Use of fibres of a glass-resin composite, for reinforcing concrete

Abstract

The invention relates to a process for the manufacture of monofilaments made of a glass-resin composite, comprising filaments of an alkali-resistant glass comprising from 5% to 30% by weight of ZrO2, embedded in a crosslinked resin, to the monofilaments obtained by this process, to a roll comprising a plurality of these monofilaments, as well as to the use thereof for reinforcing concrete, reducing the weight of the concrete, and reducing or preventing cracking of the concrete. The invention also relates to concrete comprising these monofilaments.

Description

[0001] USE OF GLASS-RESIN COMPOSITE FIBERS FOR REINFORCING CONCRETE

[0002] The present invention relates to glass-resin composite fibers for reinforcing concrete and to methods for obtaining them.

[0003] 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 construction, road construction, and civil engineering sectors.

[0004] Concrete is primarily composed of aggregates held together by a binder, most commonly Portland cement. To improve the properties of concrete, additives such as ultrafine particles (e.g., silica fume), superplasticizers (also known as water reducers), or metal, synthetic, or mineral fibers are known to be used.

[0005] Although highly resistant to compression, concrete has low tensile strength, often accompanied by the appearance of cracks. To combat this problem, the use of reinforcing fibers is known. Due to their mechanical properties, metal fibers are particularly useful for reinforcing concrete. They are therefore widely used to make concrete more ductile and improve its resistance to cracking.

[0006] However, metal fibers have the disadvantage of being susceptible 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 evenly 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 air bubbles that may have been entrained during pouring).

[0007] To solve this problem, it has been proposed to replace metal fibers with synthetic fibers. However, the mechanical strength (e.g., Young's Modulus, tensile strength) 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 (approximately between 600°C and 900°C), which may limit their use for certain applications.

[0008] Thus, it remains interesting to have fibers that 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 cracking.

[0009] Continuing its research, the Applicant unexpectedly discovered that the use of particular alkali-resistant glass-resin composite fibres makes it possible to solve the aforementioned problem.

[0010] 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 mixing phase of the various 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 distributed homogeneously 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 maximum usage temperature much higher than the synthetic fibers currently used. Furthermore, the white color of the fibers according to the invention allows their use in light-colored concrete 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 CO2 emissions compared to the use of other fibers of the prior art, at a 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 reinforcement effectiveness of the fibers over time.

[0011] Thus, the subject of the invention is a method for manufacturing single strands of glass-resin composite comprising alkali-resistant glass filaments comprising from 5% to 30% by mass of ZrO2 embedded in a crosslinked resin, comprising the following successive steps:

[0012] - making a rectilinear arrangement of alkali-resistant glass filaments comprising from 5% to 30% by mass of ZrCL and driving this arrangement in a direction of advance,

[0013] - in a vacuum chamber, degas the arrangement of glass filaments by the action of the vacuum,

[0014] - at the outlet of the vacuum chamber, after degassing, passing 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 impregnation containing the glass filaments and the resin composition,

[0015] - passing said impregnated material through a calibration die having a predefined surface section and shape, to impose a single-strand shape on it,

[0016] - 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 an irradiation tube, through which the single strand being formed circulates, traversed by a current of inert gas, the speed (denoted Vir ) of passage of the single strand in the irradiation chamber being greater than 50 m / min, the irradiation duration (noted Di r ) of the single strand in the irradiation chamber being equal to or greater than 1.5 s,

[0017] - cut the single strand to a length within a range of 5 to 85 mm.

[0018] The invention also relates to a single strand capable of being obtained by a method according to the invention, a ballotin comprising a plurality of single strands according to the invention.

[0019] 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 preferably being within a range from 0.1% to 6%.

[0020] I- DEFINITIONS

[0021] In this document, unless expressly stated otherwise, all percentages (%) indicated are percentages (%) by mass.

[0022] The expression "composition based on" means 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 partially, during the different phases of manufacture of the composition; the composition can thus be in a totally or partially crosslinked state or in a non-crosslinked state.

[0023] On the other hand, any interval of values ​​designated by the expression "between a and b" represents the range of values ​​from more than a to less than b (i.e., excluding the limits a and b), while any interval of values ​​designated by the expression "from a to b" means the range of values ​​from a to b (i.e., 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.

[0024] All glass transition temperature “Tg” values ​​described herein are measured in a known manner by DSC (Differential Scanning Calorimetry) according to ASTM D3418 (1999). II- BRIEF DESCRIPTION OF THE FIGURES

[0025] [Fig. 1] Figure 1 represents a diagram of the process for synthesizing the single strand according to the invention before the latter is cut to a determined length.

[0026] [Fig. 2] Figure 2, not shown to scale to facilitate understanding, is a drawing showing a cross-section of the single strand according to the invention.

[0027] III- DESCRIPTION OF THE INVENTION

[0028] The invention therefore relates to a method for manufacturing single strands (or fibers, the two terms being able to be used equivalently) in glass-resin composite (abbreviated as "CVR") comprising alkali-resistant glass filaments comprising from 5% to 30% by mass of ZrO? embedded in a crosslinked resin, comprising the following successive steps:

[0029] - making a rectilinear arrangement of alkali-resistant glass filaments comprising from 5% to 30% by mass of ZrO? and driving this arrangement in a direction of advance,

[0030] - in a vacuum chamber, degas the arrangement of glass filaments by the action of the vacuum,

[0031] - at the outlet of the vacuum chamber, after degassing, passing 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 impregnation containing the glass filaments and the resin composition,

[0032] - passing said impregnated material through a calibration die having a predefined surface section and shape, to impose a single-strand shape on it,

[0033] - 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 an irradiation tube, through which the single strand being formed circulates, traversed by a current of inert gas, the speed (denoted Vi r) of passage of the single strand in the irradiation chamber being greater than 50 m / min, the irradiation duration (noted Di r ) of the single strand in the irradiation chamber being equal to or greater than 1.5 s, this step resulting in obtaining a single strand in CVR,

[0034] - cut the single strand to a length within a range of 5 to 85 mm.

[0035] All the steps (arrangement, degassing, impregnation, calibration, polymerization, optional 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 other of applications EP-A-1 074 369 and EP-A-1 174 250. By "alkali-resistant glass filament" is meant a glass filament of type AR. Such filaments are well known to those skilled in the art and differ 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.

[0036] Advantageously, the alkali-resistant glass filaments comprise from 6% to 22%, preferably from 10% to 20%, by mass, of ZrCL.

[0037] Typically, the 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 may comprise several tens, hundreds or even thousands of unit 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.

[0038] Examples of alkali-resistant glass fibers that can be used in the context of the present invention include the “AR320S-720S”, “AR640S-720S” or “AR1200S-720S” fibers from Nippon Electric Glass, the “Cem-fil” fibers from Owens Corning, or the “HEJ 16.7%” fibers from Huierjie. Those skilled in the art are very good at adapting the sizing to the surface of the filaments to improve the compatibility of the filaments with the resin used in the glass-resin composite.

[0039] The resin used is by definition a crosslinkable resin (ze, curable) capable of being crosslinked, cured by any known method, in particular and preferably by UV (or UV-visible) radiation, preferably emitting in a spectrum ranging from at least 300 nm to 450 nm.

[0040] By "resin" or "resin composition" is meant here the resin as such or any composition based on this resin and comprising at least one additive (i.e. one or more additives) before crosslinking. By "crosslinked" resin is meant 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 so-called thermoplastic polymers).

[0041] Advantageously, the impregnation resin is based on at least:

[0042] - a crosslinkable resin chosen from the group consisting of vinylester resins (preferably vinylester urethane resins), epoxy, polyester and their mixtures, - a crosslinking system preferably comprising a photoimitating agent reactive to UV rays above 300 nm.

[0043] The crosslinkable resin is preferably a polyester or vinylester resin, more preferably a vinylester resin. The term "polyester" resin is understood to mean, in a known manner, a resin of the unsaturated polyester type. Vinylester resins are well known in the field of composite materials.

[0044] Without this definition being limiting, the vinylester resin is preferably of the epoxyvinylester type. More preferably, a vinylester resin is used, in particular of the epoxy type, which is at least partly based on (i.e. grafted onto a structure of the type) novolac (also called phenoplast) and / or bisphenolic, or preferably a vinylester resin based on novolac, bisphenolic, or novolac and bisphenolic.

[0045] Preferably, the initial extensional modulus of the resin, measured at 23°C, is greater than 3.0 GPa, more preferably greater than 3.5 GPa.

[0046] A novolac-based epoxyvinyl ester resin (part in brackets in formula I below) corresponds, for example, in a known manner, to the following formula (I):

[0047] An epoxy vinyl ester resin based on bisphenol A (part in brackets of formula (II) below) for example meets the formula (the "A" reminding us that the product is manufactured at

[0048] An epoxy vinyl ester resin of the novolac and bisphenol type has shown excellent results. Examples of such a resin include the vinyl ester resins "ATLAC 590" and "ATLAC E-Nova FW 2045" from AOC (diluted with approximately 40% styrene) described in the aforementioned applications EP-A-1 074 369 and EP-A-1 174 250. Epoxy vinyl ester resins are available from other manufacturers such as, for example, AOC (USA - "VIPEL" resins).

[0049] Preferably, the crosslinking system of the impregnation 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 preferably 1 to 2.5%. Preferably, the crosslinking system of the resin also comprises a crosslinking agent, for example at a rate of between 5% and 15% (% by weight of impregnation composition), the crosslinking agent being as defined above.

[0050] Preferably, this photoinitiator 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 IGM or “speedcureBPO” from Lambson) or a mono(acyl)phosphine oxide (for example, “Esacure TPO” from IGM), such phosphine compounds being able to be used in a mixture with other photoinitiators, for example, alpha-hydroxy-ketone type photoinitiators such as, for example, dimethylhydroxy-acetophenone (eg, “Omnirad 1173” from IGM) or 1-hydroxy-cyclohexyl-phenyl-ketone (eg, “Omnirad 184” from IGM), benzophenones such as 2,4,6-trimethylbenzophenone (eg, “ Esacure TZT » from IGM) and / or thioxanthone derivatives such as isopropylthioxanthone (eg « Esacure Omnirad ITX » from IGM).

[0051] The crosslinking agent is preferably chosen from the group consisting of the triacrylate family.

[0052] According to the invention, it is recalled in particular that before any impregnation of the fibres, an essential step of degassing the arrangement of fibres by the action of the 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 monostrand.

[0053] After passing through the vacuum chamber, the glass filaments enter an impregnation chamber which is completely full of impregnation resin, and therefore free of air: it is in this sense that this impregnation step can be described as "vacuum 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 on the impregnated material the shape and thickness targeted for the single strand.

[0054] 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 at the end of the process according to the invention have these diameters.

[0055] The polymerization or UV irradiation chamber then has the function of polymerizing and crosslinking the resin under the action of UV rays.

[0056] The UV irradiation chamber comprises one or more UV irradiators (or radiators). Advantageously, the irradiation chamber comprises a plurality of UV irradiators, i.e. 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 a line.

[0057] 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.

[0058] 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. Hônle 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 actually delivered being able to be adjusted with a potentiometer between 30 and 100% of the nominal power.

[0059] The diameter of the irradiation tube (preferably made of glass) is preferably between 10 and 80 mm, more preferably between 20 and 60 mm. Between the calibration die and the final receiving support, it is preferable 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 control this, it will be possible, for example, to measure these tensions directly at the outlet of the irradiation chamber, using appropriate tensiometers well known to those skilled in the art.

[0060] The final CVR monostrand thus formed through the UV irradiation chamber, in which the resin is now in the solid state, is then collected for example on a receiving reel on which it can be wound over a very long length. The process can thus include a winding step for storage of the monostrand after its passage through the UV irradiation chamber and before being cut.

[0061] Advantageously, the single strand from the irradiation chamber, possibly after storage, is cut so as to obtain single strands with a length in the range from 10 to 80 mm, for example from 15 to 60 mm.

[0062] 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.

[0063] Particularly advantageously, the method for manufacturing the CVR single strand of the invention comprises the following essential steps:

[0064] - speed (Vi r ) passage of the single strand in the irradiation chamber is greater than 50 m / min;

[0065] - the duration (Di r ) 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;

[0066] - the irradiation chamber comprises a UV-transparent tube (such as a quartz tube or preferably a glass tube), called an irradiation tube, through which the single strand being formed circulates, this tube being traversed by a current of inert gas, preferably nitrogen.

[0067] These combined steps make it possible to achieve the preferred improved properties of the CVR monostrand of the invention, namely in particular T, elongation Ar and moduli (E and E').

[0068] 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 manufacture and therefore that industrial performance was no longer guaranteed. Furthermore, if the irradiation time Di r 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 sufficiently crosslinked, which causes a degradation of the mechanical properties, including the breaking stress and the bending strength. Furthermore, if the irradiation duration Di rof 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 creating more porosity and degrading the mechanical properties, including the breaking stress. Thus, it is understood 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 Vi r and during the irradiation time Di r mentioned above, that CRV single strands are obtained with a porosity rate of less than 2% and a breaking stress greater than 1,050 MPa.

[0069] [Table 1]

[0070] It was further found that an irradiation rate Vi rhigh (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 glass filaments inside the CVR single strand, on the other hand to 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 to the vacuum chamber, and therefore to a better quality of impregnation.

[0071] Preferably, the speed Vir is between 50 and 150 m / min, more preferably in a range of 60 to 120 m / min.

[0072] Preferably, the irradiation duration Di r is between 1.5 and 10 s, more preferably in the range of 2 to 5 s.

[0073] Another subject of the invention is a CVR single strand capable of being obtained by a process according to the invention, preferably according to which:

[0074] - the speed (Vir) of passage of the single strand in the irradiation chamber is greater than 50 m / min;

[0075] - the duration (Di r ) 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;

[0076] - the irradiation chamber comprises a tube transparent to UV (such as a quartz tube or preferably a glass tube), called an irradiation tube, through which the single strand being formed circulates, this tube being traversed by a current of inert gas, preferably nitrogen,

[0077] - the CVR single strand preferably having a diameter ranging from 0.2 to 1.3 mm.

[0078] 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 in a range from 5 to 85 mm. In addition, 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.

[0079] 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 the FIJI program. To carry out the measurement, the following protocol is preferably carried out:

[0080] - we take a single strand in crosslinked CVR,

[0081] - it is coated with a cold coating resin, such as epoxy, for example in a vacuum coating device (CitoVac from Stuers for example),

[0082] - the coated CVR single strand is cut, for example using a hydraulic guillotine, such as the “SH-5214” from Baileigh,

[0083] - 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 0.25pm,

[0084] - 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 Eloïse company,

[0085] - the section of the single strand in CVR is observed under a scanning electron microscope, preferably under vacuum (15kV), and

[0086] - using an image processing program, FIJI for example, the surface percentage of porosity is calculated. By "porosity" of the CVR single strand, we mean any gas (particularly air) or vacuum present within the CVR single strand.

[0087] 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 1,050 and 1,700 MPa, preferably from 1,100 to 1,600 MPa, more preferably from 1,200 to 1,500 MPa.

[0088] Advantageously also, the CVR single strand has an initial extension modulus (noted E23), 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 E23 of between 35 and 50 GPa, preferably between 40 and 49 GPa.

[0089] The mechanical properties in extension of the CVR single strand (modulus E23, 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.

[0090] Furthermore, the CVR single-strand according to the invention advantageously has the following properties:

[0091] - the glass transition temperature (denoted T ) 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%;

[0092] - the initial extension modulus (noted E23) of the single strand, measured at 23°C, is greater than

[0093] 35 GPa, preferably greater than 40 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.

[0094] 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 the ASTM D3418 standard of 1999 (Mettler Toledo "822-2" DSC apparatus; nitrogen atmosphere; 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).

[0095] 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%.

[0096] The E'190 modulus is preferably greater than 33 GPa, more preferably greater than

[0097] 36 GPa.

[0098] For an optimized compromise of thermal and mechanical properties of the CVR single strand of the invention, the ratio E'(T g '-25) / E'23 is advantageously greater than 0.85, preferably greater than 0.90, E'23 and E'(T g ' -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

[0099] Advantageously, the ratio E'(T g ' - 10) / E'23 is greater than 0.80, preferably greater than 0.85, E'(i g ' - io) 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).

[0100] The measurements of E' and Tg' are carried out in a known manner by DMTA ("Dynamic Mechanical Thermal Analysis"), with a "DMA" viscoanalyzer +450 » from ACOEM (France), using the software « Dynatest 6.83 / 2010 » controlling bending, traction or torsion tests. According to this device, the three-point bending test does not allow in a known way to enter the initial geometric data for a single strand of circular section, one can only 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, one therefore introduces by convention in the software a square section of side « a » having the same moment of surface inertia, this in order to work with the same stiffness R of the specimens.

[0101] The following well-known relationships must apply (E being the modulus of the material, Is the surface moment of inertia of the body considered, and * the multiplication symbol):

[0102] R Ecomposite * Circular Lection Ecomposite * Square Lection aV eC . Circular Lection 7T * D 4 / 64 and Isquare section = a 4 / 12

[0103] We can easily deduce the value of the side "a" of the equivalent square of the same surface inertia as that of the (circular) section of the single strand of diameter D, according to the equation: a = D * (K / 6) 0 ' 25

[0104] In the case where the cross-section of the tested sample is not circular (nor rectangular), whatever its particular shape, the same method of calculation will apply by first determining the surface moment of inertia L on a cross-section of the tested sample.

[0105] The specimen to be tested, generally of circular section and diameter D, has a length of 35 mm. It is placed 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.

[0106] 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, the measurements of the elastic modulus E', the viscous modulus E' ' and the loss angle (ô) are obtained as a function of the temperature (where E' is the real part and E” the imaginary part of the complex modulus); Tg' is the glass transition temperature corresponding to the maximum (peak) of tan(ô). 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 1,050 MPa, more preferably greater than 1,200 MPa, in particular greater than 1,400 MPa.

[0107] The above properties in compression under bending 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 the present case, a loop is made and gradually brought to the breaking point. The nature of the break, easily observable due to the large size of the section, makes it immediately clear that the CVR single strand of the invention, stressed in bending until breaking, breaks on the side where the material is in extension, which is identified by simple observation. Since in this case the dimensions of the loop are large, it is possible at any time to read the radius of the circle inscribed in the loop. The radius of the circle inscribed just before the breaking point corresponds to the critical radius of curvature, designated by Rc.

[0108] The following formula then allows us to determine by calculation the critical elastic deformation noted Ec (where r corresponds to the radius of the single strand, i.e. D / 2):

[0109] Ec = r / (Rc + r)

[0110] The breaking stress in compression under bending noted G C is obtained by calculation using the following formula (where E is the initial module in extension): c c = Ec * E

[0111] Since, in the case of the CVR single strand according to the invention, the rupture of the loop appears in the extension part, it is concluded that, in bending, the rupture stress in compression is greater than the rupture stress in extension.

[0112] A rectangular bar can also be broken in bending using the three-point method (ASTM D 790). This method also allows visual verification that the nature of the break is in extension.

[0113] Advantageously, the pure compressive breaking stress is greater than 700 MPa, more preferably greater than 900 MPa, in particular greater than 1,100 MPa. To avoid buckling of the CVR single strand 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.

[0114] Preferably, in the CVR single strand of the invention, the alignment rate of the glass filaments is such that more than 85% (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, i.e. 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.

[0115] Preferably, the weight ratio of glass fibers (i.e. filaments) in the CVR single strand is within a range from 65% to 85%, preferably from 70% to 80%.

[0116] The weight rate is calculated by taking the ratio of the initial glass fiber title to the title of the final CVR single strand. The title (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).

[0117] Furthermore, the volume fraction of glass fiber in the CVR single strand is advantageously within a range from 40% to 60%, preferably from 45% to 55%.

[0118] The volume fraction of mineral fiber in the final GRC single strand is the surface fraction of glass fiber in a cross-section of the GRC single strand relative to its total cross-sectional area. The surface fraction of glass fiber can be determined in the same way as described below for the measurement of porosity.

[0119] 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 within a range of from 40% to 60%, preferably from 45% to 55%. The weight percentage and the volume fraction of crosslinked resin can be obtained according to a method similar to the method for obtaining the weight percentage and the volume fraction of the glass fiber described above.

[0120] Preferably, the density (or volumetric mass in g / cm 3 ) of the single-strand CVR is between 1.8 and 2.1. It is measured (at 23°C) using a specialized balance from 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.

[0121] The diameter D of the CVR single strand of the invention is preferably within a range from 0.2 to 1.3 mm, preferably from 0.25 to 1.25 mm, more preferably between 0.3 and 1.2 mm, in particular between 0.4 and 1.1 mm.

[0122] This definition covers both single strands of essentially cylindrical shape (with a circular cross-section) and single strands of different shapes, for example oblong single strands (of a more or less flattened shape) or rectangular cross-section. In the case of a non-circular cross-section and unless otherwise specifically indicated, D is by convention the so-called boundary diameter, i.e. the diameter of the imaginary cylinder of revolution surrounding the single strand, in other words the diameter of the circumscribed circle surrounding its cross-section.

[0123] Furthermore, the length L of the CVR single strand of the invention is preferably within a range from 10 to 80 mm, for example from 15 to 60 mm.

[0124] Advantageously, the length / diameter ratio L / D of the CVR monostrands of the invention is within a range from 10 to 110, preferably from 20 to 90, more preferably from 25 to less than 80.

[0125] The invention also relates to a ballotin comprising a plurality of CVR monostrands according to the invention and at least one element for holding the monostrands together. Preferably, this holding element is a breakable film, for example tearable, dispersible, water-soluble. Preferably, at least one holding element is a water-soluble thread.

[0126] 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, 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 from 300 to 20,000.

[0127] The single strands making up the ballotin may be of identical or different dimensions. For example, a ballotin may 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 exhibiting more than 10%, preferably not more than 3%, deviation from each other.

[0128] As indicated above, the monostrands according to the invention are particularly useful as an additive for concrete. Thus, the invention also relates to the use of CVR monostrands according to the invention or of a ballotin according to the invention, for reinforcing concrete and / or reducing the weight of the concrete and / or reducing or preventing cracking of the concrete.

[0129] The present invention also relates to a concrete comprising a plurality of CVR single strands according to the invention. The concrete can be prepared according to any technique well known to those skilled in the art.

[0130] Advantageously, the volume ratio of the single strands according to the invention in the concrete according to the invention is within a range from 0.1% to 6%, for example from 0.1% to 1.5% for so-called “conventional” concretes, for example of the BPS C40 / 50 XA3 type, or from 1.5% to 6% for ultra-high performance fiber-reinforced concretes (UHPFC).

[0131] Examples of the manufacture of CVR single strands according to the invention and their use for reinforcing concrete are described below.

[0132] The attached figure 1 very simply shows an example of a device 10 allowing the production of CVR single strands in accordance with the invention.

[0133] We see a reel 11a containing, in the example illustrated, glass fibers 11b (in the form of multifilaments). The reel is continuously unwound by driving, so as to produce a rectilinear arrangement 12 of these fibers 11b. In general, the reinforcing fibers are delivered in "rovings", that is to say already in groups of fibers wound in parallel on a reel; for example, alkali-resistant glass fibers marketed by Nippon Electric Glass under the designation of fiber "AR1200S-920S" are used, with a count 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 along the entire length of the installation 1.

[0134] 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 with rigid walls 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 as much) than said minimum section.

[0135] As already taught by the aforementioned application EP-A-1 174 250, the use of rigid-walled pipes, 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 is sufficient, 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 provide sufficient sealing, taking into account the speed of advancement of the fibers and the length of the pipes. 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.

[0136] 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 metering pump not shown) and a sealed impregnation tank 16 completely filled with impregnation composition 17 based on a curable resin of the vinylester type (e.g., "ALTAC® E-Nova FW 2045" from AOC). For example, the 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 subsequently be 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.

[0137] Preferably, the length of the impregnation chamber is several meters, for example between 2 and 10 m, in particular between 3 and 5 m.

[0138] Thus, an impregnation which comprises, for example (% by weight) 65% to 75% of solid fibers 11b, the remainder (25 to 35%) being constituted by the liquid impregnation matrix 17, emerges from the impregnation chamber 14, in a sealed outlet pipe 18 (still under primary vacuum).

[0139] The impregnated material then passes through calibration means 19 comprising at least one calibration die 20 whose channel (not shown here), for example circular, rectangular or conical in 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 targeted single strand. 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 accuracy of the finished product; it can also play a role in dosing the fiber content relative to the resin. According to a possible variant embodiment, the die 20 can be directly integrated into the impregnation chamber 14, which avoids, for example, the use of the outlet pipe 18.

[0140] Preferably, the length of the calibration zone is several centimeters, for example between 5 and 50 cm, in particular between 5 and 20 cm.

[0141] Thanks to the calibration means (19, 20) a "liquid" composite monostrand 21 is obtained at this stage (liquid in the sense that its impregnation resin is always liquid) whose cross-sectional shape is preferably essentially circular.

[0142] At the outlet of the calibration means (19, 20), the liquid composite monostrand 21 thus obtained is then polymerized by passing through a UV irradiation chamber (22) comprising a sealed glass tube (23) through which the composite monostrand circulates; 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 in-line UV irradiators (24) ("UVAprint" lamps from the company Dr. Hônle, with a wavelength of 200 to 600 nm) arranged at a short distance (a few cm) from the glass tube.

[0143] Preferably, the length of the irradiation chamber is several meters, for example between 2 and 15 m, in particular between 3 and 10 m.

[0144] In this example, the irradiation tube (23) is traversed by a stream of nitrogen.

[0145] The irradiation conditions are preferably adjusted in such a way that, in the irradiation chamber, the temperature of the CVR single strand, measured at the surface of the latter (for example using a thermocouple), is higher than the Tg of the crosslinked resin (in other words higher than 190°C), and more preferably lower than 270°C.

[0146] Once the resin has 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 reel (26).

[0147] We finally obtain a finished composite block of manufacture as shown very simply in Figure 2, 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.

[0148] 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.

[0149] The continuous CVR single strand (25) can be cut to a determined length (not shown in Figure 1), 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 Baileigh. 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 packaged on a final receiving reel (26). In this case, it is preferable to unwind the single strand from the reel from the end of the single strand which is located axially outermost of the reel, in order to avoid helically deforming the single strand. Indeed, if the single strand is unwound from the reel from the end of the single strand which is located axially innermost of the reel, this helically deforms the single strand which can be detrimental to the breaking stress.

[0150] IV- EXAMPLES

[0151] IV- 1 Measurements and tests used

[0152] Porosity rate

[0153] The porosity rate was measured according to the protocol:

[0154] - we took a single strand in crosslinked CVR,

[0155] - it was coated with a cold coating resin, epoxy type, in a vacuum coating device (CitoVac from the Stuers company),

[0156] -the glued CVR single strand was cut using a hydraulic guillotine (SH-5214 from Baileigh)

[0157] - the section of the CVR single strand was polished using a mechanical polisher from the Mecapol company to a final grain size of 0.25 pm, - a deposit of 1 to 4 nm of gold was carried out using a gold metallizer (Cerssington series 108 or 208 from the Eloïse company),

[0158] - the section of the single strand in CVR was observed under vacuum scanning electron microscope (15kV), and

[0159] - using an image processing program, FIJI for example, the surface percentage of porosity was calculated (%porosity = porosity area / (porosity area + fiber area + crosslinked resin area).

[0160] Mechanical properties

[0161] The mechanical properties in extension of the GRC single strand (modulus E23, breaking stress Cr and elongation at break Ar) were measured using an “INSTRON” tensile testing machine type 5944 (BLUEHILL® UNIVERSAL software supplied with the tensile testing machine), according to ASTM D2343, at a temperature of 23°C, on glued (i.e. ready-to-use) GRC single strands. Before measurement, these single strands were subjected to pre-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; humidity of 50 ± 5%)). To avoid damage to the glass reinforcements when gripping the sample in the jaws of the tensile machine, the heel bonding (Material: 50 mm long cardboard; Adhesive used: Loctite EA 9483 (two-component epoxy)) was carried out as follows.The surfaces of the two facing heels were glued as well as the reinforcement in order to limit as much as possible the "dry zones" (without adhesive). The heels were held in place for the curing time (12h 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 strain was recorded by the MultiXtens 1995DA801 extensometer. Tested samples, 260 mm long, were subjected to 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.

[0162] Alkaline solution aging protocol

[0163] Glass tubes 300 mm long and 30 mm in diameter were filled with 160 mL of an alkaline solution at a pH of 13.5. Glass tubes containing 260 mm long GRP single strands were kept at 60°C for 3 days before being washed with water. The single strands were then allowed to dry at room temperature before performing tensile tests. Tensile tests were performed on at least 5 replicates and were compared to tensile tests performed on single strands that had not undergone the alkaline aging protocol. All results given are an average of 5 measurements. Results are presented as a percentage of breaking stress loss. The lower the percentage, the less the breaking stress is degraded and the better the alkali resistance.

[0164] Concrete aging protocol

[0165] A fresh commercial concrete of the Ductal brand is prepared following the supplier's recommendations and then adding 3% by volume of CVR single strands of diameter 0.54 mm and length 18 mm at the end of the mixing cycle. The fresh fiber-reinforced concrete is poured into a large bakelized film-coated plywood panel of 745x540x15mm. Filling is done by pouring onto the edge of the mold, favoring the orientation of the fibers in the direction of pouring. After preparation, the large plate is kept at the manufacturing site under normal conditions of temperature, pressure and humidity. The plate is removed from the mold after 24 hours and then placed in a room regulated at 20°C ± 2 and humidity at 100% RH for 14 days.

[0166] The plate is then cut into mini-plates (called plates) of 325x50x15 mm in the longitudinal direction, corresponding to the direction of pouring of the fiber-reinforced concrete and therefore to the preferential orientation of the fibers.

[0167] Four plates are kept in a humid room (temperature at 20°C ± 2 and humidity at 100% RH) for an additional 14 days and then are mechanically tested in 4-point bending corresponding to a test deadline t28

[0168] Four other plates are kept immersed in hot water 60°C ± 2 in a climatic chamber for a further 98 days and then are mechanically tested in 4-point bending corresponding to a test deadline tm.

[0169] The specimens are tested in four-point bending according to standard EN 1170-5 (1998). The results presented below correspond to the average of the individual results of these four tests.

[0170] Two characteristics are noted:

[0171] (i) The limit of proportionality LOP, as the average value of the end of the stress / deflection linearity during the bending test. For each single strand (M4, M5), the LOP results at tm are presented on the basis of 100 compared to the LOP result at t28 of the single strand considered. A result greater than 100 reflects an improvement in the bending strength of the concrete matrix at low deformation.

[0172] (ii) The maximum breaking stress MOR, as the average maximum value of the stress during the bending test. For each single strand (M4, M5), the MOR results at tm are presented on the basis of 100 in relation to the MOR result at t28 of the single strand considered. A result lower than 100 indicates a deterioration in the strength of the reinforcing fibers intended to improve the bending strength at higher deformation. IV-2 Tests on single strands

[0173] Single strands (M1 to M3) in accordance with the invention in CVR were manufactured according to the process described previously with a speed Vi r passage of the single strand in the irradiation chamber of 100 m / min, an irradiation time Di r of the single strand in the irradiation chamber for 2.4 s, the length of the irradiation chamber being 4 m. The resin composition used was based on vinylester resin (“ATLAC E-NOVA FW2045” from AOC), a triacrylate hardener (“SR 368” from Sartomer) and a photoinitiator (“Omnirad 819” from IGM). The alkali-resistant glass filaments of the single strands M1, M2 and M3 were respectively “AR1200S” filaments (in fact respectively “AR320S-720S”, “AR640S-720S” and “AR1200S-720S” filaments) from 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.

[0174] [Table 2]

[0175] The porosity rate and breaking stress of these single strands were compared with prior art concrete reinforcing fibers. It was found that these prior art fibers systematically have a porosity rate greater than 2% and a breaking stress less than or equal to 1,050 MPa.

[0176] Single strands (M4 and M5) in CVR were manufactured according to the process described previously with a speed Vir of passage of the single strand in the irradiation chamber of 100 m / min, an irradiation duration Di rof the single strand in the irradiation chamber for 2.4 s, the length of the irradiation chamber being 4 m. The resin composition used was based on vinylester resin (“ATLAC E-NOVA FW2045” from AOC), a triacrylate hardener (“SR 368” from Sartomer) and a photoinitiator (“Omnirad 819” from IGM). The alkali-resistant glass filaments of the M4 single strand were “AR320S720S” filaments from Nippon Electric Glass comprising 17% by mass of ZrO2. The glass filaments of the M5 single strand were “ECR SE 1200 R25H” filaments from Owens Corning. The tex of the glass fibers in the M4 and M5 monofilaments was 320 and 300 g / km respectively and the glass fiber / resin mass ratio in the M4 and M5 monofilaments was 70 / 30 respectively. The properties of these monofilaments are shown in Table 3 below.

[0177] [Table 3]

[0178] As expected, the base 100 results of LOP at tin compared to t28 show an improvement in the flexural strength of the concrete matrix at low strain during aging of the concrete. The fibers according to the invention do not degrade this improvement. On the other hand, the fibers according to the invention (M4) greatly limit the degradation of the strength of the reinforcing fibers intended to improve the flexural strength at higher strain (MOR). Thus, the CVR single strands according to the invention make it possible to further strengthen the concrete over time.

[0179] Due to their low porosity rate and their high breaking stress, the monostrands of the invention therefore make it possible to improve the cracking resistance of concrete. It has thus been found that the monostrands in accordance with the invention present an improved compromise of performance between in particular mechanical strength, corrosion resistance, processability (in particular dispersibility during mixing, the implementation temperature and the maintenance of homogeneity during drying of the concrete).

Claims

CLAIMS A method for manufacturing single-strand glass-resin composites comprising alkali-resistant glass filaments containing 5% to 30% by mass of ZrCh embedded in a crosslinked resin, comprising the following successive steps: forming a straight arrangement of alkali-resistant glass filaments containing 5% to 30% by mass of ZrCh and conveying this arrangement in a forward direction, in a vacuum chamber, degassing the arrangement of glass filaments by the action of a vacuum, at the outlet of the vacuum chamber, after degassing, passing through a vacuum impregnation chamber so as to impregnate said arrangement of glass filaments with a photocurable resin composition, in the liquid state, called "impregnation resin", to obtain an impregnated material containing the glass filaments and the resin composition, passing said impregnated material through a calibration die having a predefined surface area and shape,to impose a single-strand shape on it, 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 the irradiation tube, through which the single strand being formed passes, traversed by a current of inert gas, the speed (denoted Vir) of passage of the single strand in the irradiation chamber being greater than 50 m / min, the irradiation time (denoted Di, rThe time spent in the irradiation chamber of the single strand is equal to or greater than 1.5 s, and the single strand is cut to a length in the range of 5 to 85 mm. A method according to claim 1, characterized in that the single strands have a diameter of 0.2 to 1.3 mm, preferably 0.25 to 1.25 mm, and preferably 0.3 to 1.2 mm. A method according to any one of the preceding claims, characterized in that the cut single strands have a length in the range of 10 to 80 mm, preferably 15 to 60 mm. A method according to claim 3, wherein the single strand has a length-to-diameter ratio of 10 to 110, preferably 20 to 90, and preferably 25 to less than 80. A 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 ZrCh. A 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 from 20% to 30%, by weight, of the single strand. A method according to any one of the preceding claims, characterized in that the impregnating resin is based on at least: a crosslinkable resin selected from the group consisting of vinyl ester, epoxy, polyester resins and mixtures thereof, and a crosslinking system comprising a photoinitiator reactive to UV light above 300 nm. Monostrand capable of being obtained by a process according to any one of claims 1 to 7.A single strand according to claim 8, characterized in that it has a porosity of less than 2%, preferably less than 1%, and preferably less than 0.5%. A single strand according to any one of claims 8 to 9, characterized in that it has a tensile strength greater than 1050 MPa, preferably greater than or equal to 1100 MPa, and more preferably greater than or equal to 1200 MPa. A single strand according to any one of claims 8 to 10, characterized in that it has an initial tensile modulus, denoted E23, of the single strand, measured at 23°C, greater than 35 GPa, and preferably greater than 40 GPa. Ballotin comprising a plurality of monostrands according to any one of claims 8 to 11, and at least one breakable film holding the monostrands together, the breakable film preferably being a water-soluble film of material selected from the group consisting of polyvinyl alcohols (PVA).Ballotin according to claim 12, wherein the number of monostrands is in a range from 300 to 20,000. Use of monofilament strands according to any one of claims 8 to 11 or of a bundle according to any one of claims 12 to 13, for strengthening concrete and / or reducing the weight of concrete and / or reducing or preventing cracking of concrete. Concrete comprising a plurality of monofilament strands according to any one of claims 8 to 11, the volume fraction of monofilament strands in the concrete preferably being in the range of 0.1% to 6%.

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