JP7465451B2 - Cement composition, mortar composition, and method for repairing concrete structure - Google Patents

Description

The present invention relates to a cement composition, a mortar composition, and a method for repairing a concrete structure.

Corrosion and deterioration of concrete structures is a problem in sewerage-related facilities. Corrosion and deterioration of concrete structures occurs due to sulfates contained in sewage. Specifically, sulfates contained in sewage are reduced by sulfate-reducing bacteria to produce hydrogen sulfide. This hydrogen sulfide is oxidized by sulfur-oxidizing bacteria to produce sulfuric acid, and as a result, the surface of the concrete structure is continuously exposed to an acidic atmosphere, causing corrosion and deterioration.

Various acid-resistant mortars have been proposed as repair materials for concrete structures that have deteriorated due to corrosion. For example, Patent Document 1 discloses a Portland cement-based acid-resistant mortar that is made of ordinary Portland cement, silica fume, and granulated blast furnace slag powder, and that contains these three components in a specified amount to suppress weight loss due to sulfuric acid erosion of the hardened body, as well as suppress the rate of sulfuric acid penetration into the hardened body and simultaneously suppress the progress of carbonation. Patent Document 2 discloses an acid-resistant hydraulic composition that contains Portland cement, blast furnace slag powder, fine aggregate, and calcium formate, and that contains alumina cement clinker aggregate in the fine aggregate, thereby improving not only acid resistance but also strength development and adhesiveness. In addition, Patent Document 3 discloses an alumina cement-based acid-resistant mortar that contains alumina cement, alumina cement clinker, blast furnace slag, silica fume, fine aggregate, and lithium carbonate, thereby providing excellent acid resistance, strength development, and adhesiveness.

JP 2010-155734 A JP 2013-170112 A JP 2016-13960 A

However, with portland cement-based acid-resistant mortar, the production of gypsum dihydrate, which causes corrosion deterioration, cannot be sufficiently suppressed because the amount of calcium hydroxide produced is large, and it is difficult to say that the acid resistance is high. Also, with alumina cement-based acid-resistant mortar, the strength of the mortar decreases due to the phase transition of alumina cement hydrate (change to a hydrate with a higher specific gravity), making it more susceptible to cracks, etc., so it is difficult to achieve both high acid resistance and crack resistance.

The present invention was made in consideration of these circumstances, and aims to provide a cement composition, a mortar composition, and a method for repairing concrete structures that are highly acid-resistant and have excellent crack resistance.

The cement composition according to the present invention is a cement composition containing Portland cement, slag, and a polymer for admixture with cement, and the polymer cement ratio (solid content ratio) between the polymer for admixture with cement and the Portland cement is 3% by mass or more and 10% by mass or less.

With this configuration, the cement composition can suppress the production of calcium hydroxide while suppressing the penetration of sulfate ions, thereby improving acid resistance. In addition, since the cement composition contains Portland cement, it has excellent crack resistance.

The cement composition according to the present invention may have a glass transition temperature of the polymer for cement admixture of 5°C or higher.

By adhering a film of the polymer for cement admixture to a portion of the slag surface, an unreacted surface of the slag is formed at the attachment point. When a crack occurs in a concrete structure and the environmental temperature falls below the glass transition temperature, the film attached to the slag surface peels off, and a hydration reaction occurs on the unreacted surface of the slag. This allows the crack to be filled with hydrates, allowing self-healing. If the glass transition temperature of the polymer for cement admixture is 5°C or higher, the hydration reaction is more likely to occur, improving the self-healing properties of the cracked area.

In the cement composition according to the present invention, the slag may have a Blaine specific surface area of less than 8000 cm ² /g.

If the Blaine specific surface area of the slag is less than 8000 cm ² /g, a film of the polymer for cement admixture can be easily attached to the surface of the slag, and as a result, the self-healing property of cracked areas can be improved.

The cement composition according to the present invention may further contain fly ash as an admixture.

With this configuration, the cement composition can increase the strength of concrete structures.

The mortar composition according to the present invention contains the cement composition, water, and fine aggregate.

With this configuration, the mortar composition of the present invention can suppress the intrusion of sulfate ions while suppressing the production of calcium hydroxide, thereby improving acid resistance. In addition, since the mortar composition of the present invention contains Portland cement, it has excellent crack resistance.

The method for repairing a concrete structure according to the present invention involves filling or applying the mortar composition to the area of the concrete structure to be repaired.

The concrete structure repair method uses the above-mentioned mortar composition to repair a concrete structure that has deteriorated due to corrosion, thereby obtaining a concrete structure that is highly acid-resistant and has excellent crack resistance.

The present invention provides a cement composition, a mortar composition, and a method for repairing a concrete structure that are highly acid-resistant and have excellent crack resistance.

<Cement Composition>
The cement composition according to this embodiment will be described below.

The cement composition according to this embodiment contains Portland cement, slag, and a polymer for cement admixture.

The Portland cement is not particularly limited, and examples thereof include ordinary Portland cement, high-early-strength Portland cement, ultra-high-early-strength Portland cement, moderate-heat Portland cement, sulfate-resistant Portland cement, and white Portland cement, as specified in JIS R 5210. Note that one type of cement may be used alone, or two or more types may be used in combination.

From the viewpoint of ensuring compressive strength and improving crack resistance, the amount of Portland cement is preferably 10 parts by mass to 60 parts by mass, and more preferably 30 parts by mass to 45 parts by mass, per 100 parts by mass of the powder components. When two or more types of cement are included, the amount is the total amount of cement. Examples of powder components include cement, slag, fly ash, aggregate, etc.

Examples of slag include blast furnace slag, converter slag, and dephosphorization slag. Among these, blast furnace slag is preferable from the viewpoint of increasing acid resistance. Note that one type of slag may be used alone, or two or more types may be used in combination.

The Blaine specific surface area of the slag is preferably less than 8000 cm ² /g from the viewpoint of improving the self-healing property. Moreover, from the viewpoint of further improving the self-healing property, it is preferably 4000 cm ² /g or more. The Blaine specific surface area is a value measured in accordance with JIS R 5201:2015 8.1.

From the viewpoint of improving self-healing properties, the amount of the slag is preferably 2.5 parts by mass or more per 100 parts by mass of the powder components. From the viewpoint of workability, the amount is preferably 20 parts by mass or less per 100 parts by mass of the powder components. When two or more types of slag are included, the amount is the total amount of the slags.

As the polymer for mixing with cement, for example, a polymer dispersion such as a liquid resin emulsion or rubber latex, or a powdered re-emulsified powdered resin can be used. Examples of the resin emulsion include polyacrylic ester, polyvinyl acetate, vinylidene chloride vinyl chloride, polyvinyl propionate, ethylene vinyl acetate, polypropylene, epoxy, asphalt, rubber asphalt, and paraffin. Examples of the rubber latex include chloroprene rubber, styrene butadiene rubber, acrylonitrile butadiene rubber, methyl methacrylate butadiene rubber, and butadiene rubber. Examples of the re-emulsified powdered resin include ethylene vinyl acetate, vinyl acetate vinyl versatate, and the like. The polymer for mixing with cement may be used alone or in combination of two or more types.

It is preferable to use a liquid polymer dispersion as the polymer for admixture with cement. The glass transition temperature of the polymer dispersion is preferably 5°C or higher from the viewpoint of improving the self-healing property of cracked areas.

The amount of the polymer for cement admixture can be 1 part by mass or more and 8 parts by mass or less in terms of solid content per 100 parts by mass of the powder component. When two or more types of polymer for cement admixture are included, the amount is the total amount of the polymer for cement admixture.

The polymer-cement ratio (solid content ratio) between the polymer for cement admixture and the Portland cement is 3% by mass or more and 10% by mass or less, preferably 5% by mass or more and 9% by mass or less, from the viewpoint of increasing acid resistance.

The cement composition according to this embodiment may further contain fly ash as an admixture. The fly ash is not particularly limited, and examples thereof include fly ash type I, type II, type III, and type IV, and those conforming to the provisions of JIS A 6201 can be used. The content of the fly ash can be 2.5 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the powder component.

The cement composition according to the present embodiment may contain other admixtures in addition to fly ash. Examples of other admixtures include inorganic fine powders such as silica fume, cement kiln dust, blast furnace fume, hemihydrate gypsum, expanding agent, limestone fine powder, quicklime fine powder, and dolomite fine powder, as well as inorganic fillers such as sodium bentonite, calcium bentonite, attapulgite, sepiolite, activated clay, acid clay, allophane, imogolite, shirasu (volcanic ash), shirasu balloons, kaolinite, metakaolin (calcined clay), synthetic zeolite, artificial zeolite, artificial zeolite, mordenite, and clinoptilolite. The admixtures may be used alone or in combination of two or more.

The cement composition according to the present embodiment may contain an admixture. Examples of the admixture include air entraining agents, air entraining water reducing agents, fluidizing agents, separation reducing agents, setting retarders (e.g., tartaric acid, etc.), setting accelerators (e.g., aluminum sulfate, etc.), quick-setting agents, shrinkage reducing agents, foaming agents, foaming agents, waterproofing agents, and defoamers. Note that one type of admixture may be used alone, or two or more types may be used in combination.

The cement composition according to this embodiment contains Portland cement, slag, and a polymer for admixture with cement. The polymer cement ratio (solid content ratio) between the polymer for admixture with cement and the Portland cement is 3% by mass or more and 10% by mass or less, so that the amount of calcium hydroxide produced can be suppressed while the intrusion of sulfate ions can be suppressed, thereby improving acid resistance. In addition, the cement composition according to this embodiment has excellent crack resistance because it contains Portland cement.

In the cement composition according to this embodiment, the glass transition temperature of the polymer for cement admixture is 5°C or higher, which facilitates hydration reactions and improves the self-healing properties of cracked areas. Specifically, a film of the polymer for cement admixture adheres to a portion of the slag surface, forming an unreacted surface of the slag at the adhesion site. When a crack occurs in a concrete structure and the environmental temperature falls below the glass transition temperature, the film adhered to the slag surface peels off and a hydration reaction occurs on the unreacted surface of the slag. This allows the cracked area to be filled with hydrate, resulting in self-healing.

In the cement composition according to the present embodiment, the Blaine specific surface area of the slag is less than 8000 ^cm2 /g, so that a film of the polymer for cement admixture can be easily attached to the surface of the slag, and as a result, the self-healing property of the cracked parts can be further improved.

The cement composition according to this embodiment further contains fly ash as an admixture, which can increase the strength of the concrete structure.

<Mortar Composition>
The mortar composition according to this embodiment will be described below.

The mortar composition according to this embodiment contains the cement composition, water, and fine aggregate.

The water is not particularly limited, and examples that can be used include tap water, industrial water, recycled water, groundwater, river water, rainwater, etc.

Fine aggregate refers to aggregate that passes entirely through a 10 mm mesh sieve and 85% or more by mass through a 5 mm mesh sieve (JIS A 0203:2014). Examples of fine aggregate include naturally occurring sand such as mountain sand, river sand, land sand, sea sand, crushed sand, and limestone crushed sand, as specified in JIS A 5308 Appendix A Aggregates for Ready Mixed Concrete, and sand derived from slag such as blast furnace slag, electric furnace oxidized slag, and ferro-nickel slag. These fine aggregates may be used alone or in combination of two or more types. When using two or more types in combination, fine aggregates with different particle sizes may be mixed.

The mortar composition according to this embodiment contains the cement composition, water, and fine aggregate, and therefore can suppress the intrusion of sulfate ions while suppressing the production of calcium hydroxide, thereby improving acid resistance. In addition, the mortar composition according to this embodiment contains Portland cement, and therefore has excellent crack resistance.

The mortar composition according to this embodiment may be further modified to form a concrete composition by adding coarse aggregate.

Coarse aggregate refers to aggregate that retains 85% or more by mass on a 5 mm mesh sieve (JIS A 0203:2014). There are no particular limitations on the coarse aggregate, and examples include natural aggregates such as river gravel, mountain gravel, and sea gravel, artificial aggregates such as crushed stone such as sandstone, hard limestone, basalt, and andesite, and recycled aggregates. Note that one type of coarse aggregate may be used alone, or two or more types may be used in combination.

<Method of repairing concrete structures>
The concrete structure repair method according to this embodiment will be described below.

The method for repairing a concrete structure according to this embodiment involves filling or applying the mortar composition to the area of the concrete structure to be repaired.

First, the above-mentioned cement composition, water, and fine aggregate are mixed in a mixer such as a handle mixer or a mortar mixer to prepare a mortar composition. Next, the mortar composition is filled or applied to the repair area where surface preparation such as removal of corroded and deteriorated parts has been performed.

The method of filling or applying is not particularly limited, and examples include plastering and spraying. In the plastering method, a craftsman places an appropriate amount of mortar on a mortar board and applies the mortar composition to the repaired area of the concrete structure using a metal trowel or the like. In the spraying method, the mortar composition is sprayed onto the repaired area of the concrete structure using a device such as a mortar pump.

The method for repairing a concrete structure according to this embodiment involves filling or applying the mortar composition to the area of the concrete structure to be repaired, thereby repairing the corroded and deteriorated concrete structure and obtaining a concrete structure with high acid resistance and excellent crack resistance.

The following describes examples of the present invention, but the present invention is not limited to the following examples.

Mortar compositions for each example and comparative example were prepared with the mix shown in Table 1. Each mortar composition was tested for compressive strength, drying shrinkage, acid resistance, and self-healing ability. Crack resistance was evaluated by compressive strength and drying shrinkage tests, and if both tests were rated as "good", the crack resistance was rated as "good". The test results are shown in Table 2.

Details of each component shown in Table 1 are given below.
Cement (NC): Ordinary Portland cement (manufactured by Sumitomo Osaka Cement Co., Ltd.)
Cement (AC): Alumina cement AC-1 (manufactured by AGC)
Slag A: Cerament (manufactured by DC Co., Ltd.), Blaine specific surface area: 4000 cm ² /g
Slag B: Fine Cerament 20A (manufactured by DC Corporation), Blaine specific surface area 6900 cm ² /g
Slag C: Slag B and Slag D mixed in a ratio of 1:1, Blaine specific surface area 7500 cm ² /g
Slag D: Fine Cerament 10A (manufactured by DC Corporation), Blaine specific surface area 8000 cm ² /g
Fly ash (FA): JIS type II (produced in Hekinan)
Sand: No. 4/No. 6 = 1/1 mixed sand Emulsion (polymer for cement mixing): Polyacrylic ester with glass transition temperatures (Tg) of 5°C, 13°C, and 23°C

(Compressive strength)
Measurements were performed according to the test method shown in the Japan Sewage Works Agency's "Manual for Corrosion Inhibition and Anticorrosion Technology for Sewage Concrete Structures." Specifically, three rectangular column specimens measuring 40 x 40 x 160 mm were prepared and used for bending tests based on JIS R 5201, and then both folded pieces (six pieces) were used for compressive strength tests. The specimens were removed from the form the day after casting and cured underwater at 20±2°C until the material age reached three days.
The compressive strength measured was rated as "○" when it was 25 N/ ^mm2 or more, and the compressive strength measured was rated as "× (poor)" when it was less ^than 25 N/mm2.

(Drying shrinkage rate)
Measurements were performed according to the test method shown in the Japan Sewage Works Agency's "Manual for Corrosion Inhibition and Anticorrosion Technology for Sewage Concrete Structures." Specifically, measurements were performed based on JIS A 1129-3. The specimens were demolded the day after casting, and were stored at 20°C ± 2°C and a relative humidity of 60 ± 5% for up to 28 days.
Those whose measured dry shrinkage (length change) was less than 1000 μ were evaluated as dry shrinkage “◯”, and those whose measured dry shrinkage was 1000 μ or more were evaluated as dry shrinkage “×”.

(acid resistance)
The measurements were performed according to the test method shown in the Japan Sewage Works Agency's "Manual for Corrosion Inhibition and Anticorrosion Technology for Sewage Concrete Structures". Specifically, a cylindrical specimen measuring φ75 mm x 150 mm was first prepared based on JIS A 1132. The specimen was demolded the day after casting and cured underwater at 20±2°C until the material was 28 days old. Next, the specimen aged 28 days was immersed in a 5% aqueous sulfuric acid solution, and the specimen after immersion was cut in half with a diamond cutter or the like, and a 1% solution of phenolphthalein was sprayed on the cut surface. Next, the diameter length of the red-colored part of the specimen was measured at five points with a caliper, and the average value was subtracted from the initial width of the specimen (75 mm) to calculate 1/2 of the value, which was used as the sulfuric acid penetration depth.
The acid resistance was evaluated as "good" when the measured sulfuric acid penetration depth was 10 mm or less, and the acid resistance was evaluated as "poor" when the measured sulfuric acid penetration depth exceeded 10 mm.

(Self-healing)
A φ50 mm×100 mm specimen was prepared from the mortar composition of each Example and Comparative Example, and a crack was introduced to the top of each specimen by splitting. After coating the sides of each specimen with epoxy resin to make a waterproofing treatment, about 50 ml of water was poured on the top of each specimen. After one month, specimens that did not pass through the bottom were evaluated as "good", and specimens that did pass through were evaluated as "bad".

As can be seen from the results in Table 2, the mortar compositions of Examples 1 to 14, which satisfy all of the constituent requirements of the present invention, have high acid resistance and excellent crack resistance. In addition, the mortar compositions of Examples 1 to 11 have excellent self-healing properties because the Blaine specific surface area of the slag is less than 8000 ^cm2 /g and the glass transition temperature of the cement admixture polymer is 5°C or higher.

Claims (4)

A cement composition comprising Portland cement, slag, and a cement-mixing polymer,
The polymer cement ratio (solid content ratio) of the polymer for cement admixture to the Portland cement is 3% by mass or more and 10% by mass or less;
The glass transition temperature of the polymer for cement admixture is 5° C. or higher,
The cement composition further comprises fly ash as an admixture . 2. The cement composition of claim 1 , wherein the slag has a Blaine specific surface area of less than 8000 ^cm2 /g. A mortar composition comprising the cement composition according to claim 1 or 2 , water, and fine aggregate. A method for repairing a concrete structure, comprising filling or applying the mortar composition according to claim 3 to a portion of the concrete structure to be repaired.