JP4545667B2 - Floor slab repair method using buried formwork - Google Patents

Description

  The present invention relates to a floor slab repair method in which a part of a floor slab supported by a beam is removed and the part is replaced with a new floor slab placed using an embedded formwork.

When the cement-based material structure deteriorates with time, repairs such as surface treatment, cathodic protection, cross-sectional repair, and FRP adhesion are performed according to the degree of deterioration. In particular, cross-sectional repair is the most commonly applied repair method for concrete structures, and the process is generally as follows.
(1) Remove the salt-containing concrete around the reinforcing bars.
(2) Remove rust on the reinforcing bar surface.
(3) Apply anticorrosion coating to the exposed steel bars.
(4) Repair the missing partial cross section.
(5) Cover the concrete surface including the old and new sections.

However, cross-sectional repair has the following drawbacks.
The construction period tends to be long. In other words, the existing cross-section repair work required many processes such as erection, dismantling and removal of work scaffolds, lifting work, rust removal and anti-corrosion coating of reinforcing bars, joint reinforcement, formwork installation, restoration material filling, and surface coating. Many types of materials are used. For this reason, construction is complicated and requires many man-days.
Macrocell corrosion is likely to occur. That is, when a reinforcing bar exists between the updated new material and the existing material, there is a high possibility that a so-called macro cell is formed due to a difference in potential between different materials, a corrosion current is generated, and re-deterioration proceeds.

  In cement-based material structures such as piers, railway bridges, and road bridges that use floor slabs supported by beams as members, repair work on floor slabs that are likely to deteriorate due to bending deformation is relatively earlier than other general members. There are many cases where it is necessary. In addition, the floor slab is accompanied by other factors that make the construction more difficult. That is, in order to repair the lower surface of the floor slab that is susceptible to deterioration, it is assumed that a scaffold is provided below the floor slab and construction is performed from below. For this reason, it is necessary to build and remove the scaffolding, which further extends the construction period and increases costs. Also, especially on jetty, work from under the slab is often affected by waves, and the construction time is often limited by the tide level and weather.

  For this reason, it is more reasonable to adopt a repair method that removes a deteriorated floor slab and replaces it with a new floor slab, rather than extending the life by repairing the cross section, especially when the bottom surface of the floor slab deteriorates. In some cases. As one of the methods, a method of replacing with a precast floor slab can be considered. According to the precast floor slab, it is possible to omit the work of installing and placing a formwork on the site, and it is expected to have a particularly great effect on a pier where it is difficult to construct a scaffold. Patent Document 1 discloses a construction method in which a plurality of precast concrete plates are arranged side by side so as to be supported by a beam. At that time, in order to prevent a gap from being formed between the precast concrete plates due to the bending, a reinforcing method is adopted in which a CFRP plate is attached to the upper surface and the lower surface to reduce the bending amount.

JP 2002-206305 A

  The installation method of the precast floor slab using the reinforcing method as in Patent Document 1 is easy to apply when the structure itself is newly designed and constructed, but the deteriorated floor slab is removed to form a new floor slab. The situation is different in the repair work to be replaced. That is, when the structure itself is newly designed, a precast floor slab suitable for the design may be prepared. However, when removing a deteriorated floor slab, the form to be removed is not necessarily uniform depending on the site conditions, and it is usually difficult to complete the intended replacement using the precast floor slab as it is. is there. Further, since it is basically difficult to pass the reinforcing bars between the precast slabs or between the precast slab and the existing floor slab, some reinforcement work is required to improve the strength at the joint. Therefore, it is often desirable to adopt a repair method based on site placement in order to perform appropriate repairs according to the site conditions.

  However, in order to repair the floor slab by on-site placement as described above, it is often difficult to implement a scaffold or a formwork because it is not always easy. In addition, plate-like members such as floor slabs are particularly susceptible to deterioration on the lower surface side due to bending, and even if a new floor slab is placed and repairs are completed, repairs are required again in a relatively short period of time. Will repeat.

  In view of such a current situation, the present invention is a rational repair that can remarkably improve workability and greatly improve the durability of the lower surface side due to bending in the floor slab repair method by on-site placement. It is about developing and providing a method.

  As a result of various studies, the inventors have remarkably suppressed the deterioration of the lower surface due to bending in a new floor slab, and improved the workability by using a precast plate-like member made of a highly durable cementitious material. It has been found that a construction method in which a floor slab made of a normal cement-based material is placed thereon is used as an embedded form forming the lower surface and is extremely advantageous.

That is, in the present invention, the existing floor slab supported by the beam is removed while leaving a part thereof on the beam, and the precast plate-like member comprising the following (A) is used as an embedded formwork, on which the cement-based material A floor slab repair method is provided in which a new floor slab is constructed in the removed portion by placing a slab.
(A) A hardened body of cement kneaded material containing 10 to 85 parts by mass of γ belite with respect to 100 parts by mass of cement , in which a short fiber is dispersed and blended, and a long fiber with “twist” is embedded A composite fiber reinforced cement-based material disposed at a position having a depth of 5 to 25 mm from the surface on the lower surface side (excluding those in which prestress due to the long fibers is introduced) .
Here, the “cement-based material” is a hardened material of mortar or concrete. γ Belite is one type of dicalcium silicate represented by 2CaO · SiO ₂ as described later, and may be expressed as “γC ₂ S”. In addition to 2CaO · SiO ₂ , oxides such as Al ₂ O ₃ , Fe ₂ O ₃ , MgO, Na ₂ O, K ₂ O, TiO ₂ , MnO, ZnO, and CuO are dissolved as impurities in γ belite. However, γ belite having such a mineral as a solid solution is also included in the γ belite referred to in the present invention.

Moreover, in this invention, the floor slab repair method which has the process of the following [1]-[3] is provided as a method for carrying out removal of a degraded floor slab and new floor slab efficiently.
[1] The existing floor slab supported by the beam is removed while leaving a part thereof on the beam, and at that time, the existing floor slab in which a part of the reinforcing bar existing in the existing floor slab is left on the beam is removed. Leave it exposed from the part of
[2] The precast plate-like member made of (A) is arranged in the removed portion to make it an embedded formwork, and a pre-assembled reinforcing bar is placed above the embedded formwork so as to expose the above. A new rebar structure is constructed by joining with the rebar left in
[3] A new floor slab is constructed by placing a cement-based material on the embedded formwork so that the new reinforcing bar structure is arranged inside.

  At that time, a support body is temporarily installed on a portion of the existing floor slab positioned on the beam in advance, and a suspension girder is temporarily installed above the existing floor slab via the support body and removed in the above [1]. A method of temporarily suspending a load on a hanging girder by hanging at least one or more of a floor slab part, an embedded formwork arranged in [2], and a reinforcing bar arranged in [2] from the hanging girder Implementation is particularly effective.

As the long fiber (A ), a CFRP stranded wire having an outer diameter of 0.5 to 2.0 mm is preferably used. Moreover, as a precast plate-shaped member, what has a carbonation layer with an average carbonation depth of 5 mm or more in the surface layer part which becomes the lower surface side of an embedding formwork becomes a suitable object.
Here, the carbonation depth can be evaluated by the depth from the surface of the region that does not turn red when a 1% phenolphthalein solution is sprayed on the fractured surface where the cementitious material is split.

  According to the present invention, in the repair method for replacing a deteriorated floor slab with a new floor slab, a precast plate-like member is disposed as an embedded formwork in a portion corresponding to the bottom of the floor slab. Workability at the time of construction was greatly improved. Since the precast plate-like member is made of a cementitious material containing γ belite, the densification of the surface layer due to carbonation is exerted, Ca component leaching, water, chloride, etc. The resistance to the invasion of the material is significantly increased. In particular, in the case of using a precast plate-like member for which composite reinforcement of short fibers and long fibers is used, cracks on the lower surface that occur over time due to bending are finely dispersed, and infiltration of water, chloride, and the like is further less likely to occur.

In addition, according to the method of temporarily suspending structural members etc. during renovation work by temporarily installing a hanging girder, workability is improved even on piers where it is difficult to install scaffolding and struts. This is advantageous in terms of cost. In comparison with the cross-section repair method, in the case of the method of the present invention, the construction is basically performed from the top surface, is hardly affected by waves and the like, and the labor for erection and removal of the scaffold can be saved.
Therefore, the present invention is expected to be widely used as a repair method for floor slabs exposed to harsh environments such as jetty.

A typical cement, alite: 3CaO · SiO ₂ (composition formula C ₃ S), belite: 2CaO · SiO ₂ (composition formula C ₂ S), aluminate: 3CaO · Al ₂ O ₃ (composition formula C ₃ A), ferrite: cement mineral such as 4CaO.Al ₂ O ₃ .Fe ₂ O ₃ (composition formula C ₄ AF) is included. Among these, belite is one of the main mineral components of Portland cement, and is considered to have functions of reducing heat of hydration and drying shrinkage and increasing chemical resistance.

Belite is a kind of dicalcium silicate containing CaO and SiO ₂ as main components, and there are α-type, α′-type, β-type, and γ-type, each having different crystal structure and density. Of these, α-type, α′-type and β-type react with water and exhibit hydraulic properties. On the other hand, the γ-type has characteristics that it does not show hydraulic properties and reacts with carbon dioxide. Ordinary cements such as Portland cement basically do not contain this γ-type belite (γ belite).

  According to recent studies by the present applicants, it has been found that carbonation of a cementitious material using γ belite can remarkably densify the surface layer in addition to improving the strength level. And it was confirmed that the densified surface layer portion has very high resistance to Ca leaching and is excellent in chloride shielding effect. Such a cementitious material exhibits excellent durability over a long period of time, and the present applicants previously proposed as Japanese Patent Application No. 2004-375549.

Although there are many unexplained parts about the mechanism by which the hardened cement enriched with γ-belite is densified with carbon dioxide or the like, it is considered as follows. That is, when the normal cement curing body is carbonation (neutralization) is Ca (OH) ₂ produced by a hydration reaction of cement is become CaCO ₃ reacted with carbon dioxide gas, cement When a large amount of γ belite exists in the cured product, the γ belite does not hydrate and reacts directly with carbon dioxide gas or the like to generate a large amount of CaCO ₃ and SiO ₂ . Furthermore, Ca (OH) ₂ generated by the cement hydration reaction also reacts with carbon dioxide or the like to become CaCO ₃ . For this reason, it is considered that a large amount of reaction product is generated at an early stage as compared with a normal hardened cement body, which fills voids in the hardened cement body and becomes dense.

  In the present invention, a precast plate-like member (for example, having a thickness of 15 to 50 mm) made of such a durable cement-based material is used for the embedded form forming the lower surface of the new floor slab. The lower surface of the floor slab undergoes bending deformation during use as a structural member, and tensile stress is generated. For this reason, cracks tend to occur over time. In particular, the slab lower surface is exposed to high humidity especially on a jetty, and a substance such as chloride that causes corrosion of the reinforcing bars is likely to adhere. In this case, by configuring the lower surface with an embedded formwork using γ belite, the cementitious matrix densified by carbonation produces a great resistance to intrusion of chloride and the like, and the durability is improved. . Carbonation is preferably performed by forcibly carbonizing at the stage of producing the precast member, but can be naturally carbonated by carbon dioxide in the atmosphere after the start of use as an embedded formwork. The carbonation depth is desirably 5 mm or more.

When the carbonation treatment is forcibly performed, for example, a method in which the surface of the cement hardened body is brought into contact with a carbonation substance (a substance capable of supplying CO ₂ , CO ₃ ²⁻ , HCO ₃ ^−, etc.) can be employed. Carbonated substances include carbon dioxide, supercritical carbon dioxide, dry ice, carbonates such as sodium carbonate, potassium carbonate and iron carbonate, bicarbonates such as sodium bicarbonate, potassium bicarbonate and iron bicarbonate, Examples include carbonated water. Appropriate moisture is required for the carbonation treatment. The carbonation temperature is preferably 20 ° C. or higher, more preferably 30 ° C. or higher.

The timing of the carbonation treatment is preferably performed after the cementitious material is sufficiently cured (for example, after demolding). Compressive strength of concrete in the hardened cement body is preferably performed carbonation process since when it reaches 20 N / mm ² or more. It is more preferable that the time is after 30 N / mm ² or more. When carbonation is performed in a state where the compressive strength is less than 20 N / mm ² , the carbonation depth (thickness of the carbonation region) can be 0.5 mm or more, but the densification is insufficient. In some cases, it is difficult to sufficiently provide resistance to Ca elution and salt damage. In addition, when the carbonation treatment is performed before the concrete is hardened yet, the target cured product (durable cement material) in the present invention cannot be obtained at all.

  The precast plate-like member to be used in the present invention is a hardened cement cement body containing 10 to 85 parts by mass of γ belite with respect to 100 parts by mass of cement. In the case where γ belite is included in this range, durability is improved by densification when carbonized. In order to realize particularly high durability, a hardened cement cement containing 30 to 85 parts by mass of γ belite with respect to 100 parts by mass of cement is preferable, and 50 to 85 parts by mass, and more preferably 70 to 85 parts by mass. preferable

  A general Portland cement etc. can be used for the cement used for a precast plate-shaped member. There are no particular restrictions on the admixture material, the aggregate, and the like, and a generally known amount may be blended in a predetermined amount. As the γ belite, a commercially available product, a product synthesized by blending 2 mol of calcium carbonate and 1 mol of silicon dioxide and firing at around 1450 ° C. can be used. Alternatively, a steelmaking slag containing a large amount of γ belite can be used. It is desirable to use γ belite having a Blaine specific surface area of 1300 to 8000, preferably 1300 to 3000. What is necessary is just to set compounding ratios, such as an admixture material and an aggregate, by making gamma belite into cement substitution. When particularly excellent durability / reliability is required, it is advantageous that the cemented cement itself has a high density, and for that purpose, the water powder ratio is 20 to 50%, preferably 25 to 35%. A hardened cemented product of kneaded material is a suitable target. The water powder ratio is a mass ratio of water and a powder component. The powder here includes cement, γ belite, and admixture, and excludes aggregates. In order to improve workability and further densify, fly ash can be added by 10-30% replacement of the binder (including γ belite, the same applies hereinafter) and silica fume can be added by 0-10% replacement of the binder. An expansion agent or a shrinkage reducing agent can also be used as a countermeasure against cracking.

Further, precast plate-like member used in the present invention shall be the short fiber reinforced cementitious material. As the short fibers, carbon short fibers, stainless fibers, wollastonite, glass fibers and the like can be used, but carbon short fibers made of CFRP stranded wires can be suitably used. The CFRP stranded wire is of the same quality as the later-described long fibers, and those having a length of 10 to 50 mm, preferably 20 to 40 mm can be suitably used. Such carbon short fibers are preferably blended in an amount of about 0.75 to 2.0% by volume in the kneaded product before placing.

The precast plate member of the present invention is obtained by a composite reinforced with short fibers and long fibers. Specifically, in the above-mentioned cementitious material reinforced with short fibers, long fibers with “twist” are placed along the surface at a depth of 5 to 25 mm from the surface on the lower surface side of the embedded formwork. Arrange. That is, it arrange | positions so that the position of the center (axis) of the said long fiber may be 5-25 mm in the distance from the surface. However, it is desirable that the cover thickness (distance from the cementitious material surface to the long fiber surface) be 3 mm or more. For example, a CFRP stranded wire is preferably used as the long fiber. The CFRP stranded wire is a stranded wire of carbon fiber reinforced resin (Carbon Fiber Reinforced Plastics). The reason for requiring “twist” is to exert an anchor effect with the cementitious matrix. It may be “one stranded wire” obtained by flattening one fiber bundle and then twisting it, or “two stranded wire” obtained by twisting together two fiber bundles. Alternatively, a plurality of fiber bundles may be combined and twisted.

  The long fibers are preferably arranged so that the axial direction has a range of ± 45 ° with respect to the direction of the main tensile stress acting near the surface of the precast plate-like member. The direction of the main tensile stress can be judged from the direction of cracks that occur during use. That is, the direction perpendicular to the average direction of cracks is the main tensile stress direction. It is effective to contain as many long fibers as possible in the axial direction near the direction of the tensile stress. For example, two or more long fibers may be arranged at intervals of 20 to 300 mm in the direction of the main tensile stress direction ± 45 °. However, when there are two main directions of tensile stress (when cracks are generated in both the vertical and horizontal directions) or when particularly improving the reliability of the structure, two or more long fibers are spaced at intervals of 20 to 300 mm. It is good to arrange | position along the said surface at intervals of 20-300 mm while arrange | positioning along the surface substantially in parallel with each along the direction orthogonal to them. Here, “perpendicular” means forming an angle of 90 ° ± 20 °.

Regarding the shape of the long fibers, those having a twist pitch L of 3 to 25 mm, an outer diameter D ₁ of 0.5 to 2.0 mm, and a concavo-convex diameter ratio D ₂ / D _{1 of} 0.5 to 0.95 mm. desirable.
FIG. 1 schematically shows the shape of a stranded wire. This is an example of a single stranded wire. The twist pitch L is an interval between adjacent convex vertexes, and the outer diameter D ₁ and the inner diameter D ₂ are a maximum diameter at the convex portion and a minimum diameter at the concave portion, respectively. This long fiber does not bear the strength as a structure, unlike the reinforcing material used in the conventional “strength reinforcing type” member such as reinforced concrete. Therefore, it is possible to use an extremely fine stranded wire having an outer diameter D ₁ shown in FIG. 1 of about 1 mm.
The short fibers dispersed and blended in the precast plate-like member can be the same as the long fibers. By doing so, the cost merit that the material can be used with short fiber and long fiber is born.

  When long fibers with such a twist are arranged substantially parallel to the surface at the predetermined depth, the anchoring effect to the cementitious matrix is brought about by the unevenness of the “twist” around the long fibers. When a tensile stress having a component in the axial direction is applied to the matrix around the long fiber, even if a crack occurs at a certain location, resistance acts against the separation of the matrix on both sides sandwiching the crack. It becomes like this. Therefore, many starting points of cracks are generated in the axial direction of the long fiber, and as a result, the cracks have a shape in which cracks with small “width” are dispersed. As long as the long fibers do not break, the anchor effect provided in the periphery acts almost evenly in the axial direction of the long fibers, so that it is very unlikely that a wide crack will occur locally. That is, the effect of reducing the crack width by the long fibers is extremely stable. According to detailed studies by the inventors, such a crack width reduction effect of long fibers is remarkably exhibited in cement-based materials reinforced with short fibers. The combined effect of the short fibers and long fibers brings about a remarkable effect of reducing the crack width.

Hereinafter, the concrete implementation method of this invention is illustrated by making into an example the case where the floor slab of an existing structure (pier) is repaired.
[Manufacture of precast plate-like members]
An example of producing a 6000 ^L × 2000 ^W × 30 ^t (mm) concrete panel reinforced with short fibers and long fibers as a precast plate-like member used as an embedded formwork will be described. For example, the following can be used as long fibers, short fibers, and concrete.

<Long fiber>
A carbon fiber bundle composed of 12,000 filaments (tensile strength: 4900 MPa, tensile elastic modulus: 230 GPa) is twisted on a “single strand”, epoxy resin (100 parts by mass of a bisphenol A type epoxy resin, and a curing agent) CFRP twisted wire impregnated with 22 parts by mass of aromatic amine) and heat-cured at 150 ° C. for 2 minutes. Twisting pitch L: 10 mm, outer diameter D _1: 1.4 mm, inner diameter D _2: 1.2 mm, the carbon fiber content: 65% by volume, the cross-sectional area 1.7 mm ^2.
<Short fiber>
The same CFRP stranded wire as the above-mentioned long fiber cut to a length of 20 mm

<Concrete of precast plate-like member>
For example, low heat Portland cement, γ belite, fly ash and silica fume are mixed at a mass ratio of 45: 35: 20: 5, the water powder ratio is 30%, and the s / a (fine aggregate ratio) is 46%. Make a concrete kneaded mixture so that The above short fibers are added to the mixture so as to be 2% by volume and mixed with stirring. Blaine specific surface area of γ belite powder is, for example, 1800 cm ² / g.

  The above-mentioned long fibers are fixed to the mold and stretched from the lower surface side, for example, at a position of 10 mm. In this panel, the L direction (longitudinal direction) is the main tension direction, and it may be considered that the main tensile direction also exists in the W direction (width direction). Accordingly, the long fibers are arranged in the L direction and the W direction, for example, at intervals of 60 mm. At that time, if the long fibers in the short W direction are stretched first, and then the long fibers in the L direction are stretched on a plurality of long fibers stretched in the W direction, the long fibers in the long L direction bend. It is easy to prevent that. The long fiber only needs to be tensioned enough to be able to be stretched at a predetermined depth position, and it is particularly necessary to apply tension when adjusting to a predetermined depth position using a spacer or suspension line. Absent. The intersecting long fibers do not need to be particularly fixed, but if they are lightly fixed with a wire or an adhesive, there is an effect that it becomes difficult to move when placing the cement kneaded material. The concrete kneaded material blended with short fibers is poured into this mold to form a precast plate member.

  FIG. 2 schematically shows a cross-sectional structure of the obtained precast plate-like member. When this precast plate-like member 1 is used as an embedded formwork, a cement-based material is placed on the upper surface 2 side. That is, the lower surface 4 becomes the lower surface in the new floor slab. In the cement matrix 3, short fibers are dispersed and blended almost randomly in a three-dimensional manner. When applied to a structure and used, tensile stress due to bending occurs near the surface on the lower surface 4 side. The arrow in the figure represents the direction of the main tensile stress. In the cement-based matrix 3 near the lower surface 4, long fibers 5 made of stranded wires are arranged along the lower surface 4 at a position where the depth from the lower surface 4 is 10 mm. The direction is generally matched to the direction of the main tensile stress. A plurality of long fibers 5 are arranged at intervals of 60 mm. Further, a plurality of similar long fibers 5 ′ are arranged in a direction orthogonal to the long fibers 5 at intervals of 60 mm.

Even if this precast plate-like member is carbonized in a natural environment after being constructed on site as an embedded formwork, the effect of densifying the surface can be obtained. However, the progress of carbonation is extremely slow especially in humid environments such as under the pier. Therefore, it is desirable to perform a forced carbonation treatment in advance in the factory. For example, after casting, initial curing is performed for 24 hours in a constant temperature and humidity chamber of 20 ° C. and 90% RH, and after demolding, 5 volume% CO ₂ , 20 ° C., 60% until the age of 28 days. By performing forced carbonation curing in an atmosphere of R.H., at least the surface to be the lower surface of the embedded formwork is carbonized. Thereby, carbonation depth can be 5 mm or more.

[Temporary construction of hanging girders]
FIG. 3 a schematically shows a cross section including an existing structure (pier) in an initial state. The hatched portion is an existing member. In this pier, there is a beam 12 on a pile 11, and an existing floor slab 13 is supported by the beam 12. Since the deterioration of the existing floor slab 13 mainly occurs in a portion other than the upper portion of the beam 12, the portion positioned in the upper portion of the beam 12 does not need to be updated and may be left. Therefore, the support 14 is temporarily installed on the existing floor slab positioned on the beam 12, and the hanging girder 15 is temporarily installed above the existing floor slab 13 through the support 14. The support 14 and the hanging girder 15 can use H-shaped steel. For example, a plurality of suspension bolts 16 are attached between the suspension girder 15 and the existing floor slab 13 so that the existing floor slab 13 can be suspended from the suspension girder 15. The suspension bolt 16 and the existing floor slab 13 are joined using, for example, a chemical anchor 17.

[Cutting and removing existing floor slabs]
FIG. 3b schematically shows a cross section at the stage where the existing floor slab is cut. The existing floor slab 13 is cut leaving a part located on the beam 12. Common cutting methods for concrete members, such as hanging and cutting, can be used. The cutting operation can be performed by a person riding on the existing floor slab 13. At the time of cutting, a part of the existing reinforcing bar 18 existing inside the existing floor slab 13 is left exposed from the part of the existing floor slab 13 ′ left on the beam 12. The exposed existing reinforcing bar 18 is processed so that it can be joined to a new reinforcing bar in a later process such as rust removal or antirust coating. The existing floor slab 13 ″ that has been cut and separated from the structure is loaded by the suspension girder 15 via the suspension bolts 16, and the existing floor slab 13 ″ can be used as a scaffold for operations such as rebar processing. . Thereafter, the separated existing slab 13 ″ is suspended by a crane ship and removed.

[Arrangement of buried formwork and reinforcing bars]
FIG. 3 c schematically shows a cross section at the stage where the embedded formwork and the reinforcing bar are arranged. The precast plate-like member made of the above highly durable concrete is used as the embedded formwork 19. Moreover, the reinforcing bar 20 previously assembled on the ground is used as a reinforcing member for a new floor slab. The embedded form 19 and the reinforcing bar 20 are carried to a predetermined position by a crane ship, and are suspended from the suspension girder 15 by, for example, a plurality of suspension wires 21 and held. The embedded mold 19 is such that the carbonized surface of the long fiber disposed at a depth of 10 mm is the lower surface. A part of the embedded form 19 is preferably supported by the beam 12. For example, the joining portion of the hanging wire 21 and the embedded mold 19 may be structured using a ceramic insert as schematically shown in FIG. The joining of the hanging wire 21 and the reinforcing bar 20 can be welding.

  When constructing a large formwork in which the size of the buried formwork exceeds 5 m per side, it is desirable to divide into a plurality of precast plate members and join them together. At that time, the precast plate-like members can be joined together by, for example, an elastic epoxy-based bond. And it is desirable to lay a water-stop sheet on the upper surface (surface on which concrete is placed) to which the plurality of precast plate-like members are joined so as to straddle the joining portion. For example, an asphalt-bentonite water-stop sheet is laid out with a width of about 200 mm. By doing so, it is possible to cut the adhesion between the embedded formwork and the concrete in the vicinity of the elastic epoxy bond, and to suppress the cracking of the upper concrete due to the elongation of the elastic epoxy.

[Reinforcement joining]
FIG. 3d schematically shows a cross section at the stage where the joining process of the reinforcing bars has been completed. The existing reinforcing bar 18 and the newly arranged reinforcing bar 20 are joined using, for example, a joint reinforcing bar 22. For the joining, it is possible to employ a method in which the joint reinforcing bars 22 whose lengths are adjusted are welded to the reinforcing bars 20, for example, and the existing reinforcing bars 18 and the joining reinforcing bars 22 are joined by a mechanical joint (FD grip) 23. At that time, it is desirable to shift the positions so that the positions of the mechanical joints are not aligned in the same plane. It is desirable to attach a sacrificial anode material 24 to some of the reinforcing bars 22. Thereby, macrocell corrosion is suppressed. These operations can be performed on the embedded form 19.

[Concrete placement]
FIG. 3e schematically shows a cross-section at the stage where concrete is placed. After the side formwork is also installed, the concrete 25 is placed so that the joined rebars 18, 22, and 20 are arranged inside. This concrete does not need to be a highly durable concrete, and can be of a general known composition.

[Removal of hanging girders]
FIG. 3f schematically shows a cross section at the stage where the temporary member such as a hanging girder is removed and the repair is completed. The cast concrete 25 is integrated with the buried form 19 to form a new floor slab. This new floor slab has a carbonated layer that is densified by the action of γ belite on the bottom surface that is most likely to deteriorate. Cracks over time due to bending due to the combined effect are finely dispersed, and the occurrence of wide cracks is remarkably suppressed. Accordingly, excellent durability is exhibited over a long period thereafter.

The figure which showed typically the shape of the long fiber which gave twist. The figure which illustrated typically the cross-sectional structure of the precast plate-shaped member used by this invention. The figure which showed typically the cross section containing the existing structure (pier) of an initial state. The figure which showed typically the cross section of the step which cut | disconnected the existing floor slab. The figure which showed typically the cross section of the step which has arrange | positioned the embedded formwork and the reinforcing bar. The figure which showed typically the cross section of the stage which finished the joining process of a reinforcing bar. The figure which showed typically the cross section of the stage which laid concrete. The figure which showed typically the cross section of the stage which removed temporary members, such as a hanging girder, and complete | finished repair. The figure which illustrated typically the cross-sectional structure of the junction part of a hanging wire and an embedded formwork.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Precast plate-like member 2 Upper surface 3 Cement-based matrix 4 Lower surface 5, 5 'Long fiber 11 Pile 12 Beam 13, 13', 13 '' Existing floor slab 14 Support 15 Suspension girder 16 Suspension bolt 17 Chemical anchor 18 Existing rebar 19 Embedded formwork 20 Reinforcing bars 21 Hanging wires 22 Reinforcing bars 23 Mechanical joints 24 Sacrificial anode material 25 Concrete

Claims (5)

Remove the existing floor slab supported by the beam, leaving part of it on the beam, use the precast plate-like member consisting of (A) below as an embedded formwork, and place cement-based material on it The floor slab repair method of constructing a new floor slab in the removed part by the above.
(A) A hardened body of cement kneaded material containing 10 to 85 parts by mass of γ belite with respect to 100 parts by mass of cement , in which a short fiber is dispersed and blended, and a long fiber with “twist” is embedded A composite fiber reinforced cement-based material disposed at a position having a depth of 5 to 25 mm from the surface on the lower surface side (excluding those in which prestress due to the long fibers is introduced) . [1] The existing floor slab supported by the beam is removed while leaving a part thereof on the beam, and at that time, the existing floor slab in which a part of the reinforcing bar existing in the existing floor slab is left on the beam is removed. Leave it exposed from the part of
[2] A precast plate-like member comprising the following (A) is arranged in the removed portion to make it an embedded formwork, and a pre-assembled reinforcing bar is placed above the embedded formwork so as to expose the above. A new rebar structure is constructed by joining with the rebar left in
[3] A new floor slab is constructed by placing a cement-based material on the embedded formwork so that the new reinforcing bar structure is arranged inside.
Floor slab repair method.
(A) A hardened body of cement kneaded material containing 10 to 85 parts by mass of γ belite with respect to 100 parts by mass of cement , in which a short fiber is dispersed and blended, and a long fiber with “twist” is embedded A composite fiber reinforced cement-based material disposed at a position having a depth of 5 to 25 mm from the surface on the lower surface side (excluding those in which prestress due to the long fibers is introduced) .   A temporary support is temporarily installed on a portion of the existing floor slab that is positioned on the beam, and a suspended girder is temporarily installed above the existing floor slab via the support, and the existing floor slab to be removed in [1] is removed. The load is temporarily borne by the suspension girder by suspending at least one or more of the portion, the embedded formwork arranged in [2], and the reinforcing bar arranged in [2] from the suspension girder. The floor slab repair method described in 1. The floor slab repair method according to any one of claims 1 to 3, wherein the long fiber is a CFRP stranded wire having an outer diameter of 0.5 to 2.0 mm. The floor slab repair method according to any one of claims 1 to 4, wherein the precast plate-like member has a carbonated layer having an average carbonated depth of 5 mm or more on at least a surface layer portion which is a lower surface side of the embedded formwork. .

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