FR3136761A1 - USE OF GLASS-RESIN COMPOSITE FIBERS FOR CONCRETE REINFORCEMENT - Google Patents

Abstract

The invention relates to a process for manufacturing glass-resin composite single strands comprising alkali-resistant glass filaments comprising from 5% to 30% by mass of ZrO2 embedded in a crosslinked resin, to the single strands obtained by this process, to a ballotin comprising a plurality of these single strands, as well as their uses for reinforcing concrete, reducing the weight of concrete, reducing or preventing cracking of concrete. The invention also relates to concrete comprising 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 as well as to their processes for obtaining them.

Concrete is probably the most widely used construction 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 fibers.

Although very resistant to compression, concrete has 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 therefore 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 containing such fibers. Furthermore, they often have densities greater than 7.7 and are therefore not distributed homogeneously in concrete with a lower density (metal fibers tend to flow under the effect of gravity, or even under the effect of vibrations when the concrete is vibrated to evacuate any air bubbles that may have been entrained during pouring).

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

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

Continuing its research, the Applicant unexpectedly discovered that the use of particular alkali-resistant glass-resin composite fibers makes it possible to resolve the aforementioned problem.

The Applicant has also noted numerous advantages provided by the fibers according to the invention. Their implementation is very easy compared to the concrete fibers of the prior art, in particular during the phase of mixing the different components of the concrete (easily dispersible), but also during the drying phase of the concrete: due to their density close to that of concrete, the fibers remain homogeneously distributed in the concrete (they do not tend to sink like metal fibers which are denser than concrete, nor to rise like synthetic fibers which are 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 their use in light concretes without impacting the aesthetics of these concretes. Also, more generally, due to their density and their reinforcing capacity, the use of the fibers according to the invention makes it possible to significantly reduce overall CO ₂ emissions compared to the use of other fibers of the prior art, at constant level of reinforcement. Finally, the use of alkali-resistant glass filaments makes it possible to resist the alkaline environment of concrete and thus prolong the effectiveness of fiber reinforcement over time.

Thus, the subject of the invention is a process for manufacturing single strands of glass-resin composite comprising alkali-resistant glass filaments comprising from 5% to 30% by mass of ZrO ₂ embedded in a crosslinked resin, comprising the following successive steps :
- produce a rectilinear arrangement of alkali-resistant glass filaments comprising from 5% to 30% by mass of ZrO ₂ and drive this arrangement in a direction of advancement,
- in a vacuum chamber, degas the arrangement of glass filaments by the action of the 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 photocrosslinkable resin composition, in the liquid state, called “impregnation resin” , to obtain an impregnated containing the glass filaments and the resin composition,
- pass said impregnated material through a calibration die having a section of predefined surface and shape, to impose on it a single-strand shape,
- downstream of the die, in a UV irradiation chamber, 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 being formed, traversed by a current of inert gas, the speed (noted V _ir ) of passage of the single strand in the irradiation chamber being greater than 50 m/min, the irradiation duration (noted D _ir ) of the single strand in the irradiation chamber being equal to or greater than 1.5 s,
- cut the single strand to a length within a range of 5 to 85 mm.

The invention also relates to a single strand capable of being obtained by a process according to the invention, a ballotin comprising a plurality of single strands according to the invention.

It also relates to the use of single strands 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 of the concrete, as well as a concrete comprising a plurality of single strands according to the invention, the volume ratio of the single strands in the concrete being preferably included in a range ranging from 0.1% to 6%.

I- DEFINITIONS

Herein, unless expressly stated otherwise, all percentages (%) shown are percentages (%) by mass.

By the expression "composition based on", is meant a composition comprising the mixture and/or the in situ reaction product of the different constituents used, some of these constituents being able to react and/or being intended to react with each other, at least less partially, during the different phases of manufacturing the composition; the composition can thus be in the totally or partially crosslinked state or in the non-crosslinked state.

On the other hand, any interval of values designated by the expression "between a and b" represents the range of values going from more than a to less than b (that is to say limits a and b excluded) while any interval of values designated by the expression "from a to b" means the range of values going from a to b (that is to say including the strict limits a and b). In the present document, when we designate an interval of values by the expression "from a to b", we also and preferentially designate the interval represented by the expression "between a and b".

All 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 process for synthesizing the single strand according to the invention before the latter is cut to a determined length.

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

III- DESCRIPTION OF THE INVENTION

The invention therefore relates to a process for manufacturing single strands (or fibers, the two terms can be used equivalently) in glass-resin composite (abbreviated "CVR") comprising alkali-resistant glass filaments comprising from 5% to 30% by mass of ZrO ₂ embedded in a crosslinked resin, comprising the following successive steps:
- produce a rectilinear arrangement of alkali-resistant glass filaments comprising from 5% to 30% by mass of ZrO ₂ and drive this arrangement in a direction of advancement,
- in a vacuum chamber, degas the arrangement of glass filaments by the action of the 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 photocrosslinkable resin composition, in the liquid state, called “impregnation resin” , to obtain an impregnated containing the glass filaments and the resin composition,
- pass said impregnated material through a calibration die having a section of predefined surface and shape, to impose on it a single-strand shape,
- downstream of the die, in a UV irradiation chamber, 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 being formed, traversed by a current of inert gas, the speed (noted V _ir ) of passage of the single strand in the irradiation chamber being greater than 50 m/min, the irradiation duration (noted D _ir ) of the single strand in the irradiation chamber being equal to or greater than 1.5 s, this step leading to obtaining a single strand in CVR,
- cut the single strand to a length within a range of 5 to 85 mm.

All the steps (arrangement, degassing, impregnation, calibration, polymerization, possible winding and cutting) of the process of the invention are, independently of each other, steps known to those skilled in the art, as are 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.

By “alkali-resistant glass filament” is meant an AR type glass filament. Such filaments are well known to those skilled in the art and are different from glass filaments of other types, type E or type C for example. They have been described for example in documents FR2644449A1, FR2907777A1 and JP2000178879.

Advantageously, the alkali-resistant glass filaments comprise from 6% to 22%, preferably from 10% to 20%, by mass, of ZrO ₂ .

Typically, glass filaments are present in the form of a single multifilament fiber or several multifilament fibers associated with each other. In the latter case, the multifilament fibers are preferably essentially unidirectional. Each of the multifilament fibers can comprise several tens, hundreds or even thousands of single glass filaments. These very fine unit filaments generally and preferably have an average diameter of the order of 5 to 30 µm, more preferably 10 to 20 µm. The section of the unit filaments is preferably cylindrical.

As an example of alkali-resistant glass fibers which can be used in the context of the present invention, mention may be made of the fibers “AR320S-920S”, “AR640S-920S” or “AR1200S-920S” from the company Nippon Electric Glass, “Cem-fil” fibers from the Owens Corning company, or “HEJ 16.7%” fibers from the Huierjie company. Those skilled in the art know very well how to adapt the sizing to the surface of the filaments to improve the compatibility of the filaments with the resin used in the glass-resin composite.

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

By “resin” or “resin composition”, we mean here the resin as such or any composition based on this resin and comprising at least one additive (that is to say one or more additives) before crosslinking. By “crosslinked” resin, we understand of course that the resin is hardened (photocured and/or thermoset), 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).

Advantageously, the impregnation resin is based on at least:
- a crosslinkable resin chosen from the group consisting of vinyl ester resins (preferably vinyl ester urethane resins), epoxy, polyester and their mixtures,
- a crosslinking system preferably comprising a photoinitiator agent reactive to UV rays greater than 300 nm.

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

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

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

An epoxyvinylester resin based on novolac (part in square brackets in formula I below) corresponds for example, in a known manner, to formula (I) which follows:
(I)

An epoxyvinylester resin based on bisphenolic A (part in brackets of formula (II) below) corresponds for example to the formula (the "A" reminding that the product is manufactured using acetone):
(II)

An epoxyvinylester resin of the novolac and bisphenolic type has shown excellent results. As an 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. Epoxyvinylester resins are available from other manufacturers such as for example AOC (USA - “VIPEL” resins).

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

According to the invention, it is 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 single strand.

After passing through the vacuum chamber, the glass filaments enter an impregnation chamber which is completely full of impregnation resin, therefore devoid of air: it is in this sense that we can describe this step as “vacuum impregnation” impregnation.

The so-called "calibration" die allows, thanks to a straight section of determined dimensions, generally and preferably circular or rectangular, to adjust the proportion of resin in relation to the glass fibers while imposing the shape and size of the impregnated material. thickness targeted for the single strand.

Advantageously, the single strand at the outlet of the calibration die has a diameter ranging from 0.2 to 1.3 mm, preferably from 0.25 to 1.25 mm, preferably from 0.3 to 1.2 mm, so that the cut single strands obtained following the process according to the invention have these diameters.

The polymerization or UV irradiation chamber then has the function of polymerizing and crosslinking the resin under the action of UV.

The UV irradiation chamber includes one or more UV irradiators (or radiators). Advantageously, the irradiation chamber comprises a plurality of UVs, that is to say at least two (two or more than two) which are arranged in a line around the irradiation tube. Each UV irradiator typically comprises one (at least one) UV lamp (preferably emitting in a spectrum of 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. Even more preferably, 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 included in a range of 3,000 to 10,000 watts per meter.

UV radiators suitable for the process 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. (high pressure mercury lamps doped with iron). The nominal (maximum) power of each radiator of this type is equal to approximately 13,000 Watts, the actual power delivered can be adjusted with a potentiometer between 30 and 100% of the nominal power.

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

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

The final CVR single strand thus formed through the UV irradiation chamber, in which the resin is now in the solid state, is then harvested for example on a receiving spool on which it can be wound over a very long length. The process can thus include a winding step for storing the single strand after passing through the UV irradiation chamber and before being cut.

Advantageously, the single strand coming from the irradiation chamber, possibly after storage, is cut so as to obtain single strands with a length comprised in a range from 10 to 80 mm, for example from 15 to 60 mm.

The single strands obtained by the process according to the invention advantageously have a length/diameter ratio ranging from 10 to 110, preferably from 20 to 90, more preferably from 25 to less than 80.

In a particularly advantageous manner, the process 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 UV-transparent tube (such as a quartz tube or preferably glass), called an 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 , elongation Ar and modules ( E and E' ).

In particular, in the absence of neutral gas sweeping such as nitrogen in the irradiation tube, it was found that the above properties of the CVR single strand were degraded quite quickly during manufacturing and therefore that the industrial performance was no longer guaranteed.

Furthermore, if the irradiation duration D _ir of the single strand in the irradiation chamber is too short (less than 1.5 s), numerous tests have revealed that the resin is not crosslinked enough, which causes degradation. mechanical properties, including breaking stress and bending resistance. Furthermore, if the irradiation duration D _ir of the single strand in the irradiation chamber is too long (greater than 10 s for example), this increases the risk of the resin boiling and therefore creating more porosity and to degrade the mechanical properties, including the breaking stress.

Thus, we understand that it is thanks to the combination of the steps of the process according to the invention, in particular thanks to the steps of degassing the arrangement of glass filaments by the action of the vacuum, in the vacuum chamber, and of polymerization in the irradiation tube traversed by a current of inert gas, at the speed V _ir and during the aforementioned irradiation duration D _ir , that CRV single strands having a porosity rate of less than 2% are obtained and a breaking stress greater than 1,050 MPa.

Director ( _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 Test 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 Test 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 was further observed 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 rate of alignment of the filaments of glass inside the CVR single strand, on the other hand better maintenance of the vacuum in the vacuum chamber with a significantly reduced risk of seeing a certain fraction of impregnation resin rise from the impregnation chamber towards the chamber empty, and therefore better impregnation quality.

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 duration D _ir is between 1.5 and 10 s, more preferably in a range of 2 to 5 s.

Another object of the invention is a CVR single strand capable of being obtained by a process according to the invention, preferably according to 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 UV-transparent tube (such as a quartz tube or preferably glass), called an 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.

The CVR single strand capable of being obtained by a process according to the invention therefore comprises alkali-resistant glass filaments embedded in a crosslinked resin and has a length comprised in a range ranging from 5 to 85 mm. Furthermore, taking into account the specific steps of the process according to the invention, the single strand advantageously has a porosity rate of less than 2% and a breaking stress greater than 1,050 MPa.

According to the invention, the CVR single strand advantageously has a porosity rate of 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 FIJI program. To carry out the measurement, the following protocol is preferably carried out :
- we take a single strand of cross-linked CVR,
- it is coated with a cold coating resin, of the epoxy type for example, for example in a vacuum coating device (CitoVac from the company Stuers for example),
- the coated CVR single strand is cut, for example using a hydraulic guillotine, such as the “SH-5214” from the Baileigh company,
- the section of the CVR single strand is polished, for example using a mechanical polisher, from the company Mecapol for example, preferably to a final grain of 0.25µm,
- a deposit of 1 to 4 nm of gold is carried out, for example using a gold metalizer, such as Cerssington from the 108 or 208 series from the company Eloïse,
- the section of the single strand in CVR is observed under a scanning electron microscope, preferably under vacuum (15kV), and
- using an image processing program, FIJI for example, we calculate the surface percentage of porosity. By “porosity” of the CVR single strand we mean any gas (notably air) or vacuum present within the CVR single strand.

According to the invention, the CVR single strand advantageously has a breaking stress Cr greater than 1,050 MPa, preferably greater than or equal to 1,100 MPa, more preferably greater than or equal to 1,200 MPa. Preferably, the single strand has a breaking stress of between 1050 and 1700 MPa, preferably from 1100 to 1600 MPa, more preferably from 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. In particular, the single strand preferably has an E ₂₃ of between 35 and 50 GPa, preferably between 40 and 49 GPa.

The mechanical properties in extension of the CVR single strand (module E ₂₃ , breaking stress Cr and elongation at break Ar ) can be measured in a known manner according to the protocol described in paragraph IV-1 below.

Furthermore, the CVR single strand according to the invention advantageously has the following properties:
- the glass transition temperature (noted Tg ) of the crosslinked resin is 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 extension modulus (denoted E ₂₃ ) of the single strand, measured at 23°C, is greater than 35 GPa, preferably greater than 40 GPa; And
the real part of the complex module (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 crosslinked resin is 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 "822-2" device from Mettler Toledo; atmosphere nitrogen; samples previously heated from room temperature (23°C) to 250°C (10°C/min), then cooled quickly to 23°C, before final recording of the DSC curve from 23°C to 250 °C, at 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 modulus E' 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 module 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, 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 module of the measured single strand 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, traction or twisting.

According to this device, the three-point bending test does not allow in a known manner to enter the initial geometric data for a single strand of circular section, we can only introduce the geometry of a rectangular (or square) section. In order to obtain a precise measurement of the module E' for a single strand of diameter D , we therefore introduce by convention into the software a square section of side " a " having the same surface moment of inertia, in order to work at the same stiffness R of the test pieces.

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 single strand of diameter D , according to the equation:

a = D * (π/6) ^0.25

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

The specimen to be tested, generally of circular section and 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 asymmetric deformation, the interior of the 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 test piece 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', the viscous modulus E'' and the loss angle (δ) as a function of the temperature (where E' is the real part and E'' the part imaginary complex module); Tg’ is the glass transition temperature corresponding to the maximum (peak) of tan(δ).

Advantageously, the elastic deformation in compression under flexion 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 flexion are measured on the CVR single strand 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 create a loop which 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 rupture, breaks on the side where the material is in extension, which can be identified by simple observation. Since in this case the dimensions of the loop are important, it is possible to read the radius of the circle inscribed in the loop at any time. The radius of the circle written just before the breaking point corresponds to the critical radius of curvature, designated 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, that is to say D/2):

Ec = r / (Rc + r)

The breaking stress in compression under flexion denoted 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 CVR single strand according to the invention, the breakage of the loop appears in the extension part, we conclude that, in bending, the breakage stress in compression is greater than the breakage stress in extension.

We can also break a rectangular bar in bending using the so-called three-point method (ASTM D 790). This method also makes it possible to verify, 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 alignment rate of the glass filaments is such that more than 85% (% by number) of the filaments have an inclination relative 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 case, 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 0 to 0.5.

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

The weight rate is calculated by making the ratio of the title of the initial fiberglass to the title of the final CVR single strand. 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 volume fraction of glass fiber in the CVR single strand is advantageously included in a range ranging from 40% to 60%, preferably from 45% to 55%.

The volume fraction of mineral fiber in the final CVR single strand corresponds to the surface fraction of glass fiber in a cross section of the CVR single strand in relation to the total surface area of its section. The surface fraction of glass fiber can be determined in the same way as described below for measuring the porosity rate.

Furthermore, the crosslinked resin represents from 15% to 35%, preferably from 20% to 30%, by weight, of the CVR single strand of the invention. Furthermore, the volume fraction of resin in the CVR single strand is advantageously included in a range ranging from 40% to 60%, preferably from 45% to 55%. The weight percentage and volume fraction of crosslinked resin can be obtained using a method similar to the method for obtaining the weight percentage and volume fraction of glass fiber described above.

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 balance from the company Mettler Toledo of the “PG503 DeltaRange” type; the samples, a few cm in size, are successively weighed in air and immersed in ethanol; the device's software then determines the average density over three measurements.

The diameter D of the CVR single strand of the invention is preferably included in a range ranging from 0.2 to 1.3 mm, preferably from 0.25 to 1.25 mm, more preferably between 0.3 and 1, 2 mm, especially between 0.4 and 1.1 mm.

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

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

Advantageously, the length/diameter ratio L/D of the CVR single strands of the invention is included in a range ranging from 10 to 110, preferably from 20 to 90, more preferably from 25 to less than 80.

The invention also relates to a ballotin comprising a plurality of CVR single strands 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 thread.

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 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 may include 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 presenting no more than 10%, preferably no more than 3%, difference from each other.

As indicated previously, the single strands according to the invention are particularly useful as an additive for concrete. Thus, the invention also relates to the use of CVR single strands 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 volume ratio of the single strands according to the invention in the concrete according to the invention is included in a range ranging from 0.1% to 6%, for example from 0.1% to 1.5% for concretes called " "conventional", for example of type BPS C40/50

Examples of manufacturing CVR single strands according to the invention and their use to reinforce concrete are described below.

There appended very simply schematizes an example of a device 10 allowing the production of CVR single strands conforming to the invention.

We see a spool 11a containing, in the example illustrated, glass fibers 11b (in the form of multifilaments). The coil is continuously unwound by drive, so as to produce a rectilinear arrangement 12 of these fibers 11b. In general, reinforcing fibers are delivered in "rovings", that is to say already in groups of fibers wound in parallel on a reel; for example, we use alkali-resistant glass fibers marketed by Nippon Electric Glass under the fiber designation "AR1200S-920S", with a density 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 the CVR single strand 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 opening onto an impregnation chamber 14, the two pipes preferably at rigid wall having for example a minimum section greater (typically twice as much) than the total section of fibers and a length much greater (typically 50 times more) than said minimum section.

As already taught by the aforementioned application EP-A-1 174 250, the use of rigid wall tubing, both for the inlet orifice into 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 ensures sufficient sealing . It is sufficient, if necessary experimentally, to search for the largest passage section, taking into account the total section of the fibers to be treated, still making it possible to provide 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 tank 15 (connected to a dosing pump not shown) and a tank of waterproof impregnation 16 completely filled with impregnation composition 17 based on a curable vinyl ester type resin (e.g., “ALTAC® E-Nova FW 2045” from AOC). By way of example, composition 17 further comprises (at a weight level of 1 to 2%) a photoinitiator agent suitable for UV and/or UV-visible radiation with which the composition will subsequently be treated, for example bis-(2,4,6-trimethylbenzoyl)-phenylphosphine oxide ("Omnirad 819" from the company IGM). It can also comprise (for example approximately 5% to 15%) of a crosslinking agent such as for example tris(2-hydroxy ethyl)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, out of the impregnation chamber 14, in a sealed outlet tube 18 (still under primary vacuum), an impregnated material which comprises for example (% by weight) from 65% to 75% solid fibers 11b, the remainder ( 25 to 35%) being constituted by the liquid impregnation matrix 17.

The impregnation then passes through calibration means 19 comprising at least one calibration die 20 whose channel (not shown here), for example of circular, rectangular or even conical shape, is adapted to the particular production conditions. For example, this channel has a minimum cross section of circular shape whose downstream orifice has a diameter slightly greater than that of the single strand in question. 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 measuring the fiber content in relation 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 single strand 21 (liquid in the sense that its impregnation resin is always liquid) is obtained at this stage, the shape of the cross section of which is preferably essentially circular.

At the outlet of 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. composite; said tube, whose diameter 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, of 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.

In this example, a nitrogen current flows through the irradiation tube (23).

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

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

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

Thanks to the operating conditions described above, the process 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 on the figure). ), 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 Baileigh company. This step can be carried out directly at the outlet of the irradiation chamber (23). It can also be carried out after the single strand has been conditioned on a final receiving reel (26). In this case, we prefer to unwind the single strand of the coil from the end of the single strand which is located most axially outside the coil, in order to avoid helically deforming the single strand. Indeed, if we unwind the single strand of the coil from the end of the single strand which is located most axially inside the coil, this helically deforms the single strand which can be detrimental for the breaking stress.

IV- EXAMPLES IV-1 Measurements and tests used

The porosity rate was measured according to the protocol :
- we took a single strand of cross-linked CVR,
- it was coated with a cold coating resin, 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 the Baileigh company)
- the section of the CVR single strand was polished using a mechanical polisher from the company Mecapol to a final grain of 0.25µm,
- a deposition of 1 to 4 nm of gold was carried out using a gold metalizer (Cerssington from the 108 or 208 series from the company Eloïse),
- the section of the single strand in CVR was observed under a vacuum scanning electron microscope (15kV), and
- using an image processing program, FIJI for example, we calculated the surface percentage of the porosity (%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 (module E ₂₃ , breaking stress Cr and elongation at break Ar ) were measured using an “INSTRON” type 5944 traction machine (BLUEHILL® UNIVERSAL software supplied with the traction machine), according to the ASTM D2343 standard, at a temperature of 23°C, on glued CVR single strands (i.e. ready to use). 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 the European standard DIN EN 20139 (temperature of 23 ± 2°C; hygrometry of 50 ± 5%)). To avoid damage to the glass reinforcements when gripping the sample in the jaws of the traction machine, heel gluing (Material: 50 mm long cardboard; Adhesive used: Loctite EA 9483 (epoxy bi- components)) was carried out as follows. The surfaces of the two opposite heels have been glued as well as the reinforcement in order to limit the “dry zones” as much as possible (without adhesive). The heels were held in place for the curing time (12 hours at 23°C) in a template with the dimensions of the test specimens, with weights on the heels to ensure good heel/reinforcement contact. 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 samples 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 5 measurements.

IV-2 Tests on single strands

Single strands (M1 to M3) in CVR were manufactured according to the process described previously with a speed V _ir of passage of the single strand in the irradiation chamber of 100 m/min, an irradiation duration D _ir of the single strand in the chamber irradiation time of 2.4 s, the length of the irradiation chamber being 4 m. The resin composition used was based on vinyl ester resin (“ATLAC E-NOVA FW2045” from the company), a triacrylate hardener (“SR 368” from the company Sartomer) and a photoinitiator (“Omnirad 819” from the company the IGM company). The alkali-resistant glass filaments of the M1, M2 and M3 single strands were respectively “AR1200S” filaments from the company Nippon Electric Glass. The diameter and tex of the single strands as well as their physical characteristics and mechanical properties are presented in table 2 below.

M1 M2 M3 Diameter
(mm) 0.55 0.75 1.05 Tex fiberglass
(g/km) 320 640 1200 Fiberglass/resin mass ratio 72/28 66/34 70/30 Porosity rate (%) 0.2 0.5 0.7 Breaking Stress (MPa) 1229 1135 1234 Young’s modulus (GPa) 42.8 37.5 40.0

The porosity rate and the breaking stress of these single strands were compared to concrete reinforcing fibers of the prior art. It was 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 1,050 MPa.

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

It was thus noted that the single strands conforming to the invention present a performance compromise between in particular mechanical strength, corrosion resistance, processability (in particular dispersibility during mixing, the implementation temperature and the maintenance of homogeneity during concrete drying).

Claims (15)

Process for manufacturing glass-resin composite single strands comprising alkali-resistant glass filaments comprising from 5% to 30% by mass of ZrO₂embedded in a crosslinked resin, comprising the following successive steps:

• produce a rectilinear arrangement of alkali-resistant glass filaments comprising from 5% to 30% by mass of ZrO ₂ and drive this arrangement in a direction of advancement,
• in a vacuum chamber, degas the arrangement of glass filaments by the action of the 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 photocrosslinkable resin composition, in the liquid state, called "impregnation resin", to obtain an impregnated containing the glass filaments and the resin composition,
• pass said impregnated material through a calibration die having a section of predefined surface and shape, to impose on it a single-strand shape,
• downstream of the die, in a UV irradiation chamber, polymerize the resin composition under the action of UV, the irradiation chamber comprising a UV-transparent tube, called an irradiation tube, through which the single strand circulates during formation, traversed by a current of inert gas, the speed (noted V _ir ) of passage of the single strand in the irradiation chamber being greater than 50 m/min, the irradiation duration (noted D _ir ) of the single strand in the irradiation chamber being equal to or greater than 1.5 s,
• cut the single strand to a length within a range of 5 to 85 mm.

Method according to claim 1, characterized in that the single strands have a diameter ranging from 0.2 to 1.3 mm, preferably from 0.25 to 1.25 mm, preferably from 0.3 to 1.2 mm. Method according to any one of the preceding claims, characterized in that the cut single strands have a length comprised in a range ranging from 10 to 80 mm, preferably from 15 to 60 mm. Method according to claim 3, in which the single strand has a length/diameter ratio ranging from 10 to 110, preferably from 20 to 90, more preferably from 25 to less than 80. Method according to any one of the preceding claims, characterized in that the alkali-resistant glass filaments comprise from 6% to 22%, preferably from 10% to 20%, by mass, of ZrO ₂ . Method according to any one of the preceding claims, characterized in that the alkali-resistant 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 20% to 30%, by weight, of the single strand. Method according to any one of the preceding claims, characterized in that the impregnation resin is based on at least:

• a crosslinkable resin chosen from the group consisting of vinyl ester, epoxy, polyester resins and their mixtures,
• a crosslinking system comprising a photoinitiator agent reactive to UV beyond 300 nm.

Single strand obtained by a process according to any one of claims 1 to 7. Single strand according to claim 8, characterized in that it has a porosity rate of less than 2%, preferably less than 1%, preferably less than 0.5%. Single strand according to any one of claims 8 to 9, characterized in that it has a breaking stress greater than 1,050 MPa, preferably greater than or equal to 1,100 MPa, more preferably greater than or equal to 1,200 MPa. Single strand according to any one of claims 8 to 10, characterized in that it has an initial extension modulus denoted E ₂₃ of the single strand, measured at 23°C, is greater than 35 GPa, preferably greater than 40 GPa. Ballotin comprising a plurality of single strands according to any one of claims 8 to 11, and at least one breakable film holding the single strands together, the breakable film preferably being a water-soluble film made of material chosen from the group consisting of polyvinyl alcohols (PVA ). Ballotin according to claim 12, in which the number of single strands is included in a range ranging from 300 to 20,000. Use of single strands according to any one of claims 8 to 11 or of a ballotin according to any one of claims 12 to 13, to reinforce concrete and/or reduce the weight of the concrete and/or reduce or prevent cracking of the concrete concrete. Concrete comprising a plurality of single strands according to any one of claims 8 to 11, the volume ratio of the single strands in the concrete being preferably included in a range ranging from 0.1% to 6%.