Cement composition

Abstract

To provide a cement composition capable of: reducing the amount of lithium nitrite to be added by partially replacing the amount of lithium nitrite to be added with calcium nitrite; and securing quality without freezing even in an environment where an outside air temperature may be -5°C or less.SOLUTION: A cement composition of the present invention comprises cement, lithium nitrite, and calcium nitrite. 0.9 to 4.5 pts.wt. of the lithium nitrite and 0.3 to 3.7 pts.wt. of the calcium nitrite are blended based on 100 pts.wt. of the cement. More preferably, 1.5 to 4.5 pts.wt. of the lithium nitrite and 0.3 to 1.9 pts.wt. of the calcium nitrite are blended based on 100 pts.wt. of the cement.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a cement composition suitable for construction of mortars such as concrete, mortar, or grout in a cold construction environment, and a method for constructing mortars in cold weather using the cement composition. In addition, in the present application, "mortars" shall include not only mortar in its original meaning but also concrete and grout materials.

Background Art

[0002] When constructing mortars made of a cement composition in cold weather, usually, in order to avoid frost damage, a snow and cold temporary enclosure that covers the entire structure or most of it is provided, and heating is performed inside.

[0003] On the other hand, technologies have been developed that impart cold resistance by adding lithium nitrite to the cement composition, eliminating the need for snow and cold temporary enclosures and heating. Examples of cement compositions added with lithium nitrite include the inventions described in Patent Documents 1 and 2.

[0004] Patent Document 1 relates to an application by the present applicant, and discloses an invention in which lithium nitrite is added to a cement-based grout material containing cement, water, and a admixture to impart cold resistance.

[0005] Patent Document 2 discloses a non-shrinking mortar material composed of a cement-based non-shrinking mortar material containing cement and fine aggregate and kneading water, in which lithium nitrite and aluminum powder are added to the non-shrinking mortar material.

[0006] In addition, calcium nitrite is known as a material having a cold resistance component similar to lithium nitrite. The characteristics of calcium nitrite are listed below.

[0007] (1) Calcium nitrite is widely used as a general concrete antifreeze. While calcium nitrite is excellent in promoting the hydration reaction of cement, if a large amount is added to impart cold resistance, it causes a rapid hydration reaction and the concrete loses its fluidity immediately after mixing. Therefore, it is difficult to prevent initial frost damage without curing in an environment below 0°C by adding only calcium nitrite.

[0008] (2) Also, 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, due to the rapid hydration reaction immediately after mixing, the nitrite ions, which are the cold-resistant components in calcium nitrite, are consumed in the reaction with cement, so the amount of nitrite ions contained in the water in the concrete decreases, which may reduce the freezing prevention effect. Therefore, in an environment below 0°C, the water in the concrete freezes and suffers initial frost damage, so cold resistance cannot be obtained.

[0009] In addition, as cement compositions containing nitrites, there are inventions described in Patent Documents 3, 4, Non-Patent Documents 1, and 2.

[0010] Patent Document 3 discloses a cold-resistant inorganic anchor material containing an ultra-high early strength binder and a nitrite, containing 10 to 50% by mass of CA and 3 to 40% by mass of C2AS as ultra-high early strength minerals in the ultra-high early strength binder, substantially not containing C12A7, and containing 3 to 13 parts by mass of the nitrite with respect to 100 parts by mass of the ultra-high early strength binder.

[0011] Patent Document 4 discloses a cement composition that also exhibits an effect of suppressing the elution of Ca, containing aluminum hydroxide and a nitrite, and using lithium nitrite or calcium nitrite as the nitrite.

[0012] Also, Non-Patent Document 1 discloses an antifreeze using a large amount of a nitrite-based admixture and an aromatic ether-based high-performance water reducer, and studies have been conducted on the fresh properties and strength development in a low-temperature environment assuming construction in severe winter.

[0013] In addition, in Non-Patent Document 2, for the cement paste added with a nitrite-based cold resistance accelerator, various physicochemical studies have been conducted for the purpose of clarifying the correlation between the strength development property and the hydration products when cured under sub-zero temperatures immediately after remixing.

Prior Art Documents

Patent Documents

[0014]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Non-Patent Documents

[0015]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0016] The cementitious grout material described in Patent Document 1 is a cementitious grout material for cold weather use assuming use in a construction environment where the outside air temperature can drop to -5°C or -10°C in the initial stage of construction, and uses lithium nitrite. The cold weather non-shrinking mortar material described in Patent Document 2 also uses lithium nitrite.

[0017] However, lithium nitrite is a material that is easy to use because even if a large amount is added to impart high cold resistance, it has almost no effect on fluidity. However, it is expensive and is effective for materials with a small usage amount such as mortar and grout, but it is not suitable in terms of cost for parts with a large usage amount such as concrete.

[0018] The cold-resistant inorganic anchor material described in Patent Document 3 is said to be able to ensure a pot life and has good workability with little sagging and excellent adhesion performance to the anchor member even in a sub-zero environment by combining an ultra-high early strength binder and a nitrate, but it has not been studied for uses other than as an anchor material.

[0019] The cement composition described in Patent Document 4 is expected to have a rust prevention effect, a chloride ion shielding effect, and a Ca elution suppression effect, but it is not for non-shrinking mortar and does not consider cold weather construction.

[0020] Under the above background, an object of the present invention is to provide a cement composition that can reduce the amount of lithium nitrite added by partially replacing the amount of lithium nitrite with calcium nitrite and can ensure quality without freezing even in an environment where the outside air temperature may be -5°C or lower.

Means for Solving the Problems

[0021] As a result of intensive studies to solve the above problems, the present inventors have found that a cement composition added with a specific amount of lithium nitrite and calcium nitrite can ensure sufficient quality without taking measures against freezing damage during cold weather construction, and have completed the present invention.

[0022] That is, the present invention 1. A cement composition comprising cement, lithium nitrite, and calcium nitrite, wherein, based on 100 parts by weight of the cement, the lithium nitrite is 0.9 to 4.5 parts by weight and the calcium nitrite is 0.3 to 3.7 parts by weight. 2. The cement composition according to 1, wherein, based on 100 parts by weight of the cement, the lithium nitrite is 1.5 to 4.5 parts by weight and the calcium nitrite is 0.3 to 1.9 parts by weight. 3. The cement composition according to 1, wherein the combined weight of the lithium nitrite and the calcium nitrite is 3.0 to 6.0 parts by weight based on 100 parts by weight of the cement. 4. The cement composition according to any one of 1 to 3, wherein the cement composition is a cold-resistant cement composition for use in mortar work in a construction environment where the outside air temperature at the initial stage of construction can drop to -5°C or lower. 5. A method for constructing mortars in cold weather, characterized in that a mixture containing the cement composition according to any one of 1 to 3 and mixing water is mixed to form a mortar, and curing is performed so that the construction environment is maintained at -5°C or higher. 6. The method for constructing mortars in cold weather according to 5, wherein when the outside air temperature at the construction site is lower than -5°C, heat insulation or heat supply is performed so that the construction environment is maintained at -5°C or higher. is provided.

Advantages of the Invention

[0023] By using the cement composition of the present invention, large-scale curing and fuel for heat supply, which were necessary for conventional measures against early frost damage, are no longer required, and the labor and cost can be significantly reduced.

[0024] By replacing a part of expensive lithium nitrite with calcium nitrite that is inexpensively available, the amount of lithium nitrite used can be reduced compared to the conventional amount, and the material cost can be significantly reduced.

[0025] By appropriately adjusting the blending amounts of lithium nitrite and calcium nitrite, it is possible to suppress the decrease in fluidity caused by the rapid hydration reaction immediately after kneading due to the large amount addition, which has been regarded as a drawback of calcium nitrite in the past, and the problem of early frost damage does not occur.

[0026] In addition, when the cement composition of the present invention is used for mortar work in a construction environment where the outside air temperature at the initial stage of construction can drop to -5°C or lower, it is possible to eliminate the need for insulation and heating equipment such as snow and cold enclosures, or to make them simple.

Brief Description of the Drawings

[0027]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0028] The present invention relates to a cement composition comprising cement, lithium nitrite, and calcium nitrite, wherein the amount of lithium nitrite is 0.9 to 4.5 parts by weight and the amount of calcium nitrite is 0.3 to 3.7 parts by weight with respect to 100 parts by weight of the cement.

[0029] When high fluidity after mixing is required, it is more preferable that the amount of lithium nitrite is 1.5 to 4.5 parts by weight and the amount of the calcium nitrite is 0.3 to 1.9 parts by weight with respect to 100 parts by weight of the cement.

[0030] When lithium nitrite and calcium nitrite are added to the cement composition, there is a risk of a decrease in the strength of the cement composition. However, in the present invention, lithium nitrite and calcium nitrite are used within a range where the cement composition satisfies the standard strength and quality.

[0031] In addition, in a construction environment where the outside air temperature at the initial stage of construction can drop to -5°C or lower than -5°C, as a formulation that can ensure sufficient cold resistance and strength, it is preferable that the combined weight of lithium nitrite and calcium nitrite with respect to 100 parts by weight of the cement is 3.0 parts by weight or more.

[0032] The present invention relates to both lithium nitrite and calcium nitrite having cold resistance performance for mortars. Since a part of expensive lithium nitrite is replaced with calcium nitrite to reduce costs, the cost reduction effect weakens as the total amount of lithium nitrite and calcium nitrite increases.

[0033] On the other hand, as the blending amount of calcium nitrite increases, the fluidity is impaired. Therefore, it is judged that the upper limit of the combined weight of lithium nitrite and calcium nitrite with respect to 100 parts by weight of the cement is preferably about 6.0 parts by weight or less.

[0034] Examples of the cement to be used include ordinary Portland cement, early-strength cement, and blended cement. However, the type of cement is not limited as long as there are no problems with quality and durability when lithium nitrite is added.

[0035] Lithium nitrite and calcium nitrite may be added either in an aqueous solution or in a solid state. Also, the concentration when made into an aqueous solution does not matter. However, the concentration of the aqueous solution is usually about 5 to 43% by weight, and from the viewpoint of handling, about 25 to 40% by weight is preferable. Examples of commercially available aqueous solutions that are easy to obtain include a 40% aqueous solution of lithium nitrite and a 30% aqueous solution of calcium nitrite.

[0036] The cement composition of the present invention can be used, for example, as a cold-resistant cement composition for use in works of mortars such as concrete, mortar, and grout in a construction environment where the outside air temperature at the initial stage of construction can drop to -5°C or lower than -5°C in a cold region during the coldest period.

[0037] That is, for example, assuming use in a construction environment where the outside air temperature at the initial stage of construction can drop to -5°C, when constructing mortars using a cement composition in which, per 100 parts by weight of cement, lithium nitrite is 0.9 to 4.5 parts by weight and calcium nitrite is 0.3 to 3.7 parts by weight, it is possible to prevent freezing of mortars such as cold-weather concrete or cold-weather mortar constructed and ensure quality without using large-scale equipment such as snow and cold enclosures for maintaining the curing temperature or fuel for heating.

[0038] Also, when the outside air temperature at the construction site is lower than -5°C, the combined dosage of lithium nitrite and calcium nitrite may be increased, or heat insulation or heating may be performed so that the construction environment is maintained at -5°C or higher. That is, when it is predicted that the outside air temperature will drop below the initially assumed temperature shortly after construction, although snow and cold enclosures or heating for maintaining an environment equivalent to -5°C or higher are required, compared with the case of constructing conventional mortars, the costs associated with the installation of snow and cold enclosures and heating equipment can be significantly reduced.

[0039] Hereinafter, tests conducted on the cement composition according to the present invention will be described.

[0040] 〔Test summary〕 (1) Assume application to cementitious grout, non-shrinking mortar, etc. that are exposed to sub-zero temperatures immediately after mixing up. (2) By mixing and adding lithium nitrite (LN) with excellent freezing point depression effect and calcium nitrite (CN) with excellent hydration reactivity with cement, develop a cementitious material with workability, strength development at sub-zero temperatures, and versatility (economy). (3) Clarify the correlation between the "fluidity" and "strength development when cured at -5°C immediately after mixing up" of the cementitious material mixed with lithium nitrite LN and calcium nitrite CN. (4) Based on the actual situation of materials and mixing environment during cold-weather construction in severe winter, set the materials and mixing environment used to +10°C.

[0041] Table 1 shows the characteristics when calcium nitrite and lithium nitrite are added to the cementitious material.

[0042]

Table 1

[0043] 〔Materials used〕 The materials in Test 1 are as follows. Cement: Ordinary Portland cement (density: 3.16 g / cm 3 , manufactured by Taiheiyo Cement Corporation) Lithium nitrite: 40 wt% aqueous lithium nitrite solution (LN, density: 1.25 g / cm 3 , manufactured by Nissan Chemical Industries, Ltd.) Calcium nitrite: 30 wt% aqueous calcium nitrite solution (CN, density: 1.30 g / cm 3 , manufactured by Nissan Chemical Industries, Ltd.)

[0044] 〔Mixing ratio 1〕 Table 2 shows the mix proportions of the cement paste. The water-cement ratio was 40%. The addition amounts of lithium nitrite (LN) and calcium nitrite (CN) were calculated as the ratio of the solid content of the nitrite to the cement weight. For the mix proportion using only lithium nitrite (LN) (L100), the addition rate was set at 3%. When lithium nitrite (LN) and calcium nitrite (CN) were used in combination, the mixing ratio of nitrite ions, which is the hardening acceleration component contained in each nitrite, was used as a parameter to vary the mixing ratio of nitrite ions and determine the addition rate of each nitrite.

[0045]

Table 2

[0046] 〔Test Conditions and Methods〕 Table 3 summarizes the test conditions and test methods for the mix proportions in Table 2 above.

[0047]

Table 3

[0048] In this test, based on the actual situation of materials and mixing environment during cold-weather construction in the severe winter, each material was temperature-controlled in an environment of 10 ± 1°C and 85 ± 5% humidity, and mixing was carried out using a hand mixer. Subsequently, in the same room, using a flow cone and a flow table, the time-dependent change in the zero-slump flow was measured in accordance with the method specified in JIS R 5201.

[0049] For the temperature history of the specimen, a T-type thermocouple was installed at the center of a lightweight tin formwork with a diameter of φ50 × 100 mm. The mixed cement paste was poured into the formwork, and the temperature history at the center of the specimen was measured in a constant-temperature bath set at -5°C immediately after that.

[0050] The compressive strength was measured by driving it into a lightweight steel formwork of φ50×100 mm, covering and sealing the driving surface with a wrap. After that, without initial curing, starting immediately after driving, assuming sub-zero temperatures, it was cured in a constant temperature bath at -5°C for sealed curing, and a compressive strength test (JSCE-G 531) was conducted at an age of 7 days. Also, after the age of 7 days, in order to confirm the presence or absence of strength recovery due to additional curing after curing under sub-zero temperatures, additional curing was carried out in a constant temperature bath at +20°C, and a compressive strength test (JSCE-G 531) was conducted at an age of 28 days.

[0051] 〔Test Results〕 Figure 1 shows, in a line graph, the change over time of the zero-slump flow for each mixture in Table 2 (+10°C environment).

[0052] From Figure 1, it can be seen that as the mixing ratio of calcium nitrite increases, the flow value (fluidity) decreases. Also, when the mixing ratio of calcium nitrite is 80% or more, the tendency for the flow value to decrease is significant.

[0053] More specifically, for L90C10 with a small mixing ratio of calcium nitrite and L100 which is excluded from the scope of the present invention, the flow value after 60 minutes was also 230 mm or more, but for L80C20, a flow value of approximately the same level was obtained.

[0054] For L70C30, a decrease in the flow value can be observed compared to L80C20, but the flow value after 60 minutes is about 210 mm, and it is good in terms of fluidity.

[0055] For L60C40, L50C50, L40C60, and L30C70, a further decrease in the flow value can be observed, but the flow value after 60 minutes is about 160 - 180 mm, which does not pose a major problem in practical use.

[0056] On the other hand, for L20C80 and L10C90, the decrease in the flow value is significant, and depending on the application, it may pose a problem in practical use.

[0057] Figure 2 is a graph showing the temperature history of the internal temperature of the specimens from immediately after remixing to curing at -5°C for each formulation in Table 2. (a) is for L100, (b) is for L80C20, (c) is for L60C40, (d) is for L50C50, (e) is for L40C60, (f) is for L30C70, (g) is for L20C80, and (h) is for L10C90.

[0058] In Figure 2, for L100 in (a), L80C20 in (b), L60C40 in (c), L50C50 in (d), and L40C60 in (e), after about 2 hours, the temperature change was small after the internal temperature of the specimen dropped to -5°C, and it is judged that there was no problem with freezing for these.

[0059] On the other hand, in L30C70 of (f), L20C80 of (g), and L10C90 of (h), once the internal temperature of the specimen dropped to -5°C, a temperature rise occurred.

[0060] This is presumably due to the influence of the latent heat caused by the freezing of the moisture in the paste of the specimen, resulting in a stagnation phenomenon in the temperature history. That is, in the case where the mixing ratio of calcium nitrite is 70% or more, there is a possibility of suffering from initial frost damage, which is more prominent in L20C80 of (g) and L10C90 of (h).

[0061] Figure 3 is a bar graph showing the time-dependent change (-5°C curing) of the compressive strength at 7 days and 28 days of age (however, after 7 days of age, it is 20°C) for each formulation in Table 2 due to curing at -5°C. Note that for the values in the bar graph, compressive strength tests were conducted on multiple specimens for each formulation, and the average values are shown.

[0062] For L90C10 and L80C20 with a small mixing ratio of calcium nitrite and L100 excluded from the scope of the present invention, there was no significant difference in the compressive strength at 7 days of age and the compressive strength at 28 days of age. Regarding the compressive strength at 28 days of age, rather, a higher compressive strength was obtained in L80C20 with a larger mixing ratio of calcium nitrite among these.

[0063] Regarding L70C30, L60C40, and L50C50, in which the mixing ratio of calcium nitrite gradually increases, relatively high compressive strengths were obtained, particularly at 28 days of age.

[0064] Next, for L40C60 and L30C70, although the compressive strengths are relatively low, the average values in the compressive strength tests conducted on a plurality of specimens each at 28 days of age exceeded 40 N / mm 2 . However, for L40C60 and L30C70, the variation in compressive strength among specimens tended to be quite large, and for L30C70, the stagnation phenomenon of the temperature history was also observed as described above. Therefore, it may not necessarily be in a favorable range.

[0065] On the other hand, for L20C80 and L10C90, the strength decreased significantly at both 7 days and 28 days of age, and it is highly likely that they were affected by early frost damage.

[0066] From the examination results of the time-dependent change of the 0-slump flow in Figure 1 above, the examination results of early frost damage based on the temperature history in Figure 2, and the test results regarding the compressive strength in Figure 3, in Mix 1, it is considered that the upper limit of calcium nitrite is appropriately about 2.6 parts by weight (corresponding to L30C70) with respect to 100 parts by weight of cement.

[0067] Note that the greater the mixing ratio of calcium nitrite, the greater the cost reduction effect. However, since a certain cost reduction effect can also be obtained in the mixing of L90C10, the result is that in Mix 1, it is preferable to mix 0.9 to 2.7 parts by weight of lithium nitrite and 0.3 to 2.6 parts by weight of calcium nitrite with respect to 100 parts by weight of cement.

[0068] Also, from the examination results of the time-dependent change of the 0-slump flow in Figure 1 above, the examination results of early frost damage based on the temperature history in Figure 2, and the test results regarding the compressive strength in Figure 3, a more preferable range is that, with respect to 100 parts by weight of cement, the lithium nitrite is 1.5 to 2.7 parts by weight and the calcium nitrite is 0.3 to 1.8 parts by weight.

[0069] [Mixing ratio 2] Furthermore, assuming that the outside air temperature drops to -10°C, a test was conducted with increased amounts of lithium nitrite LN and calcium nitrite CN.

[0070] Table 4 shows the mixing ratio of the cement paste in Mixing ratio 2. The water-cement ratio was 40%, and the addition amounts of lithium nitrite LN and calcium nitrite CN were calculated as the ratio of the solid content of nitrite to the cement weight. In the case of using only lithium nitrite LN (L100), the addition rate was 6%. When lithium nitrite LN and calcium nitrite CN were mixed and used, the mixing ratio of nitrite ions was changed with the amount of nitrite ions, which is a hardening acceleration component contained in each nitrite, as a parameter, and the addition rate of each nitrite was determined.

[0071] [Table 4]

[0072] [Test conditions and methods] The test conditions and test methods were basically the same as those in Mixing ratio 1, but as the curing condition, it was -10°C sealed curing, and the change over time of the initial flow (in a +10°C environment), the measurement of the temperature history of the specimen, and the compressive strength test were conducted.

[0073] [Test results] Figure 4 shows, in a line graph, the change over time of the initial flow (in a +10°C environment) for each mixing ratio in Table 4.

[0074] From Figure 4, Mixing ratio 2 includes only three types: L75C25 and L50C50, and the case of using only lithium nitrite LN (L100) which is outside the scope of the present invention. For L75C25 with a small mixing ratio of calcium nitrite and L100 which is excluded from the scope of the present invention, the flow value (fluidity) after 60 minutes was also 180 mm or more.

[0075] In L50C50 with an increased amount of calcium nitrite, the flow value decreased to about 120 mm or less, but it is considered that this would not cause any particular problem depending on the application.

[0076] Regarding the temperature history of the specimens, since no decrease in temperature stagnation related to the possibility of initial frost damage was observed for L50C50 either, the explanation is omitted.

[0077] Figure 5 shows, as a bar graph, the time-dependent changes in compressive strength (-10°C curing) at 7 days and 28 days of age (however, at 20°C after 7 days of age) for each mixture in Table 4 during -10°C curing. The values in the bar graph represent the average values obtained from compressive tests on multiple specimens for each mixture.

[0078] Compared with the test on Mixture 1 with different curing conditions (-5°C curing), the compressive strength at 7 days of age is lower, but the compressive strength at 28 days of age exceeds 40 N / mm 2 in all cases. For L50C50 as well, no phenomena of initial frost damage or strength reduction due to the increase in calcium nitrite were observed.

[0079] From the above examination results of the time-dependent change in the zero slump flow in Figure 4, the examination of initial frost damage based on the temperature history, and the test results regarding the compressive strength in Figure 5, for Mixture 2, when about 3.7 parts by weight of calcium nitrite (corresponding to L50C50) is mixed with 100 parts by weight of cement, although the fluidity slightly decreases, it is judged that there is no problem of reduced cold resistance.

[0080] Regarding the test of Mixture 2, when about 4.5 parts by weight of lithium nitrite and about 1.9 parts by weight of calcium nitrite are mixed with 100 parts by weight of cement (corresponding to L75C25), it was confirmed that a cement composition can be obtained that ensures a certain degree of fluidity even in an environment where the outside air temperature drops to about -10°C, and has no problems in terms of cold resistance and strength.

Claims

1. A cement composition comprising cement, lithium nitrite, and calcium nitrite, wherein the lithium nitrite is 0.9 to 4.5 parts by weight and the calcium nitrite is 0.3 to 3.7 parts by weight with respect to 100 parts by weight of the cement.

2. The cement composition according to Claim 1, wherein the lithium nitrite is 1.5 to 4.5 parts by weight and the calcium nitrite is 0.3 to 1.9 parts by weight with respect to 100 parts by weight of the cement.

3. The cement composition according to Claim 1, wherein the combined weight of the lithium nitrite and the calcium nitrite is 3.0 to 6.0 parts by weight with respect to 100 parts by weight of the cement.

4. The cement composition according to any one of Claims 1 to 3, wherein the cement composition is a cold-resistant cement composition for use in mortar work in a construction environment where the outside air temperature at the initial stage of construction can drop to -5°C or lower.

5. A method for constructing mortars in cold weather, characterized in that curing is performed so that the construction environment is maintained at -5°C or higher for a mixture containing the cement composition according to any one of Claims 1 to 3 and mixing water.

6. The method for constructing mortars in cold weather according to Claim 5, wherein when the outside air temperature at the construction site drops below -5°C, heat insulation or heat supply is performed so that the construction environment is maintained at -5°C or higher.

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