JP5371192B2 - Sulfate-resistant concrete, concrete structure constructed with the sulfate-resistant concrete, and method for producing sulfate-resistant concrete - Google Patents

Description

  The present invention relates to a sulfate resistant concrete, a concrete structure constructed with the sulfate resistant concrete, and a method for producing the sulfate resistant concrete.

In sewerage facilities constructed of concrete, the cement component (Ca (OH) ₂ ), which is the main component of concrete, is eluted by reacting with sulfuric acid generated by the action of microorganisms, and the surface of the concrete peels off due to corrosion. As a result, the strength of the concrete is reduced.

  Therefore, a sulfuric acid resistant paint is applied to the concrete surface in contact with sulfuric acid to form a film, or a resin panel or a polymer concrete panel is attached to cover the surface to prevent contact between sulfuric acid and concrete. However, a method for preventing corrosion by sulfuric acid is used.

  In addition, a method of manufacturing a structure in a part in contact with sulfuric acid, for example, a sewer pipe only with a nickel-chromium alloy having sulfuric acid resistance (for example, MC alloy: trade name, manufactured by Mitsubishi Materials Corporation) is also used. Yes.

  However, in the method of applying a sulfuric acid resistant coating to the surface of concrete or attaching a resin panel, etc., there is a need for material costs such as paint and resin panels, and labor costs related to the application work and installation work. For this reason, there is a problem that the construction cost of the structure constructed of concrete becomes high.

  Further, in the method of manufacturing the structure in contact with sulfuric acid, for example, the sewer pipe only with nickel / chromium alloy or the like, there is a problem that the cost is high because the material cost is high. In addition, it is possible to manufacture a small-diameter sewer pipe or the like using only nickel-chromium alloy, but there is a problem that it cannot be applied to a large-diameter sewer pipe because the predetermined strength cannot be secured. .

  Therefore, the present invention has been made in view of the above problems, and an object thereof is to provide a sulfate-resistant concrete that is inexpensive, excellent in sulfuric acid resistance, and capable of maintaining a predetermined strength, and a method for producing the same. Yes.

The sulfate-resistant concrete of the present invention that solves the above problems includes a first concrete layer formed by curing concrete having a first water cement ratio, and a water cement that is larger than the first water cement ratio. The second concrete layer formed by curing the concrete having a specific ratio and neutralized in the whole depth direction, and a boundary portion between the first concrete layer and the second concrete layer. And a net-like connecting member for connecting the concrete layers, wherein the first concrete layer has a two-layer structure that is denser than the second concrete layer.

According to the sulfate-resistant concrete according to the present invention, the neutralized second concrete layer is almost free of Ca (OH) _{2 as} a cement component that reacts with sulfuric acid . Accordingly, the surface portion of the concrete where the second concrete layer exists does not react with sulfuric acid and does not cause corrosion. In addition, since the sulfate-resistant concrete itself includes the second concrete layer , it is possible to omit operations such as application of a sulfate-resistant coating and attachment of a resin panel which have been conventionally performed. Therefore, it is possible to reduce material costs and labor costs. In addition, sulfate-resistant concrete is a semi-factory product that neutralizes the second concrete layer at the factory and transports it to the site. There is no need for neutralization at the site, so large-scale equipment is required at the site. do not do. Furthermore, the connectivity of each concrete layer can be enhanced by the coupling member.

Moreover, the concrete structure of the present invention is constructed of the sulfate-resistant concrete according to claim 1. According to the concrete structure of the present invention, since it is constructed of sulfate resistant concrete, it is possible to construct a concrete structure excellent in sulfuric acid resistance that does not cause corrosion due to sulfuric acid. Therefore, it is possible to reduce the number of maintenance and the like. Further, since corrosion does not occur, the durability of the concrete structure is improved, and the concrete structure can be used safely for a longer time than before.

In the method for producing sulfate-resistant concrete according to the present invention, two types of fluidized concrete having different water-cement ratios are manufactured, and the two types of fluidized concrete are sequentially filled in one mold. At the same time, a net-like connecting member is installed at the boundary portion of each concrete and hardened to produce a two-layer concrete in which the concrete layer on one end side is denser than the concrete layer on the other end side. the surface was sealed so the gas does not contact, at the two-layer concrete into the diacid carbon atmosphere, characterized by neutralizing the whole of the depth direction in the concrete layer of the other end .

According to the method of manufacturing sulfuric acid concrete according to the invention, the overall depth of the other end side of the concrete layer is possible to produce resistance to sulfuric concrete is neutralized. Also, the concrete layer on the other end side has more voids than the concrete layer on the one end side, and carbon dioxide can easily enter, so the concrete layer on the other end side can be put in a shorter time than when the concrete layer on one end side is neutralized. It becomes possible to neutralize the layer. Therefore, the sulfuric acid resistant layer can be efficiently formed.

  And since neutralization is implemented in the factory provided with the equipment which can control the density | concentration of a carbon dioxide, management of the depth etc. to neutralize becomes easy. Therefore, it is possible to produce a high quality product. Moreover, since neutralization is automatically performed by a machine, a sulfuric acid resistant layer can be formed at low cost.

  According to the present invention, sulfate-resistant concrete that does not corrode even in contact with sulfuric acid can be produced at low cost. In addition, by using this sulfate resistant concrete, it is possible to construct a concrete structure excellent in sulfuric acid resistance while sufficiently securing the strength required for the structure.

  Hereinafter, embodiments of the present invention applied to sewer facilities will be described in detail with reference to the drawings. However, it goes without saying that the present invention can be applied not only to sewer facilities but also to hot spring facilities. First, the reaction between general concrete and sulfuric acid will be described, and then the sulfate resistant concrete according to the present invention will be described.

FIG. 1 is a diagram showing a state in which corrosion due to sulfuric acid occurs in a sewer pipe 31 constructed of general concrete. As shown in FIG. 1, when the concrete comes into contact with sewage passing through the sewer pipe 31, a hydration reaction occurs and calcium hydroxide is generated. This reaction formula is shown in Formula (1) and Formula (2).
2 (CaO) ₃ · SiO ₂ + 6H ₂ O → 3CaO · 2SiO ₂ · 3H ₂ O + 3Ca (OH) ₂ (1)
2 (CaO) ₂ · SiO ₂ + 4H ₂ O → 3CaO · 2SiO ₂ · 3H ₂ O + Ca (OH) ₂ (2)
The calcium hydroxide produced in formulas (1) and (2) then reacts with sulfuric acid to produce dihydrate gypsum (CaSO ₄ .2H ₂ O).

When the sewage / sludge in the sewer pipe 31 becomes anaerobic, sulfate in the sewage / sludge is reduced by microorganisms (sulfate-reducing bacteria) to generate hydrogen sulfide. This reaction formula is shown in Formula (3).
SO ₄ ²⁻ + 2C + 2H ₂ O → H ₂ S + 2HCO ₃ −... (3)
The hydrogen sulfide generated in the formula (3) is concentrated in the gas phase in the sealed sewerage facility and re-dissolved during condensation on the concrete wall surface. Thereafter, it is oxidized by sulfur-oxidizing bacteria (such as Thiobacillus genus) in an aerobic state to produce sulfuric acid. This reaction formula is shown in (Formula 4).
H ₂ S + 2O ₂ → H ₂ SO ₄ ...... Formula (4)

Thus, sulfuric acid (H ₂ SO ₄ ) produced by the action of sulfate-reducing bacteria and sulfur-oxidizing bacteria (Thiobacillus genus, etc.) is concentrated to PH 1-2 on the concrete wall and contained in the concrete. It reacts with calcium hydroxide produced by the hydration reaction of the cement to produce dihydrate gypsum (CaSO ₄ .2H ₂ O). This reaction formula is shown in Formula (5).
H ₂ SO ₄ + Ca (OH) ₂ → CaSO ₄ .2H ₂ O Formula (5)
As shown in the formula (5), the strength of the concrete is lowered by the dissolution of Ca (OH) ₂ which is the main component of the concrete due to the influence of sulfuric acid.

The dihydrate gypsum further reacts with tricalcium aluminate in the concrete to produce an ethrin guide that is an expandable needle crystal. This reaction formula is shown in Formula (6).
3CaSO ₄ · 2H ₂ O + 3CaO · Al ₂ O ₃ + 26H ₂ O → 3CaO · Al ₂ O ₃ · 3CaSO ₄ · 32H ₂ O (6)
The ethrin guide generated by the equation (6) takes in crystal water in the concrete and expands, thereby destroying the concrete.

Therefore, in order to deal with the above-described situation, as a method for imparting sulfuric acid resistance to concrete, in the present invention, the Ca (OH) ₂ in the surface portion of the concrete in contact with sulfuric acid is neutralized and reduced. Prevents reaction with sulfuric acid.

  FIG. 2 is a view showing a sewer pipe 1 constructed of sulfate-resistant concrete according to the first embodiment of the present invention. As shown in FIG. 2, the sewer pipe 1 is made of sulfate resistant concrete 5 having an inner wall surface with a sulfate resistant layer 3 neutralized by a predetermined depth D.

  The sewer pipe 1 is constructed thicker by a predetermined depth D of the sulfuric acid resistant layer 3 in addition to a minimum thickness L necessary for ensuring a predetermined strength. The predetermined depth D (= thickness of the sulfuric acid resistant layer 3) is appropriately set at each site depending on the diameter of the sewer pipe 1, the flow rate of sewage passing through the sewer pipe 1, and the like.

This sulfuric acid resistant layer 3 does not contain Ca (OH) ₂ because the concrete is neutralized, and even if the sulfuric acid resistant layer 3 comes into contact with sulfuric acid, it reacts as shown in the above formula (5). Does not occur.

Next, a neutralization method for forming the sulfuric acid resistant layer 3 will be described. Neutralization is carried out in accordance with JISA 1 1 5 3 “Accelerated neutralization test method for concrete”.
FIG. 3 is a schematic view showing a production process of the sulfate-resistant concrete according to the first embodiment of the present invention.
As shown in FIG. 3, first, concrete in a fluid state in which cement, gravel, water or the like is mixed is filled in the mold 17. After filling the concrete, the formwork 17 is removed within 16 hours or more and 3 days, and the hardened concrete 6 is kept in a wet state (in water or in an atmosphere with a relative humidity of 95% or more) at a temperature of 20 ± 2 ° C. until the age of 4 weeks. ).

  Next, the concrete 6 is allowed to stand until the age of 8 weeks in a constant temperature and humidity chamber having a relative humidity of 60 ± 5% and a temperature of 20 ± 2 ° C. Here, the side surfaces 6a to 6d and the bottom surface 6e of the concrete 6 are sealed with aluminum foil tape during the age of 7 to 8 weeks to prevent the side surfaces 6a to 6d and the bottom surface 6e from coming into contact with carbon dioxide.

  For example, when sealing the sewer pipe 1, as shown in FIG. 4, the outer peripheral surface 7 and both end surfaces 9, 11 are sealed with an aluminum foil tape, and the outer peripheral surface 7 and both end surfaces 9, 11 are made of carbon dioxide. Prevent contact.

  The sealing method is not limited to this, and a method of applying an epoxy resin, a polyurethane resin, or the like may be used.

  Next, the concrete 6 is put in a control device capable of controlling the carbon dioxide concentration, temperature, and humidity, and the environmental conditions are such that the carbon dioxide concentration is 5 ± 0.2%, the temperature is 20 ± 2 ° C., and the relative humidity is 60 ± 5%. Then, by standing for a predetermined time and neutralizing the surface 6f (see FIG. 3) of the concrete 6 to a predetermined depth D, the sulfate resistant concrete 5 provided with the sulfuric acid resistant layer 3 is manufactured.

  For example, when the sewer pipe 1 is put in the control device, the sewer pipe made of the sulfate-resistant concrete 5 having the sulfate-resistant layer 3 is formed by neutralizing from the inner peripheral surface 13 to the predetermined depth D. 1 (see FIG. 2) is manufactured.

  The predetermined time is appropriately changed according to the desired thickness of the sulfuric acid resistant layer 3, and is calculated by calculation using a prediction formula for the progress of neutralization.

As described above, in the sewer pipe 1 made of the sulfate resistant concrete 5 of the present embodiment, the neutralized sulfuric acid resistant layer 3 has almost no Ca (OH) ₂ that reacts with sulfuric acid. Accordingly, the sewer pipe 1 made of the sulfate-resistant concrete 5 having the sulfuric acid-resistant layer 3 on the surface portion of the inner peripheral surface 13 does not react with sulfuric acid and does not corrode, so that the number of maintenance and the like can be reduced. Become. Moreover, since corrosion does not occur, the durability of the sewer pipe 1 is improved, and it can be used safely for a longer time than before.

  Further, in addition to the minimum thickness L necessary for ensuring the strength of the sewer pipe 1, the structure is further thickened by a predetermined depth D, so that the strength required for the sewer pipe 1 is sufficiently ensured. It becomes possible.

  In addition, since the sulfuric acid resistant concrete 5 itself includes the sulfuric acid resistant layer 3, it is possible to omit operations such as application of a sulfuric acid resistant coating and attachment of a resin panel which have been conventionally performed. Therefore, it is possible to reduce material costs and labor costs.

  Furthermore, the sulfate-resistant concrete 5 is a semi-factory product that neutralizes the concrete surface at the factory and transports it to the site, so there is no need to perform neutralization work at the site, so large-scale equipment is required at the site. do not do. Further, since neutralization is performed in a factory equipped with facilities capable of controlling the concentration, humidity, and temperature of carbon dioxide, it becomes easy to manage the depth of neutralization. Therefore, it is possible to produce a high quality product. And since neutralization is performed automatically by a machine, it becomes possible to manufacture the sulfate-resistant concrete 5 at low cost.

Next, a second embodiment of the present invention will be described. In the following description, portions corresponding to the first embodiment are denoted by the same reference numerals, description thereof is omitted, and differences are mainly described. In the second embodiment, the sulfate-resistant concrete 21 is manufactured by a method that is partially different from that of the first embodiment.
First, two types of concrete with different water-cement ratios are produced. In the present embodiment, the water cement ratio is, for example, 55% and 60%.

  FIG. 5 is a schematic view showing a production process of the sulfate resistant concrete 22 according to the second embodiment of the present invention. As shown in FIG. 5, after filling the formwork 17 with fluid concrete having a water cement ratio of 55%, filling the fluid concrete with a water cement ratio of 60%, the water cement ratio is 55%. A two-layer concrete 21 composed of a lower concrete layer 23 made of the above concrete and an upper concrete layer 25 having a water-cement ratio of 60% is manufactured. In the lower concrete layer 23 having a small water-cement ratio, concrete that is denser than the upper concrete layer 25 is formed.

  At the boundary between the lower concrete layer 23 and the upper concrete layer 25, a reinforced plastic or the like that does not change its component even if it comes into contact with carbon dioxide for a long time is installed in a net shape to connect the two concrete layers 23 and 25 together. Used as connecting material 29.

  And like 1st embodiment, the formwork 17 is removed within 3 hours from 16 hours or more, it cures in a moist state, and it leaves still to a material age of 8 weeks. Here, in this embodiment, as shown in FIG. 6, the side surfaces 22a to 22d and the bottom surface 22e of the two-layer concrete 21 are sealed with aluminum foil tape during the age of 7 to 8 weeks, and the side surfaces 22a to 22a are sealed. 22d and bottom 22e are prevented from coming into contact with carbon dioxide.

Next, again, as in the first embodiment, the two-layer concrete 21 is placed in a control device capable of controlling the carbon dioxide concentration, temperature, and humidity, and is allowed to stand for a predetermined time. In the present embodiment, the predetermined time is a time required to neutralize the upper cement layer 25, and is calculated by a prediction formula for the progress of neutralization.
And the sulfate-resistant concrete 22 is manufactured by neutralizing the upper side cement layer 25.

As described above, the sulfate-resistant concrete 22 of this embodiment has almost no Ca (OH) ₂ that reacts with sulfuric acid in the neutralized sulfuric acid-resistant layer 3, that is, the upper concrete layer 25. Therefore, the sulfuric acid resistant concrete 22 provided with the sulfuric acid resistant layer 3 does not react with sulfuric acid and does not cause corrosion.

Further, since the upper concrete layer 25 has more voids than the lower concrete layer 23 and carbon dioxide easily enters from the outside, the upper concrete layer 25 is medium in a shorter time than the case where the lower concrete layer 23 is neutralized. Be sexualized.
Furthermore, by making the thickness of the upper concrete layer 25 the same as the predetermined thickness D for neutralization, the sulfuric acid resistant layer 3 can be efficiently formed.

  In all the embodiments described above, reinforcing bars and the like may be installed inside the sulfate-resistant concrete 1 and 22. In this case, the reinforcing bars are arranged in a concrete portion that is not neutralized, and depending on the design or the like. It is arranged to have a predetermined concrete covering thickness (not including the thickness of the sulfuric acid resistant layer 3).

It is a figure which shows the state which the corrosion by a sulfuric acid generate | occur | produces in the sewer pipe constructed | assembled with the general concrete. It is a figure which shows the sewer pipe constructed | assembled with the sulfate resistant concrete which concerns on 1st embodiment of this invention. It is a schematic diagram which shows the manufacture process of the sulfate-resistant concrete which concerns on 1st embodiment of this invention. It is a figure which shows the sewer pipe which consists of sulfate-resistant concrete which concerns on 1st embodiment of this invention. It is a schematic diagram which shows the manufacture process of the sulfate-resistant concrete which concerns on 2nd embodiment of this invention. It is a schematic diagram which shows the manufacture process of the sulfate-resistant concrete which concerns on 2nd embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sewer pipe 3 Sulfuric acid resistant layer 5 Sulfuric acid resistant concrete 6 Concrete 6a, 6b, 6c, 6d Side surface 6e Bottom surface 6f Surface 7 Outer surface 9, 11 End surface 13 Inner surface 21 Double-layer concrete 22 Sulfuric acid resistant concrete 22a, 22b, 22c, 22d side surface 22e bottom surface 23 lower concrete layer 25 upper concrete layer 27 formwork 29 connecting material 31 sewer pipe L necessary minimum thickness D thickness of sulfuric acid resistant layer

Claims (3)

A first concrete layer formed by curing concrete having a first water-cement ratio;
A second concrete layer formed by curing concrete having a water cement ratio larger than the first water cement ratio, and neutralized in the depth direction as a whole;
A net-like connecting member that is installed at a boundary between the first concrete layer and the second concrete layer and connects the concrete layers;
The sulfate-resistant concrete, wherein the first concrete layer has a two-layer structure in which the second concrete layer is more dense than the second concrete layer . A concrete structure constructed of the sulfate-resistant concrete according to claim 1 . Produced two types of fluidized concrete with different water-cement ratios,
The molds are filled with the two kinds of fluid concrete in order, and a net-like connecting member is installed at the boundary between the concretes and hardened so that the concrete layer at one end is the concrete at the other end. Make a two-layer concrete that is denser than the layers,
Seal the surface of the concrete layer on the one end side so that gas does not contact it,
Placing the two layers of concrete in the diacid carbon atmosphere, method of manufacturing sulfuric acid concrete, characterized in that to neutralize the overall depth of the concrete layer of the other end.

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