JP2007270488A - High-strength and high-toughness cement-based soil improving body using fiber reinforcement - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-strength and high-toughness cement-based soil improving body using fiber reinforcement which is used for an underground structure of an earth-retaining wall/foundation etc. of a building or civil engineering structure. <P>SOLUTION: Polypropylene fibers are mixed by 0.4-2% based on the volume ratio of the soil improving body, and kneaded with soil so as to reinforce a matrix. In the polypropylene fibers with a fracture strength of 200-1,200 MPa, the ratio of the length of the fiber to the thickness of the fiber is adjusted to 1,000 or more so that the fibers can be intertwined with one another by being kneaded and agitated. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention belongs to the technical field of a high-strength, high-toughness cement-based ground improvement body by fiber reinforcement used for underground structures such as mountain retaining walls and foundations of buildings or civil engineering structures.

The ground improvement body is manufactured by adding cement-based hardener to the generated soil and kneading and solidifying. In general, while a rod equipped with a stirring blade penetrates into the soft ground, the cement-based hardened material produced in the plant on the ground is spouted from the tip of the rod and stirred and mixed with the excavated soil to Produces a reinforced ground improvement body. Alternatively, the cement powder is pneumatically conveyed from a ground silo, sprayed from the tip of the rod provided with the stirring blade, and stirred and mixed with the excavated soil to produce a ground improvement body. The ground improvement body is widely used for improvement of ground supporting force, prevention of liquefaction, or construction of underground structures such as mountain retaining walls and water blocking walls. The ground improvement body has a compressive strength of about 0.5 to 4 MPa, and a cement amount capable of obtaining a required strength is mixed as a cement-based hardener according to the type of the ground.
This ground improvement body causes brittle fracture when the maximum load is exceeded. In particular, when subjected to bending or pulling, it breaks at once after the maximum yield strength. For this reason, considering safety, about 1/3 to 1/10 of the compressive strength in the laboratory test is used as the allowable compressive stress level. In many cases, the tensile strength is designed to be 0.1 to 0.2 times the allowable compressive stress and the shear strength is 0.3 times.

  As a conventional technique for improving the mechanical properties of the ground improvement body, for example, Patent Document 1 below discloses a fiber-reinforced soil cement mixed with steel fibers and a construction method thereof. It is recognized that this conventional technology has a strength level of 10 MPa, which is higher than that of a general ground improvement body, and the steel fiber reinforcement can increase the bending strength by 15 to 30% of the compressive strength. It is also described that 1 to 3% of steel fibers are mixed in a cement-based hardener having a water cement ratio of 100%.

In the following Patent Document 2, a fiber-reinforced soil solidified body using a vinylon fiber having a diameter of 10 to 20 microns, a fiber length of 4 to 10 mm, and a breaking strength of 1500 to 2500 MPa, or a diameter of 25 to 50 microns and a fiber length of 10 It is described that when a fiber-reinforced soil solidified body using vinylon fibers having a breaking strength of 800 mm to 1500 mm is produced, bending strength and tensile strength against compressive strength can be improved and toughness can be improved.
The soil solidified body for ground improvement is generally constructed by determining the amount of cement that provides the required strength in accordance with the soil quality of the ground. Although the cement content may range, for example, in the sand layer 80~300Kg / ^{m 3} approximately, in the cohesive soil 100 to 300 / ^{m 3} approximately, a cement content of about 100 to 300 / ^{m 3} in the silt. However, since the disclosed technique of Patent Document 2 describes that the cement amount is 350 kg / m ³ for all soils, it is a different composition from the generally improved ground improvement body. In addition to the very large amount of cement, it is noted that expensive vinylon fibers are used.

  Patent Document 3 below discloses a method for applying the fiber-reinforced soil solidified body described in Patent Document 2. That is, in the construction method of the fiber reinforced soil solidified body described in Patent Document 2, the viscosity of the cement-based hardener is very low and fiber dispersion is difficult. A thickener and a dispersing agent are added to the cement-based hardener having a lower limit (60 to 80%) and high clay. Then, the fibers are mixed and dispersed in a volume ratio of 1% or less and 0.5% or more. Then, it is described that water is added to a required water-cement ratio and the required compressive strength is exhibited.

JP-A-6-228492 JP 2001-48609 A JP 2003-232032 A

  The fiber reinforced soil cement and its construction method disclosed in Patent Document 1 describe that 1 to 3% of steel fibers are mixed in a cement-based hardened material having a water cement ratio of 100%, but the water cement ratio is 100%. It is extremely difficult to mix and feed steel fibers exceeding 1% by volume to a cement-based hardener. It also describes that an improvement of 30% in compressive strength can be expected with respect to an improvement in bending strength. However, depending on the type of ground, only 10% volume ratio of the ground improvement body uses cement-based hardener, so that the reinforcing fiber is mixed in only 0.1-0.3% with respect to the volume of the ground improvement body. And a sufficient fiber reinforcement effect cannot be expected. Moreover, even if the maximum yield strength is improved, the presence or absence of the toughness improvement effect after the maximum yield strength is unknown, and the toughness improvement effect remains unverifiable.

The fiber-reinforced soil solidified body disclosed in Patent Document 2 is described as having a cement amount of 350 kg / m ³ with respect to any soil, and it is a different composition from the generally implemented ground improvement. It has become. In general, the amount of cement that provides the required strength is determined according to the soil quality of the ground. Even so, since the disclosed technology of Patent Document 2 uses a very large amount of cement and expensive vinylon fiber, even if a high-performance fiber-reinforced soil solidified body can be obtained, the ground improvement cost becomes significantly expensive. Not economical.
The construction method of the fiber-reinforced soil solidified body disclosed in Patent Document 3 disperses fibers by mixing them in a cement-based hardener having a low water-cement ratio and a high viscosity in a volume ratio of 1% or less and 0.5% or more. Therefore, it is indispensable to use a thickener or a dispersant, and after that, it is necessary to supply water to obtain a required water-cement ratio in order to knead uniformly, so that the on-site implementation is troublesome.

An object of the present invention is to provide a high-strength, high-toughness cement-based ground that can improve the toughness of a ground improvement body inexpensively, simply and reliably, and can obtain a higher bending strength and tensile strength than conventional products. It is to provide an improved body.
The next object of the present invention is to be used in a large amount in a wide field at present, and using polypropylene fibers that are inexpensive and economical, and kneading and stirring, the fibers are entangled with each other, a great fiber reinforcing effect It is to provide a high-strength, high-toughness cementitious ground improvement body that is reinforced by reinforcing the matrix.

As a means for solving the problems of the prior art, a high-strength, high-toughness cement-based ground improvement body by fiber reinforcement according to the invention described in claim 1,
In the ground improvement body manufactured by kneading soil and cement-based hardener,
A polypropylene fiber P having a breaking strength of 200 to 1200 MPa and a length ratio (aspect ratio) with respect to the thickness of the fiber 1 adjusted to 1000 or more so that the fiber and the fiber are entangled with each other by kneading and stirring is improved. It is characterized in that the matrix 2 is reinforced by mixing with 0.4 to 2% of the body volume ratio and kneading with soil.

The invention described in claim 2 is a high-strength, high-toughness cement-based ground improvement body by fiber reinforcement described in claim 1,
The thickness of the polypropylene fiber P is characterized by having a diameter of 100 microns or less.

The invention described in claim 3 is a high-strength, high-toughness cement-based ground improvement body by fiber reinforcement described in claim 1 or 2,
The polypropylene fiber P is characterized by having a knot-like or massive anchor portion larger than the fiber diameter by 10 microns or more at both ends.

(Theoretical basis of the invention and industrial applicability)
Polypropylene fiber has a hydrophobic surface, a breaking strength of about 200 to 1200 MPa, a Young's modulus of about 2 to 15 GPa, and is inferior in mechanical properties as compared with other organic fibers. Therefore, it has been considered that polypropylene fibers must be used in a large amount in order to obtain the fiber reinforcing effect of the ground improvement body.
However, in the present invention, the polypropylene fiber is mixed in a volume ratio of 0.4 to 2% in the ground improvement body so that the fiber reinforcing effect is exhibited, the toughness of the cement ground improvement body is greatly improved, and the bending strength is increased. , Succeeded in greatly improving the tensile strength.
That is, the general principle of fiber reinforcement is that stress is applied by the adhesion force and friction resistance between the matrix (in this specification, the matrix is used to mean the base material of the cement-based ground improvement body structure) and the fiber. It is considered that the bending strength, tensile strength, and toughness are increased by transmitting to fibers (see FIGS. 1B and 2B). In FIGS. 1B and 2B, reference numeral 1 denotes fibers, 2 denotes a matrix, and 3 denotes cracks.
However, in the present invention, when the fibers 1 are bent in the ground improvement body and mixed so as to be entangled with each other, the resistance at the time of drawing increases, and stress is transmitted to the fibers 1 to reinforce the matrix 2 ( The fact of FIG. 1B) focuses on the effect.

A general fiber reinforcement phenomenon related to a cement-based ground improvement body is caused by an applied stress being transmitted to a fiber through an adhesive force between the matrix and the fiber.
Sufficient adhesion force is acting between the matrix and the fiber, and it is assumed that the fiber and the matrix behave integrally until cracking occurs. bear. For this reason, the stress when the matrix reaches a strain causing cracks becomes higher as fibers having a higher Young's modulus are used. The average cross-sectional stress σc when cracks enter the fiber reinforced matrix is determined by the fiber orientation ratio using the fiber volume ratio Vf, fiber Young's modulus Ef, and matrix Young's modulus Em as the crack initiation stress σm of the matrix alone. If ignored, it can be evaluated by the following formula 1.
(Formula 1) (sigma) c = (sigma) m {1 + Vf (Ef / Em-1)}
Steel fibers and vinylon fibers have Young's moduli of about 250 times and 50 times, respectively, with respect to the matrix of the ground improvement body. When the fiber volume ratio Vf = 1%, the cross-sectional average stress σc at the time of crack occurrence is It is expected to be about 3.5 times and 1.5 times. On the other hand, the polypropylene fiber has a Young's modulus of about 3 times, and the cross-sectional average stress σc at the time of crack occurrence is only 1.02 times.
Further, the ultimate strength σu of the fiber reinforcement can be evaluated by the following formula 2 where the ultimate strength of the fiber is σfu.
(Formula 2) σu = σfu · Vf

Steel fibers and vinylon fibers have an ultimate strength of about 1000 MPa and 2000 MPa times with respect to the matrix of the ground improvement body, respectively. If the fiber volume ratio Vf = 1% and the ultimate strength σu is determined for simplicity, ignoring the reduction rate due to fiber orientation, they are 10 MPa and 20 MPa, respectively. On the other hand, the final strength of the polypropylene fiber is about 500 to 1000 MPa, and the final strength σu of the reinforcing body made of the fiber is 5 to 10 MPa.
However, when the test is actually performed, if the applied stress increases, the adhesion between the matrix and the fiber breaks and the fiber begins to come out, so only the frictional resistance when the fiber is pulled out is transmitted to the fiber and resists external force. It was confirmed that it was only. As a result, it was found that even if fibers having a large strength and Young's modulus were used, the above-described expected crack strength and ultimate strength could not be obtained. In other words, polypropylene fibers having low strength and Young's modulus and thought to have no effect unless added in large quantities (for example, 3% or more) for fiber reinforcement, It was found that a relatively small amount of addition was effective for reinforcing a cement-based ground improvement body having low strength, and it was confirmed that high toughness could be realized.

Thus, the present inventors have found that the cement-based ground improvement body has a rough structure compared to cement concrete, and therefore there are gaps and voids at the interface between the matrix and the fibers, and the adhesion breakage occurs from the time when the working stress is low. Since the fibers are partially pulled out and the relationship of the above formula 1 is not established, it has been found that there is almost no influence of the Young's modulus ratio between the fibers and the matrix on the cracking stress.
Most importantly, stress is more easily transmitted to the fiber by friction after the maximum stress than the strength and Young's modulus of the fiber. This phenomenon makes it possible to improve the bending strength, tensile strength and toughness of the fiber reinforced matrix.
It is considered that the strength of the fiber should not be broken by the stress generated by the frictional resistance. Even if the strength of the ground improvement body itself is about 0.5-4 MPa and the tensile stress of the fiber reinforced matrix is 1 MPa, the fiber strength ratio is 1%, the fiber strength is 100 MPa, and the fiber volume ratio is 0.5%. The fiber strength may be about 200 MPa. A fiber having a large Young's modulus will cause an adhesion failure between the fiber and the matrix at an early stage, so that the fiber strength cannot be effectively exhibited, and the efficiency of reinforcement is reduced.

  As a result of studying the structure of the ground improvement body and the interface between the ground improvement body matrix and the fiber, the present inventors have found that the matrix has 10% or more voids, and the interface between the matrix and the fiber is fragile and 5-10. It was found that micron-sized voids exist. For this reason, when the fiber diameter is small, the contact degree between the matrix and the fiber becomes insufficient. Therefore, it was confirmed that the fiber diameter should be 5 microns or more in order to transmit the stress.

  Next, in order to obtain a high (or efficient) fiber reinforcing effect by the frictional resistance between the matrix and the fiber, even if the fiber diameter is set to an appropriate thickness under the above-described conditions, as shown in FIG. With a straight fiber, a sufficiently large frictional resistance cannot be obtained between the matrix 2 and the fiber 1. As shown in FIG. 2, it was confirmed that adjusting the conditions in which the fiber 1 is bent and the fibers are intertwined with each other is extremely effective in increasing the frictional resistance during drawing. In order to obtain frictional resistance at the interface between the matrix 2 and the fiber 1, in order to obtain a state in which the fiber 1 is bent as shown in FIG. 2, it is advantageous that the aspect ratio (the ratio of the length to the thickness of the fiber) is large. is there. If the fiber material and the aspect ratio are the same and the stirring force during construction is the same, it becomes difficult to bend the fibers so that they are intertwined with each other as the fiber diameter increases. At present, when mass-producing industrially inexpensive fibers (continuous molding), it is known that the diameter of a single yarn is about 100 microns. On the other hand, in consideration of the stirrability during construction of the ground improvement body, the fluidity of the ground improvement body matrix, the fluidity after mixing the fibers, etc., in order to bend so as to obtain sufficient friction resistance against drawing The upper limit of the fiber diameter must be 100 microns. It can be said that it is preferably 50 microns or less.

When a polypropylene fiber having a fiber diameter of 10 to 50 microns and a ratio of fiber length to fiber diameter (aspect ratio) of 1000 or more is mixed in a volume ratio of 0.4 to 2% with respect to the volume of the ground improvement body, cement-based ground It was confirmed that the fiber reinforcing effect of the improved body was particularly high. It was also confirmed that when the aspect ratio is about 1200, a high fiber reinforcing effect can be obtained.
The fiber material for obtaining the above fiber reinforcement effect may be a low-rigidity fiber having a relatively low strength with a breaking strength of about 200 to 1200 MPa and a Young's modulus of 2 to 15 GPa. It has been found that polypropylene fibers that can be adapted.

  In addition, as another method for increasing the pulling frictional resistance at the interface between the matrix 2 and the fiber 1 of the cement-based ground improvement body, unevenness is provided on the surface of the fiber, or a knot-like or lump-like anchor part is provided at both ends of the fiber. It was also confirmed that it is effective to provide a (hook portion). There are 5 to 10 micron voids and fragile parts at the interface between the fiber 1 and the matrix 2, but by providing a knot-like or massive anchor part with a size that is at least 10 microns added to the fiber diameter at both ends, It was confirmed that the effect of reinforcing the matrix 2 by increasing the pulling resistance was great.

The high-strength, high-toughness cement-based ground improvement body by fiber reinforcement according to the first to third aspects of the invention can effectively greatly improve the tensile strength, bending strength, and toughness that the ground improvement body lacks. , Can exhibit excellent mechanical properties.
Therefore, by adopting a design method that makes effective use of the excellent mechanical properties of cement-based ground improvement bodies, it is possible to reduce the cross-section of the ground improvement body (economic design) for the purpose of self-supporting mountain retaining and liquefaction prevention, It is possible to achieve rationalization of the underground construction method by adopting the direct foundation type for high-rise buildings and further increasing the horizontal bearing capacity of pile-shaped improved bodies and wall piles.

The ratio of length to the thickness of the fiber so that the fiber and the fiber are entangled with each other by kneading and stirring the ground improvement body produced by kneading the soil and the cement-based hardener with a breaking strength of 200 to 1200 MPa. Polypropylene fiber P having an aspect ratio adjusted to 1000 or more is mixed in a volume ratio of 0.4 to 2% with the ground improvement body and mixed with soil to reinforce matrix 2.
The thickness of the polypropylene fiber P is preferably 50 microns or more and up to 100 microns.
Moreover, it is preferable to use the polypropylene fiber P which has a knot-like or massive anchor part larger than the fiber diameter by 10 microns or more at both ends.

Examples 1 to 12 shown in Table 1 below use blast furnace cement B, and the amount of cement is 170 so that a compressive strength of 3 to 4 MPa can be obtained according to the soil type (clay, silt, sand). Two types of polypropylene fibers having a breaking strength of 647 MPa and 935 MPa (fiber type symbols in Table 1) while kneading a cement-based hardener having a water cement ratio of 100% determined to ˜300 kg / m ³ with each soil soil P) was mixed, kneaded and stirred.
By the way, as a method of mixing polypropylene fiber with cement hardener and each soil soil, mixing and stirring, separate system from cement hardener injection pipe into in situ soil excavated with stirring excavation blade of ground improvement equipment For example, the direct method of pumping and feeding directly through a slightly thicker pneumatic conveying pipe, and excavating the original excavated soil, discharging it to the ground once, storing it in the ground kneading plant, and then cementing hardened material And the above-mentioned ground method in which the polypropylene fibers are mixed and kneaded are selectively carried out according to the working conditions. Examples 1 to 12 show the case where the latter ground system is adopted.

Regarding the polypropylene fiber P, the ratio of the length to the thickness of the fiber (aspect ratio) is set to 1000, 1200, 1770, and 1786 as a condition for the fibers to be intertwined with each other in the result of the kneading and stirring. The adjusted polypropylene fiber was used. And the polypropylene fiber mixed 0.5% or 1.0% by volume ratio with respect to the ground improvement body, knead | mixed with the said soil, and manufactured the cement-type ground improvement body which carries out fiber reinforcement of the matrix 2.
As shown in FIGS. 2A and 2B, the fiber dispersion state of the cement-based ground improvement body thus manufactured is that each fiber 1 is in a curved state, and the fibers are inherently entangled with each other in the matrix 2. I was able to confirm that.

On the other hand, Comparative Examples 1 to 17 shown in Table 1 also use blast furnace cement B, and the amount of cement so that a compressive strength of 3 to 4 MPa can be obtained according to the type of soil (clay, silt, sand). Is obtained by kneading a cement-based hardener with 170 to 300 kg / m ³ with each soil soil.
Comparative Examples 1, 7, 14, and 17 are ground improvement bodies that have been used conventionally, and no fibers are mixed therein. There are three types of fibers mixed into other comparative examples: vinylon fibers, nylon fibers, and polypropylene fibers.
More specifically, nylon fibers with a breaking strength of 960 MPa, vinylon fibers with 1950 MPa, and polypropylene fibers with 311 to 935 MPa were selectively used and mixed and stirred. The ratio of length to the thickness of each fiber (aspect ratio) was 210-800. A cement-based ground improvement body in which 1.0% of these were mixed by volume and kneaded with the soil to reinforce the matrix was produced. However, the fiber dispersion states of Comparative Examples 2 to 6, 8 to 13, and 15, 16 are as shown in FIGS. 1A and 1B, and the fibers 1 and 1 are kept in a linear state, and the fibers and the fibers are intertwined. It was confirmed that the situation was dispersed in the matrix 2.

The meaning contents of ◎, ○, ×, and △ indicate the determination results of bending and tension in the mechanical performance of each of Examples 1 to 12 and Comparative Examples 1 to 17 shown in the right column of Table 1. The determination example is as shown in FIG. 3 as a “bending / tensile / toughness determination example”.
In other words, those that fractured immediately after reaching the maximum yield strength were marked as x, and those that did not break immediately after the maximum yield strength was reached, but those that had a significant decrease in yield strength were marked with Δ, and reached the maximum yield strength A mark that retains 50% or more of the maximum proof stress even when the strain reaches 2% later, and a ◎ mark that has excellent toughness with almost no decrease in proof stress even when the strain exceeds 2%. It is represented by

Furthermore, FIG. 4 to FIG. 9 are graphs showing the influence of the fiber aspect ratio in each example and comparative example. According to this graph, the improvement effect regarding the strength and toughness of the cement-based ground improvement body can be evaluated as follows.
First, in the case of FIG. 4, 170 kg / m ³ of a cement-based hardener having a water cement ratio of 100% was mixed in silt, but the comparative example 1 having no fiber mixing was used as a matrix, and this had a diameter of 17 microns and a length of 20 mm ( Example 1 of the present invention in which polypropylene fiber P having an aspect ratio of 1190) was mixed by 1% by volume, while polypropylene fiber P, vinylon fiber B, and nylon fiber N were mixed in an aspect ratio of 210 to 600. The relationship between the stress and the strain in the tensile test and the bending test of Comparative Examples 2 to 6 each containing 1% by volume is shown.
It can be seen that Example 1 of the present invention retains a high yield strength even when a large strain occurs and exhibits excellent toughness.

In the case of FIG. 5, 200 kg / m ³ of cement-based hardener having a water cement ratio of 100% was mixed in the viscous soil, but the fiber of Comparative Example 7 having no fiber mixing was used as a matrix, and the fiber strength was 935 MPa and the diameter was 17 microns. The relationship between stress and strain in a tensile test and a bending test of a test material mixed with 1% by volume of the polypropylene fiber P with an aspect ratio of 400, 600, 800, 1000, 1200, 1786 with respect to the ground improvement body is shown.
In Example 4 of the present invention having an aspect ratio of 1000, the decrease in yield strength is maintained below 50% even when the strain reaches 2%. It can be seen that the inventive examples 3 and 2 having larger aspect ratios of 1200 and 1786 exhibit even better toughness.

FIG. 6 is a graph in which the aspect ratio and the toughness improving effect are confirmed by using polypropylene fiber P having a fiber strength of 647 MPa and a diameter of 11 microns in the same matrix of Comparative Example 7 as FIG.
In the same manner as in FIG. 5, Example 7 of the present invention with an aspect ratio of 1000 maintains a decrease in yield strength of less than 50% even when the strain reaches 2%. It can be seen that the inventive Examples 6 and 5 having larger aspect ratios of 1200 and 1770 exhibit very good toughness.

In the case of FIG. 7, 200 kg / m ³ of cement-based hardener with a water cement ratio of 100% mixed in silt is used as a matrix, and polypropylene fiber P having a fiber strength of 935 MPa and a diameter of 17 microns is used with an aspect ratio of 800, As 1200 and 1786, the relationship between the bending test stress and the bending / loading span of the test material mixed with a volume ratio of 1% is shown. In the case of Inventive Examples 9, 11 and 8 with aspect ratios of 1200 and 1786, even when the fiber mixing amount is 0.5%, the yield strength decrease when strain reaches 2% is maintained below 50%. It can be seen that it exhibits excellent toughness.

Finally, FIG. 8 shows a comparative example 17 in which a cement-based hardener having a water cement ratio of 100% is mixed with 300 kg / m ³ in sand and the comparative example 17 as a matrix, and has a fiber strength of 935 MPa, a diameter of 17 microns, The relationship between the stress of the bending test of Example 12 which mixed polypropylene fiber P of aspect ratio 1200 with a volume ratio of 1% with respect to a ground improvement body, and bending / loading span is shown.
As described above, according to the present invention, it is clear that excellent toughness and high strength can be obtained in any soil using the polypropylene fiber P.

  Although the present invention has been described based on the examples and test examples, the present invention is not limited to the configurations of the examples and test examples. It should be noted that the scope of the present invention includes a range of design changes, applications, and uses that are usually made by those skilled in the art without changing the object and gist of the present invention.

A and B are explanatory views schematically showing a fiber dispersion state and a stress transmission mechanism in general fiber reinforcement. A and B are explanatory views schematically showing a fiber dispersion state and a stress transmission mechanism in an example of the present invention. The figure of judgment of bending, tension, and toughness is shown. A and B are graphs showing the tensile test results and the bending test results of Example 1 of the present invention and Comparative Examples 1 to 6, respectively. A and B are graphs showing tensile test results and bending test results of Examples 2 to 4 and Comparative Examples 7 to 10 of the present invention. A and B are graphs showing the tensile test results and bending test results of Examples 5 to 7 and Comparative Examples 7 and 11 to 13 of the present invention. It is a graph which shows the bending test result of this invention Example 8, 9, and 11 and Comparative Examples 10, 15, and 16. FIG. It is a graph which shows the bending test result of this invention Example 12 and the comparative example 17. FIG.

Explanation of symbols

1 Fiber 2 Matrix 3 Crack

Claims (3)

In the ground improvement body manufactured by kneading soil and cement-based hardener,
A polypropylene fiber having a breaking strength of 200 to 1200 MPa and a length ratio (aspect ratio) with respect to the thickness of the fiber adjusted to 1000 or more so that the fiber and the fiber are entangled with each other by mixing and stirring, A high-strength, high-toughness cement-based ground improvement body by fiber reinforcement, comprising 0.4-2% in volume ratio and kneaded with soil to reinforce the matrix.   The high-strength, high-toughness cement-based ground improvement material by fiber reinforcement according to claim 1, wherein the polypropylene fiber has a diameter of 100 microns or less. 3. The high strength and high toughness cement-based ground improvement by fiber reinforcement according to claim 1 or 2, wherein the polypropylene fiber has a knot-like or massive anchor portion larger than the fiber diameter by 10 microns or more at both ends. body.

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