WO2025243587A1 - Method for manufacturing cured body, and cured body - Google Patents

Abstract

Provided is a method for manufacturing a cured body that has a rapid curing property and that makes it possible to suppress expansion due to delayed generation of ettringite.　The method for manufacturing a cured body comprises: a mixing step for mixing steelmaking slag, a binder containing a blast furnace slag fine powder, and water to form a mixture; and a curing step for curing the mixture. The mixture satisfies relational expression (1).　(1): 2.5 ≤ (the mass of sulfur in terms of SO₃ per 1 m³ of the cured body × 100)/(the mass of the blast furnace slag fine powder per 1 m³ of the cured body) ≤ 9.0

Description

Method for producing hardened body and hardened body

The present invention relates to a method for producing a hardened body that has rapid hardening properties and can suppress expansion due to delayed ettringite formation, and to the hardened body.

One of the slag products made from steelmaking slag, a by-product of steelworks, is hydrated steel slag compact. Hydrated steel slag compact is primarily made from steelmaking slag and ground granulated blast furnace slag, and can be manufactured using mixing equipment similar to that used for concrete.

However, because steel slag hydrated hardened concrete uses a large amount of blast furnace slag powder, it takes longer to develop strength than regular concrete. It takes a long time, from pouring after mixing to removing the form and curing, before it attains the strength required for use as a product. For this reason, there is a demand for an efficient and inexpensive manufacturing process for steel slag hydrated hardened concrete.

To address this issue, Patent Document 1 discloses a manufacturing process for hydrated hardened steel slag using an immediate demolding method. When steelmaking slag containing free CaO is used as the material for the hydrated hardened steel slag, cracks may occur in the hydrated hardened steel slag due to volume expansion associated with the hydration reaction of the free CaO. To address this issue, Patent Document 2 discloses a manufacturing method for a slag hardened body, in which a mixture of slag containing free CaO and a _SiO2- containing substance is hydrated and hardened. Patent Document 2 claims that a slag hardened body with high strength and suppressed hydration expansion of free CaO can be manufactured by adding 0.5 mass% or more of CaS and/or S, calculated as S.

Japanese Patent Application Laid-Open No. 2016-132578 Japanese Patent Application Laid-Open No. 2001-153567

The method disclosed in Patent Document 1, when developing an efficient and inexpensive manufacturing process for hydrated hardened steel slag bodies, requires vibration-pressure compaction molding equipment, which poses the problem of requiring a large capital investment. Because the formwork used is fixed, there are limitations on the dimensions of the hardened bodies that can be manufactured, which also poses the problem of it not being applicable to all of the diverse shapes required for hydrated hardened steel slag bodies.

When attempts were made to manufacture a hardened body using the slag hardened body manufacturing method disclosed in Patent Document 2, the hardened body produced suffered from the problem of cracks that were thought to be caused by delayed ettringite formation. The present invention was made in consideration of these problems with the prior art, and its purpose is to provide a hardened body manufacturing method and hardened body that has rapid hardening properties and can suppress expansion due to delayed ettringite formation.

The means for solving the above problems are as follows.
[1] A method for producing a hardened body, comprising: a mixing step of mixing steelmaking slag, a binder containing ground granulated blast furnace slag, and water to form a mixture; and a hardening step of hardening the mixture, wherein the mixture satisfies the following formula (1):
2.5≦Mass of sulfur converted to _SO3 per 1 ^m3 of hardened body × 100 / Mass of the ground granulated blast furnace slag per 1 ^m3 of hardened body≦9.0 (1)
[2] The method for producing a hardened body according to [1], wherein the steelmaking slag contains a sulfur component.
[3] The method for producing a hardened body according to [2], wherein the sulfur component concentration of the steelmaking slag calculated as _SO3 is 0.25 mass% or more.
[4] The method for producing a hardened body according to [2] or [3], wherein the number of days that have passed since the steelmaking slag was discharged is 30 days or more.
[5] The method for producing a hardened body according to any one of [1] to [4], wherein the steelmaking slag is carbonated steelmaking slag.
[6] A hardened body comprising steelmaking slag, a binder containing ground granulated blast furnace slag, and water, and satisfying the following formula (1):
2.5≦Mass of sulfur converted to _SO3 per 1 ^m3 of hardened body × 100 / Mass of the ground granulated blast furnace slag per 1 ^m3 of hardened body≦9.0 (1)
[7] The hardened body according to [6], wherein the steelmaking slag is carbonated steelmaking slag.

By implementing the method for producing a hardened body according to the present invention, it is possible to produce a hardened body that has rapid hardening properties and suppresses expansion due to delayed ettringite formation.

The inventors used a material containing sulfur as the material for the hardened body, and optimized the weight balance between the sulfur contained in the material and the ground granulated blast furnace slag. This suppressed expansion due to delayed ettringite formation, while promoting the expression of the latent hydraulic properties of the ground granulated blast furnace slag through sulfate ions, thereby increasing the rapid hardening of the hardened body and shortening the curing period compared to conventional methods, leading to the completion of this invention.

The present invention will now be described in detail through an embodiment of the present invention. In the following embodiment, an example of producing a hardened body using steelmaking slag containing sulfur components will be described, but this embodiment represents a preferred example of the present invention, and the present invention is not limited to this embodiment in any way.

The method for producing a hardened body according to this embodiment includes a mixing step in which steelmaking slag containing sulfur components, a binder containing ground blast furnace slag, and water are mixed to produce a mixture, and a hardening step in which the mixture is hardened. It is preferable to use steelmaking slag containing sulfur components as the steelmaking slag. "Steelmaking slag containing sulfur components" refers to steelmaking slag that contains sulfur or sulfur compounds.

By using steelmaking slag containing sulfur components, the hardened body of this embodiment can be produced without adding sulfur separately to the mixture. Steelmaking slag containing sulfur components is prone to powdering, making it difficult to use for roadbed materials, etc. Therefore, by using steelmaking slag containing sulfur components to produce the hardened body, it is possible to effectively utilize slag that is difficult to use for roadbed materials, etc., and it also has the effect of reducing waste.

The sulfur concentration of the steelmaking slag used to produce the hardened body, calculated as _SO3, is preferably 0.25 mass% or more. The use of such steelmaking slag not only enables the above-mentioned slag to be effectively utilized, but also promotes the elution of sulfate ions from the steelmaking slag in the mixing step, further enhancing the rapid hardening of the hardened body in the hardening step. The method for measuring the sulfur concentration of the steelmaking slag is not particularly limited, but can be measured, for example, by combustion ion chromatography, in which sulfur components are converted into sulfate ions by a combustion method, an aqueous solution is prepared, and then the sulfate ions in the aqueous solution are quantified using ion chromatography.

Steelmaking slag containing sulfur components can be one or more of the following: secondary refining slag produced during secondary refining in a vacuum degassing system; smelting reduction refining slag produced when molten mother metal is directly melted with Cr ore before the production of stainless steel; and desulfurization slag produced during the desulfurization process of molten pig iron. It is preferable to use finely powdered steelmaking slag with a particle size of 5 mm or less. A particle size of 5 mm or less means a particle size that can be sieved through a sieve with 5 mm openings.

When using steelmaking slag containing sulfur, it is preferable to use steelmaking slag that has been discharged 30 days or more since the slag was discharged. In the steel manufacturing process, sulfur-containing slag is often generated during refining processes in a reducing atmosphere. For this reason, it is thought that the sulfur contained in steelmaking slag is mainly in the form of sulfide ions. On the other hand, sulfide ions contained in steelmaking slag that has been discharged 30 days or more are oxidized to sulfate ions upon contact with oxygen in the air during storage. These sulfate ions promote the development of the latent hydraulic properties of the granulated blast furnace slag, so using steelmaking slag that has been discharged 30 days or more since the slag was discharged can further enhance the rapid hardening properties of the hardened body.

It is preferable to use carbonated steelmaking slag as the steelmaking slag. In carbonated steelmaking slag, the calcium oxide and calcium hydroxide contained in the steelmaking slag are converted to calcium carbonate, which suppresses an increase in pH when the slag comes into contact with seawater. Therefore, a hardened body produced using carbonated steelmaking slag as the steelmaking slag has the effect of increasing biocompatibility when used in marine areas. There are no particular limitations on the method for carbonating steelmaking slag, but for example, steelmaking slag can be carbonated by contacting the steelmaking slag with a gas containing _CO2 .

The binder contains ground granulated blast furnace slag. As the ground granulated blast furnace slag, ground granulated blast furnace slag conforming to JIS A 6206:2013 "Blast furnace slag for concrete" may be used. The specific surface area of the ground granulated blast furnace slag contained in the binder is preferably 3000 cm ² /g or more. Ground granulated blast furnace slag with a specific surface area of 4000 cm ² /g or more has a high activity index, which is an indicator of hydraulic properties. For this reason, it is more preferable that the specific surface area of the ground granulated blast furnace slag contained in the binder is 4000 cm ² /g or more.

The binder may contain an alkaline activator as well as a silica-containing substance with pozzolanic reactivity. Examples of alkaline activators include hydrated lime, ordinary Portland cement as specified in JIS R 5210:2019, and blast-furnace cement as specified in JIS R 5211:2019. Examples of silica-containing substances with pozzolanic reactivity include fly ash, silica fume, and fly ash for concrete as specified in JIS A 6201:2015.

The water can be, for example, tap water, river water, lake water, well water, groundwater, industrial water, recycled water, or other water that meets the quality standards set forth in JIS A 5308:2019. Seawater or hot spring water containing sulfate ions or thiosulfate ions may also be used.

In the mixing step, in addition to the sulfur-containing steelmaking slag, binder, and water, a chemical admixture such as a high-performance water reducer may be mixed. By mixing a chemical admixture, the amount of water to be mixed can be reduced and the dispersibility of the materials can be improved. Reducing the amount of water mixed into the mixture can increase the strength of the hardened body. For example, a polycarboxylic acid-based high-performance water reducer can be used as the chemical admixture. The amount of the high-performance water reducer to be mixed is preferably 0.3 mass% or more and 0.5 mass% or less of the unit binder amount. The unit binder amount is the mass of binder contained in 1 ^m3 of the hardened body.

In the mixing step, steelmaking slag containing sulfur components and ground granulated blast furnace slag are mixed so as to satisfy the following formula (1): In the following explanation, the mass of sulfur converted to _SO3 per 1 ^m3 of hardened body in the following formula (1) is referred to as " _SO3 mass." The percentage of the mass of sulfur converted to _SO3 per 1 ^m3 of hardened body × 100 / the mass of ground granulated blast furnace slag per 1 ^m3 of hardened body is referred to as " _SO3 / BFS."

2.5≦mass of sulfur converted to _SO3 per 1 ^m3 of hardened body (kg) × 100 / mass of ground granulated blast furnace slag per 1 ^m3 of hardened body (kg)≦9.0 (1)

The mass of _SO3 can be calculated by multiplying the mass (kg) of the material containing sulfur components used per 1 ^m3 of hardened body by the value (mass%) of the sulfur content of the material converted into _SO3 . When materials containing multiple types of sulfur components are used in the production of the hardened body, the mass of the sulfur content of each material converted into _SO3 can be calculated and the results of these calculations can be added together.

By setting the _SO3 /BFS to 2.5 or more, sulfate ions are eluted, accelerating the development of the latent hydraulic properties of the ground granulated blast furnace slag, thereby increasing the rapid hardening of the hardened body in the hardening step. On the other hand, if the _SO3 /BFS exceeds 9.0, the sulfate ions become excessive, and cracks occur in the hardened body due to expansion caused by delayed formation of ettringite. Therefore, the _SO3 /BFS must be 2.5 or more and 9.0 or less. _{The SO3} /BFS is preferably 3.0 or more and 8.5 or less, more preferably 4.0 or more and 8.0 or less, and most preferably 4.5 or more and 7.5 or less.

The mixing of the materials in the mixing step is not particularly limited, but for example, the materials may be mixed using a concrete mixer at room temperature to form a mixture. The mixing step is preferably carried out in an environment of 30°C or below. This prevents the temperature from rising in the mixture of the materials, reducing the risk of expansion of the hardened body due to delayed ettringite formation. It is even more preferable to carry out the mixing step in an environment of 25°C or below. This further prevents the temperature from rising in the mixture, further reducing the risk of expansion of the hardened body due to delayed ettringite formation.

The materials for the hardened body are not limited to steelmaking slag containing sulfur components, a binder containing blast furnace slag powder, and water, but may also contain other materials. For example, electric furnace slag, slag generated during non-ferrous metal smelting, crushed stone, crushed sand, natural aggregate, steelmaking slag that does not contain sulfur components, etc. may be used as aggregate.

In the hardening step, the mixture produced in the mixing step is hardened. The method for hardening the mixture can be carried out using methods used in the cement and concrete fields. In the hardening step, for example, the mixture is poured into a formwork, removed from the formwork the next day, and cured in water at 20°C. This hardens the mixture, producing a hardened body.

As explained above, in the method for producing a hardened body according to this embodiment, by satisfying the above formula (1), it is possible to produce a hardened body that has rapid hardening properties and in which expansion due to delayed ettringite formation is suppressed. The hardened body produced in this way contains steelmaking slag, a binder containing ground blast furnace slag, and water, and is a hardened body that satisfies the above formula (1). By satisfying the above formula (1), the hardened body according to this embodiment is a hardened body that has rapid hardening properties and in which expansion due to delayed ettringite formation is suppressed.

This embodiment has been described using an example in which steelmaking slag containing sulfur components is used as the material for the hardened body, but this is not limited to this. Steelmaking slag that does not contain sulfur components may also be used as the material for the hardened body. In this case, it is sufficient to mix another material containing sulfur components that satisfies the above formula (1) into the mixture. This makes it possible to produce a hardened body that has rapid hardening properties and in which expansion due to delayed ettringite formation is suppressed.

Example 1
Next, an example will be described in which a hardened body was produced by adjusting the mixing ratio of steelmaking slag, ground granulated blast furnace slag and ordinary Portland cement as binders, water, and a high-performance water-reducing agent. Three types of steelmaking slag, A to C, with different sulfur component concentrations calculated as _SO3 were used as the steelmaking slag. The sulfur component concentrations calculated as _SO3 for steelmaking slags A to C are shown in Table 1 below.

Steelmaking slag A and steelmaking slag B are steelmaking slags containing sulfur components, while slag C is steelmaking slag that does not contain sulfur components. Since the sulfur concentration of slag C, calculated as _SO3, was less than 0.05 mass%, the mass of elemental sulfur in slag C was set to 0 in the calculation of _SO3 /BFS. Steelmaking slag A and steelmaking slag B are steelmaking slags that have been discharged for more than 30 days. These steelmaking slags were crushed to a particle size of 5 mm or less and used to produce the hardened body.

The binders used were ground granulated blast furnace slag and ordinary Portland cement as specified in JIS R 5210:2019. The sulfur concentration of the ground granulated blast furnace slag, calculated as _SO3, was 2.0 mass%, and the sulfur concentration of the ordinary Portland cement, calculated as _SO3, was 2.1 mass%. In Example 1, a polycarboxylic acid-based high-performance water-reducing agent (Chupol, manufactured by Takemoto Yushi Co., Ltd.), a chemical admixture, was also used.

These materials were mixed in a concrete mixer to form a mixture, which was then poured into a cylindrical formwork measuring φ100 x 200 mm. After being sealed and cured at 20°C until the following day, the formwork was removed and the mixture was then cured underwater at 20°C until it reached the specified age, producing a hardened product for strength evaluation.

<Strength evaluation>
The strength of the hardened body was evaluated by measuring the compressive strength in accordance with JIS A 1108:2018. At the age of 1 day, the hardened body was evaluated as passing if its compressive strength was 5 N/ ^mm2 or more, which is the guideline for the strength at which the hardened body can be removed from the form after 1 day of curing and handled. At the age of 7 days, the hardened body was evaluated as passing if its compressive strength was 18 N/ ^mm2 or more, which corresponds to the strength of ordinary concrete after 28 days.

<Expansion Stability Evaluation>
The expansion stability of the hardened body was evaluated by curing the material in water at 20°C for up to 7 days, then immersing the cylindrical hardened body in a water tank maintained at 60°C for 21 days, and evaluating the expansion stability mainly based on the expansion due to delayed ettringite formation from the appearance of the hardened body after immersion. The evaluation criteria are as follows:

Good: No cracks occurred in the hardened body, and no large pop-outs occurred on the surface of the hardened body.
Δ: No cracks occurred in the hardened body, but large pop-outs occurred on the surface of the hardened body.
×: Cracks occurred in the hardened product.

<Seawater immersion evaluation>
The materials and water were mixed in a concrete mixer and the mixture was poured into a φ100 x 200 mm cylindrical formwork. The material was sealed and cured at 20°C until the next day, then removed from the formwork and sealed and cured at 20°C until it reached an age of 7 days, producing a hardened body for seawater immersion evaluation. For the seawater immersion evaluation, the hardened body was immersed in artificial seawater with a volume (mL) 10 times the mass (g) of the hardened body, and shaken at approximately 200 times per minute with a shaker for 6 hours while measuring the pH, and the maximum pH value during shaking was recorded. The material composition of the hardened body, the _SO3 /BFS value, the strength evaluation, the expansion stability evaluation, and the seawater immersion evaluation results are shown in Table 2 below.

In Table 2 above, the 1-day strength indicates the compressive strength of the hardened body at 1 day old, and the 7-day strength indicates the compressive strength of the hardened body at 7 days old. As shown in Table 2, the hardened bodies of Invention Examples 1 to 8, in which the _SO3 /BFS was adjusted to 2.5 or more and 9.0 or less, had a compressive strength of 5 N/ ^mm2 or more at 1 day old and a compressive strength of 18 N/mm2 or more at ⁷ days old in the strength evaluation, and were therefore passed. In the expansion stability evaluation, no harmful cracks or large pop-outs were found, and the evaluation was ○.

On the other hand, in Comparative Examples 1 to 4, where the SO ₃ /BFS was less than 2.5, the 1-day strength of the hardened body was less than 5 N/mm ² and the 7-day strength was less than 18 N/mm ² in the strength evaluation, and they did not pass. In particular, in Comparative Example 3, the hardened body did not have enough strength to be removed from the frame, and strength evaluation and expansion stability evaluation could not be carried out. For this reason, in Table 1, the 1-day strength of Comparative Example 3 was rated x, the 7-day strength was rated x, the expansion stability was rated -, and the seawater immersion resistance was rated -. In Comparative Example 5, where the SO ₃ /BFS was greater than 9.0, cracks occurred in the hardened body in the expansion stability evaluation, and the expansion stability was rated x.

Example 2
Next, Example 2 will be described, in which a hardened body was produced using steelmaking slags A' and B', which are the same as steelmaking slags A and B shown in Table 1, but which had been discharged less than 30 days earlier. In Example 2, a hardened body was produced under the same conditions as Example 1, except that steelmaking slags A' and B', which had been discharged less than 30 days earlier, were used, and strength, expansion stability, and seawater immersion resistance evaluations were performed. The material composition of the hardened body, the _SO3 /BFS value, and the results of the strength, expansion stability, and seawater immersion resistance evaluations are shown in Table 3 below.

In Table 3, Example 9 corresponds to Example 2 in Table 1, Example 10 corresponds to Example 6 in Table 1, and Example 11 corresponds to Example 8 in Table 1.

As shown in Table 3, even for the hardened bodies of Examples 9 to 11, which used steelmaking slags A' and B' that had been discharged less than 30 days earlier, the strength evaluations at material ages of 1 day and 7 days passed, and the expansion stability evaluation was also rated as "Good." These results confirm that even when steelmaking slags A' and B' that had been discharged less than 30 days earlier were used, the strength evaluation was passed and the expansion stability evaluation was rated as "Good" as long as the _SO3 /BFS was 2.5 or more and 9.0 or less.

On the other hand, when compared to Invention Examples 2, 6, and 8, which correspond to Invention Examples 9-11, the compressive strength of the hardened body was lower for Invention Examples 9-11 at both 1-day and 7-day ages. In the expansion stability evaluation, Invention Example 11 showed no cracks in the hardened body, but significant pop-out was observed, resulting in a rating of △. These results confirm that when using steelmaking slag containing sulfur components, it is preferable to use steelmaking slag that has been discharged 30 days or more ago.

Example 3
Next, Example 3 will be described, in which hardened bodies were produced using carbonated steelmaking slags A", B", and C", which were the same steelmaking slags as steelmaking slags A, B, and C shown in Table 1, but which were carbonated. The carbonation treatment of the steelmaking slag was carried out by passing _CO2 gas through a container filled with the steelmaking slag for 24 hours. In Example 3, hardened bodies were produced under the same conditions as Example 1, except that carbonated steelmaking slags A", B", and C" were used, and strength evaluations, expansion stability evaluations, and seawater immersion evaluations were carried out. The material composition of the hardened bodies, the _SO3 /BFS value, and the results of strength evaluation, expansion stability evaluation, and seawater immersion evaluation are shown in Table 4 below.

In Table 4, Example 12 corresponds to Example 2 in Table 1, and Example 13 corresponds to Example 6 in Table 1.

As shown in Table 4, even for the hardened bodies of invention examples 12 and 13, which used carbonated steelmaking slags A", B", and C", the strength evaluations at ages of 1 day and 7 days passed, and the expansion stability was also rated as ○.From these results, it was confirmed that even when carbonated steelmaking slags A", B", and C" are used, the strength evaluation will pass and the expansion stability will be rated as ○ if the _SO3 /BFS is 2.5 or more and 9.0 or less.

On the other hand, in Invention Examples 2 and 6, which used non-carbonated steelmaking slag, the pH of the artificial seawater in which the hardened bodies were immersed rose to 8.5 or higher, as shown in Table 2. In contrast, in Invention Examples 12 and 13, which used carbonated steelmaking slag A", B", and C", the pH of the artificial seawater in which the hardened bodies were immersed fell below 8.5, as shown in Table 4. These results confirm that hardened bodies manufactured using and containing carbonated steelmaking slag hardly raise the pH of the surrounding seawater when used in marine areas, and that these hardened bodies have high biocompatibility in those marine areas.

Claims (7)

a mixing step of mixing steelmaking slag, a binder containing ground granulated blast furnace slag, and water to form a mixture;
a curing step of curing the mixture;
and
The method for producing a cured body, wherein the mixture satisfies the following formula (1):
2.5≦Mass of sulfur converted to _SO3 per 1 ^m3 of hardened body × 100 / Mass of the ground granulated blast furnace slag per 1 ^m3 of hardened body≦9.0 (1) The method for producing a hardened body according to claim 1, wherein the steelmaking slag contains sulfur components. The method for producing a hardened body according to claim 2, wherein the steelmaking slag has a sulfur component concentration calculated as _SO3 of 0.25 mass% or more. The method for producing a hardened body described in claim 2 or claim 3, wherein the steelmaking slag has been discharged 30 days or more ago. The method for producing a hardened body according to any one of claims 1 to 4, wherein the steelmaking slag is carbonated steelmaking slag. The binder contains steelmaking slag, ground granulated blast furnace slag, and water,
A hardened body that satisfies the following formula (1):
2.5≦Mass of sulfur converted to _SO3 per 1 ^m3 of hardened body × 100 / Mass of the ground granulated blast furnace slag per 1 ^m3 of hardened body≦9.0 (1) The hardened body described in claim 6, wherein the steelmaking slag is carbonated steelmaking slag.