JP7373351B2 - Repair method for concrete structures used in high temperature ranges - Google Patents

Description

The present invention relates to a method for repairing concrete structures, and particularly to a method for repairing concrete that has deteriorated due to use in a high temperature range and in an environment with relatively large temperature changes.

Concrete structures deteriorate over time, but in many cases they deteriorate faster than the concrete's service life. Typical deterioration phenomena and causes include frost damage, which causes volumetric expansion due to freezing of moisture, which causes cracks in the concrete, and rust, which occurs in reinforcing bars due to salt such as seawater, and this expansion causes concrete to crack, float, and peel. These include salt damage, which causes carbon dioxide gas in the air, which lowers the pH and causes rust on reinforcing bars, and carbonation, which causes cracks in concrete, as well as drying shrinkage, surface abrasion, and poor construction. In addition, concrete structures used in environments with relatively large temperature changes may deteriorate due to repeated expansion and contraction due to temperature changes, or only a portion of the concrete structure, such as the front side, may become hot and the back surface may become hot. In cases where the temperature of other parts, such as the sides, is room temperature or outside temperature, deterioration occurs due to the temperature gradient that occurs inside the concrete structure.

The common method for repairing deteriorated concrete structures is to remove (chip) the deteriorated parts until a healthy concrete surface is exposed, and then use cement-based cross-sectional repair materials such as mortar to fill in the missing parts. There is. At this time, if necessary, the reinforcing bars may be treated with anti-corrosion treatment or coated with a primer.

Cement-based cross-sectional repair materials are generally mortar, which provides a hardened material that is almost the same as concrete, so the repaired area and main structure of a concrete structure after repair are expected to behave as one. considered by design. Therefore, the coefficient of linear expansion, etc. of the cement-based cross-sectional repair materials were naturally considered to be the same, and no attention was paid to this.

However, when repairs are carried out using cement-based cross-section repair materials as described above, the repaired area or its surroundings may quickly crack, float, or fall off in concrete structures used in high-temperature areas. There was a problem of deterioration. In such cases, re-repairs must be repeated frequently, so there has been a desire for a repair method that does not cause deterioration over a long period of time even in a high-temperature environment.

It is known that the coefficient of linear expansion of concrete is related to cracks, etc., and Patent Document 1 discloses controlling the coefficient of linear expansion during the concrete hardening process to 9.5×10 ⁻⁶ /°C or less. Patent Document 2 discloses controlling the linear expansion coefficient of a precast concrete formwork to 2×10 ⁻⁶ /°C or less. Patent Document 3 discloses controlling the linear expansion coefficient of a concrete buried member using a material different from concrete to 7×10 ⁻⁶ /°C to 11×10 ⁻⁶ /°C. However, these are not related to the repair of deteriorated concrete.

Regarding the repair of concrete structures, Patent Document 4 describes a repair method in which deteriorated parts of concrete structures are lifted to the extent that the reinforcing bars are not exposed, permanent formwork is placed on the surface, and the voids are filled with cement-based filler. Disclose the construction method. Patent Document 5 discloses a method in which a rust preventive material is applied to the exposed reinforcing bars on the repaired surface of a concrete structure, a cement-based frame repair material is filled in the depressions, a mortar defect repair material is laminated on top of that, and finally, final repair is performed. A repair method for applying the material is disclosed. However, none of these focuses on the coefficient of linear expansion.

Japanese Patent Application Publication No. 2009-57251 Japanese Patent Application Publication No. 2012-111211 Japanese Patent Application Publication No. 2016-23119 Japanese Patent Application Publication No. 2002-21388 Japanese Patent Application Publication No. 8-26052

An object of the present invention is to provide a repair method for concrete structures that are placed in high-temperature environments or environments with relatively large temperature changes, and also to provide a repair method that can increase the durability of repaired areas. .

As a result of various studies in order to solve the above problems, the present inventors discovered that it is important to control the coefficient of linear expansion of concrete and cross-section repair material, which has not received attention in the past, and arrived at the present invention.

That is, the present invention provides a method for repairing a repaired part of a concrete structure exposed to a high-temperature environment by removing a deteriorated part by filling or covering the repaired part with a cross-sectional repair material containing cement and aggregate. This is a repair method characterized by measuring or calculating a coefficient, selecting or preparing a cross-sectional repair material that approximates the coefficient of linear expansion, and using this as the cross-section repair material.

It is preferable that the coefficient of linear expansion of the cross-sectional repair material is within the range of -4×10 ⁻⁶ /°C to +5×10 ⁻⁶ /°C of the coefficient of linear expansion of the concrete at the repaired location.
It is preferable to calculate the coefficient of linear expansion (α) from the amount of change in strain (Δε) and the change in temperature (Δt) using the following formula.
α=Δε/Δt

The coefficient of linear expansion of the cross-sectional repair material may be adjusted by adjusting the content of SiO ₂ derived from the bone material or/and the total material, by adjusting the type or amount of the cement admixture material, or by a combination thereof. It can be adjusted with. Cement admixtures include inorganic admixtures and polymer admixtures.

According to the present invention, after repairing a concrete structure placed in a high-temperature environment or an environment with relatively large temperature changes, the occurrence of cracks near the repaired area or floating near the boundary between the repair material and the concrete can be prevented, and the occurrence of It is possible to avoid situations where re-repair is required, maintain durability over a long period of time, and suppress concrete deterioration phenomena.

FIG. 2 is a side view showing a concrete repair test specimen used in Examples (and Comparative Examples). FIG. 2 is a sectional view taken along line AA in FIG. 1, also showing a concrete repair test specimen. 2 is a temperature rise/fall graph in a test for measuring the rate of decrease in ultrasonic propagation velocity in Examples (and Comparative Examples).

The concrete structure repair method of the present invention is applied to concrete structures used in high temperature ranges. Examples of such concrete structures include buildings such as power plants and steel plants where heat sources such as boilers and furnaces are located nearby, and structures such as walls and foundations.
In addition, various concrete structures such as roads, railways, ports, bridges, dams, and buildings such as buildings are also subject to this law, even if their surfaces become temporarily heated to temperatures of 50°C or higher due to direct sunlight.

Generally, the effects of the present invention are exhibited as the environment in which it is used is at a higher temperature, but the effects of the present invention are exhibited when the temperature is 50°C or higher, preferably 100°C or higher. Furthermore, the effects of the present invention are exhibited even when the temperature difference is 40° C. or more, preferably 50° C. or more in an environment where temperature changes occur frequently. Furthermore, in an environment where the front surface is heated by radiant heat and the temperature difference with the back side becomes large, the effects of the present invention are exhibited even when the temperature difference is 30° C. or more, preferably 50° C. or more. Therefore, being used in a high temperature range includes being used in an environment where the temperature is 50° C. or higher, and this only requires that a portion of the surface or the like becomes higher than this temperature due to radiant heat. This temperature does not need to continue; it is sufficient that it temporarily exceeds this temperature; rather, it is preferable that this cycle of heating and cooling occurs repeatedly.

For example, although the temperature increase due to direct sunlight is relatively low, temperature changes occur frequently, so even if the surface temperature is relatively low, it is suitable for application of the repair method of the present invention. It is also suitable for concrete structures where boilers and furnaces are operated intermittently and where temperature changes are large and occur more than once a day. Furthermore, when the concrete structure is a wall, the temperature difference between the outer wall surface that is exposed to the outside air and the inner wall surface that is close to the heat of a boiler or furnace is large, and the temperature gradient is also large.

In the method for repairing a concrete structure of the present invention, the linear expansion coefficient of concrete at a repair location of a concrete structure is measured or calculated. This linear expansion coefficient may be a coefficient correlated with the linear expansion coefficient, for example, a volumetric expansion coefficient or an area expansion coefficient.

To measure or calculate the linear expansion coefficient of concrete, if the linear expansion coefficient of the concrete at the repair location is known or can be calculated, that value can be used. For example, concrete for large structures such as concrete walls are often made at the same time using the same materials, so even if the concrete is located a little far from the repaired area, it has almost the same coefficient of linear expansion. Therefore, it may be possible to calculate it from the concrete value at a distant location. However, since the linear expansion coefficient of concrete may change during service due to external forces, heat, etc., it is preferable to measure the value near the repaired area.
If the coefficient of linear expansion is unknown, sample concrete using a core drill or the like from near the repaired area of the concrete structure and measure the coefficient of linear expansion of the sampled concrete. If it is difficult to collect a concrete core, the coefficient of linear expansion can be directly measured while the concrete structure is in service.

The linear expansion coefficient of concrete can be measured using a strain gauge, a strain meter, an optical fiber sensor, a contact gauge, a laser displacement meter, or the like. Preferably, it is a strain gauge that can be easily measured.

The linear expansion coefficient (α) may be calculated by the following formula from the measured strain change (Δε) and temperature change (Δt) by installing a strain gauge and a thermocouple on concrete.
α=Δε/Δt

The cross-sectional repair material used shall exhibit a linear expansion coefficient that approximates the linear expansion coefficient (α1) of the concrete at the repair location. The coefficient of linear expansion (α2) of the cross-section repair material ranges from a coefficient of linear expansion 4×10 ^-6 /℃ lower to a coefficient of linear expansion 5×10 ^-6 /℃ higher than that of concrete (α1). It is better to do as follows. That is, it is preferable that the coefficient of linear expansion (α2) is between "α1 - 4×10 ^-6 /°C" and "α1 + 5×10 ^-6 /°C". Preferably, the coefficient of linear expansion (α2) is within the range of ±3×10 ⁻⁶ /°C of the coefficient of linear expansion (α1) of concrete. More preferably it is ±2×10 ⁻⁶ /°C. By having the coefficient of linear expansion (α ₂ ) of the cross-sectional repair material within the above range, deterioration can be prevented over a long period of time even if the repaired area is exposed to high temperatures or undergoes large temperature changes. Although it is not clear why it is possible to prevent early deterioration in or around the repaired area, it reduces the tensile or compressive stress generated at the interface between the cross-sectional repair material and the concrete during heating or cooling, improving durability. Then it will be understood.

The linear expansion coefficient of the cross-sectional repair material was measured by the method described in Examples. Normally, it is better to adopt an average coefficient of linear expansion between 20°C and 80°C, but if the concrete structure is exposed to higher temperatures, for example 200°C, The coefficient of linear expansion in degrees Celsius may be used. However, in many cases, the linear expansion coefficient changes little with temperature, so an average linear expansion coefficient between 20° C. and 80° C. is suitable.

Mortar containing cement is suitable as the cross-sectional repair material. Preferably, it is a cement mortar that contains cement and fine aggregate such as sand as main components, and optionally contains an inorganic or organic cement admixture. The mixing ratio of cement and fine aggregate is usually in the range of 100 to 400 parts by weight of fine aggregate to 100 parts by weight of cement. The amount of water is preferably about 20 to 60% by weight based on the cement.

As the cement, portland cement, blast furnace cement, early strength portland cement, etc. are used.
As the fine aggregate, natural sand, silica sand, limestone fine aggregate, granulated blast furnace slag fine aggregate, artificial lightweight aggregate, recycled aggregate, etc. are used. Moreover, fibers can also be used if necessary.

Since fine aggregate exhibits different linear expansion coefficients depending on its type, the linear expansion coefficient can be controlled by changing these types and usage ratios. In particular, since silica sand exhibits a relatively large coefficient of linear expansion compared to other fine aggregates, the coefficient of linear expansion can be effectively controlled by changing the content of silica sand or silica contained in the fine aggregate. .

As cement admixtures, there are admixtures that are mixed in a relatively large amount and admixtures that are mixed in a relatively small amount. As the cement admixture, inorganic or organic admixtures can be used. Examples of cement admixtures include AE agents, water reducing agents, fluidizing agents, separation reducing agents, surfactants, hardening regulators, rust preventive agents, waterproofing agents, blast furnace slag powder, fly ash, silica fume, expanding agents, There are rapid hardening materials, shrinkage reducing agents, antifoaming agents, and polymers for improving workability and water retention.
Cement admixture materials also exhibit different coefficients of linear expansion depending on their type, so the coefficient of linear expansion can be controlled by changing these types.
The inorganic admixtures, such as the blast furnace slag powder and fly ash, have hardening properties, so they can replace a part of the cement. The linear expansion coefficient can also be effectively controlled by changing this substitution rate.
In addition, the above-mentioned polymers include styrene-butadiene rubber, latex, ethylene vinyl acetate, and polyacrylic acid ester emulsion, but these are admixtures that can be used in relatively large amounts as admixtures, so these are selected and blended. By doing so, the coefficient of linear expansion can be effectively controlled.

The coefficient of linear expansion of the cross-sectional repair material can be adjusted by one or a combination of two or more of the above control methods, including adjusting the amount of fine aggregate used, adjusting the replacement rate of admixtures, or adjusting the This can be done by adjusting the type and amount of the polymeric admixture used. For example, the amount of fine aggregate used may be adjusted within the range of 50 to 85% by weight, the substitution rate of admixtures may be adjusted within the range of 0 to 25% by weight, or the amount of admixture may be adjusted between 0.05 and 2.0% by weight. It can be adjusted within a range of %. The aggregate-derived SiO ₂ content in the total material is preferably in the range of 0 to 80% by weight.

The repair method of the present invention is applied to repairing deteriorated parts of concrete structures used in high temperature ranges. Repairs to deteriorated areas typically include removal of deteriorated concrete areas, rust removal or rust prevention treatment if exposed reinforcing bars, and pretreatment such as primer application, if necessary. Then, the defective area is backfilled with the cross-sectional repair material of the present invention. This is done by filling or coating or the like. Then, if necessary, surface coating is performed to complete the process.

EXAMPLES Hereinafter, the present invention will be described in more detail based on Examples, but the present invention is not limited to the following Examples.

The concrete repair materials used in the examples and the raw materials for preparing the concrete repair materials are shown below.
(1) Concrete cross section repair material;
NEM-TP (manufactured by Nippon Steel Cement Co., Ltd.)
(2) Raw materials for concrete cross-section repair materials;
cement;
Ordinary Portland cement (manufactured by Nippon Steel Cement Co., Ltd.)
Early strength Portland cement (manufactured by Nippon Steel Cement Co., Ltd.)
Admixture;
Blast furnace slag powder (Spirits 6000, manufactured by Nippon Steel Cement Co., Ltd.)
Fly ash (manufactured by Hokuden Kogyo)
Silica fume (manufactured by SKW East Asia)
Limestone powder (for roads, manufactured by Nippon Steel Cement Co., Ltd.)
Admixture;
Mighty 100 (high performance AE water reducer, manufactured by Kao Corporation)
LDM7300P (acrylic polymer, manufactured by Nippon Gosei Kagaku Co., Ltd.)
aggregate
No. 5 silica sand (SiO ₂ content 93.7%, manufactured by Tohoku Silica Co., Ltd.)
Blast furnace slag fine aggregate (SiO ₂ content 31.8%, manufactured by Nippon Steel Cement Co., Ltd.)
Limestone fine aggregate (SiO ₂ content 1.6%, limestone from Shiriya)
Bottom ash (SiO ₂ content 59.5%, manufactured by Nippon Steel Corporation)

Examples 1 to 9
The above raw materials are mixed in the proportions (parts by weight) shown in Table 1, and water is added to 40 parts by weight for 100 parts by weight of cement when 60 parts by weight of sand is mixed, and when the mixture is 75 parts by weight of sand, cement is added. When mixing 50 parts by weight to 100 parts by weight and 80 parts by weight of sand, 55 parts by weight to 100 parts by weight of cement were mixed and kneaded to prepare mortar as a cross-sectional repair material.
Examples 1 to 9 are examples in which the linear expansion coefficient of the cross-sectional repair material was adjusted by blending various inorganic admixtures and changing the cement replacement rate.

The concrete cross-section repair material NEM-TP and the concrete cross-section repair material (mortar) prepared above were each formed into a prismatic specimen measuring 4 x 4 x 16 cm. This was used as a sample after 28 days of age.
The change in length of this sample was measured with a contact gauge at every 20°C rise from room temperature (20°C) to 80°C, and the coefficient of linear expansion (α2) was determined using the following formula.
α2=(L ₈₀ -L ₂₀ )/L ₂₀ /60℃
Here, L ₈₀ and L ₂₀ are the length at 80°C and the length at 20°C, respectively.

Examples 10-18
In the same manner as in Example 1, the raw materials were mixed in the proportions shown in Table 2 to prepare mortar. This is an example in which the linear expansion coefficient of the cross-sectional repair material was adjusted by changing the type of aggregate and changing the SiO ₂ content derived from the aggregate in all materials. Example 18 is an example in which the coefficient of linear expansion was adjusted by adding an organic admixture.

Examples 21-22, Comparative Examples 1 and 2
As shown in Figures 1 and 2, concrete 1 of 300 mm x 300 mm x 100 mm with a recess of 120 mm x 120 mm x 50 mm in the center was sealed and cured until the material age was 28 days, and then the cross-sectional repair material 2 was filled in the central recess. The sample was further sealed and cured for 28 days to be used as a test specimen. In addition, for comparison, concrete measuring 300 mm x 300 mm x 100 mm was sealed and cured in the same manner as above until the material age was 56 days, and used as a comparative test specimen.

After attaching polystyrene boards with a thickness of 10 cm to 5 sides of the above test specimen, excluding the surface filled with the cross-sectional repair material, the temperature was raised from 20 °C to 80 °C, and then lowered to 20 °C. This cycle was repeated 28 times, with temperature as one cycle.
The linear expansion coefficient (α1) of the concrete in the repaired area was also determined using the following formula.
α1=(L ₈₀ -L ₂₀ )/L ₂₀ /60℃
Here, L ₈₀ and L ₂₀ are the length at 80°C and the length at 20°C, respectively.
Measure the ultrasonic propagation velocity at 0 cycle (V ₀ ) and the ultrasonic propagation velocity at 28 cycles (V ₂₈ ) before raising and lowering the temperature, and determine the rate of decrease in ultrasonic propagation velocity due to the difference in linear expansion coefficient in a high temperature environment. I asked for The rate of decrease (%) in ultrasonic propagation velocity was determined by the following formula. The results are shown in Table 3.
(V ₂₈ -V ₀ )/V ₀ ×100
In addition, in order to exclude the influence of shrinkage stress due to drying shrinkage due to moisture evaporation, the temperature increase/decrease cycle test was conducted with the entire surfaces of the test specimens and comparison specimens covered with polyethylene film. The ultrasonic propagation velocity has a positive correlation with the compressive strength of concrete, and this measurement can non-destructively estimate the compressive strength of concrete. Furthermore, if there is a defect such as a crack, the ultrasonic wave propagates by bypassing the defect, which slows down the propagation speed of the ultrasonic wave. In other words, a decrease in ultrasonic propagation velocity means a decrease in compressive strength or the occurrence of defects.

Comparative Example 1 is an example in which the cross-section repair material of Example 1 was used and the cross-section repair material had a linear expansion coefficient smaller than that of concrete by 4.6×10 ⁻⁶ /°C. Comparative Example 2 is an example in which NEM-TP was used as a cross-sectional repair material, and the cross-section repair material had a coefficient of linear expansion 5.4×10 ⁻⁶ /°C larger than that of concrete. If the coefficient of linear expansion of the cross-section repair material is not close to that of concrete, and in particular exceeds the range of -4×10 ^-6 /℃ to +5×10 ^-6 /℃, the rate of decline of the concrete and cross-section repair material will decrease. You can see it getting bigger.
On the other hand, in Example 21, NEM-TP was used as the cross-section repair material, and the cross-section repair material was repaired with a coefficient of linear expansion that was 0.1×10 ⁻⁶ /°C smaller than that of concrete. Example 22 is an example in which the cross-section repair material of Example 1 was used and the cross-section repair material had a coefficient of linear expansion larger than that of concrete by 0.9×10 ⁻⁶ /°C. As a cross-sectional repair material, the reduction rate can be reduced by using a material whose linear expansion coefficient is close to that of concrete, especially within the range of -4 x 10 ^-6 /°C to +5 x 10 ^-6 /°C. , it is possible to suppress defects such as a decrease in compressive strength and cracks.

INDUSTRIAL APPLICABILITY The present invention can be widely used as a method for repairing concrete structures, particularly for repairing concrete that has deteriorated due to use in high-temperature areas and environments with relatively large temperature changes.

1 Concrete 2 Cross section repair material

Claims (5)

When repairing by backfilling a cement-based cross-sectional repair material containing cement and aggregate in a repaired area where deteriorated parts of a concrete structure exposed to a high-temperature environment have been removed, the coefficient of linear expansion of the concrete at the repaired area is measured or Select or prepare a cement-based cross-sectional repair material with a linear expansion coefficient in the range of -4 x 10 ^-6 /℃ to +5 x 10 ^-6 /℃ of the linear expansion coefficient of the concrete in the repaired area, and use it. A repair method characterized by its use as a cross-section repair material. The repair method according to claim 1, wherein the coefficient of linear expansion (α) is calculated from the amount of change in strain (Δε) and the change in temperature (Δt) using the following formula.
α=Δε/Δt The repair method according to claim 1, wherein the coefficient of linear expansion of the cement-based cross-sectional repair material is adjusted by the amount of aggregate and/or the content of SiO ₂ derived from the aggregate in the total material. 2. The repair method according to claim 1, wherein the cementitious cross-section repair material includes cement, aggregate, and a cement admixture, and its linear expansion coefficient is adjusted by the type or amount of the cement admixture. The repair method according to claim 4 , wherein the cement admixture is an inorganic admixture or a polymer admixture.

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