EP0154243A2 - Protected tensioning members in concrete - Google Patents

Abstract

When using unidirectionally (glass) fibre-reinforced composite material profiles (1, 21) for pretensioning in concrete construction, the unavoidable matrix cracks during tensioning must be closed in order to prevent the premature destruction of the fibres. The tensioning members (1, 21) extending in jacket tubes (7, 20) are encased by a pourable sealing compound which is sufficiently flowable and wetting, exhibits no shrinkage and permits a constant force transmission from the tensioning member to the jacket tube firmly connected to the concrete. <IMAGE>

Description

The invention relates to a method for protecting tendons, in particular unidirectionally fiber-reinforced composite profiles in cladding tubes, in concrete and for transmitting power from the tendon to the cladding tube, and to a casting compound for protecting tendons running in cladding tubes in concrete.

Concrete is one of the most important building materials because of its ability to absorb large compressive forces. Since the tensile strength of even high-quality concrete is less than a tenth of its compressive strength, it is almost always necessary to reinforce it in practice. Steel is almost exclusively used for reinforcement today.

Particularly advantageous concrete constructions can be realized if the reinforcement material is installed in a pre-stressed manner, not slack. The so-called tendon technology is particularly widespread, in which the prestressing elements are drawn into the channels provided for this purpose after the concrete has hardened and prestressed against the building. Is steel used for prestressing who? after the completion of the clamping process, the remaining cavities are pressed out with permanently strong alkaline cement mortar to protect the clamping elements.

Glass fiber composites with unidirectional fiber orientation and a high proportion of reinforcing fibers, as described, for example, in DE-OS 27 35 538, achieve the strength of high-strength prestressing steels and have an approximately four times lower modulus of elasticity.

As a result, a four times larger pretension path is required. On the other hand, the loss of prestressing force that is unavoidable due to shrinkage and shortening of the concrete is also reduced by the same factor. The low modulus of elasticity also has a positive effect in that disturbing bending stresses due to rod curvatures at planned deflection points in a building or when reeling up the rods during transport and storage only reach a quarter of the values of comparable steel rods. Since the specific weight of glass fiber composite rods is only around a quarter of the value of steel at approx. 2 g / cm, there are further advantages in transport and installation.

Despite these favorable properties, glass fiber composite profiles have so far hardly found their way into prestressed concrete technology. While the steel, which is itself sensitive to corrosion, is protected by the strong basicity of the concrete if the concrete cover is only sufficiently large, prestressed glass fiber composites are made of moist concrete and cement mortar attacked more or less over time.

Attempts to protect the glass fiber elements by coating or sheathing with alkali-resistant materials e.g. Protecting thermoplastics has so far been unsatisfactory. Because of the flow of the coating material under load, the bond strength between the tensioning element and the concrete (extrusion mortar) is adversely affected; the coating also makes the introduction of forces into the bars considerably more difficult. If unfilled or filled synthetic resins are used for grouting instead of cement mortar, the shrinkage during hardening leads to detachment or shrinkage cracks at previously undetermined locations, which can be the starting point for subsequent damage.

The object of the invention is to record a way how corrosion problems on tendons, in particular on glass fiber reinforced composites, can be permanently avoided without impairing the ability to transmit large forces in the anchoring area and by adhesive bonding between the composite element and prestressed concrete.

In procedural terms, the object is achieved in that the tendons are completely covered by the pre-casting compound by pressing in a sufficiently flowable and wetting pre-casting compound with negligible shrinkage into the cladding tube, and the casting compound ensures a constant transmission of force from the tendon to the one with the Concrete cladding tube firmly connected. The potting compound according to the invention is characterized by a viscosity of the mixture of η between 300 and 3000 mPa s, preferably between 600 and 2000 mPa s, very preferably between 800 and 1500 mPa s, which remains of this order of magnitude for at least one hour after the potting compound has been produced , negligible shrinkage, compressive strength in the range of 40 to 100 MPa and pull-out strength in the range of 15 - 26 MPa. Further training is mentioned in the subclaims.

It has been shown that, due to the relatively large elongation of the elements made of fiber-reinforced composite materials, surface cracks occur in the matrix of the composite elements during prestressing, the alkaline media allow direct access to the load-bearing reinforcing fibers and damage them in a relatively short time. With the potting compound according to the invention, the tendons are completely wetted and such matrix cracks during curing, which takes place without loss of volume, are completely eliminated. Hardening without shrinkage is essential for the achievable protective effect of the casting compound, and a slight increase in volume during hardening can be accepted. The setting of the flow behavior is very important so that very long tendons can be protected in their entire length. The viscosity of the mixture should be between 300 and 3000 mPa s, preferably between 600 and 2000 mPa s (measurement of the viscosity using the Brookfield viscometer). It should remain in this range for one to two hours.

Cold-curing, non-shrinking unsaturated polyester resins such as are described, for example, in German Laid-Open Specification 21 08 390 are particularly suitable for producing the casting compounds according to the invention. Such casting compounds can be cured with the usual peroxidic polymerization catalysts, achieve good mechanical properties in conjunction with finely divided fillers and protect prestressed glass fiber composite rods even in the area of low coverage, e.g. at planned deflection points, permanently against the attack of corrosive media e.g. the strongly basic reacting surrounding concrete.

However, other UP resins, for example vinyl ester resins, can also be used advantageously, as can casting compounds made from acrylic resins, epoxy resins and PU resins. When selecting the resin and the composition of the individual components (resin, hardening agent, fillers and additives), the flow properties, the shrinkage and the mechanical properties must be within the above-mentioned value ranges, so that complete wetting is achieved and existing imperfections on the surface after curing are eliminated.

To adjust the flow behavior and the mechanical property after curing, but also for economic reasons, the casting compounds contain fillers in proportions between 20 and 80% by weight. Mixtures of finer and coarser additives are preferred eg quartz powder, fine sand, fly ash and fillite (silica spheres, particle size 5 to 300 µm, specific weight 0.7). The proportion and the composition of the filling materials used is determined by the flow and sedimentation behavior of the casting compounds and by the mechanical properties to be achieved. With regard to the mechanical properties of the hardened casting compound, the compressive strength (determination of the compressive strength according to DIN 1048, part 1) and the bond strength (determination of the bond strength as described in: C. Rehm, "on the principles of the bond between steel and concrete" DAfStb, booklet 138, Berlin, 1961) at least the values of cement mortar can be achieved. Since filler materials also influence the expansion or shrinkage behavior of the reactive resins, the proportion and composition of the filler material must also be selected so that the casting compound does not shrink during curing.

The casting compound also contains the necessary curing agents and, if appropriate, wetting improvers, adhesives, flow aids or modifying additives to achieve certain polymer properties, for example isocyanates or additional crosslinking agents.

example 1

• Ein Gemisch aus Malein-, Adipin- und Phthalsäure in einem Molverhältnis 12:1:11 wird zusammen mit einer Mischung aus Ethylenglykol und Propylenglykol im Molverhältnis 1:2 auf 200°C erhitzt. Der dabei entstehende Polyester hat ein Molekulargewicht von ca. 2100 und eine Säurezahl von 31. Danach werden 2100 g dieses Polyesters bei 200°C in 2276 g Styrol, das 0,34 g Hydrochinon enthält, unter Rühren eingegossen. Während des Eingießens wird die Masse so weit gekühlt, daß die Temperatur 80°C nicht übersteigt.

Production of a polyester which is particularly well suited for the production of a homogeneous casting compound according to the invention:

• A mixture of maleic, adipic and phthalic acid in a molar ratio of 12: 1: 11 is heated to 200 ° C. together with a mixture of ethylene glycol and propylene glycol in a molar ratio of 1: 2. The resulting polyester has a molecular weight of approximately 2100 and an acid number of 31. Thereafter, 2100 g of this polyester are poured into 2276 g of styrene containing 0.34 g of hydroquinone at 200 ° C. with stirring. During the pouring, the mass is cooled to such an extent that the temperature does not exceed 80 ° C.

After cooling to room temperature, 500 parts by weight are removed and 160 parts by weight of a 4% by weight solution of polyvinyl acetate in styrene are added. After stirring for about 15 minutes, a homogeneous mixture is obtained which remains homogeneous even after prolonged storage and can also be used for further processing into casting compounds for several weeks after its preparation.

erhält man eine homogene Vergußmasse mit einer Viskosität η = 800 mPa s. Eine Rückstellprobe wies nach 1 1/2 Stunden Standzeit eine Viskosität von η= 1100 mPa s auf. Bei der obengenannten Vergußmasse betrug die Druckfestigkeit 89 MPa und die Auszugsfestigkeit 18.5 MPa.By mixing the following components together

a homogeneous casting compound with a viscosity η = 800 mPa s is obtained. A reserve sample had a viscosity of η = 1100 mPa s after 1 1/2 hours of standing. The compressive strength of the above-mentioned casting compound was 89 MPa and the pull-out strength was 18.5 MPa.

Example 2

erhält man eine homogene Vergußmasse. Die Viskosität dieser Mischung betrug direkt nach dem Vermischen (bei 25°C) 1000 mPa s. Eine Rückstellprobe wies nach 2 Stunden Standzeit eine Viskosität von 1400 mPa s auf. Es trat dieser Zeit keinerlei Mischung oder Sedimentation der Zuschlagstoffe auf. Die Druckfestigkeit eines aus dieser Masse hergestellten Prüfkörpers betrug 46 MPa; die Auszugsfestigkeit 16.4 MPA.By mixing the following components together

you get a homogeneous potting compound. The viscosity of this mixture was 1000 mPa s immediately after mixing (at 25 ° C.). A reserve sample had a viscosity of 1400 mPa s after 2 hours of standing. No mixing or sedimentation of the aggregates occurred at this time. The compressive strength of a test specimen made from this mass was 46 MPa; the pull-out strength 16.4 MPA.

Example 3

wurde eine homogene Masse erhalten.By mixing the following components together

a homogeneous mass was obtained.

The viscosity of this mixture was 1100 mPa s, a reserve sample showed a viscosity of 1400 mPa s after a standing time of 1.5 hours. No segregation occurred during this time. The compressive strength was 67 MPa and the pull-out strength was 15.9 MPa.

• Fig. 1 Anlage zum Verpressen der Vergußmasse;
• Fig. 2 Vorderansicht eines Verpreßankers;
• Fig. 3 Versuchsbalken mit sinusförmigem Hüllrohr.

The pressing of the potting compound in the cladding tubes and a practical test are shown in the drawing and explained in more detail below. Show it

• Fig. 1 system for pressing the sealing compound;
• Fig. 2 front view of a compression anchor;
• Fig. 3 test beam with sinusoidal cladding tube.

Fig. 1 shows a tendon 1 in a concrete block 2. The tendon is anchored with an anchor 3 against the concrete block. The tension from the concrete outstanding part of the tendon is secured by the ring 4 between the compression anchor 3 and the concrete block 2. The cross section of the tendon is shown in Fig. 2. In this case it consists of 8 unidirectional fiber-reinforced composite profiles 5 with an outer diameter of 7.5 mm. In the concrete block 2, the tendon 1 runs in a cladding tube 7. According to the invention, the space 6 must be filled with a certain sealing compound to protect the tendon.

For this purpose, a threaded sleeve 8 is attached to the compression anchor 3, which is connected to a pressure vessel 10 via a filling hose 9 (NW 18). In the pressure vessel there are approx. 25 1 potting compound 11. The reaction mixture 11 is introduced into the cladding tube 7 by means of compressed air 12 of approximately 5 bar via the dip tube 13 and the filling hose 9. It is thus possible to encase a tendon in a 100 m long cladding tube without voids.

To test the casting compound in a practical test, a cladding tube 20 with composite tendons 21 was laid sinusoidally in a concrete test beam 22 (FIG. 3). Mountain and talc curvatures each had a radius of curvature of 2.3 m; the tendon length was 12.3 m. In a cladding tube with a diameter of 34 mm, 9 composite tendons made of unidirectional glass fiber reinforced rods, 7.5 mm, were combined. The occupancy of the pipe cross-section was 37 to 40%. The preload was set to 6 t (that's 10% of the load capacity). There were a total of 3 ventilation pipes on the cladding tube present, one 23 on the press-in anchor 26, one 24 on the end anchor 27 and one 25 on the uppermost point of the "mountain curvature". The cladding tube 20 was filled as described above. After connecting the pressure vessel to the press-in anchor 26 of the cladding tube, there was an overflow at the vent pipe 2'3 of the press-in anchor after about 30 seconds and an initial pressure of 0.5 bar. After closing this valve, the potting compound emerged from the vent pipe 24 after about 60 seconds; until then the pressure rose to 1 bar. After a further 3 minutes, an overflow at the end anchor 24 and a pressure of 1.5 bar indicated that the cladding tube 20 had been completely filled. Subsequently, the vent pipe 23 was vented again.

One week after the backfilling, the cladding tube was cut into 50 cm pieces using a cutting disc. The cut surfaces showed that the casting compound was completely homogeneous even after curing and that the inorganic fillers had not settled. The cladding tubes were completely filled. Even the smallest gaps between the compressed composite bars were well filled.

Claims (4)

1. A method for protecting tendons, in particular of unidirectional fiber-reinforced composite profiles, in cladding tubes in concrete and for transmitting power from the tendon to the cladding tube, characterized in that the tendons located in the cladding tube are pressed in a form-fitting manner with a negligible flowable and wetting potting compound with negligible shrinkage will. 2. Potting compound for protecting tendons (1,21) running in cladding tubes (7.20) in concrete (2.22), characterized by a viscosity of the mixture of η between 200 and 3000 mPa s, preferably between 600 and 2000 mPa s , which remains in this order of magnitude for at least one hour after the casting compound has been produced, a negligible shrinkage, a compressive strength in the range from 40 to 100 MPa and a pull-out strength in the range from 15 to 26 MPa. 3. Potting compound according to claim 2, characterized in that the potting compound consists of a filler-containing, cold-curing, unsaturated polyester resin. 4. Potting compound according to claim 2 or 3, characterized in that it contains quartz powder-sand mixtures as fillers.

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