JP7503011B2 - Calcium aluminate for accelerators and foam-type accelerators - Google Patents

Description

The present invention relates to calcium aluminate for quick-setting additives and foam-type quick-setting additives.

Conventionally, a method of spraying quick-setting concrete in which a quick-setting agent is mixed into concrete has been used to prevent the collapse of exposed ground during tunnel excavation, etc. (Patent Document 1). This method usually involves preparing the sprayed concrete in a plant for measuring and mixing cement, aggregate, water, etc. installed at the excavation site, transporting it with an agitator truck, pumping it with a concrete pump, mixing it with the quick-setting agent pumped from the other side at a junction pipe installed midway, and spraying the quick-setting sprayed concrete onto the ground surface until it reaches a specified thickness.

Known examples of quick-setting admixtures that have been used in the past include mixtures of calcium aluminate, alkali metal aluminate, and alkali metal carbonate, etc., mixtures of calcined alum, alkali metal aluminate, and alkali metal carbonate, etc., mixtures of calcium aluminate and _3CaO.SiO2 , and mixtures of slaked lime, alkali metal aluminate, and alkali metal carbonate (Patent Documents 2 to 5).
These accelerators have the function of accelerating the setting of cement, and are mixed with cement concrete and sprayed onto the ground surface.

The method of adding a quick-setting agent usually involves mixing the powder by air transport, which results in a large amount of dust. This can lead to a poor working environment, and since it is necessary to wear protective glasses and dust masks when spraying, a method of construction with less dust has been sought. As a method of construction with less dust generation, a method has been proposed in which the quick-setting agent is made into a slurry and added and mixed with the cement concrete, and then a solution of an alkali metal aluminate is separately pumped and mixed, and sprayed (Patent Document 6). This method uses a highly alkaline liquid, which is difficult to handle, and requires protective glasses and gloves when spraying, which reduces workability.

In response to this, a quick-setting construction method has been proposed that improves the working environment by turning the quick-setting agent into a slurry and mixing alums into the cement concrete (Patent Document 7). In addition, a quick-setting construction method has been proposed that further improves workability and dust reduction effects, and improves quick-setting properties in terms of shortening construction time (Patent Document 8).

However, there is a demand for a quick-setting agent that has a lower pH value than those in which calcium aluminate is mixed with an alkali metal aluminate or an alkali metal carbonate, and is weakly alkaline, preferably neutral or weakly acidic. To solve this problem, liquid quick-setting agents have been used that are mainly composed of basic aluminum salts or organic carboxylic acids (Patent Document 9), aluminum sulfate or alkanolamine (Patent Document 10), and a basic aqueous solution of aluminum, lithium silicate, and lithium aluminate (Patent Document 11). These liquid quick-setting agents are difficult to achieve initial strength development, and there are concerns that they will peel off when sprayed thickly inside a tunnel, compared to conventional quick-setting agents mainly composed of calcium aluminate (Patent Documents 12 and 13).

A spraying material was developed that is characterized by the addition of one or more inorganic compounds selected from the group consisting of an acidic liquid quick-setting agent whose main components are aluminum and sulfur, and powdered aluminum sulfate, sulfates, aluminates, and hydroxides (Patent Document 14). In addition, a foaming quick-setting agent was developed by mixing the liquid quick-setting agent with alkaline carbonates (Patent Document 15).

Japanese Patent Publication No. 60-4149 Japanese Patent Application Laid-Open No. 64-051351 Japanese Patent Publication No. 56-27457 Japanese Patent Application Laid-Open No. 61-026538 Japanese Patent Application Laid-Open No. 63-210050 Japanese Patent Application Laid-Open No. 05-139804 Japanese Patent Application Laid-Open No. 05-097491 JP 2003-81664 A JP 2001-509124 A Japanese Patent Application Laid-Open No. 10-087358 JP 2001-130935 A JP 2002-047048 A JP 2003-246659 A JP 2007-055831 A JP 2012-017235 A

However, although the foaming quick-setting agent of Patent Document 15 has a high reactivity with cement and exhibits high strength development, it is desirable to further improve its applicability to areas where improved long-term durability is required.

The present invention provides calcium aluminate for use as a foaming quick-setting agent, which, when used as a foaming quick-setting agent, improves workability by suppressing the generation of dust that occurs during spraying work in tunnels, etc., and provides high quick-setting properties even in conditions of spring water or deteriorated ground surfaces, and can be used in places where long-term strength expression is required, as well as a foaming quick-setting agent containing the same.

As a result of intensive research into solving the above problems, the inventors discovered that calcium aluminate with specific properties can solve the above problems, and thus completed the present invention. That is, the present invention is as follows.

[1] A calcium aluminate for quick-setting additive having a _SiO2 content of 7% by mass or less, a vitrification rate of 30 to 98%, and a sulfur content of 0.007 to 0.5% by mass.
[2] The calcium aluminate for quick-setting admixture according to [1], wherein the CaO/Al ₂ O ₃ molar ratio is 1.8 to 2.8.
[3] The calcium aluminate for quick-setting admixture according to [1] or [2], containing 1 to 40 mass% of 3CaO.Al ₂ O ₃ .
[4] A foaming type quick-setting admixture comprising the calcium aluminate for quick-setting admixture according to any one of [1] to [3] and aluminum sulfate powder having a pH of 1 to 5.
[5] The foaming quick-setting admixture according to [4], which is substantially free of alkali aluminate.

According to the present invention, it is possible to provide calcium aluminate for quick-setting additives, which, when used as a foaming quick-setting additive, improves workability by suppressing the generation of dust that occurs during spraying work in tunnels, etc., and provides high quick-setting properties even in conditions of spring water or deteriorated ground surfaces, and can be applied to areas where long-term strength expression is required, as well as a foaming quick-setting additive containing the same.

The present invention will be described in detail below. In this specification, parts and percentages are based on mass unless otherwise specified.

[Calcium aluminate for quick-setting agents]
The calcium aluminate for quick-setting admixture according to one embodiment of the present invention (this embodiment) has a _SiO2 content of 7% or less, a vitrification rate of 30 to 98%, and a sulfur content of 0.007 to 0.5%.

If the _SiO2 content exceeds 7%, the quick-setting property is deteriorated, so it is not preferable, and it is preferably 6% or less, and more preferably 5% or less. In addition, in order to prevent the vitrification from becoming 30% or less, it is preferably 0.1% or more, and more preferably 1% or more. The _SiO2 content can be measured by fluorescent X-ray.
The _SiO2 content can be adjusted by adjusting the amount of _SiO2 in the raw materials when producing calcium aluminate, or by adding new _SiO2 .

If the vitrification rate is less than 30% or exceeds 98%, the quick-setting properties deteriorate. The vitrification rate is preferably 40 to 95%.
Here, the vitrification rate can be determined by measuring the main peak area S of the crystalline mineral in advance by powder X-ray diffraction of a sample before heating, heating the sample at 1000°C for 2 hours, and then slowly cooling the sample at a cooling rate of 1 to 10°C/min to determine the main peak area _S0 of the crystalline mineral after heating by powder X-ray diffraction, and then using these _S0 and S values to calculate the vitrification rate according to the following formula.
Vitrification rate (%) = 100 x (1 - S/S ₀ )
The vitrification rate can be adjusted to a desired range by, for example, the heating temperature when producing calcium aluminate and the cooling rate after heating.

Furthermore, if the sulfur content is less than 0.007%, the amount of foaming may be reduced when mixed with aluminum sulfate powder, and if it exceeds 0.5%, it tends to impair the quick-setting properties, which is undesirable. The sulfur content is preferably 0.01 to 0.3%.
The sulfur content can be measured by X-ray fluorescence. The sulfur content can be adjusted by adjusting the amount of sulfur in the raw materials used in producing calcium aluminate or by adding a sulfur source.

Here, calcium aluminate (hereinafter also referred to as CA) is a general term for compounds having CaO and Al ₂ O ₃ as main components and having hydration activity, and is a compound in which part of CaO and/or Al ₂ O ₃ is replaced with an alkali metal oxide, an alkaline earth metal oxide, silicon oxide, titanium oxide, iron oxide, an alkali metal halide, an alkaline earth metal halide, an alkali metal sulfate, an alkaline earth metal sulfate, or the like, or a substance in which a small amount of these are dissolved in a substance having CaO and Al ₂ O ₃ as main components.

The calcium aluminate used in this embodiment may contain trace amounts of alkali metals and/or alkaline earth metals from the industrial raw materials, and some CAs containing these alkali metals and/or alkaline earth metals may be produced, but the presence of these small amounts of alkali metals and/or alkaline earth metals does not impose any restrictions.

Calcium aluminate is preferably alkaline, and more preferably has a pH of 10 to 14. Being alkaline (particularly, having a pH of 10 to 14) makes it easier for the properties of calcium aluminate to be exhibited.
The pH can be measured by collecting the supernatant of an aqueous solution of calcium aluminate and water in an amount of at least 5 times the volume of the aqueous solution, and then subjecting the supernatant to a general pH measurement method such as the pH measurement method specified in JIS Z8802.

The CaO/Al ₂ O ₃ molar ratio of calcium aluminate is not particularly limited, but considering the strength development in the very early stages, the molar ratio is preferably 1.8 to 2.8. If the molar ratio is 1.8 or more, the setting property in the very early stages can be made good, and if it is 2.9 or less, good long-term strength development is easily obtained. The CaO/Al ₂ O ₃ molar ratio is more preferably 2.2 to 2.8.

In addition, calcium aluminate preferably contains 1 to 40% of 3CaO.Al ₂ O ₃ , more preferably 5 to 30%. By containing 1 to 40%, 3CaO.Al ₂ O ₃ can be quantified by X-ray diffraction. In addition, 3CaO.Al ₂ O ₃ can be adjusted by heat treating a raw material ratio that brings the CaO/Al ₂ O ₃ molar ratio close to 2.8, or by further adjusting the vitrification rate to 95% or less.

The Blaine specific surface area of calcium aluminate (hereinafter sometimes simply referred to as "Blaine") is preferably 4000 to 8000 ^cm2 /g, more preferably 5000 to 7000 ^cm2 /g. By having a Blaine specific surface area of 4000 to ⁸⁰⁰⁰ cm2/g, early strength development is easily achieved and the handling of mortar and/or concrete during spraying can be improved.
The Blaine specific surface area is measured based on the specific surface area test described in JIS R 5201 "Physical testing methods for cement."

The method for producing calcium aluminate for quick-setting additive according to the present embodiment includes a method of mixing a raw material containing calcia and a raw material containing alumina, and subjecting the mixture to heat treatment such as firing in a kiln or melting in an electric furnace. When mixing the raw materials, it is also possible to mix a raw material containing a _SiO2 component or a raw material containing a sulfur component, and there is no particular restriction on the raw materials.

The above calcium aluminate for use as an accelerator has excellent hydration activity when added to cement, and when it comes into contact with water and is mixed with something with a pH of 1 to 5, it foams, making it easier to mix with cement mortar or concrete. Since the accelerator is usually made with compressed air, it is very effective as a foaming accelerator when combined with aluminum sulfate powder with a pH of 1 to 5, which will be described later.

[Foam-type quick-setting agent]
The foaming quick-setting admixture according to this embodiment contains the calcium aluminate for quick-setting admixture of the present invention and aluminum sulfate powder having a pH of 1 to 5 (hereinafter, may be simply referred to as "aluminum sulfate powder"). This combination suppresses significant aggregation of cement concrete due to an acid-alkali reaction, so that good strength development can be obtained. In addition, the handling property is also good.

Aluminum sulfate is available in anhydrous and hydrated form, but is not limited to this. When aluminum sulfate is in liquid form (such as a slurry or suspension), it is prone to react with other components, so it is in powder form.

Here, the foaming type quick-setting admixture is a foaming type quick-setting admixture made by mixing aluminum sulfate powder with an acidic pH and the calcium aluminate for quick-setting admixture of the present invention, and the quick-setting admixture itself foams when it comes into contact with water, cement concrete, etc. This foaming generates hydrogen sulfide, but the generation of hydrogen sulfide stops as soon as it is added to concrete, so there is no effect on the human body. Since the quick-setting admixture itself foams, there is no clogging trouble when it is mixed and merged with concrete, so there is less dangerous work and safe spraying can be performed.
From the viewpoint of workability, it is preferable that the composition is substantially free of alkali aluminate. Here, "substantially free of alkali aluminate" refers to the content of alkali aluminate being 0% when measured by X-ray diffraction.

The content of calcium aluminate for quick-setting agent in the foaming quick-setting agent (calcium aluminate for quick-setting agent/(calcium aluminate for quick-setting agent + aluminum sulfate powder) x 100) is preferably 50-98%, more preferably 60-90%, from the viewpoint of initial strength development and adhesion properties.

In addition to the above-mentioned components, the foaming quick-setting agent according to this embodiment may contain materials that are commonly used in quick-setting agents for sprayed concrete, such as calcium sulfate. Calcium sulfate comes in anhydrous, hemihydrate, and dihydrate forms, but is not limited thereto.

In addition, inorganic acids such as phosphoric acid, boric acid, hydrofluoric acid, and their salts (sodium, potassium, lithium, calcium, magnesium, aluminum), and organic acids such as monocarboxylic acids, dicarboxylic acids, polycarboxylic acids, oxycarboxylic acids, amino acids, and their salts (sodium, potassium, lithium), etc., can be used in combination. Among these, the use of dicarboxylic acids, oxycarboxylic acids, and their salts is preferred in terms of solubility in water and ease of handling.

The cement used in the cement concrete into which the foaming quick-setting admixture according to this embodiment is mixed is not particularly limited, and examples include various Portland cements such as normal, early strength, extra early strength, medium heat, and low heat, filler cements in which Portland cement is mixed with blast furnace slag, fly ash, and limestone powder, and environmentally friendly cements (ecocement) made from municipal waste incineration ash and sewage sludge incineration ash as raw materials, and these can also be used in a fine powder form. The ratio of the mixture and cement in the mixed cement is not particularly limited, and it is also possible to use a mixture in which more of these admixtures than are assumed by JIS are mixed.

The cement concrete used in the present invention contains cement and aggregate, and the aggregate preferably has a low water absorption rate and high aggregate strength.
The aggregate is not particularly limited as long as it can be sprayed, but examples of fine aggregate that can be used include river sand, mountain sand, sea sand, limestone sand, and silica sand, while examples of coarse aggregate that can be used include river gravel, mountain gravel, and limestone gravel. Crushed sand and crushed stone can also be used.

In addition, various spraying methods are possible using the foaming quick-setting admixture of the present invention depending on the required physical properties, economic efficiency, workability, etc. As a spraying method using the quick-setting admixture of the present invention, either a dry spraying method or a wet spraying method is possible.

"Experimental Example 1"
(1) Preparation of calcium aluminate for quick-setting additive Calcium carbonate, aluminum oxide, silica, and sulfur were mixed in various ratios (including the case where silica was 0%) and melted at 1600°C in an electric furnace. The cooling rate was adjusted, the mixture was pulverized in a ball mill, and _then classified to prepare calcium aluminate having a Blaine value of about 8,000 ^cm2 /g and the silica content, vitrification rate, and CaO/ _Al2O3 (molar ratio) shown in Table 1.

(2) Preparation and Evaluation of Foamable Accelerators Foamable accelerators A to W were prepared by mixing each of the calcium aluminates for quick-setting admixtures A to Z with aluminum sulfate powder (16-hydrate (commercially available product), pH: 3.5, average particle size: 300 μm) so that the content of calcium aluminate for quick-setting admixture in the foamable accelerator was 80 mass% (calcium aluminate for quick-setting admixture/(calcium aluminate for quick-setting admixture+aluminum sulfate powder)×100).

800g of cement, 2000g of fine aggregate, and 480g of water were put into a mortar mixer and mixed to prepare mortar, and the foaming type quick-setting additives A to W shown in Table 2 were quickly added to the mortar in an amount of 12.5 parts per 100 parts of cement, and mixed to prepare quick-setting mortar. The setting time and compressive strength of the mortar were then measured. The results are shown in Table 2.
The cement used was ordinary Portland cement, a commercially available product with a Blaine value of 3,200 cm ² /g and a specific gravity of 3.16, and the fine aggregate used was river sand from the Himekawa River system in Itoigawa City, Niigata Prefecture, with a surface-dried specific gravity of 2.62 and a maximum particle size of 5 mm.

<Measurement method>
Setting time: Measured in accordance with the Japan Society of Civil Engineers standard "Quality Standard for Accelerator for Shotcrete (JSCE D-102)".
Compressive strength: Measured according to JIS R 5201. Comparison with various admixtures is evaluated based on the compressive strength ratio to the base mortar.

(3) Spraying test using foaming quick-setting admixture Concrete with the fresh properties and concrete mix shown in Table 3 was prepared and pumped using a concrete pump “MKW-25SMT” under conditions of a spraying pressure of 0.4 MPa and a spraying rate of 12 ^m3 /h, and the pump pressure during pumping was monitored.
On the other hand, a foaming type quick-setting agent (see Table 4) was pneumatically transported using "NATM Crete" under a pumping pressure of 0.5 MPa so that the amount was 9 parts per 100 parts of cement, and this quick-setting agent was mixed with the shotcrete pumped from the other end of the Y-shaped pipe to produce shotcrete. The concrete compressive strength, rebound rate, and dust amount of this quick-setting shotcrete were measured. After spraying was completed, the quick-setting agent side of the Y-shaped pipe was checked to confirm the solidification state. This is shown in Table 4.

<Concrete mix>

The cement used was ordinary Portland cement, a commercially available product with a Blaine value of 3,200 ^cm2 /g and a specific gravity of 3.16. The fine aggregate used was river sand from the Hime River system in Itoigawa City, Niigata Prefecture, in a surface-dried state, with a specific gravity of 2.62 and a maximum particle size of 5 mm. The coarse aggregate used was 1505 crushed stone from the Hime River system in Itoigawa City, Niigata Prefecture, in a surface-dried state, with a specific gravity of 2.67 and a maximum particle size of 15 mm. Water was used as drinking water.
The concrete was prepared using a forced twin-shaft mixer, and the properties of the mixed concrete were measured in accordance with JIS A1101.

<Measurement method>
Concrete compressive strength: The compressive strength at 1 hour and 1 day was calculated by covering a pin installed in a pull-out formwork of width 25 cm x length 25 cm with quick-setting shotcrete from the surface of the pull-out formwork, pulling the pin from the back side of the formwork, and calculating the pull-out strength from the formula: (compressive strength) = (pull-out strength) x 4 / (contact area of specimen). The compressive strength at 28 days was calculated by spraying quick-setting shotcrete on a formwork of width 50 cm x length 50 cm x thickness 20 cm, measuring the diameter of the specimen of 5 cm x length 10 cm with a 20-ton pressure machine.
Rebound rate: The quick-setting shotcrete was sprayed for 10 minutes at a pumping rate of 10 ^m3 /h into a mock tunnel 3.5 m high and 2.5 m wide, made in an arch shape with iron plates and with 10 liters of water flowing from above at a rate of 10 liters per minute, simulating spring water. The rebound rate was then calculated as follows: (rebound rate) = (amount of quick-setting shotcrete that fell without adhering to the mock tunnel + 100 kg of spring water in 10 minutes) / (amount of quick-setting shotcrete sprayed into the mock tunnel + 100 kg of spring water in 10 minutes) x 100 (%).
Amount of dust: The quick-setting shotcrete was sprayed into the simulated tunnel for 10 minutes at a pumping rate of 10 m ³ /h. After that, the amount of dust was measured at a fixed position 3 m from the spraying location.
Amount of solidification: After the test, the Y-shaped joint pipe of the concrete and the quick-setting agent was washed with water and dried, and the amount of solidification was measured. The amount of solidification was calculated as follows: Amount of solidification = weight of the Y-shaped joint pipe after use - weight of the Y-shaped joint pipe before use.

The present invention provides high quick-setting properties for spraying work in tunnels and other areas, and can be applied to areas where long-term strength development is required.

Claims (5)

Calcium aluminate for quick-setting additive, having a _SiO2 content of 7% by mass or less, a vitrification rate of 30 to 98%, and a sulfur content of 0.007 to 0.5% by mass. 2. The calcium aluminate for quick-setting admixture according to claim 1, wherein the CaO/Al ₂ O ₃ molar ratio is 1.8 to 2.8. 3. The calcium aluminate for quick-setting admixture according to claim 1 or 2, containing 1 to 40 mass % of 3CaO.Al ₂ O ₃ . A foaming quick-setting admixture comprising the calcium aluminate for quick-setting admixture according to any one of claims 1 to 3 and aluminum sulfate powder having a pH of 1 to 5. 5. The foaming quick-setting admixture according to claim 4, which is substantially free of alkali aluminate.