Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1
REINFORCEMENT CONTAINING CARBON FIBERS
Description:
The application relates to a textile reinforcement that is suitable for being
completely casted in concrete and a concrete construction part, respectively.
Concrete has a tensile strength of only about 10% compared to the compressive
strength. In order to increase the tensile strength of concrete, which was a
new
construction material at the time, people began to combine concrete with
other, more
tensile materials as early as the middle of the 19th century. Particularly
noteworthy here
are the works of the French gardener Joseph Monier, who combined concrete with
iron
mesh for planters. Today, Monier is regarded as the inventor of concrete
fortified or
reinforced with steel elements, or reinforced concrete for short. After him,
the reinforcing
elements cast in reinforced concrete are still colloquially called "Monier
irons". Other
materials for the manufacture of reinforcements are still the subject of
current research
and development, in particular textile-based reinforcements.
Various fibre and textile materials are known, the tear strength of which is
significantly higher than that of steel, but which are also significantly
lighter than steel.
Massive weight savings are therefore possible for concrete construction parts
or concrete
building structures, which has a positive effect on the statics of load-
bearing structural
elements such as bridge piers or abutments, for example. At the same time,
textiles, for
example, based on glass fibres, basalt fibres, carbon fibres ("carbon",
"carbon fibres") or
certain organic polymers, offer the great advantage of a lower susceptibility
to corrosion,
while in the case of metal reinforcements, chemical wear of the reinforcement
elements
can be expected over the long term, which can lead to a dangerous reduction in
the load-
bearing capacity of the structural elements concerned, both through failure of
the
reinforcement itself and through spalling of concrete due to expansion of the
corroding
reinforcement elements. In addition to the general oxidation sensitivity of
metals,
especially construction steel, it is also playing an important role that the
concrete matrix
in which the reinforcement elements are embedded reacts strongly alkaline and
is
therefore chemically very aggressive.
Textile reinforcements are still in the development phase. In 2005, for
example, the
world's first bridge made of textile-reinforced concrete was built on the
grounds of the
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State Horticultural Show in Oschatz (Saxony).
Carbon fibres have turned out to be interesting for the production of textile
reinforcements for concrete. Carbon fibres offer high tear strength and, at
normal
temperatures, are extremely resistant to environmental influences such as
water, oxygen
or the highly alkaline environment in concrete. Carbon fibres have a high tear
strength in
the direction of the fibres, but are very brittle transversely to the
direction of the fibres.
This disadvantage is remedied by embedding carbon fibres in a matrix resin,
which
absorbs the corresponding forces and ensures cohesion of the carbon fibres
among each
other.
The problem with textile reinforcements is their low heat resistance. Concrete
construction parts with textile reinforcement are therefore unsuitable for
applications in
which they are permanently exposed to high temperatures. At the same time,
however,
a temporary resistance to high temperatures must be guaranteed in order to
ensure the
stability of concrete construction parts with textile reinforcements in the
event of a fire.
A temporary resistance to high temperatures in the event of a fire is referred
to as "fire
resistance". It is based on the length of time a construction part retains its
function in the
event of a fire. A common requirement for building structures at risk of fire
is the fire
resistance class "F90 fire-resistant" (functional for at least 90 minutes in
the event of a
fire). With conventional reinforced concrete construction, protection for 90
minutes is
achieved primarily with a sufficiently large concrete cover.
WO 2018/202785 discloses a concrete construction part with textile
reinforcement, which has an improved resistance in case of a fire, which is
brought about
by the concrete being modified accordingly in order to prevent spalling,
inorganically
dominated matrix materials being used for the reinforcement or the
reinforcement being
surrounded by an oxidation barrier that protects the fibres from exposure to
oxygen.
The disadvantage of the state of the art, however, is that the fibres in the
textile
reinforcement are still held together by a binder that has organic proportions
that form
gases under the influence of intense heat, thus burst the surrounding concrete
and cause
the construction part to collapse.
It is the object of the present invention to provide a textile reinforcement
which is
outstandingly fire-resistant and at the same time simple to produce.
The object is achieved by a textile reinforcement for embedding in concrete,
having
carbon fibres, wherein the reinforcement is coated with a layer protecting
against
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oxidation, wherein the carbon fibres are present as an interlaced,
intertwined, twisted or
cabled thread-like structure and have a maximum of 5 wt. % of a matrix resin,
and the
layer protecting against oxidation forms a separate layer and can produce a
chemical
bond to a component of concrete.
The present invention relates to a reinforcement. It should be made clear that
the
term "reinforcement" always means that a material (namely the reinforcement)
is cast or
embedded in another material (that is to be reinforced). A textile
reinforcement that is to
be embedded in concrete (as required in claim 1) means here that at least the
upper
surface and the lower surface of the textile reinforcement - which extend as
surfaces in
the longitudinal extent of the reinforcement and run essentially parallel to
one another -
are almost completely covered by concrete (see Figure 10). The present textile
reinforcement is thus enclosed (with the exception of edge areas) by concrete
at least on
the upper and lower surfaces. A material placed on top of concrete and not
enclosed by
concrete is not a reinforcement.
A separate layer protecting against oxidation should be understood to mean a
layer
that lies essentially completely around the reinforcement as an outer surface
or coating.
The layer protecting against oxidation is preferably present in the form of a
substantially
complete coating of the reinforcement. A substantially complete coating of the
reinforcement means that less than 30% of the outer surface, less than 20% of
the outer
surface, less than 10% of the outer surface or less than 5% of the outer
surface of the
reinforcement is free of the layer protecting against oxidation. The layer
protecting
against oxidation can have isolated cracks. A separate layer protecting
against oxidation
consists essentially entirely of the material protecting against oxidation,
this means
preferably to over 75 wt.%, more preferably to over 80 wt.%, even more
preferably to
over 90 wt.% and most preferably to over 98 wt.%. According to the invention,
the carbon
fibres that form the thread-like structure of the reinforcement consequently
have no
more than 5 wt.% of matrix resin and the reinforcement is surrounded by a
separate layer
protecting against oxidation.
There is no separate layer protecting against oxidation within the meaning of
the
invention if the material protecting against oxidation is present only
sporadically and not
as a full-surface coating on the reinforcement or on the carbon fibres or on
the thread-
like structure. There is also no separate layer protecting against oxidation
if the
substances protecting against oxidation are merely admixed as additives in a
matrix
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material for coating the reinforcement or the fibres of the reinforcement.
The weight proportion of the separate layer protecting against oxidation is
less than
15 wt.%, preferably less than 10 wt.%, more preferably less than 7.5 wt.% and
most
preferably less than 3 wt.%, based on the total weight of the textile
reinforcement.
Document EP 0 861 862 describes a method for reinforcing structures. In this
case,
for example, a concrete layer is to be reinforced by applying a fibre layer to
the surface of
the concrete layer. The fibre layer is used together with a primer layer and a
putty layer
and is impregnated with a resin. The fibre layer is not set in concrete.
Consequently, the
document does not describe a reinforcement either. Furthermore, the document
does
not describe carbon fibres which are in the form of an interlaced,
intertwined, twisted or
cabled thread-like structure or carbon fibres which contain at most 5 wt.% of
a matrix
resin. A separate layer protecting against oxidation is also not disclosed in
the document.
Document WO 2015/084720 describes an adhesive tape material which can be used
for
the external repair of construction parts (see Figures 1 to 4 of the
document). The
material is not embedded in concrete and therefore no reinforcement is
described in this
document. The material has reinforcing fibres embedded in a matrix material.
There is no
reference to carbon fibres present as interlaced, intertwined, twisted or
cabled thread-
like structures. A separate layer protecting against oxidation is also not
disclosed. The
document WO 2019/091832 describes a fibre product with a coating of aqueous
polymer
dispersion, the use of which is specified, for example, as reinforcement in
concrete.
According to the examples, the entire textile formed is impregnated with a
polymeric
material for this purpose, so that the coating of polymeric material encloses
as many
individual filaments of the textile as possible, thus enabling an internal
bond between the
fibres. The document further describes the use of inorganic thickeners, which
can be used
as additives in the aqueous dispersion. A separate layer of the reinforcement
protecting
against oxidation is not disclosed in the document.
The layer protecting against oxidation is preferably applied via a water-based
system, for example, an aqueous dispersion. All common textile coating methods
- in the
case of a layer protecting against oxidation made of vermiculite, for example,
immersing
the reinforcement in an aqueous dispersion of the coating agent - could be
used. A sol-
gel method (here, inorganic and hybrid polymer layers can be produced from
colloidally
disperse solutions by wet-chemical coating methods and subsequent hardening)
or a
galvanic method could be used.
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An advantage of an aqueous dispersion for forming the layer protecting against
oxidation is that it can be processed without a solvent (with the exception of
water as the
solvent), which makes processing much easier (also with regard to occupational
safety
and environmental protection).
In a general embodiment, means for increasing stability and/or abrasion
resistance
can also be added to the layer protecting against oxidation. For example, the
layer
protecting against oxidation can have 80 wt.% of substances protecting against
oxidation
and at most 20 wt.% of a water-soluble protective polymer, such as the one
that can also
be used for the further protective layer described later. The protective
polymer should
act as a binder and can, for example, stiffen a vermiculite layer (as an
embodiment of the
layer protecting against oxidation), so that the mechanical strength will be
increased.
Furthermore, the mechanical resilience of a vermiculite layer (as an
embodiment of the
layer protecting against oxidation) and its connection to the thread-like
structure can be
improved by mixing it with binders. This creates a mixture of substances and
binders that
protect against oxidation and therefore no additional layer. Epoxy resins and
phenolic
resins, for example, can be used as organic binders for the layer protecting
against
oxidation. The mechanical strength of the layer protecting against oxidation,
for example,
a vermiculite layer, can also be increased by mixing the layer protecting
against oxidation
(or its components) with particularly heat-resistant polymers such as
bismaleimidazole,
phenolic, cyanate ester or polybenzimidazole resins. Carbon-based materials
such as
graphene and graphene oxide, silicon-based materials such as polysiloxanes or
silicone
resins, colloidal silica or nanosilica, microsilica or other inorganic
materials such as e.g.
ZnO nanoparticles (e.g. NANOBYK-3860, Fa. BYK, Wesel, Germany), lime, cement,
anhydrite, ettringite, silica sol and water glass can be used as a binder in
the layer
protecting against oxidation to improve the properties of the layer. The layer
protecting
against oxidation can also have polyelectrolytes such as polycarboxylate
ethers or lignin
sulfonate, cellulose ethers such as methyl cellulose, polyvinyl alcohol or
polyvinylpyrrolidone. For all the admixtures mentioned, that are present in
the layer
protecting against oxidation, it should however be noted that the material
protecting
against oxidation remains the main component of the layer and the admixtures
also do
not result in forming an additional layer of these admixtures in the layer
protecting against
oxidation.
Advantageously, the textile reinforcement has a proportion of organic
substance
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that is so low that the formation of gaseous decomposition products during
heating is no
longer significant and the construction part cannot be blown up in the event
of a fire. The
skilled person knows, for example, that no fire resistance tests are required
for concrete
construction parts with an organic proportion of less than 1 wt. %. With steel
reinforcements, the concrete covering of the reinforcement elements must
ensure that
the reinforcement does not heat up to more than 550 C, otherwise the steel
would lose
its strength. Carbon fibres, on the other hand, are stable at this temperature
in the
absence of oxygen and thus allow a smaller concrete cover, which results in
significant
weight savings.
A textile reinforcement within the meaning of the present application is a
material
based on thread-like structures that is embedded in a surrounding material,
for example,
concrete, for reinforcement. The thread-like structures can be present as
threads in the
narrower sense, but they can also be products made from threads. Possible
products are,
for example, yarns, cables, cords or ropes, which can also be processed into
flat products
such as woven fabrics, scrims, crocheted fabrics, braids, warp-knitted
fabrics, trebles,
grids or nets. The textile reinforcements produced in this way are
characterized by their
flexibility, which makes it possible to store the textile reinforcement in a
space-saving
manner, e.g. in roll form, and to transport it to the construction site and
only unroll it
immediately before setting it in concrete. Rigid reinforcement elements such
as rods or
rigid lattices can also be produced by using binding agents or by
appropriately intertwining
and/or interlacing of the thread-like structures. So-called wrapping yarns,
with which the
thread-like structures or the yarns, cables, cords or ropes made from them are
wrapped
or braided, can also mechanically stiffen the thread-like structures, the
yarns, cables,
cords, ropes, woven fabrics, scrims, crocheted fabrics, braids, warp-knitted
fabrics,
trebles, grids or nets made from them.
In an embodiment, the textile reinforcement consists of the thread-like
structures
mentioned.
In an embodiment, the reinforcement has a (further) protective layer in
addition to
the layer protecting against oxidation. The protective layer is preferably
located as an
outer layer on the finished reinforcement with the separate layer protecting
against
oxidation and preferably not over the entire surface around the thread-like
structure of
the carbon fibres. The protective layer preferably covers the upper surface
and/or the
lower surface of the reinforcement. The protective layer can be a coating, for
example,
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which makes it possible to (better) wind up the reinforcement and thus store
it as rolled
goods. The protective layer can also be composed of or contain substances that
simplify
and/or improve the embedding of the reinforcement in the concrete. For
example, the
protective layer can contain flow agents for concrete. Furthermore, the
protective layer
can also protect the reinforcement from the weather and/or mechanical loads as
long as
it has not yet been installed in the concrete. The protective layer can be
provided
reversible or fixed to the reinforcement. A reversible protective layer is
present if the
protective layer can be pulled off the reinforcement, for example, as a type
of foil. In this
case, all types of polymer films are conceivable as films, wherein it is also
possible for the
polymer film to be water-insoluble (for example, a polyethylene film). The
protective layer
is firmly connected to the reinforcement if the protective layer and the
reinforcement can
no longer be detached from one another without destroying the reinforcement.
In the
case of a protective layer being firmly connected to the reinforcement, the
protective
layer is preferably designed to be water-soluble, so that it dissolves in the
concrete on
contact with the water. In this way, the protective layer can protect the
reinforcement
prior to being set in concrete in, but it does not prevent or worsen the
penetration of the
reinforcement with the concrete. The protective layer can include or consist
of, for
example, polyelectrolytes such as polycarboxylate ethers or lignin sulfonate,
cellulose
ethers such as methyl cellulose, polyvinyl alcohol or polyvinylpyrrolidone.
The
reinforcement preferably has about 1 to 10 wt.%, preferably 2 to 5 wt.% of the
protective
layer, based on the total weight of the reinforcement.
In an embodiment, the textile reinforcement has more than one thread-like
structure. In an embodiment, the textile reinforcement consists of more than
one thread-
like structure. The individual thread-like structures of the reinforcement can
be
interlaced, twisted, intertwined or cabled. In addition to one or more thread-
like
structures made of carbon fibres, the textile reinforcement according to the
present
application can also contain additional thread-like structures made of other
fibres.
Thread-like structures such as polyamide fibres, aramide fibres, alkali-
resistant glass fibres
(AR glass fibres), basalt fibres, polypropylene fibres, polyvinyl alcohol
fibres, polyester
fibres or fibres made of oxidized, infusible polyacrylonitrile (e.g. Pyromex ,
available from
Teijin Carbon Europe, Wuppertal, Germany) are particularly suitable for this
purpose. In
an embodiment, the additional thread-like structure of the reinforcement is a
plurality of
wrapping threads with which the thread-like structure made of carbon fibres is
wrapped.
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The wrapping can, for example, increase the mechanical stability of the thread-
like
structure made of carbon fibres and thus of the reinforcement. The wrapping
can take
place uniformly over the entire reinforcement or there is only a wrapping in
partial areas
of the reinforcement. For example, only a central area of the reinforcement
can be
particularly mechanically reinforced by means of the wrapping threads.
In an embodiment, the thread-like structure has a structured surface due to
its
production by interlacing, intertwining, twisting or cabling. This structured
surface makes
it possible to bring the thread-like structure into a particularly intimate
form-fitting
connection with other materials, for example, coatings, the layer protecting
against
oxidation, the further protective layer or concrete. In an embodiment of the
wrapping
threads, the wrapping threads produce a structured surface in addition to the
mechanical
reinforcement or without mechanical reinforcement and thus enable an intimate
form-
fitting connection - as described above.
By interlacing, intertwining, twisting, wrapping or cabling, the carbon fibres
and/or
filaments are held together in the thread-like structure, which makes it
possible to
significantly reduce or even completely eliminate the proportion of a matrix
resin required
to hold the fibres together within the thread-like structure. If only one
thread-like
structure is used, the endless filaments that make up this thread-like
structure are
intimately connected to one another by interlacing, intertwining, twisting,
wrapping or
cabling. If several thread-like structures are used, several thread-like
structures can be
intimately connected to one another by interlacing, intertwining, twisting,
wrapping or
cabling, optionally also in addition to an intimate connection of the
filaments making up
the thread-like structures.
A major disadvantage of the matrix resin is its problematic behaviour at high
temperatures. In the case of significantly higher temperatures, the matrix
resin begins to
soften and can no longer ensure the cohesion of the carbon fibres among each
other and
can no longer compensate for the brittleness of the carbon fibres transverse
to the fibre
direction. In addition, it begins to decompose, even in the absence of air,
with the
formation of gaseous products, which can then burst the surrounding concrete.
At high
temperatures and oxygen access, carbon fibres can also oxidize themselves,
while in the
absence of oxygen they are stable even under extremely high temperatures.
In this way, a significant contribution is made to the better fire resistance
of the
carbon fibre-based textile reinforcements, since the cohesion within the
thread-like
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structure is no longer achieved by a matrix resin that quickly fails when the
temperature
increases, but mechanically by the intertwining of the fibres and/or filaments
that make
up the thread-like structure. By reducing the amount of matrix resin, the
amount of
thermally decomposable material in the thread-like structures can also be
reduced, so
that gas formation under the influence of high temperatures is minimized or
eliminated.
This is accompanied by a reduction in the risk of structural failure of
concrete parts
provided with carbon fibre-based reinforcements due to bursting in the event
of fire.
In the present application, matrix resin is understood to mean the entirety of
all
non-fibre-forming materials with which the carbon fibres, the thread-like
structures made
from them or the textile reinforcement made from them are provided before the
layer
protecting against oxidation is applied to the reinforcement. In particular,
this means
finishing agents that are applied with the aim of improving the processability
of the fibres
or thread-like structures, for example, means to prevent breakage, to reduce
static
charging or to improve the slippage of the fibres during processing. Such
fibre finishes are
known to a skilled person as "sizing" or "size". Organic synthetic resins such
as epoxy
resins or polyurethane-based resins are often used for this purpose. A
reactive
polydimethylsiloxane (e.g. SILRES BS 1042, available from Fa. Wacker, Munich,
Germany)
can also be used as sizing. In the event that a particularly temperature-
resistant finish is
necessary, particularly temperature-resistant polymers such as polyphenylene
sulphide
(PPS), polyetherketones such as polyetheretherketone (PEEK) or polyimides such
as
polyetherimides can also be used. In addition, high temperature resins such as
bismaleimide, phenolic, cyanate ester or polybenzimidazole resins can be used.
Carbon-
based materials such as graphene and graphene oxide can also be used, as can
silicon-
based materials such as colloidal silica or nanosilica (based on sol-gel
processes; e.g.
LUDOX SM 30 from the company W. R. Grace & Co.-Conn., Columbia, USA),
microsilica
(e.g. EMSAC 500 SE from the company Ha-Be Betonchemie GmbH & Co. KG, Hameln,
Germany). In addition, other inorganic materials in conjunction with water-
soluble
organic polymers such as, for example, polyvinyl alcohol or
polyvinylpyrrolidone can be
used as a binder. In the examples given, the binders are water-soluble and are
distributed
accordingly in the concrete. Ferrofluids containing paramagnetic iron can act
as radical
scavengers and thus as oxidation inhibitors. In addition, ZnO nanoparticles
(e.g.
NANOBYK-3860, from Fa. BYK, Wesel, Germany), polysiloxanes or silicone resins
or
inorganic lubricants based on molybdenum sulphide and/or graphite (e.g.
MOLYKOTE
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7400 Anti-Friction Coating from DuPont, Wilmington, USA) or so-called
ORMOCERE,
organically modified ceramics (e.g. InnoSolTEX technology from Fraunhofer ISC,
Wurzburg, Germany) are suitable. Other inorganic finishes, for example, based
on
phyllosilicates such as vermiculite, can also be used.
In addition to the mechanical properties of the fibres, the finishing agent
can also
provide better binding to other parts of the matrix resin, for example, to
binders. In
addition to finishing agents that improve the processability of the carbon
fibres or the
thread-like structures made from them, the term "matrix resin" also includes
binders that
provide cohesion of the carbon fibres or thread-like structures among each
other, but
which also compensate the brittleness of the carbon fibres transversely to the
fibre
direction or, where appropriate, stiffen the thread-like structures or the
yarns, cables,
cords or ropes made from the thread-like structures into rods or stiffen the
woven fabrics,
scrims, crocheted fabrics, braids, warp-knitted fabrics or trebles into rigid
lattices. In
addition, binders prevent uncontrolled penetration of concrete into the
material of the
textile reinforcement. This would mean that there could be telescopic pull-out
of fibres
from the textile reinforcement, wherein inner fibres or filaments that are not
in contact
with concrete can be pulled out more easily than further outwards positioned
fibres or
filaments that are in contact with concrete. Under "uncontrolled penetration",
a
penetration of the concrete between the filaments that build up the thread-
like structure
is specifically considered. Otherwise, the formation of needle-shaped
crystallites when
the concrete hardens can destroy or damage the filaments of the thread-like
structure.
By an intimate connection of the filaments of a thread-like structure among
each other
and by an intimate connection of several thread-like structures e.g. by
interlacing,
intertwining, twisting, wrapping or cabling, the penetrability through
concrete can be
drastically reduced. Binders for thread-like structures made of carbon fibres
are known to
the skilled person under the designations "impregnation" or "impregnation
mass".
Binders from the substance group of organic polymers are often used, which can
be
chemically related to the finishing agent of the fibres. As possible binders,
in particular
thermally or radically curable organic synthetic resins such as epoxy resins
or acrylates
and rubbers such as styrene-butadiene rubber or carboxylated styrene-butadiene
rubber
should be mentioned. In order to achieve the highest possible temperature
resistance of
the matrix resin, it is also possible to use inorganic binders based on
silicates or cements.
The use of silicone resins is also possible. Organopolysiloxanes, in
particular silicone
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resins, such as in particular the group of methyl resins and methylphenyl
resins, such as
siloxanes substituted with methyl-phenyl-vinyl and hydrogen groups, and
mixtures of the
relevant silicone resins and organic resins have proven to be suitable.
Although no basic
alkali resistance is to be expected with organosilicon compounds, this was
surprisingly
demonstrated with some formulations (e.g. Wacker Silres H62C and in
combination with
Silres MK, both available from Fa. Wacker, Munich, Germany) for the special
application
of textile reinforcement. In the case of methyl-phenyl-vinyl-hydrogen-
polysiloxanes (e.g.
Wacker Silres H62C, available from Fa. Wacker, Munich, Germany), methyl-
polysiloxanes
(e.g. Wacker Silres MK, available from Fa. Wacker, Munich, Germany) and, in
particular,
suitable mixtures from these two siloxanes a surprisingly high alkali
resistance has already
been demonstrated in the field of textile reinforcement. Reactive
polydimethylsiloxanes
(e.g. SILRES BS 1042, available from Fa. Wacker, Munich, Germany) have also
proved their
worth. Inorganic binders with an organic proportion, in particular
predominantly
inorganic binders that also have an organic proportion, still tend to form a
porous
structure or microcracks in the high temperature range between 500 C and 1000
C,
despite their significantly better high-temperature resistance. For this
reason, it is
desirable to minimize the amount of binder used in the reinforcement for use
in high
temperature concrete parts.
A total proportion of not more than 5 wt. % matrix resin mass based on the
entire
reinforcement is preferred for this reason in order to achieve the best
possible high-
temperature resistance of the concrete parts containing a textile
reinforcement
corresponding to the present application. As matrix resin mass, the same
material as
described above for the matrix resin can be used, but this time the matrix
material can be
present as a component not only on the carbon fibres but also in other layers
of the
reinforcement. The matrix resin mass thus comprises the matrix resin of the
carbon fibres
and other matrix components of the reinforcement in other layers of the
reinforcement.
The textile reinforcement can have a maximum of 4 wt.% matrix resin mass. The
textile
reinforcement can have a maximum of 3 wt. % matrix resin mass. The textile
reinforcement can have a maximum of 2 wt.% matrix resin mass. The textile
reinforcement can have a maximum of 1 wt.% matrix resin mass. In an
embodiment, the
textile reinforcement is free of matrix resin mass. The binder proportion of
the textile
reinforcement can be 5 wt. %, 4 wt. %, 3 wt. %, 2 wt. %, 1 wt. %, or the
textile
reinforcement can be free of binders. It is also possible to reduce the
proportion of
CA 03166240 2022- 7- 27
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finishing agent on the carbon fibres. Proportions of less than 1.5 wt. %, less
than 1 wt. %
or even less than 0.5 wt. % are possible here. In an embodiment, the carbon
fibres and
also the textile reinforcement are free of finishing agent.
In contrast to the matrix resin, which is particularly affected by thermal
decomposition in its organic proportions in the event of a fire, the carbon
fibres are largely
stable at high temperatures as long as they are kept away from oxygen. For
this reason,
according to the present application, the reinforcement is coated with a
separate layer
protecting against oxidation. In principle, all materials that do not react
with oxygen even
under the influence of high temperatures are suitable for this layer. This is
particularly the
case with inorganic compounds.
In an embodiment, the layer protecting against oxidation therefore has a
proportion of inorganic material of at least 80 wt. %. In an embodiment, the
layer
protecting against oxidation therefore has a proportion of inorganic material
of at least
70 wt. %. In an embodiment, the layer protecting against oxidation therefore
has a
proportion of inorganic material of at least 60 wt. %. In an embodiment, the
layer
protecting against oxidation therefore has a proportion of inorganic material
of at least
50 wt. %. In an embodiment, the layer protecting against oxidation therefore
has a
proportion of inorganic material of at least 40 wt. %. Particularly suitable
are oxidic
materials or materials whose components are oxidized to a high degree as long
as they
do not themselves have an oxidizing effect. Materials based on stable metal
and semi-
metal oxides, such as the oxides of calcium, magnesium, aluminium and silicon,
are of
particular importance. The oxides of these elements are characterized by high
oxidation
stability and a low oxidation effect as well as easy availability. Materials
derived from
these oxides are, for example, quartz, clay, cement or the large group of
substances called
silicates, in which the elements mentioned can be associated with other
elements in their
oxidized forms, for example, with iron or alkali metals.
What is special about this selection is that all of these materials have a
high
chemical similarity to certain components of concrete, such as cement. This
chemical
similarity enables a chemical bond to form between the material of the layer
protecting
against oxidation and certain components of concrete, allowing for a
particularly strong
adhesion between the layer protecting against oxidation of the textile
reinforcement and
the surrounding concrete of a concrete construction part.
In an embodiment, the layer protecting against oxidation has ORMOCERE, i.e. an
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13
organically modified ceramic (e.g. InnoSolTEX technology from Fraunhofer ISO,
Wurzburg,
Germany), or polysilazanes.
In an embodiment, the layer protecting against oxidation therefore contains at
least 5 wt. % silicon. This can include silicon-oxygen compounds such as
silicates or
silicones. Silicon-oxygen compounds are characterized by a particularly high
chemical
stability. In particular, due to the high chemical affinity of silicon for
oxygen, silicon-
oxygen compounds are extremely stable against reduction, do not give off
oxygen even
under the conditions of a fire, and accordingly do not change chemically. For
example, the
skilled person knows that various silicon-oxygen compounds are used as fire
extinguishing
agents. An important example of this is sand (chemically mostly silica, 5i02),
which can be
used to cover fires. Phyllosilicates such as vermiculite can also be used as
fire
extinguishing agents.
The layer protecting against oxidation lies on and around the reinforcement
and
can be present on and around the textile reinforcement in many different ways.
For
example, it is conceivable to produce the layer protecting against oxidation
by means of
a plasma treatment. In a plasma treatment, the object to be treated is exposed
to a
plasma to which a gaseous precursor for the desired surface coating is added.
For
example, a plasma treatment in the presence of hexamethyldisiloxane as a
precursor
leads to the formation of a layer containing silicon-oxygen compounds on the
treated
surface, here on the surface of the textile reinforcement. The silicon-oxygen
compounds
can be silicon dioxide, for example. Layers of amorphous silicates or polymer
layers
containing silanol groups are also possible. In an embodiment, the layer
containing silicon-
oxygen compounds consists of at least 30 wt. % silicon dioxide. In an
embodiment, the
layer containing silicon-oxygen compounds has silanol groups on its surface.
In an embodiment, the layer containing silicon-oxygen compounds has a
thickness
of less than 500 nanometres and is therefore significantly thinner than
conventional layers
protecting against oxidation. In an embodiment, the layer containing silicon-
oxygen
compounds has a thickness of less than 300 nanometres. In an embodiment, the
layer
containing silicon-oxygen compounds has a thickness of less than 100
nanometres. In an
embodiment, the layer containing silicon-oxygen compounds has a thickness of
less than
50 nanometres, less than 30 nanometres.
This also results in a high flexibility of the reinforcement compared to other
layers
protecting against oxidation. In this embodiment, the textile reinforcement
retains its
CA 03166240 2022- 7- 27
14
drapability even when coated with the layer protecting against oxidation. It
is therefore
possible to bring them into a desired shape immediately before setting them
into
concrete and, for example, to produce curved or bent concrete construction
parts with
little effort. The layer containing silicon-oxygen compounds can be chemically
bonded to
the carbon fibres themselves or to the finishing agent applied to the carbon
fibres and in
turn allows chemical bonding to components of concrete, e.g. to cement.
Silicates, which can be applied to the reinforcement by wet-chemical methods,
for
example, can also be used as a material for the layer protecting against
oxidation. In this
context, for example, phyllosilicates should be mentioned, which are able to
form flexible,
inorganic films. Inorganic films made from vermiculite have excellent
mechanical
properties (for example, related to tensile strength and tensile modulus) and
are superior
to some organic films.
In an embodiment, a flexible layer protecting against oxidation is formed by
the
phyllosilicate vermiculite. This is particularly the case when vermiculite is
applied to a
surface in the form of an aqueous suspension and then dried. Such dispersions
are
available, for example, under the name AVD (Aqueous Vermiculite Dispersion),
inter alia
as fire extinguishing agents. The layer of phyllosilicates protecting against
oxidation can
be anchored in the structured surface of the reinforcement with a form fit.
For this
purpose, for example, the phyllosilicate applied in the form of an aqueous
suspension can
form a structure that engages with the structure on the surface of the thread-
like
structure or the carbon fibres and thus ensures an intimate connection between
the
thread-like structure or the carbon fibres and the layer protecting against
oxidation. For
example, after it has been produced from the thread-like structure of carbon
fibres, the
reinforcement can be soaked in an aqueous suspension of phyllosilicate in an
immersion
bath, so that a separate layer protecting against oxidation is formed on and
around the
reinforcement (i.e. the outer surfaces of the reinforcement).
Optionally, an adhesive layer can also be used in addition, which ensures a
chemical
bond between the thread-like structure and the layer protecting against
oxidation, such
as the phyllosilicate. Both direct chemical bonds between the carbon fibres of
the layer
protecting against oxidation, such as the phyllosilicate, and chemical bonds
between the
finishing agent on the carbon fibres and the layer protecting against
oxidation are
conceivable. If epoxy resins are used as finishing agents, organically
functionalized silanes
with amino or epoxy groups can be used for the adhesive layer, which can form
a chemical
CA 03166240 2022- 7- 27
15
bond with the epoxy resin using their organic ends, while the silane groups
form a
chemical bond with the layer protecting against oxidation, such as, for
example, the
phyllosilicate. Possible products are, for example, (Dynasylan SIVO 110 and
Dynasylan
HYDROSIL 2776, both available from Evonik AG, Essen). Organically
functionalized silanes
mediate a chemical bond between the finishing agent (particularly epoxy resin)
on the
carbon fibre on the one hand and the phyllosilicate on the other hand. The
adhesive layer
is preferably applied to the reinforcement, that is, the thread-like structure
made of
interlaced, intertwined, twisted or cabled carbon fibres has the adhesive
layer. In another
embodiment, however, it is also conceivable for the carbon fibres to have the
adhesive
layer prior to the production of the thread-like structure. If an adhesive
layer is used, the
adhesive layer makes up less than 3 wt.%, preferably less than 2 wt.% and even
more
preferably less than 1.5 wt.%, even more preferably still less than 1 wt.%,
based on the
total weight of the reinforcement in all embodiments.
In an embodiment, the phyllosilicate layer has a maximum thickness of 200 p.m.
In
an embodiment, the phyllosilicate layer has a maximum thickness of 150 p.m. In
an
embodiment, the phyllosilicate layer has a maximum thickness of 100 p.m. In an
embodiment, the phyllosilicate layer has a maximum thickness of 75 p.m. In an
embodiment, the phyllosilicate layer has a maximum thickness of 50 p.m. In an
embodiment, the phyllosilicate layer has a maximum thickness of 40 p.m. In an
embodiment, the phyllosilicate layer has a maximum thickness of 30 p.m. In an
embodiment, the phyllosilicate layer has a maximum thickness of 20 p.m. In an
embodiment, the phyllosilicate layer has a maximum thickness of 10 p.m.
The phyllosilicate layer can be of uniform or non-uniform thickness on and
around
the reinforcement.
In all embodiments of the textile reinforcement, the proportion of organic
substances in all of the layers that are not reversibly and directly or
indirectly (via a layer)
connected to the reinforcement is preferably less than 5 wt.% based on the
total weight
of the textile reinforcement, wherein the thread-like structure made of carbon
fibres is
not counted as a layer. This means that even if the reinforcement has fibres
with a sizing
(matrix), a separate layer protecting against oxidation, an adhesive layer and
another
protective layer that is not reversibly connected to the reinforcement, the
reinforcement
has less than 5 wt.% of organic substances in total, related to the total
weight of the textile
reinforcement.
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16
The present application also relates to a concrete construction part that has
a
reinforcement according to the present application. In an embodiment, the
textile
reinforcement is embedded in the concrete construction part in such a way that
it has a
concrete cover of at most 10 millimetres. The concrete cover is understood to
mean the
thickness of the concrete layer that is located at least between the concrete
surface and
the surface of the textile reinforcement. In an embodiment, the reinforcement
in the
concrete part has a concrete cover of at most 15 millimetres. In an
embodiment, the
reinforcement in the concrete part has a concrete cover of at most 20
millimetres. In an
embodiment, the reinforcement in the concrete part has a concrete cover of at
most 25
millimetres. In an embodiment, the reinforcement in the concrete part has a
concrete
cover of at most 30 millimetres. In an embodiment, the reinforcement in the
concrete
part has a concrete cover of at most 35 millimetres. In an embodiment, the
reinforcement
in the concrete part has a concrete cover of at most 40 millimetres. In an
embodiment,
the reinforcement in the concrete part has a concrete cover of at most 45
millimetres. In
an embodiment, the reinforcement in the concrete part has a concrete cover of
at most
50 millimetres. In an embodiment, the concrete cover of the textile
reinforcement is lower
than the concrete cover of a comparable steel reinforcement with the same
mechanical
properties, which means a significant weight advantage. The concrete cover of
the textile
reinforcement makes a decisive contribution to the fire resistance of the
textile
reinforcement due to its heat-insulating and oxygen-protecting effect.
The concrete cover of the textile reinforcement can be designed in interaction
with
the composition and the layer thickness of the layer protecting against
oxidation in such
a way that a desired fire resistance class is achieved.
The invention is described in more detail based on tests and figures, which
should
be understood as not limiting the general spirit of the invention.
Figure 1
represents a comparison of the tensile strength of carbon fibre yarns
with a solid matrix resin proportion as a function of their intertwining
(t/m).
Figure 2
shows the influence of a vermiculite coating on the temperature
resistance of carbon fibres.
Figure 3 shows the basic structure of a single-thread coating facility
Figure 4
shows the schematic diagram of a coating eyelet (on the right side in
the cross-section)
Figure 5 shows the schematic diagram of a winding board
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17
Figure 6 shows a heating curve of a muffle furnace for
the yarn specimens
Figure 7 shows a target position of yarn strands for
example 3
Figure 8 shows the installed yarn strands for example 3
Figure 9 shows a test setup (rotated) for example 3
Figure 10 schematically shows a textile reinforcement that is embedded in
concrete.
Figures 7 to 9 originate from the reports of the TU Dortmund/WdB.
Example 1
In the present example 1 it is to be explained how the tensile strength of
thread-
like structures changes as a function of their consolidation. The thread-like
structures to
be tested are carbon fibre yarns of the type STS40 F13 24K from the company
Teijin
Carbon Europe with 1600 tex and 1% polyurethane coating as matrix resin
proportion. An
STS40 E23 24K yarn from the company Teijin Carbon Europe, which was thoroughly
impregnated with 39 wt.% of epoxy-based matrix resin, is selected as the
comparison
yarn.
The comparison yarn was impregnated with the following resin mixture:
Epicote 828: 100 parts
Epicure 113: 30 parts
Acetone: 15 parts
Specimen preparation:
For the tensile test and determination of the data, yarn specimens are
provided
with 50 mm long cardboard strips, which are used to introduce a force at the
test device.
For this purpose, a two-component adhesive is used which, after curing,
completely
encloses the specimens in the area of a cardboard strip and there are no air
pockets.
Adhesive formulation: AW 106 100 weight proportion
HV 953 80 weight proportion
A pot life of 45 minutes is referred to.
To prepare yarn tension test specimens, two cardboard strips, which are
aligned
parallel to one another using a 200 mm wide template, are firmly glued to a
glass plate
CA 03166240 2022- 7- 27
18
covered with PTFE glass using polyester adhesive tape. In order to ensure an
even
adhesive film between the cardboard strips and test specimens, these are
applied in
advance using a drawing body (which is to be selected depending on the yarn
count).
The specimens are now to be placed along the marking lines and to be fixed
with
polyester adhesive tape. It is important to ensure that there is parallelism
between the
individual test specimens. The upper cardboard strips (provided with clear
labelling),
which are also provided with an adhesive film, are placed and fixed on these.
On top of
that comes a layer of PTFE glass fabric, which is weighed down with a second
glass plate.
This setup is left in a preheated forced air oven at 70 C for one hour. After
cooling
of the yarn tension test specimens, they are to be cut with a band saw along
the outer
edges and along the provided dividing lines.
Measurement:
The specimens are stored prior to the measurement in the test room climate at
23 C/50% rel. humidity for at least 24 hours.
A tensile test using an extensometer is carried out on the impregnated carbon
fibre
strand, which is provided with force introduction elements on both sides
(cardboard glue-
on).
Device:
=Tensile/compression testing machine with a constant test speed that can be
set
with an accuracy of < 1% in the range of 0 <v 20 mm/min
=Calibrated force transducer with suitable force measuring range according to
DIN
EN ISO 7500-1
=Calibrated path measuring system with suitable path measuring range DIN EN
ISO
9531
=Extensometer (211 mm)
Test condition:
Standard atmosphere for testing impregnated yarn tension specimens, i.e. 23 C
2 and 50% 5 relative humidity.
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19
Test parameters:
Test speed: 5 mm/min
Free clamping length: 200 mm
Preload: 2 cN/tex
Measuring length probe: 100 mm
Start modulus of elasticity: 40 cN/tex
End modulus of elasticity: 80 cN/tex
Carrying out the test:
The test is carried out as follows:
The tension clamps are installed in the material testing machine (MPM),
aligned
centrically and the required clamping length between the tension clamps is set
as
specified in the required standard or specification. The specimen stops are
then set in
such a way that the specimens are loaded centrally in the MPM. During
clamping, it needs
to be ensured that the specimens are clamped perpendicular to the clamping
jaws.
Before the start of the test, the zero point of the force channel is
approached.
During the test, the testing machine drives until a fracture occurs or until
the specified
force or length change value is reached while recording the measured values.
After the
testing operation is completed, the fracture pattern is entered and the
measurement data
are saved. The specimen is removed from the test space and the device as well
as the
clamps are cleaned. In order to ensure clear traceability of the test
specimens even after
the test, the test specimen numbering is checked and, if necessary, renewed on
both
sides. The traverse of the MPM is returned to the starting position and the
next specimen
can be tested. According to this method, six tests are carried out per
specimen.
Determination of the tensile strength GB:
F
frI3s.
A F
CTEI = [NUM in2]
GB = tensile strength in N/mm2
F max = maximum tensile force in N
AF = yarn cross-sectional area in mm2
CA 03166240 2022- 7- 27
20
The yarn cross-sectional area is calculated as follows:
Tt
AF= P ' 1 ' [MM2]
AF = yarn cross-sectional area in mm2
Tt = yarn count in tex
p = yarn density in g/cm3
Yarn count and yarn density were taken from the yarn data sheets and were not
additionally determined by measurement.
Elongation at maximum force:
'LLFmax x100
EB [V0]
Lo
LB = relative change in length in %
AL = absolute change in length at maximum force in
mm
/0 = measuring length of the extensometer in mm
Modulus of elasticity:
AF x io3
E=p x-xL [N /mm]
Tc Ad
E = modulus of elasticity in N/mm2
p = yarn density in g/cm2
AF = specified force difference in N
Tt = yarn count in tex
/0 = measuring length of the extensometer in mm
A/ = length difference of the specified force
difference in mm
Results:
The results are represented graphically in Figure 1.
In Figure 1, the tensile strength in MPa is represented as a function of the
intertwining of the yarns in t/m. As also described above, the first four
specimens have 1
CA 03166240 2022- 7- 27
21
wt.% of matrix resin. The final comparative specimen is a STS40 E23 24K carbon
fibre yarn
from the company Teijin Carbon Europe with1600 tex that was thoroughly
impregnated
with an epoxy-based resin material. The resin proportion in the yarn was 39
wt.%. The
first specimen has no twisting or intertwining with OZ and reaches a tensile
strength of
1955 M Pa. With increasing twisting or intertwining, it can be seen that the
tensile strength
increases despite the same proportion of matrix resin in the fibres. With a
twisting of 15Z,
i.e. 15 t/m, rotated to the right, a tensile strength of 2309 M Pa is
achieved. There is thus
an increase of around 18%, which can be attributed to the twisting or
intertwining of the
yarn. It is assumed that by intertwining, interlacing or twisting the carbon
fibres to form
the thread-like structure a cohesion of the filaments among each other can be
effected
similarly to the one that could be obtained by impregnation of the fibres. Due
to the
cohesion of the filaments among each other, the thread-like structure then
achieves good
tensile strengths. However, due to the very low matrix proportion of the
thread-like
structure, the material is particularly suitable for use as fire-resistant
reinforcement. As
already mentioned, high temperatures, such as those that occur in a fire, can
decompose
the matrix resin under gas formation. In the process, the cohesion of the
filaments among
each other is lost and the concrete construction part can burst. As a result,
the
construction part fails. With a matrix content of at most or below 5 wt.%, it
can be
assumed that the gas formation is not sufficient to cause damage to the
construction part.
In an advantageous manner, good tensile strength of the textile reinforcement
with good
fire resistance at the same time is thus achieved.
Example 2
In example 2, the temperature resistance of carbon fibres is examined as a
function
of a vermiculite coating. The vermiculite coating represents an embodiment for
the
separate layer protecting against oxidation. The coating of the carbon fibre
is comparable
to a coating of a reinforcement, since in general the improvement of the heat
resistance
of the fibres from which the reinforcement is constructed can be shown by the
coating.
Material:
- STS40 E23 24K 1600tex, 5Z
- Vermiculite dispersion (AVD, manufacturer: Dupre Minerals Ltd., GB)
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22
- Single thread coating facility (unwinding stand with run-off spindle and
brake
for setting the thread tension, beaker bath for resin impregnation with
adjustable beaker
holder and base plate for attaching the rolls (Fig. 3) and coating eyelets
(Fig. 4))
- Winding board (Fig. 5)
- Drying cabinet with a temperature range up to at least 150 C
- Yarn shears
- Steel blade
- Plastic cutting board
- Plastic hammer
- Alsint dishes (H x Lx W: 15 mm x 200 mm x 15 mm)
- Muffle furnace with a temperature range up to at least 1000 C
- Scale with an accuracy of 0.001 g
Carrying out:
The bobbin with the intertwined thread is mounted on the unwinding stand. The
yarn is guided through a beaker bath with coating dispersion to the eyelet via
rollers that
are easy to dismantle and clean (Fig. 3). The eyelet (Fig. 4) strips the
excess dispersion
from the yarn. The drive is manual by winding the yarn after the eyelet on a
winding board
(Fig. 5). A yarn brake keeps the yarn under slight tension when it is pulled
off manually. In
this way the yarn is continuously coated. The vermiculite coating achieved is
indicated in
Table 1.
Table 1
Vermiculite bath Eyelet diameter Achieved vermiculite
concentration [%] [mm] content [%]
0 none 0
5 2.6 3.7
12 3.0 13
For each specimen, four pieces of yarn, each 16 cm, are placed in an Alsint
dish
(pure CF weight approx. 1 g) and placed in a muffle furnace at room
temperature. The
furnace is heated to 900 C, the dishes are removed immediately when this
temperature
is reached and placed on a bed of sand for cooling. When the specimens have
cooled back
to room temperature, the total mass loss is determined by back-weighing. This
is
CA 03166240 2022- 7- 27
23
converted to the mass loss of the carbon fibre. At least one duplicate
determination is
carried out.
Figure 2 represents the result of example 2.
In the case of a yarn without a vermiculite coating as a layer protecting
against
oxidation, the average mass loss is about 68 wt.%. In the case of a yarn with
a 3.7 wt.%
vermiculite coating as the layer protecting against oxidation, the average
mass loss was
reduced by about 11 wt.% and was still about 56 wt.%. In the case of a
vermiculite coating
of the carbon fibres with 13 wt.%, the average mass loss was about 30 wt.%, so
that
compared to the uncoated carbon fibre yarn, even a mass loss reduction by more
than 50
wt.% was achieved. Thus, example 2 shows that a separate coating with a layer
protecting
against oxidation can also protect the carbon fibres at high temperatures, so
that the
carbon fibres remain temperature-resistant even in the presence of oxygen. A
reinforcement that has such a separate layer protecting against oxidation thus
retains its
reinforcing properties even in the event of a fire, so that the construction
part with the
reinforcement does not fail or fails at a later point in time even in the
event of a fire.
Example 3
In example 3, a stretch body test was carried out. The fibre specimens P11 and
P12
(specimen details can be found in Table 2) were embedded in concrete and the
maximum
load was determined by means of a tensile test.
Specimen preparation:
After delivery, the yarn strands were stored dry at room climate until
concreting.
The expansion body specimens with the dimensions 800x60x15 mm3 were prepared
in
plastic moulds. Four test specimens were prepared standing (standing height 60
mm) for
each yarn type. Each specimen contained eight strands of yarn. The target
position of the
yarn strands can be seen in Figure 7.
The specimens were prepared on three consecutive days with two sets of
specimens each. Four individual specimens were prepared with one set of
specimens.
First, the strands of yarn were fixed in the mould by means of springs with a
slight pre-
tension. For fixing, the yarn strands were bent at their ends and fastened
with cable ties
and superglue. Figure 8 shows the installed strands of yarn.
CA 03166240 2022- 7- 27
24
Ready-mixed fine concrete with a maximum grain size of 1 mm was used as the
concrete (compressive strength > 60 N/mm2). The dry mixture was homogenized
for all
concreting and then filled for the individual concreting. The dry mixture was
mixed in a
bucket mixer with an automatic timer according to the manufacturer's
instructions. After
the mixing process, two moulds per concreting were poured in less than 30
minutes under
constant shaking. The test specimens were then stored covered at room climate
for 20-
24 hours until they were removed from the mould. After being removed from the
mould,
the specimens were stored in a climatic cabinet at 20 C and > 95% rel.
humidity for a
maximum of six days. Finally, they were stored at 22 C and 65% rel. humidity
up to the
test.
Test of the expansion body specimens:
The test of the expansion body specimens took place 13 or 14 days after the
preparation. The tests were performed with a universal testing machine
equipped with a
class 1 load cell with a maximum load of 50 kN (calibrated in December 2020).
For the
test, the specimens were clamped in bolted steel straps over a length of 250
mm each.
The steel straps are provided with compensating layers to compensate for
surface
inaccuracies and for secure adhesion of the specimen in the clamping area. The
connection of the clamping jaws to the testing machine was realized via ball
joint heads.
The test setup is represented (rotated) in Figure 9.
Prior to the test, the test specimens were measured with regard to their
geometric
properties. For this purpose, the specimen width (nominal size 60 mm) and the
specimen
thickness (nominal size 15 mm) were determined in the area of the free stretch
length at
the top, middle and bottom. The measured values were within the usual
tolerances. After
installing the specimen, the force was tared to zero with the specimen
suspended. The
weight of the specimen and the lower clamp construction was approx. 65 N. The
specimen
was then manually brought to a preload of < 150 N and the test started. The
approach
speed of the testing machine was 0.5 mm/min and the subsequent testing speed
was 1
mm/min. If the force dropped by > 90%, the test was automatically stopped.
During the
test, the machine path (traverse path) and the force were recorded at a
measuring rate
of 50 Hz.
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25
Results:
Table 2:
Mean
Averaged
Fibre Specimen Date of Maximum load
Average Load at first Number of Crack mean crack
type Yarn type Turns Vermiculite name preparation Test date Age
Fmax value Fmax crack cracks distance distance Mode of
failure
[MX] [d] [N]
[mm]
PU-A 3496 3920 1
300 Pull-out failure
STS40 F13
P11-B 3244 3519 1
300 Pull-out failure
PU 24K 5 0 3543 __________________________________________
300
PU-C 3588 3783 1
300 Pull-out failure
1600tex
P11-D 3844 3482 1
300 Pull-out failure
21.02.2021 03.02.2021 13
P12-1 4820 2712 2
150 Pull-out failure
STS40 F13
P12-2 5212 3690 3
100 Pull-out failure
P12 24K 30 0 4980 __________________________________________
138
P12-3 4762 3924 2
150 Pull-out failure
1600tex
P12-4 5127 3433 2
150 Pull-out failure
During the test, the number of cracks was determined in the completed crack
pattern and recorded. Cracks near the jaw exits were counted, even if they
were
positioned slightly within the jaws. The mean values indicated (arithmetic
mean) relate to
4 individual results in each case. The maximum force was determined after the
first crack.
The mean crack spacing (e) was determined as follows: e= LO/number of cracks
with LO =
free expansion length = 300 mm.
In contrast to example 1, it can thus be demonstrated that the intertwined
fibres
have good tensile strength even when embedded in concrete without matrix
impregnation. Furthermore, this example proved that the intertwining of the
fibre
specimens also embedded in concrete surprisingly has an influence on the
tensile
strength. The maximum load of the fibre specimen with only 5 turns per meter
is on
average a little less than 30% lower than the average maximum load of the same
fibre
specimen with only 30 turns per meter. The intertwining of the fibres is
therefore
surprisingly suitable for increasing the intimate connection of the fibres
among each
other, even without matrix material, and thus for improving the tensile
strength of the
entire composite. The results are represented in Table 2.
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