JP2002173380A - Method of suppressing alkaline aggregate reaction in concrete structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of suppressing an alkaline aggregate reaction, which comprises allowing an aqueous solution of a lithium salt or lithium hydroxide to penetrate or diffuse from the inside of a concrete structural body and by which the alkaline aggregate reaction can be effectively suppressed even at the deep inside of the concrete structural body having a large cross section. SOLUTION: The method of suppressing the alkaline aggregate reaction comprises forming an injection hole which reaches to the deep inside of the concrete structural body on the surface of the concrete structural body containing the aggregate causing the alkaline aggregate reaction and then injecting the aqueous solution of the lithium salt or lithium hydroxide under pressure from the injection hole.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for suppressing aging of a concrete structure due to an alkali-aggregate reaction.

[0002]

2. Description of the Related Art Concrete is generally formed by mixing cement, aggregate, water, additives and the like. Conventionally, gravel was used as aggregate, but due to depletion of resources,
Increasingly, crushed stones obtained by crushing minerals such as rocks have been used. However, using some crushed stone as aggregate, in hardened concrete structures,
An alkali-aggregate reaction occurs in which alkali metal components other than lithium, such as sodium and potassium, contained in the cement react with the aggregate. As a result, the concrete structure gradually expands from the inside, and the concrete structure This caused cracks and collapse on the surface.

[0003] As a method of solving such a problem caused by the alkali-aggregate reaction, for example, an inhibitor such as an aqueous solution of lithium nitrite or an aqueous solution of lithium hydroxide is mixed into concrete or the surface of a hardened concrete structure is exposed. Method of impregnating the inhibitor (JP-A-61-256951),
A method in which a sheet impregnated with an inhibitor is adhered to the surface of a concrete structure (Japanese Utility Model Application Laid-Open No. 63-122544). A method of backfilling a repaired mortar to which a large amount of mortar is added on a ground concrete surface is being studied. Here, "hanging" refers to removing the surface of concrete until a steel material such as a reinforcing bar is exposed.

[0004]

In each of these methods, the inhibitor is impregnated or diffused into the concrete from the concrete surface by utilizing the diffusion effect due to the concentration gradient and the capillary action of the cement matrix. However, in the conventional method described above, the distance that the inhibitor penetrates from the concrete surface into the concrete is only a few cm from the concrete surface. The distance or depth at which lithium nitrite diffuses from the repair mortar into the concrete due to the ion concentration gradient is not large. Furthermore, if the concrete surface is wet due to rainfall,
When the water content of the concrete is high, there is a problem that it hardly penetrates into the concrete. In other words, in these methods, the alkali-aggregate reaction in the concrete portion impregnated with the inhibitor near the concrete surface is suppressed, but particularly in a concrete structure having a large member cross section, the inhibitor surface is difficult to penetrate. In the distant inner part,
The alkali-aggregate reaction cannot be suppressed.

[0005]

Means for Solving the Problems As a result of intensive studies on the above problems, the present inventors have found that a permeation or diffusion of an inhibitor from the inside of a concrete structure allows the inner part of the concrete structure having a large cross section to be deepened. Also, the present inventors have found a method capable of effectively protecting from the alkali-aggregate reaction, and have reached the present invention. That is, the present invention comprises, after forming an injection hole reaching the inner part on the surface of a concrete structure containing an aggregate that causes an alkali-aggregate reaction, comprises an aqueous solution of a lithium salt or lithium hydroxide from the injection hole. The present invention relates to a method characterized by injecting an inhibitor under pressure.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. The present invention relates to a concrete structure having a composition in which an alkali-aggregate reaction occurs. The cause of such an alkali-aggregate reaction is that in the presence of water,
Occurs when aggregates such as crushed stones and alkali metal ions other than lithium ions are present. Accordingly, the present invention relates to a concrete structure containing an aggregate that causes such an alkali-aggregate reaction.

As the cement used for the concrete structure of the present invention, various cements can be used, and examples thereof include ordinary Portland cement, early-strength Portland cement, and moderately heated Portland cement. In these cements, usually, a total alkali amount of about 0.5 to 1.5% by mass in terms of oxides, for example, Na ₂ O
And K ₂ O are included.

The aggregate used in the concrete structure of the present invention is an aggregate that causes an alkali-aggregate reaction such as crushed stone. Minerals for crushed stone include protein stone, chalcedony, mafic limestone, rhyolite, andesite, tuff, quartz andesite, trachyte, obsidian, pyroxene rock, tridymite, cristobaray,
Various charts, flints and the like can be mentioned. These minerals contain a component that reacts with the alkali contained in the cement in the presence of water. The aggregate may be a coarse aggregate or a fine aggregate.

Examples of components that react with the alkali component include:
Examples thereof include silica, silicate, and carbonate. The reactivity between the aggregate and the alkali in the cement is not uniform. The reactivity of crushed aggregate is generally evaluated experimentally before incorporation into concrete. As a test method, a method of ASTM C 289 is used as a chemical method relating to reactivity with an alkali component. The reactivity can be evaluated by the method of ASTM C227 which measures the expansion rate of the aggregate by a mortar bar method.

[0010] According to JIS regulations revised in 1992, the alkali content in cement is specified to be 0.75% by mass or less. Therefore, in the concrete structure to which this enactment rule is applied, it is considered that the alkali-aggregate reaction is considerably reduced to some extent as compared with the conventional one.
Nevertheless, in the long term, cracks and collapses on the concrete structure surface may occur due to the effect of the alkali-aggregate reaction. Furthermore, in concrete structures constructed before this, since a relatively large amount of alkali exists in the concrete structure as described above, deterioration of the concrete structure due to alkali-aggregate reaction is still a problem. .

As the aqueous solution of a lithium salt used in the present invention, aqueous solutions of various lithium salts can be used. The lithium salt used in the aqueous solution of such a lithium salt is not particularly limited as long as it is soluble in water, and various lithium salts can be used. Such lithium salts include, for example, lithium nitrite,
Lithium silicate, lithium nitrate and the like can be used. These lithium salts are readily available on the market.

The aqueous solution of lithium salt or lithium hydroxide is suitably used, for example, at a concentration of 5 to 60% by mass, preferably 20 to 50% by mass. Various additives may be used in combination with the aqueous solution of lithium salt or lithium hydroxide as needed. As such an additive, for example,
Thixotropic agents, preservatives, dispersants and the like. Hereinafter, the method of the present invention will be described in more detail with reference to the drawings.
FIG. 1 is a diagram showing an example in which the method of the present invention is applied to a beam portion of a pier 1. A plurality of injection holes 2 are formed in the pier 1 at predetermined intervals using a concrete core cutter or a concrete drill. When a crack is generated on the concrete surface, it is preferable to previously close the crack using a crack repairing material such as an epoxy resin. Further, when cracks are generated on the entire concrete surface, it is preferable to apply the resin to the concrete surface.

As shown in FIG. 2, each injection hole 2 has
For example, a single packer 3 is inserted. The packer itself such as the single packer 3 has conventionally been used for stopping water in a crack portion, injecting into a concrete joint portion, injecting into a void portion, etc., but prevents an alkali-aggregate reaction. Therefore, it has not been used for the purpose of injecting the inhibitor from the inner part. This single packer 3
As shown in FIG. 2, a pipe is connected to a storage tank 5 for holding an aqueous solution (inhibitor) 4 of a lithium salt (for example, lithium nitrite) connected to a pressurizing pump P at an end on the concrete surface side. 6 are connected.

As shown in FIG. 3, the single packer 3 is made of a long cylindrical metal body 12, and has an ejection hole 16 formed at one end located on the inner side of the injection hole 2.
As shown in FIG. 2, the other end of the concrete surface side
It is adapted to be connected to a pipe 6 from a tank 5.
On the outer surface of the metal body 12, on the concrete surface side,
The rubber sleeve 15 is provided between the flange 18 and a washer 19 movably fixed with a bolt 20.

The outer diameter of the rubber sleeve 15 of the single packer 3 is set smaller than the inner diameter of the injection hole 2 in advance. Therefore, the single packer 3 can be easily inserted into the injection hole 2 (FIG. 3A). Single packer 3
Is fixed to the injection hole 2, the bolt 20 is tightened, the end of the rubber sleeve 15 is pushed in through the washer 19, and the rubber sleeve 15 is sandwiched between the flange 18 and the rubber sleeve 15.
15 contracts in the length direction. Follow this rubber sleeve
The single packer 3 is fixed in the injection hole 2 by bolting until the rubber sleeve 15 expands in the radial direction and the outer periphery of the rubber sleeve 15 contacts and is fixed to the inner wall of the injection hole 2 (FIG. 3B). ). The length of the rubber sleeve is preferably about 2 to 10 times the length (cover thickness) from the surface of a steel material such as a reinforcing bar to the surface of the closest concrete structure.

In order to send the inhibitor into the single packer 3, first, as shown in FIG. 2, as shown in FIG. The pipe 6 from the tank 5 is connected. When pressure is applied to the storage tank 5 by the pressurizing pump P, the aqueous lithium salt solution 4 is sent through the pipe 6 into the metal body 12 of the single packer 3, and the aqueous lithium salt solution 4 is ejected from the ejection hole 16. Is done. At this time, due to the repulsive force of the ejection power from the ejection hole 16, a force is applied to the metal body 12 in a direction opposite to the direction in which the lithium salt aqueous solution 4 is sent, but is provided on the outer periphery of the metal body 2. Rubber sleeve 15
Are engaged with the inner wall of the injection hole 2 and are prevented from being pushed out of the injection hole 2.

The aqueous lithium salt solution spouted from the spouting hole 16 of the single packer 3 gradually permeates or diffuses into the concrete by capillary action through the capillary space in the concrete. In this process, lithium ions contained in the aqueous lithium salt solution inhibit a reaction between the aggregate causing an alkali-aggregate reaction and an alkali metal ion other than lithium (alkali-aggregate reaction) in the concrete structure. In addition, when the aqueous lithium salt solution reaches steel materials such as steel frames, it reacts with the steel materials to immobilize the steel materials, so that corrosion prevention of the steel materials can be suppressed.

In FIG. 1, the pouring holes 2 are arranged in a lattice at 1.0 m intervals, but the intervals may be changed between 0.5 and 2.0 m, for example, depending on the physical properties of the concrete or the construction conditions. They may be arranged in a staggered manner. The diameter of the injection hole 2 is preferably as large as possible, but from the viewpoint of the capacity of the available pump and the like, usually, about 10 to 50 mm is appropriate. In addition, injection hole 2
Is half the length of the section of the concrete structure
As described above, preferably, the length of two-thirds or more is suitable for permeating or diffusing the aqueous solution of lithium salt throughout the inside of the concrete structure.

When the injection pressure is set to less than 7 MPa, it is appropriate to use an electric compressor. When the injection pressure is set to 7 MPa or more, it is appropriate to increase the pressure using a nitrogen gas cylinder. The injection amount of the inhibitor varies depending on the volume of the concrete structure and its composition, but the alkali content (total amount) of the concrete (in terms of Na ₂ O)
It is appropriate to set the molar ratio of lithium ion to sodium ion to be 1 or more, preferably 1 to 1.5. The injection of the lithium salt aqueous solution is suitably performed, for example, continuously for 1 to 3 months, preferably for 30 to 60 days. In order to make the inhibitor reach the predetermined depth earlier or to make the reach of the inhibitor deeper, it is preferable to apply a pulsation to the static pressure at the time of pressurized injection. The pulsation may have an amplitude of 30-100% of the static pressure, preferably 50-80%, and a frequency of 1-20Hz, preferably 5%.
Preferably, the frequency is set to 1515 Hz. For pulsation, for example, a pulsating pressure generating pump driven by a servo control mechanism is installed between a storage tank and a packer, and pulsating pressure having a frequency of 1 to 20 Hz is generated using this pulsating pressure generating pump. , By adding a pulsating pressure to the injection pressure.

As illustrated in FIG. 4, in order to allow the inhibitor to reach a deeper place faster, for example, the injection hole 2 is provided on the surface side of the concrete structure provided with the injection hole 2.
Alternatively, a plurality of suction holes 28 may be provided on the side opposite to the surface side of the concrete structure provided with the injection holes 22, as illustrated in FIG. Alternatively, they may be provided alternately. In this case, the suction holes 8, 28
Can be performed, for example, by installing a vacuum pump.

The suction holes 8 or 28 have the same dimensions as the injection holes 2 or 22 and are provided at the same number or less than the number of injection holes, and a maximum negative pressure of 760 mmHg is applied to the suction holes. It is appropriate to work. In this way, after the inhibitor has permeated or diffused into the concrete structure for a predetermined period, after taking out the single packer 3,
It is preferable to fill the trace of the injection hole 2 with a non-shrink mortar mixed with an inhibitor. Similarly, it is appropriate to treat the trace of the suction hole in the same manner. As the non-shrink mortar, as the cement component, for example, ordinary Portland cement, early-strength Portland cement, or the like is used. It is appropriate for the non-shrink mortar to incorporate 5 to 10% by mass of an inhibitor. Aggregates are not normally used in non-shrink mortar.

In the above embodiment, the case where a single packer is used has been described. However, as shown in FIG. 6, a double packer 33 can be used. The double packer 33 has an ejection hole 36 at the center in the longitudinal direction, and has a form in which single packers are symmetrically coupled.
The double packer 33 is inserted over the injection hole 32 formed therethrough and can be connected to the storage tank via a pipe from both ends. Also, since the ejection hole 36 is provided at the center of the double packer 33,
Since the repulsive force based on the ejection of the inhibitor from the ejection hole 36 is evenly distributed on both sides, there is little problem that the packer is displaced inside the injection hole. Accordingly, the function of the rubber sleeve 35 is mainly to seal the space formed between the outer periphery of the metal body 34 of the packer, the inner wall of the injection hole 32, and the flange 38 in an airtight manner.

In operation, first, double packer
Insert the 33 into the injection hole 32 and tighten the bolt 40 from both sides, as in the single packer, the rubber sleeve
As 35 is pushed into the inner part of the injection hole 32, its outer diameter increases, and comes into contact with the inner wall of the injection hole 32 to form a double packer 33.
Is fixed in the injection hole 32 (FIG. 6B). Next, a pipe from the storage tank is connected to one of the ends of the double packer 33, and the other end is closed, and the pressurizing pump is operated. As in the case of the single packer, the pressurizing pump sends the inhibitor from the storage tank to the inside of the metal body 34 of the double packer 33 via a pipe, and further ejects the metal body from the ejection hole 36. After filling the space formed by the outer circumference of the injection hole 32, the inner wall of the injection hole 32, and the flange 38, the water gradually permeates or diffuses from the space into the concrete structure. As a result, the lithium ions inhibit the alkali-aggregate reaction and prevent cracking and collapse of the concrete structure.

[0024]

The present invention will be described in more detail with reference to the following examples. Example 1 A test specimen having dimensions of 150 × 300 × 1800 mm was prepared. This test specimen was obtained by blending ordinary Portland cement with crushed stone (vitreous andesite) from Asukayama in the Futamiyama Mountains and hardening it. The total amount of alkali (as Na ₂ O) is NaC
1 to adjust to 8.0 kg / m ³ ,
The alkali-aggregate reaction was made to occur artificially. The composition and properties of the concrete are shown below.

Gmax (mm) 20 S.C. L. (Cm) 10 ± 1.0 Air (%) 4.0 ± 1.0 W / C (%) 50 s / a (%) 44 Unit amount (Kg / m ³ ) WCSGAE Non-reactive Reactivity 176 352 761 507.5 507.5 1.056 Mixing ratio of reactive aggregate: 50% Here, the following symbols have the following meanings. Gmax: maximum aggregate size L. : Slump value s / a: Fine aggregate ratio W: Unit water amount C: Unit cement amount W / C: Water cement ratio S: Unit fine aggregate amount G: Unit coarse aggregate amount AE: Unit AE water reducing agent amount

The test specimen was exposed outdoors (naturally exposed state) for 7 years to cause an alkali-aggregate reaction. Next, as shown in FIG. 7, an injection hole having a diameter of 32 mm was placed at a position 600 mm from one end of the specimen using a concrete drill.
Drill to a depth of 200mm, and single packer 3
Was inserted. The opening end of the injection hole is connected to a pipe 6 connected to a tank 5 for storing an aqueous solution of lithium nitrite having a concentration of 40% by mass (inhibitor). To the packer 3, and under pressure (0.5 MPa), an aqueous lithium salt solution was sprayed from the outlet at the inner part of the packer 3 for 30 days.

After the end of the injection, the diameter 7
A cylinder having a length of 5 mm and a length of 150 mm was taken out as a test sample. The position taken out is the position of the center of the sample,
From the tip of the injection hole, 10cm, 20cm, 30cm, 4cm
The positions were 0 cm, 50 cm, 60 cm and 70 cm. The results are shown below. First, the compressive strengths of the test specimens at the time of preparation and at the age of 7 years were as follows. Material Compressive strength (MPa) Remarks 28 days 40 28 days standard curing 7 years 30 After 7 years, the compressive strength of the test specimen decreased by 10 MPa from the 28 days standard curing strength. This is considered to be due to the alkali-aggregate reaction. In addition, the static elastic modulus of the test specimen after 7 years has been 60,
%Met.

Next, the lithium content in the test sample after the injection of the inhibitor is shown. The results are shown in FIG. FIG.
Shows the relationship between the distance from the injection hole and the lithium content. The molar ratio is 1 to the alkali metal ions (K ⁺ , Na ⁺ ) contained in the concrete causing the alkali-aggregate reaction.
It is known that the alkali-aggregate reaction is suppressed if the lithium ions are contained. The unit cement amount of concrete structure that causes alkali-aggregate reaction is
Assuming 300 kg / m ³ , and assuming that the alkali content (in terms of Na ₂ O) is 1 mass% of the cement amount, in order to suppress the alkali-aggregate reaction, it is 0.68 kg / m ³ or more. Of lithium ion is required. Under the conditions of this experiment, it can be seen that the required amount of lithium is contained within 50 cm from the injection hole.

FIG. 9 shows test results on the amount of residual swelling before and after the injection of the inhibitor. Samples after the injection were taken from a distance of 30 cm and 50 cm from the injection hole, respectively, and the amount of open expansion and the amount of residual expansion were measured. Before the injection of the inhibitor, the swelling amount was 1000μ or more, but the swelling amount after injection was 200μ.
It can be seen that it has been suppressed until.

[0030]

According to the present invention, since the aqueous solution of lithium salt penetrates or diffuses into the concrete from the inner part of the concrete structure, even in the inner part of the concrete structure having a large cross section, the alkali aggregate can be obtained. Effective protection from reactions.

[Brief description of the drawings]

FIG. 1 is a plan view showing a beam portion of a pier to which a method of the present invention is applied.

FIG. 2 is a side view of the pier of FIG. 1;

FIG. 3 is a view showing a state where a single packer is inserted into an injection hole.

FIG. 4 is a diagram showing an arrangement of an injection hole and a suction hole.

FIG. 5 is a diagram showing an arrangement of an injection hole and a suction hole.

FIG. 6 is a view showing a state where a double packer is inserted into an injection hole.

FIG. 7 is a diagram showing an experiment for examining the effect of the injection of an inhibitor on concrete properties.

FIG. 8 is a diagram showing a change in lithium content with respect to a distance from the tip of an injection hole.

FIG. 9 is a diagram showing a change in the amount of expansion in a concrete specimen according to the material age.

[Explanation of symbols]

2 ... Injection hole 3 ... Single packer 4 ... Lithium salt aqueous solution 5 ... Storage tank 9 ... Pressure pump

 ──────────────────────────────────────────────────続 き Continuation of the front page (71) Applicant 500559112 Sanko Paint Co., Ltd. 3-12-25 Yoshino, Fukushima-ku, Osaka-shi, Osaka (72) Inventor Akihiko Kanayoshi 3-6 Kitakyuho-cho, Chuo-ku, Osaka-shi, Osaka -1 Konoike Gumi Co., Ltd. 720 (72) Inventor Isao Iwata 13-2 Yamate-cho, Higashi-Osaka-shi, Osaka (72) Inventor Jun Kawai 8-8-27 Kamikita, Hirano-ku, Osaka-shi, Osaka No.48 701 (72) Inventor Tanimuro Hirohisa 448-5 Ogiwaracho, Ikoma City, Nara Prefecture (72) Inventor Tomoyuki Yamanouchi 2-87 Kugahigashicho, Fushimi-ku, Kyoto, Kyoto (72) Inventor Akira Noda 3-12-25 Yoshino, Fukushima-ku, Osaka-shi, Osaka Sanko Paint (72) Inventor Nobuyuki Yamada 3-12-25 Yoshino, Fukushima-ku, Osaka-shi, Osaka F-term (reference) in Sanko Paint Co., Ltd.

Claims (6)

[Claims] 1. A method for suppressing an alkali-aggregate reaction in a concrete structure, comprising: forming an injection hole reaching an inner part in a surface of a concrete structure containing an aggregate causing the alkali-aggregate reaction. And pressurizing and injecting an aqueous solution of a lithium salt or lithium hydroxide through the injection hole. 2. The method according to claim 1, wherein the diameter of the injection holes is 10 to 50 mm, and the interval between the injection holes is 0.5 to 2.0 m. 3. The method according to claim 1, wherein the aqueous solution of the lithium salt or lithium hydroxide is injected under pressure at a pressure of 0.1 to 1.5 MPa for 1 to 3 months. 4. The pressurized injection is performed at 30 to 100% of the static pressure.
2. The method according to claim 1, wherein the frequency is set to 1 to 20 Hz while giving an amplitude of 1. 5. The method according to claim 1, wherein a suction hole is provided on the same or opposite surface as the concrete structure provided with the injection hole. 6. The non-shrinkable mortar mixed with an aqueous solution of a lithium salt or lithium hydroxide is filled into the injection hole after the aqueous solution of the lithium salt or lithium hydroxide is injected into the injection hole. the method of.