REINFORCEMENT CONTAINING CARBON FIBERS

Abstract

A textile reinforcement for integrating into concrete, having carbon fibers. The reinforcement is coated with a layer which protects against oxidation, wherein the carbon fibers are provided in the form of an interlaced, twisted, or cabled thread structure and have 5 wt. % of matrix resin, and the layer which protects against oxidation is a separate layer and can produce a chemical bond to a component of the concrete. The invention additionally relates to a concrete part which has a textile reinforcement.

Claims

1. A textile reinforcement for embedding in concrete, having carbon fibers, wherein the reinforcement is coated with a layer protecting against oxidation, wherein the carbon fibers are present as an interlaced, intertwined, twisted or cabled thread-like structure and have a maximum of 5 wt. % of a matrix resin, the layer protecting against oxidation forms a separate layer and can produce a chemical bond to a component of concrete.

2. The textile reinforcement according to claim 1, wherein the textile reinforcement has at least one further thread-like structure.

3. The textile reinforcement according to claim 2, wherein the further thread-like structure can contain carbon fibers, aramide fibers, polyamide fibers, AR glass fibers, polypropylene fibers, polyvinyl alcohol fibers, oxidized, infusible polyacrylonitrile fibers, polyester fibers and/or a mixture of the fiber types mentioned.

4. The textile reinforcement according to claim 1, wherein the thread-like structure has a structured surface.

5. The textile reinforcement according to claim 1, wherein the layer protecting against oxidation consists of at least 80 wt. % of inorganic material.

6. The textile reinforcement according to claim 1, wherein the layer protecting against oxidation contains at least 5 wt. % of silicon.

7. The textile reinforcement according to claim 6, wherein the layer protecting against oxidation contains silanol groups on its surface.

8. The textile reinforcement according to claim 6, wherein the layer protecting against oxidation consists of at least 30% of silicon dioxide.

9. The textile reinforcement according to claim 1, wherein the layer protecting against oxidation contains a phyllosilicate.

10. Textile reinforcement according to claim 9, wherein the phyllosilicate is vermiculite.

11. The textile reinforcement according to claim 1, wherein there is an adhesive layer between the carbon fibers and the layer protecting against oxidation.

12. The textile reinforcement according to claim 11, wherein the adhesive layer contains organically functionalized silanes.

13. The textile reinforcement according to claim 1, wherein the textile reinforcement has a protective layer.

14. A concrete construction part, having a textile reinforcement according to claim 1.

15. The concrete construction part according to claim 14, wherein the textile reinforcement has at most one concrete cover of 50 mm and has a fire resistance class of at least R 60.

Description

[0047] 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.

[0048] FIG. 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).

[0049] FIG. 2 shows the influence of a vermiculite coating on the temperature resistance of carbon fibres.

[0050] FIG. 3 shows the basic structure of a single-thread coating facility

[0051] FIG. 4 shows the schematic diagram of a coating eyelet (on the right side in the cross-section)

[0052] FIG. 5 shows the schematic diagram of a winding board

[0053] FIG. 6 shows a heating curve of a muffle furnace for the yarn specimens

[0054] FIG. 7 shows a target position of yarn strands for example 3

[0055] FIG. 8 shows the installed yarn strands for example 3

[0056] FIG. 9 shows a test setup (rotated) for example 3

[0057] FIG. 10 schematically shows a textile reinforcement that is embedded in concrete.

[0058] FIGS. 7 to 9 originate from the reports of the TU Dortmund/WdB.

EXAMPLE 1

[0059] 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.

[0060] The comparison yarn was impregnated with the following resin mixture:

[0061] Epicote 828: 100 parts

[0062] Epicure 113: 30 parts

[0063] Acetone: 15 parts

[0064] Specimen Preparation:

[0065] 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.

[0066] 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.

[0067] Adhesive formulation: AW 106 100 weight proportion [0068] HV 953 80 weight proportion

[0069] A pot life of 45 minutes is referred to.

[0070] 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 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).

[0071] 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.

[0072] 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.

[0073] Measurement:

[0074] The specimens are stored prior to the measurement in the test room climate at 23° C./50% rel. humidity for at least 24 hours.

[0075] 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).

[0076] Device: [0077] 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 [0078] Calibrated force transducer with suitable force measuring range according to DIN EN ISO 7500-1 [0079] Calibrated path measuring system with suitable path measuring range DIN EN ISO 9531 [0080] Extensometer (211 mm)

[0081] Test Condition:

[0082] Standard atmosphere for testing impregnated yarn tension specimens, i.e. 23° C.±2 and 50%±5 relative humidity.

[0083] Test Parameters:

[0084] Test speed: 5 mm/min

[0085] Free clamping length: 200 mm

[0086] Preload: 2 cN/tex

[0087] Measuring length probe: 100 mm

[0088] Start modulus of elasticity: 40 cN/tex

[0089] End modulus of elasticity: 80 cN/tex

[0090] Carrying Out the Test:

[0091] The test is carried out as follows:

[0092] 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.

[0093] 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.

[0094] Determination of the Tensile Strength σ.sub.B:

[00001]${\sigma }_B=\frac{F_{\max }}{A_F}\left[N/{\mathrm{mm}}^2\right]$

[0095] σ.sub.B=tensile strength in N/mm.sup.2

[0096] F.sub.max=maximum tensile force in N

[0097] AF=yarn cross-sectional area in mm.sup.2

[0098] The yarn cross-sectional area is calculated as follows:

[00002]$A_F=\frac{T_t}{p.Math.\text{?}}\left[{\mathrm{mm}}^2\right]$$\text{?}\text{indicates text missing or illegible when filed}$

[0099] AF=yarn cross-sectional area in mm.sup.2

[0100] T.sub.t=yarn count in tex

[0101] ρ=yarn density in g/cm.sup.3

[0102] Yarn count and yarn density were taken from the yarn data sheets and were not additionally determined by measurement.

[0103] Elongation at Maximum Force:

[00003]$\text{?}=\frac{\Delta L_{\mathrm{Fmax}\times 100}}{L_0}\left[\%\right]$$\text{?}\text{indicates text missing or illegible when filed}$

[0104] ε.sub.B=relative change in length in %

[0105] ΔL.sub.0=absolute change in length at maximum force in mm

[0106] l.sub.0=measuring length of the extensometer in mm

[0107] Modulus of Elasticity:

[00004]$E=\rho \times \frac{\Delta F\times {10}^3}{T_t}\times \frac{\text{?}}{\Delta l}\left[N/\mathrm{mm}\right]$$\text{?}\text{indicates text missing or illegible when filed}$

[0108] E=modulus of elasticity in N/mm.sup.2

[0109] ρ=yarn density in g/cm.sup.2

[0110] ΔF=specified force difference in N

[0111] T.sub.t=yarn count in tex

[0112] l.sub.0=measuring length of the extensometer in mm

[0113] Δl=length difference of the specified force difference in mm

[0114] Results:

[0115] The results are represented graphically in FIG. 1.

[0116] In FIG. 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 wt. % of matrix resin. The final comparative specimen is a STS40 E23 24K carbon fibre yarn from the company Teijin Carbon Europe with 1600 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 MPa. 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 MPa 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

[0117] 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.

[0118] Material: [0119] STS40 E23 24K 1600 tex, 5Z [0120] Vermiculite dispersion (AVD, manufacturer: Dupre Minerals Ltd., GB) [0121] 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)) [0122] Winding board (FIG. 5) [0123] Drying cabinet with a temperature range up to at least 150° C. [0124] Yarn shears [0125] Steel blade [0126] Plastic cutting board [0127] Plastic hammer [0128] Alsint dishes (H×L×W: 15 mm×200 mm×15 mm) [0129] Muffle furnace with a temperature range up to at least 1000° C. [0130] Scale with an accuracy of ±0.001 g

[0131] Carrying Out:

[0132] 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-US-00001 TABLE 1 Vermiculite bath Eyelet diameter Achieved vermiculite concentration [%] [mm] content [%]  0 none  0    5 2.6  3.7 12 3.0 13  

[0133] 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 converted to the mass loss of the carbon fibre. At least one duplicate determination is carried out.

[0134] FIG. 2 represents the result of example 2.

[0135] 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

[0136] 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.

[0137] Specimen Preparation:

[0138] After delivery, the yarn strands were stored dry at room climate until concreting. The expansion body specimens with the dimensions 800×60×15 mm.sup.3 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 FIG. 7.

[0139] 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. FIG. 8 shows the installed strands of yarn.

[0140] Ready-mixed fine concrete with a maximum grain size of 1 mm was used as the concrete (compressive strength >60 N/mm.sup.2). 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.

[0141] Test of the Expansion Body Specimens:

[0142] 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 FIG. 9.

[0143] 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.

[0144] Results:

TABLE-US-00002 TABLE 2 Averaged Vermi- Maximum Average Load at Mean mean culite Date of load value first Number Crack crack Fibre Yarn [wt. Specimen prep- Test Age Fmax Fmax crack of distance distance Mode of type type Turns %] name aration date [d] [N] cracks [mm] failure PU STS40 5 0 PU-A 21 Feb. 3 Feb. 13 3496 3543 3920 1 300 300 Pull-out F13 2021 2021 failure 24K P11-B 3244 3519 1 300 Pull-out 1600tex failure PU-C 3588 3783 1 300 Pull-out failure P11-D 3844 3482 1 300 Pull-out failure P12 STS40 30 0 P12-1 4820 4980 2712 2 150 138 Pull-out F13 failure 24K P12-2 5212 3690 3 100 Pull-out 1600tex failure P12-3 4762 3924 2 150 Pull-out failure P12-4 5127 3433 2 150 Pull-out failure

[0145] 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=L0/number of cracks with L0=free expansion length=300 mm.

[0146] 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.