JP2006348465A - Composite precast floor slab and floor slab repairing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a precast floor slab which exerts durability over a long period of time, and an efficient floor slab repairing method using it. <P>SOLUTION: The composite precast floor slab is composed of a slab in which a carbonated cement-based member, obtained by carbonating a cement hardened body containing γC<SB>2</SB>S, and an uncarbonated concrete member are joined together. In the composite precast floor slab, at least one broad surface of the slab is composed of a surface of the carbonated cement-based member. In the floor slab repairing method, a part including a deteriorated place on the top surface of the floor slab of a concrete structure is chipped, and the composite precast floor slab is installed in place of a chipped part in such a manner that the carbonated cement-based member is positioned on an upper surface. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a precast slab suitable for a structural member of a concrete slab such as a pier, a road bridge slab, and a railway bridge slab, and a repair method of the slab using the slab.

  Conventional methods for repairing concrete slabs include a surface coating method and a cross-sectional repair method. Also, when the deterioration is particularly significant, the existing floor slab may be removed to construct a new floor slab.

In the surface coating method, there is a problem that the surface coating layer is deteriorated by ultraviolet rays or peeled off or swollen due to an increase in water vapor. In addition, there is a drawback that the surface is generally slippery.
In the cross-section repair method, since the curing time is required, it is impossible to repair the concrete structure in service. There is also a problem that the cost of repair materials such as non-shrink mortar is high.
In the method of removing the existing floor slab and constructing a new floor slab, it takes a lot of cost to remove the floor slab, and also when curing concrete by so-called “on-site casting”, it requires a curing period. Therefore, repairing while using the concrete structure is difficult. Furthermore, there are many problems in terms of workability, such as piers in the marine atmosphere and piers at high places, where the installation of scaffolding is costly and the working space is restricted.

  Therefore, there is a case where a construction method for constructing a new floor slab using a floor slab made of precast concrete (hereinafter referred to as “precast floor slab”) is sometimes employed (Patent Documents 1 and 2). In this case, the above problems are relatively easy to deal with.

JP-A-6-146220 JP 7-268808 A

  However, even if a new floor slab is simply constructed at a deteriorated portion of the floor slab, deterioration with time proceeds due to the same cause as before, and it is necessary to repeat the same repair. This is the same also in the construction method using a precast floor slab. Repeated repairs are undesirable because they cause social losses due to traffic interruptions. Therefore, it is desired to give durability to the floor slab after repair for a long period of time in an environment where the floor slab is exposed. In particular, it is important to provide durability against salt damage on a pier exposed to salt or on a road where anti-freezing agents are sprayed. In cold regions where snow melting agents are used, durability against freezing and thawing is also required. Many floor slabs exposed to wind and rain also need to be considered for deterioration due to acid rain.

  The present invention is intended to provide a precast floor slab that can exhibit particularly excellent durability against salt and acid, and to provide an efficient repair method using the same.

  As a result of detailed studies, the inventors have found that the above object can be effectively achieved by a composite precast slab partially including a high durability member that is forcibly carbonized.

That is, in the present invention, it is composed of a slab obtained by joining a carbonated cementitious member obtained by carbonizing a hardened cement body containing γC ₂ S and a concrete member that has not been carbonized, and at least one of the slabs. There is provided a composite precast slab whose wide surface is constituted by the surface of the carbonated cementitious member. Here, the cement-based member includes mortar and concrete. The wide surface is a surface perpendicular to the thickness direction of the slab.

In particular, a reinforced concrete or fiber that has a carbonated cementitious member obtained by carbonizing a cemented hardened material of kneaded material containing 8 to 70 parts by mass of γC ₂ S with respect to 100 parts by mass of cement and is not carbonized. A composite precast slab comprising a slab having a two-layer structure having a reinforced concrete member as a lower layer, wherein the upper layer member and the lower layer member are in contact with each other at an uneven surface and joined by a joint via a shear key, Become.

  Further, as a method for repairing the floor slab, there is provided a method for suspending a portion including an upper surface deterioration portion of an existing concrete structure floor slab, and installing the composite precast slab in place of the removed portion. However, when installing the composite precast slab, it is important to install so that the surface of the carbonated cementitious member is on the upper surface side.

Since the precast slab according to the present invention has a carbonated cement-based member that is densified using the reaction between γC ₂ S and carbon dioxide, the elution of Ca on the surface of the carbonated cement-based member does not occur. Remarkably suppressed and exhibits excellent durability against salt and acid, as well as scaling and freeze-thawing. On the other hand, since it has a member made of general reinforced concrete or fiber reinforced concrete, strength characteristics required for the precast slab are ensured. In addition, since the member made of the reinforced concrete or the like is not carbonized, there is no fear that the internal reinforcing bars are corroded by the neutralization of the concrete by the carbonation. Therefore, the composite precast slab of the present invention maintains the excellent durability against salt and acid and the strength characteristics necessary for the precast slab over a long period of time by arranging the carbonated cement-based member on the upper surface, and the slab material Is very suitable.

According to the repairing method of the present invention in which this precast slab is used as a new floor slab, workability is improved and the cost for making a scaffold is reduced as compared with the on-site method.
Also, since this precast floor slab is newly laid, it becomes possible to work on the floor slab at an early stage, so it is easy to repair while using the concrete structure, and there are disadvantages such as traffic interruption. Can be kept to a minimum.

  Furthermore, in the on-site construction method, it is very difficult to practically apply carbonation treatment to the concrete of the floor slab. Therefore, the repair method of the present invention using a precast floor slab in which a necessary portion has been carbonated in advance realizes excellent durability that cannot be obtained by the on-site method.

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. However, the γ type does not exhibit hydraulic properties and has the property of reacting with carbon dioxide. In the present application, this γ-type belite is expressed as “γC ₂ S”.

Ordinary cements such as Portland cement basically do not contain γC ₂ S. In addition to 2CaO · SiO ₂ , γC ₂ S includes oxides such as Al ₂ O ₃ , Fe ₂ O ₃ , MgO, Na ₂ O, K ₂ O, TiO ₂ , MnO, ZnO, and CuO as impurities. In some cases, γC ₂ S in which such a mineral is dissolved is also included in γC ₂ S in the present invention.

As a result of various studies, the inventors have made a cement kneaded material with an increased content of γC ₂ S and cured it, and the cured product has a remarkable surface layer portion by forced carbonation treatment with carbon dioxide gas or the like. It was found that it can be densified. And it has been found that the densified surface layer portion has a very high Ca elution resistance and is excellent in the shielding effect of chloride and acid.

There are many unclear parts about the mechanism by which the hardened cement enriched with γC ₂ S is densified with carbon dioxide or the like, but it is considered as follows. That is, when a normal hardened cement body is carbonated (neutralized), Ca (OH) ₂ generated by the cement hydration reaction reacts with carbon dioxide gas to become CaCO _3. When rC ₂ S in the cured body large amount exists, rC ₂ S reacts directly with carbon dioxide gas without hydration reaction generates 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 presumed that a large amount of reaction products are generated earlier than normal hardened cement bodies, which fills voids in the hardened cement bodies and densifies them.

In order to sufficiently obtain such an effect of densification, a cement kneaded material containing 8 to 70 parts by mass, preferably 20 to 50 parts by mass of γC ₂ S with respect to 100 parts by mass of cement is cured, and then forced carbonation is performed. It is desirable to perform chemical curing. This reduces the porosity of the carbonation region, suppresses Ca elution, and significantly improves resistance to salt damage, scaling, and freeze-thaw. This is disclosed in Japanese Patent Application No. 2004-375549 by the present applicants.

[Composite precast slab]
FIG. 1 schematically illustrates a cross-sectional structure of the composite precast slab of the present invention. In FIG. 1, a composite precast floor slab 1 includes a carbonated cement-based member 2 that has been subjected to a forced carbonation treatment in advance, and a reinforced concrete member 4 that has not been subjected to a forced carbonation treatment. The carbonated cement-based member 2 and the reinforced concrete member 4 are in contact with each other with an interface 5 interposed therebetween, and a shear key 6 is provided at the joint. The interface 5 has a concavo-convex shape in order to improve the adhesion between both members and avoid the intrusion of water or the like. When used for floor slabs of general piers, road bridges, and railway bridges, the shape of the composite precast slab 1 can be a slab having a thickness of about 100 to 250 mm. For example, length 4000 × width 2000 × The slab has a thickness of 200 (mm). In order to prevent water and the like from entering the back of the floor slab when laid as a floor slab, this slab is not provided with a through hole for anchor installation or the like.

  The carbonated cement-based member 2 constitutes the upper surface side of the composite precast floor slab 1 and is responsible for improving the durability of the floor slab against salt and acid. As for the thickness of the carbonated cement-based member 2, it is necessary to secure a thickness in accordance with the shape of the shear key in the vicinity of the location where the shear key 6 is provided, but in other locations, an average thickness of 10 mm or more is ensured. In general, the average thickness may be about 20 to 50 mm. For example, in a slab having a plate thickness of 200 mm, the thickness is 83 mm around the shear key 6, and the average thickness is 30 mm in other portions.

The carbonated cement-based member 2 is manufactured in advance by the following method. First, as described above, a cement kneaded material containing γC ₂ S in an amount of 8 to 70% by mass, preferably 20 to 50% by mass with respect to 100 parts by mass of cement is prepared. As an admixture other than γC ₂ S, fly ash, silica fume and the like can be used. Specifically, for example, low heat Portland cement, γC ₂ S, fly ash and silica fume are mixed at a mass ratio of 45: 35: 20: 5, respectively, so that the water powder ratio is 30% and the s / a is 46%. A kneaded product is obtained. Next, a concrete hardened body having a predetermined shape is made using this kneaded product. And after carrying out water curing for one day, forced carbonation treatment is performed by performing carbonation curing by exposing the cured body to an atmosphere of, for example, 10% by volume CO ₂ , 30 ° C., 60% RH for 7 days. The

After the carbonated cement-based member 2 is manufactured, a general reinforced concrete is placed on the surface to be the interface 5 of the carbonated cement-based member 2 to construct the reinforced concrete member 4. Fiber reinforced concrete may be placed instead of reinforced concrete. For joining the carbonated cement-based member 2 and the reinforced concrete member 4, a high-strength ceramic joint is used in consideration of non-corrosiveness. However, a steel joint may be used depending on the application. It is desirable to provide a shear key 6 at the joint. Moreover, the composite precast slab 1 is provided with a lifting device in consideration of the installation work at the site.
In this way, a composite precast floor slab having a two-layer structure having excellent durability against salt and the like and strength characteristics required for the floor slab is obtained.

[Slab repair method]
A floor slab repair method using the above composite precast slab is illustrated.
FIG. 2 schematically shows a road bridge to which the floor slab repair method of the present invention is applied. This road bridge is a concrete structure mainly composed of piers 11, beams 12 and an existing floor slab 13, and the existing floor slab 13 shown in FIG. The suspending operation can be performed by a twin header, a water jet or the like, and may be performed by hand. The thickness of the hanger is determined according to the thickness of the existing floor slab, the state of deterioration of the upper surface, the structural strength, etc., but generally about 100 to 200 mm is optimal.

  The unevenness adjusting jig 14 is installed on the existing floor slab 13 with the upper surface removed. The installation position of the unevenness adjusting jig 14 is set to an upper position of the pier 11 and, if necessary, an upper position of the beam 12. The composite precast slab 1 is installed side by side on the unevenness adjusting jig 14 using a forklift or a crane. At that time, the carbonated cement-based member 2 is placed on the upper surface. Adjacent composite precast slabs 1 are not connected with each other by a steel material or the like, and can be installed while being kept independent by adjusting the level by the unevenness adjusting jig 14. When connecting the composite precast slabs 1 to each other, a corrosion-resistant ceramic joint or the like is used.

The gap between the installed composite precast floor slab 1 and the existing floor slab 13 is filled with a filler. Specifically, for example, the interval between the composite precast floor slab 1 and the existing floor slab 13 is set to 30 mm, and the gap is wetted by steam spraying, and then the filler is self-applied from the joint between the composite precast floor slabs 1 only by water head pressure. Fill. As the filler, an inorganic non-shrink mortar or a combination of a high-fluidity mortar and an expansion material is used to prevent shrinkage and voids. The joints between the composite precast slabs 1 are filled with joint materials.
After the filler is cured, it is possible to carry out the next precast floor slab installation work on the laid composite precast floor slab 1.
In this way, the floor slab can be repaired efficiently, and excellent durability is exhibited over a long period.

Sectional drawing which showed the structure of the composite precast slab of this invention typically. The side view which showed typically the road bridge which has applied the floor slab repair method using the composite precast floor slab of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Composite precast floor slab 2 Carbonation cement-type member 3 Reinforcement 4 Reinforced concrete member 5 Interface 6 Shear key 11 Bridge pier 12 Beam 13 Existing floor slab 14 Unevenness adjustment jig

Claims (3)

It comprises a slab obtained by joining a carbonated cementitious member obtained by carbonizing a hardened cement containing γC ₂ S and a non-carbonized concrete member, and at least one wide surface of the slab has the carbonation A composite precast slab composed of the surface of a cement-based member. Reinforced concrete or fiber reinforced concrete having a carbonated cement-based member obtained by carbonizing a cemented hardened body of kneaded material containing 8 to 70 parts by mass of γC ₂ S with respect to 100 parts by mass of cement and having not been carbonized. A composite precast slab comprising a slab having a two-layer structure having the above member as a lower layer, wherein the upper layer and the lower layer are in contact with an uneven surface and are joined by a joint through a shear key.   The part including the upper surface deterioration portion of the concrete structure floor slab is suspended, and the composite precast slab according to claim 1 or 2 is installed so that the carbonated cementitious member is the upper surface in place of the removed part. Repair method for floor slabs.

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