JP7181787B6 - Alumina cement composition for salt-blocking mortar - Google Patents

Description

TECHNICAL FIELD The present disclosure relates to an alumina cement composition for salt barrier mortar.

In order to use concrete structures for a long period of time, they are repaired using repair materials and the like. In particular, from the viewpoint of suppressing deterioration due to permeation of salt or the like, it is said that it is effective to adsorb or fix chloride ions.

For example, cement compositions containing lithium nitrite are known to be effective for adsorbing chloride ions. However, since lithium nitrite is toxic, it has the problem of being expensive, in addition to the need to consider the surrounding environment.

In Patent Document 1, Portland cement and fine aggregate are mainly used, and salt adsorbent and fast-hardening material are included. Fast-hardening material includes anhydrous gypsum powder and calcium aluminate composition powder, and anhydrous gypsum powder has Blaine specific surface area. A cross-section repairing material for repairing salt damage characterized by having a surface area of 8000 cm ² /g or more has been proposed.

JP 2013-227210 A

Aluminous cements containing calcium aluminate and the like have excellent chemical stability. However, alumina cement may crack in the hardened body as the length changes due to curing. Moreover, in the case of high-temperature curing, voids may be generated due to transition of phases constituting the cured body. When a hardened body formed using alumina cement as described above is used for repairing a concrete structure, even if the material has excellent salt barrier properties, cracks and voids in the hardened body can cause damage to the inside of the concrete structure. There is a concern that the generation of rust in steel materials, etc., cannot be sufficiently suppressed.

An object of the present disclosure is to provide an alumina cement composition for a salt-blocking mortar, which has a small amount of initial length change accompanying curing and can form a hardened mortar having a salt-blocking property after curing. do.

One aspect of the present disclosure is an alumina cement composition for salt-blocking mortar comprising alumina cement and hemihydrate gypsum, wherein the alumina cement contains 55% to 75% by mass of CA and 5% by mass of C ₁₂ A ₇ % to 8% by mass, 10% to 28% by mass of C AF, and ₂ % to 6% by mass of _C AS, and the Blaine specific surface area of the alumina cement is 2000 cm ² /g to 4000 cm ² /g The gypsum hemihydrate has a Blaine specific surface area of 3000 cm ² /g to 6000 cm ² /g, and the content of the gypsum hemihydrate is 10 parts by mass to 24 parts by mass with respect to 100 parts by mass of the alumina cement. Provide an alumina cement composition for salt-blocking mortar.

The above-mentioned alumina cement composition for salt-blocking mortar contains a specific amount of specific gypsum hemihydrate relative to the alumina cement, so that the initial length change accompanying hardening is small and the salt-shielding property is high after hardening. A hardened mortar having properties can be formed.

The alumina cement composition for salt-shielding mortar may further contain at least one selected from the group consisting of calcium carbonate and silica fume. A hardened mortar formed using the alumina cement composition for salt-blocking mortar, wherein the alumina cement composition for salt-blocking mortar further contains at least one selected from the group consisting of calcium carbonate and silica fume. can improve the compressive strength of

A content of the calcium carbonate may be 15 parts by mass to 35 parts by mass with respect to 100 parts by mass of the alumina cement. When the content of calcium carbonate is within the above range, the compressive strength of the hardened mortar formed using the alumina cement composition for salt-blocking mortar can be improved.

A content of the silica fume may be 3 parts by mass to 12 parts by mass with respect to 100 parts by mass of the alumina cement. When the content of silica fume is within the above range, the compressive strength of the hardened mortar formed using the alumina cement composition for salt-blocking mortar can be improved.

According to the present disclosure, it is possible to provide an alumina cement composition for salt-blocking mortar, which has a small amount of initial length change accompanying curing and can form a hardened mortar having salt-blocking properties after curing. can.

FIG. 1 is a schematic top view of a length variation measuring device. FIG. 2 is a schematic cross-sectional view taken along line II-II of FIG.

Embodiments of the present disclosure will be described below. However, the following embodiments are examples for explaining the present disclosure, and are not intended to limit the present disclosure to the following contents.

As used herein, the term “initial stage” means a period of 24 hours from placing mortar.

One embodiment of the alumina cement composition for salt barrier mortar comprises alumina cement and gypsum hemihydrate. The alumina cement contains 55% to 75% by weight of CA, 5% to ₈ % by weight of C12A7, 10% to 28% by weight of _C4AF , and ₂ % to 6% by weight of _C2AS . Including % by mass. The Blaine specific surface area of the alumina cement is 2000 cm ² /g to 4000 cm ² /g. The gypsum hemihydrate has a Blaine specific surface area of 3000 cm ² /g to 6000 cm ² /g. Further, the content of the hemihydrate gypsum is 10 parts by mass to 24 parts by mass with respect to 100 parts by mass of the alumina cement.

The mortar, which is a mixture of the alumina cement composition for salt-blocking mortar and water, can be used, for example, as a repair material for concrete structures and the like. A concrete structure may include a concrete portion and a metal portion. The shape of the metal portion may be, for example, rod-like. Metal parts may comprise metals such as iron and steel, for example. The hardened mortar (hereinafter, also referred to as hardened mortar) is excellent in salt-shielding properties, so that it is possible to suppress the occurrence of rust on the steel material inside the concrete structure.

The term "salt barrier" as used herein means that the apparent diffusion coefficient of chloride ions is low. A low apparent diffusion coefficient of chloride ions means, for example, 0.05 cm ² /year or less. The alumina cement composition for salt-blocking mortar means that the hardened mortar has a low apparent diffusion coefficient of chloride ions when the hardened mortar is formed using the alumina cement composition for salt-blocking mortar. means

The alumina cement contains calcium aluminate as a main component. Examples of calcium aluminate include CaO.Al ₂ O ₃ (hereinafter also referred to as CA), 12CaO.7Al ₂ O ₃ (hereinafter also referred to as C ₁₂ A ₇ ), _CaO.2Al 2 O ₃ (hereinafter also referred to as CA ₂ 4CaO.Al ₂ O ₃ .Fe ₂ O ₃ (hereinafter also referred to as C ₄ AF), 2CaO.Al ₂ O ₃ .SiO ₂ (hereinafter also referred to as C ₂ AS), and the like. As used herein, the term "main component" means, for example, that the content of that component is 50% by mass or more.

The mineral composition of the above alumina cement is measured by analyzing powder X-ray diffraction data of the alumina cement by a profile fitting method. As the profile fitting method, the Rietveld analysis method or the WPF (Whole pattern fitting) analysis method is used (see Reference 1 below).

Reference 1: Practical X-ray Powder Diffraction - Introduction to the Rietveld Method, Japan Society for Analytical Chemistry, X-ray Analysis Research Council [ed.]

The mineral composition of the alumina cement is, for example, 55% to 75% by mass of CA, 5% to ₈ % by mass of C12A7, 10% to 28% by mass of _C4AF , and ₂ % by mass of _C2AS . It may be a composition containing from mass % to 6 mass %. The alumina cement preferably contains 58% to 72% by weight CA, 5.6% to _7.8 % by weight C12A7, 13% to ₂₅ % by weight _C4AF , and _C2AS 2.5% to 5.5% by mass, more preferably 62% to 68% by mass of CA, _5.4 % to 7.6% by mass of C ₁₂ A ₇ , and 16% by mass of C AF % to 22% by mass, and 3.0% to 5.0% by mass of C ₂ AS. When the mineral composition of the alumina cement is within the above range, it is possible to further improve the salt shielding properties of the hardened mortar formed. Moreover, since the mineral composition of the alumina cement is within the above range, it is possible to further reduce the initial amount of change in length accompanying hardening of the alumina cement composition for salt-impervious mortar.

The Blaine specific surface area of the alumina cement may be, for example, 2000 cm ² /g to 4000 cm ² /g. The Blaine specific surface area of the alumina cement is preferably 2300 cm ² /g to 3500 cm ² /g, more preferably 2500 cm ² /g to 3300 cm ² /g. When the Blaine specific surface area of the alumina cement is within the above range, a dense hardened mortar can be formed. Blaine specific surface area of alumina cement means a value measured according to JIS R 2521:1995 "Physical test method for alumina cement for fire resistance".

The gypsum hemihydrate may contain at least one selected from the group consisting of α-type gypsum hemihydrate and β-type gypsum hemihydrate.

The Blaine specific surface area of gypsum hemihydrate may be, for example, 3000 cm ² /g to 6000 cm ² /g. The Blaine specific surface area of the hemihydrate gypsum is preferably 3700 cm ² /g to 5500 cm ² /g, more preferably 4100 cm ² /g to 5350 cm ² /g. When the Blaine specific surface area of the hemihydrate gypsum is within the above range, the amount of change in initial length accompanying hardening of the alumina cement composition for salt-impervious mortar can be made smaller. The Blaine specific surface area of gypsum hemihydrate means a value measured according to JIS R 5201:2015 "Methods for Physical Testing of Cement".

The content of gypsum hemihydrate is 10 parts by mass to 24 parts by mass with respect to 100 parts by mass of the alumina cement. The content of gypsum hemihydrate is preferably 12 to 20 parts by mass, more preferably 13 to 18 parts by mass, with respect to 100 parts by mass of the alumina cement. When the content of gypsum hemihydrate is within the above range, the amount of change in length at the initial stage accompanying hardening of the alumina cement composition for salt-blocking mortar can be made smaller.

The alumina cement composition for salt-shielding mortar may contain other components in addition to the alumina cement and hemihydrate gypsum. Other components include, for example, admixtures, fine aggregates, water reducing agents, setting retarders, antifoaming agents, and resins. The alumina cement composition for salt-blocking mortar preferably contains an admixture.

Examples of admixtures include calcium carbonate and silica fume. The alumina cement composition for salt-shielding mortar may further contain at least one selected from the group consisting of calcium carbonate and silica fume.

A commercial item can be used for calcium carbonate. Calcium carbonate may be supplied, for example, using a material based on calcium carbonate. Materials containing calcium carbonate as a main component include, for example, limestone powder obtained by pulverizing limestone and concrete powder obtained by pulverizing waste concrete or the like.

The Blaine specific surface area of calcium carbonate is preferably 2000 cm ² /g to 6000 cm ² /g, more preferably 2400 cm ² /g to 5400 cm ² /g, even more preferably 2700 cm ² /g to 5100 cm ² /g. is g. When the Blaine specific surface area of calcium carbonate is within the above range, the compressive strength of the formed hardened mortar can be further improved. When the Blaine specific surface area of calcium carbonate is within the above range, a dense hardened mortar can be formed, and the salt-shielding property can be further improved. The Blaine specific surface area of calcium carbonate means a value measured according to JIS R 5201:2015 "Methods for Physical Testing of Cement".

The content of calcium carbonate is preferably 15 parts by mass to 35 parts by mass, more preferably 20 parts by mass to 29 parts by mass, and still more preferably 22 parts by mass to 27 parts by mass with respect to 100 parts by mass of the alumina cement. parts by mass, and more preferably 24 to 25 parts by mass. When the content of calcium carbonate is within the above range, the compressive strength of the formed hardened mortar can be further improved. When the content of calcium carbonate is within the above range, a dense hardened mortar can be formed, and the salt shielding property can be further improved.

Silica fume may be, for example, silica fume defined in JIS A 6207:2016 "Silica fume for concrete". Since the alumina cement composition for salt-blocking mortar contains silica fume, a dense hardened mortar can be formed, and the compressive strength and salt-blocking properties of the formed hardened mortar can be further improved. can.

The BET specific surface area of silica fume is preferably 10 m ² /g to 28 m ² /g, more preferably 14 m ² /g to 26 m ² /g, still more preferably 16 m ² /g to 24 m ² /g. . When the BET specific surface area of the silica fume is within the above range, a dense mortar hardened body can be formed, and the compression strength and salt barrier properties of the formed mortar hardened body can be further improved. The BET specific surface area of silica fume means a value measured by the BET multipoint method. BELSORP-mini II (product name) manufactured by Bell Japan Co., Ltd. can be used for the measurement.

The content of silica fume is preferably 3 parts by mass to 12 parts by mass, more preferably 5 parts by mass to 10 parts by mass, and still more preferably 6 parts by mass to 9 parts by mass with respect to 100 parts by mass of the alumina cement. parts, and more preferably 6 to 8 parts by mass. When the content of silica fume is within the above range, a dense hardened mortar can be formed, and the compressive strength and salt barrier properties of the hardened mortar thus formed can be further improved.

Examples of fine aggregates include sands such as silica sand, river sand, land sand, sea sand, and crushed sand. The maximum particle size of the fine aggregate is preferably 1700 µm or less, more preferably 1500 µm or less. The particle size of fine aggregate means a value measured using several sieves with different nominal sizes specified in JIS Z 8801-1: 2006 "Test sieve - Part 1: Metal mesh sieve". do.

The proportion of fine aggregate having a particle size of 1200 μm or more is preferably 20% by mass or less, more preferably 0.05% to 20% by mass, and still more preferably 0% by mass, relative to the total amount of fine aggregate. 0.01 mass % to 15 mass % or less, still more preferably 0.05 mass % to 10 mass %, even more preferably 0.1 mass % to 3.0 mass %. When the ratio of the fine aggregate having a particle size of 1200 µm or more is within the above range, the uniformity of the formed hardened mortar can be further improved, and the salt shielding property can be further improved. As used herein, the term "proportion of fine aggregate having a particle size of 1200 µm or more" means mass% of particles remaining on a sieve having a sieve mesh of 1200 µm.

The content of the fine aggregate is preferably 90 parts by mass to 200 parts by mass, more preferably 110 parts by mass to 180 parts by mass, and still more preferably 120 parts by mass to 120 parts by mass with respect to 100 parts by mass of the alumina cement. 170 parts by mass. When the content of the fine aggregate is within the above range, the compressive strength of the hardened mortar to be formed can be further improved.

Examples of water reducing agents include lignin-based, naphthalenesulfonic acid-based, aminosulfonic acid-based, polycarboxylic acid-based water reducing agents, high performance water reducing agents, and high performance AE water reducing agents. When the water reducing agent contains at least one selected from the group consisting of polycarboxylic acid water reducing agents, high performance water reducing agents and high performance AE water reducing agents, the fluidity of the mortar can be improved. The content of the water-reducing agent can be appropriately adjusted within a range that does not impair the effects of the invention.

Examples of setting retarders include organic acids such as oxycarboxylic acids, sugars such as glucose, maltose and dextrin, sodium bicarbonate, and sodium phosphate. Examples of oxycarboxylic acids include oxycarboxylic acids and salts thereof. Examples of oxycarboxylic acids include aliphatic oxyacids such as citric acid, gluconic acid, tartaric acid, glycolic acid, lactic acid, hydroacrylic acid, α-oxybutyric acid, glyceric acid, tartronic acid, and malic acid, and salicylic acid, aromatic oxyacids such as m-oxybenzoic acid, p-oxybenzoic acid, gallic acid, mandelic acid and tropic acid;

Salts of oxycarboxylic acids include, for example, alkali metal salts and alkaline earth metal salts. Alkali metal salts include, for example, sodium salts and potassium salts. Alkaline earth metal salts include, for example, calcium salts, barium salts and magnesium salts. The salt of the oxycarboxylic acid mentioned above is preferably the sodium salt, more preferably sodium tartrate. As the salt of oxycarboxylic acid, it is preferable to use sodium tartrate and sodium bicarbonate in combination.

The content of the setting retarder is preferably 0.01 parts by mass to 1.5 parts by mass, more preferably 0.05 parts by mass to 1.2 parts by mass, relative to 100 parts by mass of the alumina cement. , and more preferably 0.1 to 1.0 parts by mass. When the content of the setting retarder is within the above range, the workable time (so-called pot life) after preparation of the mortar can be extended without inhibiting curing.

Antifoaming agents include, for example, silicone-based, alcohol-based, and polyether-based synthetic substances, plant-derived natural substances, and the like. The content of the antifoaming agent can be appropriately adjusted within a range that does not impair the effects of the invention.

The resin may be, for example, powder, emulsion or fiber. When the alumina cement composition for salt-blocking mortar contains a resin as a powder or an emulsion, the salt-blocking property of the formed hardened mortar can be further improved. When the above-mentioned alumina cement composition for salt-blocking mortar contains a resin as a fiber, it is possible to further suppress the occurrence of cracks in the formed hardened mortar. The term "emulsion" means that a resin is emulsified and dispersed in water or a water-containing solvent.

The glass transition temperature (Tg) of the resin may be, for example, 0° C. or higher, 5° C. or higher, or 10° C. or higher. Since the glass transition temperature of the resin is within the above range, the mortar exhibits excellent adhesion to the surface of the concrete structure even when repairing the concrete structure in a wet state. obtain.

The glass transition temperature of a resin means a value that can be measured using a differential scanning calorimeter. More specifically, the glass transition temperature of the resin can be measured by the following method. First, the resin to be measured is heated from room temperature to 150° C. in 10 minutes (1 ^st heating) and held at 150° C. for 10 minutes to erase the thermal history of the resin. After that, the temperature was lowered to -100°C (rapid cooling, 1st ^cooling ), the temperature was raised again to 150°C at a rate of 15°C/min (2nd ^heating ), and the first Tg measurement was performed. The temperature was lowered from 150° C. to a temperature lower than the Tg measured by the 1st ^heating at a cooling rate of 15° C./min (2nd ^cooling ), and the Tg was measured for the second time. The Tg value obtained in the second Tg measurement is taken as the glass transition temperature of the resin to be measured. In addition, when the resin to be measured is in the form of an emulsion, an appropriate amount of the emulsion is dropped onto a glass plate to reduce the content of water or a water-containing solvent to form a coating film, and the coating film is the measurement target. can be

If the composition of the resin to be measured is known, the DSC measurement temperature range may be determined in advance using the estimated value T of the glass transition temperature obtained according to the following formula (1). . That is, after holding at 150 ° C. for 10 minutes, the temperature is lowered to a temperature 50 ° C. lower than the estimated value T of the glass transition temperature of the resin to be measured. may be measured.

The glass transition temperature (Tg) of the resin is determined by specifying the monomer species and composition ratio that provide the structural units constituting the resin, and using the Tg of the homopolymer of the monomer, the estimated value T is calculated from the following formula (1). can do. Since it is calculated as an estimated value T ( unit: K), it can be converted to degrees Celsius (unit: °C) and used. The following formula (1) assumes a resin that is a copolymer of n monomer species. For the Tg of the above homopolymer, for example, data described in Polymer Handbook 4th edition can be used. For example, polystyrene has a Tg of 100°C, poly(n-butyl acrylate) has a Tg of -52°C, and poly(n-ethylhexyl acrylate) has a Tg of -70°C.

1/T ₌ (Ca/ _Tga )+( _Cb / _Tgb )+...+(Cn/ _{Tgn )} ...(1)
In the above formula (1), T represents an estimated value (unit : K) of the glass transition temperature of the resin to be measured. In the above formula (1), Ca represents the weight fraction of monomer _A , Cb represents the weight fraction of monomer _B , and Cn represents the weight fraction of monomer _N. In the above formula (1), Tg _a represents the glass transition temperature (unit : K) of the homopolymer of monomer A, and Tg _b represents the glass transition temperature (unit : K) of the homopolymer of monomer B. , Tg _n indicates the glass transition temperature (unit : K) of a homopolymer of monomer N. Note that (C _a +C _b + . . . +C _n )=1.

Examples of powders (hereinafter also referred to as resin powders) include styrene-acrylic copolymers, acrylic polymers, vinyl acetate-Veova-acrylic copolymers and ethylene-vinyl acetate copolymers. The content of the resin powder is preferably 1 part by mass to 10 parts by mass, more preferably 2 parts by mass to 8 parts by mass, and still more preferably 4 parts by mass to 6 parts by mass with respect to 100 parts by mass of the alumina cement. part by mass. When the content of the resin powder is within the above range, it is possible to further improve the salt-shielding property of the hardened mortar to be formed.

The resin constituting the resin emulsion may be a homopolymer or a copolymer. The resin constituting the resin emulsion includes, for example, (meth)acrylic acid, (meth)acrylic acid derivatives such as (meth)acrylate, olefins such as vinyl acetate, ethylene and butadiene, and polymerizable components such as styrene. It may be the polymer of the polymerizable composition comprising. The polymerizable component may contain at least one selected from the group consisting of (meth)acrylic acid, (meth)acrylic acid derivatives, and styrene from the viewpoint of further improving the salt-shielding properties of the cured mortar obtained. (Meth)acrylic acid derivatives include, for example, methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

The content of the resin emulsion is preferably 1 part by mass to 10 parts by mass, more preferably 2 parts by mass to 7 parts by mass, more preferably 2 parts by mass to 7 parts by mass in terms of solid content with respect to 100 parts by mass of the alumina cement. It is 2.5 to 6 parts by mass, more preferably 3 to 5 parts by mass. By setting the content of the resin emulsion within the above range, the adhesiveness to the concrete structure and the salt shielding property can be further improved. The solid content of the resin emulsion means the solid content remaining after evaporation of the water or water-containing solvent in the resin emulsion.

The fibers (hereinafter also referred to as resin fibers) may be fibers made of resin. Examples of resins constituting resin fibers include polyolefins such as polyethylene and polypropylene, ethylene-vinyl acetate copolymer (EVA), polyester, polyamide, polyvinyl alcohol, vinylon, and polyvinyl chloride.

The fiber length of the resin fiber is preferably 0.5 mm to 15.0 mm, more preferably 1.0 mm to 12.0 mm, even more preferably 2.0 mm to 8.0 mm, and still more preferably 2.0 mm to 12.0 mm. 5 mm to 7.0 mm. By setting the fiber length of the resin fiber within the above range, the handleability when mixed with other components such as alumina cement can be improved, and the resulting hardened mortar has reduced salt-shielding properties and durability. can be suppressed. Further, by setting the fiber length of the resin fiber within the above range, the occurrence of cracks in the hardened mortar can be further suppressed. In addition, the fiber length of the resin fiber in this specification means the value measured by optical microscope observation.

The content of the resin fiber is preferably 0.01 to 3 parts by mass, more preferably 0.03 to 1 part by mass, and still more preferably 0 parts by mass with respect to 100 parts by mass of the alumina cement. 0.04 to 0.3 parts by weight, and more preferably 0.05 to 0.15 parts by weight. By setting the resin fiber content within the above range, cracking of the hardened mortar can be suppressed while suppressing deterioration of the salt barrier properties and durability of the resulting hardened mortar.

The aforementioned alumina cement composition for salt-blocking mortar can be used, for example, for repairing concrete structures. The mortar to be provided in the repaired portion of the concrete structure can be formed, for example, by blending and kneading the above-mentioned alumina cement composition for salt-impervious mortar and water. More specifically, the method for repairing a concrete structure using the above-described alumina cement composition for salt-blocking mortar comprises a step of applying mortar to the concrete structure (application step), and hardening the mortar. and a step of forming a hardened mortar (formation step). The mortar is a mixture of the alumina cement composition for salt-blocking mortar and water, and may be kneaded after mixing. The method for repairing a concrete structure may further include a step of removing a portion of the concrete structure. In the method for repairing a concrete structure described above, a more sufficient repair effect can be obtained by removing the deteriorated portion of the concrete structure in advance.

The amount of water added to the alumina cement composition for salt-shielding mortar is preferably 4 parts by mass to 25 parts by mass, more preferably 100 parts by mass of the alumina cement composition for salt-shielding mortar. It is 5 parts by mass to 20 parts by mass, more preferably 8 parts by mass to 16 parts by mass, and even more preferably 10 parts by mass to 14 parts by mass. In addition, when a resin emulsion is contained, it is preferable that the water content in the resin emulsion is included in the amount of water blended.

Since the above-described mortar uses the above-described alumina cement composition for salt-blocking mortar, the amount of change in initial length due to hardening is small. The initial amount of change in length accompanying hardening of the mortar can be, for example, −200 μm/m or more, −180 μm/m or more, −150 μm/m or more, −120 μm/m or more, or 0 μm/m or more. The initial amount of change in length accompanying hardening of the mortar can be, for example, 1000 μm/m or less, 800 μm/m or less, 500 μm/m or less, 300 μm/m or less, or 200 μm/m or less. "Greater than or equal to" in the negative range means approaching zero. Here, when the value of the initial length change amount of the hardened mortar is negative, it means that the hardened mortar has shrunk. In addition, the "length change amount" in this specification means a value determined by a method described in Examples described later.

Since the hardened mortar described above is formed using the above-described alumina cement composition for salt-shielding mortar, it has excellent salt-shielding properties. The apparent diffusion coefficient of chloride ions in the hardened mortar is, for example, 0.05 cm ² /year or less, 0.04 cm ² /year or less, 0.03 cm ² /year or less, 0.02 cm ² /year or less, or 0 .01 cm ² /year or less.

The apparent diffusion coefficient of chloride ions in the hardened mortar conforms to the test method described in JSCE-G571-2013 "Test method for effective diffusion coefficient of chloride ions in concrete by electrophoresis (draft)", It means the value obtained by using the "Appendix (reference) Apparent diffusion coefficient calculation method using effective diffusion coefficient by electrophoresis test".

The above-mentioned hardened mortar is excellent in compressive strength because it is formed using the above-mentioned alumina cement composition for salt-blocking mortar. The compressive strength of the hardened mortar at a curing temperature of 20° C. and an age of 28 days can be, for example, 40 N/mm ² or more, 45 N/mm ² or more, or 50 N/mm ² or more. The compressive strength of the hardened mortar at a curing temperature of 50° C. and an age of 28 days can be, for example, 40 N/mm ² or more, 50 N/mm ² or more, or 60 N/mm ² or more.

The compressive strength of the hardened mortar means a value measured according to the test method described in JIS R 5201:2015 "Physical Test Methods for Cement".

Since the above-mentioned hardened mortar is formed using the above-mentioned alumina cement composition for salt-impervious mortar, it is possible to suppress the generation of rust on the steel materials and the like inside the concrete structure. When a concrete structure is repaired using the hardened mortar, the burst rate can be, for example, 60% or less, 50% or less, 45% or less, or 40% or less.

The "emission rate" in this specification refers to a test piece (mortar hardening It means the value obtained by dividing the generated area of the steel bar by the effective area of the steel bar after curing in air for 2 weeks under the conditions of temperature: 20 ° C. and relative humidity: 65% RH.

Although several embodiments have been described above, the present disclosure is not limited to the above embodiments. Also, the descriptions of the above-described embodiments can be applied to each other.

Hereinafter, the contents of the present disclosure will be described in more detail with reference to examples and comparative examples. However, the present disclosure is not limited to the following examples.

(Example 1)
<Preparation of alumina cement composition for salt-blocking mortar>
An alumina cement composition for salt-blocking mortar having the following composition was prepared. The alumina cement composition for salt-shielding mortar is an alumina cement having a mineral composition of CA: 64% by mass, C12A7: ₇ % by mass, _C4AF : 18% by mass, and _C2AS : ₄ % by mass. (Blaine specific surface area: 2700 cm ² /g) is 100 parts by mass, gypsum hemihydrate (Blaine specific surface area: 4380 cm ² /g) is 20.0 parts by mass, and calcium carbonate (Blaine specific surface area: 3000 cm ² /g) is 25. 6 parts by mass, 7.7 parts by mass of silica fume (BET specific surface area: 19 m ² /g), silica sand (excluding particles with a particle size of 1700 µm or more, mass ratio of particles with a particle size of 1200 µm or more to the entire fine aggregate is 1.48% by mass, the mass ratio of particles with a particle diameter of 600 μm or more is 49.13%, the mass ratio of particles with a particle diameter of 300 μm or more is 44.04%, and the mass ratio of particles with a particle diameter of 150 μm or more is 4 .06% by mass, the mass ratio of particles with a particle size of 75 μm or more is 1.26% by mass) is 147.6 parts by mass, Na gluconate (sodium gluconate) is 0.09 parts by mass, Na tartrate (sodium tartrate) is 0.37 parts by mass, 0.37 parts by mass of Na bicarbonate (sodium bicarbonate), and 5.85 parts by mass of resin (styrene-acrylic copolymer, glass transition temperature: 21° C.) . A water-reducing agent was appropriately added to improve fluidity. A powder was used as the resin.

<Preparation of mortar>
2.0 kg of the above-mentioned alumina cement composition for salt-blocking mortar and a predetermined amount of water are weighed into a container, and the temperature is 20 ° C. and the relative humidity is 65% RH. A mortar was prepared by mixing for a minute. The amount of water to prepare the mortar is the amount of the alumina cement composition for salt-shielding mortar, where W is the mass of water and P is the total mass of the alumina cement composition for salt-shielding mortar. The ratio of the mass W of water to the total mass P (W/P) was adjusted to 0.128.

[Mineral Composition of Alumina Cement]
The mineral composition of the alumina cement was measured using the WPF analysis method utilizing X-ray powder diffraction. Powder X-ray diffraction measurement uses a powder X-ray diffractometer (manufactured by Rigaku Co., Ltd., product name: RINT-2500), tube voltage: 35 kV, tube current: 110 mA, measurement range: 2θ = 10 to 60 °, step width : 0.02°, counting time: 2 seconds, divergence slit: 1°, and receiving slit: 0.15 mm.

The WPF analysis method used powder X-ray diffraction pattern comprehensive analysis software (manufactured by Materials Data Inc., product name: JADE6.0). With respect to the mineral composition shown in Table 1, the reference document was used as the initial value, each crystal phase was refined and fitting was performed, and the mineral composition was measured with the total amount of each mineral set to 100. Table 2 shows the mineral composition obtained. In addition, CaO is represented by C, Al ₂ O ₃ by A, SiO ₂ by S, Fe ₂ O ₃ by F, and SO ₃ by S.

Reference 2: Ito, S.; , Suzuki, K., Inagaki, M.; , Naka, S.; Mater. Res. Bull. , vol. 15, p. 925 (1980)
Reference 3: Natl. Bur. Stand. (U.S.), Circ. 539, vol. 9, p. 20 (1960)
Reference 4: Colville, A.; A. , Geller, S.; Acta Crystallogr. , Sec. B, vol. 27, p. 2311 (1971)
Reference 5: Louisnathan, S.; J. Can. Mineral. , vol. 10, p. 822 (1971)

[Evaluation of initial length change due to hardening of mortar]
The mortar prepared as described above was evaluated for initial length change associated with hardening of the mortar. More specifically, the evaluation was carried out by measuring the amount of change in the initial length of the hardened mortar placed in the apparatus using a length change measuring apparatus as shown in FIG.

FIG. 1 is a schematic diagram of a length variation measuring device. FIG. 1 is a schematic top view of a length variation measuring device 10. FIG. FIG. 2 is a schematic cross-sectional view taken along line II-II in FIG. The length variation measuring device 10 has a mold 11 forming a container 20 in which mortar is cast. Side walls 11a at one end of the formwork 11 in the longitudinal direction are provided on a surface (inner surface) of the side walls 11a on the side of the housing portion 20 (inner surface) and a surface (outer surface) of the side walls 11a on the side opposite to the side of the housing portion 20 (outer surfaces). It has a cushioning material 14 . The length variation measuring device 10 has a rod 13a made of SUS arranged so as to pass through the side wall 11a and two cushioning materials 14 provided on both sides thereof. The bar 13a can move along the longitudinal direction of the mold 11 (the direction indicated by x or y in FIG. 1). Discs 12a and 12b made of SUS are provided at both ends of the rod 13a. SUS means a stainless steel material defined by JIS.

The length variation measuring device 10 further has a SUS rod 13b on the side wall 11b of the mold 11 facing the side wall 11a. A disk 12c made of SUS is provided at the end of the rod 13b opposite to the side wall 11b. The disk 12c is provided so as to face the disk 12b. The distance d between the discs 12b and 12c before the measurement of the length variation is 210 mm. As shown in FIG. 2, a fluororesin layer 16 is provided on the inner surface of the mold 11 . Here, the height of the inner wall of the formwork 11 (indicated by h in FIG. 2) is 30 mm, and the width of the bottom surface of the inner wall of the formwork 11 in the transverse direction (indicated by w in FIG. 2) is 40 mm. .

When the mortar placed in the mold 11 shrinks as it hardens, the positions of the discs 12a and 12b are displaced in the x direction from the positions before measurement. Further, when the mortar placed in the mold 11 expands as it hardens, the positions of the discs 12a and 12b are displaced in the direction of the arrow y from the positions before measurement. A displacement sensor 15 capable of measuring the displacement of the disk 12a in the xy direction is arranged outside the mold 11. As shown in FIG. The displacement sensor 15 detects displacement using a laser.

Using the length change amount measuring device 10 as described above, the mortar immediately after being mixed with water was placed in the housing portion 20 of the formwork 11 to the height of the formwork, and the temperature was 20°C and the relative humidity was: It was cured in the atmosphere under the condition of 65% RH. The change in the length of the placed mortar (semi-hardened mortar) (displacement a in the xy direction of the disk 12a) was measured every minute from immediately after placement until 24 hours later.

The initial amount of change in length accompanying hardening of the cast mortar (semi-hardened mortar) was calculated based on the following formula (2) using the above measurement results. Table 3 shows the results.

Length variation (μm/m)=(a/d)×1000 (2)
In the above equation (2), a indicates the displacement a (μm) of the disc 12a in the xy direction, and d indicates the distance d (m) between the discs 12b and 12c before measurement. A negative length change value means that the mortar shrinks as it hardens, and a positive length change value means that the mortar expands as it hardens. do.

<Evaluation of hardened mortar>
A hardened mortar formed using the mortar prepared as described above was evaluated for salt barrier properties, compressive strength, and corrosion amount.

[Salt barrier]
Regarding the hardened mortar formed using the above mortar, "Effective diffusion coefficient test method for chloride ions in concrete by electrophoresis (draft)" in "Concrete Standard Specifications JSCE-G 571-2013" edited by the Japan Society of Civil Engineers Conduct an electrophoresis test of chloride ions in accordance with , and calculate the apparent diffusion coefficient of chloride ions in the above mortar based on "Attachment (Reference) Apparent diffusion coefficient calculation method using effective diffusion coefficient by electrophoresis test" Diffusion coefficients were determined. Table 3 shows the results.

[Compressive strength]
The compressive strength of the hardened mortar formed using the above mortar was measured in accordance with JIS R 5201:2015 "Physical test method for cement". Specifically, a hardened mortar after 28 days of age at an underwater curing temperature of 20°C and a hardened mortar after 28 days of age at an underwater curing temperature of 50°C were prepared, and the compressive strength was measured. It was measured. Table 3 shows the results.

[Amount of corrosion]
For the mortar hardened body formed using the above mortar, a specimen ( (equivalent to a hardened mortar) was air-cured for 2 weeks at a temperature of 20°C and a relative humidity of 65% RH, and then the generation rate was obtained by dividing the generation area of the steel bar by the effective area of the steel bar. rice field. Table 3 shows the results.

(Examples 2-4 and Comparative Examples 1-3)
An alumina cement composition for salt-blocking mortar was prepared in the same manner as in Example 1, except that the amount (parts by mass) of each component was changed as shown in Table 3. In addition, the amount of the water reducing agent was appropriately adjusted in order to ensure the fluidity when preparing the mortar.

A mortar was prepared in the same manner as in Example 1 using the prepared alumina cement composition for salt-blocking mortar. After that, the mortar was evaluated for initial length change in the same manner as in Example 1. In addition, the hardened mortar formed using the above mortar was evaluated in the same manner as in Example 1 for salt barrier properties, compressive strength, and corrosion amount. Table 3 shows the results.

According to the present disclosure, it is possible to provide an alumina cement composition for salt-blocking mortar, which has a small amount of initial length change accompanying curing and can form a hardened mortar having salt-blocking properties after curing. can.

DESCRIPTION OF SYMBOLS 10... Length change measuring apparatus, 11... Formwork, 12a, 12b, 12c... Disk, 13a, 13b... Bar, 14... Cushioning material, 15... Displacement sensor, 16... Fluororesin layer, 20... Storage part.

Claims (4)

An alumina cement composition for salt-blocking mortar containing alumina cement , hemihydrate gypsum , calcium carbonate, silica fume, and resin powder ,
The alumina cement contains 55% to 75% by mass of CA, 5% to ₈ % by mass of C12A7, and ₁₀ % of _C4AF in the mineral composition analyzed by the profile fitting method of powder X-ray diffraction data. % to 28% by mass, and ₂ % to 6% by mass of C AS,
Blaine specific surface area of the alumina cement is 2000 cm ² /g to 4000 cm ² /g,
The gypsum hemihydrate has a Blaine specific surface area of 3000 cm ² /g to 6000 cm ² /g,
The content of the hemihydrate gypsum is 12 parts by mass to 24 parts by mass with respect to 100 parts by mass of the alumina cement ,
The content of the calcium carbonate is 15 parts by mass to 35 parts by mass with respect to 100 parts by mass of the alumina cement,
The content of the silica fume is 3 parts by mass to 12 parts by mass with respect to 100 parts by mass of the alumina cement,
An alumina cement composition for salt-blocking mortar , wherein the content of the resin powder is 1 part by mass to 10 parts by mass with respect to 100 parts by mass of the alumina cement. The alumina cement composition for salt-blocking mortar according to claim 1, wherein said calcium carbonate has a Blaine specific surface area of 2000 cm ² /g to 6000 cm ² /g. 3. The alumina cement composition for salt-blocking mortar according to claim 1, wherein the silica fume has a BET specific surface area of 10 m ² /g to 28 m ² /g. Claims 1 to 3, wherein the resin powder contains at least one selected from the group consisting of styrene-acrylic copolymer, acrylic polymer, vinyl acetate-Viova-acrylic copolymer and ethylene-vinyl acetate copolymer. The alumina cement composition for salt-blocking mortar according to any one of .

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