Cement admixture, cement composition, and hardened concrete

Abstract

To provide a cement admixture that yields a concrete suppressing the permeability of carbon dioxide and chloride ion, and having long-term durability in an environment where neutralization and salt damage act in combination.SOLUTION: Provided is a cement admixture that contains: one kind of, or two or more kinds of non-hydraulic compounds selected from a group consisting of γ-2CaO-SiO2, 3CaO-2SiO2, α-CaO-SiO2, and calcium magnesium silicate; and calcium aluminate having a CaO / Al2O3 molar ratio of 0.15 to 0.7.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a cement admixture, a cement composition, and a hardened concrete body.

Background Art

[0002] In recent years, in the fields of civil engineering and architecture, there has been an increasing demand for improving the durability of concrete structures. Examples of deterioration factors of concrete structures include deterioration such as carbonation and salt damage. Carbonation is a phenomenon in which concrete is carbonated by the action of carbon dioxide in the air, inducing corrosion of steel bars. Salt damage is a general term for deterioration caused by corrosion of steel bars due to chloride ions.

[0003] Carbonation is a phenomenon in which calcium hydroxide reacts with carbon dioxide in the air to form calcium carbonate, thereby reducing the pH of the pore solution in the concrete, destroying the passive film on the surface of the steel bars inside the concrete, and making it prone to corrosion. Therefore, it is said that concrete with a large amount of calcium hydroxide generated is less affected.

[0004] On the other hand, salt damage mainly occurs in concrete structures near the coast. Chloride ions derived from flying salts and the like penetrate from the surface into the interior of the concrete, causing corrosion of the steel bars. As a result, deterioration such as a decrease in the bearing capacity of the structure and peeling of concrete pieces occurs. In order to obtain concrete that is less affected by salt damage, it is effective to mix latent hydraulic substances such as blast furnace slag and fly ash to consume the easily eluted calcium hydroxide generated from the hydration of cement and make the concrete dense to improve chloride ion permeability.

[0005] Therefore, carbonation is more likely to be affected as the amount of calcium hydroxide generated is less, while salt damage is more likely to be affected as the amount of calcium hydroxide in the concrete is more. Therefore, imparting carbonation resistance and salt damage resistance has conventionally been a conflicting technology (see Non-Patent Document 1).

[0006] As a neutralization inhibition method, there is a known technique of obtaining highly durable concrete with a densified surface layer from CO2 absorption by forcibly carbonating and curing concrete containing a non-hydraulic compound such as γ-C2S (γ-2CaO·SiO2; also called the γ-phase of belite) as a blending material (for example, Patent Document 1). γ-C2S does not undergo a hydration reaction and reacts with CO2 to form a gel rich in CaCO3 and SiO2. These products fill the voids in the cement matrix, significantly improving the durability of the concrete surface layer.

[0007] As a chloride damage inhibition method, for the purpose of imparting early strength to cement concrete and preventing the corrosion of steel bars, a method using a cement admixture mainly composed of CaO·2Al2O3 and gypsum and containing fine powder with a Blaine specific surface area value of 8000 cm 2 / g has been proposed (see Patent Document 2). Furthermore, a method using a cement admixture containing calcium aluminate with a CaO / Al2O3 molar ratio of 0.3 to 0.7 and a Blaine specific surface area value of 2000 to 7000 cm 2 / g, which has excellent chloride ion penetration resistance and suppresses thermal cracking of mass concrete, has been proposed (see Patent Document 3). Also, a cement admixture containing a calcium ferroaluminate compound with a CaO / A12O3 molar ratio of 0.15 to 0.7 and an Fe2O3 content of 0.5 to 15% by mass has been proposed (see Patent Document 4).

Prior Art Documents

Non-Patent Documents

[0008]

Non-Patent Document 1

Patent Documents

[0009]

Patent Document 1

[0010] As described above, when producing mortar and concrete using conventional cement and pozzolanic substances, it is difficult to achieve both improved carbonation resistance and chloride attack resistance, and it has been difficult to obtain concrete having long-term durability in an environment where carbonation and chloride attack act in combination. Under such circumstances, an object of the present invention is to provide a cement admixture that suppresses the permeability of carbon dioxide and chloride ions and obtains concrete having long-term durability in an environment where carbonation and chloride attack act in combination. [Means for Solving the Problems]

[0011] The inventors of the present invention conducted intensive research to solve the above problems, and as a result, found that by using a non-hydraulic compound such as γ-C2S and a calcium aluminate having a specific CaO / Al2O3 molar ratio, a cement admixture suitable for achieving both carbonation resistance and chloride attack resistance can be obtained, and thus completed the present invention. That is, the present invention is as follows. [1] A cement admixture containing one or more non-hydraulic compounds selected from the group consisting of γ-2CaO·SiO2, 3CaO·2SiO2, α-CaO·SiO2, and calcium magnesium silicate, and a calcium aluminate having a CaO / Al2O3 molar ratio of 0.15 to 0.7. [2] The cement admixture according to [1] above, wherein Li is contained in the non-hydraulic compound, and the content of Li in the non-hydraulic compound is 0.001 to 1.0% by mass in terms of oxide conversion. [3] The cement admixture according to [1] or [2] above, wherein the amount of the non-hydraulic compound contained in the cement admixture is 65% by mass or more. [4] The cement admixture according to any one of [1] to [3] above, wherein the amount of the calcium aluminate contained in the cement admixture is 5% by mass or more. [5] A cement composition comprising the cement admixture according to any one of [1] to [4] above. [6] A cement composition wherein the content of the cement admixture according to any one of [1] to [4] above is 20 to 50% by mass. [7] A hardened concrete body containing the cement admixture according to any one of [1] to [4] above. [8] A hardened concrete body containing the cement composition according to [5] or [6] above.

Advantages of the Invention

[0012] By using the cement admixture of the present invention, effects such as being able to obtain a cement composition imparting carbonation resistance and chloride ion penetration resistance can be achieved. Therefore, the present invention is suitable for cement concrete materials used in the civil engineering and construction industries, particularly in environments susceptible to salt damage and / or carbonation.

Embodiments for Carrying Out the Invention

[0013] Hereinafter, the present invention will be described in detail. Parts and % used in the present invention are based on mass unless otherwise specified.

[0014] <Cement Admixture> The cement admixture of the present invention contains one or more non-hydraulic compounds selected from the group consisting of γ-2CaO·SiO2, 3CaO·2SiO2, α-CaO·SiO2, and calcium magnesium silicate, and calcium aluminate having a CaO / Al2O3 molar ratio of 0.15 to 0.7. As shown in Experimental Examples 1 to 3 below, the mortar containing this cement admixture has a relatively small carbonation depth and a relatively small chloride ion penetration depth, so that the permeability of carbon dioxide can be suppressed and the permeability of chloride ions can be suppressed.

[0015] <Non-hydraulic compound> [γ-2CaO·SiO2] γ-2CaO·SiO2 is a compound represented by 2CaO·SiO2 and is known as a low-temperature phase, which is completely different from the high-temperature phases α-2CaO·SiO2, α’-2CaO·SiO2, and β-2CaO·SiO2. Although all of these are represented by 2CaO·SiO2, their crystal structures and densities are different.

[0016] [3CaO·2SiO2] 3CaO·2SiO2 is a mineral containing CaO in pseudowollastonite and is called rankinite. It is a mineral that is chemically stable without hydration activity but has a relatively high reactivity with carbon dioxide.

[0017] [α-CaO·SiO2] α-CaO·SiO2 (α-type wollastonite) is a compound represented by CaO·SiO2 and is known as a high-temperature phase, which is completely different from the low-temperature phase β-CaO·SiO2. Although all of these are represented by CaO·SiO2, their crystal structures and densities are different.

[0018] [Calcium magnesium silicate] Calcium magnesium silicate is a general term for CaO-MgO-SiO2-based compounds. In this embodiment, it is preferably Merwinite represented by 3CaO·MgO·2SiO2 (C3MS2). Merwinite has a relatively high reactivity with carbon dioxide.

[0019] The cement admixture according to this embodiment preferably contains Li in a non-hydraulic compound. Also, its content is preferably 0.001 to 1.0% by mass in terms of oxide conversion. It is presumed that this predetermined amount of Li promotes the formation of vaterite, which is a type of calcium carbonate, among the carbonations of C-S-H (calcium silicate hydrate), and it is considered that a denser hardened state is more likely to be obtained by carbonation curing. From the viewpoint of being able to suppress the permeability of carbon dioxide and the permeability of chloride ions, the Li content in the non-hydraulic compound is more preferably 0.05 to 1.0% by mass in terms of oxide conversion. Here, "containing Li in a non-hydraulic compound" means a state in which Li2O is included as a chemical composition in the non-hydraulic compound (its presence can be confirmed by ICP emission spectrometry), but Li2O is not identified by X-ray diffraction measurement (no distinct peak of Li2O is observed), and it does not simply mean a state where the non-hydraulic compound and the Li compound are physically mixed. Such a state can be obtained by mixing the respective raw materials and performing heat treatment at a high temperature of 1,000 °C or higher.

[0020] The amount of the non-hydraulic compound contained in the cement admixture is preferably 65% by mass or more. When the amount of the non-hydraulic compound contained in the cement admixture is 65% by mass or more, the reactivity of the non-hydraulic compound with carbon dioxide increases, the reaction of carbon dioxide with calcium hydroxide is suppressed, and the neutralization of the hardened body is suppressed. From the viewpoint of being able to suppress the permeability of carbon dioxide and the permeability of chloride ions, the amount of the non-hydraulic compound contained in the cement admixture is more preferably 75% by mass or more.

[0021] <Calcium aluminate> Calcium aluminate is a general term for compounds mainly composed of CaO and Al₂O₃, which are obtained by mixing raw materials containing calcia and raw materials containing alumina, etc., and performing heat treatment such as firing in a kiln or melting in an electric furnace. The calcium aluminate according to the present invention is characterized in that the CaO / Al₂O₃ molar ratio is in the range of 0.15 to 0.7. When the CaO / Al₂O₃ molar ratio is less than 0.15, the progress of the hydration reaction is slow, and excellent chloride resistance cannot be obtained in a short curing period. On the other hand, when the CaO / Al₂O₃ molar ratio exceeds 0.7, the heat generation due to the hydration reaction becomes fast, and a sufficient workable time cannot be ensured. From the above viewpoints, the CaO / Al₂O₃ molar ratio is preferably in the range of 0.3 to 0.7, and more preferably in the range of 0.4 to 0.6. The amount of calcium aluminate contained in the cement admixture is preferably 5% by mass or more. When the amount of calcium aluminate contained in the cement admixture is 5% by mass or more, the hydrocalumite generated by the hydration of calcium aluminate increases, the fixation of chloride ions is promoted, and the penetration of chloride ions into the hardened body is suppressed. From the viewpoint of being able to suppress the permeability of carbon dioxide and the permeability of chloride ions, the amount of calcium aluminate contained in the cement admixture is more preferably 15% by mass or more and 40% by mass or less.

[0022] The calcium aluminate according to the present invention preferably has a Blaine specific surface area value in the range of 2000 to 6000 cm 2 / g. When the Blaine specific surface area value of calcium aluminate is 2000 cm 2 / g or more, the chloride resistance can be sufficiently exhibited. On the other hand, when the Blaine specific surface area value of calcium aluminate is 6000 cm 2 / g or less, the control of heat generation due to the hydration reaction is easy. In addition, even if the Blaine specific surface area value exceeds 6000 cm 2 / g, no further improvement in chloride resistance can be expected. From the above viewpoints, the Blaine specific surface area value of calcium aluminate is preferably 2500 to 5000 cm 2 / g, and 3000 to 4000 cm2 / g is more preferable.

[0023] The calcium aluminate according to the cement admixture of the present invention may contain impurities in addition to CaO and Al2O3. Examples of the impurities include SiO2, Fe2O3, TiO2, K2O, Na2O, B2O and the like. The presence of these impurities may have an effect of promoting the formation reaction when firing calcium aluminate, and there are also preferable aspects, so they may be present in a range of 10% by mass or less in total of the calcium aluminate.

[0024] In addition to the calcium aluminate of the present invention, one or more of admixture materials such as limestone fine powder, blast furnace slag fine powder, metakaolin, sewage sludge incineration ash and its molten slag, municipal waste incineration ash and its molten slag, pulp sludge incineration ash, thickeners, shrinkage reducing agents, polymers, setting regulators, clay minerals such as bentonite, etc. can be used in combination within a range that does not substantially inhibit the object of the present invention.

[0025] [Cement composition] The cement composition of the present invention contains the cement admixture of the present invention and cement. The cement admixture of the present invention can be used for any concrete hardened body. The content of the cement admixture contained in the cement composition is preferably 20 to 50% by mass. When the content of the cement admixture contained in the cement composition is 20% by mass or more, the hydrocalumite generated by the hydration with calcium aluminate effective for salt damage resistance increases, and the penetration of chloride ions is suppressed. When it exceeds 50% by mass, the calcium hydroxide consumed by the hydration of calcium aluminate decreases, and the pH in the hardened body relatively decreases, so the potential resistance to carbonation resistance decreases, and the appropriate mixing amount of the cement admixture is out of range. From the viewpoint of being able to suppress the permeability of carbon dioxide and the permeability of chloride ions, the content of the cement admixture contained in the cement composition is more preferably 20 to 30% by mass.

[0026] The hardened concrete of the present invention contains the cement admixture of the present invention and cement, or the cement composition of the present invention. As the cement used for the hardened concrete, various Portland cements such as ordinary, early-strength, ultra-early-strength, low-heat, medium-heat, and sulfate-resistant Portland cements are commonly used. These Portland cements are mixed with blast furnace slag, fly ash, silica, or fine limestone powder to form various blended cements. In addition, waste utilization type cements, so-called eco-cements, etc. can be mentioned. Among them, it has good compatibility with ordinary Portland cement or early-strength Portland cement.

[0027] The cement admixture and cement composition of the present invention may be mixed immediately before construction for each material, or a part or all of them may be mixed in advance. As the mixing device, any existing device can be used. For example, a mortar mixer, a tilting drum mixer, an omnimixer, a V-type mixer, a Henschel mixer, a forced double-shaft mixer, and a Nauta mixer can be used.

[0028] The cement composition of the present invention, in addition to cement, cement admixture, fine aggregates such as sand, and coarse aggregates such as gravel, may contain one or more of the following: an expansive agent, a rapid hardening agent, a water reducing agent, an AE water reducing agent, a high-performance water reducing agent, a high-performance AE water reducing agent, an antifoaming agent, a thickening agent, a conventional rust inhibitor, an antifreeze agent, a shrinkage reducing agent, a polymer emulsion, a setting regulator, clay minerals such as bentonite, anion exchangers such as hydrotalcite, slag such as blast furnace slowly cooled slag fine powder, and admixture materials such as fine limestone powder, as long as the purpose of the present invention is not substantially hindered.

Examples

[0029] The present invention will be described more specifically with reference to the following examples, but the present invention is not limited to these examples.

[0030] <Experimental Example 1> Mortar with a water / cement ratio of 50% and a ratio of cement to aggregate (sand) of 1 to 2 (by mass) was prepared, and the admixture was replaced with aggregate at the ratio shown in Table 1 per 100 parts by mass of cement. As shown below, specimens were prepared from the prepared mortar, and the carbonation depth and chloride ion penetration depth of the treated specimens were measured. The content (mass %) of the cement admixture shown in Table 1 was taken as the amount (parts by mass) of the cement admixture relative to the total amount of the amount (parts by mass) of the cement admixture and the amount (parts by mass) of cement.

[0031] [Materials Used] · The cement was a commercially available ordinary Portland cement (denoted as "OC" in Tables 1 to 4), with a Blaine specific surface area of 3200 cm 2 / g and a specific gravity of 3.15 g / cm 3 and was used. · γ-C2S: A prototype product. Li-containing γ-2CaO·SiO2 (denoted as "γ" in Tables 1 to 4). Reagent-grade calcium carbonate and reagent-grade silicon dioxide were mixed at a molar ratio of 2:1, and further reagent-grade lithium carbonate was mixed so that the Li content in the mixture was 0.1 part by mass (internal substitution) in terms of oxide (Li2O). Next, the mixed sample was heat-treated at 1400 °C for 2 hours and then allowed to cool to room temperature. Then, the cooled sample was pulverized so that the Blaine specific surface area became 4000 cm 2 / g. Note that the amount of Li2O contained in Li-containing γ-2CaO·SiO2 was 0.1 mass%. · Calcium aluminate: Reagent-grade calcium carbonate and aluminum oxide were mixed at a predetermined ratio. Next, the mixed sample was melted in an electric furnace at 1500 °C and then slowly cooled to synthesize calcium aluminate (denoted as "CA" in Tables 1 to 4). Then, the synthesized sample was pulverized so that the Blaine specific surface area value became 3000 cm 2 / g. Note that the CaO / Al2O3 (molar ratio) of calcium aluminate was 0.5. · As part of the cement admixture, a commercially available alumina cement (denoted as "AC" in Tables 1 to 4), with a Blaine specific surface area of 5000 cm 2 / g, specific gravity 3.00 g / cm 3 Products were used. · Water: Tap water · Aggregate: River sand produced from the Himekawa River system in Niigata Prefecture

[0032] [Evaluation method] · Carbonation depth For the prepared mortar, specimens with dimensions of 4 × 4 × 16 cm were fabricated and cured in water at 20°C until the age of 28 days. In accordance with JIS A 1153, accelerated carbonation was carried out in an environment of 20°C, 60% relative humidity, and 5% carbon dioxide concentration under atmospheric pressure. After 8 weeks, the specimens were cut perpendicular to the longitudinal direction of the specimens. In accordance with JIS A 1152, a phenolphthalein alcohol solution was applied to the cut cross-section, and the distance from the outer edge of the cut cross-section to the portion that turned magenta was measured at 8 points each with a vernier caliper, and the average value was taken as the carbonation depth. · Chloride ion penetration depth For the prepared mortar, specimens with dimensions of 4 × 4 × 16 cm were fabricated and cured in water at 20°C until the age of 28 days. In accordance with JSCE-G 572-2010 "Test Method for Apparent Diffusion Coefficient of Chloride Ions in Concrete by Immersion", the specimens were immersed in a 10 mass% NaCl aqueous solution. At the time of 13 weeks of immersion, the specimens were cut perpendicular to the longitudinal direction of the specimens. The penetration depth of chloride ions was measured for the cut cross-section by the silver nitrate solution spraying method. Specifically, the distance from the outer edge of the cut cross-section to the portion where the cross-section of the specimen did not change color to brown was measured at 8 points each with a vernier caliper, and the average value was taken as the chloride ion penetration depth. The results of measuring the carbonation depth and the chloride ion penetration depth are shown in Table 1 below.

[0033]

Table 1

[0034] From Table 1, the mortar shown in the examples has a relatively small carbonation depth and a relatively small chloride ion penetration depth. Therefore, the permeability of carbon dioxide can be suppressed, and the permeability of chloride ions can be suppressed. Further, in the composition of the cement admixture of the present invention, it can be seen that as the amount of γ-2CaO·SiO2 increases, the carbonation depth decreases and carbonation is reduced. It can be seen that as the amount of calcium aluminate increases, the chloride ions decrease and the chloride resistance is improved. On the other hand, when alumina cement is used as the cement admixture, it can be seen that the penetration depth of chloride ions is not reduced compared to the case where calcium aluminate is used as the cement admixture, and the effect is small.

[0035] <Experimental Example 2> The same experiment as in Experimental Example 1 was conducted when the content of Li2O contained in Li-containing γ-2CaO·SiO2 in the cement admixture was changed. Mortar with a water / cement ratio of 50% and a ratio of cement to aggregate (sand) of 1:2 (mass ratio), and with a ratio of 30 parts by mass of aggregate to 100 parts by mass of cement, was prepared by replacing the aggregate with the same amount of cement admixture. The cement admixture was assumed to contain 15 parts by mass of calcium aluminate (CA) and 85 parts by mass of γ-2CaO·SiO2 in 100 parts by mass of the cement admixture. Similar to Experimental Example 1, the carbonation depth and chloride ion penetration depth of the specimens were measured. The results of measuring the carbonation depth and chloride ion penetration depth are shown in Table 2 below.

[0036] [Materials Used] The Li-containing γ-2CaO·SiO2 was prepared in the same manner as in Experimental Example 1, except that the amount of reagent-grade lithium carbonate used was changed. ·Li+γ-C2S A: Prepared product. Li-containing γ-2CaO·SiO2. Blaine specific surface area is 4,000 cm 2 / g. Li2O content 0.1 mass%. (Same as Experimental Example 1). ·Li+γ-C2S B: Prepared product. Li-containing γ-2CaO·SiO2. Blaine specific surface area is 4,000 cm 2 / g. Li2O content 0.01 mass%. · Li+γ-C2S C: Prototype. γ-2CaO·SiO2 containing Li. Blaine specific surface area is 4,000 cm 2 / g. Li2O content is 0.05 mass%. · Li+γ-C2S D: Prototype. γ-2CaO·SiO2 containing Li. Blaine specific surface area is 4,000 cm 2 / g. Li2O content is 0.5 mass%. · Li+γ-C2S E: Prototype. γ-2CaO·SiO2 containing Li. Blaine specific surface area is 4,000 cm 2 / g. Li2O content is 1.0 mass%. · Li+γ-C2S F: Prototype. γ-2CaO·SiO2 containing Li. Blaine specific surface area is 4,000 cm 2 / g. Li2O content is 3.0 mass%.

[0037]

Table 2

[0038] From Table 2, the mortar shown in the examples has a relatively small neutralization depth and a relatively small chloride ion penetration depth, so it can suppress the permeability of carbon dioxide and the permeability of chloride ions. Also, regarding the cement admixture of the present invention, it can be seen that by adjusting the Li2O content, the neutralization depth has decreased and the neutralization has been reduced. On the other hand, it can be seen that when the Li2O content is low, the neutralization resistance shown by the decrease in the purity of γ-2CaO·SiO2 is relatively small.

[0039] <Experimental Example 3> In Experimental Example 1, the mixing ratios of γ-2CaO·SiO2 and calcium aluminate in the cement admixture were kept almost constant (except for No. 1-1). In Experimental Example 3, the same experiments as in Experimental Example 1 were conducted when the mixing ratios were changed. Mortar with a water / cement ratio of 50% and a ratio of cement to aggregate (sand) of 1 to 2 (mass ratio) was prepared. For 100 parts by mass of cement, the amount of the cement admixture shown in Table 3 was used to replace the same amount of aggregate as the cement admixture. The neutralization depth and chloride ion penetration depth of the specimens were measured in the same manner as in Experimental Example 1. The content (% by mass) of the cement admixture shown in Table 3 was defined as the amount (parts by mass) of the cement admixture relative to the total amount of the amount (parts by mass) of the cement admixture and the amount (parts by mass) of the cement. The results of measuring the neutralization depth and chloride ion penetration depth are shown in Table 3 below.

[0040]

Table 3

[0041] From Table 3, since the mortar shown in the examples has a relatively small neutralization depth and a relatively small chloride ion penetration depth, it can suppress the permeability of carbon dioxide and the permeability of chloride ions. By increasing the mixing amount of calcium aluminate in the cement admixture of the present invention, it becomes possible to reduce the chloride ion penetration depth. On the other hand, when the amount of calcium aluminate increases, the amount of γ-2CaO·SiO2 relatively decreases, so the neutralization depth tends to increase. From this, it can be seen that there is an optimal mixing ratio of the cement admixture.

[0042] <Experimental Example 4> The same experiment as in Experimental Example 1 was conducted when changing the CaO / Al2O3 molar ratio of calcium aluminate in the cement admixture. Mortar with a water / cement ratio of 50% and a ratio of cement to aggregate (sand) of 1:2 (mass ratio) was prepared, where the cement admixture replaced 30 parts by mass of sand with respect to 100 parts by mass of cement. The cement admixture contained 15 parts by mass of calcium aluminate (CA) and 85 parts by mass of γ-2CaO·SiO2 in 100 parts by mass of the cement admixture. Similar to Experimental Example 1, the carbonation depth and chloride ion penetration depth of the specimens were measured. The results of measuring the carbonation depth and chloride ion penetration depth are shown in Table 4 below.

[0043] [Materials Used] The calcium aluminate with a CaO / Al2O3 molar ratio was prepared in the same manner as in Experimental Example 1, except that the mixing amounts of reagent-grade calcium carbonate and reagent-grade aluminum oxide were changed. The prepared sample was pulverized so that the Blaine specific surface area value became 3000 cm 2 / g.

[0044]

Table 4

[0045] From Table 4, the mortar shown in the examples has a relatively small carbonation depth and a relatively small chloride ion penetration depth. Therefore, the permeability of carbon dioxide can be suppressed, and the permeability of chloride ions can be suppressed. Also, regarding the cement admixture of the present invention, it can be seen that by adjusting the CaO / Al2O3 molar ratio of calcium aluminate, the chloride ion penetration depth has decreased and the salt damage has been reduced. On the other hand, when the CaO / Al2O3 molar ratio is low or high, the amount of hydrate that fixes chlorine due to the hydration of calcium aluminate decreases, the chloride ion penetration depth increases, and the salt resistance decreases.

[0046] [Modification Example] When preparing according to the above embodiments, coarse aggregate may be further added to make concrete, and in this case, a hardened concrete body can be produced after curing. Such a hardened concrete body can suppress the permeability of carbon dioxide and the permeability of chloride ions, similarly to the above embodiments.

Industrial Applicability

[0047] By using the cement admixture of the present invention, it becomes possible to produce highly durable concrete having excellent carbonation resistance and chloride resistance, so that it can be widely used for civil engineering and construction purposes and contributes to the extension of the service life of concrete structures.

Claims

Claim 1 γ-2CaO·SiO ２ 、3CaO·2SiO ２ 、α-CaO·SiO ２ 、and one or more non-hydraulic compounds selected from the group consisting of calcium magnesium silicate, and calcium aluminate having a CaO / Al ２ O ３ molar ratio of 0.15 to 0.7, and A cement admixture in which Li is contained in the non-hydraulic compound, the Li can be confirmed to exist by ICP emission spectrometry but Li₂O is not identified by X-ray diffraction measurement, and the content of Li in the non-hydraulic compound is 0.001 to 1.0% by mass in terms of oxide. Claim 2 The cement admixture according to claim 1, wherein the amount of the non-hydraulic compound contained in the cement admixture is 65% by mass or more. Claim 3 The cement admixture according to claim 1 or 2, wherein the amount of the calcium aluminate contained in the cement admixture is 5% by mass or more. Claim 4 A cement composition comprising the cement admixture according to any one of claims 1 to 3. Claim 5 A cement composition in which the content of the cement admixture according to any one of claims 1 to 3 is 20 to 50% by mass. Claim 6 A hardened concrete body comprising the cement admixture according to any one of claims 1 to 3. Claim 7 A hardened concrete body comprising the cement composition according to claim 4 or 5.

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