro~ long tlme exposure to strongly alkaline con-
35 crete or to the atmosphere or fresh water or seawater.Although vulcanized or unvulcanized natural rubber or
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synthetic rubber may be used, it ls much preferred to
use a flexible thermoplastic such as polyethylene or
preferably plasticized polyvinyl chloride, the latter
being particularly inexpensive, strong, and highly re-
sistant to change, especially if plasticized with abouthalf its weight of plasticizer of high molecular weight
and therefore of extremely low volatility so that the
base material will not change appreciably in physical
properties over many years of time.
10The principal other material is that which
makes up the exposed surface of the lining. It must -
contain, and retain for years of time, a poison or
toxicant which will prevent attachment and growth of
living organisms. While it is conceivable that almost
15 any weather-resistant flexible or elastic material might
be used, it is presently preferred to use a vulcanizable
elastomer, and preferably one which is essentially hydro-
carbon in nature or at most contains substituents in the
molecular structure which are quite unreactive under or-
20 dinary conditions, such as chlorine or nitrile. Conse-
quently, such materials as neoprene (a polymer of chloro-
butadiene), butyl rubber (a copolymer of isobutylene with
a little isoprene), and EPDM rubbers (copolymers of -
ethylene and propylene with a little diene) are preferred
25 materials, although many other elastomers could be used,
such as natural rubber, nitrile rubbers, butadiene-sty-
rene rubbers, polyether rubbers, etc., or even plasti-
cized thermoplastics such as polyvinyl chloride or
polyvinyl butyral, or inherently resilient polymers such
30 as flexible polyethers, polyesters, polysilanes, etc.
The specific materials chosen must be extremely resistant
to weathering. If a vuicanizable rubber is chosen, it
should preferably be vulcanized to a strong and at least
somewhat resilient condition. The choice of vulcanizing
35 agents is generally unimportant, as long as they do not
decompose the toxicant which is used, or react with it.
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The other essential material is the actual
poison or toxicant which either repels or prevents the
growth of living organisms on the exposed surface. For
effective long term function, this needs to be a
material which can be dispersed in a moderately high pro-
5 portion in the surface layer and which will dissolve inthe elastomer to a slight but appreciable extent. There
will, of course, be poison or toxicant present in the
surface layer as long as any of the toxicant remains,
because the material chosen is one which is capable of
lO diffusing throughout the elastomer at a rate dependent
on its solubility and molecular weight. For long term
effectiveness, the material must therefore be somewhat :
soluble in the elastomeric surface material and have a
molecular weight sufficiently high that it will diffuse
15 throughout the mass, very slowly, and will be dissolved
into seawater from the surface at a predetermined but
extremely slow rate, so that there will be some toxi-
cant continuously at the exposed surface, effective to
repel unwanted organisms but so little that it will be
20 many years before the toxicant is exhaused and its
effect ceases.
The toxicant can be any material which is ade-
quately repellant and at the same time has a sufficiently
low solubility in water to be retained for many years.
25 For this purpose the organotin compounds disclosed in
Cardarelli U.S~ patent 3,426,~73 are preferred, because of
their effectiveness, extremely low solubility in water,
and freedom from hazard to warm-blooded animals including
people, and to food fish, at the concentration in which
30 these toxicants would be present in the water. Specific-
ally preferred is tributyl-tin oxide.
The conduit lining material of this invention
' can be made of a single material which will function both
as the base for keying into the concrete, and as the res-
35 ervoir for the toxicant, but since the toxicant is some-
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what expensive, it is greatly preferred to place it onlywhere it will be most effective and to use a different
material for the base. For the same reason, it is pre-
ferred to use a barrier film between the two materials,
5 to minimize loss of toxicant by diffusion away from
the exposed surface into the base. It is also pre-
ferred, although not always necessary, to use an ad-
hesive to bond the elastomer surface material containing
the toxicant to the base material.
EXAMPLE
Referring to the drawings, Fig. 1 shows a
section of a concrete conduit of cylindrical shape and
therefore having a circular cross-section. Such a con-
duit consists of a concrete shell 10, usually but not
15 necessarily with conventional longitudinal and circum-
ferential reinforcing rods (not shown) and a lining.
In accordance with this invention, the lining
consists of at least two layers, as shown in Fig. 2.
The base layer 11 in direct contact with the
20 concrete shell 10 is preferably made of a polyvinyl
chloride plasticized with about half its weight of non-
fugitive plasticizers, such as one of the common soft
resinous polyester plasticizers. One or more liquid
plasticizers such as didecyl phthalate may also be
25 employed, along with the usual minor quantity of a
stabilizer. Mineral fillers may also be present if
desired, for reducing cost.
The base layer 11 of the liner is fabricated
by extrusion of the vinyl composition in a thin sheet,
30 which may suitably be about 2 mm thick, having T-shaped
ribs 12 extending about 1 cm from one surface, with the
head of the T about 1 cm in width. Spacing of the ribs
may be about 5 to 8 cm. Such a sheet can be produced in
whatever width is conveniently handled in an extruder,
35 and joined edge to edge by heat sealing to form blankets
of any desired width for wrapping around a form for a
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concrete conduit.
The inner layer 15 of the lining, which faces
the hollow space of the conduit, is made from a material
which is preferably elastomeric, or at least easily flex-
5 ible, and should have a consistency in the range fromvery firm but still flexible, to soft and rubbery. It
is preferred to use a fairly resilent material having a
high resistance to weather, and particularly to moisture.
Accordingly, synthetic elastomers essentially free from
10 proteins and fatty acids are most suitable. Particularly
preferred are the rubbert polymers of chlorobutadiene,
generally known as neoprene, since properly compounded
and prepared neoprene is easily vulcanized and is strong,
resilient, resistant to weather and to oils, and can be
15 mixed with relatively high proportions of suitable toxi-
cants so as to release them at the surface in an effec-
tive amount at an extremely slow rate.
Thus a water resistant type of neoprene such as
Neoprene WRT may be mixed with conventional vulcanizing
20 materials for neoprene, and preferably with addition of a
reinforcing pigment such as carbon black (for a black
surface) or hydrated silica (for a white surface). For
each 100 parts by weight of neoprene polymer at least
about 5 parts and preferably from 10 to 20 parts of
tributyl-tin oxide are added as a long term toxicant.
Such a composition is then vulcanized in sheets of about
2 mm to as much as 12 or 15 mm thickness depending on the
duration of protection desired. The minimum thickness
of 2 mm will protect against fouling by most organisms,
and particularly barnacles and mollusks, for 5 to 10
years. The length of protection accorded by greater
thicknesses can only be estimated, but should be as much
as 30 years for 12 mm thickness.
The union of the neoprene surface with the vinyl
backing which is interlocked into the concrete can be
obtained in a very simple matter by coating each surface
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with a neoprene solution such as is known as "contact
cement", and pressing them firmly together when the
coated surfaces are tacky.
For long term protection, it is desirable to
5 bond the toxicant-containing surface layer to the base
material which is interlocked with the concrete with a
bond of maximum attainable strength and durability. It
is also desirable to assure retention of toxicant for
as long a period as possible by avoiding loss by dif-
10 fusion or otherwise in the direction away from theexposed surface. For obtaining these objectives it is
preferred to interpose between the two materials a
chemically set adhesive cement and also a diffusion
resistant barrier layer.
A suitable barrier to retard loss of the
tributyl-tin oxide, or other toxicant, by diffusion, is -
chlorinated rubber, preferably a grade containing at
least 66~ chlorine, such as can be obtained under the
trade name Parlon 125. A uniform coat of a solution of
20 such chlorinated rubber is applied to the smooth face of
the vinyl backing, to form a strongly adherent barrier
film 13 as shown in Fig. 3.
A room-temperature setting waterproof epoxy
adhesive 14 can then be used to bond the toxicant-
25 containing inner layer 15 to the barrier film 13 on thevinyl outer lining layer 11.
Alternatively, a mixture of polymers can be
used to form a strongly adhesive barrier layer~ For
example, approximately equal quantities of neoprene and
30 chlorinated rubber, together with a somewhat smaller
quantity of a 50:50 butadiene-styrene copolymer, suitably
one-third as much as the sum of the other two ingredi-
ents, can be used to function both as a ribbed backing
and as a diffusion barrier, or for either one of these
35 purposes if a different material is chosen for the other
purpose.
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The composite material, with a toxicant-
containing face, and a ribbed backing for keying into
the concrete, is made up in dimensions suitable for
lining the concrete conduit which is to be constructed.
If the concrete conduit is to be made in cylin-
drical sections subsequently assembled, the inner cylin-
drical concrete form will be wrapped with the composite
sheet, which can then be held in place by reinforcing
wires encircling the sheet on the inner form. Addi-
10 tional reinforcing wires or rods may be placed next to
the sheet lining before the outer form is assembled
around it. The concrete mix is poured in the form
around the lining. When the concrete is properly distri-
buted, it fills the spaces between the ribs 16 so as to
15 lock the outer layer 15 of the liner firmly in place
inside of the concrete shell. When the concrete has
set and the forms are removed, the conduit section can
be joined to the next previous section.
If the shape is such that the lining cannot be
20 held in place on the inner forms by wrapping with wires,
it can be held to wooden forms by finishing nails, which
can then be pulled through the elastomeric lining when
the forms are removed, with the nail holes essentially
closed by the elasticity of the material.
Whatever the shape or manufacturing procedure
for the conduit, it will be made by placing the lining
against the inner form and casting concrete around it
to interlock with the keying ribs to form an integrally
lined conduit or section of conduit.
Such a conduit may be cast in situ as an inte-
gral continuous structure, or can be made from prefabri-
cated sections with the linings of each section firmly
abutted against linings of the adjacent sections so that
there will be essentially no part of the surface exposed
35 to the water except that which is made from toxicant-
containing material.
