Cement composition and method for producing ultra-high strength cementitious hardened body

Abstract

To increase the compressive strength of an ultra-high strength cementitious hardened body and reduce the shrinkage strain, and to simplify the manufacturing process of an ultra-high strength cementitious hardened body.SOLUTION: A cement composition contains low-heat Portland cement, silica fume with a BET specific surface area of 15-25 m2 / g, an inorganic powder with a 50% volume cumulative particle size of 0.8-5 μm, aggregate A with a maximum particle size of 1.2 mm or less, a high-performance water reducing agent, an antifoaming agent and water. To the cement composition, a lightweight aggregate B is further added, in which the lightweight aggregate having a boiling water absorption ratio of 15% or more is made into a saturated water absorption state. An amount of the lightweight aggregate B added is 0.5-2.5 vol.% in a total of 100 vol.% of the aggregate A and the lightweight aggregate B.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a cement composition for an ultra-high strength cementitious hardened body and a method for manufacturing an ultra-high strength cementitious hardened body using the cement composition.

[0002] In recent years, concrete has been widely used in large-scale structures and buildings such as dams and bridges, and concrete has become an essential building material in construction. Also, as buildings become taller and civil engineering structures become longer, the demand for high-strength concrete is increasing. Under such circumstances, ultra-high strength concrete having high compressive strength and realizing "non-porosity" by reducing the voids in concrete to the extreme has been developed.

[0003] Ultra-high strength concrete is concrete having higher strength than high-strength concrete by ultimately reducing the size and number of voids that enter the interior of the concrete in the manufacturing process, which was a problem in conventional concrete.

[0004] Ultra-high strength concrete has different materials and manufacturing methods from conventional high-strength concrete. In high-strength concrete, generally, silica fume, which is an ultrafine powder material, is used as a material for filling between cement particles with a large particle size. However, since the sizes of cement particles and silica fume are significantly different, the silica fume does not spread to every corner between the cement particles, and voids remain. On the other hand, in ultra-high strength concrete, internal voids caused by the packing of materials are reduced by newly adding particles having a size between cement particles and silica fume.

[0005] High-strength concrete reduces the internal voids of the hardened body by mixing at a lower water-cement ratio than ordinary concrete or the like. However, there is a problem in that the amount of water contained is insufficient to cause a hydration reaction in the total amount of cement due to the reduction of the water-cement ratio. Therefore, in the method for manufacturing ultra-high-strength concrete, after performing a water absorption treatment from the outside after demolding, a two-stage heat curing is performed in which steam curing and heat curing are continuously performed. In the water absorption treatment before this heat curing, either a deaeration water absorption treatment in which the air in a sealed container containing the hardened body in a flooded state is deaerated and the hardened body is allowed to absorb water, or a boiling water absorption treatment in which the air in the hardened body is replaced with hot water by boiling is used.

[0006] Thus, the method for manufacturing ultra-high-strength concrete is characterized by a material design that forms a densely packed structure, water supply from the outside by a water absorption treatment after demolding, and a two-stage heat curing in which steam curing and heat curing are continuously performed. That is, the manufacture of ultra-high-strength concrete requires dedicated equipment for water absorption treatment and the like, and the problem is that the manufacturing method is complicated.

[0007] Patent Document 1 describes high-strength concrete in which a part of the aggregate is replaced with a porous aggregate having a high water absorption rate, so that the water consumed by the hydration reaction in the concrete is compensated by the water contained in the porous aggregate, thereby increasing the strength and reducing autogenous shrinkage by suppressing drying in the pore voids.

[0008] Further, Patent Document 2 describes a technique for reducing autogenous shrinkage by replacing a part of the coarse aggregate with an artificial lightweight aggregate in high-strength concrete.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

[0010] However, Patent Document 1 and Patent Document 2 relate to technologies for high-strength concrete having a compressive strength of about 100 N / mm 2 to 200 N / mm 2 and the effects of ultra-high-strength concrete having a compressive strength of 300 N / mm 2 or more have not been studied.

[0011] In view of such circumstances, the present invention has been made. By adding water-absorbed lightweight aggregate to a part of the aggregate, a cement composition for an ultra-high-strength cementitious hardened body capable of reducing shrinkage strain while exhibiting a compressive strength of 300 N / mm 2 or more, and a method for manufacturing an ultra-high-strength cementitious hardened body simplified by using the cement composition are provided.

Summary of the Invention

Means for Solving the Problems

[0012] (1) To achieve the above object, the present invention has taken the following means. That is, the cement composition of the present invention comprises a low-heat Portland cement, silica fume having a BET specific surface area of 15 to 25 m 2 / g, an inorganic powder having a 50% volume cumulative particle size of 0.8 to 5 μm, aggregate A having a maximum particle size of 1.2 mm or less, a high-performance water-reducing agent, an antifoaming agent, and water, and further added with lightweight aggregate B in a saturated water-absorbed state of lightweight aggregate having a boiling water absorption rate of 15% or more, and the addition amount of the lightweight aggregate B is 0.5 to 2.5% by volume in a total of 100% by volume of the aggregate A and the lightweight aggregate B. Thereby, it becomes possible to provide an ultra-high-strength cementitious hardened body in which shrinkage strain is reduced while exhibiting a compressive strength of 300 N / mm 2 or more.

[0013] (2) Further, the method for manufacturing an ultra-high-strength cementitious hardened body of the present invention is a method for manufacturing an ultra-high-strength cementitious hardened body from the cement composition described in (1), comprising a kneading step of kneading the cement composition, a molding step of filling the kneaded and uncured cement composition into a mold, a normal-temperature curing step of demolding after sealing and curing or air-curing the uncured cement composition filled in the mold at a temperature of 10 to 40 °C for 24 hours or more to obtain a molded body, a heating curing step of performing steam curing on the molded body obtained in the normal-temperature curing step at a temperature of 70 °C or more and less than 100 °C for 48 hours or more, and a high-temperature heating step of performing heat drying on the molded body after the heating curing step at a temperature of 150 °C or more and less than 200 °C for 48 hours or more. Thereby, the external water absorption step for the molded body, which has been necessary heretofore, becomes unnecessary, and the production of ultra-high-strength concrete and the like becomes simple.

Advantages of the Invention

[0014] According to the present invention, by adding lightweight aggregate that has absorbed water as an aggregate, it is possible to impart a compressive strength of 300 N / mm 2 or more and reduce the shrinkage strain, and it is also possible to simplify the manufacturing process of the ultra-high-strength cementitious hardened body.

Brief Description of the Drawings

[0015]

Figure 1

Embodiments for Carrying Out the Invention

[0016] The present inventors have found that by adding lightweight aggregate in a saturated water absorption state as an aggregate to the cement composition, it is possible to easily manufacture an ultra-high-strength cementitious hardened body having a compressive strength of 300 N / mm 2 or more. The present invention will be described in detail below.

[0017] The definitions of the terms used in this specification are as follows. The absolute dry density is the value obtained by dividing the mass of the aggregate in the absolutely dry state by the absolute volume of the aggregate. The absolutely dry state means a state in which the free water (water in which molecules can move around) contained in the aggregate has been removed by drying or the like. The apparent dry density is the value obtained by dividing the mass of the aggregate in the surface dry state by the absolute volume of the aggregate. The surface dry state means a state in which there is no surface water on the aggregate grains and all the voids inside the aggregate grains are filled with water. The water absorption rate is the percentage of the total amount of water contained in the aggregate in the surface dry state with respect to the mass of the aggregate in the absolutely dry state. Note that as test methods for measuring the water absorption rate, there are 24-hour water absorption, boiling water absorption, vacuum water absorption, pressure water absorption, etc. In this specification, the boiling water absorption rate by boiling water absorption, which can easily fill the voids of the aggregate, is measured. Here, the boiling water absorption rate is a value calculated from the water supply amount of the aggregate in the surface dry state after boiling the aggregate in the absolutely dry state for 2 hours and then naturally cooling it.

[0018] (Cement composition) The cement composition of the present invention is a cement composition containing low heat type Portland cement, silica fume with a BET specific surface area of 15 to 25 m 2 / g (hereinafter, also simply referred to as silica fume), inorganic powder with a 50% volume cumulative particle size of 0.8 μm (hereinafter, also simply referred to as inorganic powder), aggregate A with a maximum particle size of 1.2 mm or less, high performance water reducing agent, defoaming agent, and water, and further, lightweight aggregate B in a saturated water absorption state of lightweight aggregate with a boiling water absorption rate of 15% or more is added. The addition amount of this lightweight aggregate B is 0.5 to 2.5% by volume in the total addition amount of 100% by volume of aggregate A and lightweight aggregate B.

[0019] The low heat type Portland cement used in the cement composition of the present invention is one or more of moderate heat Portland cement or low heat Portland cement.

[0020] Further, in order to further improve the fluidity of the cement composition in an uncured state (hereinafter referred to as the fresh state), and from the viewpoint that the molded body (ultra-high strength cementitious cured body) obtained by the production method of the present invention exhibits a compressive strength of 300 N / mm 2 or more, as the low heat type Portland cement, coarse particles having a particle size of 20 μm or more with a rounded surface portion formed by polishing particles constituting moderate heat Portland cement or low heat Portland cement, and fine particles having a particle size of less than 20 μm generated by this polishing treatment are included, the 50% volume cumulative particle size is 10 to 18 μm, and the Blaine specific surface area is 2,100 to 2,900 cm 2 / g may also be used as the cement.

[0021] The BET specific surface area of the silica fume is 15 to 25 m 2 / g, preferably 17 to 23 m 2 / g, particularly preferably 18 to 22 m 2 / g. When the BET specific surface area is less than 15 m 2 / g, the compressive strength of the obtained ultra-high strength cementitious cured body decreases. When the specific surface area exceeds 25 m 2 / g, the fluidity of the cement composition in the fresh state decreases.

[0022] Examples of the inorganic powder having a 50% volume cumulative particle size of 0.8 to 5 μm (hereinafter also simply referred to as "inorganic powder") include silica powder (quartz powder), pozzolan, fly ash, slag powder, limestone powder, feldspar powder, mullite powder, alumina powder, silica sol, carbide powder, nitride powder, pulverized emery sand (artificial or natural), etc. These may be used alone or in combination of two or more. Among them, from the viewpoint of improving the fluidity of the cement composition in the fresh state and making the compressive strength of the obtained ultra-high strength cementitious cured body 300 N / mm 2 or more, it is preferable to use silica powder or fly ash. In the present invention, the low heat type Portland cement is not included in the inorganic powder having a 50% volume cumulative particle size of 0.8 to 5 μm.

[0023] The 50% volume cumulative particle size of the inorganic powder is 0.8 to 5 μm, preferably 1 to 4 μm, more preferably 1.1 to 3.5 μm, and particularly preferably 1.2 μm or more and less than 3 μm. When the particle size is less than 0.8 μm, the fluidity of the cement composition in the fresh state decreases. When the particle size exceeds 5 μm, the compressive strength of the ultra-high-strength cementitious hardened body decreases. In this specification, the 50% volume cumulative particle size of the inorganic powder can be determined using a commercially available particle size distribution measuring device (for example, manufactured by Nikkiso Co., Ltd., product name "Microtrac HRA Model 9329-X100").

[0024] From the viewpoint of making the compressive strength of the obtained ultra-high-strength cementitious hardened body 300 N / mm 2 or more, it is preferably 15 μm or less, more preferably 14 μm or less, and particularly preferably 13 μm or less. The 95% volume cumulative particle size of the inorganic powder is preferably 8 μm or less, more preferably 7 μm or less, and particularly preferably 6 μm or less from the viewpoint of making the compressive strength of the obtained ultra-high-strength cementitious hardened body 300 N / mm 2 or more.

[0025] As the inorganic powder, those mainly composed of SiO 2 , such as silica powder, are preferable. The content of SiO 2 in the inorganic powder is preferably 50% by mass or more, more preferably 60% by mass or more, still more preferably 70% by mass or more, still more preferably 80% by mass or more, and particularly preferably 90% by mass or more from the viewpoint of making the compressive strength of the obtained ultra-high-strength cementitious hardened body 300 N / mm 2 or more.

[0026] In the cement composition of the present invention, the volume ratio of the low heat type Portland cement is preferably 20 to 35% by volume, more preferably 25 to 30% by volume. When the volume ratio is 20% by volume or more, the compressive strength of the obtained ultra-high-strength cementitious hardened body becomes higher. When the volume ratio is 35% by volume or less, the fluidity of the cement composition in the fresh state is further improved.

[0027] Hereinafter, the whole of the low heat Portland cement, silica fume and inorganic powder may be referred to as "powder raw materials".

[0028] In the cement composition of the present invention, the volume ratio of silica fume is preferably 5 to 23% by volume, more preferably 10 to 18% by volume. When the volume ratio is 5% by volume or more, the compressive strength of the obtained ultra-high strength cementitious hardened body becomes higher. When the volume ratio is 23% by volume or less, the fluidity of the cement composition in the fresh state is further improved.

[0029] In the cement composition of the present invention, the volume ratio of the inorganic powder is preferably 1 to 13% by volume, more preferably 2 to 8% by volume. When the volume ratio is 1% by volume or more, the compressive strength of the obtained ultra-high strength cementitious hardened body becomes higher. When the volume ratio is 13% by volume or less, the fluidity of the cement composition in the fresh state is further improved.

[0030] Examples of the aggregate A include river sand, mountain sand, land sand, sea sand, crushed sand, silica sand, natural emery sand, artificial fine aggregates such as slag fine aggregate, recycled fine aggregate, or mixtures thereof. Among them, those having a water absorption rate of 3.5% or less and a continuous porosity of 5% or less are preferred.

[0031] From the viewpoint of making the compressive strength of the obtained ultra-high strength cementitious hardened body 300 N / mm 2 or more, silica sand is particularly preferably used. Further, from the same viewpoint, the content of SiO 2 in the silica sand is preferably 70% by mass or more, more preferably 80% by mass or more, and particularly preferably 90% by mass or more.

[0032] The maximum particle size of the aggregate A is 1.2 mm or less, preferably 1.1 mm or less, more preferably 1.0 mm or less, from the viewpoint of making the compressive strength of the obtained ultra-high strength cementitious hardened body 300 N / mm 2 or more.

[0033] The particle size distribution of aggregate A improves the fluidity of the fresh cement composition and makes the compressive strength of the resulting ultra-high-strength cementitious hardened body 300 N / mm 2 From the perspective of achieving 300 N / mm or higher, it is preferable to satisfy all three conditions: the mass ratio of aggregate with a particle size of 0.6 mm or less is 95% by mass or more, the ratio of aggregate with a particle size of 0.3 mm or less is 40 - 50% by mass, and the ratio of aggregate with a particle size of 0.15 mm or less is 6% by mass or less.

[0034] The volume ratio of aggregate A in the cement composition is preferably 20 - 50% by volume, more preferably 25 - 45% by volume, and even more preferably 30 - 40% by volume with respect to 100% by volume of the entire cement composition. If the volume ratio is 20% by volume or more, the fluidity of the fresh cement composition can be further improved, the heat of cement hydration during the hardening process of the ultra-high-strength cementitious hardened body can be reduced, and the shrinkage amount of the ultra-high-strength cementitious hardened body can be made smaller. If the volume ratio is 50% by volume or less, the compressive strength of the ultra-high-strength cementitious hardened body can be further improved.

[0035] The particle size distribution of lightweight aggregate B improves the fluidity of the fresh cement composition and makes the compressive strength of the resulting ultra-high-strength cementitious hardened body 300 N / mm 2 From the perspective of achieving 300 N / mm or higher, the average particle size is 1 - 10 mm, more preferably 1 - 3 mm.

[0036] The particle size distribution of lightweight aggregate B improves the fluidity of the fresh cement composition and makes the compressive strength of the resulting ultra-high-strength cementitious hardened body 300 N / mm 2 From the perspective of achieving 300 N / mm or higher, it is preferable to satisfy all three conditions: the ratio of lightweight aggregate with a particle size of 5 mm or less is 90% by mass or more, the ratio of lightweight aggregate with a particle size of 2.5 mm or less is 40 - 65% by mass, and the ratio of lightweight aggregate with a particle size of 0.6 mm or less is 3% by mass or less.

[0037] Lightweight aggregate B used in the cement composition is in a saturated water absorption state. Conventionally, ultra-high-strength cementitious hardened bodies have achieved ultra-high strength by subjecting them to external water absorption treatment during the manufacturing process to supply moisture to the unhydrated cement particles inside the ultra-high-strength cementitious hardened bodies. On the other hand, by using lightweight aggregate B in a saturated water absorption state, it becomes possible to supply moisture to the unhydrated cement particles inside the ultra-high-strength cementitious hardened body without performing external water absorption treatment.

[0038] The lightweight aggregate that becomes lightweight aggregate B by saturated water absorption is required to have high water retention and water permeability. Specifically, a lightweight aggregate with a boiling water absorption rate of 15% or more is preferable.

[0039] The volume ratio of lightweight aggregate B in the cement composition is preferably 0.1 to 1.5% by volume, more preferably 0.1 to 1.0% by volume, and even more preferably 0.2 to 0.8% by volume with respect to 100% by volume of the entire cement composition. If the volume ratio is 0.1 to 1.5% by volume, it becomes possible to improve the compressive strength of the obtained ultra-high-strength cementitious hardened body and reduce the shrinkage strain.

[0040] As the high-performance water reducer, high-performance water reducers such as naphthalene sulfonic acid type, melamine type, and polycarboxylic acid type can be used. Among them, from the viewpoint of improving the fluidity of the cement composition in the fresh state and making the compressive strength of the obtained ultra-high-strength cementitious hardened body 300 N / mm 2 From the above viewpoints, a polycarboxylic acid type high-performance water reducer is preferable.

[0041] The addition amount of the high-performance water reducer is preferably 1.0 to 4.0 parts by mass, more preferably 2.0 to 3.0 parts by mass in terms of solid content with respect to 100 parts by mass of the total amount of the powder raw materials. If the addition amount is 1.0 part by mass or more, the compressive strength of the obtained ultra-high-strength cementitious hardened body is improved. If the addition amount is 4.0 parts by mass or less, the workability of the cement composition in the fresh state is good.

[0042] As the defoaming agent, general-purpose defoaming agents such as nonionic surfactants can be used. The addition amount of the defoaming agent is preferably 0.1 to 0.3 parts by mass, more preferably 0.15 to 0.25 parts by mass, based on 100 parts by mass of the total amount of the powder raw materials. If the addition amount is 0.1 part by mass or more, the compressive strength of the obtained ultra-high-strength cementitious hardened body is improved. If the addition amount exceeds 0.3 parts by mass, the effect of improving the compressive strength of the ultra-high-strength cementitious hardened body reaches a plateau.

[0043] As the water, tap water or the like can be used. The blending amount of water is preferably 5 to 20 parts by mass, more preferably 7 to 15 parts by mass, based on 100 parts by mass of the total amount of the powder raw materials. If the amount is 5 parts by mass or more, the fluidity of the fresh cement composition is improved. If the amount is 20 parts by mass or less, the compressive strength of the obtained ultra-high-strength cementitious hardened body is improved.

[0044] (Method for producing ultra-high-strength cementitious hardened body) The method for producing the cementitious hardened body will be described. FIG. 1 is a flowchart showing the method for producing the ultra-high-strength cementitious hardened body of the present invention.

[0045] (1) Kneading step First, the low-heat Portland cement, silica fume, inorganic powder, aggregate A, lightweight aggregate B, high-performance water reducing agent, defoaming agent and water, which are the cement compositions described above, are kneaded using a mixer (S1). The method for kneading the cement composition is not particularly limited. Also, the apparatus used for kneading is not particularly limited, and conventional mixers such as an omnimixer, a pan-type mixer, a twin-shaft kneader, and a tilting drum mixer can be used.

[0046] (2) Molding step Next, it proceeds to the molding step (S2) of filling the kneaded cement composition into a mold. The placing method and filling method into the formwork in the molding process are not particularly limited. The fresh cement composition filled into the formwork may be one with reduced or removed air bubbles. By reducing or removing the air bubbles in the fresh cement composition, the compressive strength of the obtained ultra-high-strength cementitious hardened body can be improved.

[0047] (3) Normal temperature curing process Next, it proceeds to the normal temperature curing process. In the normal temperature curing process, the fresh cement composition filled into the formwork is subjected to sealed curing or air curing at a temperature of 10 to 40°C, preferably 15 to 30°C, for 24 hours or more, preferably 24 to 72 hours, and then demolded to obtain a molded body (S3). In this normal temperature curing process, it is preferable that the obtained molded body has a compressive strength of 20 to 100 N / mm 2 of.

[0048] (4) Heat curing process Next, it proceeds to the heat curing process. This heat curing process is a process (S4) in which the molded body obtained in the normal temperature curing process is subjected to steam curing or hot water curing at a temperature of 70°C or higher and lower than 100°C, preferably 75 to 95°C, for 6 hours or more, and autoclave curing at a temperature of 100 to 200°C, preferably 160 to 190°C, for 1 hour or more, either one or both.

[0049] In this heat curing process, when only steam curing or hot water curing is performed, the curing time is preferably 24 hours or more, more preferably 24 to 96 hours. When only autoclave curing is performed, the curing time is preferably 8 to 60 hours, more preferably 12 to 48 hours. When both steam curing or hot water curing and autoclave curing are performed, for example, when autoclave curing is performed after steam curing or hot water curing, the curing time in steam curing or hot water curing is preferably 6 to 72 hours, more preferably 12 to 48 hours, and the curing time in autoclave curing is preferably 1 to 24 hours, more preferably 4 to 18 hours.

[0050] (5) High-temperature heating process Next, proceed to the high-temperature heating process. This high-temperature heating process is a process (S5) of heating the molded body after heat curing at a temperature of 150 to 200 °C, preferably 170 to 190 °C, for 24 hours or more, preferably 24 to 72 hours, to obtain an ultra-high-strength cementitious hardened body. That is, the heating in this high-temperature heating process is carried out in a dry atmosphere.

[0051] [Examples] Hereinafter, examples will be described. However, the present invention is not limited in any way by the examples described below. [Materials used] The materials used are as shown below. (1) Low-heat Portland cement (C1): Low-heat Portland cement manufactured by Taiheiyo Cement Corporation, density 3.22 g / cm 3 (2) Ordinary Portland cement (C2): Manufactured by Taiheiyo Cement Corporation, density 3.16 g / cm 3 (3) Silica fume (SF): Manufactured by B Kogyo Co., Ltd., density 2.39 g / cm 3 (4) Inorganic powder (M): Silica powder, maximum particle size 12 μm, 95% volume cumulative particle size: 5.8 μm, density 2.69 g / cm 3 (5) Aggregate A (S): Silica sand, maximum particle size 1.0 mm, 98 mass% or less of 0.6 mm or less, 45 mass% or less of 0.3 mm or less, 3 mass% or less of 0.15 mm or less, density 2.63 g / cm 3 (6) Lightweight aggregate B (L1): Siliceous shale, average particle size 1.1 mm, absolute dry density 1.62 g / cm 3 , apparent dry density 1.88 g / cm 3 , boiling water absorption rate 32.1% (7) Lightweight aggregate B (L2): Asanolite (registered trademark) manufactured by Taiheiyo Cement Corporation, average particle size 1.3 mm, absolute dry density 1.65 g / cm 3 , apparent dry density 1.80 g / cm 3 , boiling water absorption rate 19.3% (8) Lightweight aggregate B (L3): Classified product of the above L2, average particle size 0.5 mm, absolute dry density 1.83 g / cm 3 , apparent dry density 2.09 g / cm 3 , boiling water absorption rate 14.6% (9) Lightweight aggregate B (L4): Perlite, average particle size 1.1 mm, absolute dry density 1.25 g / cm3, apparent dry density 1.54 g / cm 3 , boiling water absorption rate 38.2% (10) Lightweight aggregate B (L5): Baked product of the above L4, average particle size 1.2 mm, absolute dry density 0.20 g / cm 3 , apparent dry density 0.27 g / cm 3 , boiling water absorption rate 81.8% (11) High-performance water reducer (SP): Floric SF500U (registered trademark) manufactured by Floric Co., polycarboxylic acid type, solid content 27.4 mass% (12) Defoaming agent (DF): Master Air 404 (registered trademark) manufactured by Pozolith Solutions Co., polyalkylene glycol derivative (13) Water (W): Tap water (tap water in Sakura City)

[0052] [Preparation of Specimens] Each specimen was prepared by the following method. Low heat Portland cement (C1) or ordinary Portland cement (C2), silica fume (SF), inorganic powder (M) and aggregate A (S) were put into an omnimixer and dry mixed for 15 seconds. The mixing amount of aggregate A (S) is such that the proportion of aggregate A (S) in the cement composition is 35.0 ± 5.0% by volume. To the kneaded mixture, lightweight aggregate B (L1 - L5) in a saturated water absorption state or lightweight aggregate B (L1) in an absolute dry state of the types and amounts (volume%) shown in Table 1 was added, and dry mixing was further carried out for 15 seconds.

[0053] Next, to the kneaded mixture, an amount of water (W) of 11.3 parts by mass, an amount of high-performance water reducer (SP) of 2.5 parts by mass, and an amount of defoaming agent (DF) of 0.2 parts by mass with respect to 100 parts by mass of the powder raw materials were put into the omnimixer and kneaded for 2 minutes. After kneading, the mixture adhering to the side wall in the omnimixer was scraped off, and kneading was further carried out for 4 minutes, and the kneaded mixture was discharged from the omnimixer. Table 1 shows the formulations of each level.

[0054]

Table 1

[0055] The obtained kneaded material was filled into cylindrical molds of φ50×100 mm and φ100×400 mm, and then sealed and cured at 20°C for 48 hours. In addition, an embedded strain gauge (KM-100HB manufactured by Tokyo Sokki Kenkyujo Co., Ltd.) was embedded in the center of the φ100×400 mm specimen.

[0056] Thereafter, the molded body obtained by sealed curing was subjected to steam curing at 90°C for 48 hours, and then heat curing at 180°C for 48 hours. The compressive strength of the obtained φ50×100 mm specimen was measured in accordance with "JIS A 1108 (Test method for compressive strength of concrete)". Also, the shrinkage strain of the obtained φ100×400 mm specimen was measured from the embedded strain gauge. Table 2 shows the measurement results of the compressive strength and shrinkage strain for all Examples and Comparative Examples.

[0057]

Table 2

[0058] From the results of Examples 1 to 5, it can be seen that by using the cement composition of the present invention in the production method of the present invention, an ultra-high-strength cementitious hardened body having a compressive strength of 300 N / mm 2 or more can be easily obtained. Furthermore, it can also be seen that such an ultra-high-strength cementitious hardened body has a sufficiently small shrinkage strain.

Claims

1. 20 to 35% by volume of low-heat Portland cement, 5 to 23% by volume of silica fume with a BET specific surface area of 15 to 25 m ２ / g, 1 to 13% by volume of inorganic powder with a 50% volume cumulative particle size of 0.8 to 5 μm, aggregate A with a maximum particle size of 1.2 mm or less, a high-performance water reducing agent, an antifoaming agent, and water, and further added with lightweight aggregate B in a saturated water absorption state with a boiling water absorption rate of 15% or more and 38.2% or less. The addition amount of the aggregate A is 20 to 50% by volume based on 100% by volume of the whole cement composition, and the addition amount of the lightweight aggregate B is 0.2 to 0.8% by volume based on 100% by volume of the whole cement composition. A cement composition characterized by this.

2. A method for producing an ultra-high-strength cementitious hardened body from the cement composition according to Claim 1, a kneading step of kneading the cement composition, a molding step of filling the kneaded and uncured cement composition into a mold, a normal-temperature curing step of demolding after sealing and curing or air-curing the uncured cement composition filled in the mold at a temperature of 10 to 40°C for 24 hours or more to obtain a molded body, a heat-curing step of performing steam curing on the molded body obtained in the normal-temperature curing step at a temperature of 70°C or higher and lower than 100°C for 48 hours or more, a high-temperature heating step of performing heat drying on the molded body after the heat-curing step at a temperature of 150°C or higher and lower than 200°C for 48 hours or more, A method for producing an ultra-high-strength cementitious hardened body, comprising at least the above steps.

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