Note: Descriptions are shown in the official language in which they were submitted.
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DESCRIPTION
Method of Grouting Internal Cable of Post-Tensioned
Prestressed-Concrete Structure
Technical Field of the Invention:
The present invention relates to a method of
grouting an internal cable of a post-tensioned
prestressed-concrete structure. More particularly, the
present invention relates to a grouting method capable of
surely and easily providing an internal cable completely
filled with grout without an air trap remaining in the
internal cable.
Background Art:
In prestressed-concrete structures, e.g. bridges and
overpasses, tendon corrosion and breaking accidents have
occurred occasionally in recent years owing to the failure
to satisfactorily fill grout into the internal cables of
such prestressed-concrete structures.
The internal cable is buried in concrete in its
entirety. Therefore, it has been difficult to inspect and
confirm the filling (injected) condition of grout in the
sheath of the internal cable and the condition of the
cable after the grouting operation.
In the present state of the art, the grout filling
condition is checked by a non-destructive inspection
method, e.g. X-ray inspection, ultrasonic inspection, or
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impact reflection wave inspection. However, it is
difficult to completely grasp the condition of the grout
in the sheath.
Under these circumstances, a grout material
exhibiting favorable flowability and causing minimal
bleeding has been developed. However, in the actual
grouting operation, the grout material is pumped into the
sheath. Therefore, air is entrapped into the grout
material during the pumping operation as well as a
material mixing operation performed when the grout
material is prepared. The air is likely to collect in the
sheath in the vicinity of an elevated portion at a bend in
the internal cable or in the vicinity of an end of the
internal cable, thus forming an air trap (void)
unfavorably.
The grout material is injected to fill the space
between the sheath inner wall and the prestressing steel.
The grout material is a mixture of cement, water, and an
admixture. It is demanded that the grout material should
have the property of exhibiting excellent flowability and
causing no segregation. However, cement and water are
likely to separate in the sheath due to a difference in
specific gravity before the grout material hardens. That
is, the cement content settles downward, and the water
content remains at the upper side (in the form of bleeding
water). When the water evaporates, a void (air trap) may
be formed and remain. External water entering the void
over a long period of time will corrode the prestressing
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steel. This may result in breaking of the prestressing
steel.
Further, prestressing steel stranded wire is used as
the cable material in most applications. Therefore,
sieving action or capillary action is likely to occur
between a plurality of strands constituting the stranded
wire, causing water and cement to separate from each other.
Fig. 4 is an explanatory view illustrating the
injection of grout into an internal cable. Fig. 5 is an
explanatory view illustrating the formation of an air trap
during the injection of grout into the internal cable. As
shown in these figures, no void (air trap) V is formed in
a case (A) where a grout material G flows through a sheath
3' in such a manner as to travel upward from the lower
side. However, in a case (B) where the grout material G
flows through a downwardly bent portion of the sheath 3'
where the grout material G travels downward from the upper
side, in particular, the leading end of the flow of the
grout material G travels along the lower inner wall of the
sheath 3' while leaving a void V in the upper part of the
bore of the sheath 3' [see (a) of Fig. 5]. In a part of
the sheath 3' where the downwardly bent portion of the
cable reaches its lower extremity, the grout material G
fills the sheath 3' over the entire area of the bore of
the sheath 3' [see (b) of Fig. 5]. Thereafter, the grout
material G travels backward to rise in the sloped portion
of the sheath 3' [see (c) of Fig. 5].
The void V in the leading end of the flow of the
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grout material G decreases gradually while the grout
material G is traveling backward because the trapped air
is discharged through discharge pipes 8a and 8b (see
Fig. 4), which are generally provided in the vicinity of
the top of the upwardly bent portion of the sheath 3'.
Whether the air trap V disappears or remains depends on
the installation position of the discharge pipes 8a and 8b
and the number, bore diameter, height, etc. of the pipes
8a and 8b.
Disclosure of Invention:
Accordingly, the present invention provides a
grouting method capable of surely and easily providing an
internal cable of a post-tensioned prestressed-concrete
structure that is completely filled with grout without an
air trap remaining in the internal cable.
That is, the present invention provides a method of
grouting an internal cable of a post-tensioned
prestressed-concrete structure as follows:
(1) A method of grouting an internal cable of a
post-tensioned prestressed-concrete structure, which is
characterized by fabricating a cable for testing at a
place other than a construction site of the post-tensioned
prestressed-concrete structure. The cable for testing has
a sheath made of a transparent material and has the same
three-dimensional configuration as that of the internal
cable at the construction site except that the cable for
testing does not have a cast concrete part. Prior to
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carrying out an operation of grouting the internal cable
of the post-tensioned prestressed-concrete structure at
the construction site, grouting testing is performed by
injecting grout into the cable for testing under a
plurality of different testing conditions. The best
grouting conditions are selected from grouting testing
results obtained by visual observation through the
transparent sheath. The selected best grouting conditions
are applied to grouting actually carried out at the
construction site.
(2) A method of grouting an internal cable of a
post-tensioned prestressed-concrete structure, which is
characterized by fabricating a cable for testing as a
partial specimen at a place other than a construction site
of the post-tensioned prestressed-concrete structure. The
cable for testing has a sheath made of a transparent
material and has the same three-dimensional configuration
as that of a lengthwise part of the internal cable at the
construction site in which an air trap is likely to occur,
except that the cable for testing does not have a cast
concrete part. Prior to carrying out an operation of
grouting the internal cable of the post-tensioned
prestressed-concrete structure at the construction site,
grouting testing is performed by injecting grout into the
cable for testing under a plurality of different testing
conditions. The best grouting conditions are selected from
grouting testing results obtained by visual observation
through the transparent sheath. The selected best grouting
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conditions are applied to grouting actually carried out at
the construction site.
(3) A method of grouting an internal cable of a
post-tensioned prestressed-concrete structure as stated in
the above paragraph (1) or (2), which is characterized in
that the three-dimensional configuration of the cable for
testing having a sheath made of a transparent material is
formed by using supports.
(4) A method of grouting an internal cable of a
post-tensioned prestressed-concrete structure as stated in
any of the above paragraphs (1) to (3), which is
characterized in that the cable for testing having a
three-dimensional configuration has a transparent sheath
provided only in the vicinity of a bent portion or/and in
the vicinity of an elevated portion of the cable.
(5) A method of grouting an internal cable of a
post-tensioned prestressed-concrete structure as stated in
any of the above paragraphs (1) to (4), which is
characterized in that the sheath made of a transparent
material, which is used in grouting testing performed at a
place other than the construction site, makes it possible
to surely and easily perform, by visual observation,
inspection of the grout filling condition during grouting,
testing to find a portion in the sheath where an air trap
is formed, selection of optimal conditions for regrouting
an air-trap portion, and selection of positions where a
grout discharge pipe and an air exhaust pipe are to be
installed, and the number and bore diameter of such pipes.
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(6) A method of grouting an internal cable of a
post-tensioned prestressed-concrete structure as stated in
any of the above paragraphs (1) to (5), which is
characterized in that the testing conditions of the
grouting testing are at least one selected from the
following (1) to (6): (1) the composition of the grout,
e.g. the mix proportions of components of the grout, or
the water-cement ratio of the grout; (2) the physical
properties of the grout, e.g. the viscosity-temperature
characteristics and bleeding characteristics of the grout;
(3) grouting means, e.g. grouting pressure, grouting speed,
and grouting quantity; (4) regrouting means, e.g. the
pressure, rate and quantity of grout reinjected through an
injection pipe into a portion in the sheath where an air
trap is formed, and the position, number and bore diameter
of regrouting pipes; (5) grout discharge and air exhaust
means, e.g. the installation position, number and bore
diameter of grout discharge and air exhaust pipes; and (6)
a step of the construction procedure, i.e. a step at which,
prior to grouting, water is previously injected into the
sheath, and as the grout is injected, the injected water
is discharged from the sheath, thereby making the flow of
the grout in the sheath even more uniform by utilizing a
small difference in specific gravity between the grout and
water, or a step of lowering the temperature of concrete
and the temperature in the sheath when these temperatures
are high.
(7) A method of grouting an internal cable of a
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post-tensioned prestressed-concrete structure as stated in
any of the above paragraphs (1) to (6), which is
characterized in that.the transparent sheath is made of a
polyethylene resin.
(8) A method of grouting an internal cable of a
post-tensioned prestressed-concrete structure as stated in
any of the above paragraphs (1) to (7), which is
characterized in that the transparent sheath is made of an
ionomer resin.
Brief Description of the Drawings:
Fig. 1 is a schematic view of grouting testing
equipment.
Fig. 2 is an explanatory view illustrating the
injection of grout into a cable for preliminary testing.
Fig. 3 is an explanatory view illustrating another
example of the grouting testing.
Fig. 4 is an explanatory view illustrating grouting.
Fig. 5 is an explanatory view illustrating the
formation of an air trap during the injection of grout
into an internal cable.
Explanation of Reference Signs:
1: testing equipment for grouting cable for preliminary
testing
2: cable, 2': internal cable
3: transparent sheath, 3': sheath
4: end anchoring device (anchorage)
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5: supports (pipe supports for scaffolding)
6: grouting pipe
7: regrouting pipe
7v: open-close valve for regrouting pipe
8 (8a, 8b, 8c): discharge pipe (exhaust pipe)
8av, 8bv: open-close valves for exhaust pipes
9: exhaust pipe
G: grout
V: air trap
Best Mode for Carrying Out the Invention:
An embodiment of the present invention will be
described below with reference to the accompanying
drawings.
In the present invention, prior to grouting an
internal cable of a post-tensioned prestressed-concrete
structure at a construction site, testing equipment 1 for
grouting a cable for preliminary testing is assembled, as
shown in Fig. 1, at a place near the construction site or
at a place other than the construction site, e.g. in a
factory, by using supports (pipe supports for scaffolding)
5. The testing equipment 1 has a cable 2 fabricated with
the same (or approximately the same) three-dimensional
configuration (i.e. cubic configuration) at that of the
internal cable at the construction site. The cable 2 has a
transparent sheath 3 that allows the grout filling
condition therein to be checked by visual observation from
the outside of the sheath 3.
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The cable 2 of the testing equipment 1 has the same
three-dimensional configuration as that of the internal
cable at the construction site except that it does not
have a concrete part that would otherwise be cast at the
construction site. The cable 2 extends over a distance
equal to the full length of the internal cable at the
construction site. Testing is performed by injecting grout
(G) into the transparent sheath 3 of the cable 2 from a
grouting pipe 6.
The testing is performed under a plurality of
different testing conditions. During the testing, the
filling condition of grout (G) in the cable 2 is visually
observed through the transparent sheath 3, and observation
data is recorded.
Fig. 2 is an explanatory view illustrating the
injection of grout into a cable for preliminary testing.
Fig. 2 shows that when grout G is injected into a cable 2
in grouting testing, an air trap V is formed in an
elevated portion of the cable 2. A regrouting pipe 7 and
discharge (exhaust) pipes 8a and 8b are provided to stand
in the vicinity of the elevated portion of the cable 2. A
grouting pipe 6 and an exhaust pipe 9 are installed at an
anchorage provided at the left end of the cable 2. A
discharge pipe 8c is installed at another anchorage
provided at the right end of the cable 2. It should be
noted that open-close valves 7v, 8av and 8bv are attached
to the respective upper ends of the pipes 7, 8a and 8b.
First, grout G is injected into the transparent
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sheath 3 of the cable 2 from the grouting pipe 6 by using
a pump (not shown) at a specific pressure, delivery speed
and delivery time, for example, to determine and record
respective numerical values of the pressure, delivery
speed and delivery time at which all the trapped air is
discharged through the discharge pipes 8a and 8c and hence
the void V disappears.
Grouting testing is performed a plurality of times
under different testing conditions, i.e. with regard to
different kinds, temperatures, etc. of the grout G,
thereby selecting and recording an optimal grout, an
optimal grout temperature, etc.
From the grouting testing results thus obtained, the
best grouting conditions are selected, and all or
essential ones of the selected best grouting conditions
are applied to grouting actually carried out at the
construction site.
In general, factors in the formation of an air trap
V during grouting the internal cable are as follows: (1)
the kind of grout material; (2) equipment used for
grouting; (3) the configuration of the cable; (4) the
installation position and number of grouting and discharge
pipes and the open-close timing of the pipes; (5) whether
or not regrouting is carried out; (6) the relationship
between the configuration of the anchorage and the
installation position of the grouting and discharge pipes;
(7) temperature conditions at the construction site; and
(8) whether or not water is injected into the sheath prior
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to grouting.
For example, detailed factors in the air-trap
formation in terms of the kind of grout material as stated
in the above (1) are the flowability, viscosity and non-
segregating property of the grout material. Further, the
air-trap formation is dependent on the water-cement ratio
of the grout material, the cement particle size, the
properties of the admixture, and the temperature of mixed
grout that is determined by the atmospheric temperature
and the temperature of the constituent materials.
Next, the equipment (not shown) used for grouting as
stated in the above (2) may cause formation of an air trap.
The air-trap formation is dependent on the blade structure
and rotational speed of a mixer and the deliver pressure
and discharge quantity of the pump.
Air-trap formation factors in terms of the
configuration of the cable 2 as stated in the above (3)
include the outer diameter, bore diameter and length of
the sheath, irregularities on the outer peripheral surface
of the sheath, and the three-dimensionally curved
configuration of the cable throughout the full length
thereof.
The installation position and number of grouting and
discharge pipes as stated in the above (4) are dependent
on the installation position and number of regrouting
pipes 7 for secondary injection and the installation
position and number of discharge pipes therefor. In
addition, the air-trap formation is dependent on the bore
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diameter and length (height) of the grouting and discharge
pipes and the discharge pipe open-close timing during
grouting and immediately after the completion of grouting.
In addition, the air-trap formation is dependent on
whether or not regrouting is carried out as stated in the
above (5), and the relationship between the configuration
of the anchorage and the installation position of the
grouting and discharge pipes as stated in the above (6).
Further, the temperature conditions at the construction
site, i.e. the atmospheric temperature and the concrete
temperature, as stated in the above (7), affect
significantly the flowability of the grout and are
considered to be a factor in the air-trap formation.
Therefore, by taking into consideration the factors
in the formation of an air trap V during grouting the
cable 2, testing equipment 1 is assembled at a place other
than the construction site by using supports (pipe
supports for scaffolding) 5, as shown in Fig. 1, to grout
a cable for testing having the same (or approximately the
same) three-dimensional configuration (i.e. cubic
configuration) as that of the internal cable at the
construction site.
Thus, a cable 2 is fabricated that has the same
three-dimensional configuration as that of the internal
cable at the construction site except that it does not
have a cast concrete part and~the sheath is not black but
transparent. The cable 2 may simulate either the full
length or a part of the internal cable at the construction
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site. It is also possible to use as a specimen a
lengthwise part of the cable 2 where an air trap is likely
to occur. Then, grouting testing is performed by injecting
grout G into the sheath 3 made of a transparent material.
In consideration of the above-described factors in
the formation of an air trap during grouting, testing is
performed under a plurality of different testing
conditions. During each testing process, the filling
condition of the grout in the cable 2 is visually observed
through the transparent sheath 3, and observation data is
recorded.
By virtue of the use of a sheath made of a
transparent material in grouting testing performed at a
place other than the construction site, it is possible to
surely and easily perform, by visual observation,
inspection of the grout filling condition during grouting,
testing to find a portion in the sheath where an air trap
is formed, selection of optimal conditions for regrouting
an air-trap portion, and selection of positions where a
grout discharge pipe and an air exhaust pipe are to be
installed, and the number and bore diameter of such pipes.
Thus, the best grouting conditions can be selected.
It should be noted that if an air trap V is formed
in the transparent sheath 3, an analysis and improvement
are made on the basis of the above-described air-trap
formation factors. Then, testing is performed again, and
observation data is recorded.
The best grouting conditions are selected from the
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data obtained by the above-described testing, and the
selected best grouting conditions are applied to grouting
actually carried out at the construction site.
Testing items (conditions) of the grouting testing
are as follows: O1 the composition of the grout, e.g. the
mix proportions of components of the grout, or the water-
cement ratio of the grout; 2U the physical properties of
the grout, e.g. the viscosity-temperature characteristics
and bleeding characteristics of the grout; ~ grouting
means, e.g. grouting pressure, grouting speed, and
grouting quantity; ~ regrouting means, e.g. the pressure,
rate and quantity of grout reinjected through an injection
pipe into a portion in the sheath where an air trap is
formed, and the position, number and bore diameter of
regrouting pipes; ~5 grout discharge and air exhaust means,
e.g. the installation position, number and bore diameter
of grout discharge and air exhaust pipes; and ~ a step of
the construction procedure, i.e. a step at which, prior to
grouting, water is previously injected into the sheath,
and as the grout is injected, the injected water is
discharged from the sheath, thereby.making the flow of the
grout in the sheath even more uniform by utilizing a small
difference in specific gravity between the grout and water,
or a step of lowering the temperature of concrete and the
temperature in the sheath when these temperatures are high.
At least one selected from the above ~1 to ~. preferably
all of 01 to ~. are used as testing items.
Fig. 3 is an explanatory view illustrating another
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example of the grouting testing, in which a partial
specimen is used as a cable for preliminary testing.
Fig. 3(a) is a schematic view showing the full length of a
cable for preliminary testing that has the same (or
approximately the same) three-dimensional configuration
(i.e. cubic configuration) as that of the internal cable
at the construction site. Fig. 3(a) also shows a
lengthwise part of the cable (surrounded by the dot-dash
line in the figure) where an air trap is likely to occur.
Fig. 3(b) is an enlarged detailed view illustrating a
partial specimen of cable that comprises the lengthwise
part where an air trap is likely to occur, which is
surrounded by the dot-dash line in Fig. 3(a).
In this example, as shown in Fig. 3(b), a partial
specimen is fabricated and laid, which has the same three-
dimensional structure (i.e. cubic structure) as that of a
lengthwise part of the internal cable at the construction
site in which an air trap is likely to occur. Then, grout
(G) is injected into the transparent sheath 3 of the cable
2 from the grouting pipe 6 under various conditions, and
while visually checking the occurrence of an air trap,
grout is reinjected from the regrouting pipe 7 under
various conditions by opening and closing the open-close
valve 7v at varied timing. Further, air or/and a part of
the injected grout are discharged through the grout and
air discharge pipes 8a and 8b by opening and closing the
open-close valves 8av and 8bv at varied timing. In this
way, the grouting testing is performed under various
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conditions. It should be noted that reference numerals 8c
and 9 in the figure denote exhaust pipes provided at both
ends of the cable 2.
The results of the testing performed as stated above
are recorded, and optimal conditions are selected from the
testing results. The selected conditions are applied to
the process of grouting the internal cable at the
construction site.
This example is applied in a case where a place for
testing as large as the construction site is unavailable.
That is, a specimen comprising only an essential part of
cable where an air trap is likely to occur is fabricated
to perform testing. This example allows testing to be
performed at reduced costs and in a reduced space and
still permits the testing results to be applied favorably
to the construction site.
It should be noted that the cable 2, which comprises
either the full length of the three-dimensionally
configured structure for testing or a lengthwise part
thereof where an air trap is likely to occur, may have a
transparent sheath provided only in the vicinity of a bent
portion and in the vicinity of an elevated portion of the
cable. In this case, the other portion of the cable 2 may
be made of a black polyethylene or the like that is used
at the construction site.
The grout material injected into the three-
dimensionally configured structure for testing is
preferably the same as that used at the construction site.
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It is also possible to inject a colored grout material
prepared by mixing a grout with a small amount of an
inorganic coloring material, e.g. chromium oxide, iron
oxide, copper oxide, or manganese oxide, or an organic
coloring material. The use of a colored grout material
allows the filling condition of the grout in the
transparent sheath to be grasped even more clearly. It is
preferable to adjust the degree of pigmentation so that
the color of the grout material is not very deep but
sufficiently light to allow an air trap to be readily
found.
Examples of materials for the transparent sheath are
a polyethylene resin, a vinyl chloride resin, a
polypropylene resin, a polycarbonate resin, and a Teflon
resin. It is particularly preferable to use a material
consisting essentially of a polyethylene-based ionomer
resin, in which the ionomer resin is an a-olefin-a, ~-
unsaturated carboxylic acid copolymer having carboxyl
groups neutralized with metal ions.
It is also preferable to use a material consisting
essentially of an ionomer resin that is a binary copolymer
of a-olefin and a, a-unsaturated carboxylic acid, in which
the copolymer contains from 5 to 20~ by weight of a, a-
unsaturated carboxylic acid, and the degree of
neutralization achieved by the metal ions is from 10 to 90
mol ~ with respect to the acid group.
Further, it is preferable that the transparent
sheath should be formed from either one material selected
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from those stated above or a composite material consisting
essentially of two or more materials selected from those
stated above, and the configuration of the sheath should
be the same as that of the sheath actually used at the
construction site.
It should be noted that the term "transparent" in
the term "transparent sheath" as used in the present
invention means, for example, that the filling condition
of a grout material being filled into the sheath can be
visually observed from the outside of the sheath. It is
possible to use a sheath having any property as long as it
performs the above-described function. The term
"transparent sheath" may mean a sheath having light
transmission properties, for example. Light in this case
may mean visible light. The term "sheath" means a hollow,
typically tubular, member that can pass prestressing steel
in the hollow portion thereof. The sheath performs the
function of sheathing the prestressing steel extending
through the hollow portion.
Industrial Applicability:
With the conventional method, whether or not the
sheath is satisfactorily filled with grout without an air
trap remaining therein cannot be checked even if
influential factors are examined from various angles and
the best efforts are made because at the construction site
the internal cable is laid in concrete and hence the
sheath is hidden by the concrete. Therefore, it cannot be
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known whether the internal cable has completely been
filled with grout or the resulting internal cable has the
danger of corrosion or breaking because of insufficient
filling of grout. Thus, anxiety and danger are involved in
the conventional method.
According to the present invention, however,
grouting testing is performed by using a cable for
preliminary testing that is installed at a place other
than the construction site by using a transparent sheath.
The cable for preliminary testing may have the same
configuration as that of the internal cable at the
construction site throughout the full length thereof.
Alternatively, the cable for preliminary testing may be a
partial specimen having the same configuration as that of
a lengthwise part of the actual internal cable where an
air trap is likely to occur. By virtue of the grouting
testing, it is possible to check, before the actual
grouting process, not only the filling condition of grout
being filled into the sheath but also the grout filling
condition after the completion of the filling and also
after the grout has hardened, and optimal grouting
conditions can be selected. Therefore, during grouting
performed at the construction site thereafter, no air trap
is formed in the sheath, and an excellent post-tensioned
prestressed-concrete structure can be provided.
