JP2017036164A - Salt damage countermeasure concrete hardened body and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a salt damage countermeasure hardened body having chloride infiltration suppression effect and crack resistance and whole surface is densified, and a method for producing the same.SOLUTION: Provided is a salt damage countermeasure concrete hardened body obtained by subjecting a concrete hardened body using a binder made of low heat portland cement and/or middle heat cement of 65 to 90 pts., a calcium ferroaluminate compound of 3 to 20 pts. and an expansion material of 5 to 15 pts. to carbonization curing and whose surface is densified. Also provided is a salt damage countermeasure concrete hardened body in which the expansion material, in 100 pts. of the total of free lime and calcium alumino ferrite, includes the free lime in the ratio of 50 to 90 pts. and the calcium alumino ferrite in the ratio of 10 to 50 pts. Also provided is a salt damage countermeasure concrete hardened body in which the expansion material, in 100 pts. of the total of free lime, calcium alumino ferrite and anhydrous gypsum, includes free lime in the ratio of 30 to 70 pts., calcium alumino ferrite in the ratio of 20 to 60 pts. and the anhydrous gypsum in the ratio of 30 pts. or less. Also provided is a method for producing salt damage countermeasure concrete carbonized and cured on and after the material age 21 day after concrete placing. Also provided is a salt damage suppression method for reinforced-concrete using any salt damage countermeasure concrete.SELECTED DRAWING: None

Description

  The present invention relates to a salt damage countermeasure concrete cured body used in the field of civil engineering and architecture, a method for producing the same, and a method for suppressing salt damage of reinforced concrete using the same.

Cracks in concrete accelerate the progress of chloride penetration and neutralization, and induce the peeling and dropping of concrete pieces due to reinforcement corrosion. In particular, in coastal areas and road-related concrete, salt damage is likely to occur due to flying salt from the sea or spraying of an antifreezing agent, and development of materials and techniques for reducing cracks in the concrete is proceeding (Patent Document 1).
In addition, it is possible to densify the surface layer of hardened concrete by utilizing the effectiveness of calsim ferroaluminate compounds as a countermeasure against salt damage (Patent Document 2) and the fact that the pore structure of concrete is reduced by carbonation. (Patent Documents 3 and 4).

JP 2001-064054 A WO2011 / 108159 pamphlet JP 2006-182583 A JP 2013-107284 A

  The present invention provides a salt damage-preventing concrete hardened body with a densified surface layer having a chloride penetration inhibiting effect and crack resistance, a method for producing the same, and a salt damage inhibiting method for reinforced concrete using the same.

The present invention employs the following means in order to solve the above problems.
(1) Hardened concrete using a binder comprising 65 to 90 parts by mass of low heat Portland cement and / or moderately hot Portland cement, 3 to 20 parts by mass of calcium ferroaluminate compound, and 5 to 15 parts by mass of an expansion material. This is a hardened concrete that protects against salt damage by carbonizing and curing the surface layer.
(2) Said expansion material contains 50-90 mass parts of free lime and 10-50 mass parts of calcium aluminoferrite in a total of 100 mass parts of free lime and calcium aluminoferrite (1) It is a hardened concrete body for salt damage prevention.
(3) The expansion material is 30 to 70 parts by mass of free lime, 20 to 60 parts by mass of calcium aluminoferrite, and 30 parts by mass of anhydrous gypsum in a total of 100 parts by mass of free lime, calcium aluminoferrite, and anhydrous gypsum. The salt damage-preventing concrete hardened body according to (1) or (2), which is contained at the following ratio.
(4) It is a manufacturing method of the salt damage countermeasure concrete hardened | cured material in any one of said (1)-(3) which carries out carbonation curing after age 21 days after concrete placement.
(5) A salt damage suppression method for reinforced concrete using the salt damage-preventing concrete hardened body according to any one of (1) to (3).

  According to the present invention, the surface of the hardened concrete body is dense and has mass transfer resistance, and also has resistance to cracking. Therefore, even if the anti-freezing material is sprayed, corrosion of reinforcing bars can be prevented.

Unless otherwise specified, parts and% used in the present invention are based on mass.
The concrete referred to in the present invention is a generic term for cement paste, cement mortar, and cement concrete.

The calcium ferroaluminate compound (hereinafter referred to as CFA compound) used in the present invention is a mixture of a raw material containing calcia, a raw material containing alumina, a raw material containing ferrite, etc., and firing in a kiln or melting in an electric furnace. This is a generic term for compounds obtained by heat treatment such as CaO, Al ₂ O ₃ , and Fe ₂ O ₃ as main components.

The composition of the CFA compound is preferably such that the CaO / Al ₂ O ₃ molar ratio is 0.15 to 0.7, from the standpoint that sufficient penetration resistance of chloride ions can be obtained and the pot life can be secured. Is more preferable.
In addition, from the aspect of reducing the remaining amount of unreacted aluminum oxide, the progress of the formation reaction of calcium ferroaluminate, the workability in a high temperature environment, and the resistance to penetration of chloride ions The content of Fe ₂ O ₃ in the CFA compound is preferably 0.5 to 15%, more preferably 1 to 12%, and most preferably 3 to 10%.

The fineness of the CFA compound is preferably 2,000 to 7,000 cm ² / g in terms of the specific surface area of the brain (hereinafter referred to as the “brane value”) from the viewpoint of imparting chloride ion penetration resistance and ensuring the pot life. 6,000 cm ² / g is more preferable, and 4,000 to 5,000 cm ² / g is most preferable.

Moreover, in this invention, an expansion | swelling material is mix | blended with a CFA compound.
The expansion material used in the present invention is not particularly limited, but a commercially available ettringite-based expansion material, lime-based expansion material, or ettringite-lime-based expansion material is applicable. Among these, a low additive type ettringite / lime-based expansion material is preferable from the viewpoint of suppressing chloride permeation.
Furthermore, the expansion | swelling material which has free lime and calcium alumino ferrite or free lime, calcium alumino ferrite, and anhydrous gypsum as a main constituent compound composition is further more preferable.
The calcium aluminoferrite referred to in the present invention is 4CaO · Al ₂ O ₃ · Fe ₂ O ₃ (abbreviated as C ₄ AF) or 6CaO · 2Al ₂ O ₃ · Fe ₂ O ₃ (abbreviated as C ₆ A ₂ F). ) And 6CaO.Al ₂ O ₃ .Fe ₂ O ₃ (abbreviated as C ₆ AF).

In the case where free lime and calcium aluminoferrite are the main constituent compounds of the expansion material, 50 to 90 parts of free lime and 10 to 50 parts of calcium aluminoferrite are preferred in a total of 100 parts of free lime and calcium aluminoferrite.
In addition, when free lime, calcium aluminoferrite, and anhydrous gypsum are used as the main constituent compound composition, 30 to 70 parts of free lime is preferable in a total of 100 parts of free lime, calcium aluminoferrite, and anhydrous gypsum. The calcium aluminoferrite is preferably 20-60 parts. The anhydrous gypsum is preferably 1 to 30 parts, more preferably 3 to 10 parts.
The anhydrous gypsum may be mixed with a heat-treated product containing calcium aluminoferrite and free lime.

  The blending ratio of the CFA compound and the expansion material is such that low heat Portland cement and / or moderately heated Portland cement, binder of 100 parts of CFA compound and expansion material, low heat Portland cement and / or moderately heated Portland cement 65 to 90 parts, It is preferable that they are 3-20 parts of CFA compounds and 5-15 parts of expansion material.

In the present invention, the method of carbonation treatment is not particularly limited, but specific examples thereof include a method of bringing the surface of hardened concrete into contact with a carbonic acid component.
The carbonic acid component referred to in the present invention is a generic term for substances capable of supplying a CO ₂ component, CO ₃ ²⁻ , HCO ₃ ^−, etc., and is not particularly limited. Specific examples thereof include carbonates such as carbon dioxide, supercritical carbon dioxide, dry ice, sodium carbonate, potassium carbonate, and iron carbonate, and bicarbonates such as sodium bicarbonate, potassium bicarbonate, and iron bicarbonate. And carbonated water and the like. From the economical aspect, a method of contacting with carbon dioxide in a sealed curing tank is preferred.

The thickness of the densified layer obtained by carbonation is preferably at least 0.5 mm from the viewpoint of being less susceptible to wrinkles and the like that inevitably occur on the surface of the hardened concrete and obtaining a stable effect. It is more preferably 1 mm or more, and further preferably 2 mm or more. The upper limit of the densified layer thickness is not particularly limited. However, when a reinforcing member made of a material that may corrode such as a reinforcing bar is used, it needs to be less than the cover thickness.
Since it is desirable to secure a sufficient alkaline region around the reinforcing bar, it is preferable to set the upper limit of the densified layer thickness to “rebar cover thickness—5 mm”. A range of 10 mm or less is generally sufficient in terms of reducing the carbonation load and increasing cost merit.

In the present invention, low heat and / or moderately hot Portland cement (hereinafter, also simply referred to as cement), various mixed cements obtained by mixing at least one selected from the group consisting of blast furnace slag, fly ash, and silica, In addition, filler cement mixed with limestone powder can be used.
In particular, it is preferable to use low heat Portland cement or intermediate heat Portland cement because cracks (temperature cracks) in the concrete due to the hydration heat of the cement can be prevented.

  In the present invention, in addition to sand and gravel, water reducing agent, high performance water reducing agent, AE water reducing agent, high performance AE water reducing agent, fluidizing agent, antifoaming agent, thickener, rust preventive agent, antifreeze agent, shrinkage reducing agent , Polymer emulsion, setting modifier, cement hardener, bentonite and other clay minerals, zeolite and other ion exchangers, siliceous fine powder, calcium carbonate, calcium hydroxide, gypsum, calcium silicate, and steel fibers It is possible to use together. Examples of organic materials include fibrous substances such as vinylon fibers, acrylic fibers, and carbon fibers.

  EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these experimental examples.

Experimental example 1
CaO raw material, Al ₂ O ₃ raw material, and Fe ₂ O ₃ raw material are mixed so that the CaO / Al ₂ O ₃ molar ratio is 0.5 and the Fe ₂ O ₃ content is 2%, and using an electric furnace at 1,450 ° C. The heat-treated product thus obtained was heat-treated for 0.5 hour, and the resulting heat-treated product was pulverized with a ball mill to a brane value of 3,500 cm ² / g to prepare a CFA compound.
Furthermore, 450 g of cement (1), 1,350 g of standard sand, and 225 g of water were used as reference blends, and the amounts of CFA compound and expansion material used for cement (1) were changed as shown in Table 1 to prepare cement mortar.
After demolding at a material age of 1 day, cement mortar was cured in water at 20 ° C. until the material age was 28 days, and then subjected to carbonation treatment in an atmosphere of 10% by volume CO ₂ , 20 ° C. and 60% RH.
In addition, the carbonation period was changed and the test body from which carbonation depth differs as shown in Table 1 was created. The specimens that were not carbonated and those that had a short carbonation period were cured in a 20 ° C., 60% RH room without carbon dioxide to adjust the age. Thereafter, the compressive strength was measured at a material age of 35 days, and an immersion test in simulated seawater was started. The immersion period in simulated seawater was 3 months, and the salt penetration depth and bending cracking strength ratio of cement mortar were evaluated.

<Materials used>
CaO raw material: Calcium carbonate (fine limestone powder), 100 mesh, commercial product
Al ₂ O ₃ raw material: Bauxite, 90 µm sieve passage rate 100%, commercial product
Fe ₂ O ₃ raw material: Iron oxide powder, brane value 3,000cm ² / g, commercial cement (1): Low heat Portland cement, commercial product, density 3.23g / cm ³
Expansion material A: Commercial product, F-CaO 50 parts, 3CaO.3Al ₂ O ₃ .CaSO ₄ 12 parts, CaSO ₄ 30 parts, ettringite / lime composite type expansion material, Denki Kagaku Kogyo Co., Ltd. expansion material B: Commercial product, F -CaO 30 parts, 4CaO.Al ₂ O ₃ .Fe ₂ O ₃ 60 parts, CaSO ₄ 10 parts, Ettringite / lime composite expansion material, sand manufactured by Denki Kagaku Kogyo Co., Ltd .: JIS standard sand water: Tap water

<Test method>
Compressive strength: Conforms to JIS R5201.
Densified layer thickness: At the age of 35 days, 1% phenolphthalein solution is sprayed on the cut surface of the specimen for compressive strength, and the thickness of the area of the specimen surface layer that does not turn red is measured. Thus, the carbonation depth (the thickness of the carbonation region) was obtained. The measurement was performed at 8 locations and the average value was obtained.
Bending crack generation strength ratio: A uniaxial restraint test body according to JIS A 6202 appendix 1 was prepared and cured by the method shown in the experimental example. A bending test was performed 3 months after simulated seawater immersion. The load at the time of crack occurrence was measured, and the strength ratio with a test specimen (Experiment No. 1-1) in which no expansion material or CFA compound was mixed was calculated.
Salinity penetration depth: A uniaxial restraint specimen according to JIS A 6202 appendix 1 was prepared and cured by the method shown in the experimental example. Cement mortar was cut 3 months after immersion in simulated seawater, and an aqueous silver nitrate solution was sprayed on the cross section of the cement mortar to measure the salt penetration depth. The measurement was performed at 8 locations and the average value was obtained.

Table 1 shows the following about this invention.
Carbonation treatment is applied to a cured product using a binder composed of low heat Portland cement, calcium ferroaluminate compound, and an expansion material, resulting in a cured product with excellent resistance to chloride ion penetration and high bending crack strength ratio. can get.

Experimental example 2
CaO raw material, Al ₂ O ₃ raw material, and Fe ₂ O ₃ raw material, or CaO raw material, Al ₂ O ₃ raw material, Fe ₂ O ₃ raw material, and CaSO ₄ raw material have predetermined mineral compositions as shown in Table 2. It mixed so that it might become. This mixture was heat-treated at 1,350 ° C. for 0.5 hour using an electric furnace, and the obtained heat-treated product was pulverized to a brain value of 3,500 cm ² / g by a ball mill to prepare an expansion material.
Same as Experimental Example 1 except that an expansion material in which the mixing ratio of the CFA compound was fixed at 10 parts in 100 parts of the binder composed of cement (1), CFA compound, and expansion material was used in the mixing ratio shown in Table 2. Went to.

Table 2 shows the following about this invention.
Carbonation treatment is performed on a cured product using a binder composed of low heat Portland cement, CFA compound, and expansion material to obtain a cured product with excellent penetration resistance to chloride ions and a high bending crack strength ratio. It is done.

Experimental example 3
The test was performed in the same manner as in Experimental Example 2 except that the expansion material of Experiment No. 2-6 was used and the curing period in 20 ° C. water before carbonation treatment was changed as shown in Table 3.
The carbonation period was adjusted so that the densified depth of the hardened cement mortar was 5 mm. After the carbonation was completed, curing was carried out in water at 20 ° C. and 60% until the age of 35 days. Thereafter, the compressive strength was measured, and immersion in simulated seawater was started. After 3 months of immersion, the salt penetration depth and bending cracking strength ratio were evaluated. The results are shown in Table 3.

Table 3 shows the following about this invention.
By securing a curing period of 20 days or more in 20 ° C. water before carbonation treatment, a cured product having excellent resistance to penetration of chloride ions and a high bending crack strength ratio can be obtained.

Experimental Example 4
Curing in 20 ° C water before carbonation treatment using expansive material of Experiment No.2-6, using medium-heated Portland cement or an equivalent mixture of low heat Portland cement and medium-heated Portland cement as cement. The test was performed in the same manner as in Experimental Example 2 except that the period was 28 days. The results are shown in Table 4.
In addition, normal Portland cement and early strong Portland cement were also used.

<Materials used>
Cement (2): Medium heat Portland cement, commercial product, density 3.21 g / cm ³
Cement (3): Ordinary Portland cement, commercially available, density 3.16 g / cm ³
Cement (4): Early strong Portland cement, commercial product, density 3.14 g / cm ³

<Test method>
Adiabatic temperature rise test: A mortar kneaded in a 20 ° C environment is filled in a plastic bag in a heat-insulating dewar bin with a capacity of 5L, a thermocouple is inserted, the mortar temperature is measured, and the temperature rise after kneading is measured. Asked. Using normal Portland cement, the possibility of temperature cracking was determined on the basis of the following criteria, based on a blend that does not contain an expansion material or a CAF compound.
+ 20%: Impossible, -5 to + 20%: Acceptable, -5 to -20%: Good, -20% or less: Excellent

Table 4 shows the following about this invention.
Even when moderately hot Portland cement is used, a cured product having excellent chloride ion penetration resistance and a high bending crack strength ratio can be obtained.
Even when ordinary Portland cement or early strength Portland cement is used, a cured product with excellent chloride ion penetration resistance and a high flexural crack strength ratio can be obtained, but the temperature rise due to the heat of hydration of the cement. There is a concern that the cracks are large.

  According to the present invention, cracking resistance is improved by imparting carbonation and expansion of the surface layer, and since it has a chloride ion permeation suppressing effect, corrosion of reinforcing steel in concrete even when spraying antifreeze containing chloride is applied. It can be applied widely in the civil engineering and construction fields.

Claims (5)

  Carbonation of hardened concrete using a binder consisting of 65 to 90 parts by weight of low heat Portland cement and / or moderately hot Portland cement, 3 to 20 parts by weight of calcium ferroaluminate compound, and 5 to 15 parts by weight of expansion material Cured and hardened concrete for salt damage prevention, with the surface layer densified.   2. The salt damage countermeasure according to claim 1, wherein the expansion material contains 50 to 90 parts by mass of free lime and 10 to 50 parts by mass of calcium aluminoferrite in a total of 100 parts by mass of free lime and calcium aluminoferrite. Hardened concrete.   In the total 100 parts by mass of free lime, calcium aluminoferrite, and anhydrous gypsum, the expansion material is a ratio of 30 to 70 parts by mass of free lime, 20 to 60 parts by mass of calcium aluminoferrite, and 30 parts by mass or less of anhydrous gypsum. The hardened concrete for salt damage prevention according to claim 1 or 2, which is contained in the above.   The manufacturing method of the salt damage countermeasure concrete hardening body of any one of Claims 1-3 which carries out carbonation curing after 21 days of age after concrete placement.   The salt damage control method of the reinforced concrete using the salt damage countermeasure concrete hardening body of any one of Claims 1-3.