JP2015010010A - Salt damage-resistant concrete - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide salt damage-resistant concrete with excellent durability to salt.SOLUTION: Salt damage-resistant concrete includes cement, coarse aggregate, fine aggregate, a water-reducing agent and water. The coarse aggregate is an artificial stone material obtained by melting a mixture including dust and reduction slag generated by a steel making process. The fine aggregate may also be an artificial stone material obtained by melting a mixture including dust and reduction slag generated by a steel making process.

Description

  The present invention relates to a salt-resistant concrete excellent in durability against salts.

  The salt damage of concrete is a phenomenon in which the reinforcing bars are corroded by salts such as chloride ions that have penetrated into the concrete, and cracking occurs in the concrete due to the expansion of the generated rust, thereby reducing the durability of the concrete. In particular, offshore structures such as breakwaters and wave-dissipating blocks are susceptible to salt damage due to exposure to seawater splashes. In addition, concrete such as viaducts and tunnels can be easily peeled off if salt damage occurs, leading to a serious accident.

  In addition, as a result of the widespread diffusion of radioactive materials due to the accident at the Fukushima Daiichi Nuclear Power Station, radioactive materials were concentrated by incineration of sewage sludge containing radioactive materials even in incineration areas far from the power station within the Tokyo metropolitan area. A large amount of contaminated ash is generated. And the method of accommodating such incinerated ash in a concrete container is a useful means since it has a high radiation shielding effect and can prevent the diffusion of radioactive substances. However, since incinerated ash contains a large amount of chloride, the concrete container may suffer from salt damage and may reduce the effect of preventing the diffusion of radioactive materials.

  In order to prevent salt damage to concrete, generally, methods such as increasing the cover of the reinforcing bar or coating the surface of the concrete or the reinforcing bar with a resin are performed. Patent Document 1 discloses concrete containing Portland cement and blast furnace fume as a binder constituting the concrete, and 80 to 90% by weight of Portland cement and 10% of blast furnace fume with respect to the total amount of the binder. Salt resistant concrete containing up to 20% by weight has been proposed.

  However, there is a limit to the expansion of the rebar cover, and the rust-preventing effect is lost if the coating method is damaged. Further, the salt damage resistance of the salt damage resistant concrete is still not sufficient.

JP 2011-037690 A

  Therefore, the subject of this invention is providing the salt-resistant concrete which is excellent in durability with respect to salts.

Then, when this inventor examined various means to solve the said subject, it discovered that the concrete which has the following structure can solve the said subject, and completed this invention.
[1] Salt-resistant concrete containing cement, coarse aggregate, fine aggregate, water reducing agent, and water, wherein the coarse aggregate melts a mixture containing dust and reduced slag generated in the steelmaking process. Salt-resistant concrete, an artificial stone.
[2] The salt-resistant concrete according to [1], wherein the fine aggregate is the artificial stone.
[3] The salt-resistant concrete according to [1] or [2], wherein the content of Fe in the artificial stone is 50% by mass or less in terms of FeO.
[4] The water-reducing agent is a high-performance water-reducing agent or a high-performance AE water-reducing agent containing a formaldehyde condensate of naphthalenesulfonic acid (salt) or a polycarboxylic acid (salt) as an active ingredient. The salt-resistant concrete according to [3].
[5] The salt-resistant concrete according to [1] to [4], which contains an expansion material and / or a shrinkage reducing agent.

  The salt-resistant concrete of the present invention is excellent in durability against salts. Therefore, the salt-resistant concrete of the present invention is suitable as marine concrete such as a breakwater or a wave-dissipating block, a concrete container for storing incinerated ash, or the like.

It is a figure which shows the osmosis | permeation depth and the osmosis | permeation amount of a chloride in the salt-resistant concrete of this invention.

  As described above, the present invention is salt-resistant concrete containing cement, specific coarse aggregate, fine aggregate, water reducing agent, and water. Hereinafter, the salt-resistant concrete of the present invention will be described separately for each constituent material.

(1) Cement The cement includes ordinary portland cement, early-strength portland cement, moderately hot portland cement, lowland heat portland cement and other portland cement, blast furnace cement, fly ash cement and other mixed cement, ecocement, and the above portland cement In addition, a cement obtained by replacing a part of the ecocement with an admixture such as limestone powder, silica fume, and metakaolin can be used. Among these, ordinary Portland cement is preferable from the viewpoint of cost and versatility.
The lower limit of the unit cement amount is preferably 200 kg / m ³ , more preferably 250 kg / m ³ , still more preferably 300 kg / m ³ , and the upper limit is preferably 600 kg / m ³ , more preferably 500 kg / m ^3. More preferably, 400 is kg / m ³ . If the lower limit is less than 200 kg / m ³ , the strength of the salt-resistant concrete is insufficient, and if the upper limit exceeds 600 kg / m ³ , shrinkage strain in the long-term age of the salt-resistant concrete may increase.

(2) Coarse aggregate The coarse aggregate is an artificial stone formed by melting a mixture containing dust (hereinafter referred to as “steel-making dust”) generated in a steelmaking process and reduced slag.
The steelmaking dust is dust that is collected by a dust collector during steelmaking, charging steel scrap or the like into a furnace, and producing steel after passing through the melting, oxidizing, removing, and reducing phases, Reduced slag is slag that is discharged while steel is being produced. Incidentally, an example of the chemical composition of steelmaking dust and reduced slag is shown in Table 1.

Specifically, the coarse aggregate is a mixture of steelmaking dust and reduced slag (pulverized product), using a burner frame in which the oxygen ratio to fuel is preferably 1 or more, more preferably 1.05 or more. , An artificial stone material melted at 1200 to 1400 ° C., cooled and then ground and sorted by sieving and the like, and contains 85% by mass or more of coarse particles having a particle size of 5 mm or more.
The mixing ratio of the steelmaking dust and the reduced slag is preferably 1: 0.3 to 1: 3, more preferably 1: 0.7 to 1: 3, more preferably 1: 1 to 1: 3, in particular by mass ratio. Preferably it is 1: 1 to 1: 2. When the ratio is 1: 0.3 to 1: 3, an artificial stone material having low expansibility and high density can be obtained.

The Fe content in the coarse aggregate is preferably 50% by mass or less, more preferably 45% by mass or less, further preferably 40% by mass or less, and particularly preferably 35% by mass or less in terms of FeO. . When this value exceeds 50% by mass, salt damage resistance decreases.
The surface dry density of the coarse aggregate is preferably 3.3 g / cm ³ or more, more preferably 3.7 g / cm ³ or more, and even more preferably 4.0 g / cm ³ or more. If the value is less than 3.3 g / cm ³ , the shrinkage strain of the salt-resistant concrete tends to increase.
The lower limit of the amount of the coarse aggregate in the concrete is preferably 1000 kg / m ³ , more preferably 1100 kg / m ³ , still more preferably 1300 kg / m ³ , and the upper limit is preferably 1800 kg / m ³ , more preferably. Is 1700 kg / m ³ , more preferably 1600 kg / m ³ . When the value is 1000 to 1800 kg / m ³ , the workability and the like of the salt-damaged concrete are good.

(3) Fine aggregate The fine aggregate is composed of river sand, land sand, sea sand, crushed stone, natural lightweight aggregate, artificial lightweight aggregate, and the artificial stone aggregate (however, all passing through a 10 mm sieve and a fine aggregate of 5 mm or less) One or more selected from those containing 85% by mass or more of the grain fraction). Among these, the artificial stone is preferable because it has a high effect of reducing shrinkage strain of salt-resistant concrete. In addition, the preparation method of the said artificial stone material, the mixture ratio of steelmaking dust and reduced slag, the content rate of Fe, and the surface dry density are the same as the case of the said coarse aggregate.
The unit amount of the fine aggregate in the concrete is preferably 700 kg / m ³ , more preferably 800 kg / m ³ , and the upper limit is preferably 1700 kg / m ³ , more preferably 1600 kg / m ³ , even more preferably. Is 1500 kg / m ³ . If this value is 700-1700 kg / m < ³ >, generation | occurrence | production of the crack of salt-resistant concrete will be few, and fluidity | liquidity will be favorable.

(4) Water reducing agent The water reducing agent includes formaldehyde condensate of naphthalene sulfonic acid (salt), polycarboxylic acid (salt), formaldehyde condensate of melamine sulfonic acid (salt), polystyrene sulfonic acid (salt), and lignin sulfonic acid. (Salt) etc. are mentioned. Among these, a high-performance water reducing agent or a high-performance water-reducing agent containing a formaldehyde condensate of naphthalenesulfonic acid (salt) or polycarboxylic acid (salt) as an active ingredient in terms of workability of salt-resistant concrete and the effect of reducing shrinkage strain. A performance AE water reducing agent is preferred. Here, the acid (salt) of the polymer compound refers to an acid, a salt thereof, and a polymer compound in which these coexist. The salt refers to an alkali metal salt such as a sodium salt, an alkaline earth metal salt such as a calcium salt, and an ammonium salt.
The blending ratio of the water reducing agent is 100 parts by weight of cement, in terms of solid content, and the lower limit is preferably 0.1 parts by weight, more preferably 0.3 parts by weight, and even more preferably 0.5 parts by weight. The upper limit is preferably 5 parts by mass, more preferably 4 parts by mass, and even more preferably 2 parts by mass. If this value is 0.1-5 mass parts, the fluidity | liquidity of a salt-resistant concrete is favorable and can make slump loss small.

(5) Water The water used in the present invention can be used as long as it does not adversely affect the strength development and fluidity of the salt-resistant concrete. Examples of such water include tap water, treated sewage water, and supernatant water of ready-mixed concrete. The lower limit of the water / cement ratio is preferably 15%, more preferably 30%, and the upper limit is preferably 55%, more preferably 50%. If this ratio is 15 to 55%, the strength of the salt-resistant concrete is high and the fluidity and workability are good.

(6) Expanding material The salt-resistant concrete of the present invention may contain an expanding material and / or a shrinkage reducing agent. By including an expansion material and / or a shrinkage reducing agent, shrinkage strain can be further reduced.
Examples of the expansion material include lime-based and calcium sulfoaluminate-based materials. The unit amount of the expansion material in the concrete is preferably 40 kg or less, more preferably 10 to 30 kg. If the value exceeds 40 kg, the amount of expansion may be excessive.
Blaine specific surface area of the expansion member, the lower limit is preferably 2000 cm ² / g, more preferably 3000 cm ² / g, the upper limit is preferably 6000 cm ² / g. The said value is 2000cm less than ² / g, there is a risk that the expansion member in the concrete decreases the strength pops out, high cost exceeds 6000 cm ² / g.

(7) Shrinkage reducing agent The shrinkage reducing agent is, for example, an alkylene oxide adduct of a lower alcohol, a glycol ether / amino alcohol derivative, a polyether, an alkylene oxide copolymer, and a mixture of a polyoxyalkylene alcohol ether and an inorganic filler. 1 type or more chosen from etc. is mentioned. The mixing ratio of the shrinkage reducing agent is preferably 5.0 parts by mass or less, more preferably 0.5 to 4.0 parts by mass with respect to 100 parts by mass of cement. When the blending ratio exceeds 5.0 parts by mass, the hydration of cement may be hindered.

(8) Other optional components The salt-resistant concrete of the present invention may further contain admixtures such as an antifoaming agent and a hydration heat inhibitor. Examples of the antifoaming agent include liquid or powdered antifoaming agents such as ester, polyether, mineral oil, and silicone. The blending ratio of the antifoaming agent is preferably 0.04 parts by mass or less, more preferably 0.02 parts by mass or less with respect to 100 parts by mass of cement. If the value exceeds 0.04 parts by mass, the hydration of the cement may be hindered.
Examples of the hydration heat inhibitor include one or more selected from dextrin, modified starch, boric acid and the like. The hydration heat inhibitor has an effect of suppressing temperature cracking by suppressing heat of hydration. The blending ratio of the hydration heat inhibitor is preferably 0.5 parts by mass or less, more preferably 0.4 parts by mass or less, and still more preferably 0.3 parts by mass or less with respect to 100 parts by mass of cement. If this value is 0.5 parts by mass or less, the heat of hydration can be suppressed without delaying the setting.
The salt-resistant concrete of the present invention may further contain an admixture such as fly ash, coal ash, silica fume, and limestone powder.

Next, the characteristics of the salt-resistant concrete of the present invention will be described.
(1) Unit volume mass The unit volume mass of the salt-resistant concrete of the present invention is preferably 2.5 kg / L or more, more preferably 2.8 kg / L or more, further preferably 3.0 kg / L or more, particularly preferably. 3.3 kg / L or more. When the value is less than 2.5 kg / L, the salt damage resistance and the radiation shielding effect are not sufficient.

(2) Static elastic modulus The static elastic modulus of the salt-resistant concrete of the present invention is 7 days old, preferably 35 kN / mm ² or more, more preferably 40 kN / mm ² or more, and further preferably 45 kN / mm ² or more. There, in the age of 28 days, preferably from 40 kN / mm ² or more, more preferably 45 kN / mm ² or more, further preferably 50 kN / mm ² or more. When this value is small, the shrinkage strain may increase.

EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to these Examples.
1. Materials used Table 2 shows the materials used.

2. Chloride Penetration Test Raw materials prepared according to the formulation shown in Table 3 using the materials shown in Table 2 were kneaded for 120 seconds at 20 ° C. with a biaxial forced kneader to obtain fresh concrete. Next, the fresh concrete was put into a mold and demolded one day later, and the obtained concrete was cured in standard water until the age of 28 days to prepare a specimen.
Next, the specimen was sprayed with seawater simulating a splash environment twice a day for about 4 hours per time, and this was repeated until the age of one year.
Then, the distribution of chloride ions in the depth direction in the specimen was measured in accordance with JSCE-G 572 “Apparent diffusion coefficient test method for chloride ions in concrete by immersion”. The diffusion coefficient was determined. The distribution of chloride ions is shown in FIG. 1, and the diffusion coefficient of chloride ions is shown in Table 3.
In addition, the target slump of the fresh concrete was set to 8 ± 2.5 cm and the target air amount was set to 2.0 ± 1.0%, and was adjusted by the amount of admixture added.

  As shown in FIG. 1, compared with Comparative Examples 1-3, the Example has a small amount of chloride penetration and a small diffusion coefficient. Therefore, it can be seen that, among heavy aggregates, concrete containing artificial stone obtained by melting a mixture containing steelmaking dust and reduced slag is excellent in salt resistance.

Claims (5)

  A salt-resistant concrete containing cement, coarse aggregate, fine aggregate, water reducing agent, and water, wherein the coarse aggregate is an artificial stone formed by melting a mixture containing dust and reduced slag generated in the steelmaking process. There is salt-resistant concrete.   The salt-resistant concrete according to claim 1, wherein the fine aggregate is the artificial stone.   The salt-resistant concrete according to claim 1 or 2, wherein the content of Fe in the artificial stone is 50% by mass or less in terms of FeO.   The said water reducing agent is a high performance water reducing agent or a high performance AE water reducing agent containing the formaldehyde condensate of naphthalenesulfonic acid (salt) or polycarboxylic acid (salt) as an active ingredient. Salt resistant concrete.   The salt-resistant concrete according to claim 1, comprising an expansion material and / or a shrinkage reducing agent.

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