Concrete composition and method for increasing compressive strength of concrete composition

Abstract

To provide a concrete composition having a comparatively high mixture ratio of a granulated blast furnace slag which has sufficient flowability for concrete construction, and can exhibit excellent compressive strength both an initial period and a long period.SOLUTION: A concrete composition contains a hydraulic composition, water, a water-reducing agent, a fine aggregate and a coarse aggregate, wherein the hydraulic composition contains cement containing an alkali stimulant and a granulated blast furnace slag, and an accelerator, a content of the granulated blast furnace slag is 40.0-95.0 mass% based on the total amount of the cement, a content of gypsum in the cement is 0.05-1.70 mass% in terms of SO3, a content of the accelerator is 0.2-10.0 pts.mass with respect to 100 pts.mass of the cement, a content of the hydraulic composition is 250-600 kg / m3, a content of the water with respect to the content of the hydraulic composition is 0.25-0.60, and a content of the water-reducing agent is 0.5-3.0 mass% based on 100 mass% of the hydraulic composition.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to concrete compositions and methods for increasing the compressive strength of concrete compositions. [Background technology]

[0002] In recent years, with the increasing demand for measures to combat global warming, there has been a demand for a reduction in CO2 emissions during cement production. One method widely considered for reducing CO2 emissions is to produce cement by replacing part of the cement clinker, which generates a large amount of CO2 during preparation, with admixtures. Among these admixtures, steel slag, such as granulated blast furnace slag (BFS), is expected to improve the long-term strength of concrete and its salt-blocking effect. Therefore, research is being conducted into cement that uses steel slag as an admixture and increases its mixing ratio.

[0003] However, blast furnace slag cement with a higher mixing ratio tends to have lower initial strength when hardening compared to cement made with ordinary Portland cement (OPC) alone. Therefore, various methods are being investigated to achieve the same level of strength as cement made with OPC alone, even in the case of blast furnace slag cement.

[0004] For example, methods that have been reported include further adding calcium hydroxide fine powder (e.g., Non-Patent Document 1), and producing blast-furnace cement using Portland cement clinker with a high C3S content (e.g., Non-Patent Document 2).In addition, the use of inorganic or organic accelerators other than calcium hydroxide fine powder has also been investigated as a measure to improve the early strength of cement compositions.

[0005] Furthermore, in blast furnace cement containing a high proportion of granulated blast furnace slag, etc., gypsum is incorporated to improve early strength (e.g., Non-Patent Document 3). Aiming to achieve strength comparable to that achieved when OPC is used alone, the amount of gypsum is increased, and further studies are being conducted to improve early strength by incorporating an accelerator that accelerates the hardening reaction of cement clinker (e.g., Patent Document 1). Furthermore, Patent Document 2 discloses that in low-carbon concrete that does not contain an accelerator, blast furnace slag powder with gypsum added internally has superior quality stability.

[0006] It has been confirmed that the hydration reaction of ground granulated blast furnace slag in blast furnace cement mixed with granulated blast furnace slag is activated by the use of nitrite.Patent Document 3 discloses a cementitious hydraulic composition in which part of the cement is replaced with ground granulated blast furnace slag having latent hydraulic properties as a cement substitute, and in which nitrite is added to activate the hydration reaction of the ground granulated blast furnace slag. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-125371 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-141614 [Patent Document 3] Japanese Patent Application Publication No. 2018-076203 [Non-patent literature]

[0008] [Non-Patent Document 1] Hiroaki Yoshiga et al., "Effect of Fine Calcium Hydroxide Powder on Cement Containing Blast Furnace Slag," Cement & Concrete Journal, Vol. 67, 2013, pp. 151-156 [Non-patent document 2] Atsushi Yatagai et al., "Effect of Specific Surface Area of ​​Ground Blast Furnace Slag on the Properties of Blast Furnace Cement Using High C3S Clinker," Proceedings of the Cement and Concrete Society, Vol. 67, 2013, pp. 296-303 [Non-patent document 3] Etsuro Sakai et al., "Effect of calcium nitrite and alkanolamines on the hydration of high-blast furnace slag cement," Proceedings of the Cement and Concrete Journal, 2019, Vol. 73, pp. 52-57 Summary of the Invention [Problem to be solved by the invention]

[0009] In concrete compositions containing water, admixtures, and aggregates mixed with a hydraulic composition, a commonly known method for improving compressive strength is to reduce the amount of water added (reducing the water / cement ratio). However, reducing the amount of water added reduces the interparticle distance of the alkali activator in the concrete composition, making it difficult to ensure fluidity and potentially worsening the workability of the concrete. Therefore, from the perspective of balancing compressive strength and fluidity, there is a limit to how much water can be reduced solely for the purpose of increasing compressive strength. It would be useful to have a method for improving compressive strength other than adjusting the amount of water added.

[0010] Furthermore, in blast furnace cement containing a high proportion of granulated blast furnace slag, etc., even when gypsum and an accelerator are used in combination as described above, the expected improvement in compressive strength may not be achieved by adding an accelerator. For example, when blast furnace cement prepared with an accelerator is hardened, the initial strength is improved compared to when no accelerator is added, but the strength may not be as strong as expected as the material ages.

[0011] The present disclosure aims to provide a concrete composition containing a relatively high proportion of granulated blast furnace slag, which has sufficient fluidity for concrete construction and can exhibit excellent compressive strength both at early ages and over the long term. The present disclosure also aims to provide a method for increasing the compressive strength of a concrete composition containing a relatively high proportion of granulated blast furnace slag at early ages and over the long term. [Means for solving the problem]

[0012] The present inventors have investigated the above-mentioned problems and found that, when increasing the amount of gypsum and adding an accelerator, which are each considered to be beneficial for improving early strength, are used in combination, the gypsum can inhibit the action of the accelerator, and this inhibiting action can have an effect on accelerators in general, and can have a strong effect on alkaline earth metal nitrites intended to accelerate the hardening of granulated blast furnace slag.

[0013] A more detailed explanation follows. Gypsum in hydraulic compositions is a component that controls the reactivity of alkaline activators and adjusts the hydration reaction of the hydraulic composition. However, it also reacts with components (e.g., Ca, Al) contained in granulated blast furnace slag to form ettringite (3CaO·Al2O3·3CaSO4·32H2O), which has low solubility. This ettringite covers the particle surfaces of the granulated blast furnace slag, inhibiting its dissolution and slowing the reaction rate. In particular, in hydraulic compositions containing an accelerator, the accelerator not only promotes the dissolution and reaction of the granulated blast furnace slag in the early stages of the reaction, but also promotes the formation of ettringite through a reaction with the large amount of gypsum present in the same system. In other words, compared to a case in which an accelerator is not included, the reaction for ettringite formation described above is promoted, and the excessive production of ettringite can actually inhibit the reaction of the granulated blast furnace slag. Generally, it is believed that increasing the amount of gypsum is beneficial for increasing strength because ettringite formation increases bound water and reduces voids in the early stages of the hardening reaction. However, it was discovered that the amount of gypsum used in combination with an accelerator can actually have a negative effect. This led to the new discovery that by reducing the gypsum content in a system in which an accelerator is used in combination, contrary to conventional common knowledge, the resulting hydraulic composition can exhibit excellent compressive strength both in the early stages and over the long term. The present disclosure is based on these new findings.

[0014] One aspect of the present disclosure is a concrete composition including a hydraulic composition, water, a water-reducing agent, fine aggregate, and coarse aggregate, wherein the hydraulic composition includes cement including an alkali activator and granulated blast furnace slag, and an accelerator, the content of the granulated blast furnace slag being 40.0 to 95.0 mass% based on the total amount of the cement, the content of gypsum in the cement being 0.05 to 1.70 mass% in terms of SO3, the content of the accelerator being 0.2 to 10.0 parts by mass relative to 100 parts by mass of the cement, and the content of the hydraulic composition being 250 to 600 kg / m 3The content of the water relative to the content of the hydraulic composition is 0.25 to 0.60, and the content of the water-reducing agent is 0.5 to 3.0 mass% based on 100 mass% of the hydraulic composition.

[0015] The concrete composition described above can reduce the inhibition of the hardening-accelerating effect of the accelerator by using a hydraulic composition containing a low amount of gypsum in combination with an accelerator. This action allows the concrete composition to exhibit excellent compressive strength both in the early stages and over the long term when hardened, even when a hydraulic composition containing a relatively large amount of granulated blast furnace slag is used.

[0016] The water reducing admixture may include a high-range air-entraining water reducing admixture.

[0017] The content of the granulated blast furnace slag and the content of the gypsum may satisfy the relationship of the following formula (1): By adjusting the content of the granulated blast furnace slag and the content of the gypsum so as to satisfy the relationship of the following formula (1), it is possible to achieve a higher level of both early-stage and long-term compressive strength when the concrete composition is hardened. [Gypsum content]≦1.5−2.0([granulated blast furnace slag content]−60) / 100…Equation (1)

[0018] The accelerator may contain at least one selected from the group consisting of alkali metal salts and alkaline earth metal salts. By containing the accelerator, the reactivity of the granulated blast furnace slag can be further improved.

[0019] The accelerator may contain a salt having a monovalent anion, which adjusts the formation of hydrates on the surface of the granulated blast furnace slag and further improves the reactivity of the granulated blast furnace slag.

[0020] The accelerator may contain a calcium salt. When the accelerator contains a calcium salt, calcium ions (Ca2+ ) concentration and promote the production of calcium silicate hydrate (CSH), which is the main component of the hardened concrete, resulting in superior early compressive strength when the concrete composition is hardened.

[0021] The accelerator may contain at least one selected from the group consisting of nitrites, nitrates, and chlorides. When the accelerator contains the accelerator, the concrete composition has better early compressive strength when hardened.

[0022] The alkali activator may contain at least one selected from the group consisting of Portland cement clinker, slaked lime, and quicklime. When the alkali activator contains the above-mentioned component, the hydration reaction of the granulated blast furnace slag can be accelerated, and the hardening reaction in the concrete composition can be further accelerated.

[0023] The gypsum may contain at least one selected from the group consisting of gypsum dihydrate and gypsum hemihydrate. The inclusion of at least one of gypsum dihydrate and gypsum hemihydrate in the gypsum can further promote the initial reaction between the alkaline activator (e.g., Portland cement clinker) and granulated blast furnace slag. While gypsum can be any of gypsum anhydrite, gypsum dihydrate, and gypsum hemihydrate, the reason why the above-mentioned effect is significant when the concrete composition according to the present disclosure contains at least one of gypsum dihydrate and gypsum hemihydrate is believed to be due to the following reason. That is, gypsum dihydrate and gypsum hemihydrate have a faster dissolution rate than gypsum anhydrite and can contribute to the reaction between the alkaline activator and granulated blast furnace slag at an earlier stage of the hardening reaction. Therefore, the effect can be significantly achieved when at least one of gypsum dihydrate and gypsum hemihydrate is contained. The above-mentioned difference is particularly evident in systems with a reduced gypsum content, such as the hydraulic composition according to the present disclosure.

[0024] The basicity of the granulated blast furnace slag may be less than 1.75. Since the hydraulic composition can fully utilize the accelerator effect by reducing the gypsum content, it is possible to use granulated blast furnace slag, so-called low-grade slag, which is generally not used in order to improve early strength. Granulated blast furnace slag with a basicity of less than 1.75, which can be classified as low-grade slag, can be used in the hydraulic composition. Even in this case, the concrete composition can exhibit excellent compressive strength both in the early stages and over the long term after hardening.

[0025] The basicity of the granulated blast furnace slag may be 1.75 to 1.95. When the basicity of the granulated blast furnace slag is within the above range, the latent hydraulic properties of the granulated blast furnace slag can be more fully exhibited, making it possible to produce concrete with excellent strength development. It is generally known that a low basicity reduces the reactivity and strength development performance of granulated blast furnace slag. However, in the hydraulic composition according to the present disclosure, even when granulated blast furnace slag with a low basicity is used, by adjusting the basicity to fall within the above range, a concrete composition that can exhibit even better strength development performance can be obtained.

[0026] The aluminum oxide content of the granulated blast furnace slag may be 14.5% by mass or less. By using granulated blast furnace slag with a relatively low aluminum oxide content, the amount of ettringite that can inhibit the reaction of the granulated blast furnace slag can be further suppressed, and the reaction of the granulated blast furnace slag can be promoted over a longer period of time. Furthermore, by using granulated blast furnace slag with a relatively low aluminum oxide content, it is possible to reduce the amount of accelerator used, thereby further reducing the cost required for concrete production.

[0027] The content of the granulated blast furnace slag may be 60 to 95 mass % based on the total amount of the cement. Since the effect of the accelerator can be fully achieved by reducing the gypsum content in the hydraulic composition, even a composition containing a high amount of granulated blast furnace slag, which is generally not widely used from a practical standpoint, can exhibit compressive strength superior to that of conventional blast furnace cements.

[0028] One aspect of the present disclosure provides a method for producing a cement composition comprising an alkaline activator and granulated blast furnace slag, the cement having a content of the granulated blast furnace slag of 40.0 to 95.0 mass%, the method comprising: measuring a gypsum content in the cement and adjusting the gypsum content in the cement to 0.05 to 1.70 mass% in terms of SO; measuring a content of an accelerator in the composition and adjusting the content of the accelerator to 0.2 to 10.0 parts by mass per 100 parts by mass of the cement; and adjusting water, a water-reducing agent, a fine aggregate, and a coarse aggregate in a blending amount of the composition to 250 to 600 kg / m 3 and mixing the water so that the amount of the water to be mixed relative to the amount of the composition is 0.25 to 0.60, and the content of the water-reducing agent is 0.5 to 3.0 mass % based on 100 mass % of the composition.

[0029] The method for increasing the compressive strength of the concrete composition described above involves first adjusting the amount of gypsum in the cement and the amount of accelerator in the composition containing a predetermined cement, and then blending water, a water-reducing agent, fine aggregate, and coarse aggregate in predetermined amounts, thereby increasing the compressive strength of the resulting concrete composition when it is hardened.

[0030] In the method for increasing compressive strength, the composition may contain an accelerator. When the composition already contains an accelerator, that is, when the composition is itself a hydraulic composition, the method for increasing compressive strength can be applied. [Effects of the Invention]

[0031] According to the present disclosure, it is possible to provide a concrete composition having a relatively high mixing ratio of granulated blast furnace slag, which has sufficient fluidity for concrete construction and can exhibit excellent compressive strength both at an early stage and over the long term. According to the present disclosure, it is also possible to provide a method for increasing the compressive strength of a concrete composition having a relatively high mixing ratio of granulated blast furnace slag both at an early stage and over the long term. DETAILED DESCRIPTION OF THE INVENTION

[0032] Hereinafter, embodiments of the present disclosure will be described. However, the following embodiments are examples for explaining the present disclosure, and are not intended to limit the present disclosure to the following content. In the following description, when it is written "X to Y" (X and Y are arbitrary numbers), it means "X or more and Y or less" unless otherwise specified.

[0033] Unless otherwise specified, the materials exemplified in this specification can be used singly or in combination of two or more. When multiple substances corresponding to each component are present in the composition, the content of each component in the composition means the total amount of the multiple substances present in the composition, unless otherwise specified.

[0034] [Concrete composition] One embodiment of the concrete composition includes a hydraulic composition, water, a water-reducing agent, fine aggregate, and coarse aggregate. In the concrete composition, the content of the hydraulic composition is 250 to 600 kg / m 3 In the concrete composition, the content of the water relative to the content of the hydraulic composition is 0.25 to 0.60. In the concrete composition, the content of the water reducing agent is 0.5 to 3.0 mass% based on 100 mass% of the hydraulic composition. The concrete composition according to the present disclosure may be fresh concrete. In this specification, fresh concrete means concrete that retains fluidity from immediately after mixing until setting and hardening. Each component of the concrete composition will be described below.

[0035] The hydraulic composition contains cement containing an alkali activator and granulated blast furnace slag, and an accelerator. In the hydraulic composition, the content of the granulated blast furnace slag is 40.0 to 95.0 mass% based on the total amount of the cement, the content of gypsum in the cement is 0.05 to 1.70 mass% in terms of SO3, and the content of the accelerator is 0.2 to 10.0 parts by mass per 100 parts by mass of the cement.

[0036] In this specification, cement refers not only to the case where the alkaline activator contains cement clinker, but also to a powder containing granulated blast furnace slag as the main component and containing an alkaline activator (or, in some cases, a powder further containing gypsum). The cement may be composed of an alkaline activator, granulated blast furnace slag, and gypsum.

[0037] The alkali activator is a component that stimulates the hardening reaction of the granulated blast furnace slag and promotes the hardening reaction of the hydraulic composition. The alkali activator may contain, for example, at least one selected from the group consisting of Portland cement clinker, slaked lime, and quicklime, or may be any one of Portland cement clinker, slaked lime, and quicklime, or may be Portland cement clinker.

[0038] The Portland cement clinker may be Portland cement clinker used to prepare various Portland cements specified in JIS R 5210:2003 "Portland Cement." Examples of the various Portland cements include ordinary Portland cement, high-early-strength Portland cement, moderate-heat Portland cement, and low-heat Portland cement. The Portland cement clinker may be Portland cement clinker used to prepare ordinary Portland cement and high-early-strength Portland cement.

[0039] The mineral composition of Portland cement clinker can be calculated by the Bogue formula. Here, the Bogue formula is a widely used formula for calculating the content ratio of major minerals in Portland cement clinker from the content ratio of chemical composition. By using the Bogue formula shown below, the contents of tricalcium silicate (3CaO·SiO2, denoted as C3S), dicalcium silicate (2CaO·SiO2, denoted as C2S), and tricalcium aluminate (3CaO·Al2O3, denoted as C3A) in Portland cement clinker can be calculated. Note that "%" in the following formula means "mass%". The chemical formula represents the content ratio (mass%) of each compound shown by the chemical analysis value according to JIS R 5204:2019 "Fluorescent X-ray analysis method for cement".

[0040] <Bogue formula> C3S [%]=(4.07×CaO [%])-(7.60×SiO2 [%])-(6.72×Al2O3 [%])-(1.43×Fe2O3 [%])-(2.85×SO3 [%]) C2S [%]=(2.87×SiO2 [%])-(0.754×C3S [%]) C3A [%]=(2.65×Al2O3 [%])-(1.69×Fe2O3 [%]) C4AF [%]=3.04×Fe2O3 [%]

[0041] The amount of C3A in Portland cement clinker is preferably 0.5 to 11.0 mass%, more preferably 0.5 to 10.5 mass%, still more preferably 0.5 to 10.0 mass% or less, and particularly preferably from 0.5 to 9.5 mass%. When the amount of C3A in Portland cement clinker is within the above range, it is possible to further reduce the amount of gypsum for suppressing the hydration reaction in the hydraulic composition, and the hydration reaction of blast furnace slag can be more fully exerted.

[0042] The fineness of the Portland cement clinker may be adjusted from the viewpoint of further improving the performance of the hydration reaction in the hydraulic composition. The lower limit of the Blaine specific surface area of ​​the Portland cement clinker is, for example, 2800 cm 2 / g or more, or 3000cm 2 / g or more. By setting the lower limit of the Blaine specific surface area of ​​the Portland cement clinker within the above range, the hydration reaction with the granulated blast furnace slag can be further promoted. The upper limit of the Blaine specific surface area of ​​the Portland cement clinker can be set to, for example, 10,000 cm 2 / g or less, 5000cm 2 / g or less, 4000cm 2 / g or less, or 3500cm 2 / g or less. By setting the upper limit of the Blaine specific surface area of ​​the Portland cement clinker within the above range, it is possible to reduce the production cost of the hydraulic composition and further reduce CO2 emissions in the production of the Portland cement clinker. The Blaine specific surface area of ​​the Portland cement clinker may be adjusted within the above range, for example, 2800 to 10000 cm 2 / g, 3000-5000cm 2 / g, 3000-4000cm 2 / g, or 3000-3500cm 2 / g.

[0043] The granulated blast furnace slag may be, for example, commercially available, or slag equivalent to the granulated blast furnace slag may be prepared and used. The hydraulic composition described above can fully utilize the accelerator capabilities by adjusting the amount of gypsum in the cement, and therefore, regardless of the quality of the granulated blast furnace slag, when a concrete composition is prepared and hardened, it can exhibit superior compressive strength compared to conventional hydraulic compositions with a relatively high gypsum content.

[0044] The upper limit of the aluminum oxide content (also referred to as the Al2O3 content) in the granulated blast furnace slag may be, for example, 14.5% by mass or less, 14.0% by mass or less, 13.5% by mass or less, 13.0% by mass or less, or 12.5% ​​by mass or less. When the Al2O3 content in the granulated blast furnace slag is within the above range, it is possible to further suppress a decrease in the long-term strength development of the resulting concrete composition when it is hardened. The lower limit of the Al2O3 content in the granulated blast furnace slag may be, for example, 8% by mass or more, 10% by mass or more, or 12% by mass or more. When the lower limit of the Al2O3 content in the granulated blast furnace slag is within the above range, it is possible to more fully exhibit the latent hydraulic properties of the granulated blast furnace slag. The term "latent hydraulic properties" refers to the property of initiating a hydration reaction by adding an alkaline activator. The amount of Al2O3 in the granulated blast furnace slag may be adjusted within the above range, for example, 8 to 14.5 mass %, or 10 to 12.5 mass %.

[0045] The lower limit of the silicon dioxide content (also referred to as the SiO2 content) in the granulated blast furnace slag may be, for example, 30.0 mass% or more, 34.0 mass% or more, 34.5 mass% or more, or 35.0 mass% or more. By ensuring that the lower limit of the SiO2 content in the granulated blast furnace slag is within the above range, it is possible to suppress a decrease in the initial and long-term strength development. The upper limit of the SiO2 content in the granulated blast furnace slag may be, for example, 40.0 mass% or less, 38.0 mass% or less, 36.5 mass% or less, or 35.5 mass% or less. By ensuring that the upper limit of the SiO2 content in the granulated blast furnace slag is within the above range, it is possible to suppress a decrease in the initial strength development. The SiO2 content in the granulated blast furnace slag may be adjusted within the above range, for example, 34.5 to 40.0 mass%.

[0046] The lower limit of the calcium oxide content (also referred to as the CaO content) in the granulated blast furnace slag may be, for example, 35.0 mass% or more, 38.5 mass% or more, or 40.0 mass% or more. When the lower limit of the CaO content in the granulated blast furnace slag is within the above range, the initial strength development can be further improved. The upper limit of the CaO content in the granulated blast furnace slag may be, for example, 45.0 mass% or less, 43.5 mass% or less, 43.0 mass% or less, 42.5 mass% or less, 42.0 mass% or less, or 41.5 mass% or less. When the upper limit of the CaO content in the granulated blast furnace slag is within the above range, the deterioration of the long-term strength development can be suppressed. The CaO content in the granulated blast furnace slag may be adjusted within the above range, for example, 38.5 to 45.0 mass%.

[0047] The lower limit of the magnesium oxide content (also referred to as MgO content) in the granulated blast furnace slag may be, for example, 4.0% by mass or more, 5.0% by mass or more, 5.5% by mass or more, 6.0% by mass or more, 7.0% by mass or more, or 7.2% by mass or more. When the lower limit of the MgO content in the granulated blast furnace slag is within the above range, it is possible to suppress a decrease in the initial and long-term strength development of the concrete composition when it is hardened. The upper limit of the MgO content in the granulated blast furnace slag may be, for example, 10.0% by mass or less, 9.0% by mass or less, less than 7.5% by mass, or less than 7.4% by mass. When the upper limit of the MgO content in the granulated blast furnace slag is within the above range, it is possible to suppress a decrease in the initial strength development of the concrete composition when it is hardened. The MgO content in the granulated blast furnace slag may be adjusted within the above range, for example, 4.0 to 10.0% by mass.

[0048] Granulated blast furnace slag may contain, as other components, for example, sulfur trioxide (SO3), sodium oxide (NaO2), potassium oxide (K2O), and titanium oxide (TiO2).

[0049] The chemical composition of granulated blast furnace slag in this specification means a value measured in accordance with the description of JIS R 5202:2015 "Methods for chemical analysis of cement."

[0050] The reactivity of granulated blast furnace slag is evaluated by an index called basicity, which is expressed as the value of (CaO + MgO + Al2O3) / SiO2 (the ratio of the total content of calcium oxide, magnesium oxide, and aluminum oxide to the content of silicon dioxide in granulated blast furnace slag). Either high-basicity or low-basicity granulated blast furnace slag can be used.

[0051] As the granulated blast furnace slag with high basicity, for example, one with a basicity of 1.75 or more can be used. The upper limit of the basicity of the granulated blast furnace slag may be, for example, 1.95 or less, less than 1.95, less than 1.90, less than 1.85, or less than 1.80. The lower limit of the basicity of the granulated blast furnace slag may be, for example, more than 1.75 or 1.78 or more. When the lower limit of the basicity is within the above range, it can be easier to improve the early strength of the concrete composition when it is hardened. The basicity of the granulated blast furnace slag can be adjusted within the above range, and may be, for example, 1.75 to 1.95, or 1.75 or more but less than 1.80.

[0052] In the above-mentioned hydraulic composition, granulated blast furnace slag with low basicity can also be used. Low-basicity granulated blast furnace slag is often avoided as a low-grade slag because it is difficult to obtain sufficient compressive strength. However, in the above-mentioned hydraulic composition, even such low-grade slag can be used because it can suppress the inhibitory effect on the accelerator. The upper basicity limit of such low-grade granulated blast furnace slag may be, for example, less than 1.75, less than 1.70, or less than 1.65. The lower basicity limit of the low-grade granulated blast furnace slag is not particularly limited, but may be, for example, 1.55 or more, 1.60 or more, or 1.65 or more. The basicity of the low-grade granulated blast furnace slag may be adjusted within the above-mentioned range, for example, 1.55 or more but less than 1.75.

[0053] The basicity in this specification is a value measured in accordance with the description in JIS A 6206:2013 "Ground granulated blast furnace slag for concrete," and specifically means the value of (CaO + MgO + Al2O3) / SiO2 (the ratio of the total content of calcium oxide, magnesium oxide, and aluminum oxide to the content of silicon dioxide).

[0054] The specific surface area of ​​granulated blast furnace slag is, for example, 2500 to 10000 cm 2 / g, 2500-8000cm 2 / g, 2500-6000cm 2 / g, 2500-5000cm 2 / g, 3000-5000cm 2 / g, 4000-5000cm 2 / g, or 4000 to 4500 cm 2 / g.

[0055] In this specification, the term "Blaine specific surface area" refers to a value measured in accordance with the method described in JIS R 5201:2015 "Physical testing methods for cement."

[0056] The content of the granulated blast furnace slag is 40.0 to 95.0 mass% based on the total amount of the cement, which can contribute to reducing CO2 emissions associated with the production of the concrete composition. The hydraulic composition reduces the amount of gypsum in the cement and can exhibit a hardening acceleration effect when used in combination with an accelerator, thereby preventing a significant decrease in compressive strength when the concrete composition is hardened and allowing a higher proportion of the cement to be replaced by granulated blast furnace slag.

[0057] The lower limit of the content of granulated blast furnace slag may be, for example, 45.0 mass% or more, more than 45.0 mass%, 50.0 mass% or more, 55.0 mass% or more, 60.0 mass% or more, 65.0 mass% or more, or 70.0 mass% or more, based on the total amount of the cement. When the lower limit of the content of granulated blast furnace slag is within the above range, the amount of alkaline activator used can be further reduced. The upper limit of the content of granulated blast furnace slag may be, for example, less than 95.0 mass%, 90.0 mass% or less, 85.0 mass% or less, or 80.0 mass% or less, based on the total amount of the cement. When the upper limit of the content of granulated blast furnace slag is within the above range, the decrease in early strength can be further suppressed, and the effect of using an accelerator in combination can be further improved. The content of granulated blast furnace slag may be adjusted within the above range, and may be 45.0 to 95.0 mass %, 60.0 to 95.0 mass %, or 60.0 to 90.0 mass % based on the total amount of the cement.

[0058] The content of granulated blast furnace slag in this specification refers to a value determined by the following method. Specifically, a measurement sample is prepared by heating a hydraulic composition at 900°C for 1 hour to crystallize the granulated blast furnace slag (glass). X-ray diffraction measurement is then performed on the measurement sample, and the crystalline phases in the measurement sample are quantified by Rietveld analysis to quantify gehlenite, merwinite, and the like as crystalline phases formed by crystallization of the granulated blast furnace slag. The total amount of these is defined as the content of granulated blast furnace slag. When a hydraulic composition is manufactured by one's own manufacturing process, the blended amount (measured value) of granulated blast furnace slag added during the manufacturing process corresponds to the content.

[0059] In the hydraulic composition according to the present disclosure, the gypsum content in the cement is kept relatively low. The gypsum content in the cement is 0.05 to 1.70 mass% in terms of SO3. By keeping the gypsum content within this range, the effect of the gypsum on improving the compressive strength of the concrete composition as it hardens can be exhibited, while the action of the accelerator on inhibiting the effect of improving the compressive strength of the concrete composition as it hardens can be reduced.

[0060] The upper limit of the gypsum content in the cement, calculated as SO3, may be, for example, 1.6% by mass or less, 1.5% by mass or less, 1.4% by mass or less, 1.3% by mass or less, 1.2% by mass or less, 1.0% by mass or less, or 0.8% by mass or less. When the upper limit of the gypsum content is within the above range, the hydraulic composition containing the accelerator can exhibit better strength development. The lower limit of the gypsum content in the cement, calculated as SO3, may be, for example, 0.10% by mass or more, 0.20% by mass or more, 0.30% by mass or more, 0.40% by mass or more, or 0.50% by mass or more. Setting the lower limit of the gypsum (SO3) content within the above range makes the hydration reaction of the cement more favorable, further improving the fluidity of the concrete composition mixed with water, and further improving the early strength development upon hardening. The gypsum content in the cement may be adjusted within the above range, and may be, for example, 0.10 to 1.5 mass %, or 0.50 to 1.3 mass %.

[0061] The gypsum content in this specification refers to the total amount of gypsum components that may be contained in the alkaline activator and granulated blast furnace slag, as well as the gypsum components that are blended with the cement. The gypsum content in this specification refers to a value determined by the method described below. Specifically, the gypsum content is measured in accordance with the SO3 analysis method specified in JIS R 5202:2015 "Methods for Chemical Analysis of Cement."

[0062] The gypsum that can be used includes, for example, gypsum dihydrate, gypsum hemihydrate, and anhydrous gypsum. The gypsum may contain at least one selected from the group consisting of gypsum dihydrate and gypsum hemihydrate, or may be one selected from the group consisting of gypsum dihydrate and gypsum hemihydrate.

[0063] The Blaine specific surface area of ​​the cement is, for example, 2800 to 10000 cm 2 / g. When the alkali activator constituting the cement contains Portland cement clinker, the Portland cement clinker, granulated blast furnace slag, and gypsum may be simultaneously ground to produce cement. When simultaneously ground, the lower limit of the Blaine specific surface area of ​​the cement is, for example, 2800 cm 2 / g or more, or 3000cm 2 / g or more. By setting the lower limit of the Blaine specific surface area of ​​the cement within the above range, the hydration reaction with the granulated blast furnace slag can be further promoted. The upper limit of the Blaine specific surface area of ​​the cement can be set to, for example, 10,000 cm 2 / g or less, 5000cm 2 / g or less, 4000cm 2 / g or less, or 3500cm 2 / g or less.

[0064] The accelerator is a compound that accelerates the reaction of granulated blast furnace slag and improves its early strength.

[0065] The accelerator may contain at least one selected from the group consisting of alkali metal salts and alkaline earth metal salts. The accelerator containing an alkali metal salt or an alkaline earth metal salt can further improve the reactivity of the granulated blast furnace slag. Examples of the alkali metal include sodium and potassium, and examples of the alkaline earth metal include magnesium and calcium. From the viewpoint of promoting hydrate formation and improving compressive strength, the alkaline earth metal preferably contains calcium, and more preferably is calcium.

[0066] The accelerator may contain a salt having a monovalent anion and may also contain a calcium salt. The accelerator may contain at least one selected from the group consisting of nitrites, nitrates, and chlorides, and preferably contains nitrite. When the accelerator contains nitrite, the early strength of the concrete composition when it is hardened can be further improved. When the accelerator contains nitrite, the amount of heat generated by hydration when the concrete composition is hardened can also be reduced.

[0067] More specific examples of the accelerator include calcium nitrite, calcium nitrate, calcium chloride, calcium hydroxide, sodium nitrite, potassium nitrite, sodium nitrate, potassium nitrate, sodium chloride, potassium chloride, etc. Among the above compounds, the accelerator preferably contains an alkali metal nitrite, more preferably contains calcium nitrite, and even more preferably is calcium nitrite.

[0068] The upper limit of the accelerator content may be, for example, 10.0 parts by mass or less, 8.0 parts by mass or less, 6.0 parts by mass or less, 5.0 parts by mass or less, 4.0 parts by mass or less, 3.5 parts by mass or less, or 3.3 parts by mass or less, relative to 100 parts by mass of the cement. By keeping the upper limit of the accelerator content within the above range, the occurrence of abnormal setting when the reaction of granulated blast furnace slag or the like is excessively promoted can be more reliably suppressed. The lower limit of the accelerator content may be, for example, 0.2 parts by mass or more, 0.3 parts by mass or more, 0.5 parts by mass or more, 1.0 parts by mass or more, 2.0 parts by mass or more, or 2.5 parts by mass or more, relative to 100 parts by mass of the cement. By keeping the lower limit of the accelerator content within the above range, the reaction of granulated blast furnace slag can be further promoted. The content of the accelerator may be adjusted within the above range, and may be, for example, 0.2 to 10.0 parts by mass, 0.3 to 5.0 parts by mass, or 0.5 to 3.5 parts by mass per 100 parts by mass of the cement.

[0069] In the hydraulic composition, the content of the granulated blast furnace slag and the content of the gypsum may satisfy the relationship of the following general formula (X). In the following general formula (X), the content of gypsum is the content of gypsum in cement (unit: mass%), expressed as an SO3 equivalent value. In the following general formula (X), the content of the granulated blast furnace slag is the content (unit: mass%) based on the total amount of cement. In the following general formula (X), A is a constant, which may be, for example, 1.5 or less. When the content of the granulated blast furnace slag and the content of the gypsum satisfy the relationship of general formula (X) in which the constant A is a smaller value, the effects of the present disclosure can be more pronounced. For example, the constant A may be 1.5, 1.0, 0.8, or 0.6. For reference, the formula when the constant A is 1.5 is shown below (see formula (1)). [Gypsum content]≦A-2.0([granulated blast furnace slag content]-60) / 100...General formula (X) [Gypsum content]≦1.5−2.0([granulated blast furnace slag content]−60) / 100…Equation (1)

[0070] Examples of water include tap water, distilled water, deionized water, etc. The content of water may be 20 to 100 parts by mass or 25 to 60 parts by mass per 100 parts by mass of the hydraulic composition.

[0071] Since the concrete composition according to the present disclosure includes the hydraulic composition described above, it is not necessarily necessary to reduce the water content in order to exhibit excellent compressive strength. The upper limit of the water / cement ratio (100 × water mass / cement mass) may be, for example, 60 mass% or less, 55 mass% or less, 50 mass% or less, or 45 mass% or less. When the upper limit of the water / cement ratio is within the above range, the compressive strength of the concrete composition when hardened can be further improved. The lower limit of the water / cement ratio may be, for example, 25 mass% or more, 30 mass% or more, 35 mass% or more, or 40 mass% or more. When the lower limit of the water / cement ratio is within the above range, the fluidity of fresh concrete can be further improved, and the workability of concrete construction can be further improved.

[0072] The fine aggregate may be one specified in JIS A 5005:2020 "Crushed Stone and Crushed Sand for Concrete." Examples of fine aggregate include river sand, land sand, sea sand, crushed sand, silica sand, copper slag fine aggregate, and electric furnace oxidizing slag fine aggregate. When using fine aggregate, the amount of fine aggregate used may be, for example, 50 to 500 parts by mass, 100 to 300 parts by mass, or 200 to 250 parts by mass per 100 parts by mass of the hydraulic composition.

[0073] The coarse aggregate may be one specified in JIS A 5005:2020 "Crushed stone and crushed sand for concrete." Examples of coarse aggregate include gravel and crushed stone. When using coarse aggregate, the amount of coarse aggregate used may be, for example, 50 to 500 parts by mass, 100 to 300 parts by mass, or 200 to 250 parts by mass per 100 parts by mass of the hydraulic composition.

[0074] Fine aggregate and coarse aggregate can also be used in combination. In this case, the total amount of the fine aggregate and coarse aggregate used may be 100 to 300 parts by mass, or 200 to 250 parts by mass, per 100 parts by mass of the hydraulic composition.

[0075] The lower limit of the fine aggregate ratio may be, for example, 40% by volume or more, 43% by volume or more, 45% by volume or more, or 47% by volume or more. By setting the lower limit of the fine aggregate ratio within the above range, it is possible to improve the resistance to material separation in fresh concrete. The upper limit of the fine aggregate ratio may be, for example, 56% by volume or less, 54% by volume or less, 52% by volume or less, or 50% by volume or less. By setting the upper limit of the fine aggregate ratio within the above range, it is possible to further improve the fluidity of fresh concrete and further improve the workability in concrete construction.

[0076] The lower limit of the bulk volume of coarse aggregate is, for example, 0.500 m 3 / m 3 Over 0.520m 3 / m 3 More than 0.540m 3 / m3 or more, or 0.560m 3 / m 3 If the lower limit of the bulk volume of the coarse aggregate is within the above range, the fluidity of the fresh concrete can be further improved, and the workability of the concrete construction can be further improved. The upper limit of the bulk volume of the coarse aggregate can be, for example, 0.620 m 3 / m 3 Below, 0.600m 3 / m 3 Below, 0.580m 3 / m 3 Less than or equal to 0.565m 3 / m 3 When the upper limit of the bulk volume of the coarse aggregate is within the above range, the resistance to material separation in fresh concrete can be improved.

[0077] Examples of water-reducing agents include water-reducing agents, air-entraining water-reducing agents, superplasticizers, and superplasticizers. Standard, delayed, and accelerated types of air-entraining water-reducing agents and superplasticizers can all be used, with delayed types being preferred. Type I, II, and III types of air-entraining water-reducing agents and superplasticizers can all be used, with type I being preferred. The water-reducing agent may include a superplasticizer or may be a superplasticizer.

[0078] The content of the water-reducing agent is 0.5 to 3.0% by mass relative to 100% by mass of the hydraulic composition. The lower limit of the content of the water-reducing agent may be, for example, 0.6% by mass or more, 0.7% by mass or more, or 0.8% by mass or more relative to 100% by mass of the hydraulic composition. When the lower limit of the content of the water-reducing agent is within the above range, the fluidity of fresh concrete can be further improved. The upper limit of the content of the water-reducing agent may be, for example, 1.5% by mass or less, 1.2% by mass or less, 1.0% by mass or less, or 0.9% by mass or less relative to 100% by mass of the hydraulic composition. When the upper limit of the content of the water-reducing agent is within the above range, material separation resistance can be imparted without impairing the fluidity of fresh concrete.

[0079] Examples of other admixtures other than the water-reducing agent include air-entraining agents, superplasticizers, antifoaming agents, shrinkage-reducing agents, setting accelerators, setting retarders, thickeners, silica powder, other inorganic powders containing calcium, fly ash, inorganic minerals containing Si and Al, etc. The amount of other admixtures used may be, for example, 0.01 to 2% by mass relative to 100% by mass of the above-mentioned hydraulic composition.

[0080] The above-mentioned concrete composition can provide a hardened concrete body having excellent compressive strength by hardening. There is no difference in composition between the concrete composition and the hardened concrete body. That is, the present disclosure provides a hardened concrete body comprising a hydraulic composition, water, a water-reducing agent, fine aggregate, and coarse aggregate, the hydraulic composition comprising cement containing an alkali activator and granulated blast furnace slag, and an accelerator, the content of the granulated blast furnace slag being 40.0 to 95.0 mass% based on the total amount of the cement, the content of gypsum in the cement being 0.05 to 1.70 mass% in terms of SO3, the content of the accelerator being 0.2 to 10.0 mass parts relative to 100 mass parts of the cement, and the content of the hydraulic composition being 250 to 600 kg / m 3 It can be said that the present invention provides a hardened concrete body in which the content of the water relative to the content of the hydraulic composition is 0.25 to 0.60, and the content of the water-reducing agent is 0.5 to 3.0 mass% based on 100 mass% of the hydraulic composition.

[0081] [Method of manufacturing concrete composition] The above-mentioned concrete composition can be produced, for example, by the following method. One embodiment of the method for producing a concrete composition includes a kneading step (kneading step) in which a water-reducing agent and water are mixed with a mixture containing the above-mentioned hydraulic composition, fine aggregate, and coarse aggregate. In the kneading step, water, a water-reducing agent, fine aggregate, and coarse aggregate are mixed with the hydraulic composition in an amount of 250 to 600 kg / m 3The amount of water to be blended relative to the amount of the hydraulic composition is 0.25 to 0.60, and the content of the water-reducing agent is 0.5 to 3.0% by mass based on 100% by mass of the hydraulic composition.

[0082] In the method for producing a concrete composition, the hydraulic composition described above may be prepared in advance, or a hydraulic composition may be prepared by the following method. That is, the method for producing a concrete composition may further include a first step of preparing cement by mixing raw materials including an alkali activator and granulated blast furnace slag so that the blending amount of the granulated blast furnace slag is 40.0 to 95.0 mass%, and a second step of mixing 0.2 to 10.0 mass parts of an accelerator per 100 mass parts of the cement. The first step includes adjusting the content of gypsum in the cement to 0.05 to 1.70 mass% in terms of SO3.

[0083] The raw materials in the first step may be a mixture of an alkaline activator and granulated blast furnace slag, and may also contain gypsum.

[0084] In the first step, each component constituting the raw material may be crushed. When crushing is performed in the first step, the order of mixing and crushing is not particularly limited. That is, the various components may be mixed and then crushed, or the various components may be crushed and then mixed, or the various components may be mixed and crushed simultaneously. The mixing of the various components in the first step may be performed using a mixer such as a pan mixer, a tilting mixer, or a ribbon mixer, or may be mixed and crushed using a crusher such as a ball mill, a vertical roller mill, or a roller press, or the various components may be crushed individually and then mixed using a mixer such as a mechanical mixer.

[0085] In the first step, the gypsum content in the cement is adjusted to 0.05 to 1.70 mass% in terms of SO3. This adjustment makes it possible to prevent gypsum from inhibiting the hardening-accelerating action of the accelerator in the concrete composition.

[0086] The gypsum content in the first step may be adjusted so that the content of the granulated blast furnace slag and the content of the gypsum satisfy the relationship of the following general formula (X). In the following general formula (X), the content of gypsum is the content of gypsum in the cement [unit: mass%], expressed as an SO3 equivalent value. In the following general formula (X), the content of the granulated blast furnace slag is the content [unit: mass%] based on the total amount of cement. In the following general formula (X), A is a constant, which may be, for example, 1.5 or less. When the content of the granulated blast furnace slag and the content of the gypsum satisfy the relationship of general formula (X) in which the constant A is a smaller value, the effects of the present disclosure can be more pronounced. For example, the constant A may be 1.5, 1.0, 0.8, or 0.6. For reference, the formula when the constant A is 1.5 is shown below (see formula (1)). [Gypsum content]≦A-2.0([granulated blast furnace slag content]-60) / 100...General formula (X) [Gypsum content]≦1.5−2.0([granulated blast furnace slag content]−60) / 100…Equation (1)

[0087] In the second step, cement and an accelerator are mixed. The mixing method may be the same as or different from that in the first step. Other components may be blended in the second step or in a step other than the first and second steps. Examples of other components include silica powder, other calcium-containing inorganic powders, fly ash, and inorganic minerals containing Si and Al.

[0088] [Method for increasing the compressive strength of concrete compositions] By applying the above-mentioned findings, it is possible to provide a method for increasing the compressive strength of a composition containing a high mixing ratio of granulated blast furnace slag or the like. A concrete composition obtained by applying this method can exhibit excellent compressive strength both in the early stages and over the long term. One embodiment of the method for increasing the compressive strength of a concrete composition includes: a composition containing an alkali activator and granulated blast furnace slag, the cement containing 40.0 to 95.0 mass% of the granulated blast furnace slag; measuring the gypsum content in the cement and adjusting the gypsum content in the cement to 0.05 to 1.70 mass% in terms of SO3; measuring the accelerator content in the composition and adjusting the accelerator content to 0.2 to 10.0 mass parts per 100 mass parts of the cement; and adjusting water, a water-reducing agent, fine aggregate, and coarse aggregate to the composition in a blending amount of 250 to 600 kg / m 3 The amount of water to be blended relative to the amount of the composition is 0.25 to 0.60, and the content of the water-reducing agent is 0.5 to 3.0 mass% based on 100 mass% of the composition.

[0089] Since the content of the accelerator is adjusted in the method for increasing compressive strength, the composition may or may not contain an accelerator.

[0090] Although several embodiments have been described above, the present disclosure is not limited to the above embodiments. Furthermore, the descriptions of the above embodiments can be applied to each other. [Example]

[0091] The present disclosure will be described in more detail below with reference to examples, comparative examples, and reference examples, although the present disclosure is not limited to the following examples.

[0092] [Raw materials for concrete composition] The following materials were used as raw materials for the concrete composition.

[0093] (cement) Alkaline stimulant Ordinary Portland cement, which is commonly used, was used as the component containing cement clinker, an alkali activator. In Table 1, ordinary Portland cement is abbreviated as OPC. The chemical composition of ordinary Portland cement was measured in accordance with JIS R 5202:2015 "Methods for Chemical Analysis of Cement." The results are shown in Table 1.

[0094] Granulated blast furnace slag Granulated blast furnace slag was produced at the same facility. Slag A was the slag without gypsum added, while Slag B was the slag with gypsum added. Furthermore, Slag C was the slag with a lower basicity than typical slags such as Slag A and Slag B, but without gypsum added. The chemical composition of each slag was measured in accordance with JIS R 5202:2015, "Methods for Chemical Analysis of Cement." The results are shown in Table 1. The loss on ignition (also abbreviated as ig.loss) in Table 1 was measured at a heating temperature of 700°C in accordance with the method described in "5.2 For Materials Other Than Blast Furnace Cement and Blast Furnace Slag" in "5. Methods for Determination of Ignition Loss" of JIS R 5202:2010.

[0095] (blast furnace cement) In the Reference Examples described below, commonly used blast-furnace cement Type B was used instead of the hydraulic composition. In Table 1, blast-furnace cement Type B is abbreviated as BB. The chemical composition of the blast-furnace cement was measured in accordance with the description in JIS R 5202:2015 "Methods for chemical analysis of cement." The results are shown in Table 1.

[0096] [Table 1]

[0097] (accelerator) As the accelerator, an inorganic accelerator was used. Accelerator A: Calcium nitrite monohydrate (powder) manufactured by Kishida Chemical Co., Ltd. was used. Accelerator B: A liquid accelerator containing nitrous acid and nitrate, which is a commercially available concrete hardening accelerator conforming to JIS A 6204:2011 "Chemical admixtures for concrete," was used. Accelerator C: A liquid accelerator containing nitrates was used, which is a commercially available concrete hardening accelerator conforming to JIS A 6204:2011 "Chemical admixtures for concrete."

[0098] (admixture) A water reducing agent and an air entraining agent were used as admixtures. Water-reducing agent: "MasterEase 8050" (product name, main ingredient: polycarboxylic acid ether compound) manufactured by Pozzolith Solutions Co., Ltd. was used, which complies with the JIS A 6204:2011 "Chemical admixtures for concrete" high-performance AE water-reducing agent delayed type (Type I). Air-entraining agent: "Master Air 303A" (product name, main ingredient: alkyl ether-based anionic surfactant) manufactured by Pozzolith Solutions Co., Ltd., which complies with JIS A 6204:2011 "Chemical admixtures for concrete," was used.

[0099] (fine aggregate) The fine aggregate used was sea sand (surface dry density: 2.57 g / m 3 ) and crushed sand (surface dry density: 2.66 g / m 3 ) were mixed in a volume ratio of 1:1.

[0100] (coarse aggregate) The coarse aggregate used was "Crushed Stone 2005" (product name, surface dry density: 2.70 g / m) manufactured by Yokokawa Crushed Stone Co., Ltd. 3 ) was used.

[0101] [Mixture of hydraulic composition, water, fine aggregate, and coarse aggregate in concrete composition] The formulations of the hydraulic composition, water, fine aggregate, and coarse aggregate used to prepare a concrete composition containing the hydraulic composition, water, a water-reducing agent, fine aggregate, and coarse aggregate are shown in Table 2. In addition to the formulations of each component, Table 2 also lists the water-cement ratio (value expressed as unit amount of water / unit amount of hydraulic composition), fine aggregate rate (value expressed as unit volume of fine aggregate / unit volume of total aggregate), and coarse aggregate bulk volume. Note that the reference example is an example in which blast furnace cement was used instead of the hydraulic composition according to the present disclosure.

[0102] [Table 2]

[0103] [Composition of concrete composition] The compositions of the alkali activator, granulated blast furnace slag, accelerator, and admixture in the concrete compositions prepared in Examples 1 to 4, Comparative Examples 1 to 6, and Reference Example are shown in Table 3. Table 3 also lists the air content in fresh concrete, which will be described later.

[0104] The concrete compositions of Examples 1 to 3 and Comparative Example 1 use slag A, which does not contain gypsum, and have a gypsum-equivalent SO3 equivalent of 0.59% by mass. However, because the blast furnace slag is mixed in at 70 parts by mass, they can be considered to be compositions equivalent to blast furnace cement Class C. The concrete compositions of Comparative Examples 2 to 5 use slag B, which contains gypsum, and have a gypsum-equivalent SO3 equivalent of 1.94% by mass. However, because the blast furnace slag is mixed in at 70 parts by mass, they can be considered to be compositions equivalent to blast furnace cement Class C. Furthermore, the concrete compositions of Example 4 and Comparative Example 6 use slag C, which contains gypsum, and have a gypsum-equivalent SO3 equivalent of 0.67% by mass. However, because the blast furnace slag is mixed in at 70 parts by mass, they can be considered to be compositions equivalent to blast furnace cement Class C.

[0105] Comparative Examples 2 to 5 were designed in accordance with conventional technical common sense, increasing the amount of gypsum to improve the compressive strength obtained by hardening the concrete composition.Comparative Examples 3 to 5 were designed to further improve the compressive strength obtained by hardening the concrete composition by blending an accelerator.

[0106] [Table 3]

[0107] [Evaluation of concrete composition: Compressive strength test] For each of the concrete compositions prepared in Examples 1 to 4, Comparative Examples 1 to 6, and Reference Example, the compressive strength was measured, the compressive strength ratio was determined, and an evaluation was performed according to the methods described below. The results are shown in Table 4.

[0108] First, the hydraulic composition, fine aggregate, and coarse aggregate were placed in a horizontal biaxial forced mixer to obtain the proportions shown in Tables 2 and 3. The mixture was dry-mixed for 30 seconds, followed by the addition of water and admixtures. The mixture was then mixed for 120 seconds and allowed to stand for 5 minutes to prepare fresh concrete. The concrete compositions were mixed in a constant-temperature, constant-humidity chamber maintained at 20±2°C and 60±5% relative humidity. The air content of the resulting fresh concrete was measured. The results are shown in Table 3. The air content was measured according to the method specified in JIS A 1128, "Test Method for Air Content of Concrete by Pressure—Air Chamber Pressure Method." For all concrete compositions, the air content was well within the range of 4.5±1.0%, confirming that the resulting hardened concrete could be expected to be sufficiently inhibited from deterioration due to the freezing and thawing action of water (i.e., it is possible to provide hardened concrete with excellent resistance to freezing and thawing).

[0109] The fresh concrete obtained as described above was packed into a cylindrical formwork with an inner diameter of 10 cm and a height of 20 cm, stored in a constant temperature and humidity room at a temperature of 20±2°C and a relative humidity of 60±5%, and demolded after one day. The concrete was then submerged in a water tank at a temperature of 20±2°C until the specified age (7 days or 28 days) was reached, yielding a hardened concrete body. The resulting hardened concrete body was used as a test specimen to measure its compressive strength. The compressive strength measurement was performed in accordance with the method described in JIS A 1108:2018, "Testing Method for Compressive Strength of Concrete." Based on the measured compressive strength values, a compressive strength ratio was calculated relative to the result of Reference Example 1, which was defined as 1. Evaluation was performed based on the calculated compressive strength ratio according to the following criteria. <Evaluation criteria for compressive strength ratio> A: The compressive strength ratio at 7 days of age is 1.00 or more, and the compressive strength ratio at 28 days of age is 1.00 or more. B: The compressive strength ratio at 7 days is 1.00 or more, and the compressive strength ratio at 28 days is 0.95 or more and less than 1.00. C: The compressive strength ratio at 7 days is 0.90 or more and less than 1.00, and the compressive strength ratio at 28 days is 1.00 or more. D: The compressive strength ratio at 7 days is 0.90 or more and less than 1.00, and the compressive strength ratio at 28 days is 0.95 or more and less than 1.00. E: The compressive strength ratio at 7 days is less than 0.90, or the compressive strength ratio at 28 days is less than 0.95.

[0110] [Table 4]

[0111] As shown in Table 4, the concrete compositions of Examples 1 to 3, which used slag A as the granulated blast furnace slag, exhibited superior compressive strength compared to the concrete composition of Comparative Example 1, which did not contain an accelerator. The concrete composition of Example 4, which used slag C, which had a lower basicity than slag A, as the granulated blast furnace slag, also exhibited superior compressive strength compared to the concrete composition of Comparative Example 6, which did not contain an accelerator. Furthermore, the concrete compositions of Examples 1 to 3 were confirmed to exhibit compressive strengths equal to or greater than those of the concrete composition of the Reference Example, which simulated blast-furnace cement type B, which is considered to have superior compressive strength. Furthermore, the results of the concrete compositions of Comparative Examples 2 to 5, which used slag B, which contained gypsum as the granulated blast furnace slag, confirmed that their compressive strengths were inferior to those of the concrete compositions of Examples 1 to 3, regardless of whether an accelerator was used.

[0112] [Evaluation of concrete composition: slump test] A slump test was conducted for each of the concrete compositions prepared in Examples 1 to 4 and Comparative Examples 1 to 6 according to the method described below. First, fresh concrete was prepared in the same manner as described in the above section [Evaluation of Concrete Composition: Compressive Strength Test]. A slump test was conducted for the obtained fresh concrete. The slump test was conducted in accordance with the method described in JIS A 1101 "Method for Slump Test of Concrete." The results are shown in Tables 5 and 6. Table 5 shows the relationship between the time elapsed after mixing and the slump. Table 6 shows the relationship between the time elapsed after mixing and the slump residual rate, with the slump immediately after mixing as the reference.

[0113] [Table 5]

[0114] [Table 6]

[0115] As shown in Table 6, it was confirmed that the concrete compositions of Examples 1 to 3 and Comparative Example 1, which have a low content of gypsum equivalent, have a superior slump residual rate and workability during concrete construction compared to the concrete compositions of Comparative Examples 2 to 5, which have a higher content of gypsum equivalent. [Industrial Applicability]

[0116] According to the present disclosure, it is possible to provide a concrete composition having a relatively high mixing ratio of granulated blast furnace slag, which has sufficient fluidity for concrete construction and can exhibit excellent compressive strength both at an early stage and over the long term. According to the present disclosure, it is also possible to provide a method for increasing the compressive strength of a concrete composition having a relatively high mixing ratio of granulated blast furnace slag both at an early stage and over the long term.

Claims

1. A concrete composition comprising a hydraulic composition, water, a water-reducing agent, fine aggregate, and coarse aggregate, The hydraulic composition contains cement containing an alkali activator and granulated blast furnace slag, and an accelerator, The content of the granulated blast furnace slag is 40.0 to 95.0 mass% based on the total amount of the cement, and the content of gypsum in the cement is 0.0 to 0.5 mass%. ３ The content of the accelerator is 0.2 to 10.0 parts by mass relative to 100 parts by mass of the cement, The content of the hydraulic composition is 250 to 600 kg / m ３ and the content of the water relative to the content of the hydraulic composition is 0.25 to 0.60; The content of the water-reducing agent is 0.5 to 3.0% by mass based on 100% by mass of the hydraulic composition; In the granulated blast furnace slag, the aluminum oxide content is 8 to 14.5% by mass, the silicon dioxide content is 30.0 to 40.0% by mass, the calcium oxide content is 35.0 to 45.0% by mass, and the magnesium oxide content is 4.0 to 10.0% by mass; The basicity of the granulated blast furnace slag is 1.55 to 1.95, The accelerator contains a salt having a monovalent anion. Concrete composition.

2. A concrete composition comprising a hydraulic composition, water, a water-reducing agent, fine aggregate, and coarse aggregate, The hydraulic composition contains cement containing an alkali activator and granulated blast furnace slag, and an accelerator, The content of the granulated blast furnace slag is 40.0 to 95.0 mass% based on the total amount of the cement, and the content of gypsum in the cement is 0.0 to 0.5 mass%. ３ The content of the accelerator is 0.2 to 10.0 parts by mass relative to 100 parts by mass of the cement, The content of the hydraulic composition is 250 to 600 kg / m ３ and the content of the water relative to the content of the hydraulic composition is 0.25 to 0.60; The content of the water-reducing agent is 0.5 to 3.0% by mass based on 100% by mass of the hydraulic composition; In the granulated blast furnace slag, the aluminum oxide content is 8 to 14.5% by mass, the silicon dioxide content is 30.0 to 40.0% by mass, the calcium oxide content is 35.0 to 45.0% by mass, and the magnesium oxide content is 4.0 to 10.0% by mass; The basicity of the granulated blast furnace slag is 1.55 to 1.95, The accelerator contains at least one selected from the group consisting of nitrites, nitrates, and chlorides. Concrete composition.

3. The concrete composition according to claim 1 or 2, wherein the water reducing agent comprises a high-range air-entraining water reducing agent.

4. The content of the granulated blast furnace slag and the content of the gypsum satisfy the relationship of the following formula (1): [Gypsum content]≦1.5−2.0([granulated blast furnace slag content]−60) / 100...Equation (1) The concrete composition according to any one of claims 1 to 3.

5. The concrete composition according to any one of claims 1 to 4, wherein the accelerator contains at least one selected from the group consisting of alkali metal salts and alkaline earth metal salts.

6. The concrete composition according to any one of claims 1 to 5, wherein the accelerator contains a calcium salt.

7. The concrete composition according to any one of claims 1 to 6, wherein the alkali stimulant contains at least one selected from the group consisting of Portland cement clinker, slaked lime, and quicklime.

8. The concrete composition according to any one of claims 1 to 7, wherein the gypsum contains at least one selected from the group consisting of gypsum dihydrate and gypsum hemihydrate.

9. The concrete composition according to any one of claims 1 to 8, wherein the granulated blast furnace slag has a basicity of less than 1.

75.

10. The concrete composition according to any one of claims 1 to 8, wherein the basicity of the granulated blast furnace slag is 1.75 to 1.

95.

11. The concrete composition according to any one of claims 1 to 10, wherein the content of the granulated blast furnace slag is 60.0 to 95.0 mass% based on the total amount of the cement.

12. For a composition containing an alkali stimulant and granulated blast furnace slag, wherein the content of the granulated blast furnace slag is 40.0 to 95.0 mass %, the content of gypsum in the cement is measured, and the content of gypsum in the cement is measured by SO ３ In terms of the total mass, adjust the content to 0.05 to 1.70 mass%. measuring the content of the accelerator in the composition and adjusting the content of the accelerator to 0.2 to 10.0 parts by mass per 100 parts by mass of the cement; and The composition is mixed with water, a water-reducing agent, fine aggregate, and coarse aggregate in an amount of 250 to 600 kg / m ３ The amount of water to be blended relative to the amount of the composition is 0.25 to 0.60, and the content of the water-reducing agent is 0.5 to 3.0% by mass based on 100% by mass of the composition. Including, In the granulated blast furnace slag, the aluminum oxide content is 8 to 14.5% by mass, the silicon dioxide content is 30.0 to 40.0% by mass, the calcium oxide content is 35.0 to 45.0% by mass, and the magnesium oxide content is 4.0 to 10.0% by mass; The basicity of the granulated blast furnace slag is 1.55 to 1.95, 10. A method for enhancing the compressive strength of a concrete composition, wherein the accelerator comprises a salt having a monovalent anion.

13. For a composition containing an alkali stimulant and granulated blast furnace slag, wherein the content of the granulated blast furnace slag is 40.0 to 95.0 mass %, the content of gypsum in the cement is measured, and the content of gypsum in the cement is measured by SO ３ In terms of the total mass, adjust the content to 0.05 to 1.70 mass%. measuring the content of the accelerator in the composition and adjusting the content of the accelerator to 0.2 to 10.0 parts by mass per 100 parts by mass of the cement; and The composition is mixed with water, a water-reducing agent, fine aggregate, and coarse aggregate in an amount of 250 to 600 kg / m ３ The amount of water to be blended relative to the amount of the composition is 0.25 to 0.60, and the content of the water-reducing agent is 0.5 to 3.0% by mass based on 100% by mass of the composition. Including, In the granulated blast furnace slag, the aluminum oxide content is 8 to 14.5% by mass, the silicon dioxide content is 30.0 to 40.0% by mass, the calcium oxide content is 35.0 to 45.0% by mass, and the magnesium oxide content is 4.0 to 10.0% by mass; The basicity of the granulated blast furnace slag is 1.55 to 1.95, A method for increasing the compressive strength of a concrete composition, wherein the accelerator contains at least one selected from the group consisting of nitrites, nitrates, and chlorides.

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