Note: Descriptions are shown in the official language in which they were submitted.
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TITLE
"A STRUCTURAL ELEMENT"
FIELD OF THE INVENTION
This invention relates to a structural element. In particular, the
invention relates to a structural element constructed of polymer concrete.
BACKGROUND OF THE INVENTION
Developments in civil engineering and the building industry
have created a continual demand for building materials with new and
improved performance attributes. Polymer concretes offer possibilities for
meeting these new requirements.
Polymer concrete consists of aggregates bonded together by a
resin binder instead of a cement binder that is used in standard cement
concrete. Polymer concrete has generally good durability and chemical
resistance and is therefore used in various applications such as in pipes,
tunnel supports, bridge decks and electrolytic containers. Additional
advantages of polymer concrete includes very low permeability and very fast
curing times. The compressive and tensile strength of polymer concrete is
generally significantly higher than that of standard concrete.
As a result, polymer concrete structures are generally smaller
and significantly lighter than equivalent structures made out of standard
concrete. However, due to the relatively low Modulus of Elasticity of polymer
concrete, compared to standard concrete, polymer concrete structures have
a tendency to deflect significantly more than equivalent standard concrete
structures.
As with standard concrete, polymer concrete structures
generally require reinforcement to carry the tensile loads. Even though
reinforcement is effective in carrying tensile forces, in many situations it
cannot prevent cracks from occurring in the tensile zone of a polymer
concrete member. Traditional steel reinforcement bars can be used in a
polymer concrete structure but as polymer concrete is often used in corrosive
environments, these cracks can lead to corrosion of steel reinforcement.
Composite reinforcement has also been used in polymer
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concrete to address the corrosion problem of steel reinforcement. The
composite reinforcement used has the same shape as steel reinforcement
bars, i.e., ribbed or circular bars. However, cracks generally result in
serious
stress concentrations at the locations of the cracks which, due to the brittle
nature of composite reinforcement, can lead to premature failure of the
composite reinforcement. The latter is of particular concern in dynamic
loading environments.
In addition, cracks can seriously affect the aesthetics of the
polymer concrete members and lead to safety concerns in the general public.
In traditional concrete structures, prestressing of the reinforcement has been
used to assist in preventing cracking from occurring within the concrete
structure. Two different methods are widely used for this purpose namely
post-tensioning and pre-tensioning.
In post-tensioning the reinforcement is tensioned after the
concrete has hardened. The reinforcement is not bounded to the
surrounding concrete at the time of prestressing, but is placed in special
ducts that pass through the member. At one end, the reinforcement is
anchored to the hardened concrete using a localised anchor, and at the
other end it is jacked against the concrete until the required level of
prestress
is obtained and then locked off. Upon completion the ducts may or may not
be pressure grouted.
A member is pre-tensioned if the prestressing reinforcement is
tensioned before the concrete is cast. The reinforcement is tensioned
between two end abutments and then the concrete is cast. When the
concrete has attained sufficient strength, the prestressing force is released
from the abutments. As the reinforcement attempts to contract elastically,
the concrete is forced into compression. Slipping of the reinforcement inside
the concrete is prevented through ribs on the reinforcement or spiral twists
in
the prestressing cables which generally consist of many individual wires.
These wires are often crimped or indented in order to approve the bonding
characteristics.
Both of the above methods of tensioning work well. However,
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even though concrete cracks can be prevented by prestressing, concrete is
porous and water and chemicals may still reach the steel prestressing
reinforcement and cause corrosion, particularly in salt water environments.
In order to alleviate possible corrosion of the steel prestressing
reinforcement, composite reinforcement has also been used for the
prestressing of concrete structures. Both the post-tensioning and pre-
tensioning approach has been used with composite reinforcement.
However, due to the limited strength of fibre composite reinforcement
perpendicular to the fibre direction, longitudinal splitting and transverse
crushing at the anchors is common when using the post-tensioning method.
Worldwide, research is continuing to develop special anchors
for fibre composite post-tensioning reinforcement. In the pre-tensioning
process, it is difficult to obtain adequate anchorage/bonding between the
fibre composite reinforcement and standard concrete due to the difficulties
associated with providing the composite reinforcement with adequate ribbing
to prevent slippage.
Some examples of the attempts to use fibre composite for pre-
tensioning of standard concrete are described in US 2004/0130063 and JP
5239885. In US 2004/0130063 a method of pre-stressing utilises a variety of
anchors and rings are used to grip the concrete in order to achieve pre-
stressing. In JP 5239885 a foamable resin is used to create a composite
fibre reinforcement bar of an uneven shaped. Due to the uneven shape,
composite reinforcement bar is used to grip the concrete in order to achieve
pre-stressing. However, to date, there has been limited use of fibre
composite reinforcement for the pretensioning process.
OBJECT OF THE INVENTION
It is an object of the invention to overcome or alleviate one or
more of the above disadvantages or provide the consumer with a useful or
commercial choice.
It is a preferred object of this invention to produce structural
elements made from polymer concrete with significantly improved crack
resistance.
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It is a further preferred object of the invention to produce
polymer concrete structures with improved deflection behaviour.
It is a still further preferred object of the invention to produce
polymer concrete structures with improved recovery after overload.
It is a still further preferred object of the invention to produce
polymer concrete elements with improved strength in shear and torsion.
It is a still further preferred object of the invention to produce
polymer concrete elements with improved fatigue resistance.
It is a still further preferred object of the invention to allow
structural elements made of polymer concrete to be produced cost
effectively.
SUMMARY OF THE INVENTION
In one form, although not necessarily the only or broadest form,
the invention resides in a structural element comprising:
at least one pre-tensioned fibre reinforced plastic reinforcement
member, the pre-tensioned fibre reinforced plastic reinforcement member
having a constant cross-section through a length of the reinforcement; and
a polymer concrete member surrounding said pre-tensioned
fibre reinforced plastic reinforcement member;
wherein a force transfer between the fibre reinforced plastic
reinforcement member and the castable material is through polymer
adhesive bonding.
Preferably, a ratio of a perimeter length of the pre-tensioned
fibre reinforced plastic reinforcement member over the cross sectional area
of the pre-tensioned fibre reinforced plastic reinforcement member is
significantly larger than a ratio of a perimeter length over the cross
sectional
area of a circular bar having the same cross sectional area. This is to reduce
the magnitude of shear stresses in a contact area between the reinforcement
and the polymer concrete.
Preferably a ratio of a perimeter length of the pre-tensioned
fibre reinforced plastic reinforcement member over the cross sectional area
of the pre-tensioned fibre reinforced plastic reinforcement member is at least
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one-third larger than a ratio of a perimeter length over the cross sectional
area of a circular bar having the same cross sectional area.
More preferably, a ratio of a perimeter length of the pre-
tensioned fibre reinforced plastic reinforcement member over the cross
5 sectional area of the pre-tensioned fibre reinforced plastic reinforcement
member is at least one half larger than a ratio of a perimeter length over the
cross sectional area of a circular bar having the same cross sectional area.
Still more preferably, a ratio of a perimeter length of the pre-
tensioned fibre reinforced plastic reinforcement member over the cross
sectional area of the pre-tensioned fibre reinforced plastic reinforcement
member is at least double a ratio of a perimeter length over the cross
sectional area of a circular bar having the same cross sectional area.
Yet still more preferably, a ratio of a perimeter length of the pre-
tensioned fibre reinforced plastic reinforcement member over the cross
sectional area of the pre-tensioned fibre reinforced plastic reinforcement
member is at least quadruple a ratio of a perimeter length over the cross
sectional area of a circular bar having the same cross sectional area.
Preferably, a suitable perimeter/area ratio is achieved by using
fibre reinforced plastic reinforcement members with a thin walled cross
section. The fibre reinforced plastic reinforcement members may be solid or
hollow.
Preferably, the wall thickness of the pre tensioned fibre
reinforced plastic reinforcement member is between 1 and 5 mm.
The structural element may include at least one non pre-
tensioned fibre reinforced plastic reinforcement member.
The level of pretension in the fibre composite reinforcement
can vary from 0 up to almost 80 -100% of the ultimate tensile strength of the
reinforcement.
Preferably the level of pretension in the reinforcement is
between 20-50% of the ultimate tensile strength of the reinforcement
member.
The fibre reinforced plastic reinforcement members may be
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produced from any suitable glass, carbon or aramid fibre and/or plastic
material dependant upon the desired properties of the structural element.
Preferably, the surface area of the fibre reinforced plastic reinforcement
members that contact the castable material is abraded to increase adhesion
between the castable material and the fibre reinforced plastic reinforcement
members. Alternatively, the fibre reinforced plastic reinforcement members
may be coated with a sand and/or gravel interface to increase adhesion.
The pre-tensioned fibre reinforced plastic reinforcement
members may be pultruded fibre reinforced plastic. Preferably, the fibre
reinforced plastic reinforcement members have flat surfaces to simplify the
sanding or abrading process. The reinforcing members may be hollow to
save maximum weight.
In one embodiment, the pultruded, pre-tensioned fibre
reinforced plastic reinforcement members may be filled with standard
concrete, polymer concrete or a filled resin system and a metal or fibre
composite reinforcing bar to further increase their load carrying capacity and
stiffness.
In another embodiment the hollow, pultruded, pre-tensioned
fibre reinforced plastic reinforcement members may be filled with other
materials dependant upon the desired properties of the tubular reinforcing
element.
The hollow pultruded, pre-tensioned fibre reinforced plastic
reinforcement members may be filled before or after the pre-tensioning of the
members. Preferably the members are filled after the pre-tensioning of the
fibre reinforced plastic reinforcement members.
The fibre reinforced plastic members may extend longitudinally
and transversely through the structural element. One or more of the
longitudinal and/or transverse fibre reinforced plastic members may be pre-
tensioned.
The transverse fibre reinforced plastic members may pass
through the longitudinal fibre reinforced plastic members.
Slots may be located in either or both of the transverse and
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longitudinal fibre reinforced plastic reinforcement members to allow them to
intersect. The longitudinal fibre reinforced plastic members and transverse
fibre reinforced plastic members may be locked to each other after they
intersect.
Notches may be provided in the longitudinal fibre reinforced
plastic reinforcement members and/or transverse fibre reinforced plastic
reinforcement members to engage with the slot on the other of the members
to lock the members together.
The polymer concrete formulation may include an amount of
polymer resin, an amount of a light aggregate with a specific gravity less
than
that of the resin and an amount of a heavy aggregate with a specific gravity
larger than that of the resin.
The resin may be any suitable polyester, vinylester, epoxy,
phenolic or polyurethane resin or combination of resins dependent on the
desired structural and corrosion resistant properties of the polymer concrete.
Preferably, the resin content is between 25-30% by volume.
The light aggregate with a specific gravity less than that of the
resin can be any type of light aggregate or combination of light aggregates
dependent on the desired structural and corrosion resistant properties of the
polymer concrete. Usually, the light aggregates have a specific gravity of 0.5
to 0.9. The light aggregates usually make up 20-25% by volume of the
polymer concrete. Preferably, the light aggregate are centre spheres. The
centre spheres normally have a specific gravity of approximately 0.7.
Alternately, hollow glass microspheres with a similar specific gravity and
volume may be used.
The heavy aggregate with a specific gravity larger than that of
the resin can be any type of heavy aggregate or combination of heavy
aggregates dependent on the desired structural and corrosion resistant
properties of the polymer concrete. The heavy aggregates usually make up
40-60% by volume of the polymer concrete. The heavy aggregate has a
specific gravity of between 2 to 3.5.
Preferably the heavy aggregate is basalt. Usually the basalt is
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crushed. The crushed basalt may have a particle size 1 to 7 mm. Preferably
the basalt makes up between 40-50% by volume of the polymer concrete.
The basalt normally has a specific gravity of approximately 2.8. Alternately,
natural or artificial sand, that has a similar specific gravity as basalt, may
be
used. Preferably the sand makes up between 50-60% by volume of the
polymer concrete.
Alternatively, the heavy aggregate may be made up of one or
more of coloured stones, gravel, limestone, shells, glass or the like
material.
Preferably the resin contains a thixotrope to keep the light
aggregate in suspension.
The polymer concrete of the present invention may also include
fibrous reinforcement material to increase the structural properties of the
polymer concrete mix. The reinforcement material may be glass, aramid,
carbon, timber and/or thermo plastic fibres.
In another form, the invention resides in a method of producing
a structural element formed from polymer concrete, said method including
the steps of:
producing a mould that has a portion of an outer shape of the
structural element to be produced;
placing fibre reinforced plastic members within the mould,
tensioning at least one of the fibre reinforced plastic members;
locating polymer concrete over said fibre reinforced plastic
members;
allowing said castable material to set to form said structural
element; and
releasing said pre-tensioned members after the castable
material has set to form said structural element.
The fibre reinforced plastic members may be abraded prior to
the fibre reinforced plastic members being introduced into the mould.
Alternatively, the fibre reinforced plastic members may be coated with sand
and/or gravel interface to increase adhesion.
In one embodiment, the fibre reinforced plastic members may
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be located within the mould tensioned and polymer concrete poured over the
fibre reinforced plastic members.
In another embodiment, the fibre reinforced plastic members
may be located within the mould after sufficient castable material to complete
the structural element has been delivered into the mould. At least one of the
fibre reinforced plastic members may be tensioned before the polymer
concrete sets.
In still another embodiment, a portion of polymer concrete may
be introduced into the mould and some of the fibre reinforced plastic
members introduced into the mould and pretensioned. More polymer
concrete may then be introduced into the mould and more fibre reinforced
plastic members may be introduced into the mould and pretensioned. This
process may be continued until the structural element has been completed.
Where the fibre reinforced plastic members are hollow, the
hollow fibre reinforced plastic members may be filled with concrete, polymer
concrete or filled resin system and/or metal or reinforced plastic bar. The
hollow fibre reinforced plastic members may be filled after tensioning of the
hollow fibre reinforced plastic members. Normally, the hollow fibre reinforced
plastic members are filled after the tensioning has been removed and the
polymer concrete has set.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Embodiments of the invention, by way of examples only, will be
described with reference to the accompanying drawings in which:
FIGS. 1A to 1 D are transverse cross-sectional views of fibre
reinforced plastic reinforcement members that have large ratios of perimeter
length over cross sectional area resulting in reduced shear stresses in the
contact area and hence are suitable for pre-tensioning;
FIGS. 2A to 2C are transverse cross-sectional views of fibre
reinforced plastic reinforcement members that have small ratios of perimeter
length over cross sectional area which result in much higher stresses in the
contact area and hence are far less suitable for pre-tensioning;
FIG. 3 is a perspective view of a beam according to a first
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embodiment of the invention;
FIGS. 4A to 4F are side cross-sectional views of the beam of
FIG. 3A being formed;
FIG. 5 is a perspective view of a park bench slat according to a
5 second embodiment of the invention;
FIG. 6 is a perspective view of a telephone pole according to a
fourth embodiment of the invention;
FIG. 7 is a perspective view of another beam according to a
third embodiment of the invention; and
10 FIG. 8 is a perspective view of a of yet another beam according
to a fifth embodiment of the invention;
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
FIGS. 1A to 1 D and FIGS. 2A to 2C show transverse cross-
sectional views of fibre reinforced plastic reinforcement members 20. As is
shown, various shapes of fibre reinforced plastic reinforcement members
may be used.
FIGS. 1A to 1 D illustrate fibre reinforced plastic reinforcement
members that are suitable for use to produce a prestressed structural
element. The reasons that each of the fibre reinforced plastic reinforcement
members shown are able to be used is due to the fact that low stresses
occur throughout the members when located in a structural element. On the
other hand, the shear stress that occurs in the fibre reinforced plastic
reinforcement members shown in FIGS. 2A to 2C upon pre-tensioning is
considerable and hence they are much more likely to fail at low loads
causing failure of the corresponding structural element. In addition, the
fibre
reinforced members shown in FIGS. 2A to 2C are very vulnerable to suffer
major damage if penetrated by bolts, screws and/or nails.
The fibre reinforced plastic reinforcement members of
FIGS. 1A to 1 D operate effectively as a perimeter length 21 of each of the
fibre reinforced plastic reinforcement members is relatively large compared
to the cross-sectional area 22. The fibre reinforced plastic reinforcement
members shown in FIGS. 2A and 2B have a relatively low perimeter length
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21 when compared to the cross-sectional area 22. The large perimeter
length of the fibre reinforced plastic reinforcement members shown in FIGS.
1A to 1 D provide a large adhesion surface or a contact area to which a
polymer concrete is able to adhere to the fibre reinforced plastic
reinforcement members 20. This adhesion can be enhanced by abrading
the contact area of the fibre reinforced plastic reinforcement members.
The perimeter/area ratio has been calculated for each of the
fibre reinforced plastic reinforcement members shown in FIGS. 1A, 1 B and
2B. Each of the fibre reinforced plastic reinforcement members have the
same cross sectional area and hence the same theoretical tensile strength.
FIG 1A FIG 1 B FIG 2B
Dimensions Width = 300 Width = 50 mm Diameter =
mm
Height = 3 Height = 50 mm 33.85 mm
mm
Thickness =
5 mm
Cross- 900 mm' 900 mm' 900 mm'
Sectional
Area
Perimeter 606 mm 200 mm 106 mm
Length
P/A Ratio 0.673 mm-' 0.222 mm-' 0.117 mm-'
For the thin walled cross sections the perimeter/area ratio is
significantly larger then for the solid circular cross section.
FIG. 3 shows a structural element in the form of a prestressed
concrete beam 300. The concrete beam is formed from polymer concrete 30
that surrounds a square tubular fibre reinforced plastic reinforcement
member 20 that extends the length of the beam. Additional polymer
concrete 40 is located within the fibre reinforced plastic reinforcement
member 20 and a steel reinforcement bar 50 is imbedded within the polymer
concrete 40 and extends the length of the fibre reinforced plastic
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reinforcement member 20.
FIGS. 4A to 4F show the process that is used to form the
prestressed beam 300 of FIG. 3. In order to produce the prestressed beam
300, a mould 60 is produced. The fibre reinforced plastic reinforcement
member 20 is then tensioned. The tensioning of the fibre reinforced plastic
reinforcement member 20 can be conducted in any number of ways but
generally involves placing a clamp on either end of the fibre reinforced
plastic
reinforcement member 20 and applying opposing forces to the fibre
reinforced plastic reinforcement member 20 as indicated by arrows.
Once the fibre reinforced plastic reinforcement member 20 has
been tensioned, it is located within the mould as shown in FIG. 4A. Polymer
concrete 30 is then poured into the mould as shown in FIG. 4B until the
entire fibre reinforced plastic reinforcement member is covered as shown in
FIG. 4C.
At this point, the polymer concrete 30 is allowed to set. Once
the polymer concrete 30 has set then the tensioning of the fibre reinforced
plastic reinforcement member 20 is released to create a beam 300 that is
prestressed. At this point, if the fibre reinforced plastic reinforcement
member 20 extends past the end of the beam, it can then be cut so that the
end of the fibre reinforced plastic reinforcement member 20 is flush with the
ends of the beam 300.
To add additional strength to the beam 300, the additional
steps of FIGS. 4D and 4E can be completed. In FIG. 4E, polymer concrete
40 is added within the fibre reinforced plastic reinforcement member 20.
FIG. 4F shows that the addition of a steel reinforcement bar 50 can also be
added. By adding the polymer concrete 40 and the reinforcement bar 50,
the stiffness, strength and ductility properties of the beam are significantly
increased.
FIG. 5 is a structural element in the form of a prestressed
polymer concrete slat 400 that can be used for park benches. In this
embodiment, the fibre reinforced plastic reinforcement member 20 is a flat
planar member that extends the length of the slat and is surrounded by
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polymer concrete 30.
FIG. 6 shows a structural element in the form of a prestressed
concrete telegraph pole 500. In this embodiment, several square tubular
fibre reinforced plastic reinforcement members 20 are utilised to form the
telegraph pole. The fibre reinforced plastic reinforcement members are
surrounded by polymer concrete 30 to form the telegraph pole 500.
FIG. 7 is a structural element in the form of another prestressed
concrete beam 700.
In this embodiment different fibre reinforced plastic
reinforcement members are used. A single flat planar fibre reinforced plastic
reinforcement member 24 and four square tubular fibre reinforced plastic
reinforcement members 25 are used to form the beam. All of the fibre
reinforced plastic reinforcement members are pre-tensioned as discussed
previously. A series of ligatures 26 are located around the fibre reinforced
plastic reinforcement members to assist in tying the fibre reinforced plastic
reinforcement members together and to provide lateral confinement to the
beam 700.
In FIG. 8, a further prestressed reinforcement beam 800 is
shown. In this embodiment the beam 800 has a standard concrete top 70
and a polymer concrete base 30. A series of square tubular fibre reinforced
plastic reinforcement members 20 are located within the polymer concrete.
Two ligatures 26 extend through the traditional concrete 70 and the polymer
concrete 30 and extend around the fibre reinforced plastic reinforcement
members 20 to tie the traditional concrete 70, polymer concrete 30 and fibre
reinforced plastic reinforcement members 20 together. The beam 800 is
also produced so that a hollow 80 extends through the beam 800 to make
the beam 800 lighter. This hollow may be created by using a sacrificial foam
void former.
It should be appreciated that during installation of any of the
above structural members, holes are often made into the member to
accommodate bolts, screws, and/or nails. Because of their elongated cross
sectional geometry, thin walled solid and hollow fibre composite
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reinforcement members spread the reinforcement fibres over a large area of
the cross section of the structural member, hence the damage caused by
bolt holes, screws and/or nails is generally limited to a small number of
individual fibres. In the case of thick walled solid reinforcement members,
all
fibres are bundled together in a small area, hence a bolt or screw that
penetrates this area will damage a large number of reinforcement fibres and
will cause major damage to the reinforcement member which might lead to
failure.
In each of the above examples, the contact area provided by
the external surface of the fibre reinforced plastic reinforcement members is
sufficiently large so that the polymer concrete is able to adhere to the
surface
of the fibre reinforced plastic reinforcement members without creating large
shear stress. As the thickness of the fibre reinforced plastic reinforcement
members is also relatively small, the shear stress within the fibre reinforced
plastic reinforcement members is relatively small. This allows the fibre
reinforced plastic reinforcement members to be pre-tensioned in order to
create prestressed structural elements.
It should be appreciated that the polymer bond that is formed
between the polymer concrete and the fibre reinforced plastic reinforcement
members is high i.e. approximately 50 MPA. This enables fibre reinforced
plastic reinforcement members to be used to pre-stress polymer concrete
that previously has not been able to be achieved. Further, by increasing the
surface of the fibre reinforced plastic reinforcement members that contacts
the polymer concrete, the polymer bond formed between the polymer
concrete and the fibre reinforced plastic reinforcement members is
increased.
It should be appreciated that various other changes and
modifications may be made to the embodiments described without departing
from the spirit or scope of the invention.
