Textile Reinforced Concrete

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					            Textile Reinforced Concrete – A New Material for Restoration
                           and Strengthening of Structures


Markus Schierz, Thomas Engler, Gerd Franzke, Peter Offermann
Institute of Textile and Clothing Technology
Manfred Curbach, Rainer Hempel
Institute of Structures and Materials
Dresden University of Technology



Abstract
In civil engineering composite materials are used in order to combine the advantages of the individual
materials with one another. Reinforced concrete is the most successful example of this. There are
always attempts to develop other combinations of materials. For several decades, short fibres from, for
example, synthetic materials, steel or glass have been in use in concrete. Most recently it has been
with alkali resistant glass (AR-Glass). The use of textile reinforcement in civil engineering is a relatively
young area, that can be described as very innovative and that has a large potential for development.
This concerns not only the production of the new construction elements from textile reinforced con-
crete, but also the possibility of strengthening existing structures. Through the development of proc-
esses, through which endless fibres can be made into open textile structures, the potential of alterna-
tive reinforcement has significantly increased. The possibility exists today to make such endless fibres
into equal loading textile areas, which means that fibre materials can be orientated in the direction of
the loading.

Test methods for the stress-strain behaviour of filament yarns will be presented also for the characteri-
sation of the bearing capacity of concrete compound materials. The properties of the high-
performance threads place special requirements on the textile technical processing. Principally it is
necessary to maintain the high properties potential of the threads for the bonding element up to the
end product. The aim of this is a good processing of the material, which causes minimal damage to
the threads. It is also required to ensure the quality of the orientation and the thread distribution of the
course of the threads until in the finished textile.

An example of the subsequent reinforcement of existing building is the presented restoration concept
of concrete masts. The production of the textile reinforcement structures, with which the strengthening
of the poles against torsion and bending should be realized, is carried out by means of multi-axial sew-
ing technology. Through the use of these textiles, all appearing tensile stress directions in a concrete
pole with a circular cross-section are covered.

The potential of the innovative material in the manufacturing process of new components is shown by
means of a balustrade panel for parking garages. The aim of this development is to reduce the self-
weight by using alkali-resistant glass fibres. At the same time the possibilities of visible surface design
has to be enhanced.

Keywords: Reinforced concrete, textile reinforcement, alkali resistant glass fibre, sewing technology,
multi-axial textiles

1    Introduction

In civil engineering composite materials are used in order to combine the advantages of the individual
materials with one another. Reinforced concrete is the most successful example of this. There are
always attempts to develop other combinations of materials. For several decades, short fibres from, for
example, synthetic materials, steel or glass have been in use in concrete. Most recently it has been
with alkali resistant glass (AR-glass). The predominant basic milieu in concrete would destroy „normal“
glass in only a short time. As an alternative to AR-glass, carbon fibres can also be inserted. Carbon
has approximately double the load-bearing capacity, but is also about 3 to 4 times as expensive and
furthermore shows a poor bonding relationship with the concrete.
The use of textile reinforcement in civil engineering is a relatively young area, that can be described as
very innovative and that has a large potential for development. This concerns not only the production
of the new construction elements from textile reinforced concrete, but also the possibility of strength-
ening existing structures. Through the development of processes, through which endless fibres can be
made into open textile structures, the potential of alternative reinforcement has significantly increased.
The possibility exists today to make such endless fibres into equal loading textile areas, which means
that fibre materials can be orientated in the direction of the loading. With the use of alkali resistant
glass fibres the usual conditions of minimum wall thickness in reinforced concrete structures disap-
pears. In textile concrete, the concrete should absorb the stress and the textile reinforcement material
the tension, and the ductility for tension loading should increase as well.


2   Textile reinforcement materials
2.1  Determination of the tension-strain-relationship of filament yarns

As a basis for the investigation the international standard ISO 3341 is used for the determination of the
properties of AR-glass filament threads for the dry strength as well as for the wet strength. The main
differences of the standards from the present regulations in DIN 53834 are the higher test speed, the
different mounting lengths for normal and surrounding test holders, the uniform pre-stressing force, the
higher requirements on the construction of the clamps and the lower number of tests. The following
modifications of the experimental method are aimed for:

    -   avoidance of a time-consuming experiment preparation
    -   avoidance of clamp slipping and fracture
    -   reproducibility of the results
    -   direct measurement of strain

By use of the cable test holders, the tensile force on the thread before the clamping is reduced though
the friction finish on the radiussed clamp by about 1/3. Clamp slipping and fracture can therefore be
avoided.

For the determination of the strain the optical strain measurement is given preference, because the
mechanical variant due to a smaller measuring distance, which also does not record the breaking
place should it arise, leads to incorrect strain values. The used experimental order to the characteriza-
tion of the used filament threads is shown in Picture 1 /1/.

                                             radiussed clamp
                                                                 free gauge length




                                                  yarn
                                     ligth beam           mark




                                                         moving grip

Picture 1: Schematic portrayal of the experimental order for the filament threads

The experimental arrangement makes a quick carrying out of the experiment possible and guarantees,
in interaction with the chosen test conditions, assured characteristic values at the same time as higher
reproducibility (Picture 2).
                                                                  1500




                                                tension [N/mm²]
                                                                                mean-value curve
                                                                  1000



                                                                  500



                                                                       0
                                                                           0        0,5    1,0          1,5              2,0       2,5
                                                                                                                         strain [%]

Picture 2: Stress-strain curves of AR-glass filament threads (620 tex)



2.2       Determination of the load effect in the concrete bond

The force-deformation behaviour of a compound material cannot in general be derived from the force-
deformation behaviour of the individual basic materials, because the bond between the basic materials
takes on a significant role in the force-deformation behaviour. For the textile reinforced concrete no
work is known, that describes the properties of the bond between the fibres and the concrete suffi-
ciently, in order to make a forecast of the properties of the bonding materials possible. Under these
conditions it is necessary to investigate the properties of the bonding materials through a suitable ex-
perimental procedure and so as to gain the required information for the design and construction of
new construction members.

The force-deformation behaviour is investigated in a non-standard, single axial tension test on slice-
shaped test bodies as according to Picture 3. The abandonment of a profile of the test body in the load
application area offers crucial advantages for the production of the test body. In the longitudinal direc-
tion, the test body divides inwards into the load application area, the load distribution area and the
measurement area. Between the measurement area and the load application area, the load spreading
area is found. Here the load concentration should distribute in the load application area equally across
the cross-section and at the start of the measurement area should guarantee an equal loading over
the cross-section of the test body /2/.



                                          measuring lenght
                                                                                                    tension 




      A          F                                                              F     A                         fu /n
          100




                                                                                                                                                   ·V f
                                                                                                                                         n·E
                                                                                                                                               f


                      50   75      200 mm                         75       50
                                   450 mm
                                                                                                                x·mr                               Tension Stiffening
      A-A                                     concrete specimen                                                   mr
                F/2                                         F/2

                F/2                                                             F/2                                      fr1   fr2                      fmu fu
                inductive strain sensor     force introduction plats                                                                                             strain 


Picture 3: schematic portrayal of the test set-up                                                Picture 4: theoretical stress-strain line in the
for the single axial tension test                                                                single axial tension test

The behaviour of a textile reinforced concrete test body follows for a single tension loading no linear
elastic course, but 3 sections in the load-deformation curve are distinguishable (Picture 4). This test
method is also suitable for the investigation of textile structures. Through this, statements about the
loss of bearing capacity of the filament yarns due to the textile processing can be made.


3     Production of textile reinforcement structures
The properties of the high-performance threads place special requirements on the textile technical
processing. Principally it is necessary to maintain the high properties potential of the threads for the
bonding element up to the end product. The aim of this is a good processing of the material, which
causes minimal damage to the threads. It is also required to ensure the quality of the orientation and
the thread distribution of the course of the threads until in the finished textile.

In principle the strengthening fibres should be turned into the form of an open textile structure, with
which the fibres can be completely wrapped up by the concrete. The arrangement of the fibres is
therefore dependent not only on the biggest grain-size of the matrix and the necessary thread volume
content. It is also heavily determined by textile technical possibilities. The production of the reinforce-
ment structure follows on ITB predominantly on the basis of the sewing technology. The modern sew-
ing technology makes the production of several dimensional textile structure with desired property
profiles possible. For the production of textiles, there are three sewing machines available, which differ
essentially through the way of the entry of the strengthening threads. The following diagrams (Picture
5, Picture 6) show the newest sewing technology, which is available am ITB. The machines differ
heavily in their construction and in their technological possibilities. The main differences exist in

    -   the manner of the weft insertion and the type of stitching, as well as
    -   orientation of the weft layer.

The multi-axial sewing machine has four entry systems for the strengthening threads, whereby the
laying angle 0° (work direction) and 90° are fixed. The further thread system allows itself to be ar-
ranged infinitely variably in angles between ±45° und 90°. The parallel weft sewing machine has, in
contrast to the multi-axial sewing version, critical advantages for the production of biaxial structures.
Limited through the principal of the parallel weft store entry, the weft threads of the needles are not
pierced. Damage through piercing is therefore avoided. The weft thread stress is clearly and repro-
ducibly adjustable through the choice of the breaking force and the adjustment of the chain guidance.




Picture 5: Sewing machine, type Malimo, model           Picture 6: Sewing machine, type Malimo, model
14024 multi-axial                                       14022 parallel weft

In the example of the multi-axial technology, the textile technological border conditions for the model-
ling of the reinforcement structures are made clear (Picture 7). These arise from the available machine
delicacy, the convertible knitting construction as well as the variant of them, and the possible stitch row
thickness as well as the stitch length. Furthermore different weaving fibre materials can be used. The
arrangement and distribution of the strengthening fibres location is determined as well as by the ma-
chine or laying delicacy, also by the number, arrangement and orientation of the weft layer. With the
used chain fibre setting direction, a changeable fibre orientation during the production is realizable.
                       gauge of                     knit                angel of layer systems
                        knitting                construction             layer A: -45°...90°...+45°
                       machine                    pillar stitch,         layer B: -45°...90°...+45°
                      F 7, 12, 14 ...               tricot ...           layer C: 90°




                                                        A           B      C
                       stitch length                                    gauge of     6E, 7E, 10E ...
                                                 tension of               weft
                       0,5 mm - 5,0 mm
                                                knitting yarn           insertion
                                        .....
Picture 7: textile technological conditions

The multi-axial sewing machine offers the possibility to work with all binding, which are realizable with
a maximum rapport of 8 stitching rows and two weaving fibre systems. Additionally the possibility ex-
ists to use a transferable warp bar. Through the used binding, the properties of the textile structure are
heavily influenced. The tying up of the fibres, the intensity of the strengthening fibre connection, the
amount of the weaving fibre proportion and through that the covering of the strengthening fibres can
therefore vary in further boundaries. This on the other hand has influences on the manageability of the
structure, though also on its relaxation behaviour and so on the stress-strain behaviour of the textiles.

Two structures are shown below, which also have a use in the later-described applications (Picture 8,
Picture 9). Through the piercing of the textiles, it comes in the multi-axial technology produced struc-
tures, partially to the splitting and so widening and shifting of the weft threads. The reduced opening
widths are judged as deviation from the should-geometry. The bi-axial structure shows clearly that this
effect is avoidable through a weft insertion suitable for sewing (parallel thread sewing machine).




Picture 8: Multi-axial structure                               Picture 9: Bi-axial structure


4     Application of textile reinforcement
4.1    Restoration of concrete poles

The use of concrete poles in Germany is common. Poles serve as the above ground transfer medium
and are therefore an integral component of the infrastructure. Electricity poles in Bavaria, Germany,
that were made in the 20s, proved in 1989 that a high durability can be reached /5/. Unfortunately the
statement of the durability of concrete poles cannot be generalized without limitations. One assumes
for example nowadays that in Germany 40 % of the poles show signs of cracks for average stress
systems. Next to the external effects, for example overloading from the wind, forced forces can also
appear. The causes of this type of self stress in poles are moistness stresses, heat stresses, stresses
due to hydration heat during production and stresses due to different stiffness in the cross-section for
example. /6/. In Picture 10 and Picture 11, the cracks from forced stress are shown.
Picture 10: picture of crack (crack width < 2 mm)     Picture 11: picture of crack (crack width > 5 mm)


From an economical point of view it seems favourable to carry out renovation of damaged poles in-
stead of replacement. Experiences with preserved and renovated concrete poles confirm in every case
the expectation that considerable costs are cut with a restoration-style strategy compared with a new
construction, a replacement or a substitute through earth transfer. In comparison to known preserva-
tion and restoration processes, the concept developed at the TU Dresden therefore from the outset
aims at an additional increase in the of the bearing resistance of the poles.

The production of the textile reinforcement structures, with which the strengthening of the poles
against torsion and bending should be realized, is carried out by means of multi-axial sewing technol-
ogy. Through the use of these textiles (Picture 8), all appearing tensile stress directions in a concrete
pole with a circular cross-section are covered. The strengthening fibres in the longitudinal direction of
the structure accept the tension that exists though bending on the component surface area. The cross
fibres in the textile take the existing cross tension in the structure’s tensile zone and prevent in the
compressive zone of the cross-section the component of the longitudinal reinforcement. With torsion
on a circular cross-section, compressive and tensile stress exist on the surface area at an angle of
+45° or -45° to the longitudinal direction. The multi-axial textile fabric can bear all longitudinal forces
without any force deflection. The restoration of the stability is reached with the application of a shell
made from textile reinforced concrete over the whole pole length. 3 textile layers are therefore fitted
(Picture 12).

With the sheet concrete dispensing, which means the biggest grain size is about 1 millimetre, it is con-
cerned with a „glass fibre concrete of the second generation“. The use of microsilica and flying coal
ashes that is linked with this, has had an advantageous effect in view of the spraying behaviour. The
bulk density is about 2 t/m³. It allows a tensile bending strength of 5-6 N/mm² and compressive
strength of von 75-80 N/mm² to be reached.


     coilshaped steel               multiaxial warp
     reinforcement                   knitted fabric                              Water
                                                                              14,3 mass-%           Cement
                                                               Micro-Silica                       28,7 mass-%
                                            layer 1            5,4 mass-%
     steel beam                             layer 2
                                                            Coal flue ash
                                            layer 3         8,3 mass-%                                 Flow agent
                                                                                                       0,3 mass-%
     old concrete
                                                                                      Sand 0/1
     reinforcement layer                                                            43,0 mass-%
     (8 to 10 mm thick)


Picture 12: Strengthened pole cross-section             Picture 13: Sheet concrete dispensing

The application of textile reinforcement is carried out repeatedly in the liquid-liquid-process. The struc-
tures are applied repeatedly through wrapping (Picture 14) rather than plastered in strips (Picture 15).
By plastered poles, is the strengthened pole to be understood as one whose textile strengthening is
applied in long strips in the longitudinal direction of the pole. With wrapped poles the textile strength-
ening is applied in strips in a „bandaged“ style on the pole.




Picture 14: Wrapping                                    Picture 15: Plastering

The obtained higher loading ability is proved through load-bearing capacity tests on the un-
predamaged un-strengthened and strengthened original poles or pole fragments. The increased load-
bearing capacity is dependent on the used application technology. The plastered technology proves to
be advantageous. The bending tests give a load-bearing capacity increase of about 30%, with a 3
layer plastering strengthening with a layer thickness of in total 1 cm (Picture 16, Picture 17). In the
torsion tests a maximal load increase of about 60% is reached with the same strengthening. With the
bending tests, an improvement in the deformation behaviour in addition to the increase in the load-
bearing capacity is also established.

                                                                          150
                                                             force [kN]


                                                                                    wallpapering, 5 layer
                                                                          120
                                                                                                              wall-
                                                                                                          papering
                                                                                                        winding
                                                                           90

                                                                           60                      non-reinforced

                                                                          30


                                                                            0
                                                                                0     -20       -40         -60     -80
                                                                                                       strain [mm]
Picture 16: 3-point bending test                        Picture 17: Displacement diagram for strength-
                                                        ened and un-strengthened poles

In summary it can be shown that an additional increase in the load-bearing capacity of the concrete
poles is transferable through textile reinforced concrete. The strengthening demonstrated in the exam-
ple of the poles, offers an economical renovation possibility of long-term preservation of existing build-
ing substances and is applicable to many different building works.

4.2   Textile reinforced balustrade elements

Multi-storey car parks will increasingly be found in the near future in our town centres. The growing
private transport with cars makes this necessary. A large hindrance for the building of multi-storey car
parks in town centre areas is however their unsatisfactory architectural form. The design of buildings is
largely made under functional as well as economic aspects. It accordingly falls back on economical
prefabricated building construction for the structural transfer.

Normal reinforced concrete elements with dimensions of about 1.5 m x 2.5 m have thickness of about
100 mm. The slab thickness result from, amongst other things, the requirements for protection against
corrosion for the steel reinforcement and lead to relatively heavy and therefore cost-intensive ele-
ments, that can only be limitedly creative in their form with justifiable expenditure. The aim is therefore
to bring about a reduction of the construction element dimensions and the dead weight of the prefabri-
cated unit through the use of alkali resistant glass fibres. At the same time can the possibilities of the
form of the exposed areas be widened.

The textile reinforced balustrade elements are indicated though that no changes to the suspension of
the element from the normal reinforced concrete elements are made. That means that the present
construction parts can remain unchanged. Additionally the integration of protection against collision is
provided for. It appears that the geometry of the balustrade slabs or their formability is determined
mainly through the construction parts (Picture 18). The volume of the developed elements is merely
0.13 m³. Im comparison to the original construction part that has a volume of 0.38 m³, a saving of
about 66 % is made.

                                                   100      100




                                                                                            wind tension


                                                                                                                wind stess
                                                          90      90
                  Moun-




                                            1510
    1 10           ting
                   part
           1 10
                                                                               1 10

                   2490                                                               outside                                inside
                                                         Reinforcing textile

                                       a)                                                                  b)
Picture 18: schematic portrayal of a textile reinforced balustrade element a); Loading diagram b)

The balustrade slabs of multi-storey car parks are mainly wind loaded. Because multi-storey car parks
are open structures, wind tension and wind stress act at the same time (Picture 18b). Perpendicular to
the wind-loading acts the dead load of the balustrade element too. Additionally it should withstand a
line load of 2 kN/m, caused by a possible vehicle collision, at a height 0.5 m over the top edge of the
floor. As reinforcement textile, sewn biaxial textiles are used. For the two-axial slab stressed compo-
nent a biaxial reinforcement is sufficient. Beyond this the good drapability of these textiles prove to be
advantageous by the chosen slab geometry. Under economic considerations the use of bi-axial sew-
ing for the reinforcement of the investigated component variations is also advantageous. To stabilize
and to take the dead load of the slab, a circling steel reinforcement is incorporated.

With the dispensing development of the fine grain concrete, conventional mixtures from the glass fibre
industry cannot be falled back on. Reasons for this include that the required early strength to limit the
residence time in the form and the safety of an unproblematic surface treatment of the exposed con-
crete. The dispensing of the base course ist based therefore on Portland cement with the addition of
microsilica. In order to make bringing a textile reinforcement in the facing layer of the structural section
possible, it is necessary to also reduce the chosen dispensing for the facing view concrete in its big-
gest sized grain.

For the production of the structural section is a tipping table from GOLDBECK BAU GmbH used, on
which the production of the element is carried out. The structural part as well as the textile reinforce-
ment can be positioned exactly in the made negative form (Picture 19, Picture 20).




Picture 19: bringing in of the sheet concrete layer         Picture 20: textile reinforced balustrade element
over the textile reinforcement

To investigate the bearing behaviour, textile reinforced slabs with dimensions of 1.5 x 2.5 m are
loaded laterally and with bending (Picture 21, Picture 22). With the help of tests, the behaviour of the
element against wind-loading is simulated. The test results show that large-sized concrete prefabri-
cated units can be reinforced satisfactorily with textile structures. So for the developed balustrade
element is the full load-bearing capacity as well as a decreased durability proven.

                                                                                                15




                                                                       cylindrical force [kN]
                                                                                                12

                                                                                                 9

                                                                                                 6

                                                                                                3

                                                                                                0
                                                                                                     0   9   18   27     36    45
                                                                                                              mid-deflection [mm]
Picture 21: experiment set-up with 3 point load en-              Picture 22: force-deflection behaviour of a balus-
try                                                              trade element

The economic advantage of the textile concrete element is seen in the exploitation of the limited load
reserves through the lower dead load. Through the new textile reinforced balustrade elements are
reduced transport and erection costs, reduced construction of bearing systems or components as well
as better possibilities for facade form (profiling) expected. Lastly the prospect of a better acceptance of
future multi-storey car parks opens up at the same time.


5     Conclusion

In conclusion it can be established that renovation tasks as well as the production of new structural
components can be converted through textile reinforced concrete. The strengthening demonstrated in
the example of the concrete masts offers an economical renovation possibility to the long-term preser-
vation of existing building substances. The simple use of the developed process for bent sections as
well as for straight sections with different loading directions but also the perspective use possibilities
for new building parts, that follow from this, confirm the expectations of the new building material. The
reduced dead load of the balustrade elements makes a lower dimensioning of suspended elements
possible. At the same time the transport and installation requirements for the structural parts improve.


6     Note of thanks

The above mentioned research office thank the Deutschen Forschungsgemeinschaft (DFG) for the
financial support of the research plans SFB 528 as well as the research committee Textil e. V. for the
financial support of the research plans AiF-Nr. 11981 B and AiF-Nr. 4 ZBR/2 that resulted from the
budgetary funds of the government ministry for the economy via a subsidy of the association of indus-
trial research organisation ”Otto von Guericke” e. V. (AiF).


7     Literature

/1/   Franzke, G.; Offermann, P.; Engler, Th.; Abdkadar, A.; Schierz, M.: Erkenntnisse zur Kennwertermittlung, geometrischen
      Modellierung und Fertigung textiler Bewehrungsstrukturen : 1. Fachkolloquium der Sonderforschungsbereiche 528 und
      532. - Aachen, Feb. 2001, Tagungsband S. 71-82

/2/   Curbach, M.; Jesse, F.: Grundlegende Zugversuche an Dehnkörpern aus textilbewehrtem Beton: Techtextil Symposium
      1999. - Frankfurt/ Main, 1999, Vortrag 513

/3/   Wommelsdorf, O.: Stahlbetonbau. Bemessung und Konstruktion. Teil 1: Biegebeanspruchte Bauteile: 5. Aufl. Werner-
      Ingenieur-Texte Band 15. Düsseldorf : Werner-Verlag, 1982

/4/   Schierz, M.; Waldmann, M.; Offermann, P.: Neuartiges Konzept einer Schussfadentransporteinrichtung für offene
      Multiaxialstrukturen hoher Gelegequalität: Kettenwirkpraxis – Obertshausen. Jg. 36 (2002), Heft 01, Seite 31-33

/5/   Vereinigung Deutscher Elektrizitätswerke – VDEW – E.V.: Der Schleuderbetonmast im Freileitungsbau. Bericht über
      Betriebserfahrung, Ursachen und Erscheinungsformen von Schäden, Verfahren für deren Behandlung sowie Folgerung
      für Bemessung und Fertigung. Frankfurt am Main: VWEW-Verlag, 1989
/6/   Körner, Chr.; Richter, T.: Ringspannungszustand infolge Zwang im Herstellungs- und Nutzungszustand von
      Spannbetonmasten mit inhomogenem Kreisringquerschnitt. Bauplanung - Bautechnik. 44. Jg., Heft 4, April 1990, Seite
      170-175


Contact Information

Dipl. Ing. Markus Schierz
Institute of Textile and Clothing Technology
Department of Mechanical Engineering
University of Technology Dresden
Dresden, 01062 Germany
Phone: (+49) 351 463 34795, Fax: (+49) 351 463 34026
e-Mail: schierz@itb.mw.tu-dresden.de

				
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