Lightweight concrete

Abstract

To provide a lightweight concrete having excellent freeze-thaw resistance and pumpability despite the use of a lightweight aggregate.SOLUTION: A lightweight concrete contains Portland cement, a fine aggregate, a coarse aggregate, water, paraffin particles, and a polymer for cement admixture, wherein a unit weight of paraffin particles is 4 to 20 kg / m3, a unit weight of the polymer for cement admixture is 5 to 35 kg / m3, an amount of water to 100 pts.mass of Portland cement is 20 to 60 pts.mass, one or both of the fine aggregate and the coarse aggregate contain a lightweight aggregate, and a ratio of the fine aggregate is 35 to 65%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to lightweight concrete. [Background technology]

[0002] Using lightweight concrete with lightweight aggregates reduces the mass of the structure, allowing for more economical design. On the other hand, lightweight aggregates are porous and highly absorbent, which presents a problem as they have low resistance to freeze-thaw cycles. Despite using lightweight aggregate, Patent Document 1 describes a freeze-thaw resistant high-strength concrete characterized by having lightweight aggregate, containing 8 vol% or more of fine closed cells together with non-latent hydraulic mineral powder, and having a freeze-thaw durability index (DF) of 70 or higher. Furthermore, Patent Document 2 describes a freeze-resistant lightweight concrete characterized by the incorporation of polyvinyl alcohol fibers. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2000-264703 [Patent Document 2] Japanese Patent Publication No. 2007-230806 [Overview of the project] [Problems that the invention aims to solve]

[0004] Concrete using lightweight aggregates has the problem of reduced freeze-thaw resistance and pumpability. The objective of the present invention is to provide lightweight concrete that exhibits excellent freeze-thaw resistance (frost damage resistance) and pumpability, despite using lightweight aggregates. [Means for solving the problem]

[0005] As a result of intensive studies to solve the above problems, the present inventor has found that lightweight concrete containing Portland cement, fine aggregate, coarse aggregate, water, paraffin particles, and a polymer for cement admixture, with the unit amount of paraffin particles being 4 to 20 kg / m 3 , the unit amount of the polymer for cement admixture being 5 to 35 kg / m 3 , the amount of water relative to 100 parts by mass of Portland cement being 20 to 60 parts by mass, and either one or both of the fine aggregate and the coarse aggregate containing lightweight aggregate and having a fine aggregate ratio of 35 to 65%, can achieve the above object, and thus completed the present invention. That is, the present invention provides the following [1] to [6]. [1] Lightweight concrete containing Portland cement, fine aggregate, coarse aggregate, water, paraffin particles, and a polymer for cement admixture, wherein the unit amount of the paraffin particles is 4 to 20 kg / m 3 , the unit amount of the polymer for cement admixture is 5 to 35 kg / m 3 , the amount of water relative to 100 parts by mass of the Portland cement is 20 to 60 parts by mass, either one or both of the fine aggregate and the coarse aggregate contain lightweight aggregate, and the fine aggregate ratio is 35 to 65%, characterized in that it is lightweight concrete.

[0006] [2] The lightweight concrete according to [1], wherein the ratio of lightweight aggregate in the total 100% by volume of the fine aggregate and the coarse aggregate is 20 to 80% by volume. [3] The lightweight concrete according to [I] or [2], wherein the median diameter of the paraffin particles is 0.2 to 1.5 μm. [4] The lightweight concrete according to any one of [1] to [3], wherein the polymer for cement admixture is rubber latex and the median diameter of the polymer for cement admixture is 0.01 to 1.0 μm. [5] The lightweight concrete according to any one of [1] to [4], wherein the total value of the median diameter of the paraffin particles and the median diameter of the polymer for cement admixture is 1.5 μm or less. [6] The lightweight concrete is the lightweight concrete described in any one of [1] to [5] above, having a durability index of 70 or more measured in accordance with the "Method of Test for Freezing and Thawing of Concrete" (Method A) specified in "JIS A 1148:2010 (Method of Test for Freezing and Thawing of Concrete)".

Advantages of the Invention

[0007] The lightweight concrete of the present invention is excellent in freeze-thaw resistance and pumpability despite using lightweight aggregates.

Embodiments for Carrying Out the Invention

[0008] The lightweight concrete of the present invention is a lightweight concrete containing Portland cement, fine aggregate, coarse aggregate, water, paraffin particles, and a polymer for cement admixture, wherein the unit amount of paraffin particles is 4 to 20 kg / m 3 , the unit amount of the polymer for cement admixture is 5 to 35 kg / m 3 , the amount of water relative to 100 parts by mass of Portland cement is 20 to 60 parts by mass, and either one or both of the fine aggregate and the coarse aggregate contain lightweight aggregates, and the fine aggregate ratio is 35 to 65%. In this specification, the lightweight concrete includes both the form having fluidity before hardening and the form after hardening. This will be described in detail below.

[0009] Examples of the Portland cement contained in the cement composition of the present invention include ordinary Portland cement, early-strength Portland cement, medium-heat Portland cement, low-heat Portland cement, sulfate-resistant Portland cement, and the like. These may be used alone or in combination of two or more. Among them, ordinary Portland cement is preferable from the viewpoints of easy availability of the cement composition and strength development.

[0010] At least one or both of the fine aggregate and the coarse aggregate used in the present invention contain lightweight aggregates from the viewpoint of reducing the mass of the concrete structure. Lightweight aggregates are preferably artificial lightweight aggregates from the viewpoints of ease of quality control, less variation in the particle size and water absorption rate of each particle constituting the lightweight aggregates, and further improvement in the pumping property of lightweight concrete. Lightweight aggregates can be obtained, for example, by using one or more selected from expanded clay, expanded slate, fly ash, expanded shale, glass, and volcanic ash as raw materials and firing and foaming them. When the fine aggregate contains lightweight aggregates, the lightweight aggregates correspond to lightweight fine aggregates. When the coarse aggregate contains lightweight aggregates, the lightweight aggregates correspond to lightweight coarse aggregates.

[0011] The proportion of lightweight aggregates in the total 100% by volume of the fine aggregate and the coarse aggregate is preferably 20 to 80% by volume, more preferably 30 to 70% by volume, still more preferably 35 to 65% by volume, still more preferably 40 to 60% by volume, and particularly preferably 42 to 55% by volume. If the above proportion is 20% by volume or more, the mass of lightweight concrete can be made smaller. If the above proportion is 80% by volume or less, the strength of lightweight concrete can be increased. The water absorption rate of lightweight aggregates is preferably 10 to 40%, more preferably 20 to 35%, and particularly preferably 25 to 30%. If the above water absorption rate is 10% or more, the pumping property before the hardening of lightweight concrete is further improved. If the above water absorption rate is 40% or less, the fluidity before the hardening of lightweight concrete can be further improved, and the workability during placing or the like is further improved.

[0012] From the viewpoint of making the mass of lightweight concrete smaller, the absolute dry density of lightweight aggregates is preferably 2.0 g / cm 3 or less, more preferably 1.9 g / cm 3 or less, still more preferably 1.8 g / cm 3 or less, and particularly preferably 1.7 g / cm 3 or less. Also, from the viewpoints of ease of acquisition and improvement in the strength development property of the hydraulic composition, the absolute dry density is preferably 0.8 g / cm 3 or more, more preferably 1.0 g / cm3 In particular, 1.2 g / cm³ is preferred. 3 That's all.

[0013] Other aggregates (lightweight fine aggregates or lightweight coarse aggregates) may be used as aggregates (fine aggregates or coarse aggregates). Examples of fine aggregates other than lightweight fine aggregates include river sand, mountain sand, land sand, sea sand, crushed sand, silica sand, and slag fine aggregate. These may be used individually or in combination of two or more types. The unit quantity of fine aggregate (or, if the fine aggregate includes lightweight fine aggregate, the unit quantity of the fine aggregate including lightweight fine aggregate) is not particularly limited and can be any unit quantity that is common in concrete. For example, the unit quantity of fine aggregate is preferably 500 to 1,200 kg / m³. 3 Comfortable 600-1,000 kg / m 3 Particularly preferred is 700-900 kg / m 3 The amount is 500 kg / m³. 3 When the value is above 1,200 kg / m³, the drying shrinkage of lightweight concrete can be further suppressed. 3 The following conditions can further improve the workability of lightweight concrete. In this specification, "unit quantity" refers to the unit volume of lightweight concrete, 1 m³. 3 This refers to the amount of ingredients mixed per unit by mass.

[0014] Examples of coarse aggregates other than lightweight coarse aggregates include river gravel, mountain gravel, land gravel, sea gravel, crushed stone, and slag coarse aggregate. These may be used individually or in combination of two or more types. The unit amount of coarse aggregate (or, if the coarse aggregate includes lightweight coarse aggregate, the unit amount of coarse aggregate including lightweight coarse aggregate) is preferably 300 to 1,000 kg / m³. 3 , more preferably 400-800 kg / m 3 Particularly preferred is 500-700 kg / m 3 That is the case. The value is 300 kg / m³. 3 A value of 1,000 kg / m³ can further improve the durability of lightweight concrete.3 The following conditions can further improve the workability of concrete. The fine aggregate ratio of lightweight concrete is 35-65%, more preferably 40-60%, and particularly preferably 42-55%. If the fine aggregate ratio is less than 35%, the pumpability of the lightweight concrete decreases. If the fine aggregate ratio exceeds 65%, the workability of the lightweight concrete decreases.

[0015] The type of water used is not particularly limited and includes tap water, and recycled water as defined in "JIS A 5308:2019 (Ready-Mixed Concrete)". The amount of water per 100 parts by mass of Portland cement (when preparing lightweight concrete, the total amount of water contained in the emulsion containing paraffin particles and the polymer dispersion for cement admixture, plus the water added during the preparation of lightweight concrete) is preferably set to 20 to 60 parts by mass, more preferably 23 to 55 parts by mass, and particularly preferably 40 to 50 parts by mass. If the above amount is 20 parts by mass or more, the strength of the lightweight concrete can be increased. If the above amount is 60 parts by mass or less, the fluidity of the lightweight concrete before hardening can be further improved.

[0016] The paraffin particles used in this invention are particles made of solid paraffin (also known as paraffin wax). The median diameter of the paraffin particles is preferably 0.2 to 1.5 μm, more preferably 0.3 to 1.0 μm, even more preferably 0.4 to 0.8 μm, and particularly preferably 0.5 to 0.6 μm. If the diameter is 0.2 μm or more, it becomes easier to obtain paraffin particles having such a diameter. If the diameter is 1.5 μm or less, the freeze-thaw resistance and pumpability of the lightweight concrete are further improved.

[0017] In this specification, "median diameter" (sometimes abbreviated as "D50") refers to the particle size at which, when an aggregate of particles is divided into a smaller particle size aggregate (small particle size aggregate) and a larger particle size aggregate (large particle size aggregate) with a specific particle size as the boundary, the amounts of the smaller particle size aggregate and the larger particle size aggregate are equal (for example, 50 volume percent each) (in other words, the 50% volume cumulative particle size). In this specification, "median diameter" is volume-based and can be obtained by creating a volume-cumulative distribution using a laser diffraction particle size distribution analyzer. An example of a method for obtaining paraffin particles having a desired median diameter is to adjust the stirring conditions (stirring speed, stirring time) when adding paraffin and an emulsifier to water and stirring, thereby obtaining the desired median diameter.

[0018] The unit amount of paraffin particles is 4-20 kg / m³. 3 Preferably 5-19 kg / m 3 , more preferably 8-18 kg / m 3 More comfortably 9-17 kg / m 3 Particularly preferably 10-11 kg / m 3 The above unit quantity is 4 kg / m³. 3 If the amount is less than 20 kg / m³, the freeze-thaw resistance and pumpability of the lightweight concrete will decrease. 3 If the above is true, the cost of materials will be excessive.

[0019] Paraffin particles are preferably used in the form of an emulsion containing paraffin particles, from the viewpoint that they can be uniformly mixed when preparing lightweight concrete by mixing each material, and the pumpability of the resulting lightweight concrete can be further improved. The paraffin particle content of the emulsion containing paraffin particles is preferably 20-50% by mass, more preferably 23-45% by mass, and particularly preferably 25-40% by mass. If the above content is 20% by mass or more, the freeze-thaw resistance and pumpability of the lightweight concrete can be further improved. If the above content is 50% by mass or less, the paraffin particles can be mixed more uniformly when preparing the lightweight concrete.

[0020] Furthermore, emulsions containing paraffin particles allow for more uniform mixing of the paraffin particles when preparing lightweight concrete, and preferably include emulsifiers and defoamers from the viewpoint of further improving freeze-thaw resistance and pumpability. Examples of emulsifiers include anionic emulsifiers. From the viewpoint of enabling more uniform mixing of paraffin particles when preparing lightweight concrete, and further improving freeze-thaw resistance and pumpability, the emulsifier content (in terms of solid content in the case of liquid) of the emulsion containing paraffin particles is preferably 0.1 to 5.0% by mass, more preferably 0.5 to 3.0% by mass. Examples of defoaming agents include silicone-based defoaming agents. When preparing lightweight concrete, the amount of defoaming agent is preferably 0.1 to 8.0 parts by mass, more preferably 2.0 to 6.0 parts by mass, per 100 parts by mass of paraffin particles, from the viewpoint of uniformly mixing paraffin particles and further improving freeze-thaw resistance and pumpability. In emulsions containing paraffin particles, the only material other than the paraffin particles, emulsifier, and defoamer is usually water. The water contained in paraffin-containing emulsions is treated as part of the water contained in lightweight concrete.

[0021] The median diameter of the cement admixture polymer is preferably 0.01 to 1.0 μm, more preferably 0.02 to 0.5 μm, and particularly preferably 0.02 to 0.3 μm. If the diameter is 0.01 μm or greater, it becomes easier to obtain a cement admixture polymer having such a diameter. If the diameter is 1.0 μm or less, the freeze-thaw resistance and pumpability of the lightweight concrete are further improved. Furthermore, the sum of the median diameter of the paraffin particles and the median diameter of the cement admixture polymer is preferably 1.5 μm or less, more preferably 1.2 μm or less, even more preferably 1.0 μm or less, and particularly preferably 0.8 μm, from the viewpoint of further improving the freeze-thaw resistance and pumpability of the lightweight concrete.

[0022] The unit amount of polymer used for cement admixture is 3 to 35 kg / m³. 3 Preferably 5-30 kg / m 3 A comfortable 10-25 kg / m 3 Particularly preferably 15-20 kg / m 3 The above unit quantity is 3 kg / m³. 3 If the amount is less than 35 kg / m³, the freeze-thaw resistance and pumpability of the lightweight concrete will decrease. 3 If the above is true, the cost of materials will be excessive.

[0023] As the cement admixture polymer used in the present invention, for example, polymers specified in "JIS A 6203:2015 (Polymer Dispersion and Re-emulsifiable Powder Resins for Cement Admixture)" can be used. Examples of the polymers mentioned above include polymer dispersions and re-emulsifiable powder resins. Examples of polymer dispersions include (i) rubber latex such as synthetic rubber-based materials like styrene-butadiene rubber (SBR), natural rubber-based materials, and rubber asphalt-based materials, and (ii) resin emulsions such as ethylene vinyl acetate-based materials, acrylic acid ester-based materials, and resin asphalt-based materials. Re-emulsifiable powder resins are powdered resins that can be re-emulsified, obtained by drying rubber latex and resin emulsions, etc. Examples include synthetic rubber-based resins such as styrene-butadiene rubber (SBR), acrylic acid ester-based resins, ethylene vinyl acetate-based resins, and vinyl acetate vinyl transate-based re-emulsifiable powder resins. These may be used individually or in combination of two or more types. In particular, polymer dispersions are preferred, and rubber latex is more preferred, from the viewpoint of uniformly mixing cement admixture polymers when preparing lightweight concrete, and further improving freeze-thaw resistance and pumpability.

[0024] Polymer dispersion is a liquid substance obtained by dispersing cement admixture polymers in water. The content of the cement admixture polymer in the polymer dispersion is preferably 30 to 60% by mass, more preferably 35 to 55% by mass, and particularly preferably 40 to 50% by mass. If the content is 30% by mass or more, the freeze-thaw resistance and pumpability of the lightweight concrete can be further improved. If the content is 60% by mass or less, paraffin particles can be mixed more uniformly when preparing the lightweight concrete. Furthermore, the water contained in the polymer dispersion will be treated as part of the water contained in the lightweight concrete.

[0025] Lightweight concrete may contain, to the extent that it does not affect the effects of the present invention, (i) various admixtures such as fly ash, silica fume, and blast furnace slag fine powder, and (ii) various admixtures such as cement dispersants such as water-reducing agents, AE water-reducing agents, high-performance water-reducing agents, high-performance AE water-reducing agents, AE agents, defoaming agents, and fluidizing agents.

[0026] An example of a method for producing lightweight concrete according to the present invention is a method comprising: a cement-containing mixture preparation step of mixing cement, fine aggregate, and coarse aggregate to prepare a cement-containing mixture which is a solid component; a mixed liquid preparation step of mixing water, an emulsion containing paraffin particles, and a polymer dispersion for cement admixture to prepare a mixed liquid; and a lightweight concrete preparation step of mixing the cement-containing mixture and the mixed liquid and stirring (kneading) them to obtain lightweight concrete.

[0027] The physical properties of the lightweight concrete of the present invention are as follows: (a) Air volume The air content of lightweight concrete, calculated in accordance with "JIS A 1116:2019 (Test method for unit volume mass of fresh concrete and test method for air content by mass)," is preferably 2.0 to 7.0%, more preferably 2.5 to 6.5%, and particularly preferably 3.0 to 6.0%. If the air content is 2.0% or more, the freeze-thaw resistance of the lightweight concrete can be further improved. If the air content is 7.0% or less, the strength of the lightweight concrete can be further increased. (b) Durability index The durability index of lightweight concrete, calculated in accordance with the "Underwater Freeze-Thaw Test Method" (Method A) specified in "JIS A 1148:2010" (Test Method for Freeze-Thaw Test of Concrete), is preferably 70 or higher, more preferably 72 or higher, even more preferably 75 or higher, and particularly preferably 80 or higher. If the above durability index is 70 or higher, the freeze-thaw resistance of lightweight concrete can be further improved. [Examples]

[0028] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. [Materials used] (1) Portland cement (referred to as "cement" in Table 1): Ordinary Portland cement, manufactured by Taiheiyo Cement Corporation, density: 3.15 g / cm³ 3 (2) Coarse aggregate; Lightweight coarse aggregate (referred to as "coarse aggregate" in Table 1), manufactured by Nippon Mesalite Industries Co., Ltd., actual volume: 65.3%, water absorption rate: 28.3%, absolute dry density: 1.29 g / cm³ 3 (3) Fine aggregate; mountain sand, produced in Kakegawa City, Shizuoka Prefecture, density: 2.58 g / cm³ 3 (4) Emulsion containing paraffin particles (referred to as "paraffin" in Table 1); median diameter of paraffin particles: 0.5 μm, paraffin particle content: 30% by mass, water content: 65% by mass, emulsifier content: 1.0% by mass; amount of defoamer per 100 parts by mass of paraffin particles: 4.0 parts by mass, density: 1.0 g / cm³ 3 (5) Cement admixture polymer (referred to as "polymer" in Table 1); rubber latex (cement admixture polymer dispersion), manufactured by Taiheiyo Material Co., Ltd., trade name "CX-B", median diameter of cement admixture polymer: 0.02 μm, density: 1.00 g / cm³ 3 , polymer content for cement admixture: 45% by mass, water content: 55% by mass, (6) Water; tap water

[0029] [Example 1] A cement-containing mixture was prepared by adding cement, fine aggregate, and coarse aggregate to a mixer in the proportions shown in Table 1 and dry-mixing for 30 seconds. Next, a mixed solution was prepared by mixing water, an emulsion containing paraffin particles, and a polymer dispersion for cement admixture in the proportions shown in Table 1. Then, the mixed solution was added to the cement-containing mixture and mixed for 90 seconds to obtain lightweight concrete. The following physical properties, such as air content, were measured for the obtained lightweight concrete. (a) Air volume The air content was calculated in accordance with "JIS A 1116:2019" (Test method for unit volume mass of fresh concrete and test method for air content by mass). (b) Durability index The durability index was calculated in accordance with the "Underwater Freeze-Thaw Test Method" (Method A) specified in "JIS A 1148:2010" (Test Method for Freeze-Thaw of Concrete). Lightweight concrete specimens were cured underwater for 14 days, followed by 14 days of air curing. (c) Pressure loss inside the pipe The lightweight concrete, after mixing, was pumped from a pump truck through a flexible hose with a horizontal equivalent distance of 101.2m. The pressure inside the hose was measured using a pressure gauge at 5m and 15m from the pump truck, and the pressure loss was calculated by subtracting the pressure at 15m from the pressure at 5m (×10). ―2 MPa / m: Indicated as "Pipe pressure loss" in Table 1.) was calculated. Note that a smaller pressure loss indicates better pumping performance.

[0030] [Examples 2-9, Comparative Examples 1-6] The experiment was conducted in the same manner as in Example 1, except that the lightweight concrete materials listed in Table 1 were used. The results are shown in Table 1.

[0031] [Table 1]

[0032] Table 1 shows that the durability index of Examples 1-9 (72-84) is lower than that of Comparative Examples 1-6 (19-56), indicating that the lightweight concrete of Examples 1-9 has excellent freeze-thaw resistance. Furthermore, a comparison of the internal pressure loss between Examples 1-6 and Comparative Examples 1 and 3 (without paraffin particles), and a comparison of the internal pressure loss between Examples 7-8 and Comparative Example 5 (without paraffin particles), shows that the lightweight concrete of Examples 1-9 has superior pumpability compared to the case without paraffin particles. Also, a comparison of Examples 1-6 and Comparative Example 2 (where the unit amount of cement admixture polymer is 4.5 kg / m³) shows that the lightweight concrete of Examples 1-9 has superior pumpability compared to the case without paraffin particles. 3 The unit amount of paraffin particles is 3 kg / m³ 3 Comparative Example 4 (which does not contain cement admixture polymers and has a unit amount of paraffin particles of 15 kg / m³)3 Comparison of (the above), and Examples 7-8 and Comparative Example 6 (which does not contain cement admixture polymers and has a unit amount of paraffin particles of 15 kg / m³). 3 From a comparison of the two examples, it can be seen that the internal pressure loss values ​​for Comparative Examples 2, 4, and 6 are equivalent to those for Examples 1 to 9, but their durability index is lower.

Claims

1. Lightweight concrete comprising Portland cement, fine aggregate, coarse aggregate, water, paraffin particles, and cement admixture polymer, The above paraffin particle unit amounts are 4 to 20 kg / m³. ３ The unit amount of the above-mentioned cement admixture polymer is 5 to 35 kg / m³. ３ And, The amount of water per 100 parts by mass of the above-mentioned Portland cement is 20 to 60 parts by mass. Either or both of the above-mentioned fine aggregate and coarse aggregate contain lightweight aggregate, and the fine aggregate ratio is 35-65%. Lightweight concrete characterized in that the sum of the median diameter of the paraffin particles and the median diameter of the cement admixture polymer is 1.5 μm or less.

2. Lightweight concrete according to claim 1, wherein the proportion of lightweight aggregate in 100% by volume of the total of the fine aggregate and coarse aggregate is 20 to 80% by volume.

3. The lightweight concrete according to claim 1 or 2, wherein the median diameter of the paraffin particles is 0.2 to 1.0 μm.

4. Lightweight concrete according to any one of claims 1 to 3, wherein the cement admixture polymer is rubber latex and the median diameter of the cement admixture polymer is 0.01 to 1.0 μm.

5. The above lightweight concrete is the lightweight concrete according to any one of claims 1 to 4, wherein the durability index measured in accordance with the "Underwater freeze-thaw test method" (Method A) specified in "JIS A 1148:2010 (Test method for freeze-thaw of concrete)" is 70 or higher.

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