Note: Descriptions are shown in the official language in which they were submitted.
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PCT/AU2005/000717
A PAVEMENT JOINT
FIELD OF THE INVENTION
The present invention relates generally to the
construction of pavements and to jointing systems for use
in such pavements. The invention has particular
application to pavements that are susceptible to
differential movement by out-of-plane action such as for
example by tree root invasion, or soil movement, and which
usually bear traffic that can accept some irregularity in
the pavement surface and the invention is herein described
in that context.
BACKGROUND OF THE INVENTION
Pavements are used to facilitate the passage of
wheeled or pedestrian traffic along or over roads,
footpaths (sidewalks), playgrounds, and areas used for
storage or parking. To do its job well, such a pavement
should be relatively smooth and flat. For reasons of
economy, such pavements are often cast in substantial
lengths, with construction joints between them. However,
in some forms, pavements may be formed from preformed
slabs made from a settable material, such as concrete, or
formed from other rigid material such as steel or wood.
Footpaths are pavements that carry relatively light, low
speed traffic such as pedestrians and pedestrian vehicles
such as wheelchairs, strollers and bicycles. Other
categories of light duty pavement include cycle ways,
domestic driveways, playgrounds and the like. These
pavements generally do not need to be as smooth or flat as
those used to carry heavy or high speed traffic.
15 A pavement is subject to both direct and indirect
actions. Direct actions include traffic loads and forces
deriving from soil or foundation movement, and tree roots.
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In the case of footpaths, cycle ways and domestic
driveways for example, which are frequently built
alongside trees, uplifting actions caused by tree roots
are common. Uplifting or depressing actions can be seen as
out-of-plane, relative to that of the pavement.
Indirect actions include drying (moisture) and
temperature change. When a pavement is made from
concrete, these actions cause both temporary and permanent
volumetric changes that manifest in the form of expansion
and contraction. Shrinkage, which is caused by drying,
can be seen in this sense as a form of permanent
contraction. The effect of these actions is most
significant in the plane of the pavement. For example,
the unrestrained drying shrinkage of concrete is commonly
in the order of 800 micro strain or 1.2 mm for a slab 1500
mm long. The coefficient of thermal expansion of concrete
is commonly in the order of 12 micro strain per degree
Celsius or approximately 0.4 mm in a slab 1500 mm long
subjected to a temperature change of 20 deg C. If
contraction is restrained, it may lead to cracking of the
concrete. If expansion is restrained it may lead to any
or all of spalling and crushing of the concrete and
buckling and warping of the pavement.
Commonly, provision for contraction of concrete
pavements is made by incorporating contraction joints at
relatively close intervals effectively dividing the
pavement into a series of contiguous slabs. In the case
of an un-reinforced concrete pavement such as a footpath,
for example, contraction joints are commonly spaced at
between 15 and 20 times the thickness of the pavement.
For a 75 mm thick pavement, this implies joints at 1000 to
1500 mm. Provision for the expansion of concrete
pavements, which are subjected to solar heating, such as
roads and footpaths, is made by incorporating expansion
joints, also known as isolation joints, at relatively wide
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intervals, commonly 4 to 5 metres. Thus external
pavements commonly take the form of a series of contiguous
slabs, both separated and linked by a combination of
contraction and expansion joints.
For reasons of economy, contraction joints are
commonly formed by creating a plane of weakness in the top
surface of the concrete, by trowelling grooves in the
fresh concrete or cutting grooves in the partially or
fully hardened concrete. This encourages cracking to
occur at such grooves rather than in a random fashion,
which would be unsightly, and helps to create many narrow
cracks rather than few large cracks, which would be
detrimental. In practice, the effectiveness of this
method is subject to variations in the concrete, in the
friction between the pavement and the soil or subgrade
upon which it rests, workmanship, climatic conditions and
other factors, and contraction often accumulates over two
or more slabs so that cracks do not occur at some planes
of weakness and relatively wide cracks occur at others.
Localised direct actions such as uplifting caused by
tree roots or soil heave cause flexural stresses in the
pavement. In the case of un-reinforced concrete footpaths
for example, which have relatively closely spaced
contraction joints, the uplifting action of a tree root
will typically lead to the opening or creation of a crack
emanating from the top surface of the footpath at a
contraction joint adjacent to the point of uplifting.
However, the cracking of this construction joint only
reduces the flexural strength of a slab significantly in
one direction and the aforementioned lifting may lead to
the sudden, uncontrolled fracture of the footpath at
distances from the point of lifting corresponding to the
flexural Strength of the concrete. Further, if a crack is
relatively wide, a lifted slab may not engage its
neighbour with the result that a vertical discontinuity or
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step will be created in the pavement. In the case of
footpaths this often leads to steps of sufficient height
to impair the passage of pedestrian vehicles and to cause
pedestrians to trip or fall.
Expansion joints usually consist of a sheet of
compressible material extending the full thickness of a
pavement so as to allow the pavement to expand without
inducing excessive compressive stresses in the concrete
from which the pavement is made, which could lead to
crushing or spalling of the concrete or warping or
buckling of the pavement. Such joints have no ability to
transfer load or to limit differential displacement within
a pavement.
SUMMARY OF THE INVENTION
In a first aspect the present invention provides a
pavement joint disposed between two contiguous pavement
slabs, the joint being elongate and extending along a
joint axis and incorporating a shear key and co-operating
bearing surfaces that form at least one hinge, the shear
key and the at least one hinge being operative when at
least one of the slabs is subjected to out-of-plane action
with the shear key transferring shear between the slabs,
and the at least one hinge accommodating angular
displacement of the slabs relative to the joint axis in at
least one direction by movement of one bearing surface
relative to the other.
In the context of the specification, the term
"pavement" relates to any hard surface especially of a
public area or thoroughfare that will bear travel.
Further, the pavement slabs may be formed from any
suitable material and may be formed as precast units or
cast in-situ. Examples of pavement slabs include,
concrete slabs, hard and rigid materials like concrete,
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slabs formed from timber, or metal, such as expanded metal
mesh, or from any combination of those materials.
In accordance with the invention, the joint provides
a load transfer mechanism that inhibits differential
vertical movement of the slabs when at least one of those
slabs is affected by an out-of-plane action such as by
tree root invasion or by soil movement. By reducing the
differential vertical movement of the contiguous slabs,
potential tripping hazards to pedestrians are reduced.
Along with this, as pavements are less likely to require
repair or replacement, there is a future cost saving to
users and a reduction in waste of resources.
In general, this load transfer mechanism is provided
by the shear key. The shear key provides a means of
transferring or equalising vertical displacement between
the slabs and may take many different forms to affect that
transfer. The at least the one hinge provides a means of
accommodating angular displacement relative to the joint
axis so as to provide a mechanism whereby the pavement may
articulate to relieve stress induced by the out-of-plane
action.
The inventors have found that the magnitude of
angular displacement that needs to be accommodated in
pavements that are subjected to localised actions from
tree roots and the like and which are comprised of
relatively short slabs, is an order of magnitude greater
than that required in other pavements such as roads. For
example, a tree root may lift one end of a footpath slab
by 25mm to 50mm which implies, for a 1500mm long slab, a
rotation of 10 to 2 . This level of rotation may be
accommodated by the joint according to the present
invention through the at least one hinge whereas such
rotation could not be accommodated by a conventional
contraction joint. However, it is to be appreciated that
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the out-of-plane action may result from other than
specific localised action. For example, this action may
result from ground subsidence, or even from more violent
action such as earth tremors and the like.
In a particular embodiment, the joint may be formed
through interengagement of the respective edge surfaces of
the slabs. In that arrangement, the edges are profiled to
form, by the interengagement, the shear key and the at
least one hinge.
In one form, the shear key is provided by at least
one portion of the edge surface of one slab locating
within a recess formed in the other edge surface so that
shear is able to be transferred across that connection.
In one form, a tongue and groove connection is formed
between the contiguous slabs.
In the arrangement where the joint is formed at least
substantially from the profile of the edge surfaces of
those slabs, the mechanism used in the hinge to enable
angular displacement may take various forms. In one
embodiment, each slab may have a bearing surface along its
edge surface with the interengagement of those bearing
surfaces providing a hinge of the joint.
The bearing surface may be formed from an exposed
edge surface of the slabs. Alternatively a covering such
as a metal or polymeric skin, film or the like may extend
over that edge surface to form the bearing surface. The
advantage of using such a covering may be to improve the
surface properties of the bearing surface, or to increase
the joint strength or to facilitate manufacture of the
joint.
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In one form, one bearing surface may be able to slide
within another bearing surface so that the hinge action is
by sliding rotation.
In another form, the ends of the slab may have a
cross section akin to that of gear teeth, so as to enable
shear to be transferred in the manner of gear teeth, and
rotation to be accommodated by rolling, in the manner of a
gear wheel.
When a slab of finite thickness rotates, say from a
horizontal plane, it initially lengthens in plan. This
means that when a slab is lifted close to one end and
lifts its adjacent slab, the joint between the slabs opens
at the top and closes at the bottom, and the joint between
the slabs and their non-lifted adjacent slab close at the
top and open at the bottom.
Typically in use, the lifted slabs are prevented from
moving horizontally by their non-lifted adjacent slabs.
As such, because of this lengthening effect compressive
stresses may be induced in both the lifted and the non-
lifted slabs unless there is some facility to accommodate
this lengthening or at least minimising its affect.
Typically, the result of this lengthening is that a
pinching effect may occur between the slabs as they are
angularly displaced. This effect may be offset by
shrinkage in certain circumstances where the slabs are
formed from concrete or similar material. In other
circumstances, the joint between the slabs needs to
accommodate the lengthening effect so that there is not
undue stress occurring at the joint which would cause
failure of at least one or more of the slabs.
In the arrangement as described above where the slabs
may be akin to gear wheels, if the radii of the slab ends
are established to equal the distance from the contacting
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surface to the fulcrum about which the slabs rotate, the
pinching effect described above is obviated.
In one form, the joint may include at least two
hinges, with one hinge allowing angular displacement about
the joint axis in one direction whereas the other hinge
allowing angular displacement of the joint axis in an
opposite direction. In one form, these hinges are
displaced towards a respective outer surface the slabs. In
one form, each of these hinges use a hinge action of
sliding rotation with each hinge being formed from
cooperating arcuate bearing surfaces that slide one within
the other.
In one form, the joint includes only a single hinge
which is disposed on or about the neutral axis of the
slabs. When located in that position, the relative
lengthening of the slabs that occurs during rotation needs
to be accommodated. In one form this may be accommodated
by incorporating sufficiently sized gaps within the joint
at the outer margins of the slab so as to allow adequate
clearance for the slab to rotate through a predetermined
angular displacement (typically less than 5 and more
typically less than 3 ). However depending on the
thickness of the slab, the gap required may be excessive
and may in fact cause a tripping hazard to the pavement.
As such, in another form, the joint may include a
compressible member disposed between the contiguous slabs
and arranged to accommodate the lengthening of the slabs
under the angular displacement.
In a particular embodiment, the pavement slabs may be
pre-formed and the compressible members may be fixed to
one or both of the slabs prior to installation or located
within the joint on interconnection of the respective
slabs.
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In a particular embodiment, the pavement joint
incorporates a joint member.
In one form, where the contiguous slabs are cast in-
situ, this joint member may act as formwork for both of
the pavement slabs. In one form, the joint member may be
formed from a sheet material such as sheet steel and if
necessary may include other elements such as the one or
more compressible members mounted thereon. The joint
member in this form may be fixed to one of the slabs so
that the joint hinge is formed through engagement of a
surface of the joint member and the other slab to which
that joint member is connected.
In one form, the shear key of the joint is provided
by interengagement of the contiguous slabs with the joint
member. In a particular embodiment, the joint member
incorporates opposite lateral portions that extend into
respective ones of the slabs so as to locate the jointing
member within the slab sufficiently to enable shear to be
transferred across the contiguous slabs through said
jointing member.
In one form, at least one of the lateral portions is
profiled to incorporate an arcuate bearing surface. In
this arrangement, the at least one lateral portion forms
part of the hinge that operates by sliding rotation with
the arcuate surface forming a bearing surface of that
hinge.
In a particular embodiment, the joint member includes
a core and the lateral portions extend outwardly from the
core and are spaced apart about the joint axis through
approximately 180 . With this arrangement, one lateral
portion projects into one slab, whilst the other lateral
portion projects into the other slab.
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In one arrangement, the joint member also includes at
least one spacer that projects from the core. The at
least one spacer locates between the contiguous slabs and
is angularly spaced about the joint axis from the lateral
portions.
In a particular embodiment, the joint member includes
two spacers which are angularly spaced apart about the
joint axis through approximately 180 . In a particular
embodiment, the joint member is configured so that the
spacers extend generally in a direction which is
substantially perpendicular to the lateral portions.
However, it is to be appreciated that the configuration of
the joint member may vary so that the spacers are not at
right-angles to the lateral portions.
The spacers of the joint member may be incorporated
to accommodate the effects of lengthening of the at least
one slab on angular displacement of the slabs about the at
least one hinge. In this way, the spacers may be made
from a material which is able to be compressed to at least
some extent to accommodate this lengthening effect.
In a further form, the joint member may be arranged
so that it completely separates and links the contiguous
slabs. In this arrangement, the joint member includes two
spacers that project from the core and extend to a
respective one of the outer surfaces of the slabs. In
this arrangement, the spacers may be sufficiently
compressible so as to provide an expansion joint for the
pavement to accommodate in-plane expansion of the slabs.
The configuration of the joint member with the core,
lateral portions, and two spacers may incorporate a hinge
action that operates through an arrangement where there is
sliding or rolling rotation between a bearing surface of
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the joint member and a corresponding bearing surface
formed on the edge of abutting slab.
In a particular embodiment of the above form of joint
member, the joint member is formed with a plurality of
bearing surfaces, each of which cooperate with a
corresponding bearing surface on its opposing slab so as
to form a plurality of hinges within the pavement joint.
In one form, at least one face of the joint member
includes two hinge bearing surfaces, these bearing
surfaces extending from a distal end of the lateral
portion of the joint member to a respective distal end of
the spacers. In a particular form, these bearing surfaces
are concave.
In one form, the joint member includes a pair of
hinges of the above type on each of its opposite faces.
Therefore in this arrangement, the joint member
incorporates four (4) concave bearing surfaces each of
which are part of a hinge of the joint.
In a particular embodiment, the joint member is
elongate having a constant cross-section. In a particular
form, the joint member is formed in continuous lengths
typically by an extrusion process.
In one form, the joint member is formed from a
rigid polymeric material, such as PVC, HDPE, or a high
hardness rubber. In an alternative embodiment, the joint
member from metal such as aluminium or made of composite
construction, such as a steel reinforced polymeric
material.
In a further aspect, the invention relates to a joint
member for a pavement joint, the joint member having a
joint axis and being arranged to be disposed between
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contiguous pavement slabs, the joint member comprising
opposite first and second faces that in use oppose
respective ones of the edge surfaces of the slab, the
first face incorporating a lateral portion that projects
outwardly from the face and is arranged to inter-engage
with an edge surface of its opposing slabs so as to enable
shear to be transferred from that slab to the joint
member, and at least one bearing surface that engages with
a bearing surface of its opposing slab and wherein the
inter-engagement of those bearing surfaces provides one of
at least one hinge of the joint for accommodating angular
displacement of the slabs relative to the joint axis in at
least one direction.
In a particular embodiment, the second face also
incorporates a lateral portion that projects from that
face and is able to inter-engage with an edge surface of
its opposing slab so as to enable shear to be transferred
between that slab and the joint member. In one form, both
the first and second faces incorporate two bearing
surfaces disposed on respective opposite sides of the
lateral portions disposed on that face, the bearing
surfaces being arranged to engage with respective bearing
surfaces of the edge surfaces of the opposing slabs to
form four hinges of the joint.
In yet a further aspect, the present invention
provides a method of inhibiting differential out-of-plane
movement of contiguous slabs in a pavement under an out-
of-plane action applied to at least one of the slabs by
incorporating pavement joints between the contiguous
slabs, the joints being elongate and each extending along
a joint axis and being capable of transferring shear
between the slabs and accommodating angular displacement
of the slabs relative to the joint axis in at least one
direction.
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In yet a further aspect, the invention relates to a
pavement slab that incorporates at least one profiled end
surfaces which in use form a part of a joint with a
contiguous pavement slab to allow shear to be transferred
across the joint and angular displacement of the slabs is
accommodated. In one form, a joint member is disposed
between the slabs.
BRIEF DESCRIPTION OF THE DRAWINGS
It is convenient to hereinafter describe embodiments
of the present invention with reference to the
accompanying drawings. It is to be appreciated that the
particularity of the drawings and the related description
does not supersede the generality of the preceding broad
description of the invention.
In the drawings:
Fig. 1 is a perspective view of a joint member
according to a first embodiment;
Fig. 2 is a schematic elevation view of a pavement
having joints incorporating the joint member of Fig. 1;
Fig. 3 is the pavement of Fig. 2 when subjected to an
out-of-plane action;
Fig. 4 is a schematic view to an enlarged scale of a
connection detail of the joint member of Fig. 1;
Fig. 5 is a variation of the joint member of Fig. 1;
Fig. 6 is a further variation of the joint member of
Fig. 1;
Fig. 7 is a sectional view of an expansion joint for
use in the pavement of Fig. 2;
Fig. 8 is a modified version of the expansion joint
of Fig. 7;
Fig. 9 is a sectional elevation view of a pavement
joint incorporating a joint according to a second
embodiment;
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Fig. 10 is a sectional elevation view of a pavement
joint according to a further embodiment;
Fig. 11 is a variation of the joint of Fig. 10;
Fig. 12 is an schematic elevation view of a pavement
joint according to a further embodiment;
Fig. 13 is a variation of the pavement joint of Fig.
12; and
Fig. 14 is a schematic plan view of a pavement
testing rig; and
DETAILED DESCRIPTION
Fig. 1 illustrates a the joint member 20 arranged to
be used in pavement joints 101, 102 (see Fig. 2 and Fig.
3). The joint member 20 allows shear to be transferred
through the joints 101, 102 to the adjoining slabs and to
accommodate angular displacement of those slabs about the
joint axes CA1 and CA2.
The joint member 20 incorporates a core 21, lateral
portions 22 and 23 which extend outwardly from the core
and which are angularly spaced apart about the axis CA by
about 180 so as to extend on opposite sides of the core.
The joint member also includes spacers 24 and 25 that
project from the core. These spacers 24 and 25 are also
spaced apart approximately through 180 about the core and
also generally are at right angles to the lateral portions
22, 23 again giving the joint member 20 a cross-section
that is somewhat akin to a crucifix.
The joint member 10 is elongate and typically formed
from an extrusion process. The joint member 20 is of
rigid construction and is formed from a suitable material
such as PVC. In addition, in the illustrated form, the
joint member includes a central cavity 26 which
facilitates extrusion and which may be filled by another
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extrusion if required with the joint member being made by
a co-extrusion process.
Because of its rigid construction, the joint member
is not able to accommodate angular displacement of the
slabs about the joint axis CA by flexing or deformation of
the joint member which would otherwise enable the lateral
portions 22 and 23 to be angularly displaced relative to
one another. In contrast, in joint member 20 this angular
displacement is accommodated by relative movement of the
pavement slabs about the joint member.
To allow this movement, the joint member 20
incorporates a plurality of bearing surfaces 27, 28, 29
and 30. Two of the bearing surfaces 27, 28 are disposed
on one face 31 of the joint member 20 whereas the other
two bearing surfaces 29 and 30 are disposed on the
opposite face 32 of the joint member. Furthermore, the
bearing surfaces are arranged so that on any one face,
those bearing surfaces are disposed on opposite sides of
the lateral portions 22 and 23. With this arrangement,
the bearing surfaces of one face are arranged to inter-
engage with corresponding bearing surfaces disposed on the
edge surface of its opposing slab. These respective
inter-engaging surfaces each provide a hinge (37, 38, 39,
40), in the pavement joint 101 and 102.
As best illustrated in Fig. 1, the respective bearing
surfaces extend substantially from a distal end 33, 34 of
the respective lateral portions 22, 23 to a respective one
of the distal ends 35, 36 of the spacers 24 and 25.
Furthermore, each of the bearing surfaces are arcuate
(being concave). In particular, the arcuate surfaces are
shaped so that the action of the respective hinges (37,
38, 39, 40) formed by inter-engagement of the bearing
surfaces with corresponding bearing surfaces in the
pavement slabs is one of sliding rotation. This will be
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discussed in more detail below with reference Figs. 2 and
3.
Fig. 2 illustrates a concrete pavement 100 formed
from contiguous slabs 103, 104, 105 and having pavement
joints 101, 102. The pavement joints 101 and 102
incorporate joint members 20. For convenience, reference
to these joint members are given the superscript 1, or 2,
with the features of those joint members given similar
designations.
In the illustrated form, the pavement 100 is formed
by casting of the slabs 103/ 104 and 105 across the joint
members 201, 202. In this way, the joint members both link
and separate the slabs 103, 104 and 105. Specifically,
the lateral portions 221, 231, 222, 232 are embedded into
the edge surface of respective slabs 103, 104 and 105
whilst the spacers 241, 251, 242 and 252 separates the slabs
103, 104 and 105 with the spacers extending to the
respective slab surfaces 110, 111 of the pavement 100.
As illustrated in Fig. 2, the end surfaces 106, 107,
108 and 109 of the slabs 103, 104 and 105 are cast onto
respective ones of the faces 311, 32' and 312, 322 and as a
result, each of those end surfaces are formed with arcuate
bearing surfaces 112, 113 which correspond to respective
ones of the bearing surfaces 27, 28, 29 and 30 of the
joint member 20.
The bearing surfaces of the joint member 20 are
designed to be smoothly curved and in one form, the curve
has a constant radius so as to form a hinge which operates
by sliding rotation of the inter-engaging surfaces. This
surface profile allows good even respective load
distribution across the hinges. In one form, the shape of
the bearing surfaces on the joint member is such that
there is a change in radius. The purpose of this change
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of curvature enables the effective point at which the
pinching force is applied to one lifted slab to the joint
member to be raised or lowered along that surface. For
example, the curvature of these surfaces may be other than
circular such as elliptical and change over the length.
In one form, there is a gradual increase in the radius
from the respective distal ends 33 and 34 of the lateral
portions 22, 23 towards the distal end of the spacers 24
and 25.
In general, a pavement is subject to both direct and
indirect actions. Direct actions include traffic loads
and forces deriving from soil or foundation movement, and
tree roots. In the case of footpaths, cycle ways and
domestic driveways for example, which are frequently built
alongside trees, uplifting actions caused by tree roots
are common. Uplifting or depressing actions can be seen as
out-of-plane, relative to that of the pavement.
Indirect actions include drying (moisture) and
temperature change. When a pavement is made from
concrete, these actions cause both temporary and permanent
volumetric changes that manifest in the form of expansion
and contraction. Shrinkage, which is caused by drying,
can be seen in this sense as a form of permanent
contraction. The effect of these actions is most
significant in the plane of the pavement. For example,
the unrestrained drying shrinkage of concrete is commonly
in the order of 800 micro strain or 1.2 mm for a slab 1500
mm long. The coefficient of thermal expansion of concrete
is commonly in the order of 12 micro strain per degree
Celsius or approximately 0.4 mm in a slab 1500 mm long
subjected to a temperature change of 20 deg C. If
contraction is restrained, it may lead to cracking of the
concrete. If expansion is restrained it may lead to any
or all of spalling and crushing of the concrete and
buckling and warping of the pavement.
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Commonly, provision for contraction of concrete
pavements is made by incorporating contraction joints at
relatively close intervals effectively dividing the
pavement into a series of contiguous slabs. In the case
of an un-reinforced concrete pavement such as a footpath,
for example, contraction joints are commonly spaced at
between 15 and 20 times the thickness of the pavement.
For a 75 mm thick pavement, for example this implies
joints at 1000 to 1500 mm. Provision for the expansion of
concrete pavements, which are subjected to solar heating,
such as roads and footpaths, is made by incorporating
expansion joints, also known as isolation joints, at
relatively wide intervals, commonly 4 to 5 metres. Thus
external pavements commonly take the form of a series of
contiguous slabs, both separated and linked by a
combination of contraction and expansion joints.
In the embodiment illustrated in Fig. 2, the joints
101, and 102 form the contraction joints for the pavement
100. However, unlike conventional contraction joints, the
joints 101 and 102 are able to accommodate out-of-plane
action, typically by tree root invasion or by soil heave
so as to inhibit differential vertical movement of the
slabs. The mechanism by which the joints accommodate this
action is best explained with reference to Fig. 3.
Turning to Fig. 3, the pavement 100 is shown
displaced after the application of an out-of-plane action
P, such as may occur through tree root invasion under slab
104.
Following the application of the force P to the slab
104, the load in that slab is transferred both to the slab
103 and to slab 105 through the respective joints 101,
102. In particular, in relation to joint 101, the slab
103 applies loading to the joint member 201 through the
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bearing surface 271 as represented by the arrow p1 and a
reaction force p2 is induced in its diagonally opposite
bearing surface 291 by the other slab 103. As such, the
joint member 201 transfers shear between the slabs 103 and
104 across the joint 101.
Again, if the load P is of sufficient magnitude, the
slab 104 will lift. This lifting action will reduce the
magnitude of the load and as such, this slab will continue
to lift until such time as an equilibrium position is
reached. This lifting action is not planar but rather is
accommodated through the hinge mechanisms incorporated in
the joints 101 and 102 that result in rotation of the slab
104. As such, again the threshold loading under which the
slab 104 will lift is in part a function of the resistance
provided to rotation through the joints 101 and 102
particularly as shear is able to be transferred to
adjoining slabs so that individual slabs are not free to
lift independently of one another.
To enable the slab 104 to lift through rotation (in a
clockwise direction as illustrated in Fig. 3) the hinges
391 and 392 become activated with the bearing surfaces 1131
and 1122 of the slab 104 moving across the bearing surfaces
271 and 292. With this movement, there is also a
corresponding movement of the bearing surface 1121 of slab
103 moving across bearing surface 291.
With this movement, as illustrated in Fig. 3, there
is a tendency for the bearing surfaces 1121 and 291 to come
apart. The inventors have found that under increased
angular displacement the joint member 20 may actually
"flip" whereby in the context of the embodiment of Fig. 3,
the bearing surface 271 moves out of contact with the
bearing surface 1131 of slab 104 and moves so that the
bearing surface 291 moves into contact with the bearing =
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surface 112' of slab 103. With the action, the joint
member 20 acts as a rocker.
Under this angular rotation, there is effective
lengthening of the slab 104. This rotation causes a
closing up of the gap between the slabs 103 and 104 at the
lower end of the joint 101 and a closing up of the gap
between the slabs 104 and 105 of the upper end of the
joint 102. Conversely, the gap at the upper end of the
joint 101 opens up whereas the gap at the lower end of the
joint 102 closes.
This change in the gap distance between the slabs can
be used to assist shear transfer across the joint 101 and
102 as the slabs are caused to pinch the joint member.
Furthermore the amount and position of this "pinching
force" can be modified by the radius of curvature provided
in the respective bearing surfaces. In general, the
pinching force is designed so that it is not greater than
that which would cause damage to the slab or the joint
member.
Accordingly, under this operation the pavement 100
again effectively articulates about its respective joints
so as to accommodate the out-of-plane action. Through
this articulation movement, there is minimal vertical
differential movement at the joints 101, 102 between the
adjoining slabs. The likelihood of damage to the slabs is
greatly reduced as the joints 101 and 102 are able to
accommodate the rotation which effectively relieves the
stress induced by this out-of-plane action P.
It is to be appreciated that whilst the above
embodiment illustrates the pavement slabs 103, 104 and 105
of the pavement being cast in-situ, it will be appreciated
that those slabs could be provided as pre-formed elements.
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Fig. 4 shows a side view of the joint member 20
during installation. The joint member 20 incorporates
voids 37 and bears against a face of the formwork 500 such
that voids 37 of the joint member 20 align with the voids
501, 502 in the formwork 500. A peg 90 is then able to be
inserted into the aligned holes. The peg 90 includes
prongs 91, 92 that locate in aligned formwork voids and
joint member voids. The pegs stabilise and support the
joint member to inhibit it moving during a concrete pour.
On curing of the concrete, the pegs are removed, and the
formwork stripped leaving the contiguous slabs linked and
separated by the joint members.
As will be appreciated, other methods can be utilised
to support the joint member during casting. For example:
a. Steel pegs are used and driven through near
vertical pre-drilled holes in the joint member. The joint
member may be laid in an excavated trench and pegs are
driven into the earth holding the joint member in place;
b. A "notched inserter tool" is used which goes
over the top of the joint member and drives the joint
member into the wet concrete; or
c. An "inserting tool" is used which captures the
top of the joint member by means of a number of "cams"
that are tuned and locked on to the joint member holding
the joint member in place.
Fig. 5 shows a further embodiment of the joint member
20. The joint member 45 shown in Fig. 5 shares many of
the features of the joint member 20 and like features have
been given like reference numerals.
The joint member 45 incorporates soft end portions
46, 47. These may be soft enough to accommodate
compression on installation, such that the formulation of
a gap may lead to the soft end portion expanding with the
formation of the gap, and so maintaining a seal. In this
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way, the ingress of detritus into the gap is reduced.
Further, at the lower portion, the soft end portions
provide a compressive membrane which enables the joint
member to better accommodate the lengthening effect of the
slabs as they angularly displace about the joint axis.
These end portions 46, 47 may be fitted using a
mechanical engagement, like a clip 48, and 49.
Alternatively, the end portions may be bonded to the joint
member 45 using adhesive or welding. In one embodiment,
the end portions and joint member may be co-extruded,
providing a seamless join between the differing materials
of the joint member and the end portions.
Fig. 6 shows a further embodiment of the joint member
50, whereby, to add further rigidity, the joint member has
a rigid core 51, surrounded by a softer coating 52. The
rigid core 51, such as uPVC, steel etc provides the
required rigidity for installation and shear force
resistance, and the outer coating of rubber,
polypropylene, HDPE etc provides a positive grip with the
concrete, when the joint member transfers the
displacement.
Figs. 7 and 8 show alternative embodiments of the
joint member 20 that are modified for providing expansion
joints and construction joints between the contiguous
slabs of the pavement. As indicated above, to permit a
concrete slab to expand and contract thermally, it is
common practice to include expansion joints at
predetermined intervals in the pavement. To ensure a gap
does not appear through movement in the horizontal plane,
expansion joints have the effect of a gasket between the
slabs, for movement within the plane of the slabs. The
joint members 60 and 65 shown in Figs. 7 and 8 have been
modified over the joint member 20 to provide this
function. Nevertheless, the members 60 and 65 include many
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of the features of the earlier embodiment 20, and like
features have been given like reference numerals.
Specifically, the joint members 60 an 65 include the
lateral portions 22 and bearing surfaces 27, 28 on one
face 32 of those members.
The joint members 60 and 65 include a second face 62,
67 that is generally planar so that those members may
further act as partial stops for temporary cessation of
construction. In conducting a partial pour of a pavement,
it is beneficial to seamlessly continue the construction
at a later time, either the following day, or months into
the future. To ensure the process can continue smoothly,
it is useful to form the desired shape in the free end of
the slab, so that the new joint member can be fitted.
Fig. 7 shows the joint member 60 having an expansion
portion 61 for bearing against an adjacent slab, or
complimentary expansion joint. The expansion portion may
be of rigid construction for acting as an end stop, or a
softer material such as EPDM, to act as an expandable
joint against the adjacent slab.
Fig. 8 shows a similar joint member 65 with expansion
joint characteristics. In this embodiment an expansion
portion 66 is bonded to the second face. In one form, the
expansion portion is made from an expanded foam. Again,
the expansion portion acts by bearing against an adjacent
slab, or against a complimentary expansion joint.
Further, variations of the joints 101, 102 and
corresponding joint members are illustrated in Figs. 9 to
13. As the pavement construction shown in these drawings
include many of the features of the earlier embodiments
like features have been given like reference numerals.
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In the embodiment as illustrated in Fig. 9, the
joints 101 and 102 incorporate a generally cylindrical
joint member 70 which is embedded in the end surfaces of
the slabs opposing the respective joints. The respective
joints also include compressible members 71, 72 which
extend from the cylindrical joint member 70 to the outer
surfaces 110, 111 of the pavement 100.
In the embodiment of Fig. 9, the shear is able to be
transferred through the joints 101, 102 through the
cylindrical joint member 701, 702. In addition, the joint
members are able to rotate about both joints with the
outer surface 73' and 732 acting as bearing surfaces for
the joint. Effective lengthening of the rotated slabs is
accommodated by the compressible material 71 and 72.
In the embodiment of Fig. 10 a somewhat similar
arrangement is disclosed as to Fig. 10 except that rather
than including a specific joint member 70, a tongue and
groove arrangement 75, 76 is provided at the joints 101
and 102. With this arrangement, one end surface of the
slabs 103, 104 and 105 incorporate a groove 75 whereas the
other end surface incorporates the tongue 76. Again
compressible materials 71, 72 is provided between the
slabs and extend from the tongue and groove connection to
the outer surfaces of the pavement 110, 111. The tongue
and groove provide arcuate engaging surfaces that allow
rotation of the slabs about the connection.
Fig. 11 shows a similar embodiment to that disclosed
in Fig. 10. Again the joints 101 include a tongue and
groove connection 75 and 76, compressible material 71 and
72 are provided between adjoining slabs 103, 104 and 105.
In the embodiment in Fig. 11, at least one of those edge
surfaces of the slab is provided with a sheet covering.
In the embodiment of Fig. 11 that sheet covering is formed
from steel which provides permanent formwork for casting
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of one edge surface of the slabs. Further, this sheet
covering 77 is embedded within the cast slab so that it is
secured in place. In addition, if required the
compressible members 71, 72 can be applied to the outer
surface of the sheet covering 77. It is to be appreciated
that the arrangement of Fig. 11 could be further modified
so that both surfaces incorporate a sheet covering so that
the bearing surfaces within the tongue and groove
connection are provided by inter-engagement of the
surfaces of the sheet coverings.
Fig. 12 illustrates a simplified version of the
joints 101, 102 as disclosed in Figs. 10 and 11.
Specifically, in the arrangement of Fig. 12, the joints
101 and 102 are formed from solely from a tongue and
groove connection 75, 76. Furthermore, in the embodiment
of Fig. 15 the members include a gap 78 which allows for
limited angular displacement of the respective slabs.
Fig. 13 discloses yet a further arrangement of joint
101 and 102. In the embodiment of the Fig. 13 the end
surfaces of the respective slabs 103, 104 and 105 are
shaped as gear teeth which enable shear to be transferred
in the manner of gear teeth, and rotation to be
accommodated by rolling, in the manner of a gear wheel.
As the amount of rotation that needs to accommodate a
relatively small angle (typically less than 5 ) in the
embodiment of Fig. 13 at joint 101, the end surface of one
slab 104 includes a single gear tooth 79 whilst the
opposing end surface of the slab 103 is profiled to
include opposite shoulders 80, 81 which allow the gear
tooth 79 to roll between the shoulders 80 and 81 through
the limited angular displacement.
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EXAMPLE
It is convenient to illustrate the operation of one
of the embodiments of the pavement joint with reference to
the following non-limiting examples.
Example
A full scale prototype concrete footpath was
constructed at RMIT University, Melbourne, Australia. The
prototype was 5m long, 1.5m wide and 75mm thick. It was
cast on a steel frame, designed in such a way that the
formwork could be removed from underneath and so that the
prototype could be jacked up from virtually any point - to
simulate various scenarios of tree root invasion and soil
expansion/movement. Four joint members made from rigid PVC
were installed in the footpath. They were 1.5 m apart from
each other thus dividing the footpath into three 1.5 m
long slabs, plus two 250 mm long end slabs. The ends of
the footpath were restrained by steel angles. The cross-
sectional shape of the joint member was substantially as
the same as shown in Fig. 1.
The prototype was cast using concrete with a nominal
strength of 40 MPa. Prior to casting, the slump of the
concrete was measured at 90 mm. All tests were conducted
after the cylinder strength of concrete of slabs exceeded
20 MPa. The 7 day mean compressive strength of the
concrete was found to be 22.9 MPa.
A series of tests was conducted on the prototype,
with both concentrated and distributed loads ranging from
0 to 490 kg, applied at different locations, to assess
differential displacement between slabs.
First, the slabs were pushed up from underneath using
a long piece of solid timber, a timber packer and a
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hydraulic jack. The slabs were jacked up to a maximum of
approximately 50 mm, measured at the central joint. No
additional load was applied to the slabs at this point.
The self- weight of each slab was about 400kg. Then,
uniformly distributed loads of 200kg, 400kg and 490kg were
added to Slab 1. The layout of the test is shown in Fig.
14.
As the slabs were jacked up, the displacements at the
locations G3 to G6 were recorded by LVDT's. The
displacements at the locations Gl, G2, G7 and G8 were
negligible. The maximum differential displacement without
additional load on the slabs was 0.73 mm. The maximum
displacement when 490 kg of distributed load was put on
Slab 1 was 2.03 mm.
In a 'worst case scenario' slab 2 was jacked up close
to point G6 while a 200kg concentrated load was applied to
slab 1 close to point G4. The maximum differential
displacement at point G6 was 2.49 mm.
When a slab was jacked up and no additional load was
applied to the pavement, the joint member acted as if
attached to jacked slab. As
load was added, at a certain
point, the member flicked across to the other slab. It is
felt that this indicates that the member acts as a rocker;
a double hinge having a short range of rotation and which
acts so as to distribute localised stresses favourably.
No distress was observed in the concrete in any of
the above tests.
Accordingly, the present invention provides pavement
joints, joint members and profiled slabs that allow a load
transfer mechanism that inhibits differential vertical
movement of slabs when at least one of those slabs is
affected by an out-of-plane action. This load transfer
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mechanism is provided by the shear key which provides a
means for transferring or equalising vertical displacement
between the slabs. In addition one or multiple hinges are
provided within the joint to provide a means of
accommodating angular displacement relative to the joint
axis so as to provide a mechanism whereby the pavement may
articulate to relieve stress induced by the out-of-plane
action. The joints may incorporate joint members which
locate between contiguous slabs or may be formed from a
profile of the slabs themselves.
The joint has widespread application for pavements of
different types. These pavements may be formed from slabs
which are cast in-situ or may be constructed using
preformed components or by a combination of both. The
pavements may be used for light traffic such as footpaths
or sidewalks or may find application in heavier traffic
environments such as on roadways or the like.
In the claims which follow and in the preceding
description of the invention, except where the context
requires otherwise due to express language or necessary
implication, the word "comprise" or variations such as
"comprises" or "comprising" is used in an inclusive sense,
i.e. to specify the presence of the stated features but
not to preclude the presence or addition of further
features in various embodiments of the invention.
Variations and modifications may be made to the parts
previously described without departing from the spirit or
ambit of the invention.
