The invention provides a knitted spacer fabric having a
tightly knitted bottom layer, a more loosely knitted upper
layer and pile yarns extending across the space between the
lower and upper faces. Settable material, e.g. cement, is
introduced into the space between the upper and lower faces
and can be caused to set by the addition of a liquid, e.g.
water. Until set, the fabric is flexible and can be shaped
but after the material in space has set, the fabric is rigid
and can be used as a structural element in a wide range of
situations, e.g. to form a cover of a prefabricated shelter,
a track-way for vehicles, pedestrians or animals; a shelter
by applying the fabric to a framework; formwork for casting
concrete; barriers, e.g. to line tunnels; to repair
structures, e.g. roofs; to form floors or damp proof
structures; to reinforce earth structures, e.g. river banks;
to provide flood defences; or to repair existing pipes,
including buried water pipes or to construct new pipes.
TECHNICAL FIELD
The present invention relates to a fabric impregnated with a
material that, when mixed with a liquid, will set. Such
fabric has numerous applications.
TECHNICAL BACKGROUND
WO 2005/124063 describes a shelter that includes a ground
sheet and a cover; the space between the ground sheet and
the cover can be inflated by pumping air into the space to
raise the cover and form the shelter. The cover is made of a
fabric that has been impregnated with cement; the fabric may
be a type of felt known as “wadding”, which is a loose
non-woven fabric. Immediately before the interior space is
inflated, the cover is wetted with water, so that, after
inflation, the cement in the cover sets and forms a rigid
shell that acts as a self-supporting roof for the shelter,
which is particularly useful in providing temporary
accommodation in emergency areas.
Spacer fabric is a known material and comprises a top face
layer, a bottom face layer and pile yarns extending between
the two faces. It is commercially available, for example
from Culzean fabrics of Kilmarnock, United Kingdom; Scott
and Fyfe of Tayport, Fife, United Kingdom and W Bull and Son
Ltd (Baltex) of Ilkestone, United Kingdom. It is used to
manufacture garments and other articles where the fabric
must be thick but light and/or where the fabric should
include an air gap, for example in cycle helmets, boot
soles, fireman's clothing, body armour; mattresses and
bandages; climate-control seating in vehicles. The pile
yarns are self-supporting to space the two faces apart by a
desired distance and to resist crushing forces, i.e. forces
acting perpendicular to the plane of the faces. The
thickness of the spacer fabric is determined during
manufacture by choosing an appropriate length for the pile
yarn. The yarns used for forming the two faces can be the
same or different from each other and from the pile yarns so
that it is possible to choose the properties of the two face
layers and of the pile to provide the desired properties.
Among the fibres employed are polyethylene, polyester,
Nomex, Kevlar, polyamide and microfibre (Nomex and Kevlar
are trademarks).
JP-A-04327272 discloses a woven or knitted lattice-like
fibre sheet to which is applied a composition containing all
the components of a thermosetting resin, and containing a
large proportion of plasticizer. The resin composition is
cured to provide a sheet having high flexibility, high
strength, low elongation and good shape stability. Because
of the high amount of plasticizer in the resin, the resin is
flexible and so allows the sheet to be wound up on a roll.
U.S. Pat. No. 5,461,885 describes a hardenable substrate
that is used for forming casts and splints for immobilising
patients' limbs and joints that have been fractured, broken
or strained. The substrate is formed of a fabric having two
spaced-apart webs; a hardenable liquid composition is drawn
into the space between the webs by capillary action and
allowed to set. The liquid composition may be a resin or a
liquid dispersion of plaster of Paris. The hardenable liquid
sets in situ shortly after it has been added to the fabric.
US 2003/0077965 discloses the use of a spacer fabric in a
resin infusion process or a resin transfer moulding process
in which liquid resin is introduced into the fabric and
allowed to cure/harden.
DISCLOSURE OF INVENTION
According to the present invention, there is provided a
fabric comprising:
a first face;
a second face separated from the first face by space;
self-supporting pile yarns extending between the first and
second faces that maintain the first and second face in a
spaced-apart arrangement; and
a solid powder material, located in the space between the
first and second faces, which material is capable of setting
to a rigid or semi-rigid solid mass on the addition of a
liquid or on exposure to radiation, e.g. UV radiation.
The settable powder material may be settable on the addition
of water and in one embodiment may comprise cement,
optionally together with sand or fine aggregates and/or
plasticizers and other additives found in cement or concrete
compositions, that will set to solid cement or concrete on
the addition of water or a water-based solution.
Alternatively, the settable material may be a UV settable
material or one component of a multi-part curable resin that
cures when two or more liquid components are mixed together,
e.g. an epoxy resin system.
The amount of settable material in the space in the fabric
is preferably such that, particularly when the material has
set, it occupies substantially the whole of the space
between the first and second faces.
The settable powder material can be easily loaded into the
fabric and, in the case that it is hardened by the addition
of a liquid, the liquid can rapidly penetrate between the
powder particles to form a composition that will set over
time.
The settable powder material and/or the liquid can include
additives e.g. flexiblizers, foaming agents, fillers,
reinforcement materials etc. that are known in the art in
connection with the settable materials concerned.
The first and the second faces may be formed of yarns and
the yarns of the two faces may be the same as each other or
different.
The settable material is preferably added to the space
through pores formed in the first face of the fabric, in
which case, the first face will have pores that are large
enough to allow the material to be placed in the fabric.
However, after the material has been placed in the fabric,
it is desirable to prevent it falling out through the first
face and several techniques can be applied to achieve this
aim.
Firstly, a further layer may be bonded onto the first face
after the settable material has been introduced into the
fabric. This further layer may be permeable to the liquid
used to cause the settable material to set and, if the
permeability is brought about by the presence of pores in
the bonded layer, such pores should be sufficiently small to
prevent the settable materials from falling through the
first face material. Any suitable layer may be used to seal
the first face, e.g. a PVC layer, which can be secured to
the upper face by a variety of techniques, for example by
thermal welding or by means of an adhesive. Alternatively
the layer may be formed of a curable paste which is
subsequently cured, e.g. using heat. Such a layer is
preferably thin, typically less than or equal to 0.5 mm. The
layer may be flexible to maintain the flexibility of the
overall fabric prior to setting. Additional layers may be
applied to the sealing layer by a variety of techniques, for
example by thermal or chemical welding or by means of an
adhesive. One such layer could by way of example be a
damp-proof layer for applications, which could find
application in the construction industry or tunnelling.
Secondly, the first face may be made of, or include, an
elastomeric yarn so that the upper face can be stretched to
enlarge pores within the face to allow the settable material
to be introduced into the fabric but, once the material has
been added to the fabric, the stretching forces can be
released, to close the pores to a size such that the
settable material cannot readily escape through the first
face.
Thirdly, the first face can be treated after the settable
material has been introduced into the fabric to close the
pores of the first face. For example, it is possible to
treat the first face by applying a sealing material such as
an adhesive or to subject the first face to solvent
treatment to fully or partially close the pores. In one
example, a PVC paste may be applied (for example using a
scraper) to the first face and cured for example by heat,
e,g. by means of radiative heaters or hot air blowers.
Fourthly, the first face can be knitted from a fibres that
will shrink when heated, thereby enabling the settable
materials to be introduced through a knit having pores
sufficiently open to allow the particles to pass through;
after the particles of the settable material have been
introduced into the fabric, the first face can be heated,
e.g. using heated air, and the heat will cause the fibres to
contract sufficiently to close the pores enough as to
substantially prevent the particles of settable materials
from escaping. Such fibres that shrink when heated include
the majority of thermoplastic fibres for example
polypropylene. The method of heating fibres to cause
shrinkage described above may also have an advantage in
compacting the settable material especially if such heat
shrinkable fibres are also used to form the second face
and/or the pile yarns.
The second face is preferably substantially impervious to
the settable material so that the settable material does not
fall through the second face when added through the first
face. However, in order to assist in the penetration of
liquid into the space, the second face is preferably porous
to the liquid applied to set the material. Thus, the second
face preferably includes pores having a size allowing the
liquid to penetrate but not allowing material particles to
pass through. If nevertheless the second sheet has pores
that are too large to retain the material within the space,
it is possible to prevent the material falling out through
the second face using any of the measures discussed above.
As already mentioned, the second and in some cases the first
face of the fabric may be such that the liquid can penetrate
into the space through the faces to contact the settable
powder material within the space. Such liquid penetration
can take place either by including pores within the face (as
discussed above) and/or by making the yarns of the first and
second faces of a material that can be wetted by the liquid
concerned and therefore the liquid will be wicked through
the first and second faces to come into contact with the
settable material within the fabric. Furthermore, capillary
action between fibres within the first and second faces can
assist in providing liquid to the settable material.
Suitable materials for use in forming the first and second
faces include:
polypropylene, which is the preferred material to use when
the settable material includes cement, as it has excellent
chemical resistance to alkaline conditions;
coated glass fibres, which can provide reinforcement to the
set material;
polyethylene;
PVC fibres, which have the advantage of being relatively
easy to bond using chemical or thermal bonding.
A mixture of fibres can be used.
The length of the pile yarns controls the spacing between
the first and second faces and, as described above, they
must be self-supporting. They should be sufficiently stiff,
i.e. they should be sufficiently resistant to bending under
forces tending to crush the fabric, to maintain the spacing
between the faces when the settable material has been loaded
onto the first face to feed the material into the fabric.
The density of the pile yarns, i.e. the number of yarns per
unit area, is also an important factor in resisting crushing
forces while the material particles are being added and so
maintaining the spacing between the faces and in restricting
the movement of the material particles once they are trapped
between the upper and lower layers.
It is important, in accordance with the present invention,
that the pile yarn does not divide the space within the
fabric into individual small closed compartments since such
a division would allow cracks to propagate within the fabric
and so reduce the strength of the fabric once the material
has set.
The particle size of the settable material must be
sufficient to allow it to be introduced into the fabric but
it should not be so fine as to fall out of pores in the
first and/or second faces. Especially preferred are high
alumina cements since they provide shorter setting times
than other cements.
The first and second faces and the pile yarn are preferably
part of a spacer fabric, which can be formed with pores in
the first and second faces by the knitting process used to
make it. The second face is preferably more tightly knitted
than the first face so that the pores in the second face are
smaller than in the first face to allow the settable powder
material to be introduced into the space through the
relatively large pores in the first face and prevent the
material falling out of the fabric through the second face.
The fabric of the present has the advantage that it can be
manufactured and caused to set at will any time later by the
addition of the liquid, e.g. water. The fabric can therefore
be made at one location, transported to another location,
where it is caused to set by the addition of the liquid,
which can be supplied locally, thereby reducing the bulk
that must be transported. The fabric impregnated with the
solid powder will still be flexible and can be folded or
rolled up for transport.
The fabric of the present application has many applications.
Firstly, it can be used to form the cover of a prefabricated
shelter as described in WO 2005/124063. However, it has
wider applications and, for example, can be used:
to form a track-way for vehicles, pedestrians or animals;
to form a shelter by applying the fabric to a framework;
to make formwork for casting concrete;
to form barriers, e.g. to line tunnels;
to repair or reinforce structures, e.g. roofs;
to form floors or damp proof structures;
to reinforce earth structures, e.g. river banks and unstable
slopes;
to provide flood defences;
to repair existing pipes, including buried water pipes or to
construct new pipes;
to fireproof elements of new or existing structures e.g. as
a fireproof covering or lining for chimneys;
to form a hard surface, reduce dust hazards and contain fuel
spills for aircraft e.g. helicopter landing sites and
runways;
to reinforce sandbag structures and protect them from ultra
violet degradation and damage from the elements such as wind
and ultra violet degradation;
to line ground works and prevent the leaching of chemical
contaminants eg. for land fill or secondary fuel containment
works;
to form a waterproof lining for the containment of water
e.g. pond, canal lining and water storage or septic tanks;
to form permanent awnings or roof structures;
to form artistic or decorative forms, or
to form hulls and superstructure of floating vessels such as
boats or pontoons.
If the settable material is set by the addition of water,
the water can be added deliberately or the fabric can be put
in a place where it will come into contact with water, e.g.
in a watercourse or outside where it can absorb rain. For
example, it is possible to bury the fabric in damp earth and
allow it to absorb water from the earth, thereby causing the
settable material to set.
Once the material has set, the pile yarns also provide
reinforcement to the set material and substantially increase
its strength.
A substantial advantage of the fabric is that the pile yarns
and the fibres of the first and second faces provide
reinforcement to the material once it has set and
accordingly increase the physical properties of the set
material, as discussed more extensively below.
There is theoretically no limit to the thickness of the
fabric, although it will generally be limited by the
manufacturing techniques used to produce it. A typical
thickness would be between 2 and 70 mm, e.g. from 2 to 40
mm, and typically between 4 and 30 mm, e.g. from 4 to 20 mm.
One important consideration limiting the thickness of the
material is the ability of the liquid to penetrate through
the interior of the settable material before the outer
portions of the settable material is set. A further
limitation on the thickness comes from the increased weight
of the fabric with increased thickness and if it is too
thick, the faces may not be able to support the weight of
the settable material within the fabric.
BRIEF DESCRIPTION OF DRAWINGS
There will now be described, by way of example
only, a fabric material in accordance with the present
invention, by reference to the accompanying drawings in
which:
FIG. 1 is a cross sectional view through a
spacer fabric;
FIG. 2 is a diagrammatic illustration of the
fabric; and
FIG. 3 is a graph showing the strength of the
fabric under a load.
DETAILED DESCRIPTION OF THE BEST MODE FOR
PUTTING THE INVENTION INTO OPERATION
Referring to the accompanying drawings, FIG. 1 shows a
knitted spacer fabric having a tightly knitted bottom face
layer 10, a more loosely knitted upper face layer 12 and
pile yarns 14 extending across the space 16 between the
lower and upper face layers 10, 12. The spacer fabric is
made of knitted polyethylene and is commercially available
from Scott & Fyfe as 5 mm spacer fabric.
Settable material, e.g. cement, is introduced into the
fabric through pores 20 in the open-knit upper face layer
12. The pores 20 arise through the knitting process during
manufacture of the spacer fabric. The cement can be placed
on the spacer fabric and will fall through pores 20 into
space 16. The penetration through the pores 20 can be
assisted through vibration. It is preferred that the whole
of the space 16 is filled with cement in this way. Vibration
also has the advantage of settling the cement within the
space 16 to prevent voids or air pockets being formed.
Additionally, the settable material can be drawn into space
16 by resting the spacer fabric on a porous surface and
applying suction through the porous surface to form a
pressure drop across the spacer fabric, which assists in the
compaction of the settable material within the spacer fabric
and reduces the instances and size of residual voids and air
pockets. Additionally, compaction of the settable material
within the space 16 may be further increased by vibration of
a heavy plate resting on the spacer fabric containing the
settable material.
The bottom face 10 has a relatively tight knitted structure
and the size of the pores in the bottom face are smaller
than in the upper face layer such that the pores are
sufficiently small to prevent substantial amounts of the
cement from falling out.
After the material has been introduced into the space 16,
the upper face layer 12 is sealed by the application of a
thin coat of PVC paste which is then cured by heating the
surface.
Water can penetrate into the fabric through the pores in the
bottom face 10; hydration of the cement is aided by the pile
yarns 14, which can wick water into the interior of the
fabric.
The fabric including the settable material within the space
16 is flexible and can be formed to shape prior to the
introduction of liquid to set the material within the space.
The long fibres 18, together with the shorter fibres in the
fabric, provide reinforcement to the material, when set and
prevent crack propagation.
Example 1
Three test pieces of fabric in accordance with the present
invention having a surface area of 725 mm<2 >were
produced by introducing high alumina cement into a spacer
fabric, the spacer fabric was a polyethylene knitted fabric
manufactured by Scott and Fyfe being 5 mm thick. The fabric
was then sprayed with water and allowed to set for 4 days.
The test pieces were then subjected to the following test:
the test pieces were each placed in an Instron—5584-52536
Universal Materials Testing Machine having a movable anvil
that can apply compressive forces to the test piece. Each
test pieces was loaded so that the anvil acts
perpendicularly to the knitted faces. A load cell measures
the compressive load and the displacement of the anvil. The
compressive load was progressively increased until the test
piece failed and the load exerted on the test piece and the
displacement of the anvil at failure were logged by a
computer connected to the machine. The procedure was
repeated four times using separate samples.
The results are shown in FIG. 2, from which can be seen that
the four test pieces of fabric material in accordance with
the present invention failed at a consistently high
compressive load and that once initial failure had occurred,
when cracking could be observed in the samples, the samples
did not fail catastrophically but continued to support a
consistently high compressive load as the displacement was
increased progressively.
