JPH0920537A - Fiber reinforced cement and concrete - Google Patents

Abstract

PURPOSE: To obtain fiber-reinforced cement capable of supplementing merits of short fibers by utilizing plural short fibers as reinforcing materials. CONSTITUTION: This fiber-reinforced cement or concrete is obtained by mixing glass short fiber and vinylon short fiber into cement or concrete constituting a matrix. The mixing ratio of the vinylon short fiber is 0.8-1.5vol%. The mixing ratio of the glass short fiber to vinylon short fiber is 2 to 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of cement and concrete used as materials for curtain walls and the like, and relates to a technique for improving yield strength by mixing plural kinds of fibers.

[0002]

2. Description of the Related Art Conventionally, as fiber reinforced cement or concrete, GRC (glass fiber reinforced cement) or steel fiber reinforced concrete (SFRC) has been widely used for interior and exterior of buildings. Further, recently, synthetic fiber reinforced cement, carbon fiber reinforced cement (CFRC) and the like are being put to practical use. In these, glass fibers, steel fibers, etc. are added to cement or concrete in a necessary amount and mixed with a mixer for use.

[0003]

By the way, in the above-mentioned conventional fiber-reinforced cement or concrete, when short fibers are used as the reinforcing fibers, the short fibers as the reinforcing material are dispersed in the matrix as the base material as uniformly as possible. This is very important. However, when steel fibers such as stainless steel are used, since the specific gravity of the reinforcing material is larger than that of the matrix, there is a problem that the reinforcing material precipitates during compaction even if it can be uniformly dispersed during cement pouring.

When short glass fibers are used as a reinforcing material, even if alkali glass fibers are used, the strength of the hardened cement gradually deteriorates over many years in a highly alkaline environment. It is known that it does not function sufficiently as a reinforcing material. In order to improve this, special cement corresponding to glass fiber is sometimes used, but it is expensive, requires special temperature curing, and causes another problem that rust easily occurs on the steel formwork. It will be.

As described above, although the fiber-reinforced cement and concrete are theoretically recognized to have a sufficient reinforcing effect, there are still problems to be solved in actual use. Therefore, the inventors have conventionally conducted research on a structure in which glass short fibers and vinylon short fibers are mixed as a fiber-reinforced cement and mixed into a matrix, but in order to improve the reinforcing property and durability, the It was clarified that the allocation ratio is an important requirement.

The present invention is intended to solve the above-mentioned conventional problems, and provides a fiber-reinforced cement which can complement these advantages by utilizing a plurality of short fibers as a reinforcing material. To do.

[0007]

In order to achieve the above object, the present invention employs a means of mixing short glass fibers and short vinylon fibers into cement or concrete constituting a matrix. Further, for more effective reinforcement, the mixing ratio of short vinylon fibers is 0.8 to 1.
A means to make it 5% by volume is also used. Further, means for setting the mixing ratio of the glass short fibers and the vinylon short fibers to 2: 1 was also used.

[0008]

The glass short fibers and vinylon short fibers mixed in the matrix both have the function of reinforcing the physical properties of the matrix. In particular, short glass fibers have a high elastic modulus,
While it greatly contributes to the improvement of bending strength, it is known that even cement mortar and concrete using alkali-resistant glass fibers have a significant decrease in bending toughness and ductility in a highly alkaline environment of hardened cement. . on the other hand,
Vinylon short fibers have a lower elastic modulus than glass short fibers,
Although it does not significantly improve the bending strength, it does not deteriorate with age due to alkali and maintains a long-term reinforcing effect. Further, when they are evenly dispersed in the matrix, the effect of greatly improving the bending toughness of the fibers is exhibited.
Therefore, mixing both of them achieves the mutually complementary actions of improving the initial bending strength of the glass short fibers and, after the aging of the glass short fibers, improving the toughness of the vinylon short fibers.

The mixing ratio of vinylon short fibers is 0.8% by volume to
The significance of 1.5% by volume is that if it is less than 0.8%, the supplementary effect of vinylon short fibers is not so remarkable, and if it exceeds 1.5%, the flow value is extremely deteriorated and mortar or concrete is not poured. Because it will be difficult. Further, even if it exceeds 1.5%, the increase of the effect is not linear and reaches the upper limit stable region. Regarding the lower limit of the mixing ratio, the complementary effect of mixing the vinylon fiber is more remarkable at the boundary of about 0.8%, and therefore it can be recognized as the optimum lower limit.

The significance of setting the mixing ratio of the glass short fibers and the vinylon short fibers to 2: 1 is that the complementing effect of the vinylon short fibers after the deterioration of the glass short fibers is most optimal when the mixing ratio of this level is obtained. Because it does.

[0011]

EXAMPLE An example of the present invention will be described in detail below. As an experimental example, a plurality of types of samples having different mixing ratios of short glass fibers and short vinylon fibers were prepared, and these were mixed in a matrix to prepare a test body, and various experiments were conducted. As the matrix, cement was used in which silica sand No. 5 and shirasu balloon (lightweight fine aggregate) were added to the aggregate, and further a high-performance water reducing agent and other admixtures were added. Also, using an omni mixer with a capacity of 10 liters for mixing, add cement, aggregate and admixture and knead for 60 seconds, then add water for 2 minutes and further add fibers for 2 minutes. It was

As a sample, short glass fibers (GF) shown in Table 1 and short vinylon fibers (VF1, VF2, VF3) having different diameters and shapes were mixed as shown in Table 2.

[Table 1]

[Table 2]

(Flow Value Test) It was confirmed that the flow value, the fluidity, and the workability were deteriorated as the amounts of glass short fibers and vinylon short fibers were increased, as shown in FIG. Further, particularly in the case of vinylon short fibers, it is generally known that as the aspect ratio (fiber length / fiber diameter) becomes larger, the fibers are entangled with each other to form fiber balls (balls) and the flow value becomes worse. There is. Therefore, in order to avoid this, it is considered effective to reduce the total number of vinylon short fibers by increasing the thickness per unit to some extent.

(Bending proportional limit strength test: Limit of Propor
tionality) Next, the results of a bending strength test performed on a test body at 4 weeks of age (before immersion in warm water) will be described. Among the bending strengths, the bending proportional limit strength did not show a large difference in each test body. However, a clear difference was observed when the distribution of short glass fibers was 2% by volume and 3% by volume. As a result, it is considered that the vinylon short fibers do not exert the effect on those that have not passed a long time, and the reinforcing effect of the glass short fibers has a large influence exclusively.

(Bending Strength Test: Modulus of Rupture) Further, regarding the bending strength, the results shown in FIGS. 2 and 3 were obtained. There are two types of test pieces, one is 15mm thick and 5 widths.
0 mm, length 350 mm (hereinafter referred to as A type), another type is a curtain wall member, thickness 50
mm, width 100 mm, length 530 mm (hereinafter referred to as B type). The bending strength test was performed by two types of test methods. Fig. 2 shows the center of the A-type test piece at 300 mm fulcrum distance and 2 mm / min loading speed according to the “Construction and testing method of short fiber reinforced cementitious composite material using new material fibers” Centralized loading. On the other hand, in FIG. 3, the B type test body was set to 450 mm in the distance between fulcrums and the load was divided into three equal points, in accordance with “Standards for Testing Methods of Fiber Reinforced Concrete” of the Japan Concrete Institute. As a result, in any method, the strength of the sample containing the longest vinylon short fiber was decreased. It is considered that this is because the vinylon fibers are relatively long and cannot be sufficiently diffused during kneading, resulting in insufficient uniform dispersion of the fibers.
However, it is possible to adopt vinylon short fibers having a fiber length up to a certain extent by sufficiently kneading.

(Bending toughness test) Regarding bending toughness, the results shown in FIGS. 4 and 5 were obtained. Similar to the above bending strength test, this test also conformed to the test method of the Building Research Institute of the Ministry of Construction and the test method of the Japan Concrete Institute.
In conclusion, in FIG. 4, the toughness increases as the mixing ratio of short vinylon fibers increases, but in FIG. 5, it tends to decrease contrary to the mixing ratio. As an estimate,
In FIG. 4, the bending toughness calculation of the A type test method reflects the toughness region of a low bending strength level, while the B type test method of FIG. 5 calculates only the toughness region of a high bending strength level to the bending toughness. Therefore, it is considered that the difference in the calculation method was reflected.

What can be derived from the above test is 1.5
The strength of the test body does not decrease significantly by mixing vinylon short fibers up to about 10% by volume, and the toughness and bending proportional limit strength etc. before immersion in warm water, that is, in the state where it is considered that it has not been subject to aged deterioration It was found that the mixing ratio of the glass short fibers greatly contributes to the improvement of. On the other hand, since the flow value decreases as the mixing ratio of short vinylon fibers increases, it was also found that there is a limit to the mixing of short vinylon fibers in order to ensure uniform strength. By the way, when the vinylon short fibers were mixed in an amount of 2% by volume or more, the flow value was extremely lowered, and it was difficult to uniformly place the fibers on the mold. Further, the fibers could not be sufficiently diffused even when kneading. Moreover, the long fiber length had a large adverse effect due to the particularly high mixing ratio.

(Bending Property after Immersion in Hot Water) The purpose of immersion in hot water is to realize aging of the test body in a short time.
That is, by immersing the test body in warm water, it is generally performed as a method capable of confirming the deterioration of the mixed glass short fibers in a short period of time. Fig. 6 shows an experiment of changes in bending strength due to immersion in warm water maintained at 80 ° C, and in the fourth week, the reinforcing effect of short glass fibers almost disappeared, and the bending proportional limit strength before immersion was almost the same value. It was confirmed to be reduced to. This is because even alkali-resistant glass fibers are chemically eroded by the high alkalinity of hardened cement, and the surface of glass fibers is damaged by the calcium hydroxide crystals generated by the hydration reaction of cement. It is said that
In addition, it is said that there is a reason that, as the hydration reaction of cement proceeds for a long period of time, the adhesion between the cement matrix and the glass fiber becomes strong and the glass fiber is easily broken.

FIG. 7 shows the test result of bending toughness. The test body containing only the glass short fibers had almost no bending toughness after 4 weeks and lost toughness. On the other hand, in the test body in which the vinylon short fibers were mixed together with the glass short fibers, the bending toughness decreased to about half of the initial value in 4 weeks after immersion in warm water, but the effect was still maintained, and even after 8 weeks, it was 4 weeks. It was confirmed that the bending toughness was maintained at about the same level as. this is,
This is because the reinforcing effect of the short glass fibers disappears by soaking in warm water, but the original stickiness of the vinylon short fibers exerts its effect and complements the disappearance of the reinforcing effect due to the deterioration of the short glass fibers. In particular, as compared in FIG. 8 and FIG. 9, the bending stress degree-deflection curve of the test body mixed with only the glass short fibers after 8 weeks of hot water immersion (FIG. 8), and the test body further mixed with vinylon short fibers It is clear that the stickiness effect of short vinylon fibers greatly contributes to the maintenance of the toughness of the test body when compared with that after 8 weeks of hot water immersion (FIG. 9). As described above, it is certain that the vinylon short fibers contribute to the improvement of the toughness of the test body even before being immersed in warm water, but the elastic modulus of the vinylon short fibers is about 40% of that of the glass short fibers. Although it has not been able to complement the strong reinforcing effect of the fiber, when the effect of the short glass fiber disappears due to the immersion in warm water, the effect of the vinylon short fiber becomes apparent.

Comparing each of the above experiments, in the case where only glass short fibers are mixed in the matrix, its toughness disappears due to deterioration over time, and in terms of securing the toughness, the meaning of mixing is completely eliminated. Then, it is found that when the vinylon short fibers are reinforced, the complementary effect of the glass short fibers is revealed and the fiber reinforcing effect can be maintained for a long period of time.

The material of the present invention can be used in a premix method or sprayed on a wall or the like by a spray method. Therefore, its application is no different from ordinary mortar or concrete.

[0022]

According to the present invention, both glass short fibers and vinylon short fibers are mixed in the matrix.
Initially, the reinforcing effect of the short glass fiber is remarkably exhibited and the toughness can be improved, while after the glass short fiber has deteriorated over time, the sticking effect of the vinylon short fiber becomes apparent and can function complementarily. , It became possible to continue to exert the reinforcing effect for a long time.

Further, 0.8 to 1.5 vinylon short fibers are used.
When mixed by volume%, the sticking effect of vinylon short fibers can be optimally exhibited, and the workability can be secured without extremely deteriorating the flow value of the matrix.

Furthermore, when the mixing ratio of the glass short fibers and the vinylon short fibers is set to 2 bodies, the optimum complementing effect can be achieved without causing deterioration of the flow value.

[Brief description of drawings]

FIG. 1 is a graph showing a change in flow value according to a mixing ratio of vinylon short fibers,

FIG. 2 is a graph showing changes in bending strength according to the mixing ratio of vinylon short fibers,

FIG. 3 is a graph derived by using another method,

FIG. 4 is a graph showing changes in bending toughness according to the mixing ratio of vinylon short fibers,

FIG. 5 is a graph derived using another method,

FIG. 6 is a graph showing changes in bending strength due to immersion in warm water,

FIG. 7 is a graph showing changes in bending toughness due to immersion in warm water,

FIG. 8 is a graph showing bending stress degree-deflection curve of only glass short fibers (test sample GR3) immersed in warm water.

FIG. 9: When vinylon short fibers are added (test body GV6)
3 is a graph showing a bending stress-deflection curve by immersion in warm water of FIG.

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Claims (3)

[Claims] 1. A fiber-reinforced cement and concrete, wherein glass short fibers and vinylon short fibers are mixed in a matrix. 2. Vinylon short fibers are 0.8 to 1.5% by volume.
The fiber-reinforced cement and concrete according to claim 1, which has a mixing ratio of. 3. The fiber-reinforced cement and concrete according to claim 1, wherein the mixing ratio of the glass short fibers and the vinylon short fibers is set to 2: 1.