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CN-115667597-B - Polymer fibers for concrete reinforcement

CN115667597BCN 115667597 BCN115667597 BCN 115667597BCN-115667597-B

Abstract

The present invention relates to a raw synthetic fiber consisting of three or more partly melted filaments made of a polymer composition comprising at least one polypropylene, wherein the fiber has a multilobal cross-sectional shape with three or more lobes. The invention also relates to a method for producing coarse synthetic fibers, to cementitious materials comprising a binder and the coarse synthetic fibers of the invention, and to a method for forming a concrete surface using the coarse synthetic fiber-modified concrete mixture of the invention.

Inventors

  • F. Ferret
  • W. Durao
  • C. Rabe

Assignees

  • SIKA技术股份公司

Dates

Publication Date
20260508
Application Date
20210617
Priority Date
20200617

Claims (15)

  1. 1. A coarse synthetic fiber comprised of three or more root portions fused filaments made of a polymer composition comprising at least one polypropylene and at least one polyethylene, the at least one polypropylene comprising at least 70 wt% of the polymer composition and the at least one polyethylene comprising at least 5 wt% of the polymer composition, based on the total weight of the polymer composition, wherein the fiber has a multilobal cross-sectional shape with three or more lobes, wherein each lobe has a curved tip portion and a base portion located toward a central portion of the fiber, the tip portion having a maximum width (D1) and a width (D2) of the base portion (D1: D2) of 1.2:1, the coarse synthetic fiber being drawn at a draw ratio of at least 5:1, the coarse synthetic fiber having a fiber length of at least 20 mm, and/or an aspect ratio (l/D) of not greater than 85, and/or a fiber diameter of at least 0. 0.25 mm, the fiber having a central portion of the fiber being a solid, the plurality of holes being not formed by a method comprising extruding the composition through a solid die, the method comprising providing the coarse synthetic fiber by a method comprising at least extruding the three-hole or more than one-piece.
  2. 2. The coarse synthetic fiber of claim 1, capable of undergoing gradual fibrillation when mechanically agitated within a matrix material to be reinforced with the fiber.
  3. 3. The coarse synthetic fiber of claim 1, having a multi-lobal cross-sectional shape with three or more lobes and a central portion that extends axially through the fiber.
  4. 4. The raw synthetic fiber according to claim 1 or 2, which consists of four-root partially fused filaments.
  5. 5. The raw synthetic fiber according to claim 1 or 2, having a linear density of at least 1000 den, and/or a fiber length of at least 20 mm, and/or an aspect ratio (l/d) of not more than 85, and/or a fiber diameter of at least 0.25 mm.
  6. 6. The raw synthetic fiber according to claim 1 or 2, having a linear density of at least 1200 den, and/or a fiber length of at least 25 mm, and/or an aspect ratio (l/d) of not more than 75, and/or a fiber diameter of at least 0.35 mm.
  7. 7. A process for producing a raw synthetic fiber comprising the steps of: i) Extruding a molten polymer composition comprising at least one polypropylene and at least one polyethylene to provide an undrawn fiber composed of three or more partially fused filaments, wherein the at least one polypropylene comprises from 70 to 90 weight percent of the polymer composition and the at least one polyethylene comprises from 5 to 25 weight percent of the polymer composition, II) uniaxially stretching the undrawn fiber prepared in step I) to provide a drawn fiber, III) optionally crimping the drawn fiber prepared in step II) to provide a crimped fiber, and IV) cutting the fiber prepared in step II) or III) to a predetermined length; Wherein the fiber has a multilobal cross-sectional shape with three or more lobes, wherein each lobe has a curved tip portion and a base portion located towards a central portion of the fiber, the ratio (D1: D2) between the maximum width (D1) of the tip portion and the width (D2) of the base portion being 1.2:1 to 2.7:1, the raw synthetic fiber being drawn at a draw ratio of at least 5:1, the raw synthetic fiber having a fiber length of at least 20 mm, and/or an aspect ratio (l/D) of not more than 85, and/or a fiber diameter of at least 0.25 mm, the central portion of the fiber being solid, the raw synthetic fiber being obtained by extruding a molten polymer composition through an extruder die comprising a plurality of holes, wherein at least a portion of the holes consist of an assembly of three or more holes that are closely disposed but do not overlap each other.
  8. 8. The method of claim 7, wherein step I) comprises the steps of: i) Extruding the molten polymer composition through a spinneret comprising a plurality of spinneret orifices to provide undrawn fibers, Ii) the undrawn fiber prepared in step i) is led via an air gap into a cooling bath, Wherein at least a portion of the spinneret orifices are comprised of an assembly of three or more orifices disposed in proximity such that when the molten polymer composition is extruded through the orifices, the extruded filaments thus obtained are partially fused to one another to form undrawn fibers.
  9. 9. A method according to claim 8, wherein the distance between adjacent holes of the assembly is arranged such that the edges of the holes do not intersect each other.
  10. 10. The method of claim 8, wherein the assembly consists of four holes disposed adjacently, wherein the holes of the assembly are arranged in a quadrilateral form.
  11. 11. Crude synthetic fiber obtained by using the method according to any one of claims 7-10.
  12. 12. Use of the crude synthetic fiber according to any one of claims 1-6 or the crude synthetic fiber according to claim 11 for improving the toughness of hardened cement compositions.
  13. 13. A cementitious material comprising: a) The adhesive agent is used for the preparation of a coating, B) From 0.1 to 3.0% by volume, based on the total volume of the cementitious material, of the raw synthetic fibers according to any one of claims 1 to 6 or of the raw synthetic fibers according to claim 11, C) Aggregate, and D) And (3) water.
  14. 14. The cementitious material of claim 13, wherein b) 0.2-2.0% by volume of the coarse synthetic fibers of any one of claims 1-6 or the coarse synthetic fibers of claim 11, based on the total volume of the cementitious material.
  15. 15. A method for forming a concrete surface comprising the steps of: I. adding the coarse synthetic fibers of any one of claims 1-6 or the coarse synthetic fibers of claim 11 to a fluidized concrete mixture under mixer rotation to provide a modified concrete mixture, Pouring the modified concrete mixture prepared in the step I to provide a poured concrete body, Smoothing the surface of the cast concrete body prepared in step II, and And IV, curing the modified concrete mixture.

Description

Polymer fibers for concrete reinforcement Technical Field The present invention relates to polymer fibres for use in building materials, in particular for use in cementitious compositions. In particular, the present invention relates to coarse synthetic fibers that are capable of undergoing progressive fibrillation when mechanically agitated within the matrix material to be reinforced. Background Concrete is the most common artificial building material used in construction applications worldwide. In general, concrete is a brittle material having high compressive strength but low tensile strength (crack resistance). The tensile strength of concrete can be increased by using modifying additives such as steel bars and reinforcing mesh. Polymers, metals, glass and natural fibers have also been used to improve the tensile strength (strength before first crack initiation) and toughness (crack resistance) of concrete. Different types of fibers may be used to improve specific properties of the concrete. Synthetic microfibers (microfibers) having a linear density of no more than 580 denier (den) are commonly used to prevent plastic shrinkage cracking of concrete as it sets, i.e., to prevent microcracking of the concrete during the first 24 to 48 hours after casting. Coarse synthetic fibers (coarse fibers) having a linear density greater than 580den and a diameter equal to or greater than 0.3mm are added to the concrete composition to improve the overall toughness quantified by measuring the residual strength after the first break occurs. The crude fibers are generally added to the concrete mixture in a fiber dose of 1.8 to 8.9kg/m 3. The coarse fibers may be obtained in various shapes, such as ropes, belts or rods, and they may be twisted, serrated or embossed to enhance mechanical bonding with the concrete. The concrete reinforcing properties of synthetic fibers depend on both the strength of the fibers and the adhesion between the fibers and the concrete matrix. The benefits obtained with fiber reinforced concrete have led to the widespread use of fibers in place of conventional temperature and shrinkage and toughness reinforcement in many applications, including above ground panels. Common plastic materials for concrete reinforcing fibers include polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), aramid (e.g. Kevlar), polyamide and polyvinyl alcohol fibers. All of these suffer from one or more drawbacks such as high cost, low alkali resistance, low toughness, or low interfacial bonding between the concrete matrix and the fibers. Polypropylene and polyethylene have been widely used as raw materials for microfibers and coarse fibers. Their advantages include ease of processing into fibers by melt spinning (extrusion) processes, low cost, and high resistance to alkaline environments. However, due to the low density and hydrophobicity, the fibers tend to bloom on the surface during finishing, i.e., the fibers tend to protrude from the surface of the concrete before curing is complete. In addition, polypropylene and polyethylene do not bond well to concrete, and therefore these types of coarse fibers are often crimped or embossed to enable mechanical bonding to the matrix. The interfacial bonding between the fibers and the concrete can be controlled by using a coating applied to the surface of the fibers or by chemical modification of the surface of the fibers. However, these methods generally result in increased cost and complexity of the fiber production process. In terms of fiber aspect ratio, larger fibers are generally more suitable than smaller fibers for improving the toughness of concrete. Coarser fibers have higher breaking forces, but they also provide less interfacial bonding with the concrete due to the reduced surface area. The bonding properties of fibers can generally be improved by using longer and finer fibers. However, longer and finer fibers tend to aggregate together into hard-to-break balls (balls) when added to concrete. The balling resistance may be improved by using fibers pre-packaged in a "disc" and/or by using fibers that fibrillate into a number of smaller fibers when mechanically agitated within the matrix material to be fiber-reinforced. Fibrillation increases the surface area of the fibers, resulting in improved interfacial bonding with concrete. However, excessive fibrillation may lead to problems with processability, fiber distribution and mixing, and reduce the toughness reinforcing properties of the larger fibers. The surface finishing requirements in a ramp application vary depending on traffic, texture, indoor or outdoor or decorative appeal requirements. For most indoor concrete and composite metal decks, a smoother hard steel smear finishing is required. These smooth finishes are important for various reasons, such as reduced surface wear, ease of cleaning, and long-term durability. Concrete reinforced with coarse fibers in hard steel painting applications m