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

Abstract

The invention relates to a monofilament made of polyester-resin composite comprising polyester filaments embedded in a crosslinked resin, the monofilament having: a length in a range from 5 to 85 mm, a diameter ranging from 0.2 to 1.3 mm, and a porosity rate of less than 2%; as well as to the use thereof for reinforcing concrete. The invention also relates to a concrete comprising said monofilaments, and to the method for obtaining said monofilaments.

Description

[0001] USE OF POLYESTER-RESIN COMPOSITE FIBERS FOR THE

[0002] CONCRETE REINFORCEMENT

[0003] The present invention relates to polyester-resin composite fibers for reinforcing concrete and to the process for obtaining them.

[0004] 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.

[0005] 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.

[0006] 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.

[0007] 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). To solve this problem, it has been proposed to replace metal fibers with synthetic fibers. However, the mechanical strength (elastic modulus (Young's), 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.

[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 polyester-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 flow 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.Also, more generally, due to their density and their reinforcement 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.

[0011] Thus, the subject of the invention is a single strand of polyester-resin composite comprising polyester filaments embedded in a crosslinked resin, having a length in a range from 5 to 85 mm and a diameter from 0.2 to 1.3 mm, and characterized in that the single strand has a porosity rate of less than 2%.

[0012] It also relates to the use of at least one single strand according to the invention for reinforcing concrete and / or reducing the weight of the concrete and / or reducing or preventing cracking of the concrete, as well as a concrete comprising a plurality of single strands cut according to the invention, the volume ratio of the single strands in the concrete preferably being within a range from 0.1% to 6%.

[0013] The invention also relates to a method for manufacturing a single strand of polyester-resin composite comprising polyester filaments embedded in a crosslinked resin, comprising the following successive steps:

[0014] - making a rectilinear arrangement of polyester filaments and driving this arrangement in a direction of advance,

[0015] - in a vacuum chamber, degas the arrangement of polyester filaments by the action of vacuum,

[0016] - at the outlet of the vacuum chamber, after degassing, passing through a vacuum impregnation chamber so as to impregnate said arrangement of polyester filaments with a photocrosslinkable resin composition, in the liquid state, called “impregnation resin”, to obtain an impregnation containing the polyester filaments and the resin composition,

[0017] - passing said impregnated material through a calibration die having a predefined surface section and shape, to impose a single-strand shape on it,

[0018] - 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 duration of irradiation (denoted Di r ) of the single strand in the irradiation chamber being equal to or greater than 1.5 s,

[0019] - cut the single strand to a length within a range of 5 to 85 mm. I- DEFINITIONS

[0020] In this document, unless expressly stated otherwise, all percentages (%) indicated are percentages (%) by mass.

[0021] 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.

[0022] 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.

[0023] All glass transition temperature “Tg” values ​​described herein are measured in a known manner by DSC (Differential Scanning Calorimetry) according to ASTM D3418 (1999).

[0024] 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 single strand (or fiber, the two terms being able to be used equivalently) made of polyester-resin composite (abbreviated as "CPR") comprising polyester filaments embedded in a crosslinked resin (i.e. a resin hardened after crosslinking), having a length in a range from 5 to 85 mm and a diameter from 0.2 to 1.3 mm, and characterized in that the single strand has a porosity rate of less than 2%.

[0029] By "polyester filaments" we mean filaments, remember that it is a filament of linear macromolecules formed of groups linked together by ester bonds. Polyesters are manufactured by polycondensation by esterification between a dicarboxylic acid or one of its derivatives a diol. For example, polyethylene terephthalate can be manufactured by polycondensation of terephthalic acid and ethylene glycol. Among the known polyesters, we can cite polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), polybutylene naphthalate (PBN), polypropylene terephthalate (PPT) or polypropylene naphthalate (PPN).

[0030] Preferably, the polyester filaments are filaments selected from polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), preferably entirely made of polyethylene terephthalate (PET).

[0031] As an example of polyester fibers that can be used in the context of the present invention, mention may be made of the PET fibers marketed under the name "PET HMLS 334 TEX HSP40" by the company Hyosung, or under the name "1X50-3340-892-00" by the company Glanzstoff Longlaville.

[0032] Typically, the polyester filaments, preferably PET, 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 unitary polyester filaments, preferably PET. These very fine unitary filaments generally and preferably have an average diameter of 15 to 35 μm, more preferably 15 to 25 μm. The section of the unitary filaments is preferably cylindrical. Preferably, in the CPR monofilament of the invention, the filaments of the monofilament are essentially parallel to each other.In particular, the alignment rate of the polyester filaments is preferably such that more than 85% (number %) of the filaments have an inclination relative to the axis of the monofilament 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 CPR monofilament according to the invention is not helically deformed, i.e. it is not twisted. In any event, the CPR monofilament 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.

[0033] Preferably, the weight content of polyester fibers (i.e. filaments) in the CPR monostrand is within a range from 20% to 60%, preferably from 25% to 40%.

[0034] The weight rate of the polyester fiber is calculated by taking the ratio of the initial polyester fiber title to the title of the final CPR 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).

[0035] Furthermore, the volume fraction of polyester fiber in the CPR monostrand is advantageously within a range from 20% to 50%, preferably from 20% to 30%.

[0036] The volume fraction of polyester fiber in the final CPR monofilament is the area fraction of polyester fiber in a cross-section of the CPR monofilament relative to its total cross-sectional area. The area fraction of polyester fiber can be determined in the same way as described below for the measurement of porosity.

[0037] Furthermore, the crosslinked resin represents from 40% to 80%, preferably from 60% to 75%, by weight, of the CPR monostrand of the invention. Furthermore, the volume fraction of resin in the CPR monostrand is advantageously within a range of from 50% to 80%, preferably from 70% to 80%. 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 polyester fiber described above.

[0038] The resin used is by definition a crosslinkable (i.e., curable) resin 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.

[0039] 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).

[0040] Advantageously, the crosslinked resin is based on at least:

[0041] - a crosslinkable resin chosen from the group consisting of vinylester resins (preferably vinylester urethane resins), epoxy, polyester and their mixtures,

[0042] - a crosslinking system preferably comprising a photoinitiating 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] The diameter D of the CPR 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.

[0053] 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 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 overall 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. Furthermore, the length L of the CPR single strand of the invention is preferably within a range from 10 to 80 mm, for example from 15 to 60 mm. In this case, the length / diameter ratio L / D of the CPR monostrands of the invention is advantageously within a range from 10 to 110, preferably from 20 to 90, preferably from 25 to 80, preferably from 30 to 70.

[0054] According to the invention, the CPR single strand advantageously has a porosity rate of less than 1%, preferably less than 0.5%. Advantageously, the porosity rate of the CPR single strand is between 0% and 2%, preferably between 0.01% and 1%, preferably between 0.05% and 0.5%.

[0055] The porosity rate can be measured by microscopy, for example by scanning electron microscopy, preferably using surface area calculation software, such as FIJI Program. To perform the measurement, the following protocol is preferably carried out:

[0056] - we take a single strand in crosslinked CPR,

[0057] - it is coated with a cold coating resin, such as epoxy, for example in a vacuum coating device (CitoVac from Stuers for example),

[0058] - the coated CPR single strand is cut, for example using a hydraulic guillotine, such as the “SH-5214” from Baileigh,

[0059] - the section of the CPR single-strand is polished, for example using a mechanical polisher, from the company Mecapol for example, preferably to a final grain of 0.25 pm,

[0060] - 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,

[0061] - the section of the single strand in CPR is observed under a scanning electron microscope, preferably under vacuum (15kV), and

[0062] - using an image processing program, FIJI for example, the surface percentage of the porosity is calculated. By "porosity" of the CPR single strand is meant any gas (in particular air) or vacuum present within the CPR single strand. According to the invention, the CPR single strand advantageously has a breaking stress Cr greater than 300 MPa, more preferably greater than or equal to 320 MPa. In particular, the single strand preferably has a breaking stress of between 300 and 500 MPa, preferably 320 to 470 MPa.

[0063] Advantageously also, the CPR single strand has an initial extension modulus (noted E23), also called Young's Modulus, measured at 23°C, greater than 4 GPa, preferably greater than 4.5 GPa. In particular, the single strand preferably has an E23 of between 4 and 8 GPa, preferably between 4.5 and 7 GPa.

[0064] The mechanical properties in extension of the CPR 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.

[0065] The glass transition temperature denoted Tg of the crosslinked resin is preferably greater than 190°C, 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).

[0066] Preferably, the density (or volumetric mass in g / cm3 ) of the single-strand CPR is between 1.15 and 1.25. 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.

[0067] The invention also relates to a method for manufacturing single strands or fibers (the two terms can be used equivalently) in polyester-resin composite (abbreviated as "CPR") comprising the following successive steps: - producing a rectilinear arrangement of polyester filaments and driving this arrangement in a direction of advance,

[0068] - in a vacuum chamber, degas the arrangement of polyester filaments by the action of vacuum,

[0069] - at the outlet of the vacuum chamber, after degassing, passing through a vacuum impregnation chamber so as to impregnate said arrangement of polyester filaments with a photocrosslinkable resin composition, in the liquid state, called “impregnation resin”, to obtain an impregnation containing the polyester filaments and the resin composition,

[0070] - passing said impregnated material through a calibration die having a predefined surface section and shape, to impose a single-strand shape on it,

[0071] - 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 duration of irradiation (denoted Di r ) of the single strand in the irradiation chamber being equal to or greater than 1.5 s, step at the end of which a CPR single strand is obtained comprising polyester filaments embedded in a crosslinked resin,

[0072] - cutting the single strand to a length within a range of 5 to 85 mm, at the end of which step a CPR single strand is obtained comprising polyester filaments embedded in a crosslinked resin in accordance with the invention.

[0073] All the steps (arrangement, degassing, impregnation, calibration, polymerization, optional winding and cutting) of the process of the invention are, independently of one another, 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.

[0074] 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.

[0075] After passing through the vacuum chamber, the polyester filaments enter an impregnation chamber which is completely full of impregnation resin, therefore devoid of air: it is in this sense that this impregnation stage can be described as "vacuum impregnation".

[0076] 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 polyester fibers, preferably PET, while imposing on the impregnated material the shape and thickness targeted for the single strand.

[0077] 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.

[0078] The polymerization or UV irradiation chamber then has the function of polymerizing and crosslinking the resin under the action of UV rays.

[0079] 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.

[0080] Even more preferably, the linear power delivered by each UV irradiator is between 2,500 and 12,000 watts per meter, in particular within a range of 3,000 to 10,000 watts per meter. UV radiators suitable for the method of the invention are well known to those skilled in the art, for example those marketed by the company Dr. 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.

[0081] The diameter of the irradiation tube (preferably made of glass) is preferably between 10 and 80 mm, more preferably between 20 and 60 mm.

[0082] Between the calibration die and the final receiving support, it is preferable to maintain the tensions undergone by the polyester 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.

[0083] The final CPR 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 method can thus include a winding step for storage of the monostrand after its passage through the UV irradiation chamber.

[0084] The single strand can be cut so as to obtain single strands with a length in a range from 5 to 85 mm, preferably from 10 to 80 mm, preferably from 15 to 60 mm. In this case, the single strands advantageously have a length / diameter ratio ranging from 10 to 110, preferably from 20 to 90, preferably from 25 to 80, preferably from 30 to 70.

[0085] Particularly advantageously, the method for manufacturing the CPR single strand of the invention comprises the following essential steps:

[0086] - the speed (Vir) of passage of the single strand in the irradiation chamber is greater than 50 m / min;

[0087] - 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;

[0088] - 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.

[0089] These combined steps make it possible to achieve the preferred improved properties of the CPR monostrand of the invention, namely in particular T, elongation Ar and moduli (E and E').

[0090] 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 CPR single strand were degraded quite quickly during manufacture and therefore industrial performance was no longer guaranteed.

[0091] Furthermore, if the irradiation time Dir 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 leads to a degradation of the mechanical properties, including the breaking stress and the flexural strength. Furthermore, if the irradiation time Dir 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 degrading the mechanical properties, including the breaking stress.

[0092] Thus, it is understood that it is thanks to the combination of the steps of the method according to the invention, in particular thanks to the steps of degassing the arrangement of polyester 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 Vir and for the irradiation duration Dir mentioned above, that CPR monostrands are obtained having a porosity rate of less than 2% and a breaking stress greater than 300 MPa.It was further found that a high Vir irradiation speed (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 polyester filaments inside the CPR monostrand, 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.

[0093] Preferably, the speed Vir is between 50 and 150 m / min, more preferably in a range of 60 to 120 m / min.

[0094] Preferably, the irradiation duration Di r is between 1.5 and 10 s, more preferably in the range of 2 to 5 s.

[0095] An object described herein is a CPR monostrand capable of being obtained by a process according to the invention, preferably according to which:

[0096] - the speed (Vir) of passage of the single strand in the irradiation chamber is greater than 50 m / min;

[0097] - the duration (Dir) 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;

[0098] - 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,

[0099] - the CPR single strand having a length ranging from 5 to 85 mm, preferably from 10 to 80 mm, preferably from 15 to 60 mm,

[0100] - the CPR single strand having 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.

[0101] The CPR monofilament capable of being obtained by a process according to the invention therefore comprises polyester filaments, preferably PET, impregnated in a crosslinked resin, has a length ranging from 5 to 85 mm, a diameter ranging from 0.2 to 1.3 mm, and a porosity rate of less than 2%. All the characteristics described above for the monofilament according to the invention also apply to the monofilament capable of being obtained by the process according to the invention. In particular, taking into account the specific steps of the process according to the invention, the monofilament advantageously has a porosity rate of less than 1%, preferably less than 0.5% and / or a breaking stress greater than 300 MPa, preferably greater than or equal to 320 MPa and / or an initial extension modulus noted E23 of the monofilament, measured at 23°C, greater than 4 GPa, preferably greater than 4.5 GPa.

[0102] The invention also relates to a ballotin comprising a plurality of CPR monostrands according to the invention (or capable of being obtained by the method according to the invention) and at least one element for holding the monostrands cut 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.

[0103] 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.

[0104] The ballotin according to the invention advantageously comprises a number of cut monostrands within a range from 300 to 20,000.

[0105] 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.

[0106] 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 at least one CPR monostrand according to the invention (or capable of being obtained by the method according to the invention) or 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.

[0107] The present invention also relates to a concrete comprising a plurality of single strands cut into CPR according to the invention (or capable of being obtained by the method according to the invention). The concrete can be prepared according to any technique well known to those skilled in the art.

[0108] 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).

[0109] Examples of the manufacture of CPR monostrands according to the invention and their use for reinforcing concrete are described below.

[0110] The attached figure 1 very simply shows an example of a device 10 allowing the production of CPR single strands in accordance with the invention.

[0111] We see a reel 11a containing, in the example illustrated, polyester fibers 11b (in the form of multifilaments). The reel is continuously unwound by drive, 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, polyester fibers marketed by the company Glanzstoff Longlaville under the designation "1X50-3340-892-00" are used, with a count equal to 334 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 CPR along the entire length of the installation 1.

[0112] 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.

[0113] 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.

[0114] 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 photoinitiating 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.

[0115] 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, from the impregnation chamber 14, in a sealed outlet pipe 18 (still under primary vacuum), emerges an impregnated material which comprises for example (% by weight) from 65% to 75% of solid fibers 11b, the remainder (25 to 35%) being constituted by the liquid impregnation matrix 17.

[0116] 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.

[0117] Preferably, the length of the calibration zone is several centimeters, for example between 5 and 50 cm, in particular between 5 and 20 cm.

[0118] 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.

[0119] 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. Preferably, the length of the irradiation chamber is several meters, for example between 2 and 15 m, in particular between 3 and 10 m.

[0120] In this example, the irradiation tube (23) is traversed by a stream of nitrogen.

[0121] The irradiation conditions are preferably adjusted in such a way that, in the irradiation chamber, the temperature of the CPR single strand measured on 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.

[0122] Once the resin has polymerized (hardened), the CPR single strand (25), this time in the solid state, drawn in the direction of arrow F, then arrives on its final receiving reel (26).

[0123] We finally obtain a finished composite block of manufacture as shown very simply in Figure 2, in the form of a continuous CPR monostrand (25), of very great length, whose unit polyester filaments (251) are distributed homogeneously throughout the volume of hardened resin (252). Its diameter is for example equal to approximately 0.5 mm.

[0124] 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.

[0125] The continuous CPR 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.

[0126] IV- EXAMPLES

[0127] IV- 1 Measurements and tests used

[0128] The porosity rate was measured according to the protocol:

[0129] - we took a single strand in crosslinked CPR,

[0130] - it was coated with a cold coating resin, epoxy type, in a vacuum coating device (CitoVac from the Stuers company),

[0131] -the glued CPR single strand was cut using a hydraulic guillotine (SH-5214 from Baileigh)

[0132] - the section of the CPR single-strand was polished using a mechanical polisher from the Mecapol company to a final grain size of 0.25 pm,

[0133] - a deposit of 1 to 4 nm of gold was made using a gold metallizer (Cerssington series 108 or 208 from the Eloïse company),

[0134] - the section of the single strand in CPR was observed under a vacuum scanning electron microscope (15kV), and

[0135] - 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).

[0136] The mechanical properties in extension of the CPR 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) CPR 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 polyester 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 beads were glued as well as the reinforcement in order to limit as much as possible the "dry zones" (without adhesive). The beads 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 beads to ensure good bead / 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. The 260 mm tested samples 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.

[0137] IV-2 Tests on single strands

[0138] Single strands (Ml and M2) in CPR 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 r of the monofilament 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 the company), a triacrylate hardener (“SR 368” from the company Sartomer) and a photoinitiator (“Omnirad 819” from the company IGM). The polyester filaments of the monofilaments M1 and M2 were respectively “1X50-3340-892-00” filaments from the company Glanzstoff Longlaville. The diameter and tex of the monofilaments as well as their physical characteristics and mechanical properties are presented in Table 1 below.

[0139] [Table 1]

[0140] 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 300 MPa.

[0141] Due to their low porosity rate and high breaking stress, the monostrands of the invention 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, implementation temperature and maintenance of homogeneity during drying of the concrete).

Claims

CLAIMS A single strand made of polyester-resin composite comprising polyester filaments embedded in a cross-linked resin, having a length in the range of 5 to 85 mm and a diameter in the range of 0.2 to 1.3 mm, and characterized in that the single strand has a porosity level of less than 2%. A single strand according to claim 1, having a length in the range of 10 to 80 mm and a diameter in the range of 0.25 to 1.25 mm, preferably 0.3 to 1.2 mm. A single strand according to any one of the preceding claims, having a length / diameter ratio from 10 to 110, preferably from 20 to 90, preferably still from 25 to less than 80. A single strand according to any one of the preceding claims, wherein the polyester filaments represent from 20% to 60%, preferably from 25% to 40%, by weight of the single strand, and the crosslinked resin represents from 40% to 80%, preferably from 60% to 75%, by weight, of the single strand.A single-strand material according to any one of the preceding claims, wherein the polyester filaments each have an average diameter in the range of 15 to 35 pm, more preferably 15 to 25 pm. A single-strand material according to any one of the preceding claims, wherein the crosslinked 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. A single-strand material according to any one of the preceding claims, wherein the polyester filaments are filaments selected from polyethylene terephthalate and... Polyethylene naphthalate, preferably made entirely of polyethylene terephthalate. A single strand according to any one of the preceding claims, the single strand having a porosity of less than 1%, preferably less than 0.5%. A single strand according to any one of the preceding claims, the single strand having a tensile strength greater than 300 MPa, preferably greater than or equal to 320 MPa. A single strand according to any one of the preceding claims, wherein the initial tensile modulus, denoted E23, of the single strand, measured at 23°C, is greater than 4 GPa, preferably greater than 4.5 GPa. Use of at least one single strand according to any one of claims 1 to 10, for strengthening concrete and / or reducing the weight of concrete and / or reducing or preventing cracking of concrete.Concrete comprising a plurality of monostrands according to any one of claims 1 to 10, the volumetric content of monostrands in the concrete being preferably in the range of 0.1% to 6%. Method for manufacturing a polyester-resin composite monostrand comprising polyester filaments embedded in a crosslinked resin according to any one of claims 1 to 10, comprising the following successive steps: creating a straight arrangement of polyester filaments and driving this arrangement in a forward direction, in a vacuum chamber, degassing the arrangement of polyester 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 polyester filaments with a photocurable resin composition, in the liquid state, said. "Impregnancy resin" is used to obtain an impregnated material containing polyester filaments and the resin composition. This impregnated material is passed through a calibration die having a predefined surface area and shape, thus imposing a single-strand form. Downstream of the die, the resin composition is polymerized in a UV irradiation chamber under the action of UV light. The irradiation chamber comprises a UV-transparent tube, called the irradiation tube, through which the forming single-strand passes, carrying a current of inert gas. The speed (denoted Vir) of the single-strand passing through the irradiation chamber is greater than 50 m / min, and the irradiation time (denoted Di) is [not specified]. 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 13, characterized in that the single strand has 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 claims 13 to 14, wherein the polyester filaments are filaments selected from polyethylene terephthalate and polyethylene naphthalate, preferably entirely polyethylene terephthalate.

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