JP2021024755A - Cement admixture and hydraulic composition - Google Patents

Abstract

To provide a cement admixture which hardly lowers a storage stability even if it is previously blended to a hydraulic composition together with an alkaline admixture, and can prepare a hydraulic composition capable of obtaining a hardening body having a super quick hardening property and high strength.SOLUTION: An objective cement admixture including aluminum sulfate satisfies such conditions that (1) aluminum sulfate is amorphous; (2) a spectrum obtained by the solid 27Al-NMR of aluminum sulfate has a peak in a chemical shift of -0.20 to -20.00 ppm, and a half band width of the peak is 10.00 to 35.00 ppm; (3) pH of aluminum sulfate is in a range of 1 to 6; and (4) a grain having a grain size of 100 μm or more is 70 mass% or less, and a grain having a grain size of 10 μm or less is less than 30 mass%.SELECTED DRAWING: None

Description

The present invention relates to a cement admixture and a hydraulic composition used in the fields of civil engineering, construction and the like.

In recent years, a wide variety of performances have been required for hydraulic compositions in the fields of civil engineering and construction. Among them, simplification of construction is a very important factor in considering the safety of workers. Here, simplification of construction means, for example, comprehensive rationalization such as improvement of construction speed, unification of materials, and improvement of handleability. In order to achieve simplification of construction, for example, it is important to improve the curing speed of the hydraulic composition, premix it, etc., and in fact, it is so-called ultrafast hardness, which has high condensation and high strength development. Various hydraulic compositions having the above have been proposed (for example, Patent Documents 1 to 3). In recent years, the performance required for hydraulic compositions has been increasing more and more with further improvement in simplification of construction and support for new applications.

Japanese Unexamined Patent Publication No. 3-12350 Japanese Unexamined Patent Publication No. 1-230455 Japanese Unexamined Patent Publication No. 11-139859

A cement admixture is blended in the hydraulic composition for the purpose of improving various properties such as curing speed. Conventionally, an alkaline admixture has been used as the cement admixture, but from the viewpoint of safety, it is desired to use an acidic admixture.
However, since a hydraulic substance such as cement is strongly alkaline, it is difficult to combine it with an acidic cement admixture, and there is a problem that a hydraulic composition having desired properties cannot be obtained. In fact, when a conventional acidic cement admixture suitable for improving the curing rate and premixing is added to the hydraulic composition, the storage stability of the hydraulic composition, the strength of the cured product, and the like are lowered.

The present invention has been made to solve the above-mentioned problems, and even if it is previously blended with an alkaline admixture in a hydraulic composition, the storage stability is unlikely to decrease, and the hydraulic composition has ultrafast hardness. It is an object of the present invention to provide a cement admixture capable of giving a hydraulic composition capable of obtaining a cured product having high strength.

As a result of diligent research to solve the above problems, the present inventors have been able to solve the above problems even though the cement admixture containing aluminum sulfate having specific properties is acidic. The present invention has been completed.
That is, the present invention is as follows.

[1] A cement admixture containing aluminum sulfate that satisfies the following (1) to (4).
(1) The aluminum sulfate is amorphous.
(2) The solid aluminum sulfate ^{27 In the} spectrum obtained by Al-NMR, it has a peak at a chemical shift of -0.2 to -20.00 ppm, and the half width of the peak is 10.00 to 35.00 ppm. ..
(3) The pH of the aluminum sulfate is 1 to 6.
(4) Particles having a particle size of 100 μm or more are 70% by mass or less, and particles having a particle size of 10 μm or less are less than 30% by mass.
[2] The cement admixture according to [1], wherein an alkaline admixture having a pH of 8 or more is mixed.
[3] The cement admixture according to [2], wherein the alkaline admixture contains an alkali metal carbonate.
[4] The cement admixture according to [2] or [3], wherein the alkaline admixture contains an alkaline earth metal hydroxide.
[5] A hydraulic composition containing the cement admixture according to any one of [1] to [4] and a hydraulic substance.

According to the present invention, even if the hydraulic composition is preliminarily blended with an alkaline admixture, the storage stability does not easily decrease, and a hydraulic composition having ultrafast hardness and high strength can be obtained. It is possible to provide a cement admixture capable of giving.

Hereinafter, embodiments of the present invention will be described in detail. The parts and% used in this specification are based on mass unless otherwise specified.
[Cement admixture]
The cement admixture of the present invention contains aluminum sulfate that satisfies the following (1) to (4).
(1) Aluminum sulfate is amorphous.
When aluminum sulfate is not amorphous, it is difficult to premix it with a hydraulic substance showing strong alkalinity such as cement, and even if it can be premixed, the storage stability of the hydraulic composition is lowered.
Here, whether or not aluminum sulfate is amorphous can be determined by X-ray diffraction analysis. Specifically, if the X-ray diffraction spectrum of aluminum sulfate is broad, it can be determined that it is amorphous. For aluminum sulfate, a clear peak can be confirmed in the range of 2θ = 20 to 30 °, but those without a peak are considered amorphous.

(2) Solid aluminum sulfate ^{27 In the} spectrum obtained by Al-NMR, the chemical shift has a peak at −0.20 to −20.00 ppm, and the half width of the peak is 10.00 to 35.00 ppm. ..
If the peak chemical shift is greater than −0.20 ppm, it is difficult to premix with the hydraulic substance, and even if the premix can be achieved, the storage stability of the hydraulic composition may decrease. On the other hand, if the peak chemical shift is less than -20.00 ppm, a synergistic effect with an alkaline admixture having a pH of 8 or more may not be obtained.
The chemical shift of the peak is preferably −1.00 to -16.00 ppm, more preferably -2 to -15 ppm.

Further, if the half width of the peak is out of the above range, the curing rate of the hydraulic composition may not be sufficiently obtained. The half width of the peak is preferably 10 to 35 ppm, more preferably 25 to 32 ppm.

Here, the solid ²⁷ Al-NMR measurement of aluminum sulfate can be carried out under the following conditions using a commercially available measuring device, for example, a superconducting nuclear magnetic resonance device “ECX-400” manufactured by JEOL Ltd. ..
Observation nucleus: ²⁷ Al
Sample tube rotation speed: 10 KHz
Measurement temperature: Room temperature Pulse width: 3.3 μsec (90 ° pulse)
Waiting time: 5 seconds External standard: Aluminum nitrate

In order to obtain aluminum sulfate that satisfies the above requirements (1) and (2), for example, the heating temperature when heating a mixture of various raw materials may be adjusted.

(3) The pH of aluminum sulfate is 1 to 6.
If the pH of aluminum sulfate is out of the above range, the curing rate of the hydraulic composition will decrease. The pH is preferably 2-5, more preferably 2-4. Further, in order to adjust the pH of aluminum sulfate to 1 to 6, the above heating temperature may be adjusted.
In the present specification, the pH can be measured by adding 10 g to 100 ml of water at 20 ± 2 ° C. and stirring at 500 rpm using a pH meter.

(4) In aluminum sulfate, 70% or less of the particles have a particle size of 100 μm or more, and less than 30% of the particles have a particle size of 10 μm or less.
If the particle size of 100 μm or more exceeds 70%, the curing rate of the hydraulic substance cannot be sufficiently obtained, and if the particles having a particle size of 10 μm or less are 30% or more, an alkaline admixture having a pH of 8 or more. By coexisting with, storage deterioration becomes remarkable.
The particles having a particle size of 100 μm or more are preferably 50% or less, more preferably 30% or less. Further, the particles having a particle size of 10 μm or less are preferably 40% or more, more preferably 50% or more. The particle size can be adjusted by, for example, a sieve.
It should be noted that the admixture using aluminum sulfate in the range of (4) does not mean that a sufficient curing rate can be obtained from low temperature to high temperature, and it is expected that the curing rate will increase particularly at high temperature. Since it is thought that the curing rate can be controlled by the coexistence of alkaline substances with pH 8 or higher, it can be used in a wide temperature range from low temperature (10 ° C) to high temperature (30 ° C), so it can be applied stably in both summer and winter. is there.

Aluminum sulfate satisfying the above-mentioned (1) to (4) is prepared by mixing raw materials such as _{Al 2} O ₃ source and SO ₃ source using Al ₂ O ₃ source and SO _{3 source to prepare a mixture.} a method of heating treatment, a method of directly chemically reacting Al ₂ O ₃ source and SO ₃ source, a method is a chemical reaction after mixing was charged with Al ₂ O ₃ source and SO ₃ source in a solvent such as pure water or the like Can be used. In these methods, by controlling the production conditions, aluminum sulfate satisfying the above-mentioned (1) to (3) can be obtained.

The Al ₂ O ₃ source is not particularly limited, but aluminum sulfate, aluminate, and other inorganic aluminum compounds, organoaluminum compounds, and aluminum complexes can be used.

The sulfate of aluminum is not particularly limited, and examples thereof include ammonium alum, aluminum hydroxysulfate, and aluminum sulfate.
The alumate is not particularly limited, and examples thereof include lithium aluminate, sodium aluminate, potassium aluminate, calcium aluminate, and magnesium aluminate.
Other inorganic aluminum compounds are not particularly limited, and are, for example, bokisite, aluminum oxide, aluminum hydroxide, aluminum chloride, aluminum phosphate, aluminum nitrate, aluminum fluoride, polyaluminum chloride, aluminum carbonate, and synthetic hydrotal. Sight, aluminum metasilicate and the like.

The organoaluminum compound is not particularly limited, and examples thereof include aluminum stearate, aluminum oxalate, aluminum isopropoxide, and aluminum formate.
The aluminum complex is not particularly limited, and examples thereof include tris (8-hydroxyquinolinato) aluminum.
As the Al ₂ O ₃ source, a single species can be used, but two or more species may be used in combination. Among the various Al ₂ O ₃ sources described above, aluminum sulfate is preferable because it has high solubility in water, low production cost, and excellent cohesiveness, but aluminum hydroxide is also preferable.

The SO ₃ source, but are not limited to, in addition to elemental sulfur, such as sulfur and sulfur oxide, sulfide, sulfate, sulfate, sulfite, sulfite, thiosulfate, sulfate, and organic sulfur compounds such as Can be used.
The sulfide is not particularly limited, and examples thereof include magnesium sulfide, calcium sulfide, iron sulfide, and phosphorus pentasulfide.
The sulfate is not particularly limited, and examples thereof include aniline sulfate, aluminum sulfate, ammonium sulfate, magnesium sulfate, manganese sulfate, barium sulfate, calcium sulfate, sodium sulphate, potassium sulphate, ammonium sulphate, and hydroxylamine sulfate.

The sulfite salt is not particularly limited, and examples thereof include ammonium hydrogen sulfite and calcium sulfite.
The thiosulfate is not particularly limited, and examples thereof include ammonium thiosulfate and barium thiosulfate.
The organic sulfur compound is not particularly limited, and examples thereof include resins such as a sulfonic acid derivative, a salt of a sulfonic acid derivative, mercaptan, thiophene, a thiophene derivative, polysulfone, polyethersulfone, and polyphenylene sulfide.
The SO ₃ source, can be used single type may be used in combination of two or more. Among the various SO ₃ source of the high solubility in water, from the viewpoint of excellent cheap and caking manufacturing cost, preferably sulfuric acid or sulfates, and most preferably sulfuric acid or ammonium alum.

Here, it is preferable that the obtained aluminum sulfate is pulverized by, for example, a known mill or the like so as to satisfy the requirement (4) by sieving or the like.

The cement admixture according to the present invention is preferably mixed with an alkaline admixture having a pH of 8 or more. Examples of the alkaline admixture include alkali metal aluminate, alkaline earth metal aluminate, alkaline earth metal carbonate, alkali metal hydroxide, alkali metal carbonate, alkaline earth metal hydroxide and the like. Of these, alkali metal carbonates and alkaline earth metal hydroxides are preferably contained.

Alkali metal carbonates can impart further coagulation and rapid hardness to cement. Examples of the alkali metal carbonate include sodium carbonate, sodium hydrogen carbonate, calcium carbonate, potassium carbonate, lithium carbonate, lithium hydrogen carbonate, beryllium carbonate, magnesium carbonate, etc. Among them, sodium carbonate, sodium hydrogen carbonate, calcium carbonate, and carbon dioxide. Potassium is preferred. The content of the alkali metal carbonate in the alkaline admixture is preferably 50% or more, more preferably 80% or more.

Alkaline earth metal hydroxides can impart further cohesiveness, rapid hardness, and long-term strength development to cement. Examples of the alkaline earth metal hydroxide include calcium hydroxide, magnesium hydroxide, sodium hydroxide, potassium hydroxide, lithium hydroxide, beryllium hydroxide and the like, among which calcium hydroxide, magnesium hydroxide and hydroxide are used. Sodium and potassium hydroxide are preferable. The content of the alkaline earth metal hydroxide in the alkaline admixture is preferably 50% or more, more preferably 80% or more.

The alkaline admixture used in the cement admixture according to the present invention preferably contains a combination of an alkali metal carbonate and an alkaline earth metal hydroxide. This combination makes it possible to impart significant cement coagulation, rapid hardening, and strength development. The combination of the alkali metal carbonate and the alkaline earth metal hydroxide in the alkaline admixture is preferably 50% or more, and more preferably 80% or more. The mass ratio of alkali metal carbonate to alkaline earth metal hydroxide in the combination is preferably 30/70 to 70/30 for alkali metal carbonate / alkaline earth metal hydroxide. , 40/60 to 60/40, more preferably.

The cement admixture and the alkaline admixture according to the present invention are preferably mixed when added to the hydraulic substance, but since the cement admixture according to the present invention has excellent storage stability with respect to alkali, it can be used as a hydraulic substance. It is preferable to mix 2-3 weeks before the addition.

[Hydraulic composition]
The hydraulic composition according to the present invention contains the cement admixture and the hydraulic substance according to the present invention, and preferably further contains the above-mentioned alkaline admixture.
The cement admixture according to the present invention can be used together with various hydraulic substances to prepare a hydraulic composition. In particular, the cement admixture according to the present invention can be used together with an alkaline hydraulic substance even though it is acidic. In general, when an acidic cement admixture is used together with an alkaline hydraulic substance to prepare a hydraulic composition, the storage stability tends to decrease, but the cement admixture according to the present invention is an alkaline hydraulic substance. Even if a hydraulic composition is prepared, the storage stability is unlikely to decrease. Therefore, the hydraulic composition prepared by using the cement admixture according to the present invention can be stored for a long period of time without any special storage method, construction method or handling method. Further, this hydraulic composition has ultrafast hardness and can form a cured product having high strength. Therefore, by using this hydraulic composition, it is possible to simplify the construction.

The water-hardening substance used in the water-hardening composition is not particularly limited, but for example, various Portland cements such as ordinary, fast-strength, moderate heat, low heat, and white; manufactured from city waste incineration ash and sewage sludge incineration ash as raw materials. Eco-cement to be used; examples include mixed cement containing blast furnace slag, silica fume, limestone, fly ash, gypsum and the like.
The pH of the hydraulic substance is not particularly limited, but is preferably more than 7, more preferably 8 or more, and further preferably 10 or more.

The hydraulic composition can contain known additives that can be generally blended as long as the effects of the present invention are not impaired. Additives are not particularly limited, but are rust preventives, colorants, polymers, fibers, fluidizers, neutralization inhibitors, waterproofing agents, thickeners, waterproofing agents, retarding agents, fast-strengthening agents, and accelerators. , Water reducing agent, high performance (AE) water reducing agent, foaming agent, foaming agent, AE agent, drying shrinkage reducing agent, quick-setting agent, leavening agent, cold resistance accelerator, efflorescence inhibitor, alkaline aggregate reaction inhibitor, Examples include black unevenness reducing agents and environmental purification admixtures. These additives can be used alone or in combination of two or more.

The cement admixture according to the present invention in the hydraulic composition is preferably 1 to 30% by mass, more preferably 2 to 20% by mass. When the above-mentioned alkaline admixture is contained, the amount of the alkaline admixture is preferably 2 to 30 parts, more preferably 2 to 20 parts, based on 100 parts of the cement admixture according to the present invention.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples as long as it does not deviate from the gist thereof.

<Preparation of aluminum sulfates A to E>
The following substances were used as raw materials.
Al ₂ O ₃ source: aluminum hydroxide, reagent, purity 99%
SO ₃ source: sulfuric acid, reagent, purity 99%
Solvent: pure water

Aluminum sulfates A to E were prepared by mixing an Al ₂ O ₃ source, an SO ₃ source, and a solvent at a molar ratio of 2: 3:10, and heating and reacting the mixture at each temperature shown in Table 1. .. Then, it was pulverized using a ball mill, and pulverized by a sieve so that particles having a particle size of 100 μm or more were 30% and particles having a particle size of 10 μm or less were 20%.
The aluminum sulfate prepared above was subjected to X-ray diffraction, solid ²⁷ Al-NMR, and pH evaluation.

X-ray diffraction was measured using a Multi-Flex manufactured by Rigaku. The measurement was carried out under the conditions of 2θ = 5 ° to 60 ° and 5 ° / min with the tube voltage-tube current set to 40 KV-40 mA. In addition, PDXL was used as the analysis software. In the evaluation of X-ray diffraction, if the X-ray diffraction spectrum was broad, it was determined to be amorphous, and if it was not, it was determined to be crystalline. The results are shown in Table 1.

Solid ²⁷ Al-NMR was carried out under the above conditions using a superconducting nuclear magnetic resonance apparatus (ECX-400) manufactured by JEOL Ltd., and the chemical shift and half price width of the peak were measured. The results are shown in Table 1.

The pH of aluminum sulfate adjusted by the above method was measured by the method described above using a pH measuring meter (D-53S) manufactured by HORIBA. The results are shown in Table 1.

Next, 20 parts of the alkaline admixture A shown in Table 2 was mixed with 100 parts of aluminum sulfate of the type shown in Table 1 prepared above to prepare a cement admixture, and the number of days and the temperature 20 shown in Table 2 were 20. After storage at ° C. and humidity of 60%, a hydraulic composition composed of 100 parts of ordinary Portland cement (pH 14, industrial product) and 10 parts of cement admixture was obtained.
Then, 40 parts by mass of water (tap water) was further mixed with this hydraulic composition and mixed, and a coagulation test was conducted.
The setting test was carried out in accordance with JIS R5201 “Physical test method for cement”. The condensation test measured the onset time of condensation.
The results of each of the above evaluations are shown in Table 2.

Alkaline admixture a: Sodium carbonate, reagent, pH11
Alkaline admixture a: Sodium hydrogen carbonate, reagent, pH 8.3
Alkaline admixture c: Calcium carbonate, reagent, pH10
Alkaline admixture d: Potassium carbonate, reagent, pH12
Alkaline admixture E: Calcium hydroxide, reagent, pH10
Alkaline admixture F: Magnesium hydroxide, reagent, pH 10.5
Alkaline admixture: sodium hydroxide, reagent, pH14
Alkaline admixture: potassium hydroxide, reagent, pH13

As shown in Table 2, by using aluminum sulfate A, the setting time changed with the number of storage days. This is considered to be due to storage deterioration of the compound and the admixture. However, it was confirmed that the aluminum sulfates B to E did not show any storage deterioration, and that the aluminum sulfates B to D were particularly likely to have a promoting effect.

Next, 100 parts of aluminum sulfate C or aluminum sulfate C adjusted so that the proportion of particles having a particle size of 100 μm or more is shown in Table 3 and 20 parts of an alkaline admixture of the type shown in Table 3 are mixed and mixed. Then, the cement admixture was prepared and stored at the number of days shown in Table 3, the temperature at 20 ° C., and the humidity at 60%, and then a hydraulic composition consisting of 100 parts of ordinary Portland cement (pH 14, industrial product) and 10 parts of the cement admixture. I got something. Then, 40 parts by mass of water (tap water) was further mixed with this hydraulic composition, and a coagulation test and a measurement of compressive strength were performed.
The setting test and the measurement of the compressive strength were carried out in accordance with JIS R5201 “Physical test method for cement”. The condensation test measured the onset time of condensation.
The results of each of the above evaluations are shown in Table 3.

As shown in Table 3, it was confirmed that when the proportion of particles having a particle size of 100 μm or more of aluminum sulfate was 71% and 99%, the condensation initiation time was delayed. Further, when the proportion of particles having a particle size of 100 μm or more of aluminum sulfate was 70% or less, the cohesiveness and strength were good.

Next, 100 parts of aluminum sulfate C or aluminum sulfate C adjusted to have a particle size of 10 μm or less so as to be shown in Table 4 and 20 parts of an alkaline admixture of the type shown in Table 4 were blended. After mixing to prepare a cement admixture and storing it at the number of days shown in Table 4, temperature 20 ° C., and humidity 60%, hydraulic property consisting of 100 parts of ordinary Portland cement (pH 14, industrial product) and 10 parts of cement admixture The composition was obtained. Then, 40 parts by mass of water (tap water) was further mixed with this hydraulic composition, and a coagulation test and a measurement of compressive strength were performed.
The setting test and the measurement of the compressive strength were carried out in accordance with JIS R5201 “Physical test method for cement”. The condensation test measured the onset time of condensation.
The results of each of the above evaluations are shown in Table 4.

As shown in Table 4, it was found that when the proportion of particles having a particle size of 10 μm or less in aluminum sulfate C was 30% or more, storage deterioration was confirmed, and when it was less than 30%, no particular storage deterioration was confirmed. ..

Next, 100 parts of aluminum sulfate of the type shown in Table 5 and 20 parts of various alkaline admixtures are mixed and mixed to prepare a cement admixture, and the number of days shown in Table 5, temperature 20 ° C., and humidity 60% are adjusted. After storage, a hydraulic composition consisting of 100 parts of ordinary Portland cement (pH 14, industrial product) and 10 parts of cement admixture was obtained.
Then, 40 parts by mass of water (tap water) was further mixed with this hydraulic composition and mixed, and a strength test was conducted. The strength test was performed in accordance with JIS R5201 “Physical test method for cement”. In the strength test, the strength was measured 28 days after the addition of water to the hydraulic composition.
The results of each of the above evaluations are shown in Table 5.

As shown in Table 5, the strength of the material age 28 days changed with the number of storage days for each type of admixture, but the strength of the combination of aluminum sulfate A and various alkaline admixtures decreased with the number of storage days. On the other hand, it was confirmed that the combination of aluminum sulfate C and various alkaline admixtures had good storage stability and the strength did not decrease regardless of the number of storage days.

Next, 100 parts of aluminum sulfate of the type shown in Table 6 prepared above and 20 parts of various alkaline admixtures were mixed and mixed to prepare a cement admixture, and the number of days and the temperature of 20 ° C. shown in Table 6 were adjusted. After storage at a humidity of 60%, a hydraulic composition consisting of 100 parts of ordinary Portland cement (pH 14, industrial product) and 10 parts of cement admixture was obtained. When the alkaline admixtures A and O were mixed (Experiments No. 30 and 31), the ratio (A: O) of these was 50:50.
Then, 40 parts by mass of water (tap water) was further mixed with this hydraulic composition and mixed, and a strength test was conducted. The strength test was performed in accordance with JIS R5201 “Physical test method for cement”. In the strength test, the strength was measured 28 days after the addition of water to the hydraulic composition.
The results of each of the above evaluations are shown in Table 6.

As shown in Table 6, the strength of aluminum sulfate A was confirmed to decrease depending on the number of storage days even when the admixture types were combined with a and o, but when aluminum sulfate C was combined with a and o, the strength was further increased. It was confirmed.

Next, Experiment No. 3, No. For 6 to 17, 100 parts of ordinary Portland cement (pH 14, industrial product), cement admixture, except that the temperature (test temperature) for obtaining the hydraulic composition was set to 20 ° C. to 10 ° C. or 30 ° C. A hydraulic composition consisting of 10 parts was obtained.
Then, 40 parts by mass of water (tap water) was further mixed with this hydraulic composition and mixed, and a coagulation test was conducted.
The setting test was carried out in accordance with JIS R5201 “Physical test method for cement”. The condensation test measured the onset time of condensation.
The results of each of the above evaluations are shown in Table 7.

As shown in Table 7, the admixture using aluminum sulfate within the range of the present invention can be used in a wide temperature range from low temperature (10 ° C.) to high temperature (30 ° C.), so that it can be stably applied in both summer and winter. It is possible.

As can be seen from the above results, according to the present invention, a hydraulic composition having ultra-fast hardness and high strength of a cured product, which is unlikely to deteriorate in storage stability even when preliminarily blended with the hydraulic composition. A cement admixture that can be given can be provided. Further, according to the present invention, it is possible to provide a hydraulic composition having ultrafast hardness and high strength of a cured product, while the storage stability is unlikely to decrease.

The present invention can be suitably applied to cement admixtures used in the fields of civil engineering, construction and the like.

Claims (5)

A cement admixture containing aluminum sulfate that satisfies the following (1) to (4).
(1) The aluminum sulfate is amorphous.
(2) The solid aluminum sulfate ^{27 In the} spectrum obtained by Al-NMR, it has a peak at a chemical shift of -0.2 to -20.00 ppm, and the half width of the peak is 10.00 to 35.00 ppm. ..
(3) The pH of the aluminum sulfate is 1 to 6.
(4) Particles having a particle size of 100 μm or more are 70% by mass or less, and particles having a particle size of 10 μm or less are less than 30% by mass. The cement admixture according to claim 1, wherein an alkaline admixture having a pH of 8 or more is mixed. The cement admixture according to claim 2, wherein the alkaline admixture contains an alkali metal carbonate. The cement admixture according to claim 2 or 3, wherein the alkaline admixture contains an alkaline earth metal hydroxide. A hydraulic composition containing the cement admixture according to any one of claims 1 to 4 and a hydraulic substance.