JP2022088231A - Cement composition and concrete molded body - Google Patents

Abstract

To provide a cement composition and a concrete molded body having a high compressive strength and improved bending characteristics, especially toughness.SOLUTION: A cement composition contains cement, water, fine aggregate, and reinforcing fiber, wherein the reinforcing fiber contains thick fiber and fine fiber having different fiber diameters, a fiber diameter DA of the thick fiber exceeds 0.35 mm, a fiber diameter DB of the fine fiber is 0.026 mm or more and 0.1 mm or less, and a ratio LB/DB of a fiber length LB to a fiber diameter DB of the fine fiber is 20 or more and 800 or less, a fiber diameter ratio DA/DB between the thick fiber and the fine fiber is 10 or more, and a blending ratio by volume of the thick fiber to the fine fiber is 50/50 to 95/5.SELECTED DRAWING: None

Description

The present invention relates to cement compositions and concrete molded bodies containing reinforcing fibers.

In order to strengthen the concrete molded body obtained by hardening the cement composition, reinforcing fibers are added to the cement composition. For example, in Patent Document 1, in order to prevent peeling and explosion, an organic fiber body containing a large-diameter fiber body having a fiber diameter of 20 μm or more and a small-diameter fiber body having a fiber diameter of less than 20 μm is provided as a surface layer. A cement composition provided in the portion is proposed. Specifically, a polypropylene fiber having a fiber diameter of 49 μm and a fiber length of 20 mm is used as a large-diameter fiber, and a fiber having a fiber diameter of 18 μm as a small-diameter fiber is used. A concrete structure using a polypropylene fiber having a length of 10 mm is disclosed. Patent Document 2 describes polyvinyl alcohol fibers having a fineness of 100 to 10000 dtex and a length of 100 mm or less and polyolefin fibers having a fineness of 0.1 to 80 dtex and a length of 100 mm or less in order to enhance toughness and improve impact resistance. A water-hardened molded body containing fibers has been proposed. Patent Document 3 describes organic staple fibers A having a fiber diameter of 200 μm or more and 2000 μm or less and a fiber length of 5 mm or more and 60 mm or less, and organic staple fibers B having a fiber diameter of 10 μm or more and 150 μm or less and a fiber length of 4 mm or more and 20 mm or less. A water-hard material kneaded molded product containing a group in a mixing ratio of A: B = 70: 30 to 10:90 has been proposed.

Japanese Unexamined Patent Publication No. 2014-91668 Japanese Unexamined Patent Publication No. 2001-139360 Japanese Patent Application Laid-Open No. 2003-327462

However, in the case of the cement compositions described in Cited Documents 1 to 3, there are problems such as high toughness but low compressive strength and high compressive strength but low toughness.

In order to solve the above-mentioned conventional problems, the present invention provides a cement composition and a concrete molded body having high compressive strength and improved bending characteristics, particularly toughness.

The present invention is a cement composition containing cement, water, fine aggregates, and reinforcing fibers. The reinforcing fibers include thick fibers and fine fibers having different fiber diameters, and the fiber diameter DA of the thick fibers is 0. The fiber diameter DB of the fine fiber exceeds 35 mm, the fiber diameter DB of the fine fiber is 0.026 mm or more and 0.1 mm or less, the ratio LB / DB of the fiber length to the fiber diameter of the fine fiber is 20 or more and 800 or less, and the thick fiber and the above. The present invention relates to a cement composition characterized in that the fiber diameter ratio DA / DB of the fine fibers is 10 or more, and the blending ratio of the thick fibers and the fine fibers is 50/50 to 95/5 in volume ratio.

The present invention also relates to a concrete molded body obtained by hardening the cement composition.

According to the present invention, it is possible to provide a cement composition and a concrete molded body having high compressive strength and improved bending characteristics, particularly toughness.

FIG. 1 is a schematic diagram of a fiber cross section of an example of a thick fiber of the present invention. FIG. 2 is a schematic view of a fiber cross section of an example of a thick fiber of the present invention. FIG. 3 is a schematic diagram of a fiber cross section of an example of the fine fiber of the present invention. FIG. 4 is a schematic diagram of a fiber cross section of an example of the fine fiber of the present invention. FIG. 5 is a scanning electron micrograph of the fracture surface of the hardened cement body of Example 1 after the bending test. FIG. 6 is a schematic view illustrating each dimension of the convex portion in the fiber cross section of the fine fiber of one example of the present invention. FIG. 7 is a graph showing the relationship between the load and the opening displacement in the bending test.

As a result of diligent studies to solve the above-mentioned conventional problems, the present inventors have found that in a cement composition containing thick fibers and fine fibers having different fiber diameters as reinforcing fibers, the fiber diameters of the thick fibers and the fine fibers and their ratio thereof. By adjusting the ratio of the fiber length to the fiber diameter of the fine fibers and the blending ratio of the thick fibers to the fine fibers within a predetermined range, the concrete molded body obtained by curing the cement composition maintains high compressive strength. At the same time, it was found that the bending characteristics, especially the toughness, were improved.

The thick fiber has a fiber diameter DA of more than 0.35 mm. If the fiber diameter DA of the thick fiber is 0.35 mm or less, it may lead to a decrease in toughness. From the viewpoint of toughness, the thick fiber preferably has a fiber diameter DA of 0.4 mm or more, and more preferably 0.5 mm or more. The thick fiber is not particularly limited, but for example, the fiber diameter DA is preferably 1.5 mm or less, preferably 1.2 mm or less, from the viewpoint of evenly distributing (dispersing) the thick fiber in concrete. Is more preferable. In the present invention, the fiber diameter means the diameter D (maximum transfer length) of the circumscribed circle of the fiber cross section. In the present invention, when the circumscribed circle of the fiber cross section does not exist, the fiber diameter means the maximum transfer length of the minimum inclusion circle.

The thick fiber is not particularly limited, but the fiber length LA is preferably 15 mm or more and 48 mm or less, and more preferably 20 mm or more and 45 mm or less. When LA is 15 mm or more, toughness is likely to be improved. When the LA is 48 mm or less, the dispersibility of the fibers in the cement composition becomes good.

The thick fiber is not particularly limited, but the ratio LA / DA of the fiber length LA to the fiber diameter DA is preferably 25 or more and 60 or less, and more preferably 28 or more and 50 or less. When LA / DA is 25 or more, toughness tends to be improved. When LA / DA is 50 or less, the compressive strength is unlikely to decrease.

The fine fibers have a fiber diameter DB of 0.026 mm or more and 0.1 mm or less. When the DB is within the above range, the toughness tends to be improved and the dispersibility of the fibers in the cement composition tends to be good. The DB is preferably 0.035 mm or more and 0.09 mm or less, and more preferably 0.040 mm or more and 0.08 mm or less.

The fine fibers have a ratio LB / DB of fiber length LB and fiber diameter DB of 20 or more and 800 or less. When the LB / DB is 20 or more, the toughness tends to be improved. When the LB / DB is 800 or less, the dispersibility of the fibers in the cement composition is good, the compressive strength is unlikely to decrease, and the toughness is likely to be improved. The LB / DB is preferably 65 or more and 700 or less, and more preferably 70 or more and 650 or less.

The fine fibers are not particularly limited, but the fiber length LB is preferably 1 mm or more and 20 mm or less, and more preferably 2 mm or more and 18 mm or less. When the LB is 1 mm or more, the toughness tends to be improved. When the LB is 20 mm or less, the dispersibility in the cement composition becomes good.

The fiber diameter ratio DA / DB of the thick fiber and the fine fiber is 10 or more. When the DA / DB is 10 or more, the toughness tends to be improved. The DA / DB is preferably 12 or more and 50 or less, and more preferably 13 or more and 45 or less. When the DA / DB is 50 or less, the bending proportional limit strength (LOP) is unlikely to decrease, and the toughness tends to improve.

The fiber length ratio LA / LB of the thick fiber to the fine fiber is not particularly limited, but is preferably 1 or more and 40 or less, and more preferably 1.2 or more and 30 or less. When the fiber length of the thick fiber is equal to or longer than the fiber length of the fine fiber, the dispersibility of the fiber in the cement composition becomes good and the toughness tends to be improved.

The cross-sectional shape of the thick fiber is not particularly limited, and may be any of a circular shape, an elliptical shape, a flat shape, a cross shape, and the like, but the contact area with the base material is increased and the toughness is improved. From this point of view, it is preferable to include fibers having a flat shape or a cross-shaped cross section. FIG. 1 is a schematic view of a fiber cross section having a flat cross-sectional shape. FIG. 2 is a schematic view of a fiber cross section having a cross-shaped cross section. In FIGS. 1 and 2, D indicates a fiber diameter. In the present invention, unless otherwise specified, the fiber cross section refers to a cut surface cut so as to be a plane perpendicular to the longitudinal direction of the fiber, and the cross-sectional shape is perpendicular to the longitudinal direction of the fiber. Refers to the shape of the cut surface cut so as to be a surface.

The fine fiber is not particularly limited in the cross-sectional shape of the fiber, and may have an irregular shape such as a circular shape, an elliptical shape, a flat shape, a multi-leaf shape, or a cross shape, but has a deformed fiber cross section. A fiber is preferable in that the contact area with the base material is large and the toughness is improved. In particular, the fine fibers preferably include fibers having a cross-sectional shape that can be partially fibrillated, and more preferably contain fibers having a multi-leaf-shaped cross-sectional shape having three or more convex portions. The number of convex portions is preferably 3 or more and 16 or less, more preferably 3 or more and 8 or less, and further preferably 3 or more and 5 or less. Specifically, examples of the multi-leaf shape include a three-leaf shape having three convex portions, a four-leaf shape having four convex portions, an eight-leaf shape having eight convex portions, and the like. Since the cross-sectional shape of the fine fiber is a multi-leaf shape having three or more convex portions, the surface area in contact with the cement material can be increased, and a space for the cement material to enter can be secured. Further, in the multi-leaf-shaped cross-sectional shape, it is preferable that the convex portions are formed radially from the vicinity of the center of the fiber. By forming the convex portions in a radial pattern, the cement material can easily enter between the adjacent convex portions. Examples of the multi-leaf-shaped cross-sectional shape in which the convex portions are formed radially include a four-leaf shape shown in FIG. 3 and an eight-leaf shape shown in FIG. In FIGS. 3 and 4, D indicates a fiber diameter. The convex portion may be continuous or discontinuous with respect to the length direction of the fiber (fiber side surface), but the convex portion exists continuously on the fiber side surface in consideration of the manufacturing process. Is preferable.

It is preferable that the fine fibers are fibrillated when stress such as bending or impact is applied to the hardened cement body and cracks or cracks occur. Toughness is likely to be improved by making the fine fibers into a shape that can be made into fibril. The reason is not clear, but when a part of the cement hardened body cracks due to the initial load, the fiber also cracks, and as the crack progresses, the fiber becomes fibrilized, so the energy required for destruction (destructive energy) ) Is estimated to be large. As shown in FIG. 5, when the fracture surface of the cement hardened body after the bending test is observed with a scanning electron microscope, the fine fibers (for example, a four-leaf shape having four convex portions) have convex portions. It can also be said from the fact that some of the fibers are split and fibrillated at the constricted part toward the center of the fiber (hereinafter, also referred to as the "root part").

As the fine fibers that can be fibrillated, as described above, fibers having a multi-leaf-like cross-sectional shape having three or more convex portions can be used. This is because the contact area with the base material can be increased by having the convex portion, and the root portion is easily split at the boundary, and as a result, fibrillation is likely to occur. In the fiber having a multi-leaf cross-sectional shape, the tip portion is substantially curved in at least one convex portion existing in the fiber cross section, and the width of the root portion is smaller than the maximum width of the tip portion. Is preferable. More preferably, in all the convex portions present in the fiber cross section, the tip portion has a substantially curved shape, and the width of the root portion is smaller than the maximum width of the tip portion. Having such a shape makes it easy to deform from the root, and the cement material easily enters the recesses between the adjacent protrusions, and when stress such as bending or impact is applied to the hardened cement body, it becomes fibrillated when cracks or cracks occur. It tends to be easier.

As shown in FIG. 6, the width of the root portion of the convex portion in the fiber cross section refers to the length Wb of the line connecting the two roots of the convex portion. The width Wb of the root portion of the convex portion is preferably 3 μm or more and 40 μm or less, more preferably 4 μm or more and 30 μm or less, and further preferably 6 μm or more and 20 μm or less. When the width Wb of the root portion of the convex portion is within the above range, cement particles and aggregate having a small particle diameter can easily enter the concave portion formed between the adjacent convex portions, and the reinforcing effect is enhanced. Further, when the width Wb of the root portion is within the above range, stress such as bending or impact is applied to the hardened cement body, and when cracks or cracks occur, fibrilization tends to occur easily. The width Wb of the root portion of the convex portion can be obtained by enlarging the fiber cross section of the fiber bundle with an electron microscope or the like and averaging the values of 10 arbitrary fibers.

As shown in FIG. 6, the maximum width of the tip portion of the convex portion in the fiber cross section is drawn from the midpoint u of the line connecting the two roots of the convex portion to the tip (vertex t) of the convex portion. , The maximum length Wt when a perpendicular line is drawn from that line toward the outer shape of the convex portion. The maximum width Wt of the tip portion of the convex portion is preferably 4 μm or more and 48 μm or less, more preferably 6 μm or more and 36 μm or less, and further preferably 8 μm or more and 30 μm or less. When it is within the above range, cement particles and aggregates having a small particle diameter easily enter the concave portions formed between the adjacent convex portions, the reinforcing effect is enhanced, and stress such as bending or impact is applied to the hardened cement body. When cracks or cracks occur, the convex parts are susceptible to stress and become fibrillated. The maximum width Wt of the tip portion of the convex portion can be obtained by enlarging the fiber cross section of the fiber bundle with an electron microscope or the like and averaging the values of 10 arbitrary fibers.

In the convex portion, the ratio (Wt / Wb) of the maximum width Wt of the tip portion and the width Wb of the root portion is preferably 1.2 or more and 5.0 or less, and more preferably 1.3 or more and 3.5. It is less than or equal to, and more preferably 1.5 or more and 2.5 or less. When Wt / Wb satisfies the above range, stress such as bending or impact is applied to the hardened cement body, and when cracks or cracks occur, fibrillation tends to occur easily. The maximum width Wt of the tip portion of the convex portion and the width Wb of the root portion of the convex portion can be obtained by enlarging the fiber cross section of the fiber bundle with an electron microscope or the like and averaging the values of 10 arbitrary fibers.

As shown in FIG. 6, the length of the convex portion refers to the length L of the line connecting the midpoint u of the line connecting the two roots of the convex portion to the tip (vertex t) of the convex portion. The length L of the convex portion is preferably 12 μm or more and 45 μm or less, more preferably 16 μm or more and 41 μm or less, and even more preferably 18 μm or more and 36 μm or less. When the length L of the convex portion is 12 μm or more, the convex portion is easily deformed from the root, stress such as bending or impact is applied to the hardened cement body, and when cracks or cracks occur, it tends to be easily fibrilized. When the length L of the convex portion is 45 μm or less, the bonding or locking of the cement material in the concave portion formed between the convex portions becomes good. The length L of the convex portion can be obtained by enlarging the fiber cross section of the fiber bundle with an electron microscope or the like and averaging the values of 10 arbitrary fibers.

The ratio (L / Wb) of the length L of the convex portion to the width Wb of the root portion of the convex portion is preferably 1.2 or more and 4.0 or less, and more preferably 1.5 or more and 3.5 or less. It is more preferably 1.8 or more and 3.0 or less. When L / Wb satisfies the above range, the convex portion is easily deformed from the root, stress such as bending or impact is applied to the hardened cement body, and when cracks or cracks occur, it tends to be easily fibrilized.

The thick fibers and the fine fibers preferably contain fibers having different fiber cross-sectional shapes. This further enhances the compressive strength and toughness of the cement composition. It is more preferable that the thick fibers include fibers having a flat or cross-shaped cross-sectional shape, and the fine fibers include fibers having a multi-leaf-shaped cross-sectional shape having three or more convex portions.

The thick fiber and the fine fiber are not particularly limited, and polyolefin fiber, vinylon fiber, acrylic fiber, aramid fiber, carbon fiber, glass fiber and the like can be appropriately used. Examples of the polyolefin fiber include fibers composed of a polyolefin resin such as polypropylene, polyethylene, poly 4-methylpentene-1, a copolymer thereof, and a polymer modified with a functional group such as an acidic group.

From the viewpoint of alkali resistance and versatility, the thick fibers and the fine fibers preferably contain polyolefin-based fibers, preferably 50% by mass or more of polyolefin-based fibers, and 60% by mass or more of polyolefin-based fibers. It is preferable that the polyolefin-based fiber is contained in an amount of 75% by mass or more, the polyolefin-based fiber is preferably contained in an amount of 85% by mass or more, and it is particularly preferable that the polyolefin-based fiber is substantially composed of the polyolefin-based fiber.

The polyolefin fiber is preferably a synthetic fiber containing 50% by mass or more of the polyolefin resin, more preferably a synthetic fiber containing 60% by mass or more of the polyolefin resin, and 75% by mass or more of the polyolefin resin. It is more preferably a synthetic fiber, further preferably a synthetic fiber containing 85% by mass or more of a polyolefin-based resin, and particularly preferably a substantially polyolefin-based resin. From the viewpoint of alkali resistance, the polyolefin-based resin is preferably one or more selected from the group consisting of polypropylene and polymethylpentene.

The polypropylene is not particularly limited, but the isotactic pentad fraction (IPF: mol%) is preferably 90% or more, more preferably 90% or more, because high-strength fibers can be obtained in terms of stereoregularity. 93% or more, more preferably 94% or more polypropylene can be used. The IPF may be measured for the n-heptane insoluble component according to "Macromoleculars" (Macromoleculer, Vol. 6, 925 (1973) and Macromoleculler, Vol. 8, 687 (1975)).

The polypropylene is not particularly limited, but a Q value (Mw / Mn) of less than 6 is preferable because it has high stretchability and high-strength fibers can be obtained. A more preferable Q value is less than 5, and more preferably 4 or less.

The thick fiber and the fine fiber may be a single fiber or a composite fiber. Examples of the composite fiber include a core-sheath type composite fiber, an eccentric core-sheath type composite fiber, a side-by-side type composite fiber, a split type composite fiber and a sea-island type composite fiber. Both components, for example, both the sheath component and the core component are preferably polyolefin-based resins, and more preferably polypropylene, polymethylpentene, or a mixture of polypropylene and polymethylpentene.

In the cement composition, the blending ratio of the thick fiber and the fine fiber is 50/50 to 95/5 in volume ratio. When the blending ratio of the thick fiber and the fine fiber is within the above range, the compressive strength is less likely to decrease and the toughness is likely to be improved. In the cement composition, the blending ratio of the thick fiber and the fine fiber is preferably 65/35 to 90/10 in volume ratio.

The cement composition may contain an appropriate amount of the reinforcing fiber depending on the intended use and the like. For example, the cement composition may contain 0.05% by volume or more and 2.0% by volume or less of the reinforcing fibers (total of thick fibers and fine fibers), or 0.1% by volume or more and 0.5% by volume or less. .. Here, the content of the reinforcing fiber is volume% (vol%) when the total volume of the other components excluding the reinforcing fiber is 100% by volume in the cement composition. While improving the compressive strength and toughness of the concrete molded body by the reinforcing fiber, the workability is also improved.

The cement composition can be obtained by mixing and stirring cement, water, fine aggregate, and reinforcing fibers. Stirring can be performed using, for example, a stirrer such as a bread type mixer or an omni mixer. From the viewpoint of increasing the miscibility between the materials and enhancing the dispersibility of the reinforcing fibers, first, the cement and the fine aggregate are stirred and mixed, then water is added and mixed, and then the reinforcing fibers are added. May be stirred and mixed.

The cement composition may further contain coarse aggregate in addition to cement, water, fine aggregate, and reinforcing fibers. In this case, from the viewpoint of increasing the miscibility between the materials and enhancing the dispersibility of the reinforcing fibers, first, the cement and the fine aggregate are stirred and mixed, then water is added and stirred and mixed, and then the coarse aggregate is added. Aggregate may be added and stirred and mixed, and finally reinforcing fibers may be added and stirred and mixed.

As the cement, various cements such as ordinary Portland cement, 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. As the fine aggregate and coarse aggregate, various slags such as silica sand, river sand, sea sand, beach sand, crushed stone, blast furnace slag, ferronickel slag, copper slag, and slag under the electric furnace can be used, and the cement composition. The particle size of the aggregate can be selected according to the use of the object and used as a fine aggregate or a coarse aggregate.

The cement composition may contain an admixture, if necessary. 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 preventive, a condensation retarder, a quick-setting agent, and a shrinkage reducing agent.

The cement composition of the present invention is hardened and used as a concrete molded body, for example, mass concrete for dams, fluidized concrete such as high-rise buildings and precast factory products, high-fluidized concrete such as high-rise buildings and large structures. And low heat concrete, bridges, high-rise buildings, high-strength concrete such as precast factory products, building floors and walls, concrete products, expanded concrete for water leakage prevention, piles, poles, long bridges, prestressed building beams, etc. Concrete, thin members, low shrinkage concrete such as walls and slabs, polymer concrete such as waterproof linings, pipes and U-shaped grooves, tunnel lining concrete products, fiber reinforced concrete such as precast members, water tanks, pools, groundwater, etc. Watertight concrete such as places where pressure water acts, underwater concrete such as underwater bridge pedestal foundations, shore protections, breakwaters, road pavement, rooting of street trees, water-permeable / drainable concrete such as water storage basins, freeze-thaw and salt damage ， Repair and deterioration prevention due to alkali aggregate reaction ， Resin impregnated concrete such as waterproofing and waterproofing of underground structures ， Nuclear power generation ， Isotope storage ， Shielding concrete such as medical irradiation room ， Reinforcing wall, floor, roof Lightweight concrete such as materials, outer walls, partitions, prepacked concrete when construction is difficult with ordinary concrete in complicated places such as underwater concrete work, radiation shielding concrete work, primary lining of tunnels, spraying of lining, etc. Recycled concrete such as concrete, backfill concrete, leveled concrete, paving concrete, dam by compaction concrete method, compaction concrete pavement, super hard kneaded concrete such as products by immediate demolding method, pillow wood, block, guard fence, It is useful as precast concrete for building walls.

A concrete molded body can be obtained by curing the cement composition. Specifically, the cement composition is filled in a mold having a predetermined shape, and after the cement composition is poured, sufficient moisture is given so that the surface of the cement composition (concrete) does not dry out. As a method of giving water, it is possible to replenish water by a known method such as flooding, watering, compress curing, wet sand curing, spray curing, etc., and to cure while supplying water to the concrete surface. After removing the mold from the mold, it can be cured by a method such as underwater curing. Further, the curing environment can be performed in the air having a temperature of 5 ° C. or higher and 35 ° C. or lower, and in the case of underwater curing, the curing can be performed in water in which the water temperature is adjusted to 5 ° C. or higher and 35 ° C. or lower. When curing in air, it is preferable to cure in an atmosphere with as high a relative humidity as possible in order to prevent the concrete surface from drying out. The curing period varies depending on the curing method, but when the concrete surface is sufficiently moistened to prevent it from drying and the concrete surface is kept moist, the temperature is 20 to 30 ° C and the humidity is 20 to 30 ° C. If it is cured for 28 days or more in a state of 95% or more, a concrete molded body having a sufficiently advanced hydration reaction can be obtained.

In the case of applications requiring strength such as buildings and bridges, the concrete molded body preferably has a compressive strength of 37.2 N / mm ² or more measured according to JIS A 1108, preferably 37.5 N / mm ² . The above is more preferable.

The concrete molded body is made of concrete using the notch beam of JCI-S-001-2003 of the Japan Concrete Engineering Society for applications that require durability even after cracks such as tunnel lining, roads, and bridges. The fracture energy at an opening displacement of 7.5 mm measured based on the fracture energy test method preferably exceeds 0.510 N / mm, more preferably 0.530 N / mm or more, and 0.590 N / mm or more. It is more preferable to have.

The concrete molded body was measured based on the concrete fracture energy test method using the notch beam of JCI-S-001-2003 of the Japan Concrete Engineering Society for applications requiring strength such as buildings and bridges. The bending proportional limit strength (LOP) is preferably 4000 N or more, and more preferably 4500 N or more.

Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited to the following examples.

The measurement method and the evaluation method used in the examples will be described.

(Fiber diameter)
The cross section of the fiber was observed with a scanning electron microscope (manufactured by Hitachi High-Technologies Corporation, model number "SU3500"), and the fiber diameter was calculated with two-dimensional image measurement software (manufactured by SCARA Co., Ltd., Micro Machine).

(Compressive strength)
The cement composition was filled in a columnar mold (diameter 100 mm, height 200 mm), and the obtained specimen was measured for compressive strength according to JIS A 1108.

(Bending test)
The cement composition is filled in a formwork (height 100 mm, width 100 mm, length 400 mm), and the obtained specimen is used to break concrete using a notch beam of JCI-S-001-2003 of the Japan Concrete Engineering Society. Bending proportional limit strength (LOP) and fracture energy were measured and calculated based on the energy test method.

(Reinforcing fiber)
The thick fibers and fine fibers shown in Table 1 below were used.
The following fibers were used as the fine fibers 1 to 4.
Fine fiber 1: The fiber cross section is a four-leaf shape with four convex portions, the maximum width Wt at the tip of the convex portion is 14.2 μm, the width Wb at the root portion is 7.9 μm, Wt / Wb is 1.79, and the convex portion. A single fiber having a length L of 18.7 μm, L / Wb of 2.4, a single fiber fineness of 5.4 dtex, and a fiber length of 15 mm made of polypropylene (propylene homopolymer: Q value 3.1).
Fine fiber 2: The fiber cross section is a four-leaf shape with four convex portions, the maximum width Wt at the tip of the convex portion is 9.1 μm, the width Wb at the root portion is 5.3 μm, Wt / Wb is 1.72, and the convex portion. A single fiber made of polypropylene (propylene homopolymer: Q value 3.1) having a length L of 11.3 μm, L / Wb of 2.1, a single fiber fineness of 2.2 dtex, and a fiber length of 15 mm.
Fine fiber 3: The fiber cross section is a four-leaf shape with four convex portions, the maximum width Wt at the tip of the convex portion is 24.3 μm, the width Wb at the root portion is 13.6 μm, Wt / Wb is 1.79, and the convex portion. A single fiber made of polypropylene (propylene homopolymer: Q value 3.1) having a length L of 31.3 μm, an L / Wb of 2.30, a single fiber fineness of 15.0 dtex, and a fiber length of 12 mm.
Fine fiber 4: A single fiber having the same shape as the fiber 1 except that the fiber length of the fine fiber 1 is 3 mm.

(Example 1)
Cement (ordinary Portland cement, manufactured by Ube Mitsubishi Cement Co., Ltd.) 417 kg / m ³ , water 179 kg / m ³ , fine aggregate (Kawasago, Yodogawa, Osaka Prefecture, JIS A 1102 (2014) "Aggregate sieving test method" Coarse grain ratio 2.85 according to 6.4) 858 kg / m ³ , coarse aggregate: crushed stone (from Oume, Tokyo, JIS A 1102 (2014) "Aggregate sieving test method" According to 6.4 Coarse grain ratio 8.21) 933 kg / m ³ and a total of 1.82 kg / m ³ (0.2% by volume) of reinforcing fibers were blended and sufficiently stirred and mixed to obtain a cement composition. As the reinforcing fibers, the thick fibers and fine fibers shown in Table 2 below were used in the blending ratios shown in Table 2 below. The obtained cement composition was filled in a cylindrical mold having a diameter of 10 cm and a height of 20 cm for compressive strength, and in a mold having a diameter of 10 cm × 10 cm × a height of 40 cm for a bending test. After casting, it was cured under 20 ° C. conditions for 24 hours, then demolded, and cured in water under 20 ° C. conditions for 27 days to obtain a cement hardened body (concrete molded body).

(Examples 2 to 7)
A concrete molded body was obtained in the same manner as in Example 1 except that the thick fibers and fine fibers shown in Table 2 below were used as the reinforcing fibers in the blending ratios shown in Table 2.

(Comparative Example 1)
A concrete molded body was obtained in the same manner as in Example 1 except that no reinforcing fiber was added.

(Comparative Example 2)
A concrete molded body was obtained in the same manner as in Example 1 except that only the thick fibers shown in Table 2 below were used as the reinforcing fibers.

(Comparative Example 3)
A concrete molded body was obtained in the same manner as in Example 1 except that only the fine fibers shown in Table 2 below were used as the reinforcing fibers.

(Comparative Examples 4 to 6)
A concrete molded body was obtained in the same manner as in Example 1 except that the thick fibers and fine fibers shown in Table 2 below were used as the reinforcing fibers in the blending ratios shown in Table 2.

In Examples and Comparative Examples, the compressive strength, bending proportional limit strength (LOP) and fracture energy of the concrete molded body were measured and calculated as described above, and the results are shown in Table 2 below. In Example 2, the fracture surface of the cement hardened body after the bending test was observed with a scanning electron microscope (manufactured by Hitachi High-Technologies Corporation, model number "SU3500", 100 times), and the results are shown in FIG. FIG. 7 shows the relationship between the load and the opening displacement in the bending test of the concrete molded bodies of Comparative Example 2 and Examples 1 to 3.

As can be seen from FIG. 5, in Example 1, the four-leaf-shaped fine fibers having four convex portions are split and fibrilized at the constricted portion (root portion) as a boundary. In this way, when four-leaf-shaped fine fibers having four protrusions are used, when a part of the cement hardened body is cracked by the initial load, the fibers are cracked, and at the same time as the cracks are developed, the fibers are cracked. It is presumed that the energy required for destruction (destruction energy) is increasing due to the progress of fibrilization of the fine fibers.

As can be seen from FIG. 7, in Comparative Example 2 in which only the thick fiber is used as the reinforcing fiber, the load immediately after the crack is low. This is because thick fibers have a small number of fibers (total surface area), so if cracks occur, they tend to spread at once, and the frictional force between the thick fibers and the base metal per unit cross-sectional area is weak (adhesion area x unit area frictional force). / Since the fiber cross-sectional area is small), it is presumed that the fiber is slippery immediately after cracking in the bending test and the bending load is low.
In Examples 1 to 3 in which thick fibers having a predetermined fiber diameter and fine fibers having a predetermined fiber diameter and fiber diameter / fiber length were used as reinforcing fibers in a predetermined ratio, the load immediately after cracking and the crack opening were expanded. Both of the later loads were high and the toughness was improved. This is because fine fibers have a large number of fibers (total surface area), and immediately after cracking, the frictional force between the fine fibers and the base material per unit cross-sectional area is strong (adhesion area x unit area frictional force / fiber cross-sectional area is large). ) Therefore, the fine fibers are not slippery, the bending load is high, and after the crack opening is expanded, the load is maintained by the thick fibers, so that the bending load is high, both immediately after the crack and after the opening. It is presumed that the toughness will improve.

As can be seen from the comparison between Example 2 and Example 6, the fracture energy at the opening displacement of 7.5 mm is higher in Example 2 using fine fibers having a four-leaf shape that is easily split at the place where the load is applied. , High toughness after opening. It is presumed that since the fine fibers have a four-leaf shape, after some cracks are formed by the initial load, the cracks gradually develop in the fiber axial direction, and as a result, the energy required for fracture is increased.

The cement composition of the present invention is hardened and used as a concrete molded body, for example, fluidized concrete, high fluidized concrete, low heat generation concrete, high strength concrete, expanded concrete prestressed concrete, polymer concrete, fiber reinforced concrete, watertight concrete. , Underwater concrete, water permeable / drainable concrete, resin impregnated concrete, shielding concrete, lightweight concrete, prepacked concrete, sprayed concrete, recycled concrete, paving concrete, super hard kneaded concrete, precast concrete.

Claims (12)

A cement composition containing cement, water, fine aggregate, and reinforcing fibers.
The reinforcing fibers include thick fibers and fine fibers having different fiber diameters, and the reinforcing fibers include thick fibers and fine fibers.
The fiber diameter DA of the thick fiber exceeds 0.35 mm,
The fiber diameter DB of the fine fibers is 0.026 mm or more and 0.1 mm or less.
The ratio LB / DB of the fiber length to the fiber diameter of the fine fiber is 20 or more and 800 or less.
The fiber diameter ratio DA / DB of the thick fiber and the fine fiber is 10 or more, and the fiber diameter ratio is 10 or more.
A cement composition characterized in that the blending ratio of the thick fiber and the fine fiber is 50/50 to 95/5 in volume ratio. The cement composition according to claim 1, wherein both the thick fibers and the fine fibers contain polyolefin fibers. The cement composition according to claim 1 or 2, wherein the fine fibers include fibers having a cross-sectional shape that can be partially fibrillated. The cement composition according to any one of claims 1 to 3, wherein the fine fiber contains a multi-leaf fiber having a convex portion having a fiber cross-sectional shape of three or more. The cement composition according to any one of claims 1 to 4, wherein the thick fiber contains a fiber having a flat or cross-shaped cross section. The cement composition according to any one of claims 1 to 5, wherein the thick fiber and the fine fiber contain fibers having different fiber cross-sectional shapes. The cement composition according to any one of claims 1 to 6, wherein the fiber length ratio LA / LB of the thick fiber and the fine fiber is 1 or more and 40 or less. The cement composition according to any one of claims 1 to 7, wherein the fiber length LB of the fine fibers is 1 mm or more and 20 mm or less. The cement composition according to any one of claims 1 to 8, wherein the fiber length LA of the thick fiber is 15 mm or more and 48 mm or less. The cement composition according to any one of claims 1 to 9, wherein the ratio LA / DA of the fiber length to the fiber diameter of the thick fiber is 25 or more and 60 or less. The cement composition according to any one of claims 1 to 10, further comprising a coarse aggregate. A concrete molded body obtained by curing the cement composition according to any one of claims 1 to 11.

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