Fiber reinforcement material for cementitious compositions

Abstract

The invention is directed to fiber reinforcement material comprising a plurality of macro-synthetic fibers twisted to form a fiber bundle having a twist degree of 5 - 100 t / m, preferably 8 - 80 t / m, wherein at least a portion of the macro-synthetic fibers are self-fibrillating fibers consisting of two or more partially fused polymeric monofilaments and having a multi-lobal cross-sectional shape with two or more lobes.

Description

[0001] FIBER REINFORCEMENT MATERIAL FOR CEMENTITIOUS COMPOSITIONS

[0002] Technical field

[0003] The invention relates to polymeric fibers for use in construction materials, particularly in cementitious compositions. Particularly, the invention relates to fiber materials comprising twisted macro-synthetic fibers provided in form of a fiber bundle, which fibers are capable of undergoing a progressive fibrillation when mechanically agitated within a matrix material to be reinforced.

[0004] Background Art

[0005] Concrete is the most commonly used man-made construction material for structural applications in the world. Generally, concrete is a brittle material having a high compressive strength but low tensile strength (crack strength). The tensile strength of concrete can be improved by using modifying additives, such as rebars and reinforcing meshes. Polymeric, metal, glass, and natural fibers have also been used to improve the tensile strength (strength before first crack occurs) and toughness (resistance to cracking) of concrete.

[0006] Different types of fibers can be used to improve specific properties of concrete. Synthetic microfibers (microfibers) having a linear density of not more than 580 denier (den) are typically used to prevent plastic shrinkage cracking as the concrete sets, i.e. to prevent micro-cracking of the concrete during the first 24 to 48 hours after casting. Macro-synthetic fibers (macrofibers) having a linear density of greater than 580 den and diameters of equal or greater than 0.3 mm are added to concrete compositions to improve overall toughness quantified by measurements of residual strength after first break has occurred. Macrofibers are typically added to concrete mixtures at fiber dosages of 1 .8 to 8.9 kg / m3. Macrofibers are available in various shapes, such as rope, tape or stick and they may be twisted, serrated, or embossed to enhance mechanical bonding to concrete. The concrete reinforcement properties of synthetic fibers depend on both the strength of the fiber and on the adhesion between the fiber and the concrete matrix. The benefits obtained with fiber-reinforced concrete has led to the widespread use of fibers in lieu of conventional temperature and shrinkage reinforcement as well as toughness in many applications, including slab-on-ground. Commonly used plastic materials for concrete reinforcement fibers include polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), aramids, for example Kevlar, polyamides, and polyvinyl alcohol fibers. All of these suffer from one or more disadvantages, such as high cost, low alkaline resistance, low tenacity or low interfacial bonding between the concrete matrix and the fiber. Polypropylene and polyethylene have been widely used as raw material for both micro and macrofibers. Their advantages include easy processability to fibers through melt-spinning (extrusion) processes, low cost, and high resistance in alkaline environment. However, due to the low density and hydrophobicity the fibers tend to bloom to the surface during finishing, i.e. the fibers tend to protrude from the surface of the concrete before completion of curing. The interfacial bonding between the fiber and concrete can be controlled by using coatings applied to the surface of the fibers or by chemical modification of the fiber surface. However, these methods typically result in increased costs and complexity of the fiber production process.

[0007] Larger fibers in terms of fiber aspect ratio are generally more suitable than small fibers for use in improving the toughness of the concrete. Thicker fibers have higher breaking force, but they also provide less interfacial bonding to concrete due to the reduced surface area. Bonding properties of fibers can generally be improved by using longer and thinner fibers. However, longer and thinner fibers also tend to clump together in balls (balling) that are difficult to break when added to concrete. Resistance to balling can be improved by using fibers that fibril late into many smaller fibers when mechanically agitated within a matrix material to be reinforced with the fibers. Fibrillation also increases the surface area of the fibers resulting in improvement of the interfacial bonding to concrete. Self-fibrillating macro-synthetic fibers consisting of three or more partially fused monofilaments, which are capable of undergoing a progressive fibrillation when mechanically agitated within a matrix material to be reinforced, are disclosed in published patent application WO2021255208 A1.

[0008] Another challenge with macro-synthetic fibers and particularly with self-fibrillating fibers is their uniform distribution in the concrete mix. The uniform distribution of fibers is usually achieved by providing the fibers in form of pre-packed fiber “pucks” or bundles wrapped in a water-soluble polyvinyl alcohol film, from which the individual fibers are released in a controlled manner during mixing, thus providing more uniform fiber distribution. However, if the fiber bundles are too big, fiber entanglement, still occurs.

[0009] Furthermore, many commercially available self-fibrillating fibers have issues with either “over binding”, which causes the filaments never to separate properly, or with “under binding” causing the filaments to be separated before the fibers have been introduced into the concrete mixture. Inconsistency in fiber self-fibrillation can impact the individual fiber count, slump change in the concrete mix, concrete performance, and concrete finishing characteristics.

[0010] Thus, there is still a need for new and improved solutions that overcome the aforementioned disadvantages as far as possible.

[0011] Summary of the invention

[0012] The objective of the present invention is to provide an improved fiber reinforcement material for use in cementitious compositions, particularly in concrete mixes.

[0013] Surprisingly, it has been found out that the object can be achieved by the feature of claim 1.

[0014] Specifically, according to the invention, a fiber reinforcement material is proposed, the material comprising a plurality of macro-synthetic fibers twisted to form a fiber bundle having a twist degree of 5 - 100 t / m (turns per meter), preferably 8 - 80 t / m, wherein at least a portion of the macro-synthetic fibers are self-fibrillating fibers consisting of two or more partially fused polymeric monofilaments and having a multi-lobal cross-sectional shape with two or more lobes.

[0015] As it turned out, the fiber reinforcement material comprising self-fibrillating macro-synthetic fibers provided in form a twisted fiber bundle shows consistent self-fibrillating properties, reduced fiber entanglement (balling), and good finishing of concrete slabs, even when used in high amounts required for structural reinforcing, such as in amounts of 3.6 - 4 kg of fibers / m3of concrete mix. Additional aspects of the present invention are presented in further independent claims. Preferred embodiments of the invention are outlined throughout the description and the dependent claims.

[0016] Brief description of the Drawings

[0017] Fig. 1 shows schematically a cross-sectional shape of an exemplary self-fibrillating macrosynthetic fiber.

[0018] Fig. 2 shows a schematic presentation of an exemplary process for producing a self- fibrillating macro-synthetic fiber.

[0019] Detailed description of the invention

[0020] A first aspect of the present invention is directed to a fiber reinforcement material comprising a plurality of macro-synthetic fibers twisted to form a fiber bundle having a twist degree of 5 - 100 t / m, preferably 8 - 80 t / m, wherein at least a portion of the macrosynthetic fibers are self-fibrillating fibers consisting of two or more partially fused polymeric monofilaments and having a multi-lobal cross-sectional shape with two or more lobes.

[0021] The term “polymer” refers to a collective of chemically uniform macromolecules produced by a polyreaction (polymerization, polyaddition, polycondensation) where the macromolecules differ with respect to their degree of polymerization, molecular weight, and chain length. The term also comprises derivatives of said collective of macromolecules resulting from polyreactions, that is, compounds which are obtained by reactions such as, for example, additions or substitutions, of functional groups in predetermined macromolecules and which may be chemically uniform or chemically non- uniform.

[0022] The term “melting temperature” refers to a temperature at which a material undergoes transition from the solid to the liquid state. The melting temperature (Tm) is preferably determined by differential scanning calorimetry (DSC) according to ISO 11357 standard using a heating rate of 2 °C / min. The measurements can be performed with a Mettler Toledo DSC 3+ device and the Tm values can be determined from the measured DSC- curve with the help of the DSC-software. In case the measured DSC-curve shows several peak temperatures, the first peak temperature coming from the lower temperature side in the thermogram is taken as the melting temperature (Tm).

[0023] The “amount or content of at least one component X” in a composition, for example “the amount of the at least one thermoplastic polymer P1” refers to the sum of the individual amounts of all thermoplastic polymers P1 contained in the composition. For example, in case the composition comprises 20 wt.-% of at least one thermoplastic polymer P1 , the sum of the amounts of all thermoplastic polymers P1 contained in the composition equals 20 wt.-%.

[0024] The term “normal room temperature” refers to the temperature of 23 °C.

[0025] The fiber reinforcement material of the present invention comprises a plurality of macrosynthetic fibers twisted to form a fiber bundle having a twist degree of 5 - 100 t / m, preferably 8 - 80 t / m, more preferably 15 - 75 t / m, even more preferably 25 - 70 t / m, still more preferably 30 - 65 t / m, especially 35 - 60 t / m, for example 40 - 60 t / m.

[0026] At least a portion of the macro-synthetic fibers twisted to form a fiber bundle are self- fibrillating fibers consisting of two or more, preferably three or more partially fused polymeric monofilaments and having a multi-lobal cross-sectional shape with two or more lobes, preferably three or more lobes.

[0027] The expression “partially fused” is understood to mean in the context of the present invention that the self-fibrillating fibers have been obtained by using a process comprising extruding a molten polymer composition to provide extruded monofilaments, which are allowed to get into contact over a portion of their primary exterior surfaces and to partially fuse with each other to form an undrawn fiber. The term “primary exterior surface” of a filament refers here to the longitudinally extending surface of said filament.

[0028] Self-fibrillating fibers composed of partially fused monofilaments differ significantly from fibers composed of single filament (monofilament fibers) and from multi-filament fibers, where the filaments have been joined to each other adhesively or mechanically.

[0029] In one or more embodiments, the self-fibrillating fibers contained in the fiber reinforcement material have been obtained by using a process comprising extruding a molten polymer composition through an extruder die comprising a plurality of orifices to provide undrawn fibers, wherein at least part of said orifices consist of an assembly of two or more holes, preferably three or more holes that are proximately disposed but not overlapping each other such that when the molten polymer composition is extruded through said holes, the thus obtained extruded monofilaments are partially fused to form an undrawn fiber. The expression “overlapping each other” is understood to mean that the distance between adjacent holes of said assembly is such that the perimeters of the holes are not intersecting each other.

[0030] Due to the partially fused filament structure, the self-fibrillating fibers are particularly capable of undergoing progressive fibrillation when mechanically agitated within a matrix to be reinforced with the fibers. The first part of the fibrillation occurs during the early stage of mixing, which gives the fibers additional time to disperse within the matrix. The second part of the fibrillation happens after considerable mixing when significant portion of the fibers have already been distributed into the matrix, which decreases the tendency of the individual monofilaments separated from the fibers to clump together in balls.

[0031] In one or more embodiments, the fiber reinforcement material has been obtained by a process comprising twisting together 2 - 100, preferably 5 - 75, more preferably 5 - 50, even more preferably 5 - 35, still more preferably 6 - 25 macro-synthetic fibers into a twisted bundle using a twist degree of 5 - 100 t / m, preferably 8 - 80 t / m, more preferably 15 - 75 t / m, even more preferably 25 - 70 t / m, still more preferably 30 - 65 t / m, especially 35 - 60 t / m, for example 40 - 60 t / m.

[0032] It may be preferred that the self-fibrillating fibers have a linear density of at least 500 den, more preferably at least 1000 den. The term “den” is abbreviation of “denier”, which refers to a unit of measure for the linear mass density of fibers, i.e. the mass in grams per 9000 meters of the fiber.

[0033] In one or more embodiments, the self-fibrillating fibers have:

[0034] - a linear density of 500 - 10000 den, preferably 800 - 7500 den more preferably 1500 - 6500 den, even more preferably 2000 - 5000 den, still more preferably 2500 - 4000 den and / or

[0035] - a length of at least 15 mm, preferably at least 20 mm, more preferably at least 25 mm, even more preferably at least 30 mm, still more preferably at least 35 mm and / or - a length of not more than 100 mm, preferably not more than 85 mm, more preferably not more than 70 mm, even more preferably not more than 65 mm, still more preferably not more than 60 mm and / or

[0036] Particularly, the polymer composition of the self-fib dilating fibers may comprise at least 70 wt.-%, preferably at least 75 wt.-% of at least one polypropylene.

[0037] In one or more embodiments, the polymer composition comprises 70 - 95 wt.-%, preferably 75 - 90 wt.-%, more preferably 80 - 90 wt-%, of the at least one polypropylene.

[0038] Suitable polypropylenes for use in the polymer composition include polypropylene homopolymers (hPP), such as isotactic polypropylene (iPP) and syndiotactic polypropylene (sPP), as well as propylene copolymers, such as heterophasic propylene copolymers, propylene random copolymers, and propylene block copolymers.

[0039] The term “propylene copolymer” refers to copolymers comprising at least 50 wt.-%, more preferably at least 60 wt.-% of propylene-derived units, based on the weight of the copolymer whereas the term “ethylene copolymer” refers to copolymers comprising at least 50 wt.-%, more preferably at least 60 wt.-% of ethylene-derived units, based on the weight of the copolymer.

[0040] Heterophasic propylene copolymers are heterophasic polymer systems comprising a high crystallinity base polyolefin and a low-crystallinity or amorphous polyolefin modifier. The heterophasic phase morphology consists of a matrix phase composed primarily of the base polyolefin and a dispersed phase composed primarily of the polyolefin modifier. Suitable commercially available heterophasic propylene copolymers include reactor blends of the base polyolefin and the polyolefin modifier, also known as “in-situ TPOs” or “reactor TPOs or “impact copolymers (ICP)”, which are typically produced in a sequential polymerization process, wherein the components of the matrix phase are produced in a first reactor and transferred to a second reactor, where the components of the dispersed phase are produced and incorporated as domains in the matrix phase. Heterophasic propylene copolymers comprising polypropylene homopolymer as the base polymer are often referred to as “heterophasic propylene copolymers (HECO)” whereas heterophasic propylene copolymers comprising polypropylene random copolymer as the base polymer are often referred to as “heterophasic propylene random copolymers (RAHECO)”. The term “heterophasic propylene copolymer” encompasses in the present disclosure both the HECO and RAHECO types of the heterophasic propylene copolymers.

[0041] Specifically, he at least one polypropylene can have:

[0042] - a flexural modulus determined according to ISO 178:2019 standard of at least 1000 MPa, preferably at least 1100 MPa, more preferably at least 1200 MPa and / or

[0043] - a melting temperature (Tm) determined by differential scanning calorimetry (DSC) according to ISO 11357-3:2018 standard using a heating rate of 2 °C / min of at or above 115 °C, preferably at or above 125 °C, more preferably at or above 135 °C, even more preferably at or above 145 °C, still more preferably at or above 155 °C and / or

[0044] - a melt flow index (230 °C / 2.16 kg) determined according to ISO 1133 standard of not more than 100 g / 10 min, preferably not more than 50 g / 10 min, more preferably not more than 35 g / 10 min, even more preferably not more than 15 g / 10 min, such as 0.5 - 15 g / 10 min, preferably 1 - 10 g / 10 min, more preferably 1 - 5 g / 10 min.

[0045] In one or more embodiments, the at least one polypropylene comprises or consists of polypropylene homopolymer, preferably an isotactic polypropylene, preferably having an isotactic index determined by means of13C-NMR spectroscopy of at least 80 %, preferably at least 85 %, more preferably at least 90 %.

[0046] The polymer composition of the self-fibrillating fibers may further comprise at least 1 wt.-%, preferably at least 5 wt.-%, more preferably at least 7.5 wt.-%, of at least one polyethylene. Without being bound to any theory, it is believed that due to the polymer composition of the monofilaments comprising both polypropylene and polyethylene, the boundary between the partially fused monofilaments is more easily torn than in case of monofilaments composed of polyethylene or polypropylene alone. This is believed to enhance the ability of the fibers to undergo a progressive fibrillation when mechanically agitated within a matrix to be reinforced with the fibers.

[0047] In one or more embodiments, the polymer composition of the self-fibrillating fibers comprises 1 - 30 wt.-%, preferably 5 - 25 wt.-%, more preferably 10 - 20 wt.-%, of the at least one polyethylene.

[0048] Suitable polyethylenes for use in the polymer material include ethylene homopolymers and ethylene copolymers. According to one or more embodiments, the at least one polyethylene has:

[0049] - a melting temperature (Tm), determined by differential scanning calorimetry (DSC) according to ISO 11357-3 standard using a heating rate of 2 °C / min, of at or above 90 °C, preferably at or above 100 °C, more preferably at or above 105 °C, such as 90 - 140 °C, preferably 100 - 135 °C, more preferably 105 - 125 °C and / or

[0050] - a melt flow index (190 °C / 2.16 kg) determined according to ISO 1133 standard of not more than 100 g / 10 min, preferably not more than 50 g / 10 min, more preferably not more than 35 g / 10 min, even more preferably not more than 15 g / 10 min, such as 0.5 - 15 g / 10 min, preferably 1 - 10 g / 10 min, more preferably 1 - 5 g / 10 min.

[0051] In one or more embodiments, the at least one polyethylene comprises or consists of low- density polyethylene (LDPE) or linear low-density polyethylene (LLDPE), or high-density polyethylene (HDPE), preferably linear low-density polyethylene (LLDPE).

[0052] It may be preferred that the fiber bundle of the fiber reinforcement material of the present invention contains, in addition to the self-fibrillating fibers as discussed above, also other types of macro-synthetic fibers, such as monofilament fibers. In these embodiments, the monofilament fibers may be twisted together with the self-fibrillating fibers to form the fiber bundle.

[0053] Preferably, the proportion of the self-fibrillating fibers makes up at least 5 wt.-%, more preferably at least 10 wt.-%, even more preferably at least 15 wt.-%, of the total weight of the macro-synthetic fibers of the fiber bundle.

[0054] The monofilament fibers may be composed of a similar polymer composition than the self- fibrillating fibers.

[0055] Particularly, the monofilament fibers may be composed of a polymer composition comprising at least 70 wt.-%, preferably at least 75 wt.-% of at least one polypropylene.

[0056] In one or more embodiments, the polymer composition of the monofilament fibers comprises 70 - 95 wt.-%, preferably 75 - 90 wt.-%, more preferably 80 - 90 wt.-%, of the at least one polypropylene. The polymer composition of the monofilament fibers may further comprise at least 1 wt.-%, preferably at least 5 wt.-%, more preferably at least 7.5 wt.-%, of at least one polyethylene.

[0057] In one or more embodiments, the polymer composition of the monofilament fibers comprises 1 - 30 wt.-%, preferably 5 - 25 wt.-%, more preferably 10 - 20 wt.-%, of the at least one polyethylene.

[0058] In one or more embodiments, at least a portion of the monofilament fibers twisted together with the self-fibrillating fibers are composed of the same polymer composition as the self- fibrillating fibers.

[0059] In or more embodiments, the macro-synthetic fibers are surface structured at their outer surfaces. Especially, the macro-synthetic fibers can comprise recesses and / or embossments in their outer surface and / or the outer surfaces of the macro-synthetic fibers can be coated with particles. The surface structure can for example be achieved by embossing, grinding, sandblasting, and / or coating techniques, for example with sand particles.

[0060] Particularly, the macro-synthetic fibers can surface-structured at their outer surfaces such that a root-mean-square roughness Rq(A = 800 pm, 50 fold magnification) of the surface is 1 - 100 pm, preferably 2 - 80 pm, more preferably 3 - 60 pm, particularly 5 - 40 pm, wherein Rqis measured according to ISO 4287:1997 standard.

[0061] Furthermore, crimping has been found out to reduce the stiffness of the macro-synthetic fibers and to improve the self-fibrillation properties. Generally, the number of crimps should be high enough to provide the fiber with improved fibrillation properties while not having a negative impact on other properties, such as dispersion properties of the fibers.

[0062] In one or more embodiments, the macro-synthetic fibers to have:

[0063] - a crimp frequency of 5 - 100 crimps / 100 mm, preferably 15 - 85 crimps / 100 mm, more preferably 20 - 80 crimps / 100 mm, even more preferably 25 - 75 crimps / 100 mm and / or

[0064] - a crimp amplitude of 0.1 - 1 mm, preferably 0.2 - 1 mm, more preferably 0.5 - 1 mm, even more preferably 0.6 - 0.8 mm. In one or more embodiments, at least a portion of the macro-synthetic fibers are self- f ibrillati ng fibers having a multi-lobal cross-sectional shape with two or more lobes, preferably three or more lobes, and a central section running axially through the fiber.

[0065] The central section of the self-fibrillating fibers is preferably solid, i.e. it does not include an axial hole or a void. According to one or more embodiments, at least two of said lobes extend outwardly, preferably radially from the central section. According to one or more embodiments, at least two of said lobes are connected to each other through the central section.

[0066] Preferably, each lobe has a tip portion and a base portion situated towards the central section of the fiber. Furthermore, the tip portion of each lobe is preferably curved, more preferably convexly curved. Figure 1 shows schematically the cross-sectional shape of an exemplary self-fibrillating fiber composed of four partially fused polymeric monofilaments, wherein the fiber (1) has a quadri-lobal cross-sectional shape with four lobes (2) extending outwardly from the central section (3) of the fiber.

[0067] According to one or more embodiments, the base portion of each lobe has a width (D2) that is smaller than the maximum width (D1) of the tip portion. The term “maximum width of the tip portion” refers to the length of the longest line extending perpendicularly to a longitudinal line connecting the central section of the fiber with the tip portion of the lobe, wherein the longitudinal line extends toward the outline of the lobe. The term “width of the base portion” refers to the length of a line connecting two end points of the base portion of two adjacent lobes. In Figure 1 , the maximum width of the tip portion of a lobe (2) is indicated by the letter “D1”, the width of the base portion of the lobe (2) is indicated by the letter “D2”, and the longitudinal line connecting the central section (3) of the fiber with the tip portion of the lobe (2) is indicated with letter “L”. The widths D1 and D2 can be determined from a microscopic picture of a fiber cross-section.

[0068] According to one or more embodiments, in each lobe, the ratio between the maximum width of the tip portion to the width of the base portion (D1 : D2) is from 1.1 :1 to 3: 1 , preferably from 1.2:1 to 2.7:1 , more preferably from 1.3:1 to 2.5:1. Self-fibrillating fibers having the ratio between the maximum width (D1 ) of the tip portion to the width (D2) of the base portion in the above mentioned ranges have been found out to be advantageous since the lobes, and thus the partially fused monofilaments of the fiber, tend to be peeled away or separated from around the base portion by shearing force thus enabling progressive fibrillation when the fibers are mechanically agitated within a matrix material to be reinforced.

[0069] According to one or more embodiments, at least a portion of the macro-synthetic fibers are self-fibrillating fibers composed of four partially fused polymeric monofilaments. In these embodiments, at least a portion of the macro-synthetic fibers are self-fibrillating fibers having a quadri-lobal cross-sectional shape with four lobes, wherein preferably at least two of said lobes extend outwardly, more preferably radially from the central section of the fiber. Such self-fibrillating fibers when twisted to form a fiber bundle have been found out to be highly effective in improving the toughness of concrete and to exhibit a good dispersibility in a concrete mixture and good surface finishing properties. According to one or more embodiments, at least a portion of the macro-synthetic fibers are self-fibrillating fibers having a quadri-lobal cross-sectional shape with four lobes extending outwardly, preferably radially, from the central section of the fiber.

[0070] It may be preferable for the self-fibrillating fibers to have:

[0071] - an elastic modulus an elastic modulus determined at 23 °C and at a strain rate of 5 % / min according to EN 14889-2:2006 standard of at least 5 MPa, preferably at least 7 MPa and / or

[0072] - an elongation at break determined at 23 °C according to EN 10002-1 :2001 standard of not more than 15 %, preferably not more than 10 % and / or

[0073] - a tensile strength determined at 23 °C and at a strain rate of 5 % / min according to EN 14889-2:2006 standard of at least 250 MPa, preferably at least 350 MPa.

[0074] The self-fibrillating fibers are preferably drawn with a draw ratio of at least 5:1 , more preferably 10:1. Drawing results in orientation of the polymer chains in a longitudinal direction of the fiber, which increases the tensile strength and decrease elongation of the fiber. Furthermore, drawn fibers are typically less stretchable in a width direction. Finally, drawing also weakens the connecting region between the partially fused monofilaments resulting in more effective fibrillation during mixing with a concrete matrix.

[0075] According to one or more embodiments, self-fibrillating fibers have been uniaxially drawn with a draw ratio of from 7.5:1 to 25:1 , preferably from 10:1 to 20:1 , more preferably from 10:1 to 17.5.1 , even more preferably from 12:1 to 15:1. Preferably, the self-fibrillating fibers are separable into single monofilaments having a linear density of not more than 1250 den, preferably not more than 1000 den, more preferably not more than 900 den.

[0076] According to one or more embodiments, the self-fibrillating fibers are separable into single monofilaments having:

[0077] - a linear density of 150 - 1250 den, preferably 250 - 1150 den, more preferably 350 - 1000 den, even more preferably 400 - 950 den and / or

[0078] - an aspect ratio (l / d) of 100 - 250, preferably 105 - 200, more preferably 110 - 175, even more preferably 115 - 150 and / or

[0079] - an equivalent diameter determined according to EN 14889-2:2006 standard of 0.1 - 1.0 mm, preferably 0.15 - 0.85 mm, more preferably 0.2 - 0.7 mm, even more preferably 0.2 - 0.55 mm.

[0080] A further aspect of the present invention is directed to a method for producing a fiber reinforcement material of the present invention, the method comprising twisting together 2

[0081] - 100, preferably 5 - 75, more preferably 5 - 50, even more preferably 5 - 35, still more preferably 6 - 25 macro-synthetic fibers into a twisted bundle using a twist degree of 5 - 100 t / m, preferably 8 - 80 t / m, more preferably 15 - 75 t / m, even more preferably 25 - 70 t / m, still more preferably 30 - 65 t / m, especially 35 - 60 t / m, for example 40 - 60 t / m, wherein at least a portion of the macro-synthetic fibers are self-fibrillating fibers consisting of two or more partially fused polymeric monofilaments and having a multi-lobal cross- sectional shape with two or more lobes.

[0082] In the inventive method, the self-fibrillating fibers are defined and configured as described above in connection with the first aspect of the present invention.

[0083] Suitable methods for providing the self-fibrillating fibers are disclosed in a published patent application WO2021255208 A1 , particularly from page 15, line 12 to page 20, line 29.

[0084] In one or more embodiments, the method for producing a fiber reinforcement material comprises steps of: I) Extruding a molten polymer composition comprising a polymer composition through an extruder die to provide undrawn fibers consisting of two or more, preferably three or more partially fused monofilaments,

[0085] II) Uniaxially drawing the undrawn fibers obtained from step I) to provide drawn fibers,

[0086] III) Optionally crimping and / or embossing the drawn fibers obtained from step II) to provide crimped and / or embossed fibers,

[0087] IV) Twisting the fibers obtained from step II) or III) into form of fiber bundles, and IV) Cutting the twisted bundles obtained from step IV) to a pre-determined length.

[0088] Crimping of the fibers can be conducted employing any conventional crimping apparatus, such as a crimper box, for example a tow crimper. In case of a crimper box, the drawn fibers are loaded into the crimper box which stuffs and bends the crimps into the fibers. The drawn fibers can also be mechanically crimped by running the fibers through a gear or set of gears to provide crimps into the fibers.

[0089] The term “embossing” refers to a treatment method, where the fibers are subjected to a compressive force, for example, by placing the fibers between embossed rollers, to cut or roughen the outer surface of the fibers.

[0090] The twisting of the fibers into fiber bundles can be conducted using any conventional techniques known to a skilled person, such as by using two-for-one twisting machine or a ring twister machine.

[0091] Figure 2 shows a schematic presentation of an exemplary method for producing the fiber reinforcing material of the present invention. In the process, the constituents of the starting composition are fed using a metering and feeding apparatus (1) into an extruder apparatus (2), where the starting is melt-processed into a molten polymer composition. The melt- processed starting composition is extruded though a spinneret (3) comprising a plurality of spinneret orifices. After that the extruded fibers are conducted through an air gap into a water bath (4). The cooled fibers are conveyed from the water bath (4) into a first (stretching) oven (6) using a powered takeaway roller comprising a first roll stand (5). The undrawn fibers are orientated in the first (stretching) oven (6), drawn using a second roll stand (7), and further processed in a second (annealing) oven (8). The heating in the first and second ovens (6, 8) is preferably achieved with forced hot air at a controlled temperature. The drawn fibers are passed from the second oven (8) through a mechanical crimper (9) comprised of two matched rolls that partially engaged to deform the drawn fiber. The crimped fibers are conveyed from the crimper using a third roll stand (10), winded by using a winder (11), twisted using a twister machine, and cut to a predetermined length (not shown in Figure 2).

[0092] Still another aspect of the present invention is the use of the fiber reinforcement material of the present invention improving properties, preferably toughness, of a hardened cementitious composition.

[0093] The term “cementitious composition” refers in the present disclosure to concrete, shotcrete, grout, mortar, paste or a combination thereof. The terms "paste", "mortar", "concrete", “shotcrete”, and “grout” are well-known terms for person skilled in the art. Pastes are mixtures comprising a hydratable cement binder, usually Portland cement, masonry cement, or mortar cement. Mortars are pastes additionally including fine aggregate, for example sand. Concrete are mortars additionally including coarse aggregate, for example crushed gravel or stone. Shotcrete is concrete (or sometimes mortar) conveyed through a hose and pneumatically projected at high velocity onto a surface. Grout is a particularly flowable form of concrete used to fill gaps. The cementitious compositions can be formed by mixing required amounts of certain components, for example, a Portland cement, water, and fine and / or coarse aggregate, to produce a specific cementitious composition.

[0094] According to one or more embodiments, the cementitious composition is selected from the group consisting of concrete, shotcrete, grout, and mortar, preferably concrete and shotcrete, more preferably concrete.

[0095] According to one or more embodiments, the fiber reinforcement material is added to the cementitious composition in an amount of 0.1 - 3.0 vol.-%, preferably 0.2 - 2.0 vol.-%, more preferably 0.2 - 1.0 vol.-%, based on the total volume of the hardened cementitious composition.

[0096] According to one or more embodiments, the toughness of hardened cementitious composition measured as a residual strength after first break has occurred, is improved by at least 5 %, preferably at least by 10 %, more preferably at least by 15 %, compared to the toughness of a hardened cementitious composition not containing the fiber reinforcement material of the present invention.

[0097] Still another subject of the present invention is cementitious material comprising: a) A binder, b) 0.1 - 3.0 vol.-%, preferably 0.2 - 2.0 vol.-%, more preferably 0.2 - 1 .0 vol.-%, based on the total volume of the cementitious material, of the fiber reinforcement material of the present invention, c) Aggregates, and d) Water.

[0098] According to one or more embodiments, the binder a) is selected from the group consisting of hydraulic binders, non-hydraulic binders, latent hydraulic binders, and pozzolanic binders.

[0099] The term “hydraulic binder” refers to substances, which react with water in a hydration reaction under formation of solid mineral hydrates or hydrate phases, which are not soluble in water or have a low water-solubility. Therefore, hydraulic binders, such as Portland cement, can harden and retain their strength even when exposed to water, for example underwater or under high humidity conditions. In contrast, the term “non-hydraulic binder” refers to substances, which harden by reaction with carbon dioxide and which, therefore, do not harden in wet conditions or under water.

[0100] Examples of suitable hydraulic binders include hydraulic cements and hydraulic lime. The term “hydraulic cement” refers here to mixtures of silicates and oxides including alite, belite, tricalcium aluminate, and brownmillerite.

[0101] Commercially available hydraulic cements can be divided in five main cement types according to DIN EN 197-1 , namely, Portland cement (CEM I), Portland composite cements (CEM II), blast-furnace cement (CEM III), pozzolan cement (CEM IV) and composite cement (CEM V). These five main types of hydraulic cement are further subdivided into an additional 27 cement types, which are known to the person skilled in the art and listed in DIN EN 197-1. Naturally, all other hydraulic cements that are produced according to another standard, for example, according to ASTM standard or Indian standard are also suitable. Examples of suitable non-hydraulic binders include air-slaked lime (non-hydraulic lime) and gypsum. The term "gypsum" refers in the present disclosure to any known form of gypsum, in particular calcium sulfate dehydrate, calcium sulfate a-hemihydrate, calcium sulfate R>-hemihydrate, or calcium sulfate anhydrite or mixtures thereof.

[0102] The term "latent hydraulic binder” refers in the present disclosure to type II concrete additives with a “latent hydraulic character” as defined in DIN EN 206-1 :2000 standard. These types of mineral binders are calcium aluminosilicates that are not able to harden directly or harden too slowly when mixed with water. The hardening process is accelerated in the presence of alkaline activators, which break the chemical bonds in the binder’s amorphous (or glassy) phase and promote the dissolution of ionic species and the formation of calcium aluminosilicate hydrate phases.

[0103] Examples of suitable latent hydraulic binders include ground granulated blast furnace slag. Ground granulated blast furnace slag is typically obtained from quenching of molten iron slag from a blast furnace in water or steam to form a glassy granular product and followed by drying and grinding the glassy into a fine powder.

[0104] The term “pozzolanic binder” refers in the present disclosure to type II concrete additives with a “pozzolanic character” as defined in DIN EN 206-1 :2000 standard. These types of mineral binders are siliceous or aluminosilicate compounds that react with water and calcium hydroxide to form calcium silicate hydrate or calcium aluminosilicate hydrate phases.

[0105] Examples of suitable pozzolanic binders include natural pozzolans, such as trass, and artificial pozzolans, such as fly ash and silica fume. The term "fly ash” refers in the present disclosure to the finely divided ash residue produced by the combustion of pulverized coal, which is carried off with the gasses exhausted from the furnace in which the coal is burned. The term “silica fume” refers in the present disclosure to fine particulate silicon in an amorphous form. Silica fume is typically obtained as a by-product of the processing of silica ores such as the smelting of quartz in a silica smelter which results in the formation of silicon monoxide gas and which on exposure to air oxidizes further to produce small particles of amorphous silica. According to one or more embodiments, the binder is a hydraulic binder, preferably a hydraulic cement, such as Portland cement.

[0106] Suitable aggregates to be used in the cementitious material include both coarse and fine (sand) aggregates as well as pebbles and rocks of various sizes, typically in the range of 10 mm - 20 mm (3 / 8” - 3 / 4”). According to one or more embodiments, the cementitious material is a fiber-reinforced concrete composition.

[0107] According to one or more embodiments, the weight ratio of the amount of water to the amount of the binder is in the range of 0.2:1 to 0.7:1 , preferably 0.3:1 to 0.6:1 , more preferably 0.4:1 to 0.6:1 , even more preferably 0.45:1 to 0.55:1.

[0108] Still another subject of the present invention is a method for forming a concrete surface comprising steps of:

[0109] I. Adding fiber reinforcement material of the present invention into a fluidized concrete mixture under mixer rotation to provide a modified concrete mixture,

[0110] II. Casting the modified concrete mixture prepared in step I. to provide a casted concrete body,

[0111] III. Smoothing the surface of the casted concrete body prepared in step II., and

[0112] IV. Curing the modified concrete mixture.

[0113] According to one or more embodiments, said fluidized concrete mixture comprises a binder, aggregates, and water.

[0114] The weight ratio of the amount of water to the amount of the binder is preferably in the range of from 0.2:1 to 0.7:1 , more preferably 0.3:1 to 0.6:1 , even more preferably 0.4:1 to 0.6:1 , still more preferably 0.45:1 to 0.55:1.

[0115] Preferred binders and aggregates have already been discussed above in relation to the cementitious material of the present invention.

[0116] According to one or more embodiments, the modified concrete mixture comprises 0.1 - 3.0 vol.%, preferably 0.2 - 2.0 vol.%, more preferably 0.2 - 1 .0 vol.%, of the fiber reinforcement material, based on the total volume of the hardened cementitious composition. Smoothing of the surface of the casted concrete body can be conducted, for example, by using a pallet or a trowel.

[0117] Examples

[0118] The followings compounds shown in Table 1 were used in the examples:

[0119] Table 1

[0120] Preparation of fiber reinforcement material

[0121] The self-fibrillating fibers used for preparing the inventive and reference fiber reinforcement materials were produced using a process, which is schematically presented in Figure 2.

[0122] The proportion of the raw materials, parameters of the production process as well as dimensions and mechanical properties of the self-fibrillating fibers are show in Table 2.

[0123] All self-fibrillating fibers were produced using an extruder die with a plurality of spinneret orifices, wherein each orifice consisted of an assembly of four non-intersecting round holes arranged in form of a quadrangle. The produced fibers had a multi-lobal cross-sectional shape with four lobes extending radially from the center of the fiber as shown schematically in Figure 1. The raw materials of the self-fibrillating fibers were fed using a metering and feeding apparatus (1 ) into an extruder (2) comprising a 110 mm single screw extruder with an L / D ratio of 32:1 and two melt pumps feeding two circular dies. The melt-processed composition was extruded though an extruder die (3) comprising a plurality of spinneret orifices consisting of an assembly of holes and the extruded fibers were conducted over an air gap into a water bath (4). The downstream equipment was a powered takeaway roller comprising a first roll stand (5) equipped with five rolls and a nip roll on the exit roller.

[0124] The undrawn fibers obtained from the exit roller were orientated in a first (stretching) oven (6), drawn using a second roll stand (7) composed of seven rollers, and further processed in a second (annealing) oven (8) to obtain drawn fibers. The heating in the first and second oven (6, 8) was achieved with forced hot air at a controlled temperature.

[0125] The drawn fibers obtained from the second oven (8) were passed through a mechanical crimper (9) comprised of two matched rolls that partially engaged to deform the drawn fiber. After exiting the crimper (9), the fibers were further processed through the third roll stand (10) composed of seven rolls with the exit roll having a nip roll.

[0126] The inventive fiber reinforcement material (Ex-1) was obtained by twisting 15 individual drawn and crimped fibers using a twister (12) into fiber bundles comprising using a twist degree of 54 t / m. The fiber bundles were then winded by using a winder (11) and cut to a predetermined length.

[0127] In case of the reference fiber reinforcing materials (Ref-1 , Ref-2), the drawn and crimped fibers were not twisted into fiber bundles but winded and cut to a predetermined length and provided in form of fiber pucks containing the fibers wrapped in a water-soluble polyvinyl alcohol film. The fiber pucks of the reference materials had a diameter of 30 mm and 20 mm, respectively.

[0128] Table 2

[0129] Use of fiber materials in cementitious material

[0130] The goal was to study the effect of twisting to the self-fibrillation efficiency, entanglement (balling) behavior, and finishability of the fibers.

[0131] The inventive and reference fiber reinforcement materials were first mixed to a typical concrete mix having a compressive strength of 24 - 31 MPa at an age of 7 days. The concrete was batched and mixed in accordance with ASTM C192-19 Standard Practice for Making and Curing Concrete Test Specimens in the Laboratory. The fiber reinforcement materials were added at the beginning of the batch sequence and mixed with the rock and sand for one minute prior to the addition of the cementitious material. The concrete was then mixed for 3 minutes, allowed to rest for 3 minutes, and mixed for 2 additional minutes and casted into molds. Table 3 shows the frequency of occurrence of balling obtained with the fiber reinforcement materials and proportion (wt.-%) of non-completely fibrillated fibers and completely fibrillated fibers after mixing of the tested fiber reinforcement material with the concrete mix. In calculation of the proportions, the fibers having two, three, or four fused monofilaments were taken as “non-completely fibrillated fibers” and fibers composed of one single monofilament were considered as “completely fibrillated fibers”.

[0132] Table 3

[0133] Figures 3 and 4 show photographic presentations of concrete slabs reinforced with tested fiber reinforcing materials. The concrete slab of Figure 3 has been obtained by using the inventive fiber reinforcing material (Ex-2) exhibiting very good finishability without surface defects. Figure 4 shows a concrete slab obtained with reference fiber reinforcing material (Ref-2) after hard steel troweling treatment. The surface of this concrete slab has a hairy, “whirly bird” appearance.

Claims

Claims1 . A fiber reinforcement material comprising a plurality of macro-synthetic fibers twisted to form a fiber bundle having a twist degree of 5 - 100 t / m, preferably 8 - 80 t / m, wherein at least a portion of the macro-synthetic fibers are self-fib dilating fibers consisting of two or more partially fused polymeric monofilaments and having a multi-lobal cross-sectional shape with two or more lobes.

2. The fiber reinforcement material according to claim 1 , wherein at least a portion of the macro-synthetic fibers are self-fibrillating fibers consisting of three or more partially fused polymeric monofilaments and having a multi-lobal cross-sectional shape with three or more lobes.

3. The fiber reinforcement material according to claim 1 or 2, wherein the self- fibrillating fibers have a linear density of 500 - 10000 den, preferably 800 - 7500 den and / or a length of at least 15 mm, preferably at least 20 mm and / or a length of not more than 100 mm, preferably not more than 85 mm.

4. The fiber reinforcement material according to any one of previous claims, wherein the self-fibrillating fibers are composed of a polymer composition comprising at least 70 wt.-%, preferably at least 75 wt.-%, of at least one polypropylene.

5. The fiber reinforcement material according to claim 4, wherein the polymer composition of the self-fibrillating fibers further comprises least 1 wt.-%, preferably at least 5 wt.-%, of at least one polyethylene.

6. The fiber reinforcement material according to any one of previous claims, wherein the proportion of the self-fibrillating fibers makes up at least 2.5 wt.-%, more preferably at least 5 wt.-%, of the total weight of the macro-synthetic fibers of the fiber bundle.

7. The fiber reinforcement material according to any one of previous claims, wherein the macro-synthetic fibers are surface-structured at their outer surfaces, preferably such that a root-mean-square roughness Rq(A = 800 pm, 50 fold magnification) of the surface is 1 - 100 pm, preferably 2 - 80 pm, wherein Rqis measured according to ISO 4287:19978. The fiber reinforcement material according to any one of previous claims, wherein the macro-synthetic fibers have a crimp frequency of 5 - 100 crimps / 100 mm, preferably 15 - 75 crimps / 100 mm and / or a crimp amplitude of 0.1 - 1 mm, preferably 0.5 - 1 mm.

9. The fiber reinforcement material according to any one of previous claims, wherein at least a portion of the macro-synthetic fibers are self-fibrillating fibers having a multi-lobal cross-sectional shape with three or more lobes and a central section running axially through the macro-synthetic fiber.

10. The fiber reinforcement material according to claim 9, wherein each lobe has a curved tip portion and a base portion situated toward the central section of the self- fibrillating fiber.11 . The fiber reinforcement material according to claim 10, wherein the base portion has a width (D2) that is smaller than the maximum width (D1 ) of the tip portion.

12. The fiber reinforcement material according to any one of previous claims, wherein at least a portion of the macro-synthetic fibers are self-fibrillating fibers consisting of four partially fused monofilaments.

13. A method for producing a fiber reinforcement material according to any one of previous claims, the method comprising twisting together 2 - 100 macro-synthetic fibers, preferably 5 - 75 macro-synthetic fibers into a twisted bundle using a twist degree of 5 - 100 t / m, preferably 8 - 80 t / m, wherein at least a portion of the macrosynthetic fibers are self-fibrillating fibers consisting of two or more partially fused polymeric monofilaments and having a multi-lobal cross-sectional shape with two or more lobes.

14. A cementitious material comprising: a) A binder, b) 0.1 - 3.0 vol.-%, preferably 0.2 - 2.0 vol. -%, based on the total volume of the cementitious material, of the fiber reinforcement material according to any one of claims 1-12, c) Aggregates, and d) Water.

15. A method for forming a concrete surface comprising steps of:I. Adding fiber reinforcement material according to any one of claims 1-12 into a fluidized concrete mixture under mixer rotation to provide a modified concrete mixture,II. Casting the modified concrete mixture prepared in step I. to provide a casted concrete body,III. Smoothing the surface of the casted concrete body prepared in step II., andIV. Curing the modified concrete mixture.

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