JP2019026495A - Expansive concrete - Google Patents

Abstract

To provide an expansive concrete which can satisfy the standard of the restrained expansion ratio of the concrete for shrinkage compensation according to Japan Society of Civil Engineers (the restrained expansion ratio at the material age of 7 days is 150-250×10), even when the used amount of expansive admixture is small.SOLUTION: An expansive concrete of this invention comprises a cement composition, an expansive admixture, and a limestone aggregate, said cement composition comprising a cement clinker pulverized material and a gypsum, the total SOcontent in said cement composition is 2.5 to 5.0 mass%, and the ratio of dihydrate gypsum to the total amount of dihydrate gypsum and hemihydrate gypsum is 20% or more, calculated as SO. Preferably, a blending amount of the expansive admixture is below 20 kg/min the expansive concrete, more preferably, the restrained expansion ratio at the material age of 7 days is 150-250×10, still more preferably, a content of the limestone aggregate is 40 mass% based on the mass of the whole aggregate.SELECTED DRAWING: None

Description

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

In order to increase the durability of the concrete structure, it is effective to use a concrete expansion material as a means for suppressing cracks in the concrete. In recent years, in the civil engineering field and the building field, the use of an expanding material for the purpose of suppressing dry shrinkage cracking has increased.
The amount of concrete expansion material used to make shrinkage-compensating concrete was initially 30 kg / m ³ , but in recent years, the use amount of low-addition type concrete expansion material is 20 kg / m ^3. Has increased.
A ready mixed concrete manufacturing factory, generally called a ready-mixed concrete factory, manufactures concrete of various blends one after another with a mixing time of around 1 minute and ships in an uncured state. At this time, the concrete manufactured by one-time mixing is often about 1 to 4 m ³ . Even if a concrete expansion material is used, it is difficult from the work surface to add the expansion material at the time of predetermined mixing. Moreover, although the use of the low-addition type concrete expansion material is increasing, the addition amount is further reduced, which is beneficial in terms of cost. Therefore, there is a demand for a concrete that can satisfy the constraint expansion rate of the shrinkage compensation concrete of the Japan Society of Civil Engineers standard even with a smaller amount of use of the concrete expansion material.

By the way, by using a low heat generation type cement such as low heat Portland cement and medium heat heat Portland cement, concrete having a high constrained expansion rate of concrete has been proposed (for example, (See Patent Documents 1 and 2).
However, expanded concrete using a low heat generation type cement has a problem of poor strength development. Moreover, there exists a problem that a strength fall is easy to occur compared with concrete without an expansion material.

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

JP 2004-217514 A JP 2006-232625 A JP 2011-6276 A

The object of the present invention is to obtain the restricted expansion rate of the concrete for shrinkage compensation according to the Japan Society of Civil Engineers standards (the concrete restricted expansion rate is 150 to 250 × 10 ⁻⁶ on the age of 7) despite the small amount of the expanded material used. It is to provide a satisfactory expanded concrete.

In order to solve the above problems, the present inventor has intensively studied expanded concrete using expanded material and limestone aggregate. As a result, the total amount of SO ₃ in the cement composition to be used, and dihydrate gypsum and hemihydrate gypsum It has been found that the amount of expansion of concrete is affected, and by controlling them, it has been 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 expanded concrete represented by the following [1] to [4].
[1] An expanded concrete containing a cement composition, an expanded material, and limestone aggregate,
The cement composition comprises a cement clinker pulverized product 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 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 expansion rate 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 limestone aggregate content is 40% by mass or more based on the total aggregate amount.

According to the present invention, although the amount of expansion material is less than 20 kg / m ³ and the amount used is less than that of conventional expanded concrete, the restricted expansion rate of shrinkage compensation concrete (material age 7) Concrete exhibiting an excellent expansion performance satisfying a daily concrete constrained expansion rate of 150 to 250 × 10 ⁻⁶ ) is obtained.

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

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

As the cement composition, Portland cement manufactured industrially 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 a cement clinker. The cement clinker is manufactured by firing ordinary cement raw materials such as limestone, clay, silica sand, aluminum ash, bauxite, iron, and the like at 1200 to 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 · Fe 2} O 3 ( _{hereinafter, C} referred 4 AF) is. A trace amount of impurities may be included.

The total SO ₃ amount in the cement composition according to the present invention is the total content of the SO ₃ amount due to gypsum, alkali sulfate, and the like contained in the cement composition, and the total SO ₃ amount is 2.5-5.0 mass%. The total SO ₃ weight there is a possibility that constraining expansion of the concrete is less than 2.5 wt% is less than 0.99 × ^{10 -6,} more than 5.0 wt%, the concrete restraint expansion rate of 250 × 10 ^{- It} may be larger than ⁶ , and the cured body may expand over a long period of time and cause a decrease in strength. More preferably, it is 2.8-4.5 mass%, More preferably, it is 3.0-4.0 mass%.

The cement composition includes gypsum such as dihydrate gypsum and hemihydrate gypsum. In the present invention, the ratio of dihydrate gypsum to the total amount of dihydrate gypsum and hemihydrate gypsum is 20% or more in terms of SO ₃ . If the proportion is less than 20%, the constrained expansion coefficient of concrete may be less than 150 × 10 ⁻⁶ . More preferably, it is 25% or more, and further preferably 30% or more.

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

In the expanded concrete according to the present invention, the 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 rate of concrete may be less than 150 × 10 ⁻⁶ . More preferably, it is 10-16 kg / m < ³ >, More preferably, it is 12-15 kg / m < ³ >.

Limestone aggregate is used for the expanded concrete in the present invention. Some or all of the limestone aggregate can be used. The content of limestone aggregate is preferably 40% by mass or more with respect to the total aggregate amount. If it is less than 40% by mass, the constrained expansion coefficient of concrete may be less than 150 × 10 ⁻⁶ . More preferably, it is 45 mass% or more, More preferably, it is 50 mass% or more. The aggregate used in addition to the limestone aggregate may be any aggregate that can be used for mortar and concrete. For example, river sand, sea sand, mountain sand, crushed sand, artificial fine aggregate, slag fine aggregate, recycled fine aggregate Aggregate, quartz sand, stone powder, river gravel, land gravel, crushed stone, artificial coarse aggregate, recycled coarse aggregate, slag coarse aggregate, and the like can be used, and one or more of these can be used.

The expanded concrete according to the present invention may contain other components (admixture (material)) that can be used for, for example, mortar and concrete as long as the effects of the present invention are not lost. As such components, specifically, 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, antifoaming agents Examples thereof include agents, foaming agents, waterproofing materials, water repellents, anti-whitening agents, setting modifiers, curing accelerators (materials), pigments, polymers for cement, and fibers.

In the expanded concrete according to the present invention, the concrete constrained expansion rate at the age of 7 days satisfies 150 to 250 × 10 ⁻⁶ . Moreover, even at the age of 28 days, the concrete constrained expansion rate is maintained at 150 to 250 × 10 ⁻⁶ , and stable expansion properties can be maintained over a long period of time. For this reason, the expanded concrete which is excellent also in strength expression property is obtained.

  Next, although an Example demonstrates this invention further in detail, this invention is not limited by an Example.

  Using the crushed cement clinker shown in Table 1, a cement composition was prepared as shown in Table 2.

Using the materials in Table 3, expanded concrete was produced by kneading using 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 body of the expanded concrete described in Table 4 above. Details will be described below.

<Restrained expansion test>
A test was conducted in accordance with Method A of JIS A 6202 “Expanding material for concrete”, and the restricted expansion rate at the age of 7 and 28 days was obtained.
<Compressive strength test>
A specimen was prepared according to JIS A 1132 “How to make a specimen for concrete strength test”, and after 24 hours, it was demolded and then cured under water until the age of 28 days. The compressive strength of each obtained specimen was measured according to JIS A 1108 “Method for testing compressive strength of concrete”.

Table 5 shows the results obtained in the above test.

As shown in Table 5, the blending No. corresponding to the expanded concrete of the present invention. Each of the concretes 1 to 5 expresses a good expansion performance with a restricted expansion coefficient of 165 to 210 × 10 ⁻⁶ on the 7th day of the age, and a restricted expansion coefficient (150 to 250 × 10 ⁻ It was confirmed that ⁶ ) was satisfied. In addition, overexpansion was not confirmed in the constrained expansion rate at the age of 28 days, and even in the compressive strength at the age of 28 days, the blending no. No significant reduction in strength was confirmed for the concrete No. 6.

Formulation No. corresponding to a comparative example. The concrete of 7-10 could not satisfy the constrained expansion rate (150-250 × 10 ⁻⁶ ) necessary as a concrete for shrinkage compensation, with a constrained expansion rate of 121-141 × 10 ⁻⁶ on the 7th day of age. .

Formulation No. corresponding to a comparative example. Although the concrete of No. 11 satisfied the restraint expansion coefficient (150-250 × 10 ⁻⁶ ) required as shrinkage-compensating concrete, the restraint expansion coefficient of 28 days of age was excessively expanded, and as a result, compression of 28 days of age was achieved. The strength is blending no. Compared to 6, it was confirmed that it decreased.

Formulation No. corresponding to a comparative example. No. 12 concrete cannot satisfy the restricted expansion rate (150 to 250 × 10 ⁻⁶ ) required as concrete for shrinkage compensation, and the restricted expansion rate at the age of 28 days is excessive. The compression strength was 28 days of age, and the blending no. Compared to 6, it was confirmed that it decreased.

Claims (4)

Expanded concrete containing cement composition, expanded material, limestone aggregate,
The cement composition comprises a cement clinker pulverized product and gypsum,
The total amount of SO ₃ in the cement composition is 2.5 to 5.0% by mass;
The expanded concrete is characterized in that the ratio of dihydrate gypsum to the total amount of dihydrate gypsum and hemihydrate gypsum is 20% or more in terms of SO ₃ . 2. The expanded concrete according to claim 1, wherein the amount of the expanded material is less than 20 kg / m ^{3 in} the expanded concrete. The expansion concrete according to claim 2, wherein the expansion rate of the expansion concrete at a material age of 7 days is 150 to 250 × 10 ⁻⁶ . The expanded concrete according to any one of claims 1 to 3, wherein the limestone aggregate content is 40% by mass or more based on the total aggregate amount.