JP7653337B2 - Hardened cement and precast concrete panels - Google Patents

Description

The present invention relates to hardened cement bodies and precast concrete slabs.

Wear caused by running tires is a problem for roadway pavements and railway tracks on which trains with rubber tires run. When concrete is used for these pavements and tracks, the higher the strength of the concrete, the higher the resistance to wear, and the longer the service life can be expected. From this perspective, Patent Document 1 proposes a concrete pavement with high bending strength and wear resistance.

JP 2016-179927 A

The hardened cement product used for paving not only meets the requirements for a hardened cement product for paving, but also preferably has properties of the cement composition suitable for application. In particular, since fluidity affects application and filling properties, it is preferable that the fluidity of the cement composition is suitable for application.

The present invention was made in consideration of these circumstances, and aims to provide a hardened cement body and a precast concrete slab that are not only highly resistant to wear, but also have a cement composition whose fluidity is suitable for construction.

(1) In order to achieve the above object, the present invention provides the following means. That is, the cement hardened body of the present invention is a hardened body of a cement composition containing at least cement, silica fume, inorganic powder, fine aggregate, hard sand, a high performance water reducing agent, an antifoaming agent, and water, characterized in that the compressive strength is 300 N/ ^mm2 or more, the maximum particle size of the fine aggregate is 1.2 mm or less, the hardness of the hard sand is higher than that of the fine aggregate, the particle size of the hard sand is 1.2 mm or more in 10% cumulative particle size by weight and 5.0 mm or less in 90% cumulative particle size by weight, and the content of the hard sand in the total amount of the fine aggregate and the hard sand is 30% or more and 70% or less.

This not only provides excellent abrasion resistance, but also makes the fluidity of the cement composition suitable for application.

(2) The hardened cement product of the present invention is characterized by further containing coarse aggregate with a maximum particle size of more than 2.5 mm and not more than 20 mm. This improves dimensional stability.

(3) In the hardened cement product of the present invention, the hard sand has a new Mohs hardness of 8 or more. This improves abrasion resistance.

(4) In the hardened cement body of the present invention, the hard sand is one or more selected from quartz, alumina, and silicon carbide. This ensures sufficient fluidity of the cement composition when the hardened cement body is produced. In addition, the abrasion resistance required for a hardened cement body for paving can be easily achieved.

(5) In the hardened cement product of the present invention, the cement comprises particles of grinded moderate-heat Portland cement or low-heat Portland cement, and the ground particles have a 50% cumulative particle size by volume of 10 to 18 μm and a Blaine specific surface area of 2100 to 2900 cm ² /g.

This not only improves the fluidity of the cement composition, but also improves the strength and abrasion resistance of the hardened cement body.

(6) The hardened cement body of the present invention is characterized in that it contains one or more types of fibers selected from metal fibers, organic fibers, and carbon fibers, and the content of the fibers is 4 volume % or less. This makes it possible to improve the strength and fracture energy of the hardened cement body while maintaining the fluidity and workability of the cement composition.

(7) The precast concrete slab of the present invention is characterized by comprising the hardened cement body described in any one of (1) to (6) above. When manufacturing such a precast concrete slab, the cement composition constituting it has excellent fluidity, making it suitable for producing the precast concrete slab. In addition, the precast concrete slab has excellent abrasion resistance.

As described above, according to the present invention, not only is the abrasion resistance excellent, but the fluidity of the cement composition is also suitable for application. Therefore, the cement has sufficient application and filling properties when applied.

1 is a front view showing an example of a polishing processing apparatus, partially including a cross section cut in a direction perpendicular to the rotation axis of a rotor. 1 is a table showing the formulation of a cement composition in each example and each comparative example.

As a result of intensive research, the inventors have invented a hardened cement body that not only has excellent abrasion resistance, but also has a fluidity of the cement composition suitable for construction by controlling the particle size and content of hard sand, which is harder than fine aggregate. The following describes an embodiment of the present invention.

[Configuration of hardened cement body]
The hardened cement product of the present invention is a hardened cement composition containing at least cement, silica fume, inorganic powder, fine aggregate, hard sand, a high-performance water reducing agent, a defoaming agent, and water.

(cement)
The cement used in the present invention is not particularly limited, and examples thereof include various types of Portland cement such as ordinary Portland cement, high-early-strength Portland cement, ultra-high-early-strength Portland cement, moderate-heat Portland cement, sulfate-resistant Portland cement, and low-heat Portland cement. Among these, moderate-heat Portland cement or low-heat Portland cement is preferred because the cement composition has high fluidity.

The cement used in the present invention preferably contains particles of polished moderate-heat Portland cement or low-heat Portland cement, with the 50% volume cumulative particle size of the cement being 10-18 μm and the Blaine specific surface area of the cement being 2100-2900 cm ² /g. More preferably, the polished particles have a rounded shape at the angular surface portions of the cement particles, and contain coarse particles with a particle size of 20 μm or more, and fine particles with a particle size of less than 20 μm produced by the polishing treatment. This increases the fluidity of the cement composition and increases the compressive strength of the hardened cement body.

The upper limit of the particle size of the coarse particles is not particularly limited, but considering the general particle size of polished cement, it is preferably 200 μm or less, and more preferably 100 μm or less, since this will increase the compressive strength of the hardened cement body.

The lower limit of the particle size of the microparticles is not particularly limited, but is preferably 0.1 μm or more, more preferably 0.5 μm or more, since this increases the fluidity of the cement composition and improves workability when producing a hardened cement body.

The 50% volume cumulative particle size of the ground cement is preferably 10 to 18 μm, more preferably 12 to 16 μm, and the Blaine specific surface area is preferably 2100 to 2900 cm ² /g, more preferably 2200 to 2700 cm ² /g.

The 50% volume cumulative particle size of 10 μm or more increases the fluidity of the cement composition, the 50% volume cumulative particle size of ₁₈ μm or less increases the compressive strength of the hardened cement body, and the Blaine specific surface area of 2100 ^cm2 /g or more increases the compressive strength of the hardened cement body, while the 50% volume cumulative particle size of 10 μm or less increases the fluidity of the cement composition.

The polishing process can be carried out using a known polishing device capable of polishing medium-heat Portland cement or low-heat Portland cement. The polishing device can be, for example, a high-speed airflow agitator.

The polishing process using a high-speed airflow agitator as the polishing processing device will be described in detail below with reference to Figure 1.

The cement used in the present invention is charged from the charge port 14 at the top of the polishing processing device 10 with the on-off valve 18 open, and then the on-off valve 18 is closed. The charged cement enters the circulation circuit 13 from an opening provided midway through the circulation circuit 13, and then enters the collision chamber 17, which is a space that contains the workpiece, from the outlet 13b of the circulation circuit 13.

After the cement is poured in, the rotor (rotating body) 11 arranged inside the stator 16, which is a fixed body, is rotated at high speed, generating a high-speed airflow by the rotor 11 and the blades 12 fixed to the rotor 11, which stirs the cement in the collision chamber 17. During this stirring, the cement particles enter the circulation circuit 13 from the inlet 13a of the circulation circuit 13 provided in the collision chamber 17, and are fed back into the collision chamber 17 from the outlet 13b of the circulation circuit 13 provided in the center of the collision chamber 17, where they circulate. Note that the dotted arrows in Figure 1 indicate the flow of cement particles, coarse particles generated by the polishing process, and fine particles.

As the cement particles are stirred, they collide with the inner wall surface of the collision chamber 17, the rotor 11, and the blades 12, and also with each other, resulting in the cement particles being polished, with the angular parts of the particle surface becoming rounded, resulting in coarse particles with a particle size of 20 μm or more and fine particles with a particle size of less than 20 μm.

The rotation speed of the rotor 11 is preferably 3000 to 4200 rpm, more preferably 3500 to 4000 rpm. When the rotation speed of the rotor 11 is 3000 rpm or more, the fluidity of the cement composition is improved, and when the rotation speed exceeds 4200 rpm, the effect of improving the fluidity of the cement composition becomes saturated.

The polishing time is preferably 10 to 60 minutes, more preferably 20 to 50 minutes, even more preferably 20 to 40 minutes, and even more preferably 20 to 30 minutes. When the polishing time is 10 minutes or more, the fluidity of the cement composition is improved, and when it exceeds 60 minutes, the effect of improving the fluidity of the cement composition becomes saturated.

Finally, the resulting polished product (a mixture of coarse and fine particles) is discharged from the discharge port 15 by opening the discharge valve 19.

(Silica fume)
The BET specific surface area of the silica fume used in the present invention is 15 to 25 ^{m 2} /g, preferably 17 to 23 ^{m 2} /g, and more preferably 18 to 22 m ² /g. By making the BET specific surface area 15 m ² /g or more, the compressive strength of the hardened cement body can be improved, and by making it 25 m ² /g or less, a decrease in the fluidity of the cement composition can be suppressed.

(Inorganic powder)
The inorganic powder may be one or more of quartz powder (silica powder), volcanic ash, slag powder, limestone powder, feldspar powder, mullite powder, alumina powder, silica sol, carbide powder, nitride powder, and classified or crushed fly ash. The inorganic powder preferably has a 50% cumulative volume particle size of 0.8 to 5 μm.

Among these, quartz powder or fly ash is preferable because it improves the fluidity of the cement composition and increases the compressive strength of the hardened cement body. In this specification, the inorganic powder with a 50% cumulative volume particle size of 0.8 to 5 μm does not include cement.

The 50% volume cumulative particle size of the inorganic powder used in the present invention is 0.8 to 5 μm, preferably 1 to 5 μm, more preferably 1.1 to 3.5 μm, and even more preferably 1.2 μm or more and less than 3 μm. If the particle size is larger than 0.8 μm, the fluidity of the cement composition is improved, and if the particle size is smaller than 5 μm, the compressive strength of the hardened cement body is improved.

The 50% volume cumulative particle size of inorganic powders can be determined using a commercially available particle size distribution measuring device such as the Microtrac HRA Model 9320-X100 (manufactured by Nikkiso Co., Ltd.).

The 50% volume cumulative particle size is determined, for example, by adding 0.06 g of a sample to ²⁰ cm3 of ethanol, which is a solvent for dispersing the sample, ultrasonically dispersing the sample for 90 seconds using an ultrasonic dispersing device (for example, product name "US300" manufactured by Nippon Seiki Seisakusho), and then creating a cumulative particle size curve of the particles in the dispersion using a particle size distribution measuring device.

The maximum particle size of the inorganic powder is preferably 15 μm or less, more preferably 14 μm or less, and even more preferably 13 μm or less, since this increases the compressive strength of the hardened cement body. In addition, the 95% volume cumulative particle size of the inorganic powder is preferably 8 μm or less, more preferably 7 μm or less, and even more preferably 6 μm or less, since this increases the compressive strength of the hardened cement body.

The inorganic powder used in the present invention is preferably an inorganic powder mainly composed of SiO ₂ such as quartz powder. The content of SiO ₂ in the inorganic powder is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. If the content of SiO ₂ in the inorganic powder is 50% by mass or more, the compressive strength of the hardened cement body is higher.

The cement content in the cement composition used in the present invention is 55 to 65% by volume, preferably 57 to 63% by volume, with the total of cement, silica fume, and inorganic powder being 100% by volume. If the cement content in the cement composition is 55% by volume or more, the compressive strength of the cement hardened body is improved, and if it is 65% by volume or less, the fluidity of the cement composition is improved.

The content of silica fume in the cement composition used in the present invention is 5 to 25 vol%, preferably 7 to 25 vol%, based on 100 vol% of the total of cement, silica fume, and inorganic powder. If the content is 5 vol% or more, the compressive strength of the hardened cement body is improved, and if it is 25 vol% or less, the fluidity of the cement composition is improved.

The content of the inorganic powder in the cement composition used in the present invention is 15 to 35 vol%, preferably 17 to 33 vol%, based on 100 vol% of the total of the cement, silica fume, and inorganic powder. If the content is 15 vol% or more, the compressive strength of the hardened cement body is improved, and if it is 35 vol% or less, the fluidity of the cement composition is improved.

(Fine aggregate)
The fine aggregate used in the present invention may be one or more selected from river sand, land sand, sea sand, crushed sand, silica sand, recycled fine aggregate, and artificial fine aggregate such as slag fine aggregate or fired fine aggregate obtained by firing fly ash or the like.

The maximum particle size of the fine aggregate is 1.2 mm or less, preferably 1.1 mm or less, and more preferably 1.0 mm or less. Because the maximum particle size is 1.2 mm or less, the compressive strength of the hardened cement body is high.

The particle size distribution of the fine aggregate improves the fluidity of the cement composition and increases the compressive strength of the hardened cement body, so the content of aggregate with a particle size of 0.6 mm or less is preferably 95% by mass or more, the content of aggregate with a particle size of 0.3 mm or less is preferably 40 to 50% by mass, and the content of aggregate with a particle size of 0.15 mm or less is 6% by mass or less.

The content of fine aggregate in the cement composition is preferably 20 to 40% by volume, more preferably 22 to 38% by volume, even more preferably 30 to 37% by volume, and particularly preferably 32 to 36% by volume. When the content of fine aggregate in the cement composition is 20% by volume or more, the calorific value of the cement composition is reduced and the shrinkage of the hardened cement body is reduced, and when the content is 40% by volume or less, the compressive strength of the hardened cement body is increased.

(High performance water reducing agent)
The high performance water reducing agent used in the present invention is at least one selected from high performance water reducing agents such as naphthalenesulfonic acid-based, melamine-based, and polycarboxylic acid-based, etc. Among these, polycarboxylic acid-based high performance water reducing agents are preferred because they improve the fluidity of the cement composition and increase the compressive strength of the hardened cement body.

The mixing ratio of the high-performance water reducing agent is preferably 0.2 to 1.5 parts by mass, more preferably 0.4 to 1.2 parts by mass, calculated as solid content, per 100 parts by mass of the total of cement, silica fume, and inorganic powder. When the mixing ratio of the high-performance water reducing agent is 0.2 parts by mass or more, the water reducing performance is improved and the fluidity of the cement composition is improved, and when it is 1.5 parts by mass or less, the compressive strength of the hardened cement body is increased.

(Antifoaming agent)
The defoaming agent used in the present invention may be a commercially available product, and the blending ratio of the defoaming agent is preferably 0.001 to 0.1 parts by mass, more preferably 0.01 to 0.07 parts by mass, and even more preferably 0.01 to 0.05 parts by mass, relative to 100 parts by mass of the total of the cement, silica fume, and inorganic powder. Since the blending ratio of the defoaming agent is 0.001 parts by mass or more, the strength development of the cement composition is improved, and when it exceeds 0.1 parts by mass, the effect of improving the strength development of the cement composition is saturated.

(Hard sand)
The hard sand used in the present invention is harder than the fine aggregate, with a 10% cumulative particle size of 1.2 mm or more and a 90% cumulative particle size of 5.0 mm or less. The hard sand preferably has a new Mohs hardness of 8 or more. The hard sand is preferably one or more types selected from quartz, alumina, and silicon carbide. Since the hard sand has a 10% cumulative particle size of 1.2 mm or more, the fluidity of the cement composition is suitable for application, and since the hard sand has a 90% cumulative particle size of 5.0 mm or less, it has the wear resistance required for a paving cement hardened body.

The fact that the 10% cumulative particle size by weight of the hard sand is 1.2 mm or more can be confirmed by the fact that less than 10% of the hard sand passes through a 1.2 mm sieve. Also, the fact that the 90% cumulative particle size by weight of the hard sand is 5.0 mm or less can be confirmed by the fact that more than 90% of the hard sand passes through a 5.0 mm sieve.

The particle size of the hard sand is adjusted as follows: First, the hard sand is sieved according to JIS A 1102 "Sieving test method for aggregates" until the amount of hard sand passing through the 5.0 mm sieve in one minute is 0.1% or less of the total hard sand. As with the 5.0 mm sieve, sieving is also performed for the 2.5 mm and 1.2 mm sieves until the amount of hard sand passing through the 2.5 mm and 1.2 mm sieves in one minute is 0.1% or less of the total hard sand. The sieved material is then mixed so that the 10% cumulative particle size by weight is 1.2 mm or more and the 90% cumulative particle size by weight is 5.0 mm or less.

The content of hard sand used in the present invention is 30% or more and 70% or less of the total amount of fine aggregate and hard sand in the concrete. Because the content of hard sand is 30% or more, the abrasion resistance required for a hardened cement body for paving is satisfied, and because it is 70% or less, the fluidity of the cement composition is suitable for construction.

In the above, the hard sand is configured so that the 10% weight cumulative particle size is 1.2 mm or more, the 90% weight cumulative particle size is 5.0 mm or less, and the hard sand content of the total amount of fine aggregate and hard sand is 30% to 70%, but it may also be configured as follows using a sieve.

When the particle size distribution of the fine aggregate is such that 100% passes through a 10 mm sieve, 90% to 100% passes through a 5.0 mm sieve, 80% to 100% passes through a 2.5 mm sieve, 50% to 90% passes through a 1.2 mm sieve, 25% to 65% passes through a 0.6 mm sieve, 10% to 35% passes through a 0.3 mm sieve, and 2% to 15% passes through a 0.15 mm sieve, the hard sand is mixed to replace the fine aggregate corresponding to the 1.2 mm to 5.0 mm portion.

(fiber)
The cement composition used in the present invention may contain one or more types of fibers selected from metal fibers, organic fibers, and carbon fibers, since this improves the bending strength, fracture energy, etc. of the hardened cement body. The fiber content in the cement composition is preferably 4 vol% or less, more preferably 3 vol% or less, further preferably 0.3 to 2.5 vol%, and particularly preferably 0.5 to 2.3 vol%. Since the fiber content in the cement composition is 4 vol% or less, the bending strength, fracture energy, etc. of the hardened cement body are improved without decreasing the fluidity and workability of the cement composition.

Metal fibers include steel fibers, stainless steel fibers, and amorphous fibers. Among these, steel fibers are preferred due to their excellent strength, cost, and ease of availability.

The dimensions of the metal fibers are preferably 0.01 to 1.0 mm in diameter and 2 to 30 mm in length, more preferably 0.05 to 0.5 mm in diameter and 5 to 25 mm in length, since this prevents separation of the metal fibers in the cement composition and improves the bending strength of the hardened cement body. The aspect ratio of the metal fibers (fiber length/fiber diameter) is preferably 20 to 200, more preferably 40 to 150.

Furthermore, the shape of the metal fibers is preferably spiral or wavy, which can provide physical adhesion, rather than straight. If the shape is spiral or the like, the metal fibers and matrix maintain stress while being pulled out, improving the bending strength of the hardened cement body.

The organic fibers may be any fibers that can withstand the heating in the method for producing a hardened cement body of the present invention described below, and examples of such fibers include aramid fibers, polyparaphenylene benzobisoxazole fibers, polyethylene fibers, polyallylate fibers, and polypropylene fibers.

Examples of carbon fibers include PAN-based carbon fibers and pitch-based carbon fibers.

The dimensions of the organic fibers and carbon fibers are preferably 0.005 to 1.0 m in diameter and 2 to 30 mm in length, more preferably 0.01 to 0.5 mm in diameter and 5 to 25 mm in length, in order to prevent material separation of the fibers in the cement composition and to improve the fracture energy of the hardened cement body. The aspect ratio of the organic fibers and carbon fibers (fiber length/fiber diameter) is preferably 20 to 200, more preferably 30 to 150.

(water)
The mixing ratio of water is preferably 10 to 20 parts by mass, more preferably 11 to 18 parts by mass, and even more preferably 14 to 16 parts by mass, per 100 parts by mass of the total of cement, silica fume, and inorganic powder. When the mixing ratio of water is 10 parts by mass or more, the fluidity of the cement composition is improved, and when it is 20 parts by mass or less, the compressive strength of the hardened cement body is increased.

(Coarse aggregate)
The cement composition of the present invention may contain coarse aggregate having a maximum particle size of more than 2.5 mm and not more than 20 mm.

The coarse aggregate may be one or more selected from fine aggregates such as river sand, mountain sand, land sand, sea sand, crushed sand, silica sand, recycled fine aggregate, and artificial fine aggregates such as fired fine aggregates made by firing slag fine aggregate, fly ash, etc., as well as river gravel, mountain gravel, land gravel, crushed stone, recycled coarse aggregate, and artificial coarse aggregates such as fired coarse aggregates made by firing slag coarse aggregate, fly ash, etc.

The maximum particle size of the coarse aggregate is preferably 20 mm or less, more preferably 15 mm or less. Since the maximum particle size of the coarse aggregate is 20 mm or less, the strength development of the cement composition is improved, and for example, a compressive strength of 300 N/mm2 or ^more can be developed.

The maximum particle size of the coarse aggregate is preferably more than 2.5 mm, and more preferably 5 mm or more. In this specification, the "maximum particle size" of the coarse aggregate refers to the particle size of the coarse aggregate indicated by the nominal size of the smallest sieve among those that pass 90% or more by mass of the entire coarse aggregate (this is generally known as the definition of the maximum particle size of coarse aggregate).

The minimum particle size of the coarse aggregate is preferably a value that exceeds the maximum particle size of the fine aggregate, and is more preferably 2 mm or more, even more preferably 3 mm or more, particularly preferably 4 mm or more, and extremely preferably 5 mm or more. In this specification, the minimum particle size of the coarse aggregate refers to the particle size of the coarse aggregate when it reaches 15% by mass of the entire coarse aggregate when accumulated from the smallest particle size to the largest particle size of the coarse aggregate.

In the present invention, the total content of fine aggregate and coarse aggregate in the hardened cement body is preferably 25 to 40% by volume, more preferably 28 to 38% by volume, and even more preferably 30 to 36% by volume. When the total content of fine aggregate and coarse aggregate in the hardened cement body is 25% by volume or more, the heat generation and shrinkage of the hardened cement body are reduced, and when it is 40% by volume or less, the strength expression of the hardened cement body is improved.

The content of coarse aggregate in the total of fine aggregate and coarse aggregate is preferably 40% by volume or less, more preferably 30% by volume or less, and even more preferably 25% by volume or less. Since the content of coarse aggregate in the total of fine aggregate and coarse aggregate is 40% by volume or less, the strength expression such as compressive strength of the hardened cement body is improved.

The compressive strength of the hardened cement body obtained by hardening the cement composition containing coarse aggregate is preferably 300 N/ ^mm2 or more, more preferably 320 N/mm2 or ^more , even more preferably 340 N/ ^mm2 or more, and particularly preferably 360 N/ ^mm2 or more.

(Physical properties of cement composition (mortar) and hardened cement body)
The flow value before hardening of mortar made of the cement composition (not including coarse aggregate) measured by the method described in "11. Flow test" of JIS R 5201 "Physical test method for cement" omitting 15 dropping motions (hereinafter referred to as "zero-pump flow value") is preferably 230 mm or more, more preferably 250 mm or more. A flow value of 230 mm or more improves the workability when producing a hardened cement body. The slump flow test of concrete was performed in accordance with JIS A 1150:2007. When the cement composition contains coarse aggregate, the zero-pump flow value is preferably 450 mm or more, more preferably 500 mm or more.

The compressive strength of the hardened cement body is preferably 300 N/ ^mm2 or more, more preferably 350 N/ ^mm2 or more, and even more preferably 400 N/ ^mm2 or more. When the cement composition contains coarse aggregate, the compressive strength of the hardened cement body is preferably 300 N/ ^mm2 or more, more preferably 320 N/ ^mm2 or more, and even more preferably 360 N/ ^mm2 or more.

[Composition of precast concrete slab]
The precast concrete slab of the present invention includes at least the above-mentioned hardened cement body. In addition, the precast concrete slab may include a joint structure for joining the precast concrete slabs to each other, in addition to the hardened cement body.

[Method of manufacturing hardened cement body]
The method for producing a hardened cement body of the present invention includes (A) a molding step, (B) a room temperature curing step, (C) a heat curing step, and (D) a high temperature heating step.

The manufacturing method for hardened cement is explained below in steps (A) to (E). Note that steps (A) to (D) are essential in the present invention, and step (E) is an optional step.

(A) Molding process The molding process is a process of casting the cement composition into a formwork to obtain an unhardened molded body. The method of kneading the cement composition before casting and the device used for kneading are not particularly limited, and an omni mixer, a pan mixer, a biaxial mixer, a tilting mixer, etc. can be used. Furthermore, the method of casting and molding is also not particularly limited. In the molding process, the air bubbles in the unhardened cement composition are reduced or removed, and the strength development of the hardened concrete structure is further improved.

Methods for reducing or eliminating air bubbles in a cement composition include the following methods (i) to (iii).
(i) A method of kneading a cement composition under reduced pressure. (ii) A method of degassing the kneaded cement composition by reducing the pressure before pouring it into a formwork. (iii) A method of degassing the cement composition by reducing the pressure after pouring it into a formwork.

(B) Room temperature curing step The room temperature curing step is a step in which the uncured molded body is subjected to sealed curing or air curing at 10 to 40° C., preferably 15 to 30° C., for 24 hours or more, more preferably 24 to 72 hours, and even more preferably 24 to 48 hours, and then demolded to obtain a cured molded body.

If the curing temperature is 10°C or higher, the curing time can be shortened. Since the curing temperature is 40°C or lower, the compressive strength of the hardened cement body is higher. Also, since the curing time is 24 hours or longer, defects such as chips and cracks are less likely to occur in the hardened molded body when it is removed from the mold.

In the room temperature curing step, the hardened molded body is demolded when the compressive strength of the hardened molded body is preferably 20 to 100 N/ ^mm2 , more preferably 30 to 80 N/ ^mm2 . If the compressive strength is 20 to 100 N/ ^mm2 or more, defects such as chips and cracks are unlikely to occur in the hardened molded body when demolded. Since the compressive strength is 100 N/mm2 or ^less , the hardened molded body can absorb water with little effort in the water absorption step described below.

(C) Heat Curing Step The heat curing step is a step in which the hardened molded body obtained in the previous step is subjected to either or both of steam curing or hot water curing preferably at 70° C. or higher but lower than 100° C., more preferably 75 to 95° C., and more preferably 80 to 92° C., for 6 hours or more, and autoclave curing preferably at 100 to 200° C., more preferably 160 to 190° C., for 1 hour or more, to obtain a hardened body after heat curing.

When only steam curing or hot water curing is performed in the heat curing step, the curing time is preferably 24 hours or more, more preferably 24 to 96 hours, and even more preferably 36 to 72 hours. When only autoclave curing is performed, the curing time is preferably 8 to 60 hours, and more preferably 12 to 48 hours. When both steam curing or hot water curing and autoclave curing are performed (for example, when steam curing or hot water curing is performed followed by autoclave curing), the curing time for steam curing or hot water curing is preferably 6 to 72 hours, and more preferably 12 to 48 hours, and the curing time for autoclave curing is preferably 1 to 24 hours, and more preferably 4 to 18 hours.

In the heat curing process, if the curing temperature and curing time are within the above ranges, the curing time can be shortened and the compressive strength of the hardened cement body can be improved.

(D) High-temperature heating step The high-temperature heating step is a step in which the hardened body after heat curing is heated preferably at 150 to 200°C, more preferably at 170 to 190°C, for 24 hours or more, preferably for 24 to 72 hours, more preferably for 36 to 48 hours (excluding heating due to autoclave curing) to obtain a hardened cement body.

The heating in the high-temperature heating process is usually carried out in a dry atmosphere, in other words, without the artificial supply of water or water vapor. A heating temperature of 150°C or higher allows the heating time to be shortened, while a heating temperature of 200°C or lower improves the compressive strength of the hardened cement body. In addition, a heating time of 24 hours or more improves the compressive strength of the hardened cement body.

(E) Water Absorption Step The water absorption step is an optional step between the room temperature curing step and the heat curing step in which the hardened molded body obtained in the room temperature curing step is allowed to absorb water.

The method for making the cured molded body absorb water includes the following methods (i) to (v).
(i) A method of immersing a molded body in water under reduced pressure; (ii) A method of lowering the water temperature to 40°C or less while immersing the molded body in boiling water; (iii) A method of immersing the molded body in boiling water, removing the molded body from the boiling water, and immersing the molded body in water at 40°C or less; (iv) A method of immersing a molded body in water under pressure; (v) A method of immersing a molded body in an aqueous solution containing an agent that improves the water permeability of the molded body.

And, regarding (i) and (ii) above,
(i) The method of immersing a molded body in water under reduced pressure includes a method using equipment such as a vacuum pump or a large reduced pressure vessel,
(ii) The method of immersing the molded body in boiling water may utilize equipment such as a high-temperature, high-pressure container or a hot water tank. The time for immersing the molded body in reduced pressure water or boiling water is preferably 3 minutes or more, more preferably 8 minutes or more, and even more preferably 20 minutes or more in order to promote water absorption. The upper limit of the immersion time is preferably 60 minutes, more preferably 45 minutes in order to increase the compressive strength of the hardened cement body.

When the cement composition does not contain coarse aggregate, the water absorption rate in the water absorption step is preferably 0.2 vol% or more, more preferably 0.3 to 2.0 vol%, and even more preferably 0.35 to 1.7 vol%, assuming a hardened molded body with a diameter of 50 mm and a height of 100 mm as 100 vol%. When the cement composition contains coarse aggregate, the water content in the hardened molded body with a diameter of 100 mm and a height of 200 mm as 100 vol% is preferably 0.2 vol% or more, more preferably 0.3 to 2.0 vol%, and even more preferably 0.35 to 1.7 vol%.

If these water absorption rates are 0.2% by volume or more, the compressive strength of the hardened cement paste will be higher.

(Characteristics of hardened cement)
The hardened cement product of the present invention obtained by the above-mentioned manufacturing method has high compressive strength and is therefore less susceptible to cracks, etc. In addition, the hardened cement product can be used to reduce the weight of components, for example by reducing their thickness, and can also improve workability.

The hardened cement body of the present invention also has excellent abrasion resistance. For example, the abrasion depth of the hardened cement body after 60 minutes, measured in accordance with "ASTM C779," is preferably 0.5 mm or less, more preferably 0.4 mm or less, and even more preferably 0.3 mm or less. Since the abrasion depth of the hardened cement body is 0.5 mm or less, it has the abrasion resistance required for a hardened cement body for paving.

The hardened cement body of the present invention also has excellent water impermeability, freeze-thaw resistance, and salt impermeability.

The hardened cement product of the present invention also has excellent dimensional stability. For example, the shrinkage strain of a 40×40×160 mm test piece measured in accordance with JIS A 1129-2:2010 "Method for measuring change in length of mortar and concrete-Part 2: Contact gauge method" and stored for six months is preferably 10× ^10-6 or less, more preferably 8× ^10-6 or less, and even more preferably 6× ^10-6 or less.

[Example]
Examples and comparative examples using the method for producing a hardened cement body will be described below, but the present invention is not limited to these examples.

(Preparation of test specimen)
First, the cement composition before casting was mixed and cast into a formwork to obtain an unhardened molded body. The unhardened molded body was cured and then demolded to obtain a hardened molded body. Next, the hardened molded body was immersed in water for 30 minutes in a depressurized desiccator. For the depressurization, an "Aspirator (AS-01)" manufactured by AS ONE Corporation was used. After immersion, the molded body was steam cured at 90°C for 48 hours as a heat curing process. After lowering the temperature to 20°C, the molded body was heated at 180°C for 48 hours as a high-temperature heating process. In this manner, test specimens for each example and each comparative example were prepared.

The cement compositions in each Example and Comparative Example are as shown in Figure 2. The "spheroidized" description for the cement in Example 10 indicates that the cement has been polished. A high-speed airflow agitator, product name "Hybridizer NHS-3 Type" (manufactured by Nara Machinery Works, Ltd.), was used for the polishing process.

The cement used was low-heat Portland cement (manufactured by Taiheiyo Cement Corporation). The cement that was not polished had a Blaine specific surface area of 3320 ^cm2 /g and a 50% weight cumulative particle size of 15.6 μm. The cement that was polished had a Blaine specific surface area of 2350 ^cm2 /g and a 50% weight cumulative particle size of 15.1 μm.

The silica fume used had a BET specific surface area of 18 m ² /g.
Silica powder was used as the inorganic powder. The silica powder had a maximum particle size of 12 μm, a 50% volume cumulative particle size of 2 μm, and a 95% volume cumulative particle size of 5.8 μm.

Tap water was used.
The fine aggregate used was silica sand, which had a maximum particle size of 1.0 mm, 98% by mass of particles with a particle size of 0.6 mm or less, 45% by mass of particles with a particle size of 0.3 mm or less, and 3% by mass of particles with a particle size of 0.15 mm or less.

The hard sands used were garnet sand, quartz, alumina, silicon carbide, and granite. The garnet sand had a new Mohs hardness of 10 and a maximum grain size of 1.2 mm. The quartz had a new Mohs hardness of 8 and a maximum grain size of 4.7 mm, with 11.5% of the grains being 4.7-4.0 mm, 17% being 4.0-3.35 mm, 32% being 3.35-2.8 mm, 28.2% being 2.8-2.36 mm, and 9.2% being 2.36-2.0 mm. The alumina had a new Mohs hardness of 12 and a maximum grain size of 3.3 mm, with 20% or more by mass being 3.3-2.4 mm, 45% or more by mass being 2.4-2.0 mm, and 70% or more by mass being 2.4-1.7 mm. The silicon carbide had a new Mohs hardness of 13, a maximum grain size of 4.0 mm, 20% or more by mass of grains between 4.0-2.8 mm, 45% or more by mass of grains between 2.8-2.4 mm, and 70% or more by mass of grains between 2.4-2.0 mm. The granite had a new Mohs hardness of 7, and met the grain size specified for crushed sand in JIS A5005 "Crushable stone and crushed sand for concrete." In addition, the 10% cumulative grain size by weight for each hard sand was 1.2 mm or more, and the 90% cumulative grain size by weight was 5.0 mm or less.

In this specification, the 10% and 90% weight cumulative particle sizes of hard sand refer to the particle sizes at which the particles reach 10% and 90% by weight of the total particles when they are accumulated in order from the smallest particle size.

Crushed stone was used as the coarse aggregate, with a maximum particle size of 20 mm.
The high-performance water reducing agent used was a polycarboxylic acid-based high-performance water reducing agent with the trade name "Floric SF500U" (manufactured by Floric Co., Ltd.) The polycarboxylic acid-based high-performance water reducing agent had a solid content of 27.4 mass%.

The antifoaming agent used was "Master Air 404" (manufactured by BASF Japan).
The fibers used were steel fibers having a diameter of 0.2 mm and a length of 15 mm.

(test)
For each of the examples and comparative examples, the flow value, compressive strength, abrasion depth, and shrinkage strain were measured.

The flow value was measured using the method described in "11. Flow test" of JIS R 5201 "Physical test methods for cement", omitting the 15 drop motions, and was measured as a zero-shot flow value. In addition, using the method described in JIS A 1150:2007 "Slump flow test method for concrete", the diameter that was thought to be the largest after the concrete stopped moving and the diameter in the direction perpendicular to that were measured.

The compressive strength of the mortar after curing was measured in accordance with "JSCE G 505-2018 (Draft method for testing compressive strength of mortar or cement paste using cylindrical specimens)".

The abrasion depth was measured by manufacturing a test specimen measuring 30 x 30 x 6 cm and measuring the abrasion depth after 60 minutes in accordance with ASTM C779.

To measure shrinkage strain, 40 x 40 x 160 mm test specimens were manufactured and an embedded strain gauge (Tokyo Measuring Instruments Laboratory KM-30) and a thermocouple were embedded in the center of the test specimen in accordance with the Autogenous Shrinkage Test Method (Draft) of the Japan Concrete Institute (Report of the Research Committee on Super-Fluid Concrete (II), Japan Concrete Institute, 1994) to measure autogenous shrinkage strain.

Each example and each comparative example was evaluated according to the criteria shown in Table 1 below, and was rated as very good (A), good (B), pass (C), or fail (E).

The results of various measurements for each of the Examples and Comparative Examples are shown in Table 2 below.

The examples were rated as pass (C) or better in terms of flow value, compressive strength, abrasion depth, and shrinkage strain. In addition, in example 7, which contained 70% silicon carbide relative to the total amount of fine aggregate and hard sand, the abrasion depth was rated as very good (A), which shows that among quartz, alumina, and silicon carbide, silicon carbide in particular improves wear resistance.

In Examples 8 and 9, where coarse aggregate was added, the shrinkage strain was evaluated as extremely good (A), which indicates that the addition of coarse aggregate further improves dimensional stability. In Example 10, where two types of hard sand, alumina and silicon carbide, were used, the abrasion depth and shrinkage strain were also evaluated as extremely good (A), which indicates that the use of two or more types of hard sand further improves abrasion resistance and dimensional stability.

In Example 11, where the cement was polished, the compressive strength and abrasion depth were rated as extremely good (A), which indicates that polishing the cement improves the compressive strength and abrasion resistance. In Example 12, where 3% fiber was included, the compressive strength and abrasion depth were rated as extremely good (A). In Example 13, where 4% fiber was included, not only the compressive strength and abrasion depth but also the shrinkage strain was rated as extremely good (A). Therefore, it can be said that the inclusion of fiber improves the compressive strength, abrasion resistance, and dimensional stability.

In contrast, the comparative example was rated as failing (E) in either flow value, compressive strength, wear depth, or shrinkage strain.

From the above, the hardened cement product of the present invention not only meets the abrasion resistance required for a hardened cement product for paving, but also has the fluidity of the cement composition suitable for application. Therefore, it has sufficient application and filling properties when applying the cement.

REFERENCE SIGNS LIST 10 Polishing device 11 Rotor 12 Blade 13 Circulation circuit 13a Inlet of circulation circuit 13b Outlet of circulation circuit 14 Input port 15 Discharge port 16 Stator 17 Collision chamber 18 Opening/closing valve 19 Discharge valve

Claims (7)

A hardened product of a cement composition comprising at least cement, silica fume, an inorganic powder, a fine aggregate, hard sand, a high-performance water reducing agent, a defoaming agent, and water,
The compressive strength is 300 N/ ^mm2 or more,
The maximum particle size of the fine aggregate is 1.2 mm or less,
The hardness of the hard sand is higher than the hardness of the fine aggregate,
The grain size of the hard sand is such that the 10% weight cumulative grain size is 1.2 mm or more and the 90% weight cumulative grain size is 5.0 mm or less;
A hardened cement body, characterized in that the content of said hard sand relative to the total amount of said fine aggregate and said hard sand is 30% or more and 70% or less. The hardened cement body according to claim 1, further comprising coarse aggregate having a maximum particle size of more than 2.5 mm and not more than 20 mm. The hardened cement body according to claim 1 or 2, characterized in that the hard sand has a new Mohs hardness of 8 or more. The hardened cement body according to any one of claims 1 to 3, characterized in that the hard sand is one or more types selected from quartz, alumina, and silicon carbide. The cement comprises ground particles of medium-heat or low-heat Portland cement;
The polished particles have a 50% cumulative particle size by volume of 10 to 18 μm;
5. The hardened cement product according to claim 1, characterized in that the Blaine specific surface area is 2100 to 2900 cm ² /g. The hardened cement body according to any one of claims 1 to 5, characterized in that it contains one or more types of fibers selected from metal fibers, organic fibers, and carbon fibers, and the fiber content is 4 volume % or less. A precast concrete slab comprising the hardened cement body according to any one of claims 1 to 6.