JP6974974B2 - Expansion concrete - Google Patents

Description

The present invention relates to inflatable concrete using an inflatable material.

In order to increase the durability of the concrete structure, it is effective to use the concrete expansion material as a means for suppressing the cracking of the concrete. In recent years, in the fields of civil engineering and construction, the use of expansion materials for the purpose of suppressing drying shrinkage cracks has been increasing.
Initially, the amount of concrete expansion material used to make shrink compensation concrete was 30 kg / m ³ , but in recent years, low-additive concrete expansion materials that have been used at ^{20 kg / m 3 should be used.} Has increased.
The ready-mixed concrete manufacturing factory, which is generally called a ready-mixed concrete factory, manufactures concrete of various formulations one after another in a kneading time of about 1 minute and ships it in an uncured state. At this time, the concrete produced by one kneading is often about 1 to 4 ^{m 3.} Even if a concrete expansion material is used, it is difficult to add the expansion material at the time of predetermined kneading from the work aspect. Further, although the use of low-addition type expansion material for concrete is increasing, the addition amount is further reduced, which is beneficial in terms of cost. Therefore, there is a demand for concrete that can satisfy the restraint expansion rate of shrinkage compensating concrete according to the standards of the Japan Society of Civil Engineers even if the amount of expansion material used for concrete is smaller.

By the way, by using low heat generation type cement such as low heat Portland cement and moderate heat Portland cement, concrete having a high constraint expansion rate of concrete has been proposed even though the amount of expansion material used is small (for example). See Patent Documents 1 and 2).
However, the expanded concrete using the low heat generation type cement has a problem that the strength development is poor. Further, there is a problem that the strength is liable to decrease as compared with concrete to which no expansion material is added.

On the other hand, as one of the measures to suppress shrinkage and drying cracks of concrete, the use of coarse aggregate and fine aggregate using limestone as an aggregate has been studied in recent years. Limestone aggregate is effective in reducing shrinkage, and when combined with limestone-based expander, it is said that dry shrinkage from the expansion peak of initial curing can be effectively reduced. For example, ordinary Portland cement and limestone are the main components. A low-shrink concrete containing a neutral or high-performance AE water reducing agent and a limestone-based expanding material and having a water-cement ratio of 40 to 50% has been proposed (Patent Document 3).

Japanese Unexamined Patent Publication No. 2004-217514 Japanese Unexamined Patent Publication No. 2006-232625 Japanese Unexamined Patent Publication No. 2011-6276

The subject of the present invention is the constrained expansion coefficient of concrete for shrinkage compensation (concrete constrained expansion coefficient of 7 days old is 150 to 250 × ^10-6 ) according to the standards of the Japan Society of Civil Engineers, despite the small amount of expansive material used. It is to provide satisfactory expanded concrete.

As a result of diligent studies on expanded concrete using expanding material and limestone aggregate in order to solve the above-mentioned problems, the present inventor found that the total _{amount of SO 3} in the cement composition used, and dihydrate gypsum and semi-hydrated gypsum were found. We have found that it affects the amount of expansion of concrete, and by controlling them, we have found that a sufficient constrained expansion rate of concrete can be satisfied even if the amount of expansion material used is reduced, and the present invention has been completed.
That is, the present invention is an expanded concrete represented by the following [1] to [4].
[1] Expanded concrete containing a cement composition, an expanding material, and a limestone aggregate.
The cement composition comprises crushed cement clinker and gypsum.
_{The total amount of SO 3} in the cement composition is 2.5 to 5.0% by mass.
And gypsum and hemi expansion concrete ratio of gypsum to the total amount of gypsum is 20% or more converted to SO _3.
[2] The expanded concrete according to claim 1, wherein the blending amount of the expanded material ^{is less than 20 kg / m 3 in the expanded concrete.}
[3] The expanded concrete according to claim 2, wherein the coefficient of constrained expansion of the expanded concrete at a material age of 7 days is 150 to 250 × ^10-6.
[4] The expanded concrete according to any one of claims 1 to 3, wherein the content of the limestone aggregate is 40% by mass or more with respect to the total amount of the aggregate.

According to the present invention, although the compounding amount of the expanding material is ^{less than 20 kg / m 3} and the amount used is smaller than that of the conventional expanding concrete, the constrained expansion rate of the shrinkage compensating concrete according to the standards of the Japan Society of Civil Engineers (material age 7). It is possible to obtain concrete that exhibits excellent expansion performance with a daily concrete constraint expansion coefficient of 150 to 250 × ^10-6).

The contents of the present invention will be described in detail below.

The expanded concrete of the present invention contains a cement composition, an expanded material, and a limestone aggregate.

As the cement composition, industrially produced Portland cement can be used. Further, it is possible to use those further added gypsum Portland cement was adjusted SO ₃ amount. Or gypsum was added to the cement clinker grinding material can also be used that adjusts the SO ₃ content.

The cement clinker pulverized product can be produced by pulverizing the cement clinker. Cement clinker is produced by firing ordinary cement raw materials such as limestone, clay, silica sand, aluminum ash, bauxite and iron at 1200-1500 ° C. Major minerals phase generated, 3CaO · _SiO 2 (hereinafter, referred to as _{C 3 S), 2CaO · SiO} 2 ( hereinafter, referred to as _{C 2 S), 3CaO · Al} 2 O 3 ( hereinafter, referred to as _{C 3} A), 4CaO -Al ₂ O ₃ and Fe ₂ O ₃ (hereinafter referred to as C ₄ AF). In addition, a trace amount of impurities may be contained.

_{The total SO 3} amount in the cement composition in the present invention is the total _{content of SO 3} amount in the cement composition due to gypsum, alkali sulfate, etc. contained in the cement composition, and the total SO ₃ amount is It is 2.5 to 5.0% by mass. If the total SO ₃ amount is less than 2.5% by mass, the constrained expansion coefficient of concrete ^{may be less than 150 × 10-6,} and if it exceeds 5.0% by mass, the constrained expansion coefficient of concrete may be 250 × 10 ^{−. It} may be larger than 6 and the cured product may expand over a long period of time, causing a decrease in strength. It is more preferably 2.8 to 4.5% by mass, and even more preferably 3.0 to 4.0% by mass.

The cement composition contains gypsum such as dihydrate gypsum and hemihydrate gypsum. In the present invention, it is the ratio of gypsum to the total amount of gypsum and hemi gypsum converted to SO ₃ in 20% or more. If the ratio is less than 20%, the coefficient of constrained expansion of concrete may be less than ^{150 × 10-6.} It is more preferably 25% or more, still more preferably 30% or more.

As the expansion material in the present invention, any of quicklime-based and ettringite-based, and ettringite-quicklime-based can be used. A quicklime-based swelling material is more preferable from the viewpoint of swelling development.

In the expanded concrete in the present invention, the blending amount of the expanded material can be set as low as less than ^{20 kg / m 3 in the concrete.} On the other hand, the lower limit compounding amount is preferably ^{10 kg / m 3.} If it is less than 10 kg / m ^3, the constrained expansion coefficient of concrete may be less than ^{150 × 10-6.} It is more preferably 10 to 16 kg / m ³ , and even more preferably 12 to 15 kg / m ³ .

Limestone aggregate is used for the expanded concrete in the present invention. The limestone aggregate can be used in part or in whole. The content of the limestone aggregate is preferably 40% by mass or more with respect to the total amount of aggregate. If it is less than 40% by mass, the constrained expansion coefficient of concrete may be less than ^{150 × 10-6.} It is more preferably 45% by mass or more, and further preferably 50% by mass or more. The aggregate used other than the limestone aggregate may be any aggregate that can be used for mortar or concrete, for example, river sand, sea sand, mountain sand, crushed sand, artificial fine aggregate, slag fine aggregate, recycled fine. Aggregate, silica sand, stone powder, river gravel, land gravel, crushed stone, artificial coarse aggregate, recycled coarse aggregate, slag coarse aggregate and the like can be mentioned, and one or more of these can be used.

The expanded concrete according to the present invention may contain, for example, other components (admixture (material)) that can be used for mortar and concrete, as long as the effects of the present invention are not lost. Specific examples of such components include thickeners, water retention agents, rust preventives, water reducing agents, AE water reducing agents, high performance water reducing agents, high performance AE water reducing agents, fluidizing agents, air entraining agents, and defoaming agents. Examples thereof include agents, foaming agents, waterproof materials, water repellents, anti-whitening agents, coagulation adjusters, curing accelerators (materials), pigments, polymers for cement, and fibers.

The expanded concrete according to the present invention satisfies a concrete constrained expansion coefficient of 150 to 250 × ^{10-6 at a material age of 7 days.} Further, even at the age of 28 days, the concrete restraint expansion coefficient is ^{maintained at 150 to 250 × 10-6} , and stable expansion properties can be maintained for a long period of time. Therefore, expanded concrete having excellent strength-developing properties can be obtained.

Next, the present invention will be described in more detail with reference to examples of the present invention, but the present invention is not limited to the examples.

Using the cement clinker pulverized product shown in Table 1, the cement composition was prepared as shown in Table 2.

Using the materials shown in Table 3, the expanded concrete was produced by kneading with a concrete mixer at an environmental temperature of 20 ° C. Table 4 shows the composition of each expanded concrete produced.

Various characteristics were evaluated for the hardened concrete of the expanded concrete shown in Table 4 above. Details will be described below.

<Constriction expansion test>
The test was carried out according to the method A of JIS A 6202 "Expansion material for concrete", and the restraint expansion rate at the ages of 7 days and 28 days was determined.
<Compressive strength test>
Specimens were prepared according to JIS A 1132 "How to make specimens for concrete strength test", and after 24 hours, they were demolded and then cured in water until the age of 28 days. The compressive strength of each of the obtained specimens was measured in accordance with JIS A 1108 “Concrete Compressive Strength Test Method”.

The results obtained in the above test are shown in Table 5.

As shown in Table 5, the compounding No. corresponding to the expanded concrete of the present invention. ^{All of the concrete of 1 to 5 exhibited a good expansion performance with a constraint expansion coefficient of 165 to 210 × 10-6} on the 7th day of the material age, and the constraint expansion coefficient (150 to 250 × 10 ^{−) required for shrinkage compensating concrete.} It was confirmed that ^{6) was satisfied.} In addition, no overexpansion was confirmed at the constrained expansion rate at the age of 28 days, and even at the compressive strength at the age of 28 days, the compounding No. of no expansion material was added. No significant decrease in strength was confirmed for the concrete of No. 6.

Formulation No. corresponding to a comparative example. The concrete of 7 to 10 had a coefficient of constrained expansion of 121 to 141 × ^{10-6 at} 7 days of age, which could not satisfy the coefficient of constrained expansion (150 to 250 × ^{10-6) required for shrinkage compensating concrete.} ..

Formulation No. corresponding to a comparative example. Although the concrete of No. 11 satisfied the restraint expansion coefficient (150 to 250 × ^10-6 ) required for shrinkage compensation concrete, the restraint expansion coefficient at the age of 28 days became excessive expansion, and as a result, the compression at the age of 28 days was achieved. Strength is compounded No. It was confirmed that it was lower than that of 6.

Formulation No. corresponding to a comparative example. The constrained expansion coefficient of 12 days of age 7 days ^{could not satisfy the constrained expansion coefficient (150 to 250 × 10-6} ) required for shrinkage compensating concrete, and the constrained expansion coefficient of 28 days of age was excessive. It expands, and the compressive strength of 28 days of age is compounded No. It was confirmed that it was lower than that of 6.

Claims (2)

An expanded concrete containing a cement composition, an expanding material, and a limestone aggregate, wherein the cement composition contains a cement clinker pulverized product and a dihydric gypsum and a semi-hydrated gypsum, and the total SO _{3 in the cement composition.} the amount is 2.8 to 5.0 wt%, and the percentage of gypsum relative to the total amount of gypsum and hemi gypsum is not more than 62% more than 25% converted to SO _3, of the limestone aggregate An expanded concrete having a content of 40% by mass or more with respect to the total amount of aggregate, and the blending amount of the expanding material being 10 kg / m ³ or more and less than 20 kg / m ³ in the expanded concrete. The expanded concrete according to claim 1, wherein the coefficient of constrained expansion of the expanded concrete at a material age of 7 days is 150 to 250 × 10 ^−6.