JP7350686B2 - Cement composition and method for producing hardened cementitious body - Google Patents

Description

The present invention relates to a cement composition and a method for producing a hardened cementitious body.

Ettringite, which is a type of cement hydrate, expands in volume in a hardened cementitious body such as concrete, which may cause cracks in the hardened cementitious body. This deterioration phenomenon is called DEF (Delayed Ettringite Formation).
Examples of conditions under which DEF occurs are (i) excessive sulfate content in the cement, (ii) high temperature curing (e.g. atmospheric pressure steam curing with a maximum temperature of 70°C or higher); (iii) exposure to a high humidity environment, etc. When multiple of these conditions overlap, the risk of DEF occurring increases.
As a method for repairing concrete cracked by DEF, Patent Document 1 describes a method for repairing concrete that includes the following steps (A) and (B).
(A) A step of heating concrete that has cracked due to delayed formation of ettringite to 70 to 150°C. (B) An infiltration step of applying or permeating a water repellent and/or impregnating agent into the heated concrete.

Japanese Patent Application Publication No. 2016-186158

Generally, cement contains gypsum for the purpose of controlling setting. If a cement that does not contain gypsum (that is, a cement that does not contain sulfates) is used, DEF is less likely to occur in the hardened cementitious body containing the cement. However, with cement that does not contain gypsum, when it comes in contact with water, the aluminate phase of the cement rapidly hydrates, causing stiffness (pseudo-setting). The problem is that it cannot be done.
The purpose of the present invention is to eliminate the use of gypsum or to use a small amount of gypsum (specifically, 0 to 0.5 parts by mass in terms of _SO3 per 100 parts by mass of cement clinker powder). A cement composition that is less likely to stiffen and maintain good fluidity before hardening, and less likely to cause DEF after hardening, and a cementitious hardened product using the cement composition. An object of the present invention is to provide a manufacturing method.

As a result of intensive studies to solve the above problems, the present inventors found that at least one of cement clinker powder, limestone powder with a Blaine specific surface area of 7,000 cm ² /g or more, a high performance water reducing agent, and a high performance AE water reducing agent. A high-performance water reducing agent and a high-performance AE containing either one, the ratio of limestone powder in the total amount of cement clinker powder and limestone powder is 1 to 6% by mass, and the total amount of cement clinker powder and limestone powder is 100 parts by mass. The amount of at least one of the water reducing agents is 0.1 to 1.5 parts by mass in terms of solid content, and the proportion of sulfur compounds in the cement composition is 0.1 to 1.0 in terms of _SO3 . The inventors have discovered that the above object can be achieved by using a cement composition with a specific mass %, and have completed the present invention.
That is, the present invention provides the following [1] to [6].
[1] A cement composition comprising cement clinker powder, limestone powder having a Blaine specific surface area of 7,000 cm ² /g or more, and at least one of a high-performance water reducer and a high-performance AE water reducer, the cement composition comprising: The ratio of the limestone powder in the total amount of the clinker powder and the limestone powder is 1 to 6% by mass, and the high performance water reducing agent and the high performance AE water reducing agent are based on the total of 100 parts by mass of the cement clinker powder and the limestone powder. The amount of at least one of the above is 0.1 to 1.5 parts by mass in terms of solid content, and the proportion of the sulfur compound in the cement composition is 0.1 to 1.0 parts by mass in terms of _SO3 . %.
[2] The cement composition described in [1] above, wherein the amount of gypsum contained in the cement composition is 0 to 0.5 parts by mass in terms of SO ₃ based on 100 parts by mass of the cement clinker powder. cement composition.
[3] The above-mentioned [1] further contains a hardening accelerator in an amount of 0.2 to 1.2 parts by mass in terms of solid content, based on a total of 100 parts by mass of the cement clinker powder and the limestone powder. The cement composition according to [2].
[4] A hardened cementitious body, which is a hardened body of a mixture containing the cement composition according to any one of [1] to [3] above and water.
[5] A preparation step of mixing the cement composition according to any one of [1] to [3] above with water to obtain a mixture, and steam curing the mixture at a temperature of 55° C. or higher for 1 hour or more. a steam curing step for obtaining a mixture after steam curing; and a curing step for curing the mixture after steam curing to harden the mixture to obtain a cementitious hardened body. A method for producing a characteristic hardened cementitious material.
[6] The method for producing a hardened cementitious body according to the above [5], wherein the steam curing in the steam curing step is normal pressure steam curing.

According to the cement composition of the present invention and the method for producing a cementitious hardened body using the cement composition, gypsum is not used or the amount of gypsum (specifically, 100 mass of cement clinker powder) is used. Despite the low content of 0 to 0.5 parts by mass (calculated as SO ₃ ), stiffness does not easily occur before curing and good fluidity can be maintained, and after curing , it is possible to obtain a cementitious hardened body in which DEF is less likely to occur.

The cement composition of the present invention is a cement composition containing cement clinker powder, limestone powder having a Blaine specific surface area of 7,000 cm ² /g or more, and at least one of a high performance water reducer and a high performance AE water reducer. The ratio of limestone powder in the total amount of cement clinker powder and limestone powder is 1 to 6% by mass, and the amount of high performance water reducing agent and high performance AE water reducing agent is 1 to 6% by mass. The amount of at least one of them is 0.1 to 1.5 parts by mass in terms of solid content, and the proportion of the sulfur compound in the cement composition is 0.1 to 1.0 parts by mass in terms of _SO3 . It is something.

Examples of cement clinkers include various types of Portland cement clinker, such as ordinary Portland cement clinker, early strength Portland cement clinker, moderate heat Portland cement clinker, and low heat Portland cement clinker.
The Blaine specific surface area of the cement clinker powder is preferably 2,000 to 10,000 cm ² /g, more preferably 2,500 to 8,000 cm ² /g, particularly preferably 3,000 to 6,000 cm ² /g. be. When the Blaine specific surface area is 2,000 cm ² /g or more, the strength development of the cement composition is further improved. When the Blaine specific surface area is 10,000 cm ² /g or less, the fluidity of the cement composition is further improved.

The Blaine specific surface area of the limestone powder is 7,000 cm ² /g or more, preferably 8,000 to 30,000 cm ² /g, more preferably 9,000 to 26,000 cm ² /g, particularly preferably 10,000 to 10,000 cm 2 /g. It is 24,000 cm ² /g. If the Blaine specific surface area is less than 7,000 cm ² /g, the strength development of the cement composition will decrease. If the Blaine specific surface area is 30,000 cm ² /g or less, the labor required to crush limestone can be reduced.
The proportion of limestone powder in the total amount (100% by weight) of cement clinker powder and limestone powder is 1 to 6% by weight, preferably 1.5 to 5% by weight, particularly preferably 2 to 4.5% by weight. . When the above ratio is less than 1% by mass, stiffness occurs after kneading the cement composition and water, resulting in decreased workability. If the above ratio exceeds 6% by mass, the strength development of the cement composition will decrease.

The high performance water reducing agent and high performance AE water reducing agent may be those commonly used as admixtures for mortar and concrete, such as naphthalene sulfonic acid, melamine, polycarboxylic acid, etc. High performance water reducers or high performance AE water reducers may be mentioned. Among these, from the viewpoint of further improving the fluidity of the cement composition, polycarboxylic acid-based high-performance water reducers or high-performance AE water-reducing agents are preferred, and polycarboxylic acid ether-based high-performance water reducers or high-performance AE water reducers are preferred. More preferred.
The amount of at least one of the high performance water reducer and the high performance AE water reducer based on a total of 100 parts by mass of the cement clinker powder and the limestone powder (if the cement composition contains both the high performance water reducer and the high performance AE water reducer) (if it contains, the total amount) is 0.1 to 1.5 parts by mass in terms of solid content, preferably 0.15 to 1.0 parts by mass, more preferably 0.2 to 0.8 parts by mass, Particularly preferably, the amount is 0.2 to 0.6 parts by mass, and is used in place of kneading water. If the amount is less than 0.1 part by mass, the fluidity of the cement composition will decrease. If the amount exceeds 1.5 parts by mass, the cost will be excessive.

The amount of gypsum contained in the cement composition is preferably 0 to _0.5 parts by mass, more preferably 0 to 0.3 parts by mass, and even more preferably is 0 to 0.2 part by weight, more preferably 0 to 0.1 part by weight, particularly preferably 0 part by weight. When the amount exceeds 0.5 part by mass, stiffness (pseudo-setting) is less likely to occur, and the desired fluidity can be maintained until the driving is completed without adding limestone powder. However, if the amount exceeds 0.5 parts by mass, the amount of sulfur compounds in the cement composition will increase, increasing the risk of cracks occurring in the hardened cementitious material due to delayed formation of ettringite.

The proportion of sulfur compounds in the cement composition of the present invention is 0.1 to 1.0% by mass, preferably 0.15 to 0.8% by mass, more preferably 0.2 to 0.0% by mass in terms of _SO3 . .6% by weight, particularly preferably 0.25-0.5% by weight. Cement compositions in which the above proportion is less than 0.1% by mass are difficult to manufacture. If the above ratio exceeds 1.0% by mass, the risk of cracking due to delayed formation of ettringite increases.
Examples of sulfur compounds in the cement composition include sulfur, sulfur trioxide, and the like. Note that the above ratio of sulfur compounds includes both sulfur compounds derived from gypsum and sulfur compounds derived from cement clinker powder.

The cement composition of the present invention may further contain a hardening accelerator from the viewpoint of promoting hydration and shortening the curing time.
The curing accelerator may be one commonly used as an admixture for mortar or concrete, such as nitrite-based, thiocyanate-based, sulfate-based, thiosulfate-based, chloride-based, Examples include carbonate-based and alumina-based hardening accelerators. Among these, nitrite-based curing accelerators are preferred, and calcium nitrite-based curing accelerators are more preferred, from the viewpoint of being able to speed up the initial setting time without reducing fluidity.
The amount of hardening accelerator is preferably 0.2 to 1.2 parts by mass, more preferably 0.4 to 1.0 parts by mass in terms of solid content, based on a total of 100 parts by mass of cement clinker powder and limestone powder. The amount is particularly preferably 0.6 to 0.9 parts by mass, and is used in place of kneading water. If the above amount is 0.2 parts by mass or more, the strength development of the cement composition will improve, so that the desired strength can be achieved in a pre-curing period of about 1 to 4 hours (the time required for general pre-curing). A hardened cementitious body can be obtained. If the amount is 1.2 parts by mass or less, costs can be reduced.
Note that in this specification, the cement composition does not include paste, mortar, or other materials for preparing concrete (fine aggregate, coarse aggregate, water, etc.).

The hardened cementitious body of the present invention is a hardened body (specifically, paste, mortar, or concrete) of a mixture containing the above-mentioned cement composition, water, and other materials blended as necessary. . The cementitious hardened body can be obtained by mixing the cement composition with water and the like.
An example of a method for producing a cementitious hardened body using the cement composition of the present invention includes a preparation step of mixing the above-mentioned cement composition and water to obtain a mixture, and a step of heating the obtained mixture at 55°C or higher. A steam curing step in which the mixture is steam-cured at a temperature of 1 hour or more to obtain a mixture after steam curing, and the mixture after steam curing is cured to harden the mixture to obtain a cementitious hardened body. Examples include those including a curing step.
Each step will be explained in detail below.

[Preparation process]
This step is a step in which the above-mentioned cement composition, water, and other materials blended as necessary are mixed to obtain a mixture.
The mixer used to mix each material is not particularly limited, and conventional mixers such as a pan-type mixer and a twin-screw mixer can be used.
The amount of water blended is not particularly limited, and may be any amount commonly used in mortar, concrete, etc. For example, the amount of water blended is preferably such that the mass ratio of water to cement composition (water/cement composition) is 0.2 to 0.6.

Examples of other materials that may be mixed as necessary include aggregates, cement dispersants (excluding high performance water reducers and high performance AE water reducers), expansion agents, shrinkage reducers, and air volume regulators. etc.
Examples of the aggregate include fine aggregate alone or a combination of fine aggregate and coarse aggregate.
Examples of the fine aggregate include one or more selected from river sand, mountain sand, land sand, sea sand, crushed sand, silica sand, slag fine aggregate, lightweight fine aggregate, and the like. In addition to natural aggregate, recycled aggregate can be used as the fine aggregate.
Examples of the coarse aggregate include one or more types selected from gravel, crushed stone, slag coarse aggregate, lightweight coarse aggregate, and the like. Further, as the coarse aggregate, as with the fine aggregate, recycled aggregate can be used in addition to natural aggregate.
The blending amount of aggregate (the total amount when fine aggregate and coarse aggregate are used together) is not particularly limited, and may be a common blending amount for mortar, concrete, etc. For example, the amount of aggregate is such that the mass ratio of aggregate to cement composition (aggregate/cement composition) is preferably 1 to 7, more preferably 2 to 5.

The mixing method is not particularly limited, and all the materials may be put into a mixer at once and mixed, or cement clinker powder, limestone powder, and aggregate mixed as necessary are mixed in a mixer. After dry kneading is performed, water, a high performance water reducing agent, and other materials blended as necessary may be added and mixed.
After the mixing step, the obtained mixture is usually cast (cast) into a mold, and then subjected to a pre-curing step (described later) and a steam curing step.

[Pre-curing process]
This step is a step that is optionally provided between the mixing step and the steam curing step, and the mixture obtained in the mixing step is heated for 1 hour or more (preferably 1.5 to 6 hours, more preferably 2 to 5 hours). ) It is a process of air curing. The temperature during air curing is usually room temperature (eg, 5°C or higher and lower than 40°C, preferably 10 to 30°C). When the air curing time is 1 hour or more, the strength of the hardened cementitious material is further improved.

[Steam curing process]
This step is a step in which the mixture obtained in the previous step (mixing step or pre-curing step) is steam-cured at a temperature of 55° C. or higher for 1 hour or more to obtain a steam-cured mixture.
Steam curing may be normal pressure steam curing performed under atmospheric pressure, or high temperature high pressure steam curing performed under pressure higher than normal pressure using an autoclave. Among these, normal pressure steam curing is preferred from the viewpoint of ease of production.
In steam curing, the temperature is increased over 1 hour or more (preferably 2 to 5 hours, more preferably 2 to 4 hours) until the desired maximum temperature is reached. The temperature increase rate (width of temperature increase per unit time) until the desired maximum temperature is reached is preferably 10 to 30° C./hour.
The time for steam curing in an atmosphere of 55°C or higher (preferably 60 to 80°C) is 2 hours or more, preferably 2 hours and 15 minutes or more, more preferably 2 hours, from the viewpoint of increasing the strength of the hardened cementitious material. The duration is 30 minutes or more. Moreover, from the viewpoint of shortening the time required for producing the cementitious hardened body, the above-mentioned time is preferably 5 hours or less, more preferably 4 hours and 30 minutes or less.
The maximum temperature during steam curing is 55°C or higher, preferably 60 to 80°C, from the viewpoint of increasing the strength of the cementitious hardened body and shortening the time required for steam curing.

Next, the temperature is lowered to room temperature (about 20° C.) over a period of 2 to 10 hours (preferably 3 to 9 hours).
The rate of temperature drop (width of temperature drop per unit time) until reaching room temperature (about 20°C) is preferably 3 to 40°C/hour, more preferably 5 to 20°C/hour, particularly preferably 6 to 10°C/hour. °C/hour.
The time required for the steam curing step (the time from the start of temperature increase to the end of temperature decrease) is preferably 16 hours or less, more preferably 15 hours or less, from the viewpoint of shortening the time required for product manufacture.

[Curing process]
This step is a step in which the mixture after steam curing is cured for hardening, and a cementitious hardened body is obtained by hardening the mixture. The above-mentioned curing is usually performed by leaving the product at room temperature.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited to these Examples.
[Materials used]
(1) Cement clinker powder (indicated as "clinker" in Table 1): Ordinary Portland cement clinker powder, Blaine specific surface area: 3,190 cm ² /g, density: 3.15 g/cm ³
(2) Half-hydrated gypsum; calcined gypsum (reagent)
(3) Gypsum dihydrate; calcium sulfate dihydrate (reagent)
(4) Limestone powder A; Blaine specific surface area: 4,000 cm ² /g, density: 2.72 g/cm ³ , manufactured by Bihoku Funka Kogyo Co., Ltd., product name “BF200”
(5) Limestone powder B; Blaine specific surface area: 12,000 cm ² /g, density: 2.72 g/cm ³ , manufactured by Bihoku Funka Kogyo Co., Ltd., trade name “Softon 1200”
(6) Limestone powder C; Blaine specific surface area: 22,000 cm ² /g, density: 2.72 g/cm ³ , manufactured by Bihoku Funka Kogyo Co., Ltd., trade name “Softon 2200”
(7) Fine aggregate; mountain sand, surface dry density 2.57 g/cm ³
(8) High-performance water reducing agent; Polycarboxylic acid ether-based high-performance water reducing agent, manufactured by BASF Japan, trade name "Master Glenium 8000S, Type M", solid content 30% by mass
(9) Air amount regulator; polyalkylene glycol derivative, manufactured by BASF Japan, trade name "Master Air 404"
(10) Hardening accelerator: Calcium nitrite hardening accelerator, manufactured by Manol Co., Ltd., trade name "Manol Antifreeze", solid content 20% by mass

[Examples 1-2]
Cement clinker powder, limestone powder of the type shown in Table 1, and aggregate were placed in a 5-liter Hobart mixer, and dry kneading was performed for 15 seconds. Next, a liquid material prepared by pre-mixing a high-performance water reducing agent, an air volume control agent, and water was put into a mixer and kneaded at low speed for 60 seconds. After scraping off the material adhering to the inner wall of the mixer, it was mixed at high speed. The first kneading was completed by kneading for 60 seconds. Next, the kneaded material was allowed to stand still in the mixer for 180 seconds, and then kneaded at a low speed for 60 seconds for a second kneading to prepare a mortar.
The blending amount of each material is shown in Table 1. Further, the amounts of the high performance water reducing agent and the air amount adjusting material were adjusted so that the mortar flow value was 180±20 mm and the air amount of the mortar was 4.5±1.5%.
The reason why the kneaded material was allowed to stand still in the mixer for 180 seconds after the first kneading was completed was to intentionally create stiffness and then knead it again, thereby minimizing changes in the state of the mortar after kneading. It's for a reason.
The flow value and temperature of the obtained mortar were measured, and the workability and stiffness were evaluated according to (1) and (2) below. The results are shown in Table 2.

(1) Measurement of mortar flow value and temperature Immediately after the completion of the first kneading (indicated as "1st time" in Tables 2 to 3), Immediately after the completion of the second kneading (in Tables 2 to 3, 20 minutes after pouring water into the mixer (indicated as ``20 minutes later'' in Tables 2 and 3), and after pouring water into the mixer. The flow value of the mortar after 30 minutes (indicated as "30 minutes later" in Tables 2 and 3) was determined by dropping it 15 times in accordance with "JIA R 5201:2015 (Physical test method for cement)". Measurements were taken during exercise.
In addition, the temperature of the mortar was measured immediately after the first kneading and immediately after the second kneading.
Note that if the mortar flow value is about 155 to 165 mm, it can be judged that the workability is good.
(2) Evaluation of mortar workability and stiffness Also, mortar work immediately after the first kneading, immediately after the second kneading, and 30 minutes after water was poured into the mixer. The gender was evaluated on a three-level scale. Specifically, "〇" indicates that the mortar is soft, easy to drive, and has good workability, and "○" indicates that the mortar is somewhat rough and flows when vibrated, but takes time to drive. "△" and "x" where the mortar was rough and did not flow easily even when subjected to vibrations, making it impossible to drive.
In addition, the stiffness of the mortar was evaluated in three stages. Specifically, "〇" indicates that the effect of stiffness is small and a pot life of 30 minutes can be secured after pouring water, and "△" indicates that a pot life of 30 minutes after pouring water cannot be secured due to the influence of stiffness. , Those that have a large stiffness effect and quickly reach a tight state (a state that is difficult to deform even when subjected to vibration) were evaluated as "x".

Further, the mortar 30 minutes after pouring water was poured into a steel mold of φ5 x 10 cm, and then pre-cured for 3 hours at a temperature of 20°C. After pre-curing, the temperature was raised to 65°C over 2 hours and 15 minutes (heating rate: 20°C/hour), maintained at 65°C (maximum temperature) for 3 hours, and then lowered to 20°C over 4 hours ( Steam curing was performed with a temperature history of 7.5° C./hour). After steam curing, the mold was left standing in a sealed state at 20°C for 14 days, and then removed from the mold to obtain a hardened cementitious body. The compressive strength of the mortar of the obtained cementitious hardened body was measured according to the method (3) below.
(3) Measurement of compressive strength of mortar The compressive strength of mortar at 14 days of age was measured in accordance with "JIS R 5201:2015 (Physical test method for cement)".
Mortars containing and not containing a curing accelerator were prepared, and the compressive strength of each mortar was measured.
The amount of hardening accelerator was set to be 0.8 parts by mass in terms of solid content, based on a total of 100 parts by mass of cement clinker powder and limestone powder. Further, the curing accelerator was used by mixing with water together with a high performance water reducing agent when preparing the mortar.
The results are shown in Table 3.

[Comparative example 1]
A mortar was prepared in the same manner as in Example 1, except that no limestone powder was used and no mortar containing a hardening accelerator was prepared, and a cementitious hardened body was obtained.
In the same manner as in Example 1, the flow value, temperature, and compressive strength of the obtained mortar were measured, and the workability and stiffness were evaluated.
[Comparative example 2]
Mortar was prepared in the same manner as in Example 1, and a cementitious hardened body was obtained.
In the same manner as in Example 1, the flow value, temperature, and compressive strength of the obtained mortar were measured, and the workability and stiffness were evaluated.

[Example 3]
A mortar was prepared in the same manner as in Example 1 except that limestone powder B was used instead of limestone powder C, and a cementitious hardened body was obtained.
In the same manner as in Example 1, the flow value, temperature, and compressive strength of the obtained mortar were measured, and the workability and stiffness were evaluated.
[Comparative example 3]
A mortar was prepared in the same manner as in Example 1, except that limestone powder A was used instead of limestone powder C, and a mortar containing a hardening accelerator was not prepared, to obtain a cementitious hardened body.
In the same manner as in Example 1, the flow value, temperature, and compressive strength of the obtained mortar were measured, and the workability and stiffness were evaluated.

[Reference example 1]
A mortar was prepared in the same manner as in Example 1, except that gypsum hemihydrate and gypsum dihydrate were used in the amounts shown in Table 1 instead of limestone powder, and a mortar containing a hardening accelerator was not prepared. A hardened product was obtained.
In the same manner as in Example 1, the flow value, temperature, and compressive strength of the obtained mortar were measured, and the workability and stiffness were evaluated.
[Reference example 2]
A mortar was prepared in the same manner as in Example 1, except that ordinary Portland cement was used instead of cement clinker powder and limestone powder, and a mortar containing a hardening accelerator was not prepared, to obtain a cementitious hardened body.
In the same manner as in Example 1, the flow value, temperature, and compressive strength of the obtained mortar were measured, and the workability and stiffness were evaluated.

From Tables 2 and 3, when comparing Examples 1 to 3 and Comparative Example 1 (which did not use limestone powder and did not contain gypsum), it was found that the mortar flow values of Examples 1 to 3 (first kneading Immediately after the completion of the second kneading: 179-182 mm, Immediately after the completion of the second kneading: 160-162 mm, 20 minutes after pouring water into the mixer: 156-159 mm, 30 minutes after pouring water into the mixer The mortar flow values of Comparative Example 1 (immediately after the first kneading: 137 mm, immediately after the second kneading: 151 mm, and 20 minutes after pouring water into the mixer: 148 mm, 30 minutes after pouring water into the mixer: 145 mm). Further, it can be seen that the workability evaluation and stiffness evaluation of Examples 1 to 3 are all "○", whereas the workability evaluation of Comparative Example 1 is "x" or "△".
In addition, the mortar flow value, workability evaluation, and stiffness evaluation of Comparative Example 2 (in which the proportion of limestone powder in the total amount of cement clinker powder and limestone powder was 8% by mass) were the same as those of Examples 1 to 3. However, the compressive strength of the mortar of Comparative Example 2 (with CN: 50.4 N/mm ² , without CN: 29.8 N/mm ² ) is the same as that of the mortar of Examples 1 to 3 (CN With CN: 56.1 to 61.1 N/mm ² , without CN: 33.2 to 37.5 N/mm ² ).

The workability evaluation at the end of the second kneading of Comparative Example 3 (same as Example 2 except that limestone powder with a Blaine specific surface area of 4,000 cm ² /g was used) was "△", and the mixer It can be seen that the workability evaluation after 30 minutes had elapsed from the time when water was poured into the container was "x", and the stiffness evaluation was "x". In addition, the mortar flow values of Comparative Example 3 (immediately after the first kneading: 178 mm, immediately after the second kneading: 148 mm, 20 minutes after pouring water into the mixer: 139 mm, and It can be seen that the mortar flow value after 30 minutes from the time of injection: 141 mm) is smaller than the mortar flow values of Examples 1 to 3.
It can also be seen that the compressive strength of the mortar of Comparative Example 3 (without CN: 27.9 N/mm ² ) is smaller than the compressive strength of the mortar of Examples 1 to 3.
Reference Examples 1 and 2 are excellent in mortar flow value, workability evaluation, stiffness evaluation, and compressive strength, but because they contain gypsum, cracks may occur due to DEF (delayed formation of ettringite). The risk may be considered higher than others.

Claims (6)

A cement composition comprising cement clinker powder, limestone powder having a Blaine specific surface area of 7,000 cm ² /g or more, and at least one of a high performance water reducer and a high performance AE water reducer,
The proportion of the limestone powder in the total amount of the cement clinker powder and the limestone powder is 1 to 6% by mass,
The amount of at least one of the high performance water reducing agent and the high performance AE water reducing agent based on a total of 100 parts by mass of the cement clinker powder and the limestone powder is 0.1 to 1.5 parts by mass in terms of solid content. can be,
A cement composition characterized in that the proportion of sulfur compounds in the cement composition is 0.1 to 1.0% by mass in terms of SO ₃ . The cement composition according to claim 1, wherein the amount of gypsum contained in the cement composition is 0 to 0.5 parts by mass in terms of SO ₃ based on 100 parts by mass of the cement clinker powder. . The method according to claim 1 or 2, further comprising a hardening accelerator in an amount of 0.2 to 1.2 parts by mass in terms of solid content, based on a total of 100 parts by mass of the cement clinker powder and the limestone powder. Cement composition. A hardened cementitious body, which is a hardened body of a mixture containing the cement composition according to any one of claims 1 to 3 and water. A preparation step of mixing the cement composition according to any one of claims 1 to 3 with water to obtain a mixture;
A steam curing step of steam curing the mixture at a temperature of 55° C. or higher for 1 hour or more to obtain a steam-cured mixture;
A curing step of curing the mixture after the steam curing to obtain a hardened cementitious body by curing the mixture;
A method for producing a hardened cementitious body, the method comprising: The method for producing a hardened cementitious body according to claim 5, wherein the steam curing in the steam curing step is atmospheric pressure steam curing.