FR3117481A1 - USE OF GLASS-RESIN COMPOSITE FIBERS FOR CONCRETE REINFORCEMENT - Google Patents

Abstract

The invention relates to a single strand of glass-resin composite comprising glass filaments embedded in a crosslinked resin, the single strand having a length within a range ranging from 5 to 85 mm, a diameter ranging from 0.2 to 1.3 mm , and a porosity rate of less than 2%, to a ballotin comprising a plurality of these single strands, as well as to their uses for reinforcing concrete, reducing the weight of concrete, reducing or preventing the cracking of concrete. The invention also relates to the concrete comprising these single strands as well as to the process for obtaining these single strands. Figure for abstract: Figure 2

Description

USE OF GLASS-RESIN COMPOSITE FIBERS FOR CONCRETE REINFORCEMENT

The present invention relates to glass-resin composite fibers for reinforcing concrete.

Concrete is arguably the most widely used building material today due to its high compressive strength, durability, longevity, and resilience. Its properties make it a material of choice, particularly in the fields of building, roads and engineering structures.

Concrete is mainly composed of aggregates held together by a binder, most often Portland cement. To improve the properties of concrete, it is known to use additives such as ultrafine particles (silica fume for example), superplasticizers also called water reducers or metallic, synthetic or mineral fibres.

Although very resistant to compression, concrete has a low tensile strength, often accompanied by the appearance of cracks. To combat this problem, it is known to use reinforcing fibers. Due to their mechanical properties, metal fibers are particularly interesting for reinforcing concrete. They are thus very widely used to make concrete more ductile and improve its resistance to cracking.

However, mechanical fibers have the disadvantage of being sensitive to corrosion, which can be detrimental to the longevity of concrete comprising such fibers. In addition, it has densities often greater than 7.7 and are therefore not distributed evenly in concrete with a lower density (metal fibers tend to sink under the effect of gravity).

To solve this problem it has been proposed to replace the metal fibers with synthetic fibers. However, the mechanical strength (Elastic Modulus (of Young), tensile strength for example) of these fibers is not as good as that of metal fibers. Furthermore, their operating temperature (between 100°C and 160°C generally) is much lower than that of metal fibers (between 600°C and 900°C approximately), which may limit their use for certain applications.

Thus, it remains advantageous to have fibers which are both resistant to corrosion, to improve the service life of the concrete, and which have improved mechanical properties compared to current non-metallic fibers, to improve the resistance to corrosion. cracking.

Pursuing its research, the Applicant has unexpectedly discovered that the use of specific glass-resin composite fibers comprising glass filaments embedded in a cross-linked resin makes it possible to solve the aforementioned problem.

The Applicant has also observed numerous advantages procured by the fibers according to the invention. Their implementation is very easy compared to the fibers for concrete of the prior art, in particular during the phase of mixing the various components of the concrete (easily dispersible), but also during the phase of drying of the concrete: due to their density close to that of concrete, the fibers remain evenly distributed in the concrete (they do not tend to flow like metal fibers denser than concrete, nor to rise like synthetic fibers less dense than concrete) . The fibers of the invention also have a much higher maximum use temperature than the synthetic fibers currently used. Furthermore, the white color of the fibers according to the invention allows them to be used in light concretes without impacting the aesthetics of these concretes. . Finally, more generally, because of their density and their capacity for reinforcement, the use of the fibers according to the invention makes it possible to greatly reduce the overall CO ₂ emissions compared to the use of other fibers of the prior art, at a constant level of reinforcement.

Thus, the subject of the invention is a single strand of glass-resin composite comprising glass filaments embedded in a crosslinked resin, the single strand having a length within a range ranging from 5 to 85 mm, a diameter ranging from 0.2 to 1.3 mm, and a porosity rate of less than 2%.

The invention also relates to a ballotin comprising a plurality of these single strands, the use of these single strands or of this ballotin for the reinforcement of concrete, a concrete comprising these single strands, as well as a method of manufacturing these single strands.

I- DEFINITIONS

In the present, unless otherwise expressly indicated, all the percentages (%) indicated are percentages (%) by mass.

The expression "composition based on" means a composition comprising the mixture and/or the in situ reaction product of the various constituents used, some of these constituents being able to react and/or being intended to react with one another, less partially, during the various phases of manufacture of the composition; the composition thus possibly being in the totally or partially crosslinked state or in the non-crosslinked state.

On the other hand, any interval of values denoted by the expression "between a and b" represents the domain of values going from more than a to less than b (i.e. limits a and b excluded) while any interval of values denoted by the expression “from a to b” signifies the range of values going from a to b (that is to say including the strict limits a and b). In this document, when an interval of values is designated by the expression "from a to b", the interval represented by the expression "between a and b" is also and preferably designated.

All the glass transition temperature “Tg” values described herein are measured in a known manner by DSC (Differential Scanning Calorimetry) according to standard ASTM D3418 (1999).

II- BRIEF DESCRIPTION OF THE FIGURES

There represents a diagram of the single strand synthesis process according to the invention before the latter is cut to a determined length.

There , not shown to scale to facilitate understanding, is a drawing showing a cross section of the single strand according to the invention.

III- DESCRIPTION OF THE INVENTION

The invention therefore relates to a single strand (or fiber, the two terms being able to be used in an equivalent manner) made of glass-resin composite (abbreviated "CVR") comprising glass filaments embedded in a crosslinked resin, characterized in that the single strand has a length within a range ranging from 5 to 85 mm, a diameter ranging from 0.2 to 1.3 mm, and a porosity rate of less than 2%.

Typically, glass filaments are present as a single multifilament fiber or multiple multifilament fibers associated with each other. In the latter case, the multifilament fibers are preferably essentially unidirectional. Each of the multifilament fibers may comprise several tens, hundreds or even thousands of individual glass filaments. These very fine individual filaments generally and preferably have an average diameter of the order of 5 to 30 μm, more preferably of 10 to 20 μm. The section of the individual filaments is preferably cylindrical. By way of example of fiberglass that can be used in the context of the present invention, mention may be made of the “R25H” or “SE1200” fibers from the company Owens Corning.

By “resin”, we mean here the resin as such and any composition based on this resin and comprising at least one additive (that is to say one or more additives). By "crosslinked" resin, it is understood of course that the resin is cured (photocured and/or thermocured), in other words in the form of a network of three-dimensional bonds, in a state specific to so-called thermosetting polymers (as opposed to to so-called thermoplastic polymers).

Thus, the single strand CVR according to the invention comprises a plurality of individual glass filaments, preferably essentially parallel to each other, embedded in a hardened resin after crosslinking.

According to the invention, the CVR single strand has a porosity rate of less than 2%, preferably less than 1%, preferably less than 0.5%. Advantageously, the porosity rate of the CVR single strand is between 0% and 2%, preferably between 0.01% and 1%, preferably between 0.05% and 0.5%.

The porosity rate can be measured by microscopy, for example by scanning electron microscopy, preferably using surface calculation software, such as Program FIJI. To perform the measurement, the following protocol is preferably carried out :
- we take a single strand in reticulated CVR,
- it is coated with a cold mounting resin, of the epoxy type for example, for example in a vacuum coating device (CitoVac from the company Stuers for example),
- the single strand in coated CVR is cut, for example using a hydraulic guillotine, such as the "SH-5214" from the company Baileigh,
- the section of the single strand CVR is polished, for example using a mechanical polisher, from the company Mecapol for example, preferably to a final grain of 0.25 μm,
- a deposit of 1 to 4 nm of gold is made, for example using a gold metallizer, such as Cerssington of the 108 or 208 series from the company Eloïse,
- the section of the single strand is observed in CVR under a scanning electron microscope, preferably under vacuum (15kV), and
- using an image processing program, FIJI for example, the surface percentage of the porosity is calculated. The term "porosity" of the CVR single strand means any gas (in particular air) or vacuum present within the CVR single strand.

Advantageously, the CVR single strand has a breaking stress Cr greater than 1050 MPa, preferably greater than or equal to 1100 MPa, more preferably greater than or equal to 1200 MPa. Preferably, the single strand has a breaking stress of between 1050 and 1600 MPa, preferably of 1200 to 1500 MPa.

Also advantageously, the CVR single strand has an initial extension modulus (denoted E ₂₃ ), also called Young's Modulus, measured at 23° C., greater than 35 GPa, preferably greater than or equal to 40 GPa, preferably greater than or equal to equal to 42 GPa, preferably greater than or equal to 48 GPa.

The mechanical properties in extension of the single strand in CVR (modulus E ₂₃ , breaking stress Cr and elongation at break Ar ) can also be measured in a known manner using an “INSTRON” tensile machine of the 5944 type (BLUEHILL software ® UNIVERSAL supplied with the tensile machine), according to the ASTM D2343 standard, on glued (ready to use) CVR single strands. Before measurement, these single strands are subjected to prior conditioning (storage of the single strands for at least 24 hours in a standard atmosphere according to European standard DIN EN 20139 (temperature of 23 ± 2°C; humidity of 50 ± 5%)). The tensile modulus is determined by linear regression of the stress curve as a function of the strain, between 0.1% and 0.6% strain. This deformation is recorded by the MultiXtens 1995DA801 extensometer. The 260 mm specimens tested undergo traction at a nominal speed of 5 m/min, under a pre-test preload of 0.5 MPa (reference length 50 mm, distance between the jaws: 150 mm). All results given are an average of 10 measurements.

Furthermore, the single-strand CVR in accordance with the invention advantageously has the following properties:
- the glass transition temperature (denoted Tg ) of the resin is equal to or greater than 180° C., preferably equal to or greater than 190° C.;
- the elongation at break (denoted Ar ) of the single strand, measured at 23° C., is equal to or greater than 3.0%, preferably greater than 4.0%;
- the initial tensile modulus (denoted E ₂₃ ) of the single strand, measured at 23° C., is greater than 35 GPa, preferably greater than 48 GPa; And
the real part of the complex modulus (denoted E′ ₁₉₀ ) of the single strand, measured at 190° C. by the DTMA method, is greater than 30 GPa.

The glass transition temperature denoted Tg of the resin is preferably greater than 190°C, more preferably greater than 195°C, in particular greater than 200°C. It is measured in a known manner by DSC ( Differential Scanning Calorimetry ), on the second pass, for example and unless otherwise specified in the present application, according to standard ASTM D3418 of 1999 (DSC apparatus "822-2" from Mettler Toledo; atmosphere nitrogen; samples previously brought from room temperature (23°C) to 250°C (10°C/min), then rapidly cooled to 23°C, before final recording of the DSC curve from 23°C to 250 °C, according to a ramp of 10°C/min).

The elongation at break noted Ar of the CVR single strand, measured at 23° C., is preferably greater than 4.0%, more preferably greater than 4.2%, in particular greater than 4.4%.

The E′ modulus ₁₉₀ is preferably greater than 33 GPa, more preferably greater than 36 GPa.

For an optimized compromise of thermal and mechanical properties of the CVR single strand of the invention, the ratio E′ _{(Tg′ – 25)} / E′ ₂₃ is advantageously greater than 0.85, preferably greater than 0.90, E′ ₂₃ and E' _{(Tg' – 25)} being the real part of the complex modulus of the single strand measured by DMTA, respectively at 23°C and at a temperature expressed in °C equal to (Tg' - 25), expression in which Tg' represents the glass transition temperature measured this time by DMTA .

Advantageously again, the ratio E' _{(Tg' – 10)} / E' ₂₃ is greater than 0.80, preferably greater than 0.85, E' _{(Tg' – 10)} being the real part of the complex modulus of the single strand measured by DMTA at a temperature expressed in °C equal to (Tg' - 10).

The measurements of E' and Tg' are carried out in a known manner by DMTA (" Dynamic Mechanical Thermal Analysis" ), with a "DMA ⁺ 450" viscoanalyzer from ACOEM (France), using the "Dynatest 6.83 / 2010" software controlling tests bending, pulling or twisting.

According to this device, the three-point bending test not allowing in a known way to enter the initial geometric data for a single strand of circular section, it is only possible to introduce the geometry of a rectangular (or square) section. In order to obtain an accurate measurement of the modulus E' for a single strand of diameter D , we therefore introduce by convention into the software a square section with side " a " having the same surface moment of inertia, in order to work at the same stiffness R of the specimens.

The following well-known relationships must apply (E being the modulus of the material, I _s the surface moment of inertia of the body considered, and * the multiplication symbol):

R = E _composite * I _{circular section} = E _composite * I _{square section}

with: I _{circular section} = π * D ^4/64 and I _{square section} = a ^4/12

We easily deduce the value of the side “ a ” of the equivalent square with the same surface inertia as that of the (circular) section of the monofilament of diameter D , according to the equation:

a = D * (π/6) ^0.25

In the case where the cross section of the sample tested is not circular (nor rectangular), whatever its particular shape, the same method of calculation will apply by determining beforehand the surface moment of inertia I _s on a straight section of the sample tested.

The specimen to be tested, generally of circular section and of diameter D , has a length of 35 mm. It is arranged horizontally on two supports 24 mm apart. A repeated bending stress is applied perpendicular to the center of the specimen, halfway between the two supports, in the form of a vertical displacement of amplitude equal to 0.1 mm (therefore asymmetrical deformation, the interior of the specimen being only stressed in compression and not in extension), at a frequency of 10 Hz.

The following program is then applied: under this dynamic stress, the specimen is gradually heated from 25°C to 260°C with a ramp of 2°C/min. At the end of the test, we obtain the measurements of the elastic modulus E', of the viscous modulus E'' and of the loss angle (δ) as a function of the temperature (where E' is the real part and E'' the part imaginary of the complex module); Tg' is the glass transition temperature corresponding to the maximum (peak) of tan(δ).

Advantageously, the elastic deformation in compression under bending is greater than 3.0%, more preferably greater than 3.5%, in particular greater than 4.0%. According to another preferred embodiment, the breaking stress in compression under bending is greater than 1050 MPa, more preferably greater than 1200 MPa, in particular greater than 1400 MPa.

The above properties in compression under bending are measured on the single strand in CVR as described in application EP 1 167 080, by the so-called loop test method (D. Inclair, J. App. Phys. 21, 380, 1950 ). In this case, we make a loop that we gradually bring to the breaking point. The nature of the break, easily observable due to the large size of the section, immediately makes it possible to realize that the CVR single strand of the invention, stressed in bending until it breaks, breaks on the side where the material is in extension, what is identified by simple observation. Given that in this case the dimensions of the loop are important, it is possible at any time to read the radius of the circle inscribed in the loop. The radius of the inscribed circle just before the breaking point corresponds to the critical radius of curvature, denoted by Rc.

The following formula then makes it possible to determine by calculation the critical elastic deformation noted Ec (where r corresponds to the radius of the single strand, i.e. D/2):

Ec = r / (Rc + r)

The breaking stress in compression under bending noted σ _c is obtained by calculation using the following formula (where E is the initial modulus in extension):

σ _c = Ec * E

Since, in the case of the single strand in CVR according to the invention, the rupture of the loop appears in the part in extension, it is concluded that, in bending, the breaking stress in compression is greater than the breaking stress in extension.

It is also possible to break a rectangular bar in bending using the so-called three-point method (ASTM D 790). This method also makes it possible to check, visually, that the nature of the rupture is indeed in extension.

Advantageously, the breaking stress in pure compression is greater than 700 MPa, more preferably greater than 900 MPa, in particular greater than 1100 MPa. To avoid buckling of the single strand in CVR under compression, this quantity is measured according to the method described in the publication “Critical compressive stress for continuous fiber unidirectional composites” by Thompson et al, Journal of Composite Materials, 46(26), 3231-3245 .

Preferably, in the CVR single strand of the invention, the degree of alignment of the glass filaments is such that more than 85% (% by number) of the filaments have an inclination with respect to the axis of the single strand which is less than 2.0 degrees, more preferably less than 1.5 degrees, this inclination (or misalignment) being measured as described in the above publication by Thompson et al. Also preferably, the CVR single strand according to the invention is not helically deformed, that is to say it is not twisted. In any event, the CVR single strand has a number of turns per meter of less than 5, preferably less than 2, preferably less than 0.5, preferably from 0 to 0.5.

Preferably, the weight content of glass fibers (that is to say filaments) in the CVR single strand is included in a range ranging from 65% to 85%, preferably from 70% to 80%.

This weight rate is calculated by taking the ratio of the titer of the initial glass fiber to the titer of the single strand in final CVR. The titer (or linear density) is determined on at least three samples, each corresponding to a length of 50 m, by weighing this length; the title is given in tex (weight in grams of 1000 m of product – as a reminder, 0.111 tex is equivalent to 1 denier).

Furthermore, the crosslinked resin represents from 15% to 35%, preferably from 20% to 30%, by weight, of the CVR single strand of the invention.

Preferably, the density (or density in g/cm ³ ) of the CVR single strand is between 1.8 and 2.1. It is measured (at 23° C.) using a specialized scale from Mettler Toledo of the “PG503 DeltaRange” type; the samples, a few cm long, are successively weighed in air and immersed in ethanol; the device software then determines the average density over three measurements.

The diameter D of the CVR single strand of the invention is preferably within a range ranging from 0.25 and 1.25 mm, more preferably between 0.3 and 1.2 mm, in particular between 0.4 and 1, 1mm.

This definition covers both single strands of essentially cylindrical shape (with a circular cross section) and single strands of a different shape, for example single strands that are oblong (of more or less flattened shape) or with a rectangular cross section. In the case of a non-circular section and unless otherwise specifically indicated, D is by convention the so-called overall diameter, i.e. the diameter of the cylinder of imaginary revolution enveloping the single strand, in other words the diameter of the circumscribed circle surrounding its cross section.

Furthermore, the length L of the CVR single strand of the invention is preferably within a range ranging from 10 to 80 mm, for example from 15 to 60 mm.

Advantageously, the length/diameter L/D ratio of the CVR single strands of the invention is within a range ranging from 10 to 110, for example from 11 to 90, for example from 12 to 75, preferably from 15 to 65, preferably from 20 to less than 60.

The resin used is by definition a crosslinkable resin ( ie , hardenable) capable of being crosslinked, hardened by any known method, in particular by UV (or UV-visible) radiation, preferably emitting in a spectrum ranging from at least 300 nm to 450 nm.

Advantageously, the crosslinked resin is based:
- a crosslinkable resin chosen from the group consisting of vinyl ester resins (preferably vinyl ester urethane resins), epoxy, polyester and mixtures thereof,
- a crosslinking system preferably comprising a photoinitiator reactive to UV above 300 nm.

When we speak of the "resin composition", it is the composition from which the resin is made, that is to say before crosslinking.

As crosslinkable resin, a polyester or vinyl ester resin is preferably used, more preferably a vinyl ester resin. By “polyester” resin is meant in known manner a resin of the unsaturated polyester type. Vinyl ester resins are well known in the field of composite materials.

Without this definition being limiting, the vinylester resin is preferably of the epoxyvinylester type. A vinyl ester resin, in particular of the epoxy type, is more preferably used, which at least in part is based (that is to say grafted on a structure of the type) novolac (also called phenoplast) and / or bisphenolic, preferably a vinyl ester resin based on novolac, bisphenol, or novolac and bisphenol.

Preferably, the initial tensile modulus of the resin, measured at 23° C., is greater than 3.0 GPa, more preferably greater than 3.5 GPa.

A novolak-based epoxy vinyl ester resin (part in brackets in formula I below) corresponds, for example, in a known manner, to formula (I) which follows:
(I)

A bisphenol A-based epoxy vinyl ester resin (part in square brackets of formula (II) below) corresponds for example to the formula (the "A" reminding that the product is manufactured using acetone):
(II)

A novolak and bisphenol type epoxy vinyl ester resin has shown excellent results. By way of example of such a resin, mention may be made in particular of the vinyl ester resins "ATLAC 590" and "ATLAC E-Nova FW 2045" from the company AOC (diluted with approximately 40% styrene) described in the EP applications A-1 074 369 and EP-A-1 174 250 cited above. Epoxy vinyl ester resins are available from other manufacturers such as, for example, AOC (USA - "VIPEL" resins).

Preferably, the curing system of the impregnating resin (resin composition) comprises a photoinitiator sensitive (reactive) to UV above 300 nm, preferably between 300 and 450 nm. This photoinitiator is used at a preferential rate of 0.5 to 3%, more preferentially of 1 to 2.5%. Preferably, the resin crosslinking system also comprises a crosslinking agent, for example at a rate of between 5% and 15% (% by weight of impregnating composition), the crosslinking agent being as defined above. -above.

Preferably, this photo-initiator is from the family of phosphine compounds, more preferably a bis(acyl)phosphine oxide such as for example bis-(2,4,6-trimethylbenzoyl)-phenylphosphine oxide ("Omnirad 819" from the company IGM or "speedcureBPO" from the company Lambson) or a mono(acyl)phosphine oxide (for example "Esacure TPO" from the company IGM), such phosphine compounds being able to be used as a mixture with other photo- initiators, for example photoinitiators of the alpha-hydroxy-ketone type such as for example dimethylhydroxy-acetophenone (e.g. "Omnirad 1173" from IGM) or 1-hydroxy-cyclohexyl-phenyl-ketone (e.g. "Omnirad 184" from IGM), benzophenones such as 2,4,6-trimethylbenzophenone (e.g. “Esacure TZT” from IGM) and/or thioxanthone derivatives such as for example isopropylthioxanthone (e.g. “Esacure Omnirad ITX” from IGM).

The crosslinking agent is preferably chosen from the group consisting of the family of triacrylates.

The single strand in CVR can be prepared according to the method described in application WO 2015/014579 followed by a step of cutting the single strand to a desired length.

Thus, the present invention also relates to a process for manufacturing single strands of glass-resin composite comprising glass filaments embedded in a crosslinked resin comprising the following successive steps:
- make a rectilinear arrangement of glass fibers (filaments) and drive this arrangement in a forward direction,
- in a vacuum chamber, degas the arrangement of glass filaments by the action of vacuum,
- at the outlet of the vacuum chamber, after degassing, pass through a vacuum impregnation chamber so as to impregnate said arrangement of glass filaments with a photo-crosslinkable resin composition, in the liquid state, "called impregnation resin" , to obtain an impregnated containing the glass filaments and the resin composition,
- pass said impregnated through a calibration die having a predefined surface section and shape, to impose a single strand shape on it (for example a single strand of round cross section or a ribbon of rectangular cross section),
- downstream of the die, in a UV irradiation chamber, polymerize the resin under the action of UV,
- cutting the filament so as to obtain single strands of a length comprised in a range ranging from 5 to 85 mm.

Advantageously, the polymerization is carried out in an irradiation chamber comprising a tube transparent to UV, called irradiation tube, through which circulates the single strand being formed, traversed by a current of inert gas, the speed (denoted V _ir ) passage of the single strand in the irradiation chamber being greater than 50 m/min, the irradiation time (denoted D _ir ) of the single strand in the irradiation chamber being equal to or greater than 1.5 seconds.

The method can of course include a rolling step for storage of the single strand after it has passed through the UV irradiation chamber and before being cut.

All of the above steps (arrangement, degassing, impregnation, calibration, polymerization, optional winding and cutting) of the process of the invention are steps known to those skilled in the art, as well as the materials (multifilament fibers and resin compositions ) used; they have for example been described in one and/or the other of applications EP-A-1 074 369 and EP-A-1 174 250.

It will be recalled in particular that before any impregnation of the fibers, an essential step of degassing the arrangement of fibers by the action of a vacuum must be carried out, in particular in order to reinforce the effectiveness of the subsequent impregnation and above all to guarantee the absence of bubbles inside the final composite monofilament.

After passing through the vacuum chamber, the glass filaments enter an impregnation chamber which is completely full of impregnation resin, and therefore devoid of air: it is in this sense that this stage can be qualified as impregnation of "vacuum impregnation".

The so-called "calibration" die makes it possible, thanks to a cross section of determined dimensions, generally and preferably circular or rectangular, to adjust the proportion of resin in relation to the glass fibers while imposing on the impregnated the shape and l target thickness for the monofilament.

The polymerization or UV irradiation chamber then has the function of polymerizing and cross-linking the resin under the action of UV. The UV irradiation chamber comprises one or preferably several UV irradiators, each consisting for example of a UV lamp with a wavelength of 200 to 600 nm.

The final CVR single strand thus formed through the UV irradiation chamber, in which the resin is now in a solid state, is then collected, for example, on a take-up spool on which it can be rolled up over a very long length.

Between the calibration die and the final receiving support, it is preferred to maintain the tensions undergone by the glass fibers at a moderate level, preferably between 0.2 and 2.0 cN/tex, more preferably between 0.3 and 1.5 cN/tex; to check this, it is possible, for example, to measure these voltages directly at the output of the irradiation chamber, using appropriate tensiometers well known to those skilled in the art.

In a particularly advantageous manner, the method for manufacturing the CVR single strand of the invention comprises the following essential steps:
- the speed ( V _ir ) of passage of the single strand in the irradiation chamber is greater than 50 m/min;
- the duration ( D _ir ) of passage of the single strand in the irradiation chamber is equal to or greater than 1.5 s and equal to or less than 10 s;
- the irradiation chamber comprises a tube transparent to UV (such as a quartz or preferably glass tube), called the irradiation tube, through which the single strand being formed circulates, this tube being traversed by a stream of inert gas, preferably nitrogen.

These combined steps make it possible to achieve the preferred improved properties of the CVR single strand of the invention, namely in particular Tg , Ar elongation and moduli ( E and E′ ).

In particular, in the absence of scavenging of inert gas such as nitrogen in the irradiation tube, it has been found that the above properties of the CVR single strand being degraded fairly quickly during manufacture and therefore that the industrial performance was no longer guaranteed.

Furthermore, if the irradiation time D _ir of the single strand in the irradiation chamber is too short (less than 1.5 s), numerous tests have revealed (see results in the table below, tests conducted at different speeds V _ir greater than 50 m/min) that either the Tg values were insufficient, less than 190° C., or the Ar values were too low, less than 4.0%. Furthermore, if the duration of irradiation D _ir of the single strand in the irradiation chamber is too long (greater than 10 s for example), this increases the risk of bringing the resin to a boil and therefore of creating more porosity and degrade the mechanical properties, including the breaking stress.

Dir ( _s ) Tg (°C) Ar (%) Trial 1 1.2 186.1 3.4 1.3 188.8 3.8 1.45 189.1 3.9 1.7 194.8 4.3 2.0 195.7 4.5 Trial 2 1.5 190.0 4.0 1.65 192.7 4.1 1.8 195.0 4.1 2.0 199.2 4.3 Trial 3 2.0 192.8 4.3 2.4 193.7 4.5 3.0 196.9 4.6 4.0 195.0 4.7 Trial 4 1.0 184.7 4.3 1.2 187.3 4.2 1.6 190.5 4.2 2.0 200.5 4.3

It has also been found that a high irradiation speed V _ir (greater than 50 m/min, preferably between 50 and 150 m/min) was favorable on the one hand to an excellent alignment rate of the filaments of glass inside the single strand in CVR, on the other hand to a better maintenance of the vacuum in the vacuum chamber with a markedly reduced risk of seeing a certain fraction of impregnation resin rise from the impregnation chamber towards the chamber empty, and therefore to a better quality of impregnation.

The diameter of the irradiation tube (preferably glass) is preferably between 10 and 80 mm, more preferably between 20 and 60 mm.

Preferably, the speed V _ir is between 50 and 150 m/min, more preferably in a range of 60 to 120 m/min.

Preferably, the irradiation time D _ir is between 1.5 and 10 s, more preferably in a range of 2 to 5 s.

Advantageously, the irradiation chamber comprises a plurality of UV irradiators (or radiators), that is to say at least two (two or more than two) which are arranged in line around the irradiation tube. Each UV irradiator typically comprises one (at least one) UV lamp (preferably emitting in a spectrum from 200 to 600 nm) and a parabolic reflector at the focus of which is the center of the irradiation tube; it delivers a linear power preferably between 2,000 and 14,000 watts per meter. More preferably still, the irradiation chamber comprises at least three, in particular at least four UV irradiators in line.

Even more preferably, the linear power delivered by each UV irradiator is between 2,500 and 12,000 watts per meter, in particular within a range of 3,000 to 10,000 watts per meter.

UV radiators suitable for the method of the invention are well known to those skilled in the art, for example those marketed by the company Dr. Hönle AG (Germany) under the reference "1055 LCP AM UK", equipped with "UVAPRINT" lamps. (iron doped high pressure mercury lamps). The nominal (maximum) power of each radiator of this type is equal to approximately 13,000 Watts, the power delivered actually being adjustable with a potentiometer between 30 and 100% of the nominal power.

Preferably, the temperature of the resin (resin composition), in the impregnation chamber, is between 50°C and 95°C, more preferably between 60°C and 90°C.

According to another preferred embodiment, the irradiation conditions are adjusted in such a way that the temperature of the single strand in CVR, at the outlet of the impregnation chamber, is higher than the Tg of the crosslinked resin; more preferably, this temperature is higher than the Tg of the crosslinked resin and lower than 270°C.

Another object of the invention is a single strand in CVR which can be obtained by a process as described above, in particular a single strand in CVR which can be obtained by a process comprising the following successive steps:
- make a rectilinear arrangement of glass fibers (filaments) and drive this arrangement in a forward direction,
- in a vacuum chamber, degas the arrangement of glass filaments by the action of vacuum,
- at the outlet of the vacuum chamber, after degassing, pass through a vacuum impregnation chamber so as to impregnate said arrangement of glass filaments with a photo-crosslinkable resin composition, in the liquid state, "called impregnation resin" , to obtain an impregnated containing the glass filaments and the resin composition,
- pass said impregnated through a calibration die having a predefined surface section and shape, to impose a single strand shape on it (for example a single strand of round cross section or a ribbon of rectangular cross section),
- downstream of the die, in a UV irradiation chamber, polymerize the resin under the action of UV,
- cutting the filament so as to obtain single strands of a length comprised in a range from 5 to 85 mm,
preferably in which:
- the speed ( V _ir ) of passage of the single strand in the irradiation chamber is greater than 50 m/min;
- the duration ( D _ir ) of passage of the single strand in the irradiation chamber is equal to or greater than 1.5 s and equal to or less than 10 s;
- the irradiation chamber comprises a tube transparent to UV (such as a quartz or preferably glass tube), called the irradiation tube, through which the single strand being formed circulates, this tube being traversed by a stream of inert gas, preferably nitrogen,
- the CVR single strand preferably having a diameter ranging from 0.2 to 1.3 mm.

Examples of the manufacture of CVR single strands according to the invention and their use as tire reinforcements are described below.

There appended very simply schematizes an example of a device 10 allowing the production of CVR single strands in accordance with the invention.

It shows a coil 11a containing, in the example shown, glass fibers 11b (in the form of multifilaments). The reel is unwound continuously by driving, so as to produce a rectilinear arrangement 12 of these fibers 11b. In general, the reinforcing fibers are delivered in "rovings", i.e. already in groups of fibers wound in parallel on a reel; for example, fibers marketed by Owens Corning under the designation “Advantex” fiber are used, with a titer equal to 1200 tex (as a reminder, 1 tex=1 g/1000 m of fiber). It is for example the traction exerted by the rotating reception 26 which will allow the advancement of the fibers in parallel and of the single strand in CVR all along the installation 1.

This arrangement 12 then passes through a vacuum chamber 13 (connected to a vacuum pump, not shown), arranged between an inlet pipe 13a and an outlet pipe 13b leading to an impregnation chamber 14, the two pipes preferably rigid wall having for example a minimum section greater (typically twice as much) than the total section of fibers and a much greater length (typically 50 times more) than said minimum section.

As already taught by the aforementioned application EP-A-1 174 250, the use of pipes with rigid walls, both for the inlet orifice in the vacuum chamber and for the outlet orifice of the vacuum chamber and the transfer from the vacuum chamber to the impregnation chamber proves to be compatible both with high rates of passage of the fibers through the orifices without breaking the fibers, but also makes it possible to ensure sufficient sealing . It suffices, if necessary experimentally, to seek the largest passage section, taking into account the total section of the fibers to be treated, still making it possible to offer sufficient sealing, taking into account the speed of advancement of the fibers and the length tubing. Typically, the vacuum inside the chamber 13 is for example of the order of 0.1 bar, the length of the vacuum chamber is approximately 1 meter.

At the outlet of the vacuum chamber 13 and the outlet pipe 13b, the arrangement 12 of fibers 11b passes through an impregnation chamber 14 comprising a supply reservoir 15 (connected to a metering pump not shown) and a reservoir of Impregnation 16 sealed completely filled with impregnating composition 17 based on a curable resin of the vinyl ester type (e.g., "ALTAC® E-Nova FW 2045" from AOC). By way of example, composition 17 further comprises (at a weight rate of 1 to 2%) a photoinitiator agent suitable for UV and/or UV-visible radiation with which the composition will be subsequently treated, for example bis-(2,4,6-trimethylbenzoyl)-phenylphosphine oxide ("Omnirad 819" from the company IGM). It may also comprise (for example approximately 5% to 15%) of a crosslinking agent such as, for example, tris(2-hydroxyethyl)isocyanurate triacrylate (“SR 368” from the company Sartomer). Of course, the impregnation composition 17 is in the liquid state.

Preferably, the length of the impregnation chamber is several meters, for example between 2 and 10 m, in particular between 3 and 5 m.

Thus, spring from the impregnation chamber 14, in a sealed outlet pipe 18 (still under primary vacuum), an impregnated material which comprises for example (% by weight) from 65% to 75% of solid fibers 11b, the remainder ( 25 to 35%) being constituted by the liquid impregnation matrix 17.

The impregnated then passes through calibrating means 19 comprising at least one calibrating die 20 whose channel (not shown here), for example of circular, rectangular or even conical shape, is adapted to the particular conditions of production. By way of example, this channel has a minimal cross-section of circular shape, the downstream orifice of which has a diameter slightly greater than that of the targeted monofilament. Said die has a length which is typically at least 100 times greater than the minimum dimension of the minimum section. Its function is to ensure high dimensional precision in the finished product, it can also play a role in dosing the fiber content with respect to the resin. According to a possible alternative embodiment, the die 20 can be directly integrated into the impregnation chamber 14, which avoids, for example, the use of the outlet pipe 18.

Preferably, the length of the calibration zone is several centimeters, for example between 5 and 50 cm, in particular between 5 and 20 cm.

Thanks to the calibration means (19, 20), a "liquid" composite monofilament 21 (liquid in the sense that its impregnating resin is always liquid) is obtained at this stage, the shape of the cross-section of which is preferably essentially circular.

On leaving the calibration means (19, 20), the liquid composite single strand 21 thus obtained is then polymerized by passing through a UV irradiation chamber (22) comprising a sealed glass tube (23) through which the single strand circulates. compound; said tube, the diameter of which is typically a few cm (for example 2 to 3 cm), is irradiated by a plurality (here, for example 4) of UV irradiators (24) in line ("UVAprint" lamps from the company Dr Hönle, wavelength 200 to 600 nm) arranged at a short distance (a few cm) from the glass tube.

Preferably, the length of the irradiation chamber is several meters, for example between 2 and 15 m, in particular between 3 and 10 m.

The irradiation tube (23) in this example is traversed by a stream of nitrogen.

The irradiation conditions are preferably adjusted in such a way that, at the outlet of the impregnation chamber, the temperature of the single strand in CVR, measured at the surface of the latter (for example using a thermocouple), is higher to the Tg of the crosslinked resin (in other words greater than 190°C), and more preferably less than 270°C.

Once the resin has polymerized (cured), the CVR single strand (25), this time in the solid state, driven in the direction of the arrow F, then arrives on its final receiving reel (26).

We finally obtain a composite block finished manufacturing as schematized very simply in the , in the form of a single strand in continuous CVR (25), of very great length, whose individual glass filaments (251) are distributed in a homogeneous manner throughout the volume of hardened resin (252). Its diameter is for example equal to about 1 mm.

Thanks to the operating conditions described above, the method of the invention can be implemented at high speed, greater than 50 m / min, preferably between 50 and 150 m / min, more preferably in a range of 60 to 120 m/min.

The continuous CVR single strand (25) can be cut to a determined length (not shown in the ), for example 45 mm by any means known to those skilled in the art, for example using a hydraulic guillotine, such as the “SH-5214” from the company Baileigh. This step can be carried out directly at the exit from the irradiation chamber (23). It can also be made after being packaged on a final receiving reel (26). In this case, it is preferred to unwind the single strand from the coil from the end of the single strand which is the most axially outer of the coil, in order to avoid helically deforming the single strand. Indeed, if the single strand of the coil is unrolled from the end of the single strand which is located the most axially inside the coil, this helically deforms the single strand which can be detrimental for the breaking stress.

The invention also relates to a ballotin comprising a plurality of single strands in CVR according to the invention and at least one element for holding the single strands together. Preferably, this holding element is a breakable film, for example tearable, dispersible, water-soluble. Preferably, the at least one holding element is a water-soluble yarn.

Advantageously, the holding element is a water-soluble film, preferably made of a material chosen from the group consisting of polyvinyl alcohols (PVA) or any water-soluble or bioplastic polymer, such as bioplastics derived from milk casein. Preferably, the at least one water-soluble film is made of a material chosen from the group consisting of polyvinyl alcohols.

The ballotin according to the invention advantageously comprises a number of single strands comprised in a range ranging from 300 to 20,000.

The single strands making up the ballotin can be of identical or different dimensions. For example, a ballotin can comprise single strands of different length, diameter and/or length to diameter ratio. Advantageously, the ballotin comprises single strands according to the invention having lengths and diameters not having more than 10%, preferably not more than 3%, of difference with respect to each other.

As indicated above, the single strands according to the invention are particularly useful as an additive for concrete. Thus, the invention also relates to the use of single strands in CVR according to the invention or of a ballotin according to the invention, to reinforce concrete and/or reduce the weight of the concrete and/or reduce or prevent cracking concrete.

The present invention also relates to a concrete comprising a plurality of CVR single strands according to the invention. The concrete can be prepared using any technique well known to those skilled in the art.

Advantageously, the volumetric content of the single strands according to the invention in the concrete according to the invention is comprised in a range ranging from 0.1% to 6%, for example from 0.1% to 1.5% for concretes called " conventional”, for example of the BPS C40/50 XA3 type, or from 1.5% to 6% for ultra-high performance fiber-reinforced concrete (UHPFRC).

IV- EXAMPLES

IV-1 Measurements and tests used

The porosity rate was measured according to the protocol :
- we took a cross-linked CVR monofilament,
- it was coated with a cold mounting resin, of the epoxy type in a vacuum coating device (CitoVac from the company Stuers),
- the glued CVR single strand was cut using a hydraulic guillotine (SH-5214 from Baileigh)
- the section of the single strand was polished in CVR using a mechanical polisher, from the company Mecapol to a final grain of 0.25 µm,
- a deposit of 1 to 4 nm of gold was made using a gold metallizer (Cerssington of the 108 or 208 series from the company Eloïse),
- the section of the single strand was observed in CVR under a scanning electron microscope under vacuum (15kV), and
- using an image processing program, FIJI for example, the surface percentage of the porosity was calculated (%porosity = area of porosity / (area of porosity + area of the fibers + area of the crosslinked resin ).

The mechanical properties in extension of the CVR single strand (modulus E ₂₃ , breaking stress Cr and elongation at break Ar ) were measured using an "INSTRON" type 5944 tensile machine (BLUEHILL® UNIVERSAL software supplied with the tensile machine), according to the ASTM D2343 standard, at a temperature of 23° C., on glued CVR single strands (that is to say ready to use). To prevent damage to the glass reinforcements when gripping the sample in the jaws of the traction machine, the bead bonding (Material: Cardboard 50 mm long; Adhesive used: Loctite EA 9483 (epoxy bi- components)) was made in the following way. The surfaces of the two facing heels have been glued as well as the reinforcement in order to limit the "dry zones" as much as possible (without adhesive). The beads were held in place for the curing time (12 h at 23° C.) in a template with the dimensions of the test specimens, with weights on the beads to ensure good bead/reinforcement contact. Before measurement, these single strands were subjected to prior conditioning (storage of the single strands for at least 24 hours in a standard atmosphere according to European standard DIN EN 20139 (temperature of 23 ± 2° C.; humidity of 50 ± 5%)). The tensile modulus was determined by linear regression of the stress versus strain curve, between 0.1% and 0.6% strain. This deformation was recorded by the MultiXtens 1995DA801 extensometer. The 260 mm specimens tested underwent traction at a nominal speed of 5 m/min, under a pre-test preload of 0.5 MPa (reference length 50 mm, distance between the jaws: 150 mm). All results given are an average of 10 measurements.

IV-2 Tests on single strands

Single strands (M1 to M4) in CVR were manufactured according to the process described previously with a mass percentage of glass/resin of 70/30. The resin composition used was based on vinylester resin (“ATLAC E-NOVA FW2045” from the company), a triacrylate hardener (“SR 368” from the company Sartomer) and a photoinitiator (“Omnirad 819” from IGM company). The glass fibers of the single strands M1 and M2 were “R25H” fibers from the company Owens Corning and that of the single strands M3 and M4 were “SE1200” fibers from the company Owens Corning. The diameter and the tex of the single strands as well as their physical characteristics and the mechanical properties are presented in Table 2 below.

M1 M2 M3 M4 Diameter
(mm) 1.05 0.70 0.5 0.3 Glass fiber tex
(g/km) 1200 600 300 100 Porosity rate (%) 0.27 0.43 0.14 0.01 Breaking stress (MPa) 1415 1281 1441 1329 Young's modulus (GPa) 49.1 49.5 48.8 46.2

The porosity rate and the breaking stress of these single strands were compared to reinforcing fibers for concrete of the prior art. It has been found that these fibers of the prior art systematically have a porosity rate greater than 2% and a breaking stress less than or equal to 1050 MPa.

Due to their low level of porosity and their high breaking stress, the single strands of the invention make it possible to improve the resistance to cracking of concrete.

It has thus been found that the single strands in accordance with the invention have a performance compromise between in particular the mechanical strength, the corrosion resistance, the processability (in particular the dispersibility during mixing, the processing temperature and the maintenance of homogeneity during the drying of the concrete).

Claims (15)

Single strand of glass-resin composite comprising glass filaments embedded in a crosslinked resin, characterized in that the single strand has a length within a range ranging from 5 to 85 mm, a diameter ranging from 0.2 to 1.3 mm, and a porosity rate of less than 2%. Single strand according to Claim 1, having a length comprised in a range ranging from 10 to 80 mm. Single strand according to any one of the preceding claims, having a diameter comprised in a range ranging from 0.25 to 1.25, preferably from 0.3 to 1.2 mm. Single strand according to any one of the preceding claims, having a length/diameter ratio ranging from 10 to 110, preferably from 15 to 65, more preferably from 20 to less than 60. Single strand according to any one of the preceding claims, not being helically deformed. Single strand according to any one of the preceding claims, in which the glass filaments represent from 65% to 85%, preferably from 70% to 80%, by weight of the single strand, and the crosslinked resin represents from 15% to 35%, preferably from 20% to 30%, by weight, of the single strand. Monofilament according to any one of the preceding claims, in which the crosslinked resin is based:

• a crosslinkable resin chosen from the group consisting of vinylester, epoxy, polyester resins and mixtures thereof,
• of a crosslinking system comprising a photoinitiator reactive to UV above 300 nm.

Single strand according to any one of the preceding claims, the single strand having a porosity rate of less than 1%, preferably less than 0.5%. Single strand according to any one of the preceding claims, the single strand having a breaking stress greater than 1050 MPa, preferably greater than or equal to 1100 MPa, more preferably greater than or equal to 1200 MPa. Single strand according to any one of the preceding claims, in which the initial tensile modulus denoted E ₂₃ of the single strand, measured at 23°C, is greater than 35 GPa, preferably greater than 42 GPa. Ballotin comprising a plurality of single strands of glass-resin composite comprising glass filaments embedded in a crosslinked resin according to any one of claims 1 to 10, and at least one breakable film holding the single strands together, the breakable film preferably being a water-soluble film of material chosen from the group consisting of polyvinyl alcohols (PVA). Ballotin according to Claim 11, in which the number of single strands is comprised in a range ranging from 300 to 20,000. Use of single strands of glass-resin composite comprising glass filaments embedded in a crosslinked resin according to any one of Claims 1 to 10 or of a ballotin according to any one of Claims 11 to 12, for reinforcing concrete and/ or reduce concrete weight and/or reduce or prevent concrete cracking. Concrete comprising a plurality of single strands of glass-resin composite comprising glass filaments embedded in a crosslinked resin according to any one of Claims 1 to 10, the volume ratio of the single strands in the concrete preferably being within a range ranging from 0, 1% to 6%. Process for manufacturing single strands of glass-resin composite comprising glass filaments embedded in a crosslinked resin according to any one of Claims 1 to 10, comprising the following successive steps:

• make a rectilinear arrangement of glass filaments and drive this arrangement in a direction of advance,
• in a vacuum chamber, degas the arrangement of glass filaments by the action of vacuum,
• at the outlet of the vacuum chamber, after degassing, pass through a vacuum impregnation chamber so as to impregnate said arrangement of glass filaments with a photo-crosslinkable or thermosetting resin composition, in the liquid state, "called impregnation resin », to obtain an impregnated containing the glass filaments and the resin composition,
• passing said impregnated through a calibration die having a surface section and predefined shape, to impose a single-strand shape on it,
• downstream of the die, in a UV irradiation chamber, to polymerize the resin composition under the action of UV, the irradiation chamber comprising a tube transparent to UV, called irradiation tube, through which the single strand circulates during formation, traversed by a current of inert gas, the speed (denoted V _ir ) of passage of the single strand in the irradiation chamber being greater than 50 m/min, the duration of irradiation (denoted D _ir ) of the single strand in the irradiation chamber being equal to or greater than 1.5 s,
• cutting the filament so as to obtain single strands of a length comprised in a range ranging from 5 to 85 mm.