JP7717538B2 - Mortar composition and method of use thereof - Google Patents

Description

The present invention relates to a mortar composition and a method for using the same.

Cement composite materials containing reinforcing fibers are known as road repair materials. For example, Patent Document 1 proposes a construction method in which ultra-high-strength fiber-reinforced concrete, created by mixing reinforcing fibers, fine aggregate, a water-reducing agent, a shrinkage-reducing agent, an antifoaming agent, and water, is poured into the joint surface. It is stated that this construction method allows for thinner walls because the hardened body has a higher strength than conventional repair materials.

Patent Document 2 proposes a cement-based repair material for use in repairing roads, bridges, etc., obtained by mixing reinforcing fibers with cement paste, which is made by adding water, a water-reducing agent, an antifoaming agent, a thixotropic agent, and a hardening agent to a binder made of cement, silica fume, and limestone filler.

JP 2017-133344 A Japanese Patent Application Laid-Open No. 2020-175600

In recent years, there has been an increasing demand for repairs to expressway decks. Because repairs must be carried out in a planned manner, there is a need for technology that can temporarily reduce damage to expressways, allowing them to continue operating until repair work is available. Such technology requires materials that have sufficient strength, toughness, and durability to prevent cracking without the need for waterproofing agents, and that exhibit appropriate fluidity during construction while also exhibiting excellent strength development in a short period of time, in order to shorten the closure period for repair work. For example, because expressways have both transverse and longitudinal gradients, repair work can be carried out smoothly by using materials that have appropriate fluidity while also exhibiting excellent strength development in a short period of time.

However, even if a mortar composition has suitable fluidity in the summer, it may not necessarily have sufficient fluidity in the winter, raising concerns that repair work may not proceed smoothly. Furthermore, suitable fluidity and the ability to develop strength in a short period of time may be required not only for repairing inclined highways, but also for repairing and covering a variety of structures. Therefore, the present invention provides a mortar composition that has suitable fluidity even in low-temperature environments and is excellent at developing strength in a short period of time, and is suitable for a variety of situations, including repairing and covering not only inclined highways, but also for repairing and covering structures such as roads, bridges, port structures, river structures, and underground structures. It also provides a method for using the mortar composition, which enables smooth repair work even in low-temperature environments in similar situations.

In one aspect, the present invention provides a mortar composition comprising cement, high-tensile fibers, a hardening accelerator, a retarder, and a water-reducing agent, wherein, when the unit amount of the hardening accelerator per 1 ^m3 of mortar composition is A [kg/ ^m3 ], the unit amount of the retarder is B [kg/ ^m3 ], and the unit amount of the water-reducing agent is C [kg/ ^m3 ], A is 100 to 180 kg/ ^m3 , B is ¹ to 10 kg/ ^m3 , C is 5 to 30 kg/m3, A/B is 22.0 to 55.0, and C/B is 2.1 to 5.5.

The mortar composition contains high-tensile fibers, a hardening agent, a retarder, and a water-reducing agent. The mortar composition contains predetermined amounts of hardening agent, retarder, and water-reducing agent, with the ratio of hardening agent to retarder (A/B) and the ratio of water-reducing agent to retarder (C/B) each falling within a predetermined range. Because these three components are contained in a balanced manner, the fluidity of the mortar composition during construction can be maintained within an appropriate range, even in low-temperature environments. Furthermore, the appropriate fluidity improves filling properties and provides excellent strength development in a short period of time. In other words, because the mortar composition contains a balanced amount of high-tensile fibers, a hardening agent, a retarder, and a water-reducing agent, it has appropriate fluidity in low-temperature environments and excellent strength development in a short period of time. Note that, in this specification, "low-temperature environments" refers to environments where the temperature is below 20°C.

The mineral composition of the cement preferably has a _C3S content of 25.0 to 75.0 mass%, a _C3A content of less than 4.0 mass%, and a 45 μm sieve residue of less than 25.0 mass%, which allows for both fluidity and rapid strength development at an even higher level.

The high-tensile fibers preferably contain at least one type of fiber selected from the group consisting of metal fibers, carbon fibers, aramid fibers, PP fibers, PVA fibers, PE fibers, glass fibers, nylon fibers, and PBO fibers. This allows for the formation of a hardened mortar with sufficiently high strength and durability.

It is preferable that the high-tensile fiber has a tensile strength of 100 to 10,000 N/mm ² , an aspect ratio of 40 to 250, and a unit amount of the high-tensile fiber of 10 to 500 kg/m ^3. By including such high-tensile fibers, the toughness and tensile strength of the hardened mortar can be sufficiently increased.

The mortar composition further contains fine aggregate and inorganic fine powder, and the inorganic fine powder preferably has a Blaine specific surface area of 3000 to 5000 cm ² /g. This further increases the fluidity of the mortar composition. The Blaine specific surface area of the inorganic fine powder in this specification can be measured using a Blaine air permeation device described in JIS R 5201:1997.

The mortar composition preferably further contains silica fume. The average particle size of the silica fume is preferably 0.05 to 2.0 μm. The unit amount of silica fume per 1 ^m3 of the mortar composition is preferably 30 to 350 kg/ ^m3 . This can further increase the compressive strength of the hardened body of the mortar composition and the fluidity of the mortar composition.

The above mortar composition is preferably used for road repair in an environment below 20°C. In such an environment, the above mortar composition has appropriate fluidity and excellent strength development. Therefore, it has excellent workability and reliability.

In one aspect, the present invention provides a method for using a mortar composition, which includes a step of repairing a road using any of the above-mentioned mortar compositions, and involves pouring the mortar composition into the road in a low-temperature environment of less than 20°C. This method uses a mortar composition that has adequate fluidity during construction even in a low-temperature environment. Therefore, this method allows road repair work to be carried out smoothly even in a low-temperature environment of less than 20°C.

The above-mentioned method of use preferably includes a step of adjusting the mixing ratio of at least one selected from the group consisting of a hardening accelerator, a retarder, and a water-reducing agent according to the temperature. The fluidity of mortar compositions varies greatly depending on the temperature. By including this step, the properties of the mortar composition can be adjusted within an appropriate range to match the temperature.

The present invention provides a mortar composition that has appropriate fluidity even in low-temperature environments and exhibits excellent strength development in a short period of time. It also provides a method for using the mortar composition that allows for smooth repair work even in low-temperature environments.

1 is a ¹ H-NMR spectrum of the antifoaming agent used in the examples.

One embodiment of the present invention will be described below. However, the following embodiment is merely an example for explaining the present invention, and is not intended to limit the present invention to the following content.

One embodiment of the mortar composition includes cement, high-tensile fibers, a hardening accelerator, a retarder, and a water-reducing agent.

The mineral composition of the cement may be, for example, a _C3S content of 25.0 to 75.0 mass% and a _C3A content of less than 4.0 mass%. The _C3S content is preferably 40.0 to 73.0 mass%, more preferably 48.0 to 70.0 mass%, and even more preferably 50.0 to 68.0 mass%. The _C3A content is preferably less than 2.7 mass%, more preferably less than 2.3 mass%. There is no particular restriction on the lower limit of the _C3A content, and it may be, for example, 0.1 mass%. By having such a mineral composition, it is possible to sufficiently increase the compressive strength of the hardened mortar while sufficiently increasing the fluidity.

The C ₂ S content is preferably 9.5 to 40.0 mass%, more preferably 10.0 to 35.0 mass%, and even more preferably 12.0 to 30.0 mass%. The _{C 4} AF content is preferably 9.0 to 18.0 mass%, more preferably 10.0 to 15.0 mass%, and even more preferably 11.0 to 15.0 mass%. By having such a mineral composition, it is possible to sufficiently increase the compressive strength of the hardened mortar while sufficiently increasing the fluidity.

The mineral composition described above is calculated using the Bogue formula below. The chemical components of the cement used in the Bogue formula can be measured in accordance with JIS R 5202:2010, "Methods for Chemical Analysis of Cement."

C ₃ S content = (4.07 x CaO) - (7.60 x SiO ₂ ) - (6.72 x Al ₂ O ₃ ) - (1.43 x Fe ₂ O ₃ ) - (2.85 x SO ₃ )
C ₂ S content = (2.87 x SiO ₂ ) - (0.754 x C ₃ S)
C ₃ A content = (2.65 x Al ₂ O ₃ ) - (1.69 x Fe ₂ O ₃ )
C ₄ AF content = 3.04 x Fe ₂ O ₃

The 45 μm sieve residue of the cement may be, for example, less than 25.0% by mass, preferably less than 20.0% by mass, more preferably less than 18.0% by mass, and even more preferably less than 16.0% by mass. The 45 μm sieve residue may be 0% by mass or 1.0% by mass or greater. A cement particle size within the above range ensures high compressive strength. Furthermore, because mortar compositions containing such cement have appropriate viscosity, sufficient dispersibility can be ensured even when high-tensile fibers are included. The 45 μm sieve residue of the cement can be measured in accordance with the Cement Association Standard Test Method JCAS K-02, "Test Method for Cement Fineness Using a 45 μm Mesh Sieve."

The Blaine specific surface area of the cement is preferably 2500 to 4800 ^{cm 2} /g, more preferably 2800 to 4000 cm ² /g, even more preferably 3000 to 3600 cm ² /g, and particularly preferably 3100 to 3500 cm ² /g. If the Blaine specific surface area of the cement is too small, the strength of the mortar composition tends to be low, and if it is too large, the fluidity at low water-cement ratios tends to be reduced. The Blaine specific surface area of the cement can be measured in accordance with JIS R 5201:1997 "Physical Testing Methods for Cement."

The unit amount of cement per 1 ^m3 of the mortar composition may be 700 to 1100 kg/ ^m3 , or may be 750 to 1000 kg/ ^m3 .

The high-tensile fibers include at least one fiber selected from the group consisting of metal fibers, carbon fibers, aramid fibers, PP (polypropylene) fibers, PVA (polyvinyl alcohol) fibers, PE (polyethylene) fibers, glass fibers, nylon fibers, and PBO (polyparaphenylene benzobiz oxazole) fibers. Metal fibers include steel fibers, stainless steel fibers, and amorphous alloy fibers. The tensile strength of the high-tensile fibers is preferably 100 to 10,000 N/ ^mm² , more preferably 500 to 5,000 N/ ^mm² , even more preferably 2,000 to 3,000 N/ ^mm² , and particularly preferably 2,000 to 2,500 N/ ^mm² . The aspect ratio (fiber length/fiber diameter) of the high-tensile fibers is preferably 40 to 250, more preferably 50 to 200, and even more preferably 60 to 170. The inclusion of such high-tensile fibers can sufficiently increase the toughness and tensile strength of the hardened mortar.

The fiber diameter of the high-tensile fibers may be, for example, 0.05 to 1.20 mm. The fiber length of the high-tensile fibers may be 3 to 60 mm. The unit amount of the high-tensile fibers may be preferably 10 to 500 kg/ ^m3 , more preferably 50 to 300 kg/ ^m3 , even more preferably 100 to 200 kg/ ^m3 , and even more preferably 120 to 180 kg/ ^m3 .

The hardening agent is an admixture that promotes the strength development of the mortar composition, and examples thereof include a mixture of calcium aluminate and inorganic sulfate. Such hardening agents contain _{Al2O3 ,} CaO, and _SO3 as chemical components. Commercially available products include, for example, Biform (registered trademark) manufactured by Denka Co., Ltd.

If the content of the hardening agent is too low, the mortar composition will not be able to develop sufficient strength in a short time. On the other hand, if the content is too high, the hardening will proceed too quickly, reducing filling properties and preventing sufficient strength development. In addition, fluidity will decrease and workability will deteriorate. Therefore, from the viewpoint of obtaining a mortar composition that has appropriate fluidity even in low-temperature environments and is excellent in short-term strength development, the unit amount A [kg/m ³ ] of the hardening agent per 1 m ³ of the mortar composition is 100 to 180 kg/m ^3. The lower limit of the unit amount A [kg/m ³ ] of the hardening agent is preferably 110 kg/m ³ , more preferably 120 kg/m ³ , and even more preferably 125 kg/m ^3. The upper limit of the unit amount A [kg/m ³ ] of the hardening agent is preferably 170 kg/m ³ , more preferably 160 kg/m ³ , and even more preferably 150 kg/m ³ .

Retarder, also known as a set adjuster or retarder, is an admixture that delays the initial hardening of the mortar composition. Examples of retarders include lignin sulfonic acid, silicon fluoride, or those based primarily on alkali carbonate and citric acid. Commercially available products include Setter D-300 manufactured by Denka Co., Ltd.

If the content of retarder is too low, hardening will be accelerated too much in a short time, resulting in reduced filling properties and insufficient strength development. Furthermore, fluidity will decrease, worsening workability. On the other hand, if the content of retarder is excessive, the flow will be reduced, workability will be reduced, and the target strength will tend not to be achieved in a short time. From the viewpoint of obtaining a mortar composition that has appropriate fluidity in a low-temperature environment and ensures excellent strength development in a short time, the unit amount B [kg/m ³ ] of retarder per 1 m ³ of mortar composition is 1 to 10 kg/m ³ . The lower limit of the unit amount B [kg/m ³ ] of retarder is preferably 2 kg/m ³ , more preferably 3 kg/m ³ . The upper limit of the unit amount B [kg/m ³ ] of retarder is preferably 8 kg/m ³ , more preferably 7 kg/m ³ , and even more preferably 5 kg/m ³ .

Water-reducing agents have the effect of improving the fluidity of mortar compositions, and include lignin-based, naphthalenesulfonic acid-based, aminosulfonic acid-based, and polycarboxylic acid-based water-reducing agents, as well as high-performance water-reducing agents and high-performance air-entraining (AE) water-reducing agents. From the perspective of improving the fluidity of mortar compositions, polycarboxylic acid-based water-reducing agents are preferred. Such water-reducing agents form steric hindrances between cement clinkers, improving the fluidity of mortar compositions.

If the content of the water-reducing agent is too low, the fluidity of the mortar composition decreases, resulting in poor workability. On the other hand, if the content of the water-reducing agent is excessive, material separation occurs and the mortar composition cannot develop sufficient strength. From the viewpoint of obtaining a mortar composition that has appropriate fluidity in a low-temperature environment and is excellent in short-term strength development, the unit amount C [kg/m ³ ] of the water-reducing agent per 1 m ³ of the mortar composition is 5 to 30 kg/m ^3. The lower limit of the unit amount C [ ^kg /m ³ ] of the water-reducing agent per 1 m 3 of the mortar composition is preferably 7 kg/m ³ , more preferably 9 kg/m ³ , and even more preferably 10 kg/m ^3. The upper limit of the unit amount C [kg/m ³ ] of the water-reducing agent is preferably 25 kg/m ³ , more preferably 22 kg/m ³ , and even more preferably 20 kg/m ³ .

As described above, the mortar composition of this embodiment contains a hardening accelerator, a retarder, and a water-reducing agent as admixtures. The ratio (A/B) of the unit amount A of the hardening accelerator to the unit amount B of the retarder is 22.0 to 55.0. The upper limit of the ratio (A/B) is preferably 51.0, more preferably 45.0, and particularly preferably 41.0. This prevents the mortar composition from hardening too quickly, improving workability. The lower limit of the ratio (A/B) is preferably 23.0, more preferably 25.0. This allows the mortar composition to sufficiently develop strength in a short period of time. In addition, the mortar composition can be sufficiently prevented from flowing excessively when cast on roads or the like having a transverse gradient and/or longitudinal gradient.

The ratio (C/B) of the unit amount C of the water-reducing agent to the unit amount B of the retarder is 2.1 to 5.5. The upper limit of the ratio (C/B) is preferably 5.2, and more preferably 4.5. This ensures sufficient fluidity of the mortar composition. The lower limit of the ratio (C/B) is preferably 2.2, more preferably 2.3, and even more preferably 2.4. This ensures that the excellent fluidity of the mortar composition is sufficiently maintained even when the amount of water added is reduced.

The ratio (A/C) of the unit amount A of the rapid hardening agent to the unit amount C of the water reducing agent is 20.0 or less, preferably 16.0 or less, and more preferably 14.0 or less. This prevents the mortar composition from hardening too quickly, ensuring fluidity and improving workability. The ratio (A/C) is preferably 4.0 or more, and more preferably 6.0 or more. This allows the mortar composition to develop sufficient strength in a short period of time.

The mortar composition of this embodiment contains a balanced mixture of hardening agents, retarders, and water-reducing agents as admixtures. Therefore, it has appropriate fluidity during application, even in low-temperature environments, and exhibits excellent strength development in a short period of time. For this reason, it is particularly useful, for example, for highway repair applications, where good application properties and rapid strength development are required.

The mortar composition of this embodiment may contain, in addition to the above-mentioned admixture, an inorganic fine powder and a fine aggregate. Examples of inorganic fine powders include limestone powder, silica powder, and crushed stone powder. The inorganic fine powder may be a fine powder obtained by pulverizing and/or classifying limestone powder, silica powder, crushed stone powder, etc. The inorganic fine powder may be blended for the purpose of supplementing the fine particle content of the fine aggregate. The Blaine specific surface area of the inorganic fine powder is preferably 3000 to 5000 ^{cm 2} /g, more preferably 3200 to 4700 cm ² /g, and even more preferably 3400 to 4600 cm ² /g. The inclusion of such inorganic fine powders can further improve the fluidity of the mortar composition. The unit amount of the inorganic fine powder per 1 m ³ of the mortar composition is preferably 100 to 300 kg/m ³ , more preferably 150 to 250 kg/m ³ .

Examples of fine aggregate include river sand, land sand, sea sand, crushed sand, silica sand, limestone aggregate, blast furnace slag fine aggregate, ferronickel slag fine aggregate, copper slag fine aggregate, and electric furnace oxidizing slag fine aggregate. The fine aggregate may have a particle size that passes entirely through a 10 mm sieve and 85% by mass or more through a 5 mm sieve. The particle size of the fine aggregate measured in accordance with JIS A 1102:2014 is preferably 5.0 mm or less, and the coarseness ratio is preferably 2.0 to 2.5. The fine particle content of the fine aggregate measured in accordance with JIS A 1103:2014 is preferably 9% or less. The unit amount of fine aggregate per cubic ^meter of mortar composition is preferably 600 to 1,050 kg/ ^m3 , more preferably 700 to 950 kg/ ^m3 , and even more preferably 800 to 900 kg/ ^m3 . The fine aggregate may be prepared by mixing a plurality of fine aggregates having different particle sizes.

The total unit amount of fine aggregate and inorganic fine powder per 1 ^m3 of mortar composition is preferably 800 to 1200 kg/ ^m3 , more preferably 900 to 1150 kg/ ^m3 , and even more preferably 1000 to 1100 kg/ ^m3 .

The mortar composition of this embodiment may contain silica fume. Silica fume is a by-product obtained by collecting dust in exhaust gas generated during the production of metal silicon, ferrosilicon, electrofused zirconia, or the like. Silica fume contains, as a main component, amorphous _SiO2 that dissolves in an alkaline solution. The average particle size of silica fume is preferably 0.05 to 2.0 μm, more preferably 0.10 to 1.5 μm, and even more preferably 0.18 to 0.28 μm. By using such silica fume, it is possible to sufficiently increase the compressive strength of the hardened mortar while maintaining the high fluidity of the mortar composition.

The content of silica fume based on cement is preferably 3 to 30 mass%, more preferably 5 to 20 mass%, and even more preferably 8 to 18 mass%, and the unit amount of silica fume per cubic ^meter of mortar composition is preferably 30 to 350 kg/ ^m3 , more preferably 50 to 250 kg/ ^m3 , and even more preferably 100 to 130 kg/ ^m3 .

The mortar composition of this embodiment may contain water. The unit amount of water per 1 ^m3 of the mortar composition is preferably 150 to 280 kg/ ^m3 , more preferably 180 to 250 kg/ ^m3 , and even more preferably 190 to 230 kg/ ^m3 . From the viewpoint of achieving appropriate fluidity, the water-binder ratio is preferably 10 to 30 mass%, more preferably 15 to 25 mass%. Examples of binders include cement, silica fume, and quick-hardening agents.

In addition to the above-mentioned components, the mortar composition may contain, as necessary, at least one selected from an expansive material, an antifoaming agent, a shrinkage-reducing agent, a thickener, glass fiber, organic fiber, a synthetic resin powder, a polymer emulsion, and a polymer dispersion. The expansive material is commercially available, and for example, an ettringite-lime composite or lime-based material can be used. The unit amount of the expansive material per 1 ^m3 of mortar composition is preferably 1 to 50 kg/ ^m3 , more preferably 2 to 40 kg/ ^m3 , and more preferably 5 to 30 kg/ ^m3 .

Examples of antifoaming agents include special nonionic surfactants, polyalkylene derivatives, hydrophobic silica, polyethers, etc. The unit amount of antifoaming agent per 1 ^m3 of mortar composition is preferably 0.1 to 20 kg/ ^m3 , more preferably 0.5 to 10 kg/ ^m3 , and more preferably 1 to 5 kg/ ^m3 .

The mortar composition of this embodiment exhibits appropriate fluidity and excellent strength development in a short period of time when used in a low-temperature environment where the temperature is below 20°C. For example, fluidity can be evaluated by the mortar zero-pump flow. The mortar zero-pump flow immediately after mixing is preferably 130 mm or more, more preferably 140 mm or more, and even more preferably 150 mm or more. Such mortar compositions have excellent filling properties when poured, excellent workability, and can achieve sufficiently high compressive strength. The mortar zero-pump flow immediately after mixing is preferably 300 mm or less, more preferably 250 mm or less. Such mortar compositions can prevent the mortar composition from immediately flowing downward, for example, when the pouring location has a transverse gradient and/or a longitudinal gradient. Therefore, they exhibit excellent workability. Note that the mortar zero-pump flow in this specification is a value measured under non-drop conditions in accordance with JIS R 5201:1997, "Physical Testing Methods for Cement."

The strength development in a short time can be evaluated, for example, by the compressive strength at a 3-hour age. The compressive strength of the mortar composition at a 3-hour age is preferably 20 N/mm ² or more, more preferably 24 N/mm ² or more. The compressive strength can be measured by preparing a 5 cm x 10 cm cylindrical specimen with reference to JIS A 1132:2006 "Method for preparing specimens for concrete strength tests" and conducting a compressive strength test with reference to JIS A 1108:2006 "Method for testing the compressive strength of concrete."

The mortar composition may be used in an environment where the temperature is 15°C or below, 10°C or below, or 5°C or below. From the perspective of maintaining good workability, the mortar composition is preferably used in an environment where the temperature is above 0°C. The use of the mortar composition is not particularly limited, and it may be used, for example, as a repair material or coating material. Specifically, it may be used as a repair material or coating material for roads (expressways), bridges, port structures, river structures, underground structures, etc. The mortar composition has excellent workability and excellent initial strength development, making it suitable for use in expressway repairs, where construction must be completed in a short period of time.

The mortar composition may be manufactured by simultaneously blending and mixing all of the raw materials, or by pre-mixing only some of the raw materials and then blending and mixing the remaining raw materials simultaneously or sequentially. For example, the raw materials other than water may be blended and mixed, and water may be added to the powder mixture, which is then placed in a mixer and kneaded to prepare the mortar composition. Mixers that can be used for mixing include mortar mixers, forced mixers, pan mixers, and grout mixers. Note that the above-mentioned manufacturing methods are merely examples, and manufacturing methods other than those described above may also be used.

A method of using a mortar composition according to one embodiment includes a step of repairing a road using the mortar composition. The mortar composition may be the mortar composition according to the above embodiment. Therefore, the above description of the mortar composition can be applied to this method of use. The description of this method of use can also be applied to the above description of the mortar composition. In the above step, the mortar composition is poured into the road in an environment where the temperature is below 20°C. The road is preferably a highway where construction must be completed in a short period of time. The above step may be performed in an environment where the temperature is below 15°C, below 10°C, or below 5°C. From the perspective of maintaining good workability, the above step is preferably performed in an environment where the temperature is above 0°C.

The above-mentioned method of use preferably includes, before the above step, a step of adjusting the blending ratio of at least one selected from the group consisting of a hardening accelerator, a retarder, and a water-reducing agent, depending on the air temperature when the mortar composition is used. The fluidity of a mortar composition varies greatly depending on the air temperature. For this reason, for example, the blending ratios (unit amounts) of the hardening accelerator, retarder, and water-reducing agent may be determined based on measured air temperature, and the mortar composition may be prepared to achieve those blending ratios (unit amounts). By including such a step, the properties of the mortar composition can be adjusted to achieve optimal fluidity appropriate for the air temperature.

The above describes an embodiment of the present invention, but the present invention is not limited to the above embodiment.

The present invention will be explained in more detail with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[Preparation of mortar composition]
In order to prepare the mortar compositions of each of the Examples and Comparative Examples, the following raw materials were prepared.

(1) Cement The chemical components of the cement were measured in accordance with JIS R 5202:2010 "Methods for Chemical Analysis of Cement," and the mineral composition was calculated using the Bogue formula described above. The 45 μm sieve residue of the cement was measured in accordance with the Cement Association Standard Test Method JCAS K-02 "Method for Testing Cement Fineness Using a 45 μm Mesh Sieve," and the Blaine specific surface area of the cement was measured in accordance with JIS R 5201:1997 "Physical Testing Methods for Cement." The results are shown in Table 1.

(2) Silica fume (SF)
Silica fume was prepared. The average particle diameter of this silica fume was 0.24 μm. This average particle diameter was determined by the following procedure. First, the particle diameter distribution of this silica fume was measured using a laser diffraction/scattering particle diameter distribution measuring device (manufactured by Horiba, Ltd., product name "LA-950V2"). Based on the measurement results, a particle diameter vs. cumulative % passing curve was calculated, and the particle diameter at which the cumulative passing amount was 50% by volume was determined from the particle diameter vs. cumulative % passing curve. This particle diameter was defined as the average particle diameter.

(3) Fine aggregate: Silica sand (produced in Tochigi Prefecture, particle size: 5.0 mm or less, fine particle content: 0.62%, coarse particle ratio: 2.35) was prepared.

(4) Inorganic Fine Powder Limestone fine powder (density: 2.71 g/cm ³ , Blaine specific surface area: 4570 cm ² /g) was prepared.

(5) Hardening Accelerator Biform (registered trademark) manufactured by Denka Co., Ltd. was prepared as the hardening accelerator. The analysis results of the chemical components of this hardening accelerator are shown in Table 2.

(6) Retarder As a retarder, Setter D-300 (trade name) manufactured by Denka Co., Ltd. was prepared.
(7) Water-reducing agent A polycarboxylic acid-based high-performance water-reducing agent (solid content: 25% by mass) was prepared as a water-reducing agent.
(8) Antifoaming Agent A special nonionic surfactant was prepared as an antifoaming agent. Figure 1 shows the 1H-NMR spectrum of this antifoaming agent dissolved in deuterated methanol and measured using ^an NMR spectrometer (manufactured by BRUKER, trade name "AVANCE"). The molar ratios of the structural units of the antifoaming agent, namely, polyoxypropylene (hereinafter abbreviated as "POP") structural units, polyoxyethylene (hereinafter abbreviated as "POE") structural units, and alkyl chain structural units, were calculated based on the integral value of the signal derived from the methyl group in POP. The molar ratio of POE to POP was calculated by subtracting the integral value of the signal derived from the hydrocarbon group other than the methyl group of POP from the integral value of the signal derived from the hydrocarbon group other than the methyl group of POP appearing around 3.5 ppm and the signal derived from the hydrocarbon group of POE. The molar ratios of POP, POE, and alkyl chain structural units in the antifoaming agent are shown in Table 3.

(9) Expansive Material An ettringite-lime composite expansive material manufactured by Denka Co., Ltd. was prepared as the expansive material.
(10) High-tensile fiber Steel fiber (manufactured by Tokyo Rope Mfg. Co., Ltd., product name "CW9416", density: 7.87 g/cm ³ , fiber diameter: 0.16 mm, fiber length: 13 mm, aspect ratio: 81.25, tensile strength: 2200 N/mm ² ) was prepared as the high-tensile fiber.
(11) Tap water was prepared as mixing water (W).

(Examples 1-1 to 1-9)
The above-mentioned raw materials were mixed in the proportions shown in Table 4 in an environment with an ambient temperature of 5°C to prepare a mortar composition. The cement, silica fume, inorganic fine powder, antifoaming agent, expansive agent, and fine aggregate were dry-mixed using a Hobart mixer for 30 seconds, and then water and a high-performance water-reducing agent were added and mixed for 5 minutes. The retarder was then added and mixed for 1 minute, and the steel fiber was added and mixed for an additional 2 minutes. The hardener was then added and mixed for 1 minute. The values in Table 4 are in kg/ ^m³ , representing the mass (unit amount) per 1 ^m³ of mortar composition. The water/binder ratio was kept constant at 19% by mass.

(Examples 2-1 to 2-14)
Mortar compositions were prepared by blending the above-mentioned raw materials in the proportions shown in Table 4 in an environment with an air temperature of 10°C. Mixing was performed in the same manner as in Example 1-1. The units of values in Table 4 are kg/ ^m3 , which indicate the mass (unit amount) per 1 ^m3 of mortar composition. The water/binder ratio was kept constant at 19% by mass.

(Examples 3-1 to 3-9)
Mortar compositions were prepared by blending the above-mentioned raw materials in the proportions shown in Table 4 in an environment with an air temperature of 15°C. Mixing was performed in the same manner as in Example 1-1. The units of values in Table 4 are kg/ ^m3 , which indicate the mass (unit amount) per 1 ^m3 of mortar composition. The water/binder ratio was kept constant at 19% by mass.

(Example 4-1, Comparative Examples 4-1 and 4-2)
Mortar compositions were prepared by blending the above-mentioned raw materials in the proportions shown in Table 4 in an environment with an air temperature of 19°C. Mixing was performed in the same manner as in Example 1-1. The units of values in Table 4 are kg/ ^m3 , which indicate the mass (unit amount) per 1 ^m3 of mortar composition. The water/binder ratio was kept constant at 19% by mass.

[Evaluation of mortar composition]
(1) Fresh Properties The mortar zero-pressure flow immediately after mixing of the mortar compositions prepared in each Example and Comparative Example under each temperature environment was measured. The mortar zero-pressure flow was measured in accordance with JIS R 5201:1997 "Physical Testing Methods for Cement" under conditions of no dropping. The measurement results are shown in the "Immediately after" column of flow values in Table 5. The "15 minutes after" and "30 minutes after" columns of flow values in Table 5 are the flow values 15 minutes and 30 minutes after mixing.

(2) Strength Test 5cm x 10cm cylindrical specimens were prepared with reference to JIS A 1132:2006 "Method of preparing specimens for strength tests of concrete," and the compressive strength was measured under various temperature conditions with reference to JIS A 1108:2006 "Method of testing compressive strength of concrete." The measurement results at ages of 3 hours and 7 days are shown in Table 5. Table 5 also shows the ratio of hardener to retarder (A/B), the ratio of water-reducing agent to retarder (C/B), and the ratio of hardener to water-reducing agent (A/C).

As shown in Table 5, the mortar zero-pump flow values "immediately after" mixing for each example were in the range of 139 to 230 mm, confirming that the mortar had adequate fluidity even in a low-temperature environment. In addition, the compressive strength at 3 hours was 24 N/ ^mm2 or more, confirming that the mortar had excellent strength development in a short period of time.

Table 6 shows data for Examples 1-1, 2-9, and 3-1, which have nearly the same formulations as the Examples shown in Tables 4 and 5.

As shown in Table 6, it was confirmed that even when the mix proportions are roughly the same, the mortar zero-cast flow value changes depending on the temperature. For this reason, it is preferable to adjust the mix proportions depending on the temperature environment in which construction is performed.

The present invention provides a mortar composition that has appropriate fluidity in low-temperature environments and exhibits excellent strength development in a short period of time. It also provides a method for using the mortar composition that enables smooth repair work in low-temperature environments.

Claims (8)

The cement has a mineral composition with a C ₃ S content of 40.0 to 75.0 mass % and a C ₃ A content of less than 4.0 mass %, and a 45 μm sieve residue of less than 25.0 mass %, silica fume with an average particle size of 0.05 to 2.0 μm, inorganic fine powder with a Blaine specific surface area of 3000 to 5000 cm ² /g, fine aggregate , high-tensile fiber, a hardening accelerator , a retarder , and a water-reducing agent,
The unit amount of the cement per 1 ^m3 of the mortar composition is 750 to 1000 kg/ ^m3 , the unit amount of the silica fume is 100 to 130 kg/m3 ^, the unit amount of the inorganic fine powder is 150 to 250 kg/m3 ^, the unit amount of the fine aggregate is 800 to 900 kg/m3 ^, and the unit amount of the high-tensile fiber is 120 to 200 kg/ ^m3 ,
When the unit amount of the hardening accelerator per 1 ^m3 of mortar composition is A [kg/ ^m3 ], the unit amount of the retarder is B [kg/ ^m3 ], and the unit amount of the water-reducing agent is C [kg/ ^m3 ],
A is 110 to 160 kg/m ³ , B is 2 to 7 kg/m ³ , and C is 9 to 22 kg/m ³ ;
A/B is 22.0 to 55.0,
A mortar composition in which C/B is 2.1 to 5.5. 2. The mortar composition of claim 1, wherein the C3A _content is less than 2.7 wt%. The mortar composition according to claim 1 or 2, wherein the high-tensile fibers include at least one type of fiber selected from the group consisting of metal fibers, carbon fibers, aramid fibers, PP fibers, PVA fibers, PE fibers, glass fibers, nylon fibers, and PBO fibers. The mortar composition according to any one of claims 1 to 3, wherein the high-tensile strength fibers have a tensile strength of 100 to 10,000 N/mm ² and an aspect ratio of 40 to 250. The mortar composition according to any one of claims 1 to 4 , wherein the silica fume has an average particle size of 0.18 to 0.28 µm. Further, the mortar composition contains an antifoaming agent. ³ The unit amount of the defoaming agent per unit area is 0.1 to 20 kg/m ³ The mortar composition according to any one of claims 1 to 5. The mortar composition according to any one of claims 1 to 6 , which is used for repairing roads in an environment of less than 20°C. A method for repairing a road using the mortar composition according to any one of claims 1 to 7 ,
A method for using the mortar composition, comprising pouring the mortar composition into the road in an environment of less than 20°C.