Cold-resistant cement composition

Abstract

To provide a cold-resistant cement composition capable of securing quality without freezing even under an environment where the outside air temperature may become - 5 °C or lower even if lithium nitrite is not added by mixing and using calcium nitrite and a retarder.SOLUTION: A cold-resistant cement composition of the present invention includes cement, calcium nitrite, and a retarder, wherein the calcium nitrite is 4.0 to 6.0 parts by mass and the retarder is 0.3 to 1.2 parts by mass with respect to 100 parts by mass of the cement. The cold-resistant cement composition obtained by mixing and using a specific amount of calcium nitrite and a retarder suppresses the lowering of fluidity of a case in which the addition amount of calcium nitrite is increased, and can secure sufficient quality without taking measures against freezing damage in construction in cold weather.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a cold-resistant cement composition suitable for the construction of mortars such as concrete, mortar, and grout in cold construction environments, and a method for constructing mortars in cold weather using the cold-resistant cement composition. Note that the term "mortars" as used herein includes not only mortar in its original sense, but also concrete and grout materials. [Background technology]

[0002] When grouting work is carried out in harsh environmental conditions, such as when the concrete is exposed to sub-zero temperatures immediately after mixing, the water in the cementitious material freezes between the time it is filled into the concrete structure and the time it hardens. This can inhibit the hydration reaction and cause poor hardening. To prevent this, it is necessary to keep the concrete structure heated and insulated for a certain period of time using a jet heater or similar.

[0003] However, in order to heat the concrete framework around the filling area and maintain its thermal insulation, a large-scale temporary enclosure must be constructed to cover the entire structure or most of it, and the entire space must be heated. In this case, the curing equipment is too large for the amount of grout used, and a lot of manpower is required to assemble and disassemble the temporary enclosure and to manage the temperature.

[0004] In contrast, nitrite-based cold-resistant additives are admixtures that promote the hydration reaction of cement, prevent early frost damage to mortars, including grout materials, and lower the freezing point of water in mortars.

[0005] The more nitrite is used, the more it promotes the hydration reaction of C3A and C3S, accelerating the formation of ettringite (AFt: 3CaO·Al22O3·3CaSO4·32H2O) immediately after mixing. In addition, it also promotes the formation of C3A (3CaO·Al2O3) and nitrite ions (NO2 - ) reacts to form nitrite hydrates, which are known to be effective in increasing the early strength of concrete.

[0006] One effective way to solve the problems associated with conventional energy-intensive methods for constructing mortars, including grout materials, in winter is to use cementitious materials that have been given cold resistance by adding lithium nitrite. Lithium nitrite has a small effect on the fluidity of cementitious materials, and can be added in large quantities. Its strong freezing-point depressant effect allows it to exhibit excellent strength in construction environments where it is exposed to sub-zero temperatures immediately after filling.

[0007] Lithium nitrite is particularly useful for cementitious materials that must be applied to concrete structures exposed to low temperatures, such as PC grout and non-shrinkage mortar used in bridge footings. Cold-resistant cement compositions containing lithium nitrite include those described in Patent Documents 1 and 2 and Non-Patent Document 1.

[0008] Patent Document 1 relates to an application filed by the present applicant, and discloses an invention in which lithium nitrite is added to a cement-based grout material containing cement, water, and an admixture to impart cold resistance.

[0009] Patent Document 2 discloses a cold weather non-shrinkage mortar material made of a cement-based non-shrinkage mortar material containing cement and fine aggregate and mixing water, in which lithium nitrite and aluminum powder are added to the non-shrinkage mortar material.

[0010] Non-Patent Document 1 aims to develop a cold-resistant PC grout that does not require special curing in a freezing environment of about -10°C, and investigates the effect of adding a hardening accelerator containing lithium nitrite on the fluidity of PC grout and on the strength development when curing is performed in a freezing environment immediately after mixing.

[0011] Calcium nitrite is also known as a material that has cold resistance properties similar to those of lithium nitrite. The characteristics of calcium nitrite are listed below.

[0012] (1) Calcium nitrite is widely used as a cold-resistant additive for general concrete. While calcium nitrite is excellent at accelerating the hydration reaction of cement, adding large amounts to impart cold resistance causes a rapid hydration reaction, resulting in the concrete losing its fluidity immediately after mixing. For this reason, adding calcium nitrite alone makes it difficult to prevent early frost damage without curing in environments below 0°C.

[0013] (2) Furthermore, even if a large amount is added to impart high cold resistance, sufficient cold resistance cannot be obtained. Even if a large amount is added, a rapid hydration reaction occurs immediately after mixing, and the nitrite ions, which are the cold-resistant components in calcium nitrite, are consumed in the reaction with cement. This reduces the amount of nitrite ions contained in the water in the concrete, which may reduce the anti-freezing effect. Therefore, in environments below 0°C, the water in the concrete freezes and suffers initial frost damage, making it impossible to obtain cold resistance.

[0014] In addition, Patent Documents 3 and 4 and Non-Patent Documents 2 and 3 disclose inventions of cement compositions to which nitrite has been added.

[0015] Patent Document 3 discloses a cold-resistant inorganic anchor material that includes an ultra-rapid-hardening binder and a nitrite, in which the ultra-rapid-hardening binder contains 10 to 50 mass % of CA and 3 to 40 mass % of C2AS as ultra-rapid-hardening minerals, is substantially free of C12A7, and the nitrite is contained in an amount of 3 to 13 mass parts per 100 mass parts of the ultra-rapid-hardening binder.

[0016] Patent Document 4 discloses a cement composition that contains aluminum hydroxide and a nitrite, with lithium nitrite or calcium nitrite being used as the nitrite, as a cement composition that also exhibits the effect of inhibiting Ca leaching.

[0017] Furthermore, in Non-Patent Document 2, various physicochemical studies have been conducted on cement paste containing a nitrite-based cold resistance accelerator, with the aim of clarifying the correlation between strength development and hydration products when cured below freezing immediately after mixing.

[0018] Furthermore, Non-Patent Document 3 discloses a cold resistance agent that uses a large amount of nitrite-based admixture and an aromatic ether-based high-performance water-reducing agent, and studies have been conducted on the fresh properties and strength development in low-temperature environments that simulate construction in the harsh winter. [Prior art documents] [Patent documents]

[0019] [Patent Document 1] International Publication No. 2021 / 039133 [Patent Document 2] Japanese Patent Publication No. 2023-095802 [Patent Document 3] Patent Publication No. 2021-155281 [Patent Document 4] Japanese Patent Application Laid-Open No. 2007-153715 [Non-patent literature]

[0020] [Non-Patent Document 1] Masumi Inoue, Kenichi Yoshioka, Yuji Sudo, Hee-seop Choi, Kohei Tian: Fundamental Properties and Practical Use of Cold-Resistant PC Grout Containing Lithium Nitrite, Journal of the Japan Society of Civil Engineers, E2, Vol. 78, No. 3, pp. 210-223, August 2022. [Non-patent document 2] Masumi Inoue, Hee-Sop Choi, Kohei Tianya, Yuji Sudo, Kenichi Yoshioka, Strength development characteristics of cement paste containing nitrite at sub-zero temperatures, Materials, Vol. 71, No. 4, pp. 388-394, 2022 [Non-patent document 3] Tomohito Akama, Masumi Inoue, Yuji Sudo, and Tsuneyoshi Okada, Development of a new cold-resistant agent using nitrite-based admixtures and various water-reducing agents, Proceedings of the Japan Concrete Institute, Vol. 35, No. 1, pp. 139-144, 2013 Summary of the Invention [Problem to be solved by the invention]

[0021] The cement-based grout material described in Patent Document 1 is a cold weather cement-based grout material that uses lithium nitrite and is intended for use in construction environments where the outside temperature at the beginning of construction can drop to -5°C or -10°C. The cold weather non-shrinkage mortar material described in Patent Document 2 also uses lithium nitrite.

[0022] However, lithium nitrite is an easy-to-use material that has almost no effect on fluidity even when added in large amounts to impart high cold resistance, but it is expensive, and while it is effective for applications where small amounts are used, such as mortar and grout, it is not suitable for applications where large amounts are used, such as concrete, from a cost perspective.In addition, there have been concerns recently about the risk of price fluctuations for lithium, the raw material for lithium nitrite, and there are issues with its versatility, so there is a strong desire to develop a low-cost material that can exhibit high cold resistance without relying on lithium nitrite.

[0023] The cold-resistant inorganic anchor material described in Patent Document 3 is a combination of an ultra-fast-hardening binder and nitrite, which ensures usable time even in sub-zero environments, and is said to have good application performance with little sagging and excellent adhesion to anchor members. However, no use other than as an anchor material has been considered.

[0024] The cement composition described in Patent Document 4 is expected to have anti-rust effects, chloride ion blocking effects, and calcium leaching suppression effects, but it is not intended for use as a non-shrinkage mortar, nor is it designed for cold weather construction.

[0025] In general concrete construction in winter, when the hydration reaction of cement needs to be forcibly accelerated at low temperatures to ensure strength development, calcium nitrite-based cold weather additives have been widely used. This is because calcium nitrite is chloride-free and alkali-free, has excellent compatibility with cement, and has excellent hydration reactivity. Its unit price is significantly cheaper than that of lithium nitrite, which is also a nitrite, making it an advantageous agent for versatility.

[0026] However, if calcium nitrite is added in large amounts, the fluidity of cementitious materials drops significantly immediately after mixing, hindering workability. Therefore, the upper limit of calcium nitrite addition to cement is about 4% by mass, and because its freezing point depressant effect is limited, there is an issue that needs to be improved when using it in environments where it is exposed to sub-zero temperatures immediately after mixing.

[0027] In this invention, we focused on the use of a retarder to suppress the decrease in fluidity that is an obstacle when adding large amounts of calcium nitrite. Generally, cement-based materials gradually lose fluidity after mixing, and typically reach the setting stage after several hours. A retarder slows this setting process, and according to JIS A 0203, it is defined as "an admixture used to delay the hydration reaction of cement and extend the time required for setting." If the use of this retarder can suppress the decrease in fluidity that occurs when increased amounts of calcium nitrite are added and demonstrate a freezing point depressant effect, it could be used as an alternative to lithium nitrite.

[0028] Under the circumstances described above, the present invention aims to provide a cold-resistant cement composition that uses calcium nitrite and a retarder without adding lithium nitrite, and that will not freeze even in environments where the outside temperature may drop to -5°C or below, thereby ensuring quality. [Means for solving the problem]

[0029] As a result of extensive research into solving the above problems, the inventors of the present invention have discovered that a cold-resistant cement composition containing a specific amount of calcium nitrite and a retarder can suppress the decrease in fluidity that occurs when the amount of calcium nitrite added is increased, and can ensure sufficient quality during cold weather construction without the need for measures to prevent frost damage, thereby completing the present invention.

[0030] That is, the present invention is 1. A cold-resistant cement composition comprising cement, calcium nitrite, and a retarder, wherein the calcium nitrite is present in an amount of 4.0 to 6.0 parts by mass and the retarder in an amount of 0.3 to 1.2 parts by mass per 100 parts by mass of the cement; 2. The cold-resistant cement composition according to 1, wherein the retarder is an oxycarboxylic acid or a salt thereof. 3. The cold-resistant cement composition according to 1, wherein the retarder is contained in an amount of 7.5 to 20.0 parts by mass per 100 parts by mass of the calcium nitrite. 4. The cold-resistant cement composition according to 3, wherein the retarder is an oxycarboxylic acid or a salt thereof. 5. The cold-resistant cement composition according to any one of 1 to 4, characterized in that the cold-resistant cement composition is a cold-resistant cement composition for use in mortar construction in a construction environment in which the outside air temperature at the initial stage of construction may drop to -5°C or below -5°C; 6. A method for applying mortars in cold weather, which is prepared by mixing a mixture containing the cold-resistant cement composition according to any one of 1 to 4 and mixing water, and which is characterized in that when the outside air temperature at the application site falls below -5°C, the application environment is maintained at -5°C or higher for curing. to provide. [Effects of the Invention]

[0031] Use of the cold-resistant cement composition of the present invention eliminates the need for extensive curing and fuel for heating, which have conventionally been required as countermeasures against early frost damage, and can significantly reduce the labor and costs involved.

[0032] By using inexpensive calcium nitrite, it is possible to significantly reduce material costs without using expensive lithium nitrite.

[0033] Even if calcium nitrite is added at 4 to 6% of the cement mass (2 to 3 times the normal amount), good fluidity and retention performance can be obtained by mixing it with a retarder.

[0034] By adjusting the amount of calcium nitrite and retarder to an appropriate level, the decrease in fluidity caused by the rapid hydration reaction immediately after mixing due to the addition of large amounts, which has traditionally been considered a drawback of calcium nitrite, can be suppressed, and the problem of initial frost damage can be avoided.

[0035] Furthermore, when the cold-resistant cement composition of the present invention is used for mortar construction in a construction environment where the outside air temperature at the initial stage of construction can drop to -5°C or lower, it can eliminate or simplify the need for insulation or heat supply equipment such as temporary enclosures against snow and cold. [Brief explanation of the drawings]

[0036] [Figure 1] 10 is a graph showing the change in 0-hit flow value over time immediately after mixing, where (a) is for CN4%, (b) is for CN5%, and (c) is for CN6%. [Figure 2] This graph shows the temperature history inside the specimen from immediately after pouring into the formwork until 20 hours of curing in a -10°C environment, where (a) is for CN4%, (b) is for CN5%, and (c) is for CN6%. [Figure 3] This graph shows the results of compressive strength tests when the concrete was sealed and cured in a sub-zero temperature environment of -5°C from immediately after pouring until it was 7 days old. (a) is for CN4%, (b) is for CN5%, and (c) is for CN6%. DETAILED DESCRIPTION OF THE INVENTION

[0037] The present invention is a cold-resistant cement composition comprising cement, calcium nitrite, and a retarder, characterized in that the calcium nitrite is 4.0 to 6.0 parts by mass and the retarder is 0.3 to 1.2 parts by mass per 100 parts by mass of cement.

[0038] When calcium nitrite and a retarder are added to a cold-resistant cement composition, there is a risk that the strength of the cold-resistant cement composition will decrease. However, in the present invention, calcium nitrite and a retarder are used in an amount that allows the cold-resistant cement composition to satisfy the standard strength and quality, and sufficient cold resistance and strength can be ensured in a construction environment where the outside temperature at the initial stage of construction may drop to -5°C or even lower.

[0039] The present invention aims to reduce costs by using calcium nitrite instead of lithium nitrite, which has the cold resistance properties of mortars. However, if the amount of calcium nitrite used increases, the fluidity is impaired, and therefore the amount of retarder used also increases.

[0040] Therefore, it is considered preferable that the amount of retarder added is about 7.5 to 20.0 parts by mass per 100 parts by mass of calcium nitrite.

[0041] The cement to be used may be, for example, ordinary Portland cement, high-early-strength cement, or blended cement, but the type of cement is not limited as long as there are no problems with quality or durability when calcium nitrite is added.

[0042] The retarder to be used is not particularly limited as long as it does not cause any problems in quality or durability when calcium nitrite is added, but it is preferably an oxycarboxylic acid or a salt thereof. Any appropriate oxycarboxylic acid can be used as the oxycarboxylic acid. Examples of oxycarboxylic acids include glycolic acid, gluconic acid, tartaric acid, citric acid, malic acid, glucoheptonic acid, and arabinonic acid. Preferred oxycarboxylic acids that can more effectively achieve the effects of the present invention are glycolic acid, gluconic acid, tartaric acid, citric acid, and malic acid.

[0043] Examples of salts that can be used as the salt of hydroxycarboxylic acid include inorganic salts and organic salts such as sodium, potassium, calcium, magnesium, ammonium, and triethanolamine.

[0044] A particularly preferred example of the salt of hydroxycarboxylic acid is sodium gluconate.

[0045] Calcium nitrite and retarder may be added in the form of an aqueous solution or a solid. When they are added as an aqueous solution, their concentrations are not important.

[0046] The cold-resistant cement composition of the present invention can be used as a cold-resistant cement composition for use in mortar-type construction such as concrete, mortar, grout, etc. in construction environments in which the outside air temperature at the initial stage of construction can drop to -5°C or even lower in cold regions during the coldest season.

[0047] That is, for example, assuming use in a construction environment where the outside air temperature at the beginning of construction can drop to -5°C, when constructing mortar using a cold-resistant cement composition in which the calcium nitrite is 4.0 to 6.0 parts by mass and the retarder is 0.3 to 1.2 parts by mass per 100 parts by weight of cement, it is possible to prevent freezing of the constructed mortar, such as cold weather concrete or cold weather mortar, and ensure quality, without using large-scale equipment such as a snow and cold temporary enclosure to maintain the curing temperature or fuel for heating.

[0048] Furthermore, if the outside temperature at the construction site drops below -5°C, the amount of calcium nitrite and retarder can be increased, or heat insulation or heating can be provided to maintain the construction environment at above -5°C. In other words, if it is predicted that the outside temperature will drop below the initially expected temperature shortly after construction, temporary fencing and heating will be required to maintain an environment equivalent to above -5°C, but compared to when conventional mortar is used, the costs of installing temporary fencing and heating equipment can be significantly reduced.

[0049] Tests carried out on the cold-resistant cement composition according to the present invention will be described below.

[0050] [Test Overview] (1) It is intended for application to cementitious grout and non-shrinkage mortar, which are exposed to sub-zero temperatures immediately after mixing. (2) Development of a cement-based material that is workable, has strength development below freezing point, and is versatile (economical) by mixing and adding calcium nitrite (CN), which has excellent hydration reactivity with cement, and a retarder (SG), without using lithium nitrite (LN), which has excellent freezing point depressant properties. (3) To clarify the correlation between the "fluidity" of cement-based materials to which calcium nitrite (CN) and retarder (SG) have been mixed and the "strength development when cured at -5°C immediately after mixing." (4) Taking into account the actual conditions of materials and mixing environment during construction in the coldest winter months, the materials used and mixing environment shall be +10°C.

[0051] [Materials used] The materials in Test 1 were as follows: Cement: Ordinary Portland cement (density: 3.16 g / cm 3 (manufactured by Taiheiyo Cement Corporation) Calcium nitrite: 30 wt% calcium nitrite aqueous solution (CN, density: 1.30 g / cm 3 , manufactured by Nissan Chemical Co., Ltd.) Retarder: Sodium gluconate (SG, density 1.80 g / cm 3 , manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0052] [Composition] The cement paste mix is ​​shown in Table 1. The water-cement ratio (W / C) was set at 40%, based on the fact that the water-cement ratio of typical cement-based grout materials is around 35-40%. In this experiment, the CN addition rate was set at 4-6% as the ratio of the fixed amount of nitrite to the cement mass, assuming that the mixture would be exposed to a sub-zero temperature environment of -5°C immediately after mixing.

[0053] [Table 1]

[0054] This is based on calculating the freezing point depression of an aqueous solution containing CN for each blend using the freezing point depression formula shown below. The freezing point depression of an aqueous solution containing CN in a blend with 4% CN added was -4.2°C, and -6.3°C when 6% CN was added. The addition rate of nitrite, which is generally used as a cold-resistant additive, is approximately 1.5-2% of the cement mass (3-5 L per 100 kg of cement), and the 4% and 6% CN used in the blends used in this experiment is two to three times the amount typically used.

[0055] ΔT f =K f m Here, ΔT f :Freezing point depression degree (℃) K f : Molar freezing point depression (K kg / mol) *When water is the solvent, it is 1.85 m: molar mass concentration (mol / kg)

[0056] When selecting the SG addition rate, the approximate range of SG addition rates that would provide good fluidity was confirmed through test mixing, and the SG addition rate was set for each CN addition rate. The retarder addition rates were set at three levels of 0.3%, 0.5%, and 0.7% of the cement mass for the 4% CN mixture, 0.6%, 0.8%, and 1.0% for the 5% CN mixture, and 1.0%, 1.1%, and 1.2% for the 6% CN mixture. A mixture without SG addition was also prepared for comparison.

[0057] [Test conditions and methods] (1) Mixing The Standard Specifications for Concrete (Japan Society of Civil Engineers) recommends that the concrete pouring temperature be maintained at around 10°C when construction is carried out in cold weather and is susceptible to freezing and thawing. In this experiment, taking into account the actual situation of grouting on-site in cold weather, the materials were temperature-controlled in a constant temperature and humidity room with a temperature of 10±1°C and a humidity of 85±5%, and mixed using a hand mixer in the same room.

[0058] (2) Flow test After mixing, the spread of the paste immediately after lifting it vertically was measured in the same room using a flow cone and a steel flow plate for mortar flow testing, in accordance with JIS R 5201, as the 0-hit flow value.

[0059] (3) Compressive strength The specimens for the compressive strength tests were cast into a φ50 x 100 mm lightweight tinplate formwork, and the casting surface was covered and sealed with plastic wrap. After casting, the specimens were sealed and cured in a -5°C thermostatic chamber to simulate a sub-zero temperature environment until they were 7 days old, and then a compressive strength test (JSCE-G 531) was conducted. After 7 days, the specimens were cured again in a +20°C thermostatic chamber to check for early frost damage, and a compressive strength test was conducted at 28 days old. For the 7-day compressive strength test, which was conducted after curing at -5°C, the specimens were removed from the -5°C thermostatic chamber and immersed in water, and the test was conducted once the internal temperature of the specimens had reached 5°C.

[0060] (4) Temperature history The temperature history of the specimen was measured by placing a T-type thermocouple in the center of a lightweight tin formwork measuring φ50 x 100 mm, and measuring the temperature history of the center of the specimen in a constant temperature bath set at -5°C immediately after casting, just as in the compressive strength test.

[0061] [Test results and discussion] Figure 1 shows the change in flow value over time measured in a 10°C environment from immediately after mixing to 60 minutes later. In the case of CN4% (CN4-SG0.0) without SG, the flow value could be measured immediately after mixing, but after 15 minutes stiffness occurred and flow measurement was no longer possible. In the case of 0.3% SG addition, the flow value could be measured after 15 minutes, but the flow value dropped significantly. On the other hand, in the cases of 0.5% and 0.7% SG addition, the change in flow value from immediately after mixing to 60 minutes later was small, confirming that good fluidity was maintained.

[0062] In the case of CN5% (CN5-SG0.0) without SG, the paste stiffened during mixing, making it impossible to measure the flow. In the cases where SG was added at 0.6% and 0.8%, the tendency for the flow value to decrease was suppressed by increasing the SG addition rate. In the case where SG was added at 1.0%, it was confirmed that good fluidity was maintained from immediately after mixing until 60 minutes later.

[0063] Even in the case of CN6% (CN6-SG0.0) without SG, the paste stiffened during mixing, making it impossible to measure the flow value.When SG was added, the changes in flow were small in the cases of 1.1% and 1.2% addition, and good fluidity was maintained.

[0064] From the above, it was confirmed that even when a large amount of CN is added (4-6% of the cement mass), good fluidity can be maintained from immediately after mixing until 60 minutes later by increasing the SG addition rate. It was also confirmed that as the CN addition rate increases, the SG addition rate required to obtain good fluidity must also increase.

[0065] Figure 2 shows the temperature history inside the test specimens that were cured in a -5°C environment immediately after being poured into the formwork. In both cases, it was confirmed that the paste temperature dropped by being exposed to below freezing points immediately after being poured into the formwork.

[0066] In the case of CN4%, the paste temperature rose once at about 9 hours for SG0.3% and at about 15 hours for SG0.5%, and then tended to drop again. This is thought to be the effect of latent heat due to the freezing of water in the paste. On the other hand, no temperature change that could be attributed to the effect of latent heat was observed in the case of SG0.7%.

[0067] In the case of CN5%, a temperature rise thought to be due to the influence of latent heat was observed after approximately 6 hours at SG0.6% and after approximately 16 hours at SG0.8%, but not at SG1.0%.

[0068] In the case of 6% CN, regardless of the SG addition rate, no changes that could be attributed to the influence of latent heat were observed in any of the mixes from immediately after pouring into the formwork up to -5°C, and it is thought that the concrete was not affected by freezing.

[0069] Figure 3 shows the results of compressive strength tests when sealed curing was performed in a sub-zero temperature environment of -5°C from immediately after casting until the material was 7 days old. After 7 days, the material was allowed to recover and cure at +20°C, and the compressive strength was measured at the specified age.

[0070] In the case of CN4%, the strength at 7 days was 0.7 to 1.4 N / mm 2 After that, after 28 days of recovery and curing at +20°C, differences in strength due to differences in SG addition rate were confirmed, with SG 0.3% and 0.5% achieving a strength of 10 N / mm 2 While the strength is less than 70N / mm for SG0.7% 2 As shown in the temperature history in Figure 2, in the cases of 0.3% and 0.5% SG, it is thought that the concrete was affected by freezing during the setting and hardening process, and that strength did not develop after recovery curing.

[0071] In the case of CN 5%, the strength at 7 days tends to decrease as the SG addition rate increases. After recovery curing, in the case of SG 0.6% and 0.8%, which were judged to have been affected by freezing in the temperature history of Figure 2, the strength at 28 days was 22 to 25 N / mm 2 In contrast, SG1.0% is approximately 60N / mm 2 In the case of CN6%, as the amount of retarder added increases, the strength at 7 days tends to decrease, but in all cases, the strength at 28 days is 56-62N / mm 2 A strength of 1000kJ / cm was obtained.

[0072] When cured at -5°C immediately after mixing, in the case of 6% CN, regardless of the SG addition rate, it was not affected by freezing and achieved good strength development after recovery curing. On the other hand, even in the case of 4% and 5% CN, CN4-SG0.7 and CN5-SG1.0, which have the highest SG addition rates, were not affected by freezing and achieved good strength development after recovery curing. This is thought to be because the freezing point of water in the cement paste was lowered by increasing the addition rate of SG in addition to CN.

[0073] The above experimental results clarified the relationship between the "fluidity" of cement paste to which CN and SG have been mixed and the "strength development when cured in a -5°C environment immediately after mixing." From this relationship, it was discovered that by optimizing the CN and SG addition ratio (CN4-SG0.7, CN5-SG1.0, CN6-SG1.1), it is possible to manufacture a cold-resistant cementitious material that combines fluidity retention and strength development at sub-zero temperatures of -5°C.

Claims

1. A cold-resistant cement composition comprising cement, calcium nitrite, and a retarder, wherein the calcium nitrite is 4.0 to 6.0 parts by mass and the retarder is 0.3 to 1.2 parts by mass per 100 parts by mass of the cement.

2. 2. The cold-resistant cement composition according to claim 1, wherein said retarder is an oxycarboxylic acid or a salt thereof.

3. 2. The cold-resistant cement composition according to claim 1, wherein the amount of the retarder is 7.5 to 20.0 parts by mass per 100 parts by mass of the calcium nitrite.

4. 4. The cold-resistant cement composition according to claim 3, wherein said retarder is an oxycarboxylic acid or a salt thereof.

5. 5. The cold-resistant cement composition according to claim 1, wherein the cold-resistant cement composition is a cold-resistant cement composition for use in mortar construction in a construction environment where the outside air temperature at the initial stage of construction may drop to −5° C. or below −5° C.

6. A method for applying mortars in cold weather, which is prepared by mixing a mixture containing the cold-resistant cement composition according to any one of claims 1 to 4 and mixing water, and which is characterized in that when the outside air temperature at the application site becomes lower than -5°C, curing is carried out in such a way that the application environment is maintained at -5°C or higher.

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