Hydraulic composition and method for producing hardened body of hydraulic composition

Abstract

Provided are: a hydraulic composition capable of improving production efficiency by shortening the pre-setting time in production of a hardened body of concrete or the like subjected to steam curing, capable of producing a hardened body of concrete or the like excellent in strength even when the pre-setting time is shortened, and capable of reducing carbon dioxide emissions by using a carbonated cement hydrate obtained by fixing carbon dioxide as part of the raw materials; and a method for producing a hardened body of the hydraulic composition. This hydraulic composition comprises cement, a carbonated cement hydrate, an aggregate, and water, wherein the ratio of the carbonated cement hydrate is 1%-50% by mass in 100% by mass of the total of the cement and carbonated cement hydrate, and the amount of water is 30-60 parts by mass based on 100 parts by mass of the total of the cement and carbonated cement hydrate.

Description

Hydraulic composition and method for producing hardened product of hydraulic composition

[0001] The present invention relates to a hydraulic composition and a method for producing a hardened product of the hydraulic composition.

[0002] Steam curing is typically used to improve the productivity of concrete products. However, steam-cured concrete tends to have reduced strength (especially long-term strength) and durability compared to conventionally cured concrete. This tendency is more pronounced the shorter the curing time before steam curing (hereinafter also referred to as "pre-setting time"). Patent Document 1 describes a method for shortening concrete production time: a segment production method in which high-fluidity concrete is poured into a formwork, hardened until the high-fluidity concrete is self-supporting and ready for surface finishing, and then the cover formwork is removed and the surface is finished. The method further includes adding a hardening accelerator to the high-fluidity concrete to accelerate its hardening. Patent Document 2 describes acid-resistant concrete produced by blending water, industrial by-products, an alkali activator, an expansive additive, fine aggregate, coarse aggregate, and a high-range water-reducing agent and compacting the mixture using centrifugal molding. It also describes that the acid-resistant concrete can shorten the steam curing time (pre-setting time) by centrifugal molding compared to vibration molding.

[0003] JP 2007-69366 A International Publication No. 2019 / 172349

[0004] Measures for improving strength (especially long-term strength) and durability include extending the pre-setting time and performing moist curing by spraying water after steam curing. However, extending the pre-setting time delays the time for demolding, which reduces production efficiency. Furthermore, moist curing can cause uneven color on the product surface, resulting in poor appearance. The object of the present invention is to provide a hydraulic composition and a method for producing a hardened product of the hydraulic composition that can improve production efficiency by shortening the pre-setting time in the production of hardened products such as concrete that are subjected to steam curing, and that can produce hardened products such as concrete with excellent strength even with a shortened pre-setting time, and that can reduce carbon dioxide emissions by using a carbonated cement hydrate obtained by fixing carbon dioxide in part of the cement or cement hydrate in the raw materials.

[0005] As a result of intensive research to solve the above problems, the present inventors have found that the above objects can be achieved by a hydraulic composition containing cement, carbonated cement hydrate, aggregate, and water, wherein the proportion of the carbonated cement hydrate is 1 to 50 mass% out of a total of 100 mass% of the cement and the carbonated cement hydrate, and the amount of water is 30 to 60 mass parts per 100 mass parts of the cement and the carbonated cement hydrate, and have completed the present invention. That is, the present invention provides the following [1] to [7]. [1] A hydraulic composition containing cement, carbonated cement hydrate, aggregate, and water, wherein the proportion of the carbonated cement hydrate is 1 to 50 mass% out of a total of 100 mass% of the cement and the carbonated cement hydrate, and the amount of the water is 30 to 60 mass parts per 100 mass parts of the cement and the carbonated cement hydrate. [2] The hydraulic composition according to [1], wherein the hydraulic composition contains fine aggregate and coarse aggregate as the aggregate, and the fine aggregate ratio is 35 to 65%.

[0006] [3] a mixing step of mixing the carbonated cement hydrate-containing material with a second cement, a second water, and the aggregate to obtain the unset hydraulic composition; a molding step of casting the unset hydraulic composition into a formwork to obtain an unset compact; a pre-curing step of pre-curing the unset compact in an atmosphere at a temperature of 10 to 40°C for 0.1 to 5 hours; a steam curing step of steam-curing the pre-cured compact to obtain a hardened compact; and a demolding step of demolding the hardened compact from the formwork to obtain a hardened product of the hydraulic composition. [4] A method for producing a hardened product of the hydraulic composition according to [3] above, comprising a water adjusting step between the carbonation step and the mixing step, for adjusting the water ratio contained in the carbonated cement hydrate-containing material. [5] A method for producing a hardened product of the hydraulic composition according to [3] or [4] above, wherein the proportion of water contained in the carbonated cement hydrate-containing material is 0 to 95 mass% out of a total of 100 mass% of the water contained in the carbonated cement hydrate-containing material and the second water. [6] A method for producing a hardened product of the hydraulic composition according to any of [3] to [5] above, wherein in the cement hydrate slurry preparation step, the mass ratio of the first water to at least one of the first cement and cement hydrate (the first water / at least one of the first cement and cement hydrate) is 1.0 to 5.0. [7] A method for producing a hardened product of the hydraulic composition according to any of [3] to [6] above, wherein in the steam curing step, steam curing is performed in an atmosphere at a temperature of 40 to 80°C for 3 hours or more.

[0007] According to the hydraulic composition and the method for producing a hardened product of the hydraulic composition of the present invention, in the production of hardened products such as concrete that are subjected to steam curing, the production efficiency can be improved by shortening the pre-setting time, and hardened products such as concrete that have excellent strength can be produced even with a short pre-setting time. Furthermore, by using carbonated cement hydrate obtained by fixing carbon dioxide as part of the raw materials, carbon dioxide emissions can be reduced.

[0008] FIG. 2 is a diagram showing temperature histories in an example of the present invention and a comparative example.

[0009] The hydraulic composition of the present invention is a hydraulic composition containing cement, carbonated cement hydrate, aggregate, and water, wherein the proportion of carbonated cement hydrate is 1 to 50 mass% out of a total of 100 mass% of the cement and carbonated cement hydrate, and the amount of water is 30 to 60 mass parts per 100 mass parts of the total of the cement and carbonated cement hydrate. This will be explained in detail below. Examples of cement include various Portland cements such as ordinary Portland cement, high-early-strength Portland cement, moderate-heat Portland cement, low-heat Portland cement, and sulfate-resistant Portland cement; blended cements such as blast-furnace cement, fly ash cement, and silica cement; alumina cement; and ecocement. These may be used alone or in combination of two or more.

[0010] Carbonated cement hydrate is obtained by carbonating cement or cement hydrate. In this specification, "carbonation" refers to absorbing and fixing carbon dioxide. As the cement hydrate, for example, a hardened product of a cement composition containing cement hydrate, such as fresh concrete sludge, lightweight aerated concrete scraps, and waste concrete, may be used. The cement hydrate is in a powder form similar to that of cement. Carbonated cement hydrate includes calcium silicate hydrate (CaO-SiO ２ -H ２ O), calcium hydroxide (Ca(OH) ２ ), ettringite (3CaO·Al ２ O ３ 3CaSO４・ 32H ２ O), calcium aluminate hydrate (3Ca·Al ２ O ３ ・6H ２ O), and monosulfate hydrate (3CaO·Al ２ O ３ CaSO ４ ・12H ２ O) and the like. The carbonated cement hydrate can be obtained by a cement hydrate slurry preparation step and a carbonation step, which will be described later. The hydraulic composition of the present invention may contain cement hydrate that remains without being carbonated. The hydraulic composition of the present invention uses carbonated cement hydrate obtained by fixing carbon dioxide in cement or cement hydrate as part of the raw materials, and therefore can reduce carbon dioxide emissions.

[0011] The proportion of carbonated cement hydrate in a total of 100% by mass of cement and carbonated cement hydrate is 1 to 50% by mass, preferably 5 to 45% by mass, more preferably 8 to 43% by mass, even more preferably 12 to 40% by mass, and particularly preferably 20 to 37% by mass. If the proportion is 1% by mass or less, the strength development of the hydraulic composition (particularly when the pre-setting time during curing is shortened) decreases. Also, the reduction in carbon dioxide emissions decreases. If the proportion exceeds 50% by mass, the strength (e.g., compressive strength) of the set product of the hydraulic composition decreases, and the viscosity of the hydraulic composition before hardening increases.

[0012] The aggregate may be fine aggregate alone or a combination of fine and coarse aggregate. Natural aggregate, artificial aggregate, or recycled aggregate may all be used. The fine aggregate is not particularly limited, and examples thereof include river sand, mountain sand, land sand, sea sand, crushed sand, silica sand, limestone aggregate, slag fine aggregate, lightweight fine aggregate, clinker fine aggregate, and CCU fine aggregate (fine aggregate in which carbon dioxide is fixed from one or more materials selected from recycled aggregate, waste concrete, blast furnace slab, and steelmaking slag). These may be used alone or in combination of two or more.

[0013] The coarse aggregate is not particularly limited, and examples thereof include river gravel, mountain gravel, land gravel, sea gravel, crushed stone, limestone aggregate, slag coarse aggregate, lightweight coarse aggregate, clinker coarse aggregate, and CCU coarse aggregate (coarse aggregate in which carbon dioxide is fixed in one or more materials selected from recycled aggregate, waste concrete, blast furnace slab, and steelmaking slag), etc. These may be used alone or in combination of two or more.

[0014] When the hydraulic composition contains fine aggregate and coarse aggregate as aggregates, the fine aggregate ratio (s / a) is preferably 35 to 65%, more preferably 40 to 60%, and particularly preferably 43 to 50%. When the fine aggregate ratio is within the above range, the workability and ease of molding of mortar or concrete are improved. The fine aggregate ratio is the ratio of the volume of fine aggregate to the total volume of fine aggregate and coarse aggregate. The aggregate content in the hydraulic composition (the total amount when both fine aggregate and coarse aggregate are contained) is preferably 200 to 750 parts by mass, more preferably 300 to 650 parts by mass, per 100 parts by mass of the total of cement and carbonated cement hydrate. When the content is within the above range, the strength of the set body of the hydraulic composition is increased and the shrinkage rate of the set body is reduced.

[0015] The water is not particularly limited, and examples include tap water, industrial water, and sludge water. The amount of water is 30 to 60 parts by mass, preferably 35 to 55 parts by mass, and particularly preferably 40 to 52 parts by mass, per 100 parts by mass of the total of cement and carbonated cement hydrate. If the amount is less than 30 parts by mass, the fluidity of the hydraulic composition before hardening decreases, resulting in poor workability. If the amount exceeds 60 parts by mass, the strength of the hardened product of the hydraulic composition decreases. The hydraulic composition of the present invention may optionally contain cement dispersants such as water-reducing agents, air-entraining water-reducing agents, high-performance water-reducing agents, and high-performance air-entraining water-reducing agents, as well as various admixtures such as air-entraining agents, and various admixtures such as silica fume, fly ash, and ground granulated blast furnace slag, within ranges that do not impair the object of the present invention.

[0016] When a carbonated slurry (a mixture of carbonated cement hydrate and water) is used as a raw material, the water contained in the carbonated slurry is considered to be included in the above-mentioned water. Furthermore, when a carbonated slurry is used as a raw material, the proportion of water derived from the carbonated slurry in the total amount of water (100% by mass) contained in the hydraulic composition is preferably 55 to 95% by mass, more preferably 58 to 90% by mass, even more preferably 60 to 80% by mass, and particularly preferably 65 to 70% by mass. When the proportion is 55% by mass or more, the strength of the set product of the hydraulic composition can be increased. When the proportion is 95% by mass or less, the amount of air contained in the cement composition increases, improving the fluidity of the hydraulic composition before hardening.

[0017] The hydraulic composition of the present invention is suitable for a method in which steam curing is performed when producing a hardened product of the hydraulic composition, since it exhibits excellent strength development even when the pre-setting time is shortened in the process of producing a hardened product of the hydraulic composition. Examples of the method for producing a hardened product of the hydraulic composition of the present invention include: (A) a cement hydrate slurry preparation step of mixing at least one of a first cement and a cement hydrate with first water to obtain a cement hydrate slurry; (B) a carbonation step of supplying carbon dioxide gas into the cement hydrate slurry to obtain a carbonated cement hydrate-containing material; (C) a mixing step of mixing the carbonated cement hydrate-containing material, a second cement, second water, and an aggregate to obtain the unhardened hydraulic composition; (D) a molding step of casting the unhardened hydraulic composition into a formwork to obtain an unhardened molded body; (E) a pre-curing step of pre-curing the unhardened molded body for 0.1 to 5 hours in an atmosphere at a temperature of 10 to 40°C; (F) a steam curing step of steam-curing the pre-cured molded body to obtain a hardened molded body; and (G) a demolding step of demolding the hardened molded body from the formwork to obtain a hardened product of the hydraulic composition. Each step will be explained in detail below.

[0018] [Step (A): Cement Hydrate Slurry Preparation Step] Step (A) is a step of mixing at least one of a first cement and a cement hydrate with first water to obtain a cement hydrate slurry. The first cement, cement hydrate, and first water are not particularly limited, and the same cement, cement hydrate, and water as those contained in the hydraulic composition described above can be used. The mass ratio of the first water to at least one of the first cement and cement hydrate in the cement hydrate slurry (water-solid ratio: first water / at least one of the first cement and cement hydrate) is preferably 1.0 to 5.0, more preferably 1.5 to 4.5, and particularly preferably 2.5 to 3.5. When this ratio is 1.0 or more, the fluidity of the cement hydrate slurry is improved, and carbon dioxide gas can be more easily and uniformly supplied into the cement hydrate slurry in the carbonation step described below. If the ratio is 5.0 or less, carbonation of the first cement or cement hydrate contained in the cement hydrate slurry can be further promoted. The method of mixing the first water with at least one of the first cement and cement hydrate and is not particularly limited, and for example, the first water may be introduced into a stirring tank or the like, and then at least one of the first cement and cement hydrate may be introduced, or the first water and at least one of the first cement and cement hydrate may be introduced into a stirring tank or the like simultaneously, and then mixed.

[0019] [Step (B): Carbonation Step] Step (B) is a step of supplying carbon dioxide gas into the cement hydrate slurry obtained in the cement hydrate slurry preparation step to obtain a carbonated cement hydrate-containing material. In this specification, the term "carbonated cement hydrate-containing material" includes (i) a slurry in which carbonated cement hydrate particles are suspended in water (also referred to as "carbonation slurry"); (ii) a material containing carbonated cement hydrate and water but lacking fluidity; and (iii) a powdery carbonated cement hydrate obtained by removing water in the water adjustment step described below. Carbon dioxide gas is preferably supplied while stirring the cement hydrate slurry, from the viewpoints of being able to supply carbon dioxide gas uniformly into the cement hydrate slurry and shortening the time required for the carbonation treatment. Specifically, a method of supplying carbon dioxide gas while stirring the cement hydrate slurry may be exemplified, in which a carbon dioxide gas supplying means for supplying carbon dioxide gas is installed in a stirring tank for containing and stirring the cement hydrate slurry, and carbon dioxide gas is supplied while stirring the cement hydrate slurry in the stirring tank.

[0020] Carbon dioxide gas is supplied until the pH of the cement hydrate slurry falls within a range of preferably 9.0 or less, more preferably 5.0 to 8.0, even more preferably 5.5 to 7.5, and particularly preferably 6.0 to 6.8. By supplying carbon dioxide gas until the pH falls within a range of 9.0 or less, the cement contained in the cement hydrate slurry can be sufficiently carbonated, thereby preparing a cement hydrate slurry containing carbonated cement hydrate. The carbon dioxide gas supply time required to sufficiently carbonate the cement contained in the cement hydrate slurry varies depending on the mass ratio of the first water to at least one of the first cement and cement hydrate, the carbon dioxide concentration of the carbon dioxide-containing gas, the amount of carbon dioxide gas supplied per unit time, and the like. Therefore, the timing for terminating the carbon dioxide gas supply is preferably determined based on the actual measured pH of the cement hydrate slurry.

[0021] Carbon dioxide may be supplied as a gas consisting solely of carbon dioxide, or may be supplied to the cement hydrate slurry as a gas containing carbon dioxide from the viewpoint of ease of availability, etc. The proportion of carbon dioxide in the carbon dioxide-containing gas is preferably 5 vol% or more, more preferably 20 vol% or more, even more preferably 50 vol% or more, even more preferably 80 vol% or more, and particularly preferably 90 vol% or more. When the proportion is 5 vol% or more, the time required to obtain a cement hydrate slurry by sufficiently carbonating the cement can be shortened. Examples of carbon dioxide-containing gases include exhaust gas generated in a cement production process (carbon dioxide concentration: approximately 20 vol%), exhaust gas generated in a steelmaking process (carbon dioxide concentration: approximately 20 vol%), exhaust gas generated in a thermal power generation process (carbon dioxide concentration: approximately 10 vol%), and gases separated and recovered from these exhaust gases (carbon dioxide concentration: approximately 100 vol%).

[0022] After preparing the carbonated cement hydrate-containing material, the carbonated cement hydrate-containing material may be temporarily stored in a separate storage tank for storing the carbonated cement hydrate-containing material (e.g., carbonated slurry), and when performing the mixing step (described later), the carbonated cement hydrate-containing material may be appropriately transferred to a mixing tank for performing mixing.

[0023] [Step (H): Moisture Adjustment Step] Step (H) is an optional step between the carbonation step and the mixing step, and is a step for adjusting the moisture content of the carbonated cement hydrate-containing material. Methods for adjusting the moisture content of the carbonated cement hydrate-containing material (usually a carbonation slurry) include removing moisture using solid-liquid separation means such as a sedimentation separator, vacuum dehydrator, or pressure dehydrator, heating the carbonated cement hydrate-containing material to evaporate the moisture, and adding and mixing water to the carbonated cement hydrate-containing material in order to increase the water content. Alternatively, the carbonated cement hydrate-containing material (usually a carbonation slurry) may be dried using methods such as natural drying, hot air drying, vacuum drying, cooling drying, infrared drying, freeze drying, and contact drying to obtain a powder of only carbonated cement hydrate.

[0024] [Step (C): Mixing Step] Step (C) is a step of mixing the carbonated cement hydrate-containing material obtained in the carbonation step or the optional water adjustment step with a second cement, second water, and aggregate to obtain an unset hydraulic composition. When the hydraulic composition contains various admixtures and additives, these are typically mixed in this step. The second cement and second water are not particularly limited, and the same cement and water as those contained in the hydraulic composition described above can be used. The method of mixing the carbonated cement hydrate-containing material, second cement, second water, and aggregate is not particularly limited. For example, after the carbonated cement hydrate-containing material is introduced into a mixer, the ingredients other than the carbonated cement hydrate-containing material may be introduced and mixed separately, or the ingredients may be introduced into the mixer and mixed simultaneously. The amounts of each ingredient may be appropriately determined so that the hydraulic composition obtained in this step has the blending ratio of each ingredient of the hydraulic composition of the present invention described above.

[0025] The proportion of water contained in the carbonated cement hydrate-containing composition, out of a total of 100% by mass of the water and second water contained in the carbonated cement hydrate-containing composition, is preferably 0 to 95% by mass, more preferably 55 to 92% by mass, even more preferably 58 to 90% by mass, even more preferably 60 to 80% by mass, and particularly preferably 65 to 70% by mass. If the proportion is 55% by mass or more, the strength of the set body of the hydraulic composition can be increased. If the proportion is 95% by mass or less, the amount of air contained in the cement composition increases, improving the fluidity of the hydraulic composition before hardening.

[0026] [Step (D): Molding Step] Step (D) is a step of casting the uncured hydraulic composition obtained in the mixing step into a formwork to obtain an uncured molded body. [Step (E): Pre-curing Step] Step (E) is a step of pre-curing (air curing) the uncured molded body obtained in the molding step for 0.1 to 5 hours in an atmosphere at a temperature of 10 to 40°C (preferably 15 to 35°C). The pre-curing time is 0.1 to 5 hours, preferably 0.2 to 4 hours, more preferably 0.5 to 3 hours, and particularly preferably 0.5 hours or more but less than 1 hour. If the pre-curing time is 0.1 hours or more, the strength of the cured body of the hydraulic composition can be increased. If the pre-curing time is 5 hours or less, production efficiency can be improved.

[0027] [Step (F): Steam Curing Step] Step (F) is a step in which the pre-cured molded body is steam-cured to obtain a hardened molded body. Steam curing is preferably carried out in a temperature atmosphere of 40 to 80°C (more preferably 45 to 75°C, particularly preferably 55 to 70°C) for 3 hours or more (more preferably 4 to 12 hours, even more preferably 5 to 10 hours, particularly preferably 6 to 9 hours). Steam curing is carried out by raising the temperature from the temperature atmosphere after the pre-curing step to a desired maximum temperature, maintaining the maximum temperature preferably for 2 to 6 hours, and then lowering the temperature to room temperature (for example, about 20°C). The heating rate when raising the temperature atmosphere to the desired maximum temperature is preferably 10 to 30°C / hour, more preferably 15 to 25°C / hour, from the viewpoint of further improving the strength development and productivity of the concrete. From the viewpoint of further improving the strength development and productivity of concrete, the maximum temperature is preferably 50 to 80°C, more preferably 55 to 70°C, and the time for which the maximum temperature is maintained is preferably 2 to 6 hours, more preferably 3 to 5 hours. The temperature is usually lowered to room temperature at a natural cooling rate (natural cooling). Steam curing may be atmospheric pressure steam curing carried out under atmospheric pressure, or high-temperature, high-pressure steam curing carried out under pressure higher than atmospheric pressure using an autoclave. [Step (G): Demolding Step] Step (G) is a step in which the hardened molded body after steam curing is demolded from the formwork to obtain a hardened body of the hydraulic composition.

[0028] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. [Materials Used] (1) Cement: Ordinary Portland cement manufactured by Taiheiyo Cement Corporation (2) Fine aggregate: Mountain sand (3) Coarse aggregate: Crushed stone (4) Water: Tap water (5) Cement hydrate: Pulverized ready-mixed concrete sludge

[0029] [Examples 1 to 6, 8 to 11] A cement (first cement) and water were mixed in amounts such that the water-solid ratio (the mass ratio of the first water to the first cement (first water / first cement), or the mass ratio of the total amount of the first water and the water in the cement hydrate-containing material to the solids in the cement hydrate-containing material (the total amount of the first water and the water in the cement hydrate-containing material / the solids in the cement hydrate-containing material), shown as "water-solid-liquid ratio" in Table 1; the same applies hereinafter) would satisfy the values ​​shown in Table 1, to obtain a cement hydrate slurry. A carbonation treatment was carried out by blowing a carbon dioxide-containing gas having a carbon dioxide content of 99% by volume or more into the obtained cement hydrate slurry, thereby obtaining a carbonated slurry containing carbonated cement hydrate in which the cement was sufficiently carbonated. The carbonation treatment was carried out until the pH of the carbonated slurry reached 6.5. The contents (mass%) of water and carbonated cement hydrate contained in the carbonated slurry were measured using an infrared moisture meter (manufactured by Kett Electric Laboratory), and water was removed to adjust the mass ratio of water to carbonated cement hydrate in the carbonated slurry (the water / carbonated cement hydrate: shown as "slurry water / carbonated cement hydrate" in Table 1) to the values ​​shown in Table 1. A hydraulic composition was obtained by mixing the carbonated slurry (a slurry containing carbonated cement hydrate and first water), cement (second cement), water (second water: shown as "mixed water" in Table 1), fine aggregate, and coarse aggregate in the unit amounts shown in Table 1. In Table 1, the water contained in the carbonated slurry is shown as "slurry water." After mixing, the hydraulic composition was poured into a formwork and then subjected to air curing at 20°C for the pre-setting time shown in Table 2. Next, the temperature was raised to 60°C at a temperature rise rate of 20°C / hour, and then the maximum temperature (60°C) was maintained for 3 hours, followed by a temperature drop rate of 4.5°C / hour to 20°C (see Figure 1). After steam curing, the composition was demolded to obtain a hardened hydraulic composition. The compressive strength of the hardened composition was measured at 1 day and 14 days in accordance with JIS A 1108:2018 (Method for compressive testing of concrete).

[0030] [Example 7] A cement hydrate slurry obtained by mixing water and cement (first cement) so that the water-to-solid ratio was 3.0 was carbonated, and then the carbonated slurry was dried by hot air drying to remove water, thereby obtaining carbonated cement hydrate. A hardened product of the hydraulic composition was obtained in the same manner as in Example 1, except that the carbonated cement hydrate was used instead of the carbonated slurry, and the compressive strength of the hardened product was measured at 1 day and 14 days of age. [Examples 12 and 13] A hardened product of the hydraulic composition was obtained in the same manner as in Example 1, except that cement hydrate (pulverized ready-mixed concrete sludge) was used instead of cement (first cement) to obtain a cement hydrate slurry, and the compressive strength of the hardened product was measured at 1 day and 14 days of age.

[0031] [Comparative Examples 1 to 6] Cement, water ("mixed water" in Table 1), fine aggregate, and coarse aggregate were mixed in the amounts shown in Table 1 to obtain a hydraulic composition, and the compressive strength of the hardened body at 1 day and 14 days of age was measured in the same manner as in Example 1, except that the pre-setting time was set to the time shown in Table 2. [Comparative Example 7] A cement hydrate slurry was prepared by mixing cement (first cement) and water in amounts such that the water-solid ratio of the cement hydrate slurry was set to the value shown in Table 1, and the cement hydrate slurry was subjected to a carbonation treatment. The mass ratio of water to carbonated cement hydrate in the carbonated slurry was adjusted to the value shown in Table 1, and the pre-setting time was set to the time shown in Table 2. A hardened body of the hydraulic composition was obtained in the same manner as in Example 1, and the compressive strength of the hardened body at 1 day and 14 days of age was measured.

[0032] [Comparative Example 8] A hardened hydraulic composition was obtained in the same manner as in Comparative Example 7, except that ground fresh concrete sludge (cement hydrate) was used instead of cement (first cement). The compressive strength of the hardened hydraulic composition was then measured at ages of 1 day and 14 days. For Examples 1 to 7, 12 to 13, and Comparative Examples 7 to 8, the compressive strength at each age of the reference Comparative Example was calculated using Comparative Example 1 as the reference (referred to as "strength ratio to reference Comparative Example" in Table 2). Furthermore, the compressive strength ratio was calculated in the same manner using Comparative Example 3 for Example 8, Comparative Example 4 for Example 9, Comparative Example 5 for Example 10, and Comparative Example 6 for Example 11 as the reference. The results are shown in Table 2.

[0033]

[0034]

[0035] From Table 2, it can be seen that the compressive strengths of Examples 1 to 13 are greater than those of the comparative examples (same pre-setting time and W / C), and that the hydraulic composition of the present invention can further increase the strength of the hardened body. In particular, it can be seen that the strength of the hardened body can be further increased even when the pre-setting time is 0.5 to 1 hour (Examples 8 and 9).

Claims

1. A hydraulic composition comprising cement, carbonated cement hydrate, aggregate, and water, wherein the proportion of the carbonated cement hydrate is 1 to 50 mass% out of a total of 100 mass% of the cement and the carbonated cement hydrate, and the amount of water is 30 to 60 mass parts per 100 mass parts of the cement and the carbonated cement hydrate.

2. The hydraulic composition according to claim 1, wherein the hydraulic composition contains fine aggregate and coarse aggregate as the aggregate, and the fine aggregate ratio is 35 to 65%.

3. A method for producing a hardened product of the hydraulic composition according to claim 1 or 2, comprising: a cement hydrate slurry preparation step of mixing at least one of a first cement and a cement hydrate with first water to obtain a cement hydrate slurry; a carbonation step of supplying carbon dioxide gas into the cement hydrate slurry to obtain a carbonated cement hydrate-containing material; a mixing step of mixing the carbonated cement hydrate-containing material, a second cement, second water and the aggregate to obtain the unhardened hydraulic composition; a molding step of casting the unhardened hydraulic composition into a form to obtain an unhardened green body; a pre-curing step of pre-curing the unhardened green body for 0.1 to 5 hours in an atmosphere at a temperature of 10 to 40°C; a steam curing step of steam-curing the pre-cured green body to obtain a hardened green body; and a demolding step of demolding the hardened green body from the form to obtain a hardened product of the hydraulic composition. A method for producing a hardened product of a hydraulic composition comprising the above compound.

4. A method for producing a hardened product of the hydraulic composition according to claim 3, comprising a water adjusting step, which is provided between the carbonation step and the mixing step, and which adjusts the water content of the carbonated cement hydrate-containing material.

5. A method for producing a hardened product of a hydraulic composition according to claim 3, wherein the proportion of water contained in the carbonated cement hydrate-containing material is 0 to 95 mass % out of a total of 100 mass % of the water contained in the carbonated cement hydrate-containing material and the second water.

6. A method for producing a hardened product of a hydraulic composition according to claim 3, wherein in the cement hydrate slurry preparation step, the mass ratio of the first water to at least one of the first cement and cement hydrate (the first water / at least one of the first cement and cement hydrate) is 1.0 to 5.

0.

7. The method for producing a hardened hydraulic composition according to claim 3, wherein the steam curing step is carried out in an atmosphere having a temperature of 40 to 80°C for 3 hours or more.

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