JP7437207B2 - Mortar for reinforced concrete and reinforcement method for reinforced concrete - Google Patents

Description

The present invention relates to a repair material for reinforced concrete, its mortar and cured product, and a method for reinforcing reinforced concrete.

Concrete slabs for road bridges are often made of reinforced concrete with reinforcing bars, etc., which has excellent strength and toughness. ) will deteriorate due to infiltration, and this will cause a decrease in yield strength. As one of the methods for reinforcing and extending the life of a concrete slab whose bearing strength has decreased in this way, a method of increasing the thickness of the upper surface of the concrete slab is known.

As a construction method for increasing the thickness of the top surface of the deck slab, it is widely adopted to remove the asphalt pavement and pour a thickened layer of steel fiber reinforced concrete on the top surface of the concrete deck slab. On the other hand, a method of increasing the thickness without using steel fiber reinforced concrete has also been proposed. Patent Document 1 describes a method for increasing the thickness of the top surface of a concrete slab, in which a thickening layer is formed by pouring concrete with a strip steel plate that also serves as reinforcing bars fixed on the top surface of the concrete slab. There is. Patent Document 2 describes a method for increasing the thickness of the upper surface of a concrete slab, in which a thickening layer is formed by forming a resin mortar layer on the upper surface of the concrete slab, with a fiber reinforced layer interposed as an intermediate layer. ing. Patent Document 3 describes a method for increasing the thickness of the upper surface of a concrete slab, in which a thickening layer is formed on the upper surface of the concrete slab using a highly elastic resin mortar having a Young's modulus that is 1/3 or more of the Young's modulus of concrete. Are listed.

Japanese Patent Application Publication No. 9-59929 Japanese Patent Application Publication No. 2004-169346 Japanese Patent Application Publication No. 2011-149244

However, if the conventional method of thickening the top surface is adopted to reinforce the reduced yield strength, the minimum thickness of the thickening layer is approximately 50 mm, which significantly increases the weight of the concrete slab and imposes a load on it. There was a problem. Additionally, the construction thickness is directly linked to cost. Therefore, there is a need for materials that can increase the strength of concrete even when the construction thickness is reduced.

Therefore, an object of the present invention is to provide a repair material for reinforced concrete that can be applied in a thin layer and that can improve the strength and toughness of reinforced concrete, its mortar and cured product, and a method for reinforcing reinforced concrete. do.

As a result of intensive study on the above-mentioned issues, the inventor of the present invention adjusted the contents of pozzolanic substances and fine aggregate, and as a result, created a repair material that can be applied in a thin layer and improves the bearing strength while maintaining the toughness of concrete. I found out what I can do.

That is, the present invention includes the following [1] to [4].
[1] Contains a quick-hardening cement, a pozzolanic substance, an expansive material, and a fine aggregate, with a pozzolanic substance content of 3 to 28 parts by mass and a fine aggregate content of 60 to 380 parts by mass per 100 parts of quick-hardening cement. Repair material for reinforced concrete, which is the mass part.
[2] A mortar for repairing reinforced concrete, comprising the repair material according to [1] and water, the water content being 20 to 40 parts by mass per 100 parts by mass of quick-setting cement.
[3] A cured product of the mortar according to [2], which has a compressive strength of 75 N/mm ² or more at 28 days of age.
[4] A method for repairing reinforced concrete, comprising applying the mortar described in [2] to a thickness of 8 to 40 mm on the surface of the reinforced concrete.

According to the present invention, it is possible to provide a repair material for reinforced concrete that can be applied in a thin layer and that can improve the strength and toughness of reinforced concrete, its mortar and cured product, and a method for reinforcing reinforced concrete.

In this specification, reinforced concrete refers to concrete with excellent strength or toughness, and includes, for example, fiber-reinforced concrete, reinforced concrete, prestressed concrete, and the like.

Hereinafter, one embodiment of the present invention will be described in detail.

[Repair material for reinforced concrete]
The reinforced concrete repair material of this embodiment includes a fast-setting cement, a pozzolanic substance, an expansive material, and a fine aggregate.

Preferably, the fast-setting cement contains calcium aluminates as an active ingredient, and 11CaO.7Al ₂ O _{3.CaX 2} (X represents a halogen atom) or 3CaO.3Al _{2 O} 3.CaSO ₄ (Auin). Those containing it as an active ingredient are more preferred. 11CaO.7Al ₂ O _{3.CaX 2} is a so-called calcium aluminate halide cement. The halogen atom is preferably a fluorine atom. Auin is also called calcium sulfoaluminate cement (auin cement). These are called super-fast hardening cements and are commercially available under the trade name Jet Cement or Super Jet Cement. The most preferred quick-hardening cement is Auin-based cement.
Other examples of calcium aluminates include C ₃ A, C ₂ A, C1 ₂ A ₇ , C ₅ A 3 when CaO is expressed as C, Al ₂ O ₃ is expressed as A, and Fe ₂ O ₃ is expressed as _F. , CA, C ₃ A ₅ , CA _{2, etc.} , calcium aluminoferrite, alumina cement, and these, as well as SiO ₂ , _{K 2} It includes solid solutions or combinations of O, Fe ₂ O ₃ , TiO ₂ and the like. Calcium aluminates may be either crystalline or amorphous, or a mixture of crystalline and amorphous. A fast-setting admixture prepared by blending these calcium aluminates and an inorganic salt such as gypsum can also be used as a fast-setting cement by adding it to Portland cement.

Pozzolanic substances include various fly ash described in JIS A 6201:2015, silica fume, slag powder, amorphous aluminosilicate, etc. described in JIS A 6207:2016. As the pozzolan substance, silica fume and amorphous aluminosilicate are preferable from the viewpoint of long-term strength development and workability. One type of pozzolan substance may be used alone, or two or more types may be used in combination.

The content of the pozzolanic substance is 3 to 28 parts by mass per 100 parts by mass of fast-setting cement. If the content of the pozzolanic substance is outside the above range, the mortar properties will not be excellent and thin layer workability will deteriorate, and it will be difficult to obtain the strength and toughness of the repaired concrete. The content of the pozzolanic substance is preferably 4 to 25 parts by mass, and 5 to 20 parts by mass, based on 100 parts by mass of quick-setting cement, from the viewpoint of improving the strength and toughness of the repaired concrete. It is more preferable that

The expansion material may be any expansion material as long as it is a JIS-compliant expansion material (JIS A 6202:2008) that is generally used as an expansion material for concrete. Examples of the expanding material include an expanding material whose main component is free quicklime (quicklime-based expanding material), an expanding material whose main component is Auin (ettringite-based expanding material), and a composite expanding material of free quicklime and ettringite-forming substances. Can be mentioned. Among these, quicklime-based expansion materials are preferred. One type of expansion material may be used alone, or two or more types may be used in combination. It is preferable to use an expanding material having a Blaine specific surface area of 2000 to 6000 cm ² /g.

The content of the expanding agent is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 8 parts by mass, and 1 to 5 parts by mass based on 100 parts by mass of quick-hardening cement. More preferably. If the content of the expanding material is within the above range, the compressive strength, dimensional change rate, etc. will be even better.

The fine aggregate is not particularly limited, and includes, for example, river sand, silica sand, crushed sand, kansui stone, limestone sand, slag aggregate, and the like. Among these, silica sand is preferable as the fine aggregate. One type of fine aggregate may be used alone, or two or more types may be used in combination. As the fine aggregate, it is preferable to use a commonly used particle size of 5 mm or less (the amount that passes through a 5 mm sieve).

The content of fine aggregate is 60 to 380 parts by mass per 100 parts by mass of quick-hardening cement. If the content of fine aggregate is outside the above range, the mortar properties will not be excellent, workability will be reduced, and strength development will be difficult to obtain. From the viewpoint of further improving workability, the content of the fine aggregate is preferably 70 to 350 parts by mass, more preferably 80 to 320 parts by mass, based on 100 parts by mass of cement.

The reinforced concrete repair material of this embodiment may contain a water reducing agent. Water reducers include superplasticizers, super AE water reducers, AE water reducers, and superplasticizers. Examples of such water reducing agents include water reducing agents specified in JIS A 6204:2011 "Chemical admixtures for concrete". Examples of the water reducing agent include polycarboxylic acid water reducing agents, naphthalene sulfonic acid water reducing agents, lignin sulfonic acid water reducing agents, melamine water reducing agents, and acrylic water reducing agents. Among these, naphthalenesulfonic acid water reducing agents are preferred. One type of water reducing agent may be used alone, or two or more types may be used in combination.

The content of the water reducing agent is preferably 0.1 to 10 parts by mass, more preferably 0.3 to 5 parts by mass, and 0.5 to 2.5 parts by mass based on 100 parts by mass of quick-setting cement. More preferably, it is parts by mass. If the content of the water reducing agent is within the above range, better fluidity and troweling properties can be easily obtained when made into mortar, and strength development during curing can also be more easily improved.

The reinforced concrete repair material of this embodiment may contain a setting retarder. Examples of setting retarders include organic acids or salts thereof such as citric acid, gluconic acid, malic acid, and tartaric acid; borates such as boric acid and sodium borate, phosphates, alkali metal carbonates, and alkali metal heavy Examples include inorganic salts such as carbonates; sugars. Among these, citric acid, citrates, tartaric acid, tartrates, and alkali metal carbonates are preferred. The setting retarder may be in the form of a powder or a liquid (eg, in the form of an aqueous solution, emulsion, or suspension). The setting retarder may be used alone or in combination of two or more.

The content of the setting retarder is preferably 0.1 to 8 parts by mass, more preferably 0.5 to 5 parts by mass, and 0.8 to 3 parts by mass based on 100 parts by mass of fast-setting cement. It is more preferable that it is part. If the content of the setting retarder is within the above range, it is easy to ensure a long pot life.

The reinforced concrete repair material of this embodiment may contain various admixtures (materials) as long as the effects of the present invention are not impaired. Examples of admixtures (materials) include gypsum, cement polymers, foaming agents, antifoaming agents, waterproofing agents, rust preventives, shrinkage reducing agents, water retention agents, pigments, water repellents, anti-efflorescence agents, and thickeners. Examples include sticky agents, dust reducers, strength enhancers, stone powder, earth mineral powders, and fibers.

The method for manufacturing the reinforced concrete repair material of this embodiment is not particularly limited, and examples include gravity mixers such as V-type mixers and tilting concrete mixers, Henschel mixers, injection mixers, ribbon mixers, and paddle mixers. It can be manufactured by mixing with a mixer such as a mixer.

[Repair mortar for reinforced concrete]
The reinforced concrete repair material of this embodiment can be mixed with water to prepare a reinforced concrete repair mortar, and the water content may be adjusted as appropriate depending on the application. The water content is preferably 20 to 40 parts by mass, more preferably 25 to 38 parts by mass, and even more preferably 28 to 35 parts by mass, based on 100 parts by mass of the quick-hardening cement. When the water content is within the above range, it is easier to ensure workability, and it is easier to suppress the occurrence of material separation and increase in shrinkage of the cured product.

The preparation of the repair mortar for reinforced concrete of this embodiment can be carried out using the same kneading equipment as for ordinary repair materials for reinforced concrete, and is not particularly limited. Examples of the kneading device include a mortar mixer, grout mixer, hand mixer, tilting mixer, and twin-screw mixer.

In the cured product of repair mortar for reinforced concrete, the compressive strength after 28 days is preferably 75 N/mm ² or more, more preferably 78 to 150 N/mm ² , and more preferably 80 to 130 N/mm ² . More preferably. If the compressive strength of the cured product is within the above range, it will not easily deteriorate, and the repaired concrete will have even better yield strength and toughness. Compressive strength can be measured according to JIS A 1108:2018 "Testing method for compressive strength of concrete".

[Repair method for reinforced concrete]
The reinforced concrete repair method of this embodiment is performed by applying the above-mentioned reinforced concrete repair mortar on the surface of reinforced concrete. The thickness of the reinforced concrete repair mortar to be applied is preferably 8 to 40 mm, more preferably 10 to 30 mm, and even more preferably 12 to 25 mm. If the thickness of the mortar is within the above range, it tends to be possible to sufficiently reinforce the yield strength and toughness of the reinforced concrete while suppressing an increase in its own weight.

The method of applying mortar for repairing reinforced concrete is not particularly limited, and can be selected from methods such as filling the recesses with a trowel, leveling the filling with a vibrator, etc., and finishing with a trowel.

By using the reinforced concrete repair material or the reinforced concrete repair mortar of the present embodiment, when reinforced concrete is repaired, the strength can be improved while maintaining the toughness of the reinforced concrete. Moreover, since the reinforced concrete repair material or the reinforced concrete repair mortar of this embodiment can be applied in a thin layer, it is possible to suppress an increase in dead weight when repairing reinforced concrete. Therefore, the reinforced concrete repair material or the reinforced concrete repair mortar of this embodiment can be suitably used in the repair of civil engineering structures using reinforced concrete. Examples of civil engineering structures include roads, bridges, port structures, river structures (such as sea walls and piers), underground structures (such as tunnels and box culverts), and dams.

EXAMPLES Hereinafter, the present invention will be explained in detail with reference to Examples, but the present invention is not limited thereto.

[Production of repair material for reinforced concrete and repair mortar for reinforced concrete]
・Material cement:
Quick setting cement (CSA)
Ordinary Portland cement (NC)
Pozzolanic substance: silica fume (SF)
Fine aggregate: Silica sand Expanding material: Quicklime-based expanding agent Water reducing agent: Naphthalene sulfonic acid-based water reducing agent Set retardant: Citric acid

The composition was designed using 100 parts by mass of cement, silica fume and fine aggregate in the proportions shown in Table 1, 2 parts by mass of expanding agent, 1 part by mass of water reducing agent, and 1 part by mass of setting retarder. In a 20°C environment, 100 parts by mass of cement and 32 parts by mass of water were added to a 10L cylindrical container, each material of the reinforced concrete repair material designed to be mixed was added, and the mixture was kneaded for 90 seconds with a hand mixer to form mortar. Approximately 3L of was made.

[Preparation of base material concrete]
・Material cement: Early strength Portland cement (C)
Fine aggregate: Mountain sand (S)
Coarse aggregate: Crushed stone (G)
Fiber: Steel fiber (F)
Expanding material: Quicklime-based expanding material (Ex)
Water reducing agent: High performance AE water reducing agent (AE)

In a 20°C environment, each material of the concrete composition designed in the ratio shown in Table 2 was added and mixed for 120 seconds with a forced mixing mixer to prepare about 25 L of base material concrete.

[Evaluation method]
Each item was evaluated using the following method. The evaluation results are shown in Table 3.
1) Compressive strength The compressive strength of the repair mortar for reinforced concrete at an age of 28 days was measured according to JIS A 1108:2018 "Testing method for compressive strength of concrete". The dimensions of the specimen were 100 mm in diameter and 200 mm in height. The specimens were demolded the next day and then cured in water until the age of the specimen. Curing was always carried out in a constant temperature bath at 20°C.
2) Static elastic modulus The static elastic modulus of the reinforced concrete repair mortar at 28 days of age was measured according to JIS A 1149:2017 "Test method for static elastic modulus of concrete." The dimensions of the specimen were 100 mm in diameter and 200 mm in height. The specimens were demolded the next day and then cured in water until the age of the specimen. Curing was always carried out in a constant temperature bath at 20°C. The measurement was also performed as a compressive strength test.
3) Bending strength (yield strength)
The bending strength at the age of 28 days was measured according to JIS A 1106:2018 "Test method for bending strength of concrete". The dimensions of the specimen were 100 mm in width, 100 mm in height, and 400 mm in length. The specimens were molded from base material concrete to a height of 85 mm, removed from the mold the next day, and then cured in water until the material age was 7 days. After that, surface treatment was performed, and the remaining height of 15 mm was molded with mortar, and the specimen was cured in water to a predetermined specimen size until the material age was 28 days. Curing was always carried out in a constant temperature bath at 20°C.
4) Bending toughness coefficient (toughness)
The flexural toughness coefficient at 28 days of age was measured according to JSCE-G552-2013 "Bending strength and flexural toughness test method of steel fiber reinforced concrete". The dimensions of the specimen were 100 mm in width, 100 mm in height, and 400 mm in length. The specimens were molded from base material concrete to a height of 85 mm, removed from the mold the next day, and then cured in water until the material age was 7 days. Thereafter, the remaining height of 15 mm was molded with mortar, and the sample was cured in water until the age of the sample was 28 days. Curing was always carried out in a constant temperature bath at 20°C. The measurement was also performed as a bending strength test.
5) Thin layer workability A formwork (30 x 30 x 3 cm) was installed at a slope of 5%, and after applying mortar, it was leveled with a trowel and the sagging properties of the mortar were visually observed. Those in which sag occurred were evaluated as poor (×), and those in which sag did not occur were evaluated as good (◯).

In the test specimen of the example, the toughness coefficient was maintained and the bending strength was improved compared to the base material concrete, and the proof strength (bending strength) and toughness (bending toughness coefficient) were improved by the repair material for reinforced concrete. Ta. On the other hand, in the test specimens of comparative examples, there were cases where thin layer construction was not possible, and where the bending strength and toughness coefficient did not improve compared to the base material concrete, and no reinforcing effect on yield strength and toughness was observed.

Claims (4)

A mortar for repairing reinforced concrete, comprising a repair material for reinforced concrete containing a quick-setting cement, a pozzolanic substance, an expansive material, a fine aggregate, a water reducing agent and a setting retarder, and water, the mortar comprising:
Contains no metal powder,
With respect to 100 parts by mass of the quick-hardening cement, the content of the pozzolan substance is 3 to 28 parts by mass, the content of the fine aggregate is 60 to 380 parts by mass, and the content of the water reducing agent is 0.1 parts by mass. ~2.5 parts by mass, the content of the setting retarder is 0.1 to 3 parts by mass, and the content of water is 20 to 40 parts by mass,
A mortar for repairing reinforced concrete, wherein the compressive strength of the cured mortar at 28 days of age is 75 N/mm ² or more. The mortar according to claim 1, wherein the water reducing agent is a naphthalene sulfonic acid water reducing agent. The mortar according to claim 1 or 2, wherein the setting retarder is citric acid. A method for repairing reinforced concrete, comprising applying the mortar according to any one of claims 1 to 3 to a thickness of 8 to 40 mm on the surface of reinforced concrete.