Low-carbon type concrete

Abstract

To provide a low-carbon type concrete: capable of reducing CO2 (carbon dioxide) emissions; capable of securing initial strength required for application to general structures; having reduced shrinkage compared with conventional concrete; capable of further promoting carbon fixation after being put into service; and having high durability.SOLUTION: A low-carbon type concrete comprises cement, an admixture, aggregate, nitrite, urea, and water, wherein the admixture includes blast furnace slag fine powder and / or fly ash.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to low-carbon concrete. [Background technology]

[0002] In today's social climate, there is a strong demand for efforts to achieve carbon neutrality. In particular, concrete-related industries emit more CO2 than other sectors and industries, and are expected to make a significant contribution to the realization of a low-carbon society from cement and concrete manufacturing to construction and after use.

[0003] As a method for reducing and capturing CO2 emissions in the concrete field, it is known to replace portland cement with fly ash or blast furnace slag (for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-088278 [Patent Document 2] Japanese Patent Application Publication No. 2024-005273 Summary of the Invention [Problem to be solved by the invention]

[0005] Research and development is underway into various concrete manufacturing methods and products that focus on reducing and capturing CO2 emissions. However, the results have been limited to applications in plain concrete and small precast products. Furthermore, when large amounts of admixtures (ground granulated blast furnace slag, fly ash) are used as cement substitutes, issues arise, such as the need to ensure early strength, the occurrence of early cracks due to increased shrinkage, accelerated carbonation, and reduced durability due to a decrease in the critical chloride ion concentration at which corrosion occurs. For these reasons, the use of concrete in general structures has not progressed.

[0006] Under these circumstances, the present invention aims to provide a low-carbon concrete that can reduce CO2 emissions, ensures the early strength required for application to general structures, reduces drying shrinkage compared to conventional ordinary concrete and marine concrete, and exhibits higher rebar corrosion prevention performance than the above-mentioned conventional concrete even after carbonation or chloride ion penetration after service. [Means for solving the problem]

[0007] The present inventors have conducted extensive research to solve the above problems and have found that the following inventions meet the above objectives, thereby completing the present invention.

[0008] <1> A low-carbon concrete comprising cement, admixtures, aggregate, nitrite, urea, and water, wherein the admixtures include ground granulated blast furnace slag and / or fly ash. <2> The binder is composed of the cement and the admixture, and the content of the admixture is 50% by weight or more. <1> The low-carbon concrete described in <3> The amount of the nitrite is 1 kg / m 3 The above <1> or <2> The low-carbon concrete described in <4> The substitution rate of the urea for the water is 50% by volume or less. <1> from <3> The low-carbon concrete according to any one of the above. <5> The aggregate includes carbon-adsorbed recycled aggregate that has adsorbed carbon dioxide. <1> from <4> The low-carbon concrete according to any one of the above. [Effects of the Invention]

[0009] According to the present invention, in addition to being able to reduce CO2 emissions, a low-carbon concrete is provided that can ensure the early strength required for application to general structures, has reduced shrinkage compared to conventional concrete, and exhibits anti-corrosion properties against carbonation and chloride ions after use, making it highly durable. DETAILED DESCRIPTION OF THE INVENTION

[0010] The following describes in detail an embodiment of the present invention, but the following description of the constituent elements is one example (typical example) of an embodiment of the present invention, and the present invention is not limited to the following content unless the gist of the present invention is changed. Note that when the expression "to" is used in this specification, it is used as an expression including the numerical values ​​or physical property values ​​before and after it.

[0011] <Concrete> The present invention relates to a low-carbon concrete (hereinafter, sometimes referred to as "the concrete of the present invention") that contains cement, an admixture, an aggregate, a nitrite, urea, and water, wherein the admixture contains ground granulated blast furnace slag and / or fly ash.

[0012] In this way, replacing cement with admixtures containing ground granulated blast furnace slag and / or fly ash reduces CO2 emissions. Furthermore, the combined use of nitrite and urea ensures early strength, reduces shrinkage, maintains durability over the long term after use, and increases the amount of atmospheric CO2 immobilized in the concrete.

[0013] In addition, the combined use of nitrite and urea improves the concrete's moisture retention, so even if the form is removed early, the hydration reaction will proceed properly due to the internal curing effect. As a result, the curing process and period can be significantly shortened compared to ordinary concrete or marine concrete.

[0014] In this specification, "concrete" includes "mortar containing cement, water, fine aggregate, and coarse aggregate" as well as "concrete containing cement, water, and fine aggregate," and also includes both pre-hardened and hardened concrete.

[0015] (cement) The concrete of the present invention contains cement. The cement is not particularly limited, but examples thereof include various cements such as ordinary Portland cement, high-early-strength Portland cement, moderate-heat Portland cement, and low-heat Portland cement.

[0016] (Admixture) The concrete of the present invention contains an admixture containing ground granulated blast furnace slag and / or fly ash.

[0017] Fine granulated blast furnace slag is produced by drying and pulverizing granulated blast furnace slag, which is molten blast furnace slag produced at the same time as shear iron in blast furnaces at steelworks. The molten blast furnace slag is rapidly cooled with water, and the granulated blast furnace slag is then dried and pulverized to adjust the particle size. JIS A 6206 standardizes four types of blast furnace slag powder: Ground Granulated Blast Furnace Slag 3000, Ground Granulated Blast Furnace Slag 4000, Ground Granulated Blast Furnace Slag 6000, and Ground Granulated Blast Furnace Slag 8000. Any of these may be used.

[0018] Fly ash is the ash collected by a dust collector from coal ash generated when pulverized coal is burned at a coal-fired power plant. JIS A 6201 standardizes four types of fly ash: Type I, Type II, Type III, and Type IV, and any of these may be used.

[0019] In the concrete of the present invention, the content of the admixture in the binder composed of cement and admixture is set appropriately depending on the application, etc., but is preferably 50% by weight or more, more preferably 70% by weight or more, and even more preferably 75% by weight or more. In addition, the content of the admixture in the binder composed of cement and admixture is preferably 95% by weight or less, and more preferably 85% by weight or less.

[0020] Furthermore, it is preferable that the fly ash replacement rate (i.e., the weight ratio of fly ash to the total weight of the binder composed of cement and admixture) is 30% by weight or less, it is more preferable that the fly ash replacement rate is 30% by weight or less and the blast furnace slag replacement rate (i.e., the weight ratio of blast furnace slag to the total weight of the binder) is 40% by weight or more, it is even more preferable that the fly ash replacement rate is 0% to 30% by weight and the blast furnace slag replacement rate is 40% to 95% by weight, and it is even more preferable that the fly ash replacement rate is 0% to 30% by weight and the blast furnace slag replacement rate is 45% to 85% by weight.

[0021] The admixture may contain materials other than ground granulated blast furnace slag and fly ash, such as silica fume, volcanic ash, expansive materials, ground limestone, fine siliceous powder, etc. On the other hand, the admixture preferably contains 90% by weight or more, more preferably 95% by weight or more of ground granulated blast furnace slag and fly ash, and even more preferably consists of ground granulated blast furnace slag and fly ash.

[0022] (aggregate) The concrete of the present invention contains aggregate. Either fine aggregate or coarse aggregate may be used as the aggregate depending on the intended use. Examples of fine aggregate include river sand, mountain sand, land sand, sea sand, crushed sand, silica sand, slag fine aggregate, artificial fine aggregate, and recycled fine aggregate. Examples of coarse aggregate include gravel, crushed stone, slag coarse aggregate, artificial coarse aggregate, and recycled coarse aggregate.

[0023] From the perspective of carbon neutrality, it is preferable to use carbon-adsorbed recycled aggregate, which is aggregate that has carbon dioxide pre-adsorbed. In other words, by using carbon-adsorbed recycled aggregate, it is possible to neutralize the CO2 emissions from materials generated during concrete production. Carbon-adsorbed recycled aggregate is made by exposing recycled aggregate outdoors for a certain period of time or by leaving it in a high-concentration CO2 environment, and then carbonate the mortar attached to the recycled aggregate. Carbonation densifies the attached mortar, increasing the density of the recycled aggregate and reducing its water absorption rate.

[0024] (nitrites) The concrete of the present invention contains a nitrite. The nitrite is not particularly limited, but examples include lithium nitrite, sodium nitrite, and calcium nitrite. Among these, lithium nitrite and / or calcium nitrite are preferred because they can increase the amount of carbon fixed in the concrete after use. Furthermore, lithium nitrite is more preferred from the viewpoints of the hardening speed and fresh properties of fresh concrete.

[0025] In the concrete of the present invention, the amount of nitrite is appropriately set depending on the application, etc., but it is 1 kg / m 3 More than 2kg / m is preferable. 3 The upper limit is not particularly limited as long as it does not impair the effects of the present invention, and is, for example, 30 kg / m 3 or less, 25 kg / m 3 Below 20kg / m 3 Below 15kg / m 3 Below, 13kg / m 3 For example, in the case of concrete, the amount of nitrite can be 1 kg / m 3 ~20kg / m 3 Or 2kg / m 3 ~20kg / m 3 , 3 kg / m 3 ~15kg / m 3 , 6 kg / m 3 ~15kg / m 3 , 8 kg / m 3 ~13kg / m 3If a 40% by weight aqueous solution of nitrite is used, 3 The amount of nitrite can be 2.5kg-50kg, 5kg-50kg, 7.5kg-37.5kg, 15kg-37.5kg, or 20kg-32.5kg per m. In the case of mortar, the amount of nitrite is 5kg / m. 3 ~30kg / m 3 Or 10 kg / m 3 ~25kg / m 3 , 15 kg / m 3 ~25kg / m 3 If a 40% by weight aqueous solution of nitrite is used, 3 The formulation can contain 12.5kg to 75kg, 25kg to 62.5kg, or 37.5kg to 62.5kg per unit.

[0026] (urea) The concrete of the present invention contains urea. In the concrete of the present invention, the substitution rate of urea for water is preferably 50% by volume or less. That is, the volume ratio of urea to the total volume of water and urea is preferably 50% or less. The substitution rate of urea for water may be 40% by volume or less, 30% by volume or less, 20% by volume or less, or 15% by volume or less. The lower limit is not particularly limited as long as it does not impair the effects of the present invention, and may be, for example, 0.1% by volume or more, 0.3% by volume or more, 1% by volume or more, 1.5% by volume or more, or 3% by volume or more.

[0027] (water) The concrete of the present invention contains water. The water is not particularly limited, and examples thereof include tap water, industrial water, groundwater, and river water.

[0028] In the concrete of the present invention, the amount of water is preferably 35 to 65 parts by weight per 100 parts by weight of the total of cement and admixture.

[0029] (Other ingredients) The concrete of the present invention may contain components other than cement, admixtures, aggregate, nitrite, urea, and water, and may include chemical admixtures such as water-reducing agents, air-entraining agents, and calcium-based aqueous solutions to impart properties to the concrete.

[0030] The concrete of this invention has the advantage that it is not significantly different from precast concrete secondary products or general concrete in terms of fresh properties and hardening speed, making it suitable for general construction. This gives it the advantage of being widely available throughout Japan.

[0031] (Method of manufacturing concrete of the present invention) The method for producing the concrete of the present invention is not particularly limited, and it can be produced by any known method. The nitrite and urea may be used as they are or may be dissolved in water beforehand, but it is preferable to dissolve them in mixing water beforehand. For example, the concrete of the present invention can be obtained by charging cement, admixture, aggregate, and mixing water in which the nitrite and urea have been dissolved into a mixer and kneading them. [Example]

[0032] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as the gist of the present invention is not changed.

[0033] <Production Example 1> The following materials were used: Cement: OPC (OPC / Aso Cement / Pacific Cement, ordinary Portland cement) 2)Admixture BB (Esment G): (Nippon Steel Blast Furnace Cement Co., Ltd. / Esment G) Fly ash FA: (Kyuden Sangyo Co., Ltd. / Fly ash JIS type II) 3) Fine aggregate: S (Fukuoka Construction Materials Co., Ltd. / Genkai Sea sand) 4) Li: Lithium nitrite aqueous solution (Fukutoku Giken Co., Ltd. / Procon 40) 5) Urea (U): (Urea, Mitsui Chemicals, Inc.) 6)Water:

[0034] (No. 1, No. 2) The formulation shown in Table 1 (parts by weight, 1 m 2 Mortar was produced and tested by mixing mixing water, cement, admixtures, and fine aggregate in a mortar mix (approximately 1000 sq. m). No. 1 was made by replacing 50% of the cement with ground granulated blast furnace slag, and No. 2 was made by replacing 70% with ground granulated blast furnace slag. Taiheiyo Cement's ordinary Portland cement was used for the OPC.

[0035] (No.3, No.4, No.5) No. 3: 281 kg of water and 15 kg of a 40% lithium nitrite aqueous solution were mixed to prepare mixing water. No. 4: 267 kg of water and 30 kg of a 40% lithium nitrite aqueous solution were mixed to prepare mixing water. No. 5: 238 kg of water and 60 kg of a 40% lithium nitrite aqueous solution were mixed to prepare mixing water. Next, mixing water, cement, admixture (70% of the cement was replaced with ground granulated blast furnace slag), and fine aggregate were mixed according to the proportions shown in Table 1 to produce mortar, which was then tested. Ordinary Portland cement from Taiheiyo Cement was used for the OPC.

[0036] (No.6) Mortar was produced by mixing mixing water, cement, admixtures, and fine aggregate according to the mix ratio shown in Table 1, and then tested. No. 6 is a mixture in which 50% of the cement has been replaced with ground granulated blast furnace slag. Ordinary Portland cement from Aso Cement is used for the OPC.

[0037] (No.7, No.8) No. 7 and No. 8 are cement mixtures in which 80% of the cement has been replaced with ground granulated blast furnace slag. No. 7: 224 kg of water, 56 kg of a 40% lithium nitrite aqueous solution, and mixing water were prepared. No. 8: 207 kg of water, 56 kg of a 40% lithium nitrite solution, and 20 kg of urea (equivalent to 17 L) were mixed to prepare the mixing water. Aso Cement's ordinary Portland cement was used for the OPC. Next, mixing water, cement, admixtures, and fine aggregate were mixed according to the proportions shown in Table 1 to produce mortar, which was then subjected to testing.

[0038] (No.9) Mortar was produced and tested by mixing mixing water, cement, admixtures, and fine aggregate according to the proportions shown in Table 1. No. 9 is a mixture in which 50% of the cement has been replaced with ground granulated blast furnace slag and 30% with fly ash. Ordinary Portland cement from Aso Cement is used for the OPC.

[0039] (No. 10, No. 11) Based on the formulation of No. 9, No. 10 and No. 11 used lithium nitrite and urea in the mixing water. No. 10: 221 kg of water, 55 kg of a 40% lithium nitrite aqueous solution, and mixing water were prepared. No. 11: 208 kg of water, 55 kg of a 40% lithium nitrite solution, and 15 kg of urea (equivalent to 13 L) were mixed to prepare the mixing water. Aso Cement's ordinary Portland cement was used for the OPC. Next, mixing water, cement, admixtures, and fine aggregate were mixed according to the proportions shown in Table 1 to produce mortar, which was then subjected to testing.

[0040] (No.12) Mortar was produced by mixing mixing water, cement, admixtures, and fine aggregate according to the mix ratio shown in Table 1, and then tested. No. 12 is a mortar in which 90% of the cement has been replaced with ground granulated blast furnace slag. Ordinary Portland cement from Taiheiyo Cement Corporation is used for the OPC.

[0041] (No. 13, No. 14, No. 15) No. 13: 279 kg of water and 15 kg of a 40% lithium nitrite aqueous solution were mixed to prepare mixing water. No. 14: 265 kg of water and 30 kg of a 40% lithium nitrite aqueous solution were mixed to prepare mixing water. No. 15: 237 kg of water and 59 kg of a 40% lithium nitrite aqueous solution were mixed to prepare mixing water. Next, mixing water, cement, admixtures, and fine aggregate were mixed according to the proportions shown in Table 1 to produce mortar, which was then tested. Ordinary Portland cement from Taiheiyo Cement was used for the OPC.

[0042] [Table 1]

[0043] (Test results) 1) Neutralization depth Test method: Accelerated carbonation test method for concrete (JIS A 1153, 2012) Test specimens: No. 6 to No. 11

[0044] ·Consideration The results are shown in Table 2. As shown in Table 2, the carbonation depth of specimens No. 7, 8, 9, 10, and 11 is greater than that of specimen No. 6, which is made with blast-furnace cement equivalent to Type B, which is used for marine structures. Therefore, the carbonation depth progresses faster than that of conventional marine concrete, but specimens No. 8 and 11 have suppressed the progress of carbonation compared to specimens No. 7, 9, and 10. Furthermore, even if carbonation progresses, corrosion is suppressed as shown in "5) Corrosion current density and corrosion suppression rate" described below.

[0045] 2) Carbon fixation amount, carbon fixation increase, carbon fixation increase during the same period Test method: Carbon content in the carbonized area after 56 days of accelerated carbonation was measured using ICP.

[0046] ·Considerations: The results are shown in Table 2. As shown in Table 2, the amount of carbon fixed within the test specimens during accelerated carbonation (56 days) was 165% to 350% for No. 7, 8, 9, 10, and 11, assuming that No. 6, a marine concrete equivalent to conventional blast-furnace cement Type B, was 100. No. 8 and 11 were able to absorb more CO2 and fix more carbon within the concrete than conventional concrete over the same period.

[0047] [Table 2]

[0048] 3) Compressive strength Test method: Compressive strength test method for concrete (JIS A1108, 2018)

[0049] ·Considerations: The results are shown in Table 3. Nos. 1 to 5 used ordinary Portland cement from Taiheiyo Cement for the OPC. As shown in Table 3, the compressive strength of Nos. 3 to 5, in which 70% of the cement was replaced with ground granulated blast furnace slag, was 100% to 116% of the compressive strength of test specimen No. 1, which is equivalent to blast furnace cement Type B used for marine structures, when cured in air (28 days old), and 96% of that of No. 5 when cured underwater (28 days old), achieving equivalent compressive strength.

[0050] Next, Nos. 6 to 11 use Aso Cement's ordinary Portland cement for the OPC. As shown in Table 3, the compressive strength of No. 8, in which 80% of the cement was replaced with ground granulated blast furnace slag, was 99% of that of the test specimen (No. 6) which is equivalent to blast furnace cement type B used for marine structures, after underwater curing (7 days of age). Furthermore, the compressive strength of No. 8 was higher than that of No. 7 (which used only lithium nitrite), and by adding urea, it was possible to obtain a strength equivalent to that of No. 6.

[0051] Nos. 9 to 11 use a combination of ground granulated blast furnace slag and fly ash as admixtures, replacing 80% of the cement. While No. 9, which does not contain lithium nitrite or urea, exhibits a clear decrease in compressive strength of approximately 60%, No. 11, which contains urea, achieves over 90% of the strength of No. 6 at 7 days and approximately 80% at 28 days. In other words, even when replacing approximately 80% of the admixture, the specified strength required for general structures can be easily achieved by utilizing the present invention and setting a slightly lower water-binder ratio.

[0052] Furthermore, when we look at the compressive strength of Nos. 3 to 5 and Nos. 13 to 15, we see that the difference in compressive strength due to curing is small. While ordinary concrete requires a curing process and period to promote the hydration reaction after pouring, the concrete of the present invention has the characteristic of being able to obtain appropriate strength development without the need for a curing process or period.

[0053] [Table 3]

[0054] 4) Drying shrinkage Test method: Length change measurement method for mortar and concrete (JIS A 1129)

[0055] ·Considerations: The results are shown in Table 4. As shown in Table 4, the drying shrinkage of Nos. 3 to 5 was all suppressed compared to test specimen No. 1, which is equivalent to blast-furnace cement type B used in marine structures, and the suppression effect increased as the amount of lithium nitrite added increased. Furthermore, Nos. 8 and 11, which used a combination of lithium nitrite and urea, were able to suppress shrinkage by about 50%. In other words, Nos. 8 and 11 have good strength development and significantly suppress drying shrinkage, which reduces the occurrence of drying cracks and makes it possible to produce high-quality concrete structures.

[0056] [Table 4]

[0057] 5) Corrosion current density and corrosion inhibition rate Test Method: Salt damage: Chloride ion amount 10 kg / m 3 The test specimen was prepared by adding the above to the test piece in advance → humidity 90% (91 days) → corrosion current density was measured. Complex deterioration: Intrinsic chloride ion content 10 kg / m 3 The test specimen was prepared by adding the above to the test specimen in advance → 90% humidity (7 days) → Neutralization was promoted (CO2 concentration 5%, humidity 60%) (28 days) → 90% humidity (7 days) → Measurement of corrosion current density.

[0058] Consideration: The results are shown in Table 5. Nitrite ions prevent rusting of rebars. Because urea does not have a rust-preventing mechanism, the rust-preventive performance of concrete rebars was evaluated using Nos. 5, 7, and 15. Therefore, the rust-preventive performance of Nos. 7 and 8 is equivalent. No. 1 is a test specimen simulating marine concrete equivalent to blast-furnace cement type B. Based on these results, the corrosion rate of the concrete of the present invention is predicted to be approximately 10 or less in all deterioration environments, assuming No. 1 is 100. It is generally believed that the higher the replacement rate of admixture, the lower the rust-preventive performance of rebars. However, by utilizing this invention, it is possible to produce low-carbon concrete that is significantly more durable than conventional concrete.

[0059] [Table 5]

Claims

1. A concrete comprising cement, an admixture, an aggregate, a nitrite, urea, and water, A low-carbon concrete, wherein the admixture comprises ground granulated blast furnace slag and / or fly ash.

2. 2. The low-carbon concrete according to claim 1, wherein the content of the admixture in the binder composed of the cement and the admixture is 50% by weight or more.

3. The amount of the nitrite is 1 kg / m 3 The low-carbon concrete according to claim 1 or 2.

4. 3. The low-carbon concrete according to claim 1, wherein a substitution rate of the urea for the water is 50% by volume or less.

5. 3. The low-carbon concrete according to claim 1, wherein the aggregate comprises carbon-adsorbed recycled aggregate that has adsorbed carbon dioxide.

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