JP6168550B2 - Method for suppressing cracks in reinforced concrete, reinforced concrete, and method for constructing reinforced concrete - Google Patents

Description

  The present invention particularly relates to a technique for suppressing cracks in reinforced concrete.

Cracks in concrete structures include initial cracks due to cement hydration and dry shrinkage, a phenomenon in which moisture in the concrete dissipates over the long term. As shown in Table 1 below, countermeasures are taken for these cracks according to the crack countermeasure level.
Table-1
Countermeasure level Crack generation probability Safety factor γ _cr
If you want to prevent cracking 5% or less 1.85 or more If you want to limit the occurrence of cracks as much as possible 15% or less 1. Allow 40 or more cracks to occur, but want to limit the crack width so that it does not become a problem
50% or less 1.0 or more

  Here, the crack occurrence probability is the minimum value of the crack index. The crack index is an index representing the ease of cracking. The crack index is expressed by (tensile strength of concrete of a certain age) / (maximum principal tensile stress degree of concrete of a certain age). Recently, the crack index can be calculated by numerical analysis. For this reason, the crack index is synonymous with numerical evaluation for cracks. In general, the crack index is calculated by numerical analysis, and the maximum crack width is calculated using the "Concrete Standard Specification for Civil Engineering [Design]".

  By the way, when the factor which shows an effect with respect to a crack cannot be integrated in numerical analysis, evaluation cannot be performed by said numerical analysis. And even if it becomes clear that there is a place where the occurrence of cracks is a concern, until now, countermeasures have been mainly performed by a method of increasing the reinforcing bar ratio.

  The applicant of the present application has proposed a technique for suppressing cracking by a technique of arranging a glass fiber net instead of a technique of increasing the reinforcing bar ratio (see Patent Documents 1, 2, and 3).

JP 2011-137341 A JP 2012-132189 A JP2012-132190A

  However, it has been found that even the techniques proposed in Patent Documents 1, 2, and 3 are not satisfactory.

  Therefore, the problem to be solved by the present invention is to provide a technique capable of efficiently suppressing cracking of reinforced concrete at good workability and at low cost.

The present invention
A method for suppressing cracks in reinforced concrete,
Proposed method for suppressing cracks in reinforced concrete, wherein N (N is an integer of 1 or more) glass fiber nets are arranged so that the index represented by the following formula [I] satisfies a predetermined standard. To do.

The present invention
A method for suppressing cracks in reinforced concrete,
Preferably, a reinforced concrete characterized in that N (N is an integer of 1 or more) is the minimum number of glass fiber nets provided that the index represented by the following formula [I] satisfies a predetermined standard. A crack suppression method is proposed.

The present invention
A method for suppressing cracks in reinforced concrete,
Proposed method for suppressing cracking in reinforced concrete, wherein N (N is an integer of 1 or more) glass fiber nets are arranged so that the index represented by the following formula [II] satisfies a predetermined standard. To do.

The present invention
A method for suppressing cracks in reinforced concrete,
Preferably, a reinforced concrete characterized in that N (N is an integer of 1 or more) is the minimum number of glass fiber nets provided that the index represented by the following formula [II] satisfies a predetermined standard. A crack suppression method is proposed.

The present invention
A method for suppressing cracks in reinforced concrete,
Proposed method for suppressing cracks in reinforced concrete, wherein N (N is an integer of 1 or more) glass fiber nets are arranged so that the index represented by the following formula [III] satisfies a predetermined standard. To do.

The present invention
A method for suppressing cracks in reinforced concrete,
Preferably, a reinforced concrete characterized in that N (N is an integer of 1 or more) is the minimum number of glass fiber nets provided that the index represented by the following formula [III] satisfies a predetermined standard. A crack suppression method is proposed.

The present invention
A method for suppressing cracks in reinforced concrete,
Preferably, N (N is an integer of 1 or more) glass fiber nets are arranged so that the index represented by the following formulas [I] and [II] satisfy a predetermined standard. We propose a method for suppressing cracking.

The present invention
A method for suppressing cracks in reinforced concrete,
Preferably, N (N is an integer of 1 or more) glass fiber nets are arranged so that an index represented by the following formula [I] {III} satisfies a predetermined standard. We propose a method for suppressing cracking.

The present invention
A method for suppressing cracks in reinforced concrete,
Preferably, N (N is an integer of 1 or more) glass fiber nets are arranged so that the index represented by the following formulas [II] and [III] satisfy a predetermined standard. We propose a method for suppressing cracking.

The present invention
A method for suppressing cracks in reinforced concrete,
Preferably, N (N is an integer of 1 or more) glass fiber nets are arranged so that an index represented by the following formula [I] [II] [III] satisfies a predetermined standard. We propose a method for suppressing cracks in reinforced concrete.

The present invention
A method for suppressing cracks in reinforced concrete,
Preferably, a glass fiber net having a minimum number N (N is an integer of 1 or more) is provided while the index represented by the following formula [I] [II] satisfies a predetermined standard. We propose a method for suppressing cracks in reinforced concrete.

The present invention
A method for suppressing cracks in reinforced concrete,
Preferably, a glass fiber net having a minimum number of N (N is an integer of 1 or more) is provided while the index represented by the following formula [I] [III] satisfies a predetermined standard. We propose a method for suppressing cracks in reinforced concrete.

The present invention
A method for suppressing cracks in reinforced concrete,
Preferably, N (N is an integer of 1 or more) is provided with a minimum number of glass fiber nets while the index represented by the following formula [II] [III] satisfies a predetermined standard. We propose a method for suppressing cracks in reinforced concrete.

The present invention
A method for suppressing cracks in reinforced concrete,
Preferably, a glass fiber net having a minimum number of N (N is an integer of 1 or more) is provided while the index represented by the following formula [I] [II] [III] satisfies a predetermined standard. We propose a method for suppressing cracks in reinforced concrete.

Formula [I]
1-0.027 × (N · S ₂ / S ₁ ) × 100
Formula [II]
1 + 0.055 × (N · S ₂ / S ₁ ) × 100
Formula [III]
(1-0.027 × (N · S ₂ / S ₁ ) × 100) / (1 + 0.055 × (N · S ₂ / S ₁ ) × 100)
(In the formulas [I], [II], and [III], S ₁ is the total cross-sectional area of the reinforcing bar in the plane orthogonal to the longitudinal direction, and S ₂ is the cross-sectional area per one glass fiber net in the plane orthogonal to the longitudinal direction)

  In the above, the index represented by the formula [I] is preferably a value of 0.45 to 0.95. The index represented by the formula [II] is preferably a value of 1.10 to 2.00. The index represented by the formula [III] is preferably a value of 0.20 to 0.80.

In the above, (N · S ₂ / S ₁ ) is preferably 0.05 to 0.20. The reinforcing bar ratio is preferably 0.2 to 1%. The glass fiber net preferably has a width of 10 to 50 cm.

  In the above, the arrangement of the glass fiber net is preferably a laminated arrangement. The arrangement is preferably buried.

  The present invention proposes a reinforced concrete in which the method for suppressing cracking of the reinforced concrete is carried out.

The present invention is a method for constructing the reinforced concrete,
Rebar placement process in which rebars are placed in the mold,
A glass fiber net placement step in which a glass fiber net is placed in the mold,
The present invention proposes a method for constructing reinforced concrete comprising a concrete filling step in which concrete is filled in a mold after the placing step.

  Reinforced concrete cracks can be easily controlled at low cost.

Top view of an alkali-resistant glass fiber net Graph showing the relationship between crack index and maximum crack width Schematic of test specimen Schematic of test specimen Graph showing the effect of reducing crack width Graph showing crack dispersion effect Graph showing cracking suppression effect

Embodiments of the invention are described. The first invention is a method for suppressing cracks in reinforced concrete. This method is a method in which N (N is an integer of 1 or more) glass fiber nets are arranged so that the index represented by the formula [I] satisfies a predetermined standard. Alternatively, N (N is an integer of 1 or more) glass fiber nets are arranged so that the index represented by the formula [II] satisfies a predetermined standard. Alternatively, N (N is an integer of 1 or more) glass fiber nets are arranged so that the index represented by the formula [III] satisfies a predetermined standard. Preferably, N (N is an integer of 1 or more) glass fiber nets are arranged so that the index represented by the above formulas [I] and [II] satisfies a predetermined standard. Preferably, N (N is an integer of 1 or more) glass fiber nets are arranged so that the index represented by the above formula [I] [III] satisfies a predetermined standard. Preferably, N (N is an integer of 1 or more) glass fiber nets are arranged so that the index represented by the formula [II] [III] satisfies a predetermined standard. Preferably, N (N is an integer of 1 or more) glass fiber nets are arranged so that the index represented by the above formula [I] [II] [III] satisfies a predetermined standard. . Preferably, the glass fiber net having a minimum number N (N is an integer of 1 or more) is provided while the index represented by the above formula satisfies a predetermined standard. The arrangement of the glass fiber net is preferably a laminated arrangement. The arrangement is preferably buried. The index represented by the formula [I] was preferably a value of 0.45 to 0.95. In particular, it was 0.55 or more. In particular, it was 0.85 or less. The index represented by the formula [II] was preferably a value of 1.10 to 2.00. In particular, it was 1.20 or more. In particular, it was 1.90 or less. The index represented by the formula [III] was preferably a value of 0.20 to 0.80. In particular, it was 0.30 or more. In particular, it was 0.70 or less. (N · S ₂ / S ₁ ) was preferably 0.05 to 0.20. When (N · S ₂ / S ₁ ) is less than 0.05, the glass fiber net required for the arrangement is reduced, so that it may be difficult to arrange effectively, and the crack suppression effect May be so small that the effect is not clearly produced. On the other hand, if (N · S ₂ / S ₁ ) exceeds 0.20, the number of glass fiber nets necessary for the arrangement increases, and therefore, when arranged too densely, there is a risk of hindering concrete construction. Moreover, since it may be economical to take measures to increase the reinforcing bars, it is not realistic. The reinforcing bar ratio was preferably 0.2 to 1%.

  The second invention is reinforced concrete. The reinforced concrete is a reinforced concrete formed by the method for suppressing cracking of the reinforced concrete.

  The third invention is a method for constructing reinforced concrete. The method for constructing the reinforced concrete includes a reinforcing bar arranging step in which a reinforcing bar is arranged in a mold, a glass fiber net arranging step in which a glass fiber net is arranged in the mold, and the inside of the mold after the arranging step. And a concrete filling step in which concrete is filled.

The glass fiber net is in particular an alkali resistant glass fiber net. A part of an example of this net is shown in FIG. Yarn in the present invention, (in FIG. 1, the vertical direction) longitudinally S ₂ (cross-sectional area per sheet) cross-sectional area of the glass fiber nets in the plane perpendicular to, in FIG. 1, for example, projecting the upper end side Is the sum of the areas of the end faces. The net preferably had a width (in the left-right direction in FIG. 1) of 10 cm to 50 cm. If the net width was too short, the crack suppression effect was small unless so many nets were used. If a large number of nets must be used, the workability is reduced accordingly. On the contrary, when the net width is too long, the filling property at the time of placing the concrete is lowered. For this reason, an alkali-resistant glass fiber net having the above-described size was preferred.

  The net is preferably a first yarn (for example, an alkali-resistant glass fiber yarn) and a second yarn (for example, an alkali-resistant glass fiber yarn) having a shorter length than the first yarn. It is structured like a net. And, preferably, (tensile stiffness of the first yarn) / (tensile stiffness of the second yarn) = 1.5-30. The net is a yarn existing in at least two directions (simply referred to as a yarn, but this is a fiber itself, a plurality of fibers twisted, or a plurality of fibers twisted). The twisted one is a twisted one, or a string or a narrow sheet-like one) is a crossed net-like one. The shape surrounded by this intersection (intersection) (opening shape: window shape) is, for example, a square, a rhombus, or a rectangle. In addition to the quadrangular shape, other polygonal shapes may be used. However, since it is expensive to produce a net having a shape other than the quadrangular shape, the opening shape is preferably quadrangular (square or rectangular). In particular, it is a rectangular net. Yarn existing in the first direction (first yarn) and yarn existing in the second direction (second yarn: second yarn having a shorter length than the first yarn) ) Preferably has the following relationship: The two directions are, for example, a vertical direction and a horizontal direction. When an attempt is made to produce a net, generally, the yarn in the longitudinal direction is the warp and the yarn in the short direction is the weft. (Tension stiffness of the first yarn (for example, longitudinal yarn: warp)) / (Tension stiffness of the second yarn (for example, lateral yarn: weft)) is preferably 1.5 to 30 there were. More preferably, the value was 1.8 or more. More preferably, the value was 5 or more. More preferably, the value was 25 or less. More preferably, the value was 20 or less. That is, the effect of suppressing cracking of the concrete by the net configured so that (tensile stiffness of the first yarn) / (tensile stiffness of the second yarn) becomes the above value was great. The tensile rigidity of the yarn can be obtained by (yarn elastic modulus) × (yarn cross-sectional area). When several fibers are twisted to form a thread, if the cross section is taken, there is a gap between the fibers in the cross section. However, in the case of (tensile stiffness of warp) / (tensile stiffness of weft), there is almost no problem even if the gap is neglected in the cross-sectional area of the yarn. Therefore, the cross-sectional area of the yarn is an area determined by the outer shape in the cross-section. This is the value obtained in. In order to configure the net so that (the tensile stiffness of the first yarn) / (the tensile stiffness of the second yarn) becomes the above value, each of the yarns whose tensile stiffness ratio becomes the above value should be selected. However, this can be achieved by considering the width of the yarn and the number of yarns when using an equivalent yarn. For example, when substantially the same yarn is used, this can be achieved by using a plurality of first yarns. That is, this can be achieved by knitting the net with a ratio of M (M is an integer of 2 or more) of the first yarn to one second yarn.

The net preferably has a ratio (total area of the opening having a size of 10 mm or more in the opening and a size of 10 mm or more in the net) / (total area of the net) of 0.2 to 0.9. . That is, from the viewpoint of the crack suppression effect, the net is preferably (total area of the opening having a size of 10 mm or more and 10 mm or more in the opening in the net) / (total area of the net). .2 to 0.9. More preferably, the value is 0.4 or more. The value was 0.8 or less. Magnitude of the lateral 10mm or more openings in the longitudinal 10mm or more (rectangular conversion area), ^preferably, was 100mm ² ~10000mm 2. In particular, when converted into a rectangular shape, the long side was preferably 10 mm or more. And it was 400 mm or less. More preferably, it was 15 mm or more. And it was 300 mm or less. Especially preferably, it was 20 mm or more. And it was 200 mm or less. From the viewpoint of the effect of suppressing cracks, the net is preferably a net having four or more intersections between the first yarn and the second yarn per 10 cm square. More preferably, it was 20 or more. And it was 500 or less. Most preferably, it was 40 or more. And it was 300 or less. This is because when the opening is as described above, it is difficult to adversely affect the filling of concrete or the like. Moreover, the width of the yarn was preferably about 0.1 to 30 mm. More preferably, it was 1 mm or more. And it was 10 mm or less. That is, since the strength is poor with a thread that is too small, conversely, with a thread that is too wide, the integrity of the mass concrete body located on both sides of the crack suppression material is reduced so much. Dimensional width yarns were preferred. Since the second yarn (weft yarn) having a short length is waved at the intersection point and positioned above and below the first yarn (warp yarn) having a long length, the first yarn (warp yarn) is also provided. It was preferable to make the thickness of the first yarn (warp yarn) thicker than the thickness of the second yarn (weft yarn). In addition, it was preferable to make the width of the first yarn (warp yarn) wider than the width of the second yarn (weft yarn).

The net is made of glass fiber. Among these, from the viewpoint of affinity with cement, a net made of alkali-resistant glass fiber (for example, glass fiber containing 14% by mass or more of zirconium oxide (ZrO ₂ )) was preferred.

  The reason for suppressing cracks in reinforced concrete by arranging glass fiber nets (especially buried) is as follows. Cracks in reinforced concrete are basically suppressed by the embedded steel bars. If the number of reinforcing bars increases, cracking is suppressed accordingly. This can also be understood from FIG. That is, the larger the reinforcing bar ratio, the smaller the maximum crack width. However, in a reinforced concrete structure (structure), the number of reinforcing bars is determined in advance at the design stage. In addition, it is not always preferable to increase the number of reinforcing bars darkly from the viewpoint of bar arrangement work efficiency and cost. For this reason, the present applicant has proposed the arrangement (particularly embedding) of the glass fiber net. However, until now, how much glass fiber nets should be arranged (especially embedded) has not been studied much. Even if the glass fiber net is attached to the reinforcing bar, it is expected that it is not preferable from the viewpoint of workability and cost if it is attached darkly. Therefore, the present invention has been made from the viewpoint of how much and how a glass fiber net is disposed (especially embedded) to effectively suppress cracks in reinforced concrete. If a glass fiber net is disposed (particularly embedded) so as to satisfy the above formulas [I] [II] and / or [III], the reinforced concrete can be manufactured with good workability and at a low cost. It was found that cracking of the steel can be suppressed.

  The cement constituting the reinforced concrete of the present invention may be any cement. For example, hydraulic cement. Specifically, for example, Portland cement (various Portland cements that are normal, early strength, very early strength, low heat, and moderate heat) can be used. Examples include eco-cement. Furthermore, various mixed cements in which, for example, fly ash, blast furnace slag, silica fume, limestone fine powder, or the like is mixed with the cement are also included. Alumina cement is also included. A super fast cement is also included. Furthermore, various admixtures and aggregates are used as appropriate. Examples of admixtures include cement polymers, expansive materials, gypsum, cement dispersants (water reducing agents, AE water reducing agents, high performance AE water reducing agents, high performance water reducing agents, fluidizing agents, etc.), waterproof materials, rust preventive agents, Shrinkage reducing agent, thickener, water retention agent, pigment, fiber, water repellent agent, anti-whitening agent, quick setting agent (material), quick hardening agent (material), setting retarder, antifoaming agent, foaming agent, blast furnace Slag fine powder, stone powder, silica fume, volcanic ash, air entraining agent, surface hardening agent and the like can be mentioned. Examples of the aggregate include river sand, land sand, sea sand, crushed sand, quartz sand, river gravel, land gravel, crushed stone, artificial aggregate such as perlite and foamed glass particles (glass balloon), slag aggregate, and the like.

  Hereinafter, more specific description will be given. However, the present invention is not limited to the following description. Various modifications and application examples are included as long as the features of the present invention are not greatly impaired.

  An alkali-resistant glass fiber net (hereinafter, simply abbreviated as HN) having the structure described above and shown in FIG. 1 was prepared. In order to confirm the effect of reducing the crack width by this HN, a test body was produced in which only one crack was generated by bending loading. Using this specimen, the crack width was evaluated by bending loading. The test was conducted with or without HN. The effect of reducing the crack width was confirmed by relative evaluation of the crack width. FIG. 3 shows an outline of the specimen. The test body has a length of 700 (mm), a width of 200 (mm), and a height of 100 (mm). The cover thickness of the reinforcing bar is 35 (mm). In the center of the test body, a notch (cross-sectional defect: −7 mm) is provided to prevent cracks from being dispersed and generated. HN is laid on a reinforcing bar and fixed with a wire.

  In order to confirm the effect of HN crack dispersion, a test specimen was produced in which a plurality of cracks were generated by bending loading. Using this specimen, the crack width was evaluated by bending loading. The test level was performed with or without HN. The effect of reducing the crack width was confirmed by relative evaluation of the crack width. FIG. 4 shows an outline of the specimen. The test body has a length of 700 (mm), a width of 200 (mm), and a height of 100 (mm). The cover thickness of the reinforcing bar is 35 (mm). HN is laid on a reinforcing bar and fixed with a wire.

Table 2 shows the characteristics of the reinforcing bars and HN used in the above example.
Table-2

The test results are shown in Table 3 and FIGS.
Table-3

Regarding the effect of reducing the crack width, from the bending load test using the specimen shown in FIG. 3, from the ratio of each bending crack width generated at the same bending load after the crack generation until the reinforcing steel reaches the yield strain, the formula (1 ) Was used to obtain an index W representing the effect of reducing the crack width.
Formula [1]
W = W _HN / W _PL
W _PL : Bending crack width generated in a specimen not using HN W _HN : Bending crack width occurring in a specimen using HN

About the crack dispersion | distribution effect, it evaluated using the area of the part enclosed by the load-displacement curve from the bending loading test by the test body of FIG. An index D representing a crack dispersion effect was determined from the area until the yield of the reinforcing bar in the load-displacement curve with and without HN, using Equation (2).
Formula [2]
D = D _HN / D _PL
D _PL : Area up to the reinforcing bar yield load in the load-displacement curve when HN is not used D _HN : Area up to the reinforcing bar yield load in the load-displacement curve when using HN

The index W representing the effect of reducing the crack width indicates the effect of reducing the total crack width when HN is used. The index D indicating the crack dispersion effect indicates the number of cracks. As shown in Equation (3), by dividing the total crack width by the number of cracks, crack suppression for unreinforced concrete when HN is used. The effect (cracking suppression coefficient α) is obtained quantitatively.
Formula [3]
α = W / D

From these Table-3 and FIGS. 5, 6 and 7, it can be seen how much cracking can be suppressed by using HN. That is, it can be understood that cracking of reinforced concrete can be effectively suppressed by configuring as in the present invention.

Claims (9)

A method for suppressing cracks in reinforced concrete,
N (N is an integer of 1 or more) glass fiber nets are arranged so that the index represented by the following formula [I] is a value of 0.45 to 0.95. Crack control method.
Formula [I]
1-0.027 × (N · S ₂ / S ₁ ) × 100
(In the formula [I], S ₁ is the total cross-sectional area of the reinforcing bar in the plane orthogonal to the longitudinal direction, and S ₂ is the cross-sectional area per one glass fiber net in the plane orthogonal to the longitudinal direction). A method for suppressing cracks in reinforced concrete,
N (N is an integer of 1 or more) glass fiber nets are arranged so that the index represented by the following formula [II] is a value of 1.10 to 2.00. Crack control method.
Formula [II]
1 + 0.055 × (N · S ₂ / S ₁ ) × 100
(In the formula [II], S ₁ is the total cross-sectional area of the reinforcing bar in the plane orthogonal to the longitudinal direction, and S ₂ is the cross-sectional area per one glass fiber net in the plane orthogonal to the longitudinal direction). A method for suppressing cracks in reinforced concrete,
N (N is an integer of 1 or more) glass fiber nets are disposed so that the index represented by the following formula [III] is a value of 0.20 to 0.80. Crack control method.
Formula [III]
(1-0.027 × (N · S ₂ / S ₁ ) × 100) / (1 + 0.055 × (N · S ₂ / S ₁ ) × 100)
(In the formula [III], S ₁ is the total cross-sectional area of the reinforcing bar in the plane orthogonal to the longitudinal direction, and S ₂ is the cross-sectional area per one glass fiber net in the plane orthogonal to the longitudinal direction) N (N is an integer of 1 or more) cracking of claims 1 to 3 or of reinforced concrete, characterized in that glass fiber net minimum number is arranged suppression method in which the index satisfies the condition . The method for suppressing cracks in reinforced concrete according to any one of claims 1 to 4, wherein a glass fiber net is laminated and disposed. (N · S ₂ / S ₁ ) is 0.05 to 0.20, The method for suppressing cracks in reinforced concrete according to any one of claims 1 to 5. The method for inhibiting cracking of reinforced concrete according to any one of claims 1 to 6, wherein the reinforcing bar ratio is 0.2 to 1%. The method for suppressing cracks in reinforced concrete according to any one of claims 1 to 7, wherein the glass fiber net has a width of 10 to 50 cm. A method for constructing reinforced concrete in which the method for inhibiting cracking of reinforced concrete according to any one of claims 1 to 8 is implemented ,
Rebar placement process in which rebars are placed in the mold,
A glass fiber net placement step in which a glass fiber net is placed in the mold,
A method for constructing reinforced concrete, comprising a concrete filling step in which concrete is filled into a mold after the placing step.

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