JPH0768740B2 - Fiber reinforced cement-based material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a fiber-reinforced cement-based member obtained by arranging and embedding fiber-reinforced materials in a cement-based matrix.

<Prior Art> Generally, a fiber-reinforced cement-based member is widely used as a member for civil engineering / construction in a shape such as a plate, a cylinder, a hollow plate, and a block.

So-called asbestos slate was a typical example of conventional fiber-reinforced cement-based members, but recently, from the viewpoint of environmental pollution prevention by asbestos, various organic, inorganic, and metal fibers have come to be used as reinforcing fibers. I came.

<Problems to be Solved by the Invention> However, most of these are produced by a method in which short fibers are two-dimensionally or three-dimensionally dispersed in a cement-based matrix, so that a high-strength and high-toughness molded article is obtained. Requires a large amount of fiber and is wasteful.

In particular, when high-performance fibers are used, there is a drawback that the strength and elasticity of the fibers cannot be sufficiently drawn out and the cost tends to increase.

For this reason, there has been considered a method in which long fibers are preliminarily formed into a linear shape or a lattice shape, and the physical properties of the molded body are improved by predominantly orienting one-dimensionally or two-dimensionally in the cement-based matrix cross section.

According to this method, compared with a molded product having two-dimensional or three-dimensional random orientation, a small amount of fiber is required to obtain the same bending or tensile strength, and the material can be designed. It has the advantage that it can be used effectively.

On the other hand, high-performance fibers such as carbon fibers, aramid fibers, alkali-resistant glass fibers, and high-strength vinylon fibers have a significantly higher tensile strength than the cement-based material itself, so the tensile or tensile strength of the cement-based member in which these fibers are arranged or This has the effect of increasing the maximum bending stress.

However, in addition to high tensile strength, these high-performance fibers are fibers having a large tensile elastic modulus with a tensile elongation at break of only a few percent or less.

Among them, carbon fibers, which have no problems of deterioration due to alkalinity of cement, have excellent durability, and have the advantage of withstanding high temperature steam curing during the production of the member, have a very high tensile elastic modulus with a tensile breaking elongation of about 2% or less. It is a fiber.

Therefore, in a fiber-reinforced cementitious member using these high-performance fibers having a small tensile elongation at break, the fibers are broken at the time when the maximum stress of tension or bending is reached, and the tensile strain or bending deflection is small. It also has the drawback of poor toughness.

Therefore, as a conventional technique for improving such stress level and toughness, the amount of fibers in the lower half of the plate thickness is made larger than that in the upper half, and the amount of aggregate in the lower half of plate thickness is made smaller than that in the upper half. Fiber-reinforced cement plate (Japanese Patent Laid-Open No. 54-150420), a lower fiber-reinforced layer in which a large amount of fibers are mixed, and an upper layer in which a small amount of fibers are mixed as needed are integrated, and the thickness of the lower layer is A fiber reinforced cement board (Japanese Patent Laid-Open No. 54-80324), which is 0.4 to 0.7 times the total thickness of the upper and lower layers, and fibers in which the fibers are dispersed and oriented in the surface layer portion within 3 mm from the surface. Reinforced cement hardened material (JP-A-57-11861
Or a high-toughness ferro-cement board formed by laminating and reinforcing steel mesh as a stress material, and interposing meshes of alkali-resistant glass fiber, aramid fiber, and carbon fiber between the steel mesh. JP-A-60-125606) is known.

However, these conventional techniques still have the following problems.

That is, in the case of ~, although there is an effect of increasing the bending stress degree by disposing the fiber reinforcing layer in the region where the tensile stress of the bending member acts, the maximum bending stress degree is reached,
When the fiber breaks, the stress level sharply decreases, and there is a problem that it is difficult to obtain a member having excellent toughness that can maintain a sufficiently large stress level in a bending deflection range exceeding the maximum bending stress level.

In the other case, there is a drawback that the steel mesh to be reinforced is corroded due to severe use conditions or a long period of time, resulting in poor durability.

<Means for Solving the Problems> Then, as a result of intensive studies made by the present inventors in view of such problems, as a result of disposing at least two layers of long fibers in a region where tensile stress of the cement-based bending member acts, The inventors have found that these problems can be solved by using long fibers having different tensile strengths and arranging long fibers having higher tensile strengths at a position closer to the bending neutral axis of the member, and arrived at the present invention.

That is, an object of the present invention is to provide a fiber-reinforced cementitious member having high strength and high toughness by devising a device in which a small amount of reinforcing fibers are arranged so that the reinforcing effect is excellent.

And the purpose is a fiber reinforced segment-based member that receives bending stress, with respect to the neutral axis of bending stress of the member,
In the region where the tensile stress acts, the long fibers having different tensile strengths, which are expressed as the product of the tensile strength per unit cross-sectional area of the long fibers used and the cross-sectional area of the fibers arranged in the cement matrix, are used. It is easily achieved by arranging at least substantially two layers or more so as to bear the tensile stress of the member, and arranging the long fibers having higher tensile strength at a position closer to the neutral axis among the long fiber arranging positions. It

Hereinafter, the present invention will be described in detail.

The cement used in the present invention is not particularly limited as long as it is a normal Portland cement, a high-strength Portland cement, a blast furnace cement, an alumina cement, or a hydraulic cement that is usually used for producing cement products.

The long fibers to be used may be of any material such as organic or inorganic, but high performance fibers such as carbon fiber, aramid fiber, alkali resistant glass fiber and high strength vinylon fiber are particularly preferred.

FIG. 1 shows an example of a method of arranging long fibers in cement matrix in the present invention.

In FIG. 1, reference numeral 1 is a fiber-reinforced cement-based member that receives bending stress in a central one-point loading bending test. 2 is a member of the member in a region (a portion below the line NN 'in FIG. 1) where tensile stress acts with respect to the neutral axis of the bending stress of the member (line NN' in FIG. 1). Long fibers with a higher tensile strength, arranged so that they can bear tensile stress and arranged at a position closer to the neutral axis (represented by the distance L ₁ from the neutral axis in FIG. ₁ ) Is.

Here, it is preferable that the longitudinal direction of the long fibers is the same as the direction of the tensile stress of the member because the tensile stress bearing effect is most excellent. However, even if the longitudinal direction of the long fibers is not exactly the same as the tensile stress direction of the member, if the tensile stress can be substantially borne, the respective directions may be slightly different.

3 has a smaller tensile cooperation and is located farther from the neutral axis (represented by the distance L ₂ from the neutral axis in Fig. 1)
It is a long fiber which is arranged and arranged in the same longitudinal direction as 2 except that.

Here, the tensile strength of the fiber in the present invention is expressed as a value of the product of the tensile strength per unit cross-sectional area of the long fiber used and the cross-sectional area of the fiber arranged in the cement matrix.

And the tensile strength and cross-sectional area are
It can be measured by the method of JIS standard R7601, and also for other fibers, it can be measured according to the same method.

What is important in the present invention is that two or more layers of long fibers are arranged in the cement matrix, and the tensile strength of the long fibers arranged at a position close to the neutral axis of the tensile stress of the member is arranged at a position far from the neutral axis. It is arranged so as to be larger than the tensile strength of the long fibers to be provided. The load-deflection curve in bending of the fiber-reinforced cementitious member in which long fibers are arranged as in the present invention is shown in FIG. 2a.

That is, when the deflection increases, the long fibers with a small tensile strength, which are located farther from the neutral axis and receive a larger tensile strain, first break, and the load temporarily decreases, but at a position closer to the neutral axis, the small The load increases again due to the reinforcing capacity of the long-strand long fibers that have undergone tensile strain and have not yet broken. Finally, the long fibers with high tensile strength themselves break, and the load gradually decreases to zero.

On the other hand, when long fibers having the same tensile strength are arranged at positions far from and close to the neutral axis, the load at the time when the long fibers at the far position is broken as shown in FIG. Although it is larger than the case, since the strength of the fiber at the closer position is smaller than that of the case of a, the load drop is large, and if the bending is further added, the load does not increase significantly, and the fiber at the closer position finally breaks, The amount of deflection is smaller than that in the case of a.

Contrary to the case of a, when the long fiber arranged at the far position has a higher tensile strength, the load at the time when the fiber at the far position is broken as shown in FIG. 2c is the largest, Since the strength of the fibers in the near position is small, the load drop is the largest, and when further bending is applied, the fibers in the near position are broken with almost no increase in the load, and the amount of bending is smaller than in the case of a.

In this way, from the comparison of the three tensile strengths different from each other, in order to obtain a bending member excellent in toughness while maintaining a sufficiently large stress level when the flexural force is exceeded by exceeding the maximum bending stress level, Obviously, it is preferable to arrange the fibers having higher tensile strength so as to be located closer to the neutral axis as in the invention.

In the present invention, as a method of arranging the tensile strength of the long fibers differently depending on the arrangement position, long fibers having the same kind of tensile strength are used, and a large number of them are arranged at a position closer to the neutral axis. By increasing the cross-sectional area and increasing the tensile strength required as the product of the tensile strength and the cross-sectional area, or using two or more types of fibers with different tensile strength, the position near and away from the neutral axis As the product of the tensile strength and the cross-sectional area of the fibers respectively arranged, the tensile strength of each is obtained,
There is a method such as arranging so that the fiber strength near the neutral axis is large. More specifically, the value of each fiber strength depends on factors such as the tensile strength of the fiber to be used and the cross-sectional area of the fiber, the distance of the position of the fiber from the neutral axis, and the size of the fiber-reinforced bending member. It may be appropriately set so that the bending stress and the amount of bending required for the member can be obtained, and the fiber strength at a position close to the neutral axis is 1.2 times or more, preferably 1.5 to 4 times that at a distant position. More preferably, it is arranged so as to be 2 to 3.5 times.

Further, in order to obtain more excellent bending toughness in the present invention, it is preferable to use two or more kinds of long fibers having different breaking elongations in combination.

For example, when two types of fibers having different breaking elongations are used and the fibers are arranged as in the present invention, the load-deflection curve in bending of the fiber-reinforced member is medium when the deflection increases as shown in Fig. 3a. Fibers with a small elongation at break located far from the vertical axis rupture first, the load is slightly reduced, then fibers with a small elongation at break near the vertical axis rupture, and fibers with a large elongation at break further away from the neutral axis. Becomes a bending mode in which a fiber with a large elongation at break, which is located near the end, breaks.

On the other hand, FIG. 3b shows a case where one kind of fiber having the same breaking elongation is used and arranged as in the present invention. As can be seen from the comparison between the two, by using fibers that have different breaking elongations in combination, the load drop during the deflection is small, the deflection can be increased while maintaining a large load, and it is a very excellent member with large toughness. Is obtained.

From the bending mode when two kinds of fibers having different breaking elongations are used, if more kinds of fibers having different breaking elongations are used in combination, a larger load is maintained and a larger deflection is practically used. It is possible to obtain a member having higher toughness.

Further, in the present invention, in order to obtain a large bending stress,
It is preferable to combine two or more kinds of fibers having different tensile elastic moduli, and to arrange the fibers having a large tensile elastic modulus at a position farther from the neutral axis. For example, the load-deflection curve when the fiber having a large tensile elastic modulus is arranged at a position far from the neutral axis and the fiber having a small elastic modulus is arranged at a close position is the fourth curve.
As shown in FIG. A, as compared with the curve of FIG. 4b in which only fibers having the same elastic modulus are arranged in two layers, a load with the same amount of deflection is large and a member having high bending strength is obtained, which is preferable.

In the present invention, the long fibers are arranged in at least substantially two layers or more. Here, when the long fibers are arranged in a substantially layered form, it means that substantially the same tensile stress is applied to the neutral axis of the tensile stress of the member. This means that the regions to be added are arranged so that the distance from the neutral axis is almost the same. The number of long fibers arranged in layers is not particularly limited, and is appropriately determined according to the reinforcing effect desired to be added to the member.

In the present invention, long fibers are usually used in the form of a bundle of hundreds to tens of thousands of single fibers having a diameter of several microns to several tens of microns.

And to secure the tensile strength as a bundle when placing it in the cement matrix, to prevent damage during handling,
It is preferable to use by impregnating and adhering various polymer substances and binding the single systems to each other.

As a specific polymer substance, epoxy resin, urethane resin, phenol resin, polyvinyl alcohol, etc. are used.

In addition, in order to improve the adhesiveness with cement matrix,
The fiber is subjected to a surface treatment such as surface oxidation treatment, or an uncured epoxy resin having a softening point of 40 ° C. or more as a polymer substance to be attached, or a carboxyl-modified rubber polymer is further attached onto the epoxy resin layer. A method or the like may be used.

In order to further improve the adhesion with the cement matrix, fine sand or the like may be further adhered to the surface impregnated with the polymer substance with a resin so as to have an anchoring effect on the cement matrix.

In the above description, a method of arranging two kinds of fibers having different tensile strengths by changing their positions with respect to the neutral axis has been described. However, in the present invention, as long as the fibers have different tensile strengths of two or more kinds. However, there is no problem in using more kinds than that, and in that case, fibers having a larger tensile strength may be arranged closer to the neutral axis.

Further, the shape of the long fibers used in the present invention is not limited to a linear one-dimensional shape, but may be a lattice shape, a net shape or a woven shape, and can be two-dimensionally laminated. Especially in the case of mesh
It is preferable that the entangled fibers are arranged in the longitudinal direction of the fibers as referred to in the present invention, since the entangled fibers are formed by the entangled weave, because a fiber reinforcing member having higher strength and high toughness can be obtained.

The embedding of the long fiber of the present invention into the cement matrix may be carried out by a conventional method.

For example, a conventional stacking / embedding method may be used, or a matrix material may be preliminarily three-dimensionally incorporated into the mold, and then a matrix material may be injected and cured.

At this time, if defoaming is performed by vibrating with a vibrator or the like, the adhesion between the cement matrix and the reinforcing fiber assembly becomes even tighter, and good mechanical properties can be obtained.

The member of the present invention may be a plate-shaped member, a tubular member, or a bent member such as a hollow plate or a block, and the shape thereof is not particularly limited.

<Effects of the Invention> As described above, according to the present invention, effective and rational reinforcement with a small amount of fiber is carried out by a very simple method of adjusting the tensile strength according to the position of the reinforcing fiber. It is possible to obtain a cement-based member having excellent performance and excellent bending toughness and strength.

Further, like the reinforced concrete structure, it becomes possible to effectively and easily design the cross section according to the application and the load condition, and it is also highly practical.

Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to the following examples unless it exceeds the gist.

Example 1 A high-strength carbon fiber made of coal tar made from coal tar pitch (consisting of about 4000 single fibers with a diameter of about 11 microns)
Was hardened with an epoxy resin solution and cured by heating to obtain linear long fibers having a resin content of 47%. The physical properties thereof are shown in Table 1.

A length of 2 mm from the bending neutral axis of the cement-based bending member of width: 40 x height; 20 x length; 320 mm, which is obtained by joining three long fibers in the lengthwise direction with an epoxy adhesive to form a bundle. (First
(Denoted by L ₁ in the figure), 5 bundles were arranged at equal intervals such that the longitudinal direction of the fiber was the same as the tensile stress direction.

Table 1 shows the fiber cross-sectional area and tensile strength obtained by totaling 5 bundles.

On the other hand, each one of the same long fibers is also placed at a distance of 7 mm (represented by L ₂ in FIG. 1) from the neutral axis so that its longitudinal direction is the same as the tensile stress direction of the member, and 5 fibers are equal. The intervals and the cross-sectional areas and tensile strengths thereof are shown in Table 1.

The cement is early-strength Portland cement, the aggregate is river sand (maximum 2.5 mm particle size), water / cement ratio is 0.4 / 1, aggregate /
The cement ratio was 0.67 / 1.

260m span of fiber reinforced cement-based specimen after curing for 1 week
The bending stress test-flexure curve obtained by conducting a single point central bending test at m is shown in Fig. 5a. The bending strength of the cement-based plain sample without fiber reinforcement was 81 kg / cm ² .

Comparative Example 1 Two bundles of the same long fibers as in Example 1 were joined in the same manner to form a bundle, and in the same manner as in Example 1, a distance of 2 mm from the neutral axis and 7
Five bundles were arranged at a distance of mm.

These cross-sectional areas and tensile strengths are shown in Table 1, and the bending stress-deflection curves obtained are shown in FIG. 5b.

Comparative Example 2 Five long fibers same as in Example 1 were placed at a distance of 2 mm from the neutral axis,
7 mm from the neutral axis with 5 bundles of 3 same long fibers joined together
It was arranged at a distance of.

The cross-sectional area and tensile strength are shown in Table 1, and the obtained bending stress-deflection curve is shown in FIG. 5c.

Example 2 Mesophase low elongation carbon fiber made from coal tar pitch (consisting of about 2000 single fibers with a diameter of about 10 microns)
Was obtained in the same manner as in Example 1 to obtain linear long fibers having a resin content of 45%, and the physical properties thereof are shown in Table 1.

Two bundles of these three low-elongation long fibers joined together to form one bundle and three bundles of the high-elongation long fibers of Example 1 were arranged at equal distances of 5 mm from the neutral axis.

On the other hand, at a distance of 7 mm from the neutral axis, the high elongation long fiber 4 of Example 1
A total of 5 pieces of a book and one of the above low elongation long fibers were arranged at equal intervals.

These cross-sectional areas and tensile strengths are shown in Table 1, and the bending stress-deflection curves obtained are shown in FIG.

Example 3 Using alkali-resistant glass fiber (trade name "Alpha Iver" AR R2400TB, manufactured by Asahi Glass Co., Ltd.), linear filaments were obtained in the same manner as in Example 1, and the physical properties thereof are shown in Table 1.

A distance of 4 mm from the neutral axis, 3 bundles obtained by joining 2 long glass fibers into 1 bundle and 2 bundles obtained by joining 2 high elongation carbon long fibers of Example 1 into 1 bundle Are arranged at equal intervals.

On the other hand, one long glass fiber and two high-elongation carbon long fibers were arranged at equal intervals at a distance of 7 mm from the neutral axis.

These cross-sectional areas and tensile strengths are shown in Table 1, and the bending stress-deflection curves obtained are shown in FIG.

Example 4 Aramid fiber (trade name “Kevlar 49” manufactured by Dupont, USA)
1420 denier) was used to obtain linear long fibers in the same manner as in Example 1, and the physical properties thereof are shown in Table 1.

Four bundles obtained by joining four aramid filaments into one bundle and two glass filaments used in Example 3 were arranged at a distance of 3 mm from the neutral axis at equal intervals.

On the other hand, aramid filament 4 equivalent to a distance of 7 mm from the neutral axis
The book and one long glass fiber were arranged at equal intervals.

These cross-sectional areas and tensile strengths are shown in Table 1, and the bending stress-deflection curves obtained are shown in FIG.

[Brief description of drawings]

FIG. 1 is a plan view of a fiber reinforced cement-based member and its cross section. 2 to 4 are views for explaining a load-deflection curve in a bending test of the fiber-reinforced cement-based member according to the present invention. 5 to 8 show flexural stress-deflection curves of the fiber-reinforced cementitious members in the examples and comparative examples of the present invention during the bending test. 1 …… Fiber reinforced cementitious member 2 …… Longer fiber with higher tensile strength 3 …… Longer fiber with lower tensile strength L ₁ …… Longer fiber with higher tensile strength Distance from neutral axis L ₂ …… Tensile Distance from the neutral axis of strong smaller filaments

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP 62-133240 (JP, A) JP 63-151749 (JP, A) JP 55-87541 (JP, A) JP 52- 34518 (JP, A) Actual public Sho 51-53071 (JP, Y2)

Claims (4)

[Claims] 1. A fiber-reinforced cement-based member that receives bending stress, wherein the tensile strength per unit cross-sectional area of the long fibers used in the region where tensile stress acts on the neutral axis of the bending stress of the member and the cement. The long fibers having different tensile strengths, which are expressed as the product of the cross-sectional area of the fibers arranged in the matrix, are arranged so as to bear the tensile stress of the member, and at least substantially two layers are arranged, and A long-fiber-reinforced cement-based member, characterized in that large-strength, long-fibers are arranged at a position closer to the neutral axis among the long-fiber disposition positions. 2. The tensile strength of the long fibers arranged at a position closer to the neutral axis of the member is 1.2 times or more the tensile strength of the long fibers arranged at a position farther from the neutral axis. The fiber-reinforced cementitious member according to claim 1. 3. The fiber-reinforced cementitious member according to claim 1 or 2, wherein the long fibers have different breaking elongations. 4. The fiber-reinforced cementitious member according to claim 1, wherein the long fibers are carbon fibers, aramid fibers, alkali-resistant glass fibers or vinylon fibers.