JP2022141768A - Fiber for preventing cement hardened body from peeling off, and cement hardened body containing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fiber for effectively preventing a cement hardened body from peeling off, and to provide a cement hardened body containing the same.

SOLUTION: This invention relates to a fiber for preventing a cement hardened body, wherein: single fiber fineness is 0.3 dtex or more and 50 dtex or less; fiber length is 2 mm or more and 50 mm or less; an aspect ratio, the ratio of the fiber length to a fiber diameter, is 200 or more and 1,000 or less; The shape of a cross section of the fiber is in a multilobar shape having 3 or more and 16 or less convex parts; a fiber-treating agent is adhered to the surface of the fiber; and the fiber-treating agent is polyoxyethylene alkyl phosphate.

SELECTED DRAWING: None

COPYRIGHT: (C)2022,JPO&INPIT

Description

TECHNICAL FIELD The present invention relates to a fiber for preventing spalling of hardened cement, such as concrete and mortar, and a hardened cement including the same.

Cementitious materials have excellent compressive strength, fire resistance, and durability, and can be processed into any size and shape by using formwork. It is suitably used for building structures and civil engineering structures. On the other hand, cement-based materials such as concrete are subject to stress, volumetric changes due to temperature changes and drying, and are exposed to direct sunlight heating and wind and rain for a long period of ten years to several decades. Cracks occur due to factors such as deterioration caused by Cement-based materials are reinforced by inserting reinforcing bars into the hardened cement body, but the cracks that have occurred may propagate and reach the reinforcing bars. When the crack reaches the reinforcing bar, moisture such as rainwater penetrates into the hardened cement from the crack and corrodes the reinforcing bar. When rebar corrosion begins, the rebar expands, which further enlarges the cracks and invites further moisture penetration, thus accelerating corrosion and cracking of the rebar. If the cracks become large in this way, part of the hardened cement may peel off and fall. In the case of bridge decks, tunnel lining concrete, etc., if the cement hardened body falls off, there is a risk that a third party will be damaged by the dropped cement hardened body fragment, and countermeasures are required. In order to prevent the hardened cement from falling off, fillers were injected after cracks were formed, and waterproofing and water stoppage were applied during the construction of the structure. However, such follow-up measures cannot suppress the occurrence of cracks themselves, and there are problems such as increased costs and a prolonged construction period depending on the location and scale of cracks.

In order to prevent the occurrence of spalling of the hardened cement, countermeasures have been devised to prevent the occurrence of cracks in the hardened cement, the development of cracks that have occurred, and the spalling of hardened cement pieces. For example, Patent Literatures 1 to 5 propose the use of cement reinforcing fibers having projections on the fiber cross section and a fineness of 100 dtex or more to prevent cracking and spalling of hardened cement bodies. Patent Literature 6 proposes a fiber for reinforcing a hydraulic hardening body, which has a multilobal cross section with a plurality of convex portions. Patent Document 7 proposes a synthetic fiber for self-healing cracks in hardened cement, which has a multilobal cross section with a plurality of protrusions.

JP 2004-26619 A JP-A-2005-220498 JP 2006-348584 A Japanese Unexamined Patent Application Publication No. 2008-1338 JP 2009-234796 A International Publication No. 2012/133763 JP 2014-1129 A

However, a higher level of anti-stripping performance is required for commercially available anti-stripping fibers. In addition, the cement reinforcing fibers described in Patent Documents 1 to 5 have a fiber fineness as large as 100 dtex, so the volume per fiber is large. As a result, when comparing the hardened cement to which only fine fineness fibers are added and the hardened cement to which only large fineness fibers are added at the same volume ratio, the hardened cement using thick fineness fibers has a certain volume per volume. Not only does the number of fibers contained decrease, but the diameter of the fibers increases, the effect of reinforcing fine cracks decreases, and the effect of suppressing the occurrence and progress of cracks may be inferior. In addition, the cement-reinforcing fibers described in Patent Documents 1 to 5 have irregularities in the fiber cross section parallel to the longitudinal direction of the fiber, and the fiber diameter is not constant. Although it is thought that the locking effect to the hardened cement can be enhanced by doing this, the unevenness provided on the side surface of the fiber causes local areas with a small fiber diameter and the presence of areas with low strength. This may cause a decrease in the strength of the single fiber and, in turn, a decrease in the strength of the hardened cement. In Patent Documents 6 and 7, the effect of preventing the hardened cement body from spalling was not verified, and there was a possibility that the effect of preventing the hardened cement body from peeling was inferior.

In order to solve the above-mentioned conventional problems, the present invention provides a fiber for preventing the hardened cement material from spalling, and a hardened cement material containing the same.

The present invention provides a fiber for preventing exfoliation of hardened cement, which prevents exfoliation of hardened cement, the fiber for preventing exfoliation has a single fiber fineness of 0.3 dtex or more and 50 dtex or less, and a fiber length of 2 mm or more and 50 mm. or less, the aspect ratio, which is the ratio of the fiber length to the fiber diameter, is 200 or more and 1000 or less, and the cross-sectional shape of the peeling-preventing fiber is a multilobed shape having 3 or more and 16 or less protrusions, and the peeling The present invention relates to fibers for preventing spalling of hardened cement bodies, wherein a fiber treatment agent is attached to the surfaces of the fibers for prevention, and the fiber treatment agent is a polyoxyethylene alkyl phosphate ester salt.

The present invention also relates to a hardened cement body containing the anti-stripping fibers of the hardened cement body, coarse aggregate and fine aggregate.

INDUSTRIAL APPLICABILITY The present invention can provide a fiber for preventing the hardened cement body from spalling, which is included in the hardened cement body to effectively prevent the hardened cement body from spalling. In addition, the present invention can provide a hardened cement body that is less likely to flake off by incorporating the above-described anti-stripping fiber into the hardened cement body.

FIG. 1 is a schematic cross-sectional view of fibers for preventing spalling of hardened cement bodies according to one or more embodiments of the present invention. FIG. 2 is a schematic diagram illustrating each dimension of the protrusions in the fiber for preventing spalling of the hardened cement body of one embodiment of the present invention. FIG. 3 is a schematic diagram for explaining the outline of a test piece used in the impact test. FIG. 4 is a schematic diagram explaining the outline of the impact test. FIG. 5 is a photograph showing cracks occurring in the specimen of Example 3, which was filled with an expanding material and cured in the air for one week. FIG. 6 is a photograph showing the state of the impact test specimen of Example 3 after being impacted with a rubber hammer. FIG. 7 is a photograph showing cracks occurring in the specimen of Example 4 after filling the specimen for impact test with an expansive material and curing in the air for one week. FIG. 8 is a photograph showing the state of the impact test specimen of Example 4 after being impacted with a rubber hammer. FIG. 9 is a photograph showing the state of the impact test specimen of Example 4 after impact with a Schmidt hammer. FIG. 10 is a photograph showing cracks occurring in the specimen of Comparative Example 3, which was filled with an expansive material and cured in the air for one week. FIG. 11 is a photograph showing the state of the impact test specimen of Comparative Example 3 after being impacted with a rubber hammer. FIG. 12 is a photograph showing the state of the impact test specimen of Comparative Example 3 after impact with a Schmidt hammer. FIG. 13 is a photograph showing cracks occurring in the specimen of Comparative Example 4, which was filled with an expanding material and cured in the air for one week. FIG. 14 is a photograph showing the state of the impact test specimen of Comparative Example 4 after being impacted with a rubber hammer. FIG. 15 is a photograph showing the state of the impact test specimen of Comparative Example 4 after impact with a Schmidt hammer.

As a result of intensive studies, the present inventors found that fibers having a specific fineness, fiber length, ratio of fiber length to fiber diameter (aspect ratio) and cross-sectional shape for hardened cement containing cement, The present inventors have found that the inclusion of fibers having a surface to which a specific fiber treatment agent is attached can effectively prevent the hardened cement body from peeling off, leading to the present invention. Specifically, the single fiber fineness is 0.3 dtex or more and 50 dtex or less, the fiber length is 2 mm or more and 50 mm or less, and the aspect ratio, which is the ratio of the fiber length to the fiber diameter (converted to a circular cross section), is 200 or more and 1000. or less, and the cross section of the fiber has a multilobal shape with 3 or more and 16 or less protrusions, and the surface of the fiber is treated with a polyoxyethylene alkyl phosphate salt as a fiber treatment agent. By attaching the fibers, when the fibers are included in the hardened cement body, the fibers are uniformly dispersed inside the hardened cement body, and the compatibility with the cement, coarse aggregate and fine aggregate is improved, and the hardened cement body The present inventors have found that exfoliation of the hardened cement body can be effectively prevented by increasing the number of fibers contained in a given volume of the cement, leading to the present invention.

The delamination-preventing fibers of the hardened cement body (hereinafter also simply referred to as "separation-preventing fibers") have a single fiber fineness of 0.3 dtex or more and 50 dtex or less. When the single fiber fineness of the flaking prevention fiber is within the above range, not only is it excellent in miscibility when mixed with cement, coarse aggregate, and fine aggregate, but also the number of fibers contained in a fixed volume of hardened cement. With an increase in the amount of carbon fiber, a large number of reinforced parts are formed by cross-linking of fibers formed between cement particles, coarse aggregate, and fine aggregate. Even if the pressure is generated and increased, the hardened cement body can be prevented from falling off. In the anti-peeling fiber, the single fiber fineness is preferably 0.5 dtex or more and 40 dtex or less, more preferably 0.8 dtex or more and 30 dtex or less, particularly preferably 1 dtex or more and 25 dtex or less, and 1.5 dtex. It is most preferable to be not less than 20 dtex.

The fiber length of the peeling prevention fiber is 2 mm or more and 50 mm or less, preferably 3 mm or more and 30 mm or less, more preferably 5 mm or more and 25 mm or less, particularly preferably 7 mm or more and 20 mm or less, and 8 mm. It is most preferable that the distance is greater than or equal to 18 mm or less. If the single fiber fineness and fiber length are within the above ranges, in addition to good miscibility when mixed with cement and stirred, the spalling prevention fiber has an appropriate length, so that cement particles and coarse aggregates can be obtained. In addition, the effect of bridging between fine aggregates can be easily obtained, and even if expansion pressure is generated inside the cement hardened body due to corrosion of reinforcing bars, cracks can be prevented from occurring and progressing.

The flaking-preventing fiber has an aspect ratio (fiber length/fiber diameter) of 200 to 1000, which is the ratio of fiber length to fiber diameter. If the aspect ratio of the anti-stripping fiber is within the above range, the miscibility when the anti-stripping fiber is mixed with cement and stirred is further enhanced, and the thickness and length of the fiber are well balanced. , the effect of bridging between the cement particles, coarse aggregate and fine aggregate is increased. The aspect ratio of the flaking-preventing fiber is preferably 230 or more and 800 or less, more preferably 250 or more and 750 or less, and particularly preferably 280 or more and 700 or less.

The exfoliation-preventing fiber has a multi-lobed cross section and has 3 or more and 16 or less protrusions in the cross section of the fiber. Therefore, when determining the aspect ratio of the flaking-preventing fiber, the fiber diameter of the fiber having the same fineness as that of the fiber having a round cross-section is taken as the fiber diameter of the fiber. That is, in the present invention, when determining the aspect ratio of the flaking-preventing fiber, the fineness of the fiber is first measured. Next, the fiber diameter of a fiber having a round cross-section, which has the same fineness as the measured fineness, is calculated, and the obtained fiber diameter is taken as the fiber diameter in terms of the aspect ratio.

In addition, when converting the fineness of the peeling-preventing fiber to the fiber diameter using a fiber with a round cross section that is the same fineness as the peeling-preventing fiber, the round cross-section fiber used for conversion has a fineness The same material and composition as the anti-peeling fiber for which you want to convert. That is, when the peeling-preventing fiber is a single fiber, the fiber assumed for conversion is made of the same thermoplastic resin as the peeling-preventing fiber, and is assumed to be made of a thermoplastic resin having the same density. In the case of conjugate fibers (for example, core-sheath type conjugate fibers, split type conjugate fibers, and side-by-side conjugate fibers) composed of a plurality of thermoplastic resin components. The round cross-section fiber assumed for conversion is composed of the same thermoplastic resin component (that is, thermoplastic resin of the same type and density) as the peeling prevention fiber, and the ratio of the resin components (so-called composite ratio. core-sheath type If it is a composite fiber, the core-sheath ratio.) is also converted by assuming the same round cross-section fiber.

The anti-scalding fiber has a multi-lobed cross section. Specifically, the cross-sectional shape of the peeling-preventing fiber has 3 to 16 protrusions, preferably 3 to 8 protrusions, and particularly preferably 3 to 5 protrusions. It has 1 or less protrusions. Examples of the multi-leaf shape include three lobes having three protrusions, four lobes having four protrusions, eight lobes having eight protrusions, and the like. By using fibers having a multilobed cross-section in which the number of protrusions satisfies the above range, the area of contact with cement particles, coarse aggregate and fine aggregate is increased, and the fibers are mixed with cement particles, coarse aggregate and fine aggregate. Since the materials are bridged (bridged), even if expansion pressure (hereinafter simply referred to as expansion pressure) is generated due to corrosion of the reinforcing steel, the fiber bridges the particles, making it easier to prevent the hardened cement from falling off. Conceivable. Moreover, it is preferable that the convex part is formed radially from the vicinity of the center of the fiber in the multi-lobed cross-sectional shape. It is presumed that the radial formation of the projections makes it easier for the cement particles to enter between the adjacent projections, strengthens the cross-linking between the cement particles, and enhances the effect of preventing spalling. Examples of multi-lobed cross-sectional shapes in which convex portions are formed radially include a four-leaf shape shown in FIG. 1A and an eight-leaf shape shown in FIG. 1B. There are two types of fiber cross sections: a fiber cross section cut perpendicular to the longitudinal direction of the fiber and a fiber cross section cut parallel to the longitudinal direction of the fiber. In the present invention, unless otherwise specified, the cross section of the fiber refers to a cut surface perpendicular to the longitudinal direction of the fiber, and the cross-sectional shape is perpendicular to the longitudinal direction of the fiber. It refers to the shape of the cut surface cut so that it becomes a smooth surface.

The exfoliation-preventing fiber has a substantially curved tip portion in at least one convex portion present in the cross section of the fiber, and the width of the root portion toward the center of the fiber is smaller than the maximum width of the tip portion. is preferred. More preferably, all protrusions present in the cross section of the fiber have tip portions that are substantially curved, and the width of the root portion toward the center of the fiber is smaller than the maximum width of the tip portion. By having such a shape, it is easy to deform from the root, and the cement particles contained in the hardened cement body can easily enter the concave portions between the adjacent convex portions. As shown in FIG. 2, the maximum width of the tip portion of the protrusion on the fiber end surface of the peeling-preventing fiber is from the midpoint u of the line connecting the two roots of the protrusion to the tip of the protrusion (apex t ) is drawn, and a perpendicular line is drawn from the line to the outer shape of the protrusion. The width of the base of the protrusion in the fiber cross section is as shown in and the length W of the line connecting the two roots of the projection. In the convex portion, the ratio (D/W) of the maximum width D of the tip portion to the width W of the root portion is preferably 1.1 or more and 4.0 or less, more preferably 1.3 or more and 3.0. It is 0 or less, particularly preferably 1.4 or more and 2.4 or less, and most preferably 1.5 or more and 2.0 or less. When D/W satisfies the above range, the maximum width of the tip portion of the projection becomes larger at a constant rate than the width W of the root portion of the projection, so that the cement particles and particle diameter It is presumed that since the protrusions of the fibers that have bitten into the small aggregates become difficult to pull out, the fiber bridges are strengthened and peeling is prevented even if the expansion pressure is generated and increased. The maximum width of the tip portion of the protrusion and the width of the root portion of the protrusion can be determined by magnifying the fiber cross section of the fiber bundle with an electron microscope or the like and averaging the values of any five fibers.

It is preferable that the maximum width D of the tip portion of the convex portion is 3 μm or more and 45 μm or less. It is more preferably 5 µm or more and 35 µm or less, still more preferably 6 µm or more and 30 µm or less, and particularly preferably 7 µm or more and 28 µm or less. When it is within the above range, cement particles and aggregates with small particle diameters are likely to enter the recesses formed between adjacent protrusions, and in the cement hardened body, the added fibers are difficult to pull out, resulting in an excellent locking effect. (anchor effect).

It is preferable that the width W of the root portion of the convex portion is 1.5 μm or more and 32 μm or less. It is more preferably 2 μm or more and 26 μm or less, still more preferably 2.5 μm or more and 23 μm or less, and particularly preferably 3.5 μm or more and 18 μm or less. When the width W of the root portion of the projections is within the above range, cement particles and aggregates with small particle diameters are likely to enter the recesses formed between adjacent projections, making it difficult for fibers to be pulled out. Further, when the width W of the root portion is within the above range, when water is added to and mixed with the cement, coarse aggregate, fine aggregate, and anti-spinning fiber, the anti-spinning fiber Some of the protrusions in the root tend to be easily exfoliated, fibrillated, or separated from the vicinity of the root.

In the peeling-preventing fiber, the length of the convex portion in the cross section of the fiber is, as shown in FIG. is indicated by the length L of the line connecting In the anti-peeling fiber, it is preferable that the ratio L/S of the length L of the convex portion to the maximum span length S when viewed in the cross section of the fiber is 0.3 or more and 0.48 or less, more preferably , 0.35 or more and 0.45 or less, and particularly preferably 0.38 or more and 0.42 or less. By using fibers with a multilobed cross-section that satisfies the above range, not only the area of contact with cement particles, coarse aggregate and fine aggregate increases, but also the recesses formed between adjacent protrusions become deeper. It is presumed that the cross-linking effect of the fibers, particularly the increase in the contact area between the fibers and the cement particles, promotes the strengthening of the cross-links, preventing the hardened cement from falling off even if the expansion pressure is generated and increased.

In the anti-peeling fiber, the length L of the protrusion is preferably 2 μm or more and 70 μm or less, more preferably 4 μm or more and 60 μm or less, still more preferably 6 μm or more and 50 μm or less, and most preferably 8 μm. It is more than 40 μm or less. When the length L of the protrusion is 2 μm or more, the protrusion is likely to be deformed from its base. When the length L of the protrusions is 70 μm or less, the recesses formed between the adjacent protrusions are not blocked by the deformed protrusions, and cement particles and the like easily enter the recesses, making it difficult for fibers to be pulled out. . The length L of the convex portion can be obtained by magnifying the fiber cross section of the fiber bundle with an electron microscope or the like and averaging the values of any five fibers.

The ratio (L/W) of the length L of the protrusion to the width W of the base of the protrusion (L/W) is preferably from 1.0 to 3.0, more preferably from 1.2 to 3.0. It is 0 or less, more preferably 1.5 or more and 2.8 or less, particularly preferably 1.7 or more and 2.7 or less, and most preferably 1.8 or more and 2.6 or less. When L/W satisfies the above range, the concave portions formed between adjacent convex portions are not blocked, and the convex portions are easily deformed from their roots, so that the fibers in the cement hardened body firmly adhere to the cement particles and the like. It is presumed that the cement is prevented from falling off even if the expansion pressure is generated due to corrosion of the reinforcing steel and increases due to the fact that the fiber is hard to pull out, and the fiber bridge is strengthened.

In the peeling-preventing fiber, the convex portion present in the cross section of the fiber may be continuous or discontinuous in the fiber length direction (fiber side surface). It is preferable that the part exists continuously on the side surface of the fiber.

In the flaking-preventing fiber, the shape of the cross section of the fiber cut perpendicular to the longitudinal direction of the fiber is, as described above, a multilobal shape having 3 or more and 16 or less protrusions, preferably at least One projection has a substantially curved tip portion, and the width of the root portion toward the center of the fiber is smaller than the maximum width of the tip portion. The ratio (D/W) to the width W of the portion is 1.1 or more and 4.0 or less. On the other hand, in the peeling-preventing fiber of the present invention, the shape of the cross section of the fiber cut so as to be parallel to the longitudinal direction of the fiber is not particularly limited, but it is preferable that the cross section be parallel to the longitudinal direction of the fiber. In the shape of the cut fiber cross-section, it is preferred that the sides forming the longitudinal sides are substantially free of depressions. As a result, when focusing on a single fiber, the flaking-preventing fiber of the present invention has little variation in thickness and is less likely to have thin portions locally, so that the single fiber strength is stabilized and the cement hardened body can be obtained. It is considered that when added, a stable reinforcing effect is exhibited. In the present invention, in the shape of the cross section of the fiber cut so as to be parallel to the longitudinal direction of the fiber, the sides forming the sides in the longitudinal direction do not substantially have recesses, which means that the fiber is arranged in the longitudinal direction of the fiber. Observe the cross section of the fiber cut so as to be parallel to the surface with a scanning electron microscope or the like, and the sides forming the sides in the longitudinal direction are recessed by 25 μm or more, preferably 20 μm or more, from the peripheral portion to form a recess. indicates that there is no part

The flaking-preventing fiber has a polyoxyethylene alkyl phosphate salt as a fiber treatment agent adhered to the surface of the fiber. As a result, polar groups can be imparted to the fiber surface, which not only improves the miscibility when mixed with cement and stirred, but also improves compatibility with cement particles and enhances the bridging effect of the flaking-preventing fiber. considered to be enhanced.

The polyoxyethylene alkyl phosphate ester salt is not particularly limited, but is, for example, one or more compounds selected from the group consisting of compounds represented by the following chemical formula (1) and compounds represented by the following chemical formula (2). is preferred.

However, in chemical formula (1), R is an alkyl group having 2 to 20 carbon atoms, A is an alkali metal element or an alkaline earth metal element, and n is 1 to 20.

However, in chemical formula (2), R ₁ and R ₂ are alkyl groups having 2 to 20 carbon atoms, A is an alkali metal element or alkaline earth metal element, and n and m are 1 to 20.

The polyoxyethylene alkyl phosphate ester salt may be a mixture of the compound represented by the chemical formula (1) and the compound represented by the chemical formula (2). In this case, the ratio of the compound represented by the chemical formula (1) is preferably in the range of 20 to 80 mol%, more preferably in the range of 50 to 80 mol%, relative to 100 mol% of the polyoxyethylene alkyl phosphate ester salt. is more preferable. Further, the ratio of the compound represented by the chemical formula (2) is preferably in the range of 20 to 80 mol% with respect to 100 mol% of the polyoxyethylene alkyl phosphate ester salt, and in the range of 20 to 50 mol% It is more preferable to have When the ratio of the compound represented by the above chemical formula (1) is 20 mol % or more, it is easily dissolved in water and easily applied to fibers. In addition, when the ratio of the compound represented by the above chemical formula (1) is 50 mol% or more, the compound containing two -O ^- A ⁺ groups in 1 mol is included in a large amount, resulting in poor affinity with cement. A fiber having particularly excellent properties can be obtained.

In the chemical formula (1) or the chemical formula (2), the alkali metal element for A is preferably Li, Na, K, Rb, or the like. Potassium (K) is particularly preferred. As the polyoxyethylene alkyl phosphate ester salt, a compound represented by the following chemical formula (3) or chemical formula (4) is preferable.

However, in chemical formula (3), R is an alkyl group having 2 to 20 carbon atoms, and n is 1 to 20.

However, in chemical formula (4), R ₁ and R ₂ are alkyl groups having 2 to 20 carbon atoms, and n and m are 1 to 20.

In the chemical formula (1), chemical formula (2), chemical formula (3), and chemical formula (4), n and m representing the number of moles of oxyethylene groups are more preferably 1-15, more preferably 3-7. When the number of moles of oxyethylene groups n and m increases, the affinity with the hardened cement tends to improve. sometimes. In the chemical formula (1), chemical formula (2), chemical formula (3) and chemical formula (4), R, R ₁ and R ₂ preferably have 8 to 18 carbon atoms, more preferably 6 to 16 carbon atoms. As the alkyl chain length (carbon chain length) of R, R ₁ and R ₂ increases, the hydrophilicity tends to decrease, and as the length decreases, the fiber treatment agent tends to fall off the fibers. When the number of moles n and m of oxyethylene groups and the alkyl chain lengths of R, _R1 and _R2 are within the ranges, the fiber treatment agent is less likely to fall off and the affinity with hardened cement is enhanced.

The adhesion amount of the polyoxyethylene alkyl phosphate ester salt is preferably in the range of 0.05% by mass or more and 10% by mass or less, more preferably 0.1 to 5% with respect to the mass of the peeling-preventing fiber (100% by mass). It is in the range of % by mass. Within this range, the fiber treatment agent is less likely to come off from the fiber surface, and the effect of preventing the hardened cement body from coming off is enhanced.

The thermoplastic resin constituting the anti-peeling fiber is not particularly limited, and resins such as polyester resin, polyolefin resin, polyamide resin, aramid resin, polyvinyl alcohol resin (vinylon fiber), and acrylic resin can be used as the anti-peeling fiber of the present invention. Available. The peeling-preventing fiber is preferably a fiber mainly composed of one thermoplastic resin selected from the group consisting of polyolefin resin, polyamide resin, and polyacetal resin. As used herein, the term "main body" means that the anti-stripping fiber contains 50% by mass or more of one thermoplastic resin selected from the group consisting of polyolefin resins, polyamide resins, and polyacetal resins. More preferably, the anti-stripping fiber contains 75% by mass or more, particularly preferably 80% by mass or more, of one thermoplastic resin selected from the group consisting of polyolefin resins, polyamide resins, and polyacetal resins.

Examples of the polyolefin resin include, but are not limited to, polyethylene (including low-density polyethylene, high-density polyethylene, linear low-density polyethylene, ultra-high molecular weight polyethylene, etc.), polypropylene, polybutene-1, polymethylpentene, Ethylene-propylene copolymer, ethylene-vinyl alcohol copolymer, ethylene-vinyl acetate copolymer, ethylene-methacrylic acid copolymer, ethylene-acrylic acid copolymer, ethylene-methyl methacrylate copolymer and ethylene- Examples include methyl acrylate copolymers. As the polyolefin resin, polyolefin resins such as polyethylene, polypropylene, polybutene-1, polymethylpentene, and ethylene-propylene copolymers, as well as acrylic acid, methacrylic acid, maleic acid, maleic anhydride, and the like. A carboxyl group-containing polyolefin resin obtained by copolymerizing a monomer containing a carboxyl group such as a saturated carboxylic acid may also be used. The polyolefin is preferably one or more polyolefin resins selected from the group consisting of polyethylene, polypropylene, polymethylpentene, ethylene-propylene copolymer, ethylene-vinyl alcohol copolymer and carboxyl group-containing polyolefin resin, It is more preferably one or more polyolefin resins selected from the group consisting of polyethylene, polypropylene, ethylene-propylene copolymers and carboxyl group-containing polyolefin resins, and one selected from the group consisting of polypropylene and carboxyl group-containing polyolefin resins. The above polyolefin resin is particularly preferred.

The polyamide resin is not particularly limited. above polymers), homopolymers such as nylon 6, nylon 6I, nylon 610, nylon 6T, mixed resins blended with the above polyamide resins, copolymers of the above polyamide resins (e.g., nylon 66, nylon 6, nylon 6I, nylon 610, nylon 6T, etc.). The polyamide resin is preferably nylon 66 or nylon 6.

The polyacetal resin is also called polyoxymethylene resin, and is a polymer having oxymethylene units as main repeating units. The polyacetal resin (hereinafter also referred to as POM) may be a POM homopolymer or a POM copolymer. The above POM homopolymer is usually obtained by a polymerization reaction using formaldehyde or trioxane as a main raw material. Said POM copolymers usually consist mainly of oxymethylene units and have from 2 to 8 contiguous carbon atoms in the main chain and optionally substituted oxyalkylene units, preferably CH ₂ CH ₂ O. The content is 10% by mass or less, more preferably 0.5 to 8% by mass in terms of ethylene oxide. In said POM copolymer, substituents that can be attached to the oxyalkylene groups are, for example, alkyl groups, phenyl groups, or other organic groups. Moreover, the polyacetal resin may be any of copolymers containing structural units other than oxymethylene units, that is, block copolymers, terpolymers, and crosslinked polymers.

The peeling prevention fiber may be a fiber mainly composed of one thermoplastic resin selected from the group consisting of polyolefin resin, polyamide resin, and polyacetal resin, and various polyolefin resins, polyamide resins, and polyacetal resins are not particularly limited. can be used. For example, if the stability in hardened cement is emphasized, it is preferable to use polyolefin resin as the main component, and fresh concrete (generally refers to concrete that has not yet hardened. In the present specification, in addition to this, , cement paste in an unhardened state, cement mortar, etc.), it is preferable to mainly use a polyamide resin or a polyacetal resin. In the case of the flaking-preventing fiber, it is required that it does not deteriorate even if it is placed in an alkaline environment for a long time, so it is preferable that it is mainly composed of polyolefin resin. Fibers made of polypropylene resin are particularly preferred.

The fiber surface of the flaking-preventing fiber may be hydrophilized. Hydrophilization of the fiber surface can be performed by a hydrophilization treatment for imparting polar groups. In the case where the anti-stripping fiber is a fiber mainly composed of polyolefin resin, hydrophilization treatment gives it polar groups such as hydroxyl groups, carbonyl groups, and carboxyl groups. Improves miscibility when used. In addition, when the flaking-preventing fiber is a fiber mainly composed of polyamide resin, the hydrophilization treatment introduces another functional group to the fiber surface in addition to the polar group originally possessed by the polyamide resin. In addition to increasing the affinity between fibers and cement and improving the miscibility when mixing and stirring with cement, the fibers are less likely to be pulled out of the cement structure in the hardened cement, increasing the mechanical strength of the hardened cement. By improving it, even if expansion pressure occurs inside the hardened cement body due to corrosion of reinforcing bars, cracks can be prevented from occurring and progressing.

Examples of the hydrophilic treatment include corona discharge treatment, plasma treatment, and fluorine gas treatment (for example, treatment using a mixed gas containing fluorine gas and oxygen gas, and a mixed gas containing fluorine gas and sulfurous acid gas. ), ozone treatment (for example, treatment with ozone aqueous solution, ozone gas treatment, etc.), sulfonation treatment (in addition to sulfonation treatment using anhydrous sulfuric acid gas, sulfonation treatment using fuming sulfuric acid, sulfurous acid gas and sulfonation treatment using hot concentrated sulfuric acid), and corona discharge treatment and plasma treatment are preferred. When the polar group is introduced onto the surface of the peel-preventing fiber by corona discharge treatment, the treatment conditions are not particularly limited, but the amount of discharge per corona discharge treatment is set to 10 W/m ² /min or more. Preferably, the total discharge amount is 10 W/m ² /min or more and 5000 W/m ² /min or less, and the total discharge amount is 12 W/m ² /min or more and 4000 W/m ² /min or less. more preferred. When the polar group is introduced onto the surface of the peel-preventing fiber by plasma treatment, the treatment conditions are not particularly limited, but atmospheric pressure plasma treatment is preferred. It should be processed at a frequency of 500 to 3000 pps. The normal-pressure plasma treatment is advantageous because the treatment can be performed at a low voltage, so that the fibers are less deteriorated.

In the anti-peeling fiber, although not particularly limited, the single fiber strength of the fiber is preferably 3.3 cN/dtex or more, more preferably 3.7 cN/dtex or more, and 4.0 cN/dtex or more. 4.3 cN/dtex or more is particularly preferable. When the single fiber strength is within the above range, not only is it excellent in miscibility when mixed with cement, coarse aggregate, and fine aggregate, but it is also easy to obtain a hardened cement body having sufficient strength. The upper limit of the single fiber strength of the flaking-preventing fiber is not particularly limited, but from the viewpoint of reducing the production cost, the single fiber strength is preferably 10 cN/dtex or less, more preferably 8 cN/dtex or less, and particularly It is preferably 7.8 cN/dtex or less.

In the anti-peeling fiber, although not particularly limited, the breaking elongation of the fiber is preferably 10% or more and 150% or less, more preferably 15% or more and 100% or less, and 18% or more and 70% or less. 18% or more and 60% or less is most preferable. If the breaking elongation of the spalling-preventing fiber is within the above range, not only is it excellent in miscibility when mixed with cement, coarse aggregate, and fine aggregate, but also a hardened cement body having sufficient strength can be obtained. easy. Moreover, the manufacturing cost of the flaking-preventing fiber can be reduced.

In one embodiment of the present invention, the anti-stripping fiber can be produced by the following procedure. First, raw material thermoplastic resins are prepared so that thermoplastic resins such as polyolefin resins, polyamide resins, and polyacetal resins are the main components. The prepared thermoplastic resin is melt-spun at a temperature at which the resin melts, using a single-type or multiple-type nozzle capable of forming a predetermined shape. When the anti-peeling fibers are fibers mainly composed of polyolefin resin, the spinning temperature may be, for example, 200 to 350° C. When the anti-peeling fibers are fibers mainly composed of polyamide resin, the spinning temperature is, for example, 260 to 350. °C, and if the fiber for preventing flaking is mainly composed of polyacetal resin, the spinning temperature may be, for example, 180 to 250°C. The take-up speed in melt spinning may be 100 to 2000 m/min, and can be adjusted according to the fineness of the finally obtained flaking-preventing fiber. The melted raw material resin is taken up at a take-up speed within the above range to obtain unstretched spun filaments having a fineness of 2 to 100 dtex.

The unstretched spun filaments obtained by the above procedure are stretched as necessary. The stretching temperature is appropriately set according to the type of thermoplastic resin. For example, if the flaking-preventing fiber is a fiber mainly composed of polyolefin resin, the drawing temperature is preferably 80° C. or higher and 160° C. or lower and the draw ratio is 1.2 times or more and 8 times or less. A more preferable stretching temperature is 110° C. or higher and 155° C. or lower. A more preferable draw ratio is 3 times or more and 6 times or less. If the flaking-preventing fiber is mainly composed of a polyamide resin, it is preferably drawn at a drawing temperature of 10° C. to 230° C. and a drawing ratio of 1.2 to 8 times. A more preferable stretching temperature is 30° C. or higher and 200° C. or lower. A more preferable draw ratio is 1.5 times or more and 6 times or less. If the flaking-preventing fiber is a fiber mainly composed of polyacetal resin, the drawing temperature is preferably 120° C. to 165° C. and the draw ratio is 1.2 times to 10 times. A more preferable stretching temperature is 125° C. or higher and 160° C. or lower. A more preferable draw ratio is 1.5 times or more and 7 times or less. The drawing method is not particularly limited, and includes wet drawing in which drawing is performed while heating with a high-temperature liquid such as hot water, dry drawing in which drawing is performed while heating in a high-temperature gas or with a high-temperature metal roll, etc., 100 ° C. The drawing treatment can be performed by a known method such as steam drawing in which the fiber is drawn while heating the fiber under normal pressure or pressurized water vapor. The stretching process may be carried out by either one-stage stretching or a so-called multi-stage stretching process performed in a plurality of stages.

A polyoxyethylene alkyl phosphate ester salt, which is a fiber treatment agent, is applied to the obtained drawn filaments. The method of applying the fiber treatment agent may be any of dipping method, spray method and coating method. The drawn filaments are subjected to at least one hydrophilization treatment selected from fluorine gas treatment, plasma discharge treatment and corona discharge treatment in order to further increase affinity with the hardened cement before applying the fiber treatment agent. It may be hydrophilized. The fiber for preventing flaking is made hydrophilic by at least one hydrophilization treatment selected from fluorine gas treatment, plasma discharge treatment and corona discharge treatment, and a fiber treatment agent is attached to the fiber, and cement and The affinity of the cement is further improved, and the effect of preventing the hardened cement from spalling is also enhanced. After application of the fiber treatment agent, crimping treatment is applied if necessary, and the fiber is cut into a predetermined fiber length.

In one embodiment of the present invention, the hardened cement body includes the anti-scalding fiber, cement, coarse aggregate, and fine aggregate. The hardened cement is obtained by adding the anti-scalding fiber to a cement composition containing cement, coarse aggregate, and fine aggregate at a certain ratio, adding an appropriate amount of water, and kneading the mixture sufficiently, followed by hardening, It can be obtained by adding the spalling-preventing fibers to fresh concrete in which a cement composition and water are mixed in advance, kneading them sufficiently, and then curing them. Although the hardened cement body is not particularly limited, it may contain an anti-scalding fiber in a proportion of 0.05% by volume (vol%) or more and 4.8 vol% or less. That is, in the cement hardened body, the total amount of components such as various cements, fine aggregates, coarse aggregates, admixtures, and water excluding the anti-stripping fiber is set to 100 vol%, and the anti-stripping fiber of the present invention is set to 100 vol%. may be included in a ratio of 0.05 vol% or more and 4.8 vol% or less. The hardened cement body preferably contains 0.08 vol% or more and 3 vol% of the exfoliation preventing fiber, and more preferably 0.1 vol% or more and 2.5 vol%.

The cement composition contains cement, coarse aggregate, and fine aggregate, and if necessary, functional agents such as admixtures may be added. As the cement, various cements such as ordinary Portland cement, high-early-strength Portland cement, ultra-early-strength Portland cement, moderate-heat Portland cement, low-heat Portland cement, and sulfate-resistant Portland cement can be used. Examples of the fine aggregate and coarse aggregate include silica sand, river sand, sea sand, beach sand, crushed stone, etc. In addition, various slags such as blast furnace slag, ferronickel slag, copper slag and electric furnace oxidation slag can be used. The particle size of the aggregate can be selected from among these according to the application of the cement hardened body, and can be used as fine aggregate or coarse aggregate. Examples of the admixture include an AE agent, an AE water reducing agent, a high-performance AE water reducing agent, a fluidizing agent, a curing accelerator, a rust inhibitor, a setting retarder, a quick setting agent, and a shrinkage reducing agent. These admixtures can be appropriately selected and used depending on the purpose and application.

EXAMPLES The present invention will be described in more detail below using examples. In addition, the present invention is not limited to the following examples.

(Example 1)
A polypropylene resin (trade name “SA01A” manufactured by Japan Polypropylene Corporation) was prepared. This resin was melt-extruded at a spinning temperature of 270° C. using a spinning nozzle having a four-lobed nozzle hole shape, and was taken up at a take-up speed of 568 m/min to produce a spun filament (undrawn yarn) with a fineness of 7.6 dtex. The obtained spun filament was used and dry drawn at 145° C. to 4.0 times. The obtained drawn filaments were passed through a corona discharge treatment machine and subjected to corona discharge treatment at a discharge rate of 72 W/m ² /min (per discharge) to impart functional groups such as hydroxyl groups to impart hydrophilicity. Then, as a fiber treatment agent, polyoxyethylene potassium lauryl phosphate containing 5 mol of oxyethylene groups and having a carbon chain length of 12 was applied so that the amount of the fiber treatment agent adhered to the fiber mass was 3% by mass. , to obtain a polypropylene fiber having a single fiber fineness of 2.2 dtex.

The obtained polypropylene fiber has a multilobed fiber cross-sectional shape with four protrusions, and the tip of the protrusion has a substantially curved shape, and the width of the root toward the center of the fiber is the maximum width of the tip. was smaller than When viewed in fiber cross section, the maximum span length S is 25.0 μm, the length L of the protrusion is 12.1 μm, the maximum width D at the tip of the protrusion is 8.3 μm, and the width W at the root is 4. 5 μm, L/S was 0.48, D/W was 1.8, and L/W was 2.7.

(Example 2)
A polypropylene resin (trade name “SA01A” manufactured by Japan Polypropylene Corporation) was prepared. This resin was melt extruded at a spinning temperature of 270° C. using a spinning nozzle having a four-lobed nozzle hole shape, and was taken up at a take-up speed of 205 m/min to produce a spun filament (undrawn yarn) with a fineness of 26 dtex. The obtained spun filament was used and dry drawn at 155° C. to 4.7 times. The obtained drawn filaments were passed through a corona discharge treatment machine and subjected to corona discharge treatment at a discharge rate of 23.8 W/m ² /min (per discharge) to impart functional groups such as hydroxyl groups to impart hydrophilicity. Next, as a fiber treatment agent, polyoxyethylene potassium lauryl phosphate containing 5 mol of oxyethylene groups and having a carbon chain length of 12 was added so that the amount of the fiber treatment agent adhered to the fiber weight was 2.15% by mass. and cut into fibers of 15 mm in length to obtain polypropylene fibers with a single fiber fineness of 5.4 dtex.

The obtained polypropylene fiber has a multilobed fiber cross-sectional shape with four protrusions, and the tip of the protrusion has a substantially curved shape, and the width of the root toward the center of the fiber is the maximum width of the tip. was smaller than When viewed in fiber cross section, the maximum span length S is 39.3 μm, the length L of the protrusion is 19.5 μm, the maximum width D at the tip of the protrusion is 15.8 μm, and the width W at the root is 8. .2 μm, L/S was 0.50, D/W was 1.9, and L/W was 2.4.

(Comparative example 1)
As the fiber of Comparative Example 1, a commercially available polypropylene resin short fiber for preventing spalling of concrete (manufactured by Ube Exsimo Co., Ltd., product name "Simlock (registered trademark) SX", fiber length 20 mm, single fiber fineness 1000 dtex, X-shaped cross section) was used. Using. In this fiber, the width of the convex portion of the fiber cross section is maximum at the root portion, and the convex portion has the maximum width at the root portion, and the width gradually narrows toward the tip portion. When viewed in fiber cross section, the maximum span length S is 555.9 μm, the length L of the convex portion is 162.4 μm, the maximum width D of the convex portion, that is, the width of the root portion of the convex portion is 230.6 μm, L /S was 0.29 and L/W was 0.70.

(Comparative example 2)
As the fiber of Comparative Example 2, a commercially available nylon fiber for preventing spalling of concrete (purchased from AOB and da Vinci International Co., Ltd.; product name "New Crete", fiber with a round cross section mainly composed of nylon 66, fiber length 12 mm, single fiber fineness 3.2 dtex, with 0.5% by mass of fiber treatment agent attached to the fiber mass).

The single fiber strength and breaking elongation of the fibers of Examples and Comparative Examples were measured as follows, and the results are shown in Table 1 below. Table 1 below also shows the single fiber fineness, fiber length, density and fiber diameter.

<Single fiber strength and breaking elongation>
According to JIS L 1015, a tensile tester was used to measure the load value and elongation at the time of fiber cutting when the sample was gripped at a distance of 20 mm.

(Examples 3-4, Comparative Examples 3-5)
(Method for preparing test body)
The types of cement, fine aggregates, coarse aggregates, admixtures and water shown in Table 2 were blended to give the compositions shown in Table 3. In Table 3, W/C represents the mass ratio of water to cement, and s/a represents the volume ratio of fine aggregate to total aggregate (total of fine aggregate and coarse aggregate). After sufficiently mixing fresh concrete containing cement, fine aggregate, coarse aggregate, admixture and water, when the volume of the fresh concrete is 100 vol%, the amount of fiber mixed in is determined by dividing the outside so that the specified amount of fiber is mixed. 2. was put into the fresh concrete and thoroughly mixed. In addition, in Comparative Example 3, no fibers were added.

[Fresh concrete fluidity evaluation (slump test)]
The fluidity of fresh concrete was evaluated according to JIS A 1101 "Concrete slump test method". For the measurement, the slump cone was filled with the fresh concrete prepared as described above, the slump cone was extracted within 3 minutes after filling, and the slump was measured. The results are shown in Table 3 above.

[Compressive strength test]
The fresh concrete prepared as described above was filled into a cylindrical mold with a diameter of 10 cm and a height of 20 cm. After placing, the cement was cured in the air for 14 days in a room at a temperature of 20°C to obtain a hardened cement body. Using the obtained hardened cement body, the compressive strength of the hardened cement body was measured according to JIS A 1108 "Concrete Compressive Strength Test Method". The results are shown in Table 3 above.

[Evaluation of peeling prevention performance]
In order to evaluate the resistance performance against spalling of the hardened cement body, a hardened cement body with artificial cracks was prepared, and the hardened cement body was hit. A test was conducted to measure the number of times. First, each fresh concrete was prepared as described above. Next, this fresh concrete was poured into a mold to form hardened cement bodies of 600 mm, 150 mm, and 150 mm in size. A hole was made in the specimen to induce cracking. As shown in Fig. 3, the hole for filling the expansive material is a through hole b with a cover thickness of 20 mm and a center-to-center distance of 60 mm between adjacent holes. Five positions were provided on the body a. After providing the hole b for filling the expansive material, the specimen a was air-cured in a room at 20° C. for 14 days.

The expansion material was filled into the specimen a which had been cured in the air for two weeks after the hole b for injecting the expansion material was provided. As the expansive material, ordinary Portland cement, water, and expansive material (ettringite/lime-based expansive material: density 3.0 g/cm ³ ) shown in Table 2 were used, and cement: water: expansive material (mass ratio) = 1:0.6. : 0.8, and the mixture was thoroughly mixed and injected from the hole b provided on the side surface of the specimen a. After injecting the expansive material into all of the five holes b, the specimen a was further air-cured in a room at 20°C for one week. In order to prevent the specimen from collapsing when the amount of expansion increases, as shown in FIG.

An impact test using a rubber hammer and a Schmidt hammer was performed on the specimen a in which cracks were artificially introduced by the expansive material. First, an impact test using a rubber hammer was performed. A rubber hammer with a mass of 770 g is swung down from a height of 50 cm above the specimen a with only the force of the hammer's own weight (in other words, the rubber hammer is shaken against the specimen without applying external force. lowering) and hit the specimen a. As shown in FIG. 4, the rubber hammer was repeatedly hit on the portion between the holes b filled with the expansive material from the left side of the specimen a. The impact was continued until hardened cement fragments were generated from the specimen a and the specimen a fell off or collapsed, or until the number of impacts reached 320 times. In addition, when hitting with a rubber hammer, only a specific person performed the hitting, and different workers did not perform the hitting. After 320 impacts with a rubber hammer, the rubber hammer (mass: 770 g) was applied to the specimen that did not peel off or collapse even after being impacted 320 times with a rubber hammer of 770 g. The impact energy was changed to 2.207 N·m), and 320 impacts were applied in the same manner. When applying the impact with a Schmidt hammer, as shown in FIG. Repeatedly hitting.

The specimens of Examples 3 and 4 and Comparative Examples 3 and 4 were filled with an expansive material and cured in the air for one week. , as shown in FIG. 6, 8, 11 and 14 show photographs of the specimens of Examples 3 and 4 and Comparative Examples 3 and 4 after being hit with a rubber hammer, respectively. 9, 12 and 15 show photographs of the specimens of Example 4, Comparative Examples 3 and 4 after being hit with a Schmidt hammer, respectively. In addition, Table 3 shows the number of hits in the hit test using a rubber hammer and a Schmidt hammer and the state of disintegration of the specimen. The impact test was conducted with n = 3, but in the hardened cement body of Comparative Example 3 in which fibers were not added to the cement, the test body 1 had already fallen off due to the filling expansion material, so it was subjected to hammer and Schmidt It has not been tested with a hammer. When calculating the average value of the number of hits with the Schmidt hammer, the number of hits for this specimen was assumed to be 0.

As can be seen from FIGS. 9, 12, 15 and Table 4, in Examples 3 and 4, the average number of impacts was higher than in Comparative Examples 3 to 5, effectively preventing the hardened cement bodies from falling off. .

The fibers for preventing spalling of hardened cement bodies of the present invention have a specific cross-sectional shape, so that they not only have good compatibility with cement particles, fine aggregates and coarse aggregates, but also have projections that are cement-hardened. It becomes firmly anchored inside the body, and the effect of preventing exfoliation can be obtained by bridging and strengthening cement particles, cement hydrates produced by hydration reactions, and fine aggregate particles. . The hardened cement containing the fibers for preventing spalling of the hardened cement of the present invention has been found to be less likely to spall from the results of impact tests, and the concrete to which an appropriate amount of the fibers for preventing spalling of the present invention have been added can be used for railway viaducts and road bridges. Structures that are used outdoors for a long period of time, such as bridge floor slabs and tunnel lining concrete that composes the inside of tunnels, may cause secondary disasters in the unlikely event that spalling occurs and concrete pieces fall. It can be preferably used for buildings.

a Specimen b Hole c Reinforcing bar

Claims (8)

A fiber for preventing the hardened cement from peeling off, comprising:
The flaking-preventing fiber has a single fiber fineness of 0.3 dtex or more and 50 dtex or less, a fiber length of 2 mm or more and 50 mm or less, and an aspect ratio, which is the ratio of the fiber length to the fiber diameter, of 200 or more and 1000 or less,
The peeling-preventing fiber has a multi-lobed cross-sectional shape with 3 or more and 16 or less protrusions, and a fiber treatment agent is attached to the surface of the peeling-preventing fiber, and the fiber treatment agent is polyoxyethylene. A fiber for preventing exfoliation of hardened cement, which is an ethylene alkyl phosphate. At least one convex portion has a substantially curved tip portion, the width of the root portion toward the center of the fiber is smaller than the maximum width of the tip portion, and the maximum width D of the tip portion of the convex portion is 2. The fiber for preventing spalling of hardened cement according to claim 1, wherein the ratio (D/W) to the width W of the root portion is 1.1 or more and 4.0 or less. 3. The fiber for preventing exfoliation of hardened cement according to claim 1 or 2, wherein said projections are continuous in the longitudinal direction of said fiber for exfoliation prevention. The fiber for preventing exfoliation of the hardened cement product according to any one of claims 1 to 3, wherein in the cross section of the fiber for preventing exfoliation, the distance between adjacent protrusions is random due to deformation of the protrusions. Any one of claims 1 to 4, wherein the polyoxyethylene alkyl phosphate salt is one or more compounds selected from the group consisting of compounds represented by the following chemical formula (1) and compounds represented by the following chemical formula (2). 1. Fibers for preventing the hardened cement body from spalling according to item 1.

However, in chemical formula (1), R is an alkyl group having 2 to 20 carbon atoms, A is an alkali metal element, and n is 1 to 20.

However, in chemical formula (2), R ₁ and R ₂ are alkyl groups having 2 to 20 carbon atoms, A is an alkali metal element or alkaline earth metal element, and n and m are 1 to 20. The fiber for preventing exfoliation of the hardened cement body according to any one of claims 1 to 5, wherein the surface of the fiber for preventing exfoliation is hydrophilized. 7. A hardened cement body comprising the fibers for preventing spalling of the hardened cement body according to any one of claims 1 to 6, cement, coarse aggregate, and fine aggregate. 8. The hardened cement body according to claim 7, wherein the ratio of the anti-scalding fibers contained in the hardened cement body is 0.05 vol % or more and 4.8 vol % or less.

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