JP5165436B2 - Concrete composition and hardened concrete - Google Patents

Description

  The present invention relates to a concrete composition and a concrete cured body, and more particularly to a concrete composition capable of suppressing abnormal expansion due to the addition of an expandable admixture, and a concrete cured body obtained by curing the concrete composition.

In recent years, from the viewpoint of further effective use of land, the tendency of building to become super high-rise or large-scale has become remarkable. In order to manufacture such a super high-rise building or large-scale building, it is required to increase the strength of the concrete, and for that purpose, development of an ultra-high strength concrete having a compressive strength of about 150 N / mm ² or more. Has been done.

Such ultra-high-strength concrete increases the amount of binder in the entire hardened concrete by adding a binder such as silica fume having a low BET specific surface area (for example, about 10 m ² / g) to cement, and a water reducing agent. It is possible to develop high strength (for example, 100 N / mm ² or more) by lowering the water binder ratio using, for example, 25% by mass or less. There is a problem that the self-shrinkage strain of the hardened concrete body is significantly increased by lowering.

  When self-shrinkage strain occurs in the hardened concrete, it may cause cracks. The cracks generated in this way not only detract from the aesthetics of the hardened concrete, but also the corrosion of the steel in the hardened concrete and the concrete. This will cause a decrease in the water tightness of the hardened body and reduce the strength of the concrete hardened body.

  In view of such circumstances, the present invention is a concrete that exhibits high compressive strength, can reduce shrinkage strain due to self-shrinkage, drying shrinkage, etc., and can prevent the occurrence of cracks due to shrinkage strain. It aims at providing a composition and a concrete hardening body.

In order to solve the above problems, the present invention includes a cement, and silica _{fume, 3CaO · SiO 2 -2CaO · SiO} 2 -CaO- gap material based composition, 3CaO _· SiO 2 -CaO- gap material based composition, 2CaO · _SiO 2 -CaO- gap material based composition, and CaO-1 kind selected from the group consisting of interstitial material based composition or comprises two or more compositions, and when the content ratio is 50 to 92 wt% of CaO A concrete composition comprising an clinker composition, and an expansive admixture containing gypsum and having a brain specific surface area of 4000 to 7000 cm ² / g is provided ( Invention 1).

According to the above invention ( Invention 1), ettringite (3CaO.Al ₂ O) is obtained by a reaction between gypsum (CaSO ₄ ) and calcium aluminate (particularly tricalcium aluminate (C ₃ A)) in the expandable admixture. _{for 3 · 3CaSO 4 · 32H 2 O} ) is generated, by curing such concrete compositions, by ettringite concrete cured body in, it is possible to reduce shrinkage strain of the concrete hardened body, cracking due to shrinkage strain Can be prevented.

Here, in the present invention, “3CaO · SiO ₂ −2CaO · SiO ₂ —CaO—interstitial material composition” means 0.5% by mass or more of alite (3CaO · SiO ₂ ) and 0.5% by mass. It refers to a composition containing the above belite (2CaO · SiO ₂ ), a CaO crystal, and a gap substance.

In the present invention, the “3CaO · SiO ₂ —CaO—interstitial material composition” includes 0.5% by mass or more of alite (3CaO · SiO ₂ ), CaO crystal, and interstitial material, This refers to a composition having a belite (2CaO.SiO ₂ ) content of less than 0.5% by mass.

Furthermore, in the present invention, “2CaO · SiO ₂ —CaO—interstitial material composition” includes 0.5% by mass or more of belite (2CaO · SiO ₂ ), CaO crystals, and interstitial materials, This refers to a composition having an alite (3CaO.SiO ₂ ) content of less than 0.5% by mass.

Furthermore, the "CaO- gap material based composition" in the present invention contains a CaO crystal and the gap material, the content of alite (3CaO · SiO ₂₎ and belite (2CaO · SiO ₂₎ both It means less than 0.5% by weight.

In the said invention ( invention 1), it is preferable that the said expandable admixture contains 5-50 mass parts of said gypsum with respect to 100 mass parts of said clinker compositions ( invention 2).

According to the above invention (Invention 2), Within the above range, the amount of gypsum in the expandable admixture, by the generated ettringite _{(3CaO · Al 2 O 3 ·} 3CaSO 4 · 32H 2 O), concrete curing Body contraction can be effectively suppressed.

Moreover, in the said invention ( invention 1), it is preferable that the said expansive admixture further contains quicklime ( invention 3). According to this invention ( invention 3), quick lime contained in the expandable admixture expands with the hydration reaction, so that the shrinkage of the hardened concrete can be further suppressed.

In the said invention ( invention 3), the said expansive admixture contains 20 mass parts or more of the said clinker composition in a total of 100 mass parts of the said clinker composition and the said quicklime, The said clinker composition and the said It is preferable that 5-50 mass parts of said gypsum is included with respect to a total of 100 mass parts with quicklime ( invention 4).

If it is the mixture ratio in the said invention ( invention 4), a concrete hardened | cured material will not expand too much, the shrinkage | contraction of a concrete hardened | cured material can be suppressed effectively, and the crack by shrinkage | contraction distortion can be prevented.

In the above invention (invention 1 to 4), that the expandable admixture in the concrete hardened body 1 m ³ obtained by curing the concrete composition contains the expandable admixture to include 10~60kg Preferred ( Invention 5). If the blending amount of the expansive admixture is the blending amount of the invention ( Invention 5), the shrinkage of the hardened concrete can be effectively suppressed, and the occurrence of cracks due to shrinkage strain can be prevented.

Moreover, this invention knead | mixes the concrete composition which concerns on the said invention ( invention 1-5), and is made to harden | cure, The compounding ratio of the said concrete composition and the said water is 4-10: 1. There is provided a hardened concrete body ( Invention 6).

According to the said invention ( invention 6), since the compounding ratio of a concrete composition and water is in the said range, the compounding ratio of the binder in a concrete hardening body can be increased, and high intensity | strength is expressed. The shrinkable strain of the hardened concrete can be reduced by the expansive admixture contained in the concrete composition, and cracking due to the shrinkage strain can be prevented.

  ADVANTAGE OF THE INVENTION According to this invention, the concrete composition and concrete hardened | cured material which can express the high compressive strength, can reduce the shrinkage | contraction distortion by self shrinkage, drying shrinkage, etc., and can prevent generation | occurrence | production of the crack by a shrinkage distortion, etc. Can be provided.

The present invention will be described below.
The concrete composition of the present invention contains cement, silica fume, and an expandable admixture.

  The cement is not particularly limited, and examples thereof include various portland cements such as ordinary portland cement, early-strength portland cement, moderately hot portland cement, and low heat portland cement; various mixed cements such as blast furnace cement and fly ash cement; Cement (eco-cement) composed of a pulverized product of gypsum and gypsum produced using municipal waste incineration ash and / or sewage sludge incineration ash as raw materials can be used.

BET specific surface area of silica fume is preferably 5 to 15 m ² / g, more preferably 7~13m ² / g. When the BET specific surface area of silica fume is less than 5 m ² / g, the viscosity of the concrete becomes too small and material separation is likely to occur, and the amount of admixtures such as water reducing agents and high performance water reducing agents becomes too small and the slump flow. There is a risk that the loss of change over time will increase. On the other hand, if it exceeds 15 m ² / g, the viscosity becomes too high, making it difficult to mix concrete, resulting in poor workability and excessive use of admixtures such as water reducing agents and high performance water reducing agents. There is a risk of delay, and the effect of the expandable admixture may be difficult to obtain.

The expandable admixture includes a clinker composition and gypsum, and preferably further includes quicklime. The clinker _{composition, 3CaO · SiO 2 -2CaO · SiO} 2 -CaO- gap material based composition, 3CaO _· SiO 2 -CaO- gap material based composition, 2CaO _· SiO 2 -CaO- gap material based composition, And one or more compositions selected from the group consisting of CaO-interstitial material-based compositions, and the CaO content is 50 to 92% by mass.

Gap substances contained in the clinker composition in expandable admixture is one similar to the mineral filling between the cement clinker minerals in alite (3CaO · SiO ₂₎ and belite (2CaO · SiO _2). Such gap material, for example, calcium ferrite minerals such as 2CaO · _Fe 2 _{O 3;} calcium aluminate minerals such as _{3CaO · Al 2 O 3; 6CaO} · Al 2 O 3 · Fe 2 O 3, 4CaO · Al _{2 O 3 · Fe 2 O 3} , calcium such as _{6CaO · 2Al 2 O 3 · Fe} 2 O 3 alumino ferrite minerals, and the like.

  The content rate of CaO in a clinker composition is 50-92 mass% with respect to the total mass of a clinker composition. If the CaO content is less than 50% by mass, it may be difficult to develop strength at an early stage. If the CaO content exceeds 92% by mass, the content of interstitial materials will be relatively reduced, and the hardened concrete body. There is a risk that it will be difficult to suppress the shrinkage of the resin.

The clinker composition may contain alite (3CaO · SiO ₂ ) or belite (2CaO · SiO ₂ ), or may not contain these alite or belite, The clinker composition containing these alite and belite can significantly suppress the hydration rate of CaO, and the hydrate of these alite and belite contributes to the development of cement strength.

  The clinker composition is prepared by mixing raw materials such as calcareous raw material, clay raw material, silica stone, slags, gypsum and the like so as to have the above composition, and preparing the raw material mixture until the target clinker mineral composition is obtained. It can be obtained by baking the mixture sufficiently at a temperature of 1300 to 1600 ° C. in a rotary kiln or the like.

In addition, when baking a raw material mixture, you may add a mineralizer (flux) to a raw material mixture. Thereby, the manufacturing efficiency of a clinker composition can be improved. As a mineralizer, what is generally used when a cementitious compound is fired can be used. Specifically, gypsum, fluorite, serpentinite and the like containing compounds such as CaSO ₄ , CaF ₂ , Fe ₂ O, MgO, and Al ₂ O ₃ can be used as mineralizers. The addition amount of these mineralizers should just be about 10 mass% or less with respect to the mass of a raw material mixture.

The expandable admixture includes gypsum together with the clinker composition. By containing gypsum in the expandable admixture, ettringite (3CaO · Al ₂ O ₃ · 3CaSO ₄ · 32H ₂ O) is generated, which can suppress shrinkage of the hardened concrete, and concrete. The initial strength (demolding strength during simple steam curing) of the cured body can be increased.

  As the gypsum, commercially available gypsum can be used. Gypsum is classified into anhydrous gypsum, hemihydrate gypsum, and dihydrate gypsum according to its crystal form, and any gypsum may be used, and anhydrous gypsum can be preferably used.

  The amount of gypsum in the expandable admixture is preferably 5 to 50 parts by mass with respect to 100 parts by mass of the clinker composition. When quick lime is contained in the expandable admixture, the blending amount of gypsum is preferably 5 to 50 parts by mass with respect to 100 parts by mass as the total amount of the clinker composition and quick lime. If the blending amount of gypsum is less than 5 parts by mass, it is difficult to suppress shrinkage of the hardened concrete body, and there is a possibility that strength will not be developed at an early stage. There is a risk of cracking.

  The expandable admixture preferably further contains quick lime. Quick lime expands and generates heat due to the hydration reaction, so it can further suppress the shrinkage of the hardened concrete, and the calorific value of the entire expandable admixture increases, further improving the early strength development of the hardened concrete. Can be made.

  Quick lime is classified into extremely soft calcined quick lime, soft calcined quick lime, medium calcined quick lime, hard calcined quick lime, and extremely hard calcined quick lime, and the evaluation method is generally a coarse-grain titration test method using 4N hydrochloric acid of the Japan Lime Association. Is used. According to this coarse-grain titration test method, quick lime is classified based on the total amount of 4N hydrochloric acid used for the titration, extremely soft calcined quick lime has a usage amount of 4N hydrochloric acid of 800 mL or more, and soft calcined quick lime is composed of 4N hydrochloric acid. The amount used is 650 mL or more and less than 800 mL, the medium-burnt quicklime is one whose 4N hydrochloric acid is used in an amount of 300 mL or more and less than 650 mL, and the hard-burned quicklime is one whose 4N hydrochloric acid is used in an amount of 130 mL or more and less than 300 mL, Extremely hard calcined quicklime has a usage amount of 4N hydrochloric acid of less than 130 mL.

  The quicklime that can be contained in the expandable admixture may be quicklime that is generally commercially available, but among the quicklime that is classified in this way, it is possible to use quicklime that uses 4N hydrochloric acid in an amount of 650 mL or less. Particularly, it is preferable to use quick lime in which the amount of 4N hydrochloric acid used is 400 mL or less. By including such quicklime, the workability of fresh concrete can be improved.

  When quick lime is included in the expandable admixture, the content of quick lime is preferably 80% by mass or less of the total mass of the clinker composition and quick lime. If the content of quicklime exceeds 80% by mass of the total mass of the clinker composition and quicklime, the amount of expansion of the hardened concrete body due to the hydration reaction may increase excessively.

  The expandable admixture contains the above clinker composition and gypsum, preferably further contains quicklime, and is preferably a mixed pulverized product obtained by pulverizing these mixtures. The mixed pulverized product may be obtained by pulverizing each of the clinker composition, gypsum, and quicklime, or may be pulverized after mixing the clinker composition, gypsum, and quicklime. The pulverization can be performed using a pulverizer used for pulverizing ordinary cement such as a ball mill and a roll mill.

The mixed pulverized product (expandable admixture) thus obtained has a Blaine specific surface area of 4000 to 7000 cm ² / g, preferably 4200 to 6000 cm ² / g. If the Blaine specific surface area of the mixed pulverized product (expandable admixture) is less than 4000 cm ² / g, abnormal hardening of the hardened concrete may occur, and it is costly to produce a product exceeding 7000 cm ² / g. It will take.

In the concrete composition, the expansive admixture is preferably blended in an amount of 10-60 kg in 1 m ^{3 of the} hardened concrete body obtained by curing the concrete composition, and 15-50 kg in 1 m ^{3 of the} hardened concrete body. It is more preferable to mix the occupied amount. If the amount of the expandable admixture in the hardened concrete body 1 m ³ is within the above range, the self-shrinkage strain can be reduced while maintaining high strength. In particular, even if the blending amount of the expandable admixture is increased in the concrete composition of the present invention, there is no risk of abnormal expansion after setting, and the self-shrinkage strain can be effectively reduced while maintaining high strength. it can.

  The concrete composition may further contain a coarse aggregate or a fine aggregate. As the coarse aggregate, for example, gravel, crushed stone, various lightweight coarse aggregates, various slag aggregates, recycled coarse aggregate, or a mixture thereof can be used. Examples of the fine aggregate include river sand, mountains Sand, land sand, sea sand, crushed sand, quartz sand, various lightweight fine aggregates, various slag aggregates, recycled fine aggregates, or a mixture thereof can be used.

The concrete composition may contain other components other than the cement, the silica fume, and the expandable admixture as long as the effect of reducing the shrinkage strain of the hardened concrete is not hindered. The components that may be included in the concrete composition, for example, alite (3CaO · _SiO 2), belite Portland cement clinker containing (2CaO · SiO ₂₎ or the like; lignin, naphthalene sulfonic acid, melamine, polycarboxylic Acid-based water reducing agents, AE water reducing agents, high-performance water reducing agents, high-performance AE water reducing agents, and the like; and other additives. The blending amount of Portland cement clinker and various water reducing agents in the hydraulic composition may be an amount that does not hinder the effect of reducing the shrinkage strain of the hardened concrete.

  By adding a predetermined amount of water to the concrete composition of the present invention and kneading, pouring the kneaded product into a mold or the like, curing by curing with heat curing, underwater curing, steam curing, autoclave curing, etc. A hardened concrete body can be produced. When producing a hardened concrete body, cement, silica fume, and the above expandable admixture may be mixed in advance, and then a predetermined amount of water may be added and kneaded, or a predetermined amount of water may be added to cement and silica fume. Then, the above expandable admixture may be added and further kneaded, but the former is preferable because the expandable admixture is more uniformly mixed with the hardened concrete.

The water-bonding material ratio is 25% by mass or less, preferably 20% by mass or less, so that the hardened concrete obtained in this way can exhibit high compressive strength (for example, 100 N / mm ² or more). Particularly preferably, it is 17% by mass or less. By reducing the water binder ratio, the compressive strength of the hardened concrete is generally improved, but abnormal expansion tends to occur. However, according to the concrete composition of the present invention, the compressive strength of the hardened concrete can be improved without causing abnormal expansion in the obtained hardened concrete.

  The hardened concrete thus obtained contains the above-mentioned expansive admixture in the concrete composition, so that the shrinkage strain of the hardened concrete body is reduced and cracks due to shrinkage strain and the like can be prevented. In addition, high compressive strength can be expressed. Therefore, the hardened concrete body of the present invention can be suitably used as a concrete product requiring high strength and durability, such as a super high-rise building.

  EXAMPLES Hereinafter, although an Example and a test example demonstrate this invention further in detail, this invention is not restrict | limited at all to the following Example and test example.

[Examples 1-5, Comparative Examples 1-3]
Fine aggregate S (mountain sand from Kato, Kikukawa City, Shizuoka Prefecture, surface dry density: 2.61 g / cm ³ , water absorption: 1.66%, unit volume mass: 1.70 kg / L, actual volume ratio: 66.2% , Coarse particle ratio: 2.88, fine powder content: 1.4%) and silica fume mixed cement C (trade name: silica fume premix cement (SFPC), density: 3.07 g / cm ³ , specific surface area: 6160 cm ² / g, manufactured by Taiheiyo Cement Co., Ltd.) and expandable admixture EX (trade name: Pacific N-EX, density: 3.19 g / cm ³ , Blaine specific surface area: 4920 cm ² / g, manufactured by Taiheiyo Materials Co., Ltd.) For 30 seconds, water W, high-performance water-reducing agent SP (polycarboxylic acid-based high-performance water-reducing agent, trade name: Leo Build SP8HU, manufactured by NMB), and air amount regulator (trade name: Micro Air 404). , N After being mixed for 120 seconds, coarse aggregate G (crushed stone from Iwase, Ibaraki Prefecture, Iwase, coarse aggregate maximum dimension: 20 mm, surface dry density: 2.64 g / cm ³ , water absorption: 0.67%, unit volume mass: 1.59 kg / L, actual volume ratio: 60.1%, coarse grain ratio: 6.74, fine powder content: 0.2%), and kneaded for 90 seconds, concrete Compositions were obtained (Examples 1-3).

Implemented except that expandable admixture EX (density: 3.16 g / cm ³ , brane specific surface area: 4280 cm ² / g) having a different Blaine specific surface area was used instead of expandable admixture EX in Examples 1 to 3. Concrete compositions were obtained in the same manner as in Examples 1 to 3 (Example 4). Moreover, it replaced with the expansible admixture EX in Examples 1-3, except having supplied the expansible admixture EX (density: 3.16g / cm < ³ >, brane specific surface area: 4580cm < ² > / g) from which a specific surface area of a brane differs. Obtained a concrete composition in the same manner as in Examples 1 to 3 (Example 5).

Table 1 shows the blending ratio of each raw material. In Comparative Example 1, no expansive admixture was added, and in Comparative Example 2, an expansive admixture EX having a different Blaine specific surface area from the expansive admixture blended in the hardened concrete bodies of Examples 1 to 3 ( Product name: Taiheiyo Hyperexpan, density: 3.16 g / cm ³ , Blaine specific surface area: 3280 cm ² / g), and Comparative Example 3 is “Denka Power” manufactured by Denki Kagaku Kogyo Co., Ltd. as an expandable admixture EX. CSA "(density: 3.10 g / cm ³ , brain specific surface area: 3904 cm ² / g) was used.

  The concrete composition thus obtained was poured into a steel mold and subjected to underwater curing or sealing curing to obtain hardened concrete (Examples 1 to 5, Comparative Examples 1 to 3).

[Test Example 1] Slump Flow Test A slump flow test was performed on the fresh concrete obtained at the blending ratios of Examples 1 to 5 and Comparative Examples 1 to 3 based on JIS-A1150. The air amount was measured according to JIS-A1128, and the setting test was performed according to JIS-A1147.
The results are shown in Table 2.

  As shown in Table 2, it was confirmed that the concrete hardened | cured material of Examples 1-5 has a slump flow equivalent to the concrete hardened | cured material of Comparative Examples 1-3. From this, it was confirmed that the concrete hardened | cured material of Examples 1-5 can ensure sufficient workability. Moreover, it was confirmed that both the hardened concrete bodies of Examples 1 to 5 and the hardened concrete bodies of Comparative Examples 2 and 3 were shortened by about 2 hours compared with the hardened concrete body of Comparative Example 1. From this, it was confirmed that the setting time was shortened by about 2 hours by adding the expandable admixture to the concrete composition regardless of the type of the expandable admixture.

[Test Example 2] Compressive Strength Test The compressive strength test was performed on the hardened concrete bodies obtained in Examples 1 to 5 and Comparative Examples 1 to 3 based on JIS-A1108. This strength test consists of a hardened concrete body of 28 and 91 days of age produced by underwater curing, 7 days of age produced by sealing curing (Examples 3 to 5, only Comparative Examples 1 to 3), 28 days and The test was carried out on a 91-day hardened concrete body.
The results are shown in Table 3.

As shown in Table 3, in the cured concrete bodies of Comparative Examples 2 and 3, the compressive strength at 91 days of age was lowered in both the underwater curing and the sealing curing. From the result of the self-shrink test described later, it is considered that the compressive strength is reduced due to abnormal expansion caused by increasing the amount of the expandable admixture added. On the other hand, the hardened concrete bodies of Examples 1 to 5 have a compressive strength of about 150 N / mm ² at the age of 91 days and maintain high strength without lowering the compressive strength. confirmed. From this, it was confirmed that the concrete composition and hardened concrete body of the present invention can exhibit sufficient compressive strength as a concrete product for high-rise buildings.

[Test Example 3] Self-shrinkage test and setting test The concrete hardened bodies obtained in Examples 1 to 5 and Comparative Examples 1 to 3 are reported in the JCI committee report "Self-shrinkage test method for (temporary) high-fluidity concrete". The self-shrinkage test was conducted accordingly. The results of the self-shrink test are shown in FIGS.

  FIG. 1 is a graph showing the self-shrinkage strains for the hardened concrete bodies of Examples 1 to 3 and Comparative Example 1, and FIG. 2 is a self-shrinkage strain for the hardened concrete bodies of Example 3 and Comparative Examples 1 to 3. FIG. 3 is a graph showing the self-shrinkage strains of the concrete hardened bodies of Examples 3 to 5 and Comparative Examples 1 to 3.

  As shown in FIG. 1, it was confirmed that the self-shrinkage strain can be reduced by adding an expandable admixture. It was also confirmed that the effect of reducing the self-shrinkage strain can be controlled by the amount of the expandable admixture added.

As shown in FIG. 2, the cured concrete bodies of Comparative Examples 2 and 3 showed abnormal expansion after 35 to 40 days from the start of setting, whereas the cured concrete body of Example 3 showed abnormal expansion. I couldn't. From this, it can be considered that the hardened concrete bodies of Comparative Examples 2 and 3 are causing strength reduction due to abnormal expansion (see Table 3 in Test Example 2), but the hardened concrete bodies of Example 3 are due to abnormal expansion. It was confirmed that high strength (about 150 N / mm ² ) can be maintained without causing strength reduction.

As shown in FIG. 3, the hardened concrete bodies of Examples 4 and 5 also showed no abnormal expansion. From this, if the Blaine specific surface area of the expansive admixture contained in the concrete composition is 4000 cm ² / g or more, particularly 4200 cm ² / g or more, high strength (150 N / It was confirmed that it was possible to maintain (mm ² ).

  The hardened concrete body of the present invention is useful as a concrete product for high-rise buildings requiring high strength, and the concrete composition of the present invention is useful as a raw material for concrete for producing such a hardened concrete body. .

It is a graph which shows the result of the self-shrink test about the concrete hardened | cured material of Examples 1-3 in the test example 3, and the comparative example 1. FIG. It is a graph which shows the result of the self-shrinkage test about the concrete hardened body of Example 3 and Comparative Examples 1-3 in Test Example 3. It is a graph which shows the result of the self-shrink test about the concrete hardened | cured material of Examples 3-5 in Comparative Example 1-3 and Comparative Examples 1-3.

Claims (6)

Cement,
Silica fume,
_{3CaO · SiO 2 -2CaO · SiO 2} -CaO- gap material based composition, 3CaO _· SiO 2 -CaO- gap material based composition, 2CaO _· SiO 2 -CaO- gap material based composition, and CaO- gap material system A clinker composition containing 1 or 2 or more types of compositions selected from the group consisting of the composition and having a CaO content of 50 to 92% by mass and gypsum, and a Blaine specific surface area of 4000 to 7000 cm ² A concrete composition containing an expandable admixture of
The coarse aggregate contained in the concrete composition is composed of one or more selected from the group consisting of gravel, crushed stone, lightweight coarse aggregate, and recycled coarse aggregate, and the fine aggregate contained in the concrete composition. The aggregate consists of one or more selected from the group consisting of river sand, mountain sand, land sand, sea sand, crushed sand, quartz sand and lightweight fine aggregate,
A concrete composition used for a hardened concrete having a water bonding ratio of 17% by mass or less.   The concrete composition according to claim 1, wherein the expandable admixture contains 5 to 50 parts by mass of the gypsum with respect to 100 parts by mass of the clinker composition.   The concrete composition according to claim 1, wherein the expandable admixture further contains quicklime. The expansive admixture contains 20 parts by mass or more of the clinker composition in a total of 100 parts by mass of the clinker composition and the quicklime.
The concrete composition according to claim 3, comprising 5 to 50 parts by mass of the gypsum with respect to a total of 100 parts by mass of the clinker composition and the quicklime. 5. The expandable admixture is contained so that the expandable admixture is included in 10 to 60 kg of the expandable admixture in 1 m ^{3 of a} hardened concrete body obtained by curing the concrete composition. The concrete composition according to 1. The concrete composition according to any one of claims 1 to 5 and water are kneaded and cured.
A hardened concrete body, wherein a water binding ratio between the concrete composition and the water is 17% by mass or less.

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