Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Patent application of
Gerard Drouin for
Waterstop having improved water and moisture sealing features
BACKGROUND OF THE INVENTION
Field of the invention
This invention relates generally to concrete structures but more particularly
to a water
sealing element for concrete joints.
Background
Preventing the passage of water through concrete joints is essential for
liquid-
containing or liquid-excluding structures such as foundation walls, tunnels,
swimming
pools, reservoirs, water and sewage treatment plants, retaining walls,
culverts, bridge
abutments, cisterns, dams and other such structures.
Building these structures, however, often requires separate concrete pours,
that is one
pour for the first horizontal element of the structure followed a second pour
for the
vertical element of the structure and sometimes additional pours are needed
just for
continuing an extremely long horizontal surface. Waiting for one element of
the
structure to dry before starting the second pour results in an imperfect
mating of the
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two adjoining elements of the structure since there is no adherence between
dry and
wet concrete. This imperfect mating plus the normal concrete shrinkage that
occurs as
concrete dries can create a passage for water.
To prevent this problem, a number of solutions have been developed. The most
popular is the use of PVC strips known in the industry as PVC waterstops.
These are
long strips inserted vertically and halfway into fresh concrete and when the
second
pour is done, the PVC waterstop is totally immersed into concrete and will act
as a
dam for water that would normally follow the passage between the two pours.
PVC waterstops currently in use are far from perfect and one of the
inconveniences of
using them is that since polyvinyl chloride has zero adhesion with concrete,
the
smallest shrinkage of concrete, which is normal during the curing process.
Even for
walls 150mm thick, it can take 850 days for moisture to drop to below 50% at
the
center, as is described in an information brochure published by Portland
cement. As
moisture level drops, shrinkage occurs which creates a gap between the
concrete and
the PVC waterstop since PVC doesn't adhere to concrete. This is when a passage
for
water is formed.
More and more contractors and consultants refuse to use or recommend the use
PVC
waterstops and do not want to be responsible for any leaks that should occur
if PVC
waterstops are used.
A newer method to seal concrete joints involvesd the use of a hydro expansive
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compound, the most popular being EPDM (Ethylene Propylene Diene Monomer)
combined with an hydro expansive resin, but other such compounds can offer
similar
properties. The hydro expansive compound is cut into long strips that are
slightly
narrower than the width the second pour will be and is laid flat on top of the
first pour,
after it has dried and just before the second pour. After both pours have
cured and
shrinkage has created a passage for water, the hydro expansive compound
inflates as
it gets in contact with water. By inflating, it is able to block the passage
of water.
The use of the hydro expansive compound in this fashion is not without flaws
however.
The curing process of concrete is quite complex and must be understood in
order to
realize why this approach is flawed
Due to segregation and bleeding, the uppermost layer of cured concrete is more
fragile
and brittle, this layer is about 0-5mm in thickness and is characterized by a
white
powder on the surface. It is necessary to remove this fine layer by using
various
abrading means such as sandblasting or high pressure water. This has to be
done
before laying the hydro expansive compound. This can fix half of the problem
but this
bleeding and segregation can also occur at the bottom of the second pour for
which
there is no way it can be fixed. Moreover, another factor to consider in
making
separate pours is that if the first pour is unusually dry, it will absorb
moisture from the
second pour and upset the water to concrete ratio and if the first pour is too
humid,
again it can upset the ratio of the second pour. This also affects a layer
about 0-5mm
in thickness at the junction between the two pours where the concrete can be
more
fragile. Also, in the case of a vertical structure, such as a wall, the higher
the wall is,
the harder it is to get a good compacting of the concrete by way of a
vibrator.
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This zone of higher risk of porosity is situated at between 0 - 20 mm in
height starting
from the joint between the two pours.
Since the hydro expansive compound lays flat, it cannot handle the problem of
difficult
compacting in the 0 - 20 mm zone and although the hydro expansive compound can
stop water at the joint, another passage for water can be created just above
it,
rendering the hydro expansive compound less efficient.
Because both the PVC waterstops and the hydro expansive compound are
deficient,
there is a need for a better waterstop.
SUMMARY OF THE INVENTION
It is a first object of this invention to provide for an efficient waterstop
which can
maintain its waterstopping characteristics even after the concrete has shrunk
and
separated from it and has created a preferential passage for water.
It is a second object of this invention to provide for an efficient waterstop
which can
provide waterstopping capabilities beyond the zone of higher risk of porosity
which is
situated at 20 mm and below.
In order to do so, the present invention consists of an improved waterstop
configured
and sized much like existing PVC waterstops but with the important added
feature of
an hydro expansive compound. Current technology allows for up to 600%
expansion in
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volume for hydro expansive compound when subjected to water. By expanding, the
hydro expansive compound effectively blocks the passage of water that leaks
into the
gaps created during the shrinkage of the concrete surrounding the improved
waterstop.
All that is required are two narrow strips of judiciously positioned hydro
expansive
compound at opposite ends of the improved waterstop.
The foregoing and other objects, features, and advantages of this invention
will
become more readily apparent from the following detailed description of a
preferred
embodiment with reference to the accompanying drawings, wherein the preferred
embodiment of the invention is shown and described, by way of examples. As
will be
realized, the invention is capable of other and different embodiments, and its
several
details are capable of modifications in various obvious respects, all without
departing
from the invention. Accordingly, the drawings and description are to be
regarded as
illustrative in nature, and not as restrictive.
BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 Side elevation of a waterstop from the prior art in context.
FIG. 2 Side elevation of various models of prior art waterstops.
FIG. 3 Side elevation of improved waterstop in context.
FIG. 4a Side elevation of an improved waterstop with the expansion strip dry.
FIG. 4b Side elevation of an improved waterstop with the expansion strip wet.
FIG. 5 Side elevation of waterstop from the prior and how it can cause a
fissure.
FIG. 6 Side elevation of fictional waterstop and how a bad position of the
hydro
expansive compound could cause a fissure.
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FIG. 7 An improved waterstop with its joining element.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
More specifically in FIG. 1, a waterstop of the prior art (10) is a vertical
strip rather thin,
ribbon like, and is inserted so that it overlaps both the first pour (12) and
the second
pour (14). The waterstop of the prior art (10) suffers from the fact that PVC
doesn't
adhere to concrete (50) and that over time, such as with twenty years of
aging, there
is a loss in plasticizer as well as a migration and segregation of internal
components
and shrinkage of both thePVC waterstop and the concrete (50). This shrinkage
creates
an empty space (16) which results in water (18) infiltrating alongside the
waterstop of
the prior art (10) which renders it useless.
More specifically in FIG. 2, there are many variations in the design of
waterstops of the
prior art (10). They are all thin compared to their height and have small
ridges (20)
protruding from both sides along the height of the waterstop (10), also, all
have a round
hollow core (22) halfway across the height of the waterstop (10).
More specifically in FIG. 3, an improved waterstop (24),appearing at first
glance to be
shaped like the waterstop of the prior art (10), that is ribbon like, will not
allow water to
infiltrate because of an expansion strip (28) which fills the empty space
(16). This
expansion strip (28) can be positioned by two different methods, either it is
bonded to
the improved waterstop (24) by use of an adhesive or it is bonded by the
process of
co-extrusion where the hydro expansive compound of the expansion strip (28) is
conjoined with the rest of the improved waterstop (24) while both are still in
a soft state.
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Although the expansion strips (28) appear as rectangles in the accompanying
drawings, they can be shaped differently such as with rounded or beveled
edges..
More specifically in FIG. 4a, the improved waterstop (24) has ribs (30)
extending
perpendicularly from both of its sides and has an oval core (26) situated
halfway along
its heigth. In this figure, the expansion strip (28) is dry. When first
installed, it is
important that the improved waterstop (24) be inserted in the fresh concrete
(50)
halfway between two pairs of little horns (32) situated proximal and on each
side of the
oval core (26). Improper positioning of the improved waterstop (24) can void
warranty.
Also, care must be taken with the kind of concrete (50) used, it should be 25
MPA in
density and use a 24.5 mm diameter head on a vibrator operating at 200 Hz and
positioned vertically no closer than 15cm from the improved waterstop (24),
otherwise,
an improper vibrator can cause a resonance again the improved waterstop (24)
which
could result in porosity around the improved waterstop (24). When properly
done, air
bubbles are removed from the concrete (50) and a proper curing can occur.
More specifically in FIG. 4b, the same improved waterstop (24) but with its
expansion
strip (28) wet. The volume of the expansion strip (28) increases so that it
can block any
gaps between the improved waterstop (24) and the concrete pours (12, 14, of
fig. 2).
Seasonal variations can also affect concrete (50). It is well known that cold
temperatures can shrink many materials, including concrete (50) and PVC.
Counterintuitively, water flow is generally stopped in cold temperature even
with
waterstop of the prior art (10) since, as is the case with the improved
waterstop (24),
the traction of concrete (50) along the height of the improved waterstop (24)
stretches
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it somewhat. The ribs (30) act as anchors and actually stretch the improved
waterstop
(24) so that the ribs (30), or the small ridges (20) as for the waterstop of
the prior art
(10), actually make contact with the concrete (50) and can stop or slow down
the
infiltration of water. The stretching of the improved waterstop (24) is aided
by the oval
core (26) which flattens as it stretches. The oval shape which is longer in
the direction
of stretching favors stretching in that direction, more so than the round
hollow cores
(22) of waterstops of the prior art (10).
During warm periods, the concrete (50) and improved waterstop (24) expand and
release tension and water can circulate until the expansion strip (28) stops
it. Because
the exansion strip (28) absorbs water slowly and therefore expands slowly, it
doesn't
have much time for expansion during the curing process. However, once the
concrete
(50) has dried, cured and has begun to shrink and water starts leaking, it may
allow
minute amounts of water to pass as it begins to expand but after some time,
water will
be stopped completely. Also, the expansion strip (28) will also retain their
expansion
for a long time as the moisture inside concrete (50) will remain for a long
time. The
expansion strip (28) will practically never have time to fully shrink but will
rather stay
relatively expanded so that when there is a second passage of water, it will
be more
quickly blocked. Typically the hydro expansive compound will take 24 hours to
expand
110 - 350% in volume, 72 hours for 230 - 550% and after 28 days, 600%.
Therefore,
all depending upon the void that needs to be filled, and the flow rate, it
will take more
or less time to block the passage of water.
More specifically in FIG. 5, each extemity of the improved waterstop (24) is
terminated
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by a circular bulb (34) as seen more clearly in FIGS. 4Ab, 6 and 7, the
roundness, as
opposed to a square edged end as found in the waterstops of the prior art (10)
reduces
the incidence of the creation of a fissure (36) at this location, this fissure
is caused
when a force is exerted on a wall before it had time to cure, i.e. 7 days
after pouring
concrete has generally reached about 70% of its MPA and is therefore still
sensitive to
stress. Should pressure, tension or stress be applied to the concrete prior to
7 days,
the probability of having a fissure (36) at this location is much lower when
using of a
circular bulb (34)as opposed to asquare edged end as with a waterstop of the
prior art
(10).
More specifically in FIG. 6, another way of limiting the creation of a 2"d set
of fissures
(38) is by the judicious positioning of the expansion strip (28). Since a
pressure of less
than 60 Ibs / square inch can be created against the concrete (50) by the
expansion of
the expansion strip (28), this pressure can create a 2"d set of fissures (38)
if the
expansion strip (28) would be placed too close to the junction between the
first pour
(12) and the second pour (14), as is seen with a fictional waterstop (not
reallfy the
improved waterstop (24) ) having too short a distance to the joint. Therefore,
a minimal
distance is recommended which has to be above the 20 mm zone of higher risk of
porosity previously described in the background of the invention. Ideally it
should be
between 38mm and 59mm above and below the oval core (26). Also, the improved
waterstop (24) should have its expansion strip (28) no closer than 70mm from
the edge
of the wall it is expanding toward. The range in distance of the expansion
strip (28) is in
relation with the overall height of the improved waterstops (24) which varies
between
110mm and 178mm. The thickness of the improved waterstops (24) is also
proportional, varying between 4mm and 6mm and finally, the thickness of the
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expansion strip (28) also varies between 2mm to 6 mm when dry. The larger size
improved waterstops (24) is for use where water pressure is higher. The
variety in
choices allows for the use of the proper improved waterstop (24) for a
particular need.
More specifically in FIG. 7, to counteract the less than 60 pound / sq in.
pressure, the
opposite side (40) of the expandable strip (28) is convex to distribute the
load over a
larger area, it also acts as additional support to eliminate the risk of
deformation of the
improved waterstop (24) and, finaly, also serves as additional anchoring
means, like
the ribs (30) descibed above.
When a length of improved waterstop (24) comes to an end, a second strip of
improved waterstop (24) begins and a joining element (42) is mated to the two
ends of
the improved waterstop (24) by using a fast drying adhesive. The joining
element (42)
is configured and sized to complement the shape of the improved waterstops
(24) in
order to insure proper bonding. The fact that the joining element (42)
overlaps the
junction point between the two lengths of improved waterstops (24) provides an
excellent protection against the passage of water even if there is a gap at
the junction.
The junction point of waterstops of the prior art (10) is simply done by heat
welding the
two ends of the waterstops (10) and does not benefit from the added sealing
capabilities of an overlapping joining element (42).
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