JP2012180720A - Method for improving cracked concrete - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for changing an undesirable cement hydration reaction to a normal reaction by suppressing or stopping the undesirable cement hydration reaction causing a crack in cracked concrete using current cement.SOLUTION: A water retaining material 2, a heater 3, and a thermal insulating material 4 sequentially abut on a surface of a cracked concrete wall balustrade 1, and are fixed to the wall balustrade 1 by an anchor via a stiffening plate 5. The water retaining material 2 is wetted with water, and a water temperature in the water retaining material 2 is set at 80°C or higher by the planar heater 3. Thus, hydrolytic and heat curing is applied to the wall balustrade 1.

Description

  The present invention relates to a method for improving a cracked concrete product or concrete structure, that is, a method for suppressing or preventing the progress of cracks.

  Traditionally, reinforced concrete structures made of reinforced concrete and concrete (cement, aggregate, water) are highly durable and have been said to last for 100 years. It is well known that cracks in concrete are often deteriorated in a short period of time, and cracks in highway bridges and side walls are taken up as major problems by newspapers and the like.

  At present, repair of concrete cracks due to alkali aggregate reaction or the like is carried out by filling the cracks with synthetic resin or cement milk and applying or coating various materials on the concrete surface. (See Patent Documents 1 and 2)

  However, the cracking phenomenon continues even after repair, and often requires re-repair and re-repair.

According to recent research [Non-Patent Documents 1 to 3], the cement hydration product (generated mineral) produced in the hardened concrete cement that has been cracked by the alkali-aggregate reaction is portlandite ( calcium hydroxide, Ca _{(OH) 2,} calcium aluminate-hydrate (such as _{3CaO · Al 2 O 3 · 8~12} 2 0 and _{4CaO · Al 2 O 3 · 13H} 2 0) and wherein it is ettringite It is.

  FIGS. 1A to 1D are powder X-ray diffraction diagrams (2θ low-angle portions) of cracked portions of bridge concrete where cracks have occurred in various places, which are well shown.

  It is well known that the rapid formation of ettringite causes cracking in concrete, but in the cracked concrete, the formation of portlandite and calcium aluminate hydrate is prominent. The product continues to grow.

  Portlandite and calcium aluminate hydrate are small in mass, and the formation thereof is an expansion reaction. If the expansion reaction proceeds, cracking will occur again after repair.

In healthy concrete, C—S—H (called tobermorite gel, chemical composition is 3CaO.2SiO.3H ₂ O), portlandite, monosulfate and unreacted alite or belite are detected. Other minerals are not detected.

  As described above, the cause of the occurrence of cracks in recent bridge concrete where cracks have occurred has been explained, but the present inventor has not seen any changes in the 70-year old and 100-year old concrete concrete under the bridge. In recent concrete, cracks are observed, and in order to investigate the main causes of cracks, the chemical composition, grain size, constituent minerals, and cement hydration products of commercial cement were further investigated. It was.

(1) There is no difference in chemical composition between the ordinary Portland cement and blast furnace cement.
(2) The constituent mineral of cement is 3CaO.SiO ₂ (Alite), 2CaO.
SiO ₂ (Belite), 4CaO.Al ₂ O ₃ .Fe ₂ O ₃ , and gypsum, and there is no difference between manufacturers.
(3) As for the physical properties of ordinary Portland cement, the density is 3.15 to 3.16, the specific area is 3.200 to 3.600 cm ² / g, and the density of blast furnace cement is 3.
01 to 3.02, the specific surface area is 3.700 to 3,800 cm ² / g, and more recently it is 4,000 cm ² / g or more. Compared to 100-3,200 cm ² / g, the fineness is high.
(4) Cement is classified into three types as shown in Table 1 depending on the type of cement hydrated product and its combination.

(5) The type of cement hydration product varies depending on the cement production company, but the cement hydration product does not change even if the water cement ratio (W / C), curing time, and age are different.
(6) Cement hydration products are slow to form if the cement particle size is coarse or W / C is low. In other words, portlandite, ettringite, monosulfate, calcium / aluminate / hydrate do not grow rapidly.
(7) The current commercial cement has a fine particle size, and concrete has a large amount of unit water, so portlandite, ettringite, calcium aluminate, ha
Idrate grows fast, especially boltlandite and calcium aluminate hydrates and gels (unlike tobermorite-like gels)
Is produced in large quantities.
(8) Portlandite, calcium, aluminate, and hydrate are prominently produced in concrete that has recently suffered from defects such as cracks.
(9) The grain size of cement used in old concrete is rough, and the grain size of cement in recent concrete is fine.

  When comparing old concrete with recent concrete, portlandite and calcium aluminate hydrate are produced in all cases, but in old concrete, these cement hydration products are few and the production reaction is slow. C—S—H, which is a skeleton of the hardened cement body, is also ideally generated.

  On the other hand, recent concrete has a fine cement particle size and a large amount of water, so calcium and aluminum, which have a high ionization tendency, are ionized, and portlandite, calcium aluminate, and hydrate grow rapidly in the initial stage. To do. The calcium, aluminate, and hydrate that is produced should react with gypsum to become ettringite.However, because the growth of calcium, aluminate, and hydrate is fast, the reaction with gypsum cannot catch up, and the hardened cement body. A large amount of calcium, aluminate, and hydrate is formed inside.

  When portlandite and calcium aluminate hydrate are produced in large quantities, the calcium necessary for producing ideal C—S—H is insufficient, and C—S—H with less calcium is formed. It is thought that the amount of gel substance increases and the hardened cement body becomes physicochemically unstable.

  Recent cement has been finely pulverized in order to improve the economics of construction, that is, the strength of concrete quickly.

  As the cement becomes finer, the specific surface area increases, so the amount of unit water required for placing concrete increases, and the amount of water increases further in order to increase fluidity in pump construction.

  If there is a large amount of water, the possibility of dry cracking increases, and it is not unreasonable to think that cracking occurs due to portlandite and calcium, aluminate, and hydrate that form and grow early. It is done.

Japanese Patent No. 3656417 JP 2006-226365 A

Akio Maru, “Rock mineralogy of abnormal cracks in concrete structures”, Concrete Engineering, Vol. 42, No. 12, Japan Concrete Institute, December 1, 2004, pp. 32-81 Akio Maru, “Mineralogical Consideration of Structural Concrete with Abnormal Cracks”, Clay Science, Vol. 45, No. 2, Japan Clay Society, March 6, 2006, pp. 75-89 Akio Maru, "Mineralogical study of structural concrete with abnormal cracks using lime-based aggregates", Clay Science Vol. 46, No. 2, Japan Clay Society, June 4, 2007, 106-111 page

  According to the above-mentioned research results, the occurrence of many cracks in recent concrete structures is thought to be due to the fact that the grain size of the cement is made finer in order to increase the strength of the concrete quickly.

Whatever the cement (ordinary Portland cement, blast furnace cement, moderately hot Portland cement, fly ash cement, etc.), if the particle size is made finer, the hydration reaction proceeds favorably and the reaction that is easy to react, for example, , Causing an abrupt formation reaction of Ca (OB) ₂ .

When the cement becomes finer, the amount of water necessary for kneading increases, and when the amount of water is large, the above Ca (OH) ₂ , 3CaO · Al ₂ O ₃ · 8 to 12H ₂ O or 4CaO · Al ₂ O ₃ · 13H ₂ O or The production of ettringite and the like will be promoted.

  And since the management of concrete in Japan is managed with strength, in order to remove the formwork when the planned strength is obtained (the concrete strength will appear faster if the cement is made finer), the curing time is shorter than in the past This is one of the causes leading to a bad cement hydration reaction.

  The ideal cement hydration reaction is as shown in FIG. 2 (a), but the present cracked cement hydration reaction in the concrete is as shown in FIG. 2 (b). The reaction proceeds.

  Therefore, an object of the present invention is to provide a method of suppressing or stopping an undesired cement hydration reaction that generates cracks in a concrete that has been cracked using current cement, thereby obtaining a normal reaction. It is.

  The present invention has been made to solve the above problems, and as a result of various experimental studies, hydrothermal curing of cracked concrete caused by an abnormal cement reaction such as an alkali aggregate reaction is carried out with hot water or steam. As a result, it was found that the reaction can be suppressed or normalized.

  The present invention is based on this finding, and the invention according to claim 1 is a method for improving cracked concrete, characterized in that the cracked part or the whole is hydrothermally cured with hot water or steam at 80 ° C. or higher. is there.

  According to a second aspect of the present invention, a water retaining material, a planar heater, and a heat retaining material are sequentially brought into contact with the surface of a cracked concrete structure, and water is moistened to the water retaining material and the planar heater is used. It is a method for improving cracked concrete, characterized in that the water temperature in the water-retaining material is set to 80 ° C. or higher and hydrothermally cured.

  The invention described in claim 3 is a method for improving cracked concrete, characterized in that, in the invention described in claim 2, the water retaining material is one having an upper edge inclined toward the concrete structure. is there.

  The invention according to claim 4 is characterized in that a concrete structure having cracks is covered with a heat insulating sheet, steam of 80 ° C. or higher is injected into the heat insulating sheet, and the concrete structure is hydrothermally cured. This is a method for improving cracked concrete.

  In the invention of claim 5, a water tank forming cover is attached so as to cover the cracked portion of the concrete structure where the crack has occurred, water and a heater are put in the cover, and the temperature of the water is raised to 80 ° C. or higher. It is a method of improving concrete that has cracked by hydrothermal curing.

  According to the present invention, the chemical properties of the hardened cement body are stabilized, the crack expansion reaction is suppressed, and worries about the expansion reaction continuing in the repair work are eliminated. Therefore, it contributes greatly to the industry.

Powder X-ray diffraction pattern of cracked parts of bridge concrete in various places where cracks occurred. The figure which shows the product in the case of the ideal hydration reaction of cement, and the case of the hydration reaction of the cement in the concrete which the crack generate | occur | produced. Powder of cement hydrated product in concrete after hydrocracking the core sample of a cracked concrete structure in a sealed container at various temperatures such as 70 ° C, 80 ° C, 90 ° C, 100 ° C, etc. X-ray diffraction diagram. Hydration of cement in hardened cement cement over time when the core sample of cracked bridge concrete is hydrothermally cured in 100 ° C water or 97-99 ° C steam using andesite crushed stone and natural sand as aggregates The powder X-ray diffraction diagram which shows how a thing changes. Andesite crushed rock as coarse aggregate, and andesite crushed stone and natural sand as fine aggregate cracked bridge concrete core sample before hydrothermal treatment and hydrothermal treatment for 24 hours in water controlled at 100 ° C Later powder X-ray diffraction pattern. X-ray powder diffraction diagram of cement hydration product before and after hot water heating treatment of cracked Hokkaido bridge concrete core sample. Powder X-ray diffraction pattern of cement hydration product before and after hot water heat treatment of a cracked core sample of bridge concrete in Tohoku region. Powder X-ray diffraction pattern of cement hydration product before and after hydrothermal heating treatment of core samples of other Tohoku bridge concrete with cracks. The powder X-ray diffraction pattern of the hydration product of the cement before and after the hot water heat processing of the core sample of the bridge concrete of the Chubu district where the crack generate | occur | produced. Powder X-ray diffraction pattern of the hydrated product of cement before and after hot water heat treatment of the core sample of wall concrete in the Kanto region where cracks occurred. Powder X-ray diffraction pattern of cement hydration product before and after hot water heat treatment of cracked Kinki bridge concrete core sample. X-ray powder diffraction diagram of cement hydration product before and after hydrothermal treatment of core samples of bridge concrete in Kyushu where cracks occurred. The typical sectional view at the time of applying the present invention to the wall slope of the expressway where the crack occurred. Typical sectional drawing which shows an example of the hydrothermal curing based on this invention in the case of using water vapor | steam. The typical perspective view which shows an example in the case of hydrothermal curing with hot water. The longitudinal cross-sectional view of FIG.

  Example 1 relates to a case where a core sample obtained by boring a cracked portion of a concrete structure in which a crack has occurred is placed in a sealed container and subjected to underwater heating curing or hydrothermal heating curing with steam.

  Fig. 3 shows curing when core samples collected by drilling cracks in a cracked concrete structure are placed in a sealed container and cured by hydrothermal heating in water at 70 ° C, 80 ° C, 90 ° C, and 100 ° C. It is a powder X-ray diffraction pattern of the cement hydration product in the concrete before and after the treatment, and the following can be read from this figure.

At a temperature of 70 ° C. or lower, 4CaO · Al ₂ O ₃ · 13H ₂ O that causes cracks grows.

However, when the temperature is 80 ° C. or higher, the generated 4CaO.Al ₂ O ₃ .13H ₂ O decreases or disappears. Ettringite decreases or disappears, and monosulfate forms and grows.

  The above phenomenon progresses rapidly as the temperature increases, and progresses with time.

  Therefore, the temperature of hot water is preferably 100 ° C., which is easy to manage. However, the water temperature is controlled at 97 to 99 ° C. under normal pressure.

  Fig. 4 shows the cement in the hardened cement body with time when the core sample of cracked bridge concrete was hydrothermally cured with 100 ° C water or 97-99 ° C water vapor using andesite crushed stone and natural sand as aggregates. This is shown by a powder X-ray diffraction diagram showing how the hydration product changes.

That is, ettringite, 4CaO · Al ₂ O ₃ · 13H ₂ O, monosulfate and portlandite, which are the cause of cracking, are detected in the hardened cement in the concrete before being heated in water (2θ is 20 ° or less However, when heated in water at 100 ° C. for 6 hours, the diffraction line of ettringite disappeared and a strong diffraction line of monosulfate was detected. Subsequent superheating in water was continued until 24 hours, but the only cement hydrate products were monosulfate and portlandite.

  In addition, the situation where the cement hydration product changes with time when the concrete core sample is kept in a humid air with steam at 97 to 99 ° C., ettringite, monosulfate and portlandite are recognized before treatment. After 6 hours of steam treatment, the diffraction line of ettringite disappeared, and only that of monosulfate and portlandite was obtained. Thereafter, when heating was continued for 12 hours and 24 hours, only monosulfate and portlandite diffraction lines were detected. That is, the expansion reaction stopped.

FIG. 5 shows a hydrous heat treatment of a cracked bridge concrete core sample using andesite crushed stone as coarse aggregate, andesite crushed stone and natural sand as fine aggregate, and in water controlled at 100 ° C. for 24 hours. The powder X-ray diffraction pattern after hydrothermal treatment is shown. Before hydrothermal treatment, cement hydration products such as ettringite, monosulfate, 4CaO · Al ₂ O ₃ · 13H ₂ O, C—S—H, etc. , Unhydrated alite (3CaO · SiO ₂ ) or belite (2CaO · SiO ₂ ), and quartz and feldspar, which are constituent minerals of aggregates, were detected, but after hydrothermal treatment, ettringite and 4CaO · Al ₂ The diffraction lines of O ₃ · 13H ₂ O disappeared, and the diffraction lines of monosulfate and C—S—H became stronger. That is, the progress of cracks is suppressed.

6 to 12 are powder X-ray diffraction diagrams of the hydrated cement produced when hot water heat treatment is applied to bridge concrete or wall concrete in each region where cracks have occurred. In concrete before heat treatment, ettringite is used. 4CaO · Al ₂ O ₃ · 13H ₂ O, 3CaO · Al ₂ O ₃ · 8 to 12H ₂ O, portlandite, etc. are seen, but in any case, the concrete heated in water at a temperature of 100 ° C. , _{ettringite, 4CaO · Al 2 O 3 ·} 13H 2 O, disappears _{3CaO · Al 2 O 3 · 8~12H} 2 O of the diffraction lines, strong diffraction lines of monosulfate appeared.

However, _{ettringite, 4CaO · Al 2 O 3 ·} 13H 2 O, 3CaO · Al 2 O 3 · 8~12H 2 O hydration products of cement, such as, in most cases, disappeared in water heated 24 hours. In several cases, slightly remaining weak ettringite and _{4CaO · Al 2 O 3 · 13H} 2 O, 3CaO · Al 2 O 3 · 8~12H 2 O of diffraction lines also did not show in this figure, an additional 48 All disappeared as a result of heating to time.

Even if it is a secondary product of steam-cured concrete, cracking occurs if the curing treatment is insufficient. In the case where Ca (OH) ₂ , 3CaO · Al ₂ O ₃ · 8 to 12H ₂ O, 4CaO · Al ₂ O ₃ · 13H ₂ O, or ettringite is produced in this type of concrete, the method of the present invention. Is applicable.

  The effect of water heating on the cracked concrete is the same whether it is performed in steam or in water.

  Steam curing of secondary concrete products is to accelerate cement hydration and accelerate concrete hardening, and the hydration heat treatment of the present invention causes cement hydration to generate undesirable cracks. Is performed to lead to a normal reaction.

  The hydrothermal treatment of the present invention is to normalize the cement hydration reaction regardless of the curing action.

As is clear from the results of the examples described above,
(A) When concrete that has cracked due to an abnormal reaction of cement such as alkali aggregate reaction is hydrothermally treated with the hot water or hot steam of the present invention, the cement hydration product in the concrete is as follows. Change.
1) All ettringite changes to monosulfate.
2) 3CaO · Al ₂ O ₃ · 8 to 12H ₂ O and 4CaO · Al ₂ O ₃ · 13
H ₂ O disappears and monosulfate grows.
3) CSH grows.
4) Portlandite grows but cracks do not expand because the growth is small.
(B) The temperature which heats concrete is 80 degreeC or more in a normal pressure.
(C) The concrete heating time is long when the temperature is low, and short when the temperature is high. For example, at 100 ° C., it is at least 6 hours or longer.
(D) The chemical properties of cement in concrete do not change even if heating is continued after it has been changed by heating for the required time.
(E) The hydrothermally treated concrete does not expand in the wet air accelerated expansion test.
(F) Hydrothermally treated concrete tends to have a slight decrease in compressive strength and elastic modulus.

  Example 2 shows an example in which the present invention is applied to a wall slope of a highway where a crack has occurred, and FIG. 13 is a schematic cross-sectional view thereof.

  In FIG. 13, 1 is a concrete wall wall, 2 is a water retaining material in contact with the surface, 3 is a flexible surface heater provided on the outside, 4 is a heat insulating material, 5 is a contact plate using a plywood, Fit an appropriate number of U-shaped fasteners to the edges, insert anchors from the outside of the plate 5, and insert the water retaining material 2, the flexible planar heater 3 and the heat retaining material 4 through the plate 5 into the wall slope. Fix to 1.

  As the water retentive material 2, a woven fabric or non-woven fabric of a chemical fiber such as cotton or hemp or a chemical fiber such as polyester having a thickness of 2 to 10 mm or a water supply water retaining synthetic resin sheet is used. Using.

  In this embodiment, a commercially available flexible planar heater having a thickness of 1 to 5 mm was used as the heater, but other heaters can also be used. In the examples, a flexible planar heater having a thickness of 1 mm was used.

  As the heat insulating material 4, a plate-shaped heat insulating material made of foamed polystyrene having a thickness of 20 to 50 mm, which is easily available, is suitable. For easy hydration.

  Moisture was previously moistened in the water retaining material 2, the flexible planar heater 3 was energized, the temperature of the water retaining material 2 was raised to 97 to 99 ° C, and hydrothermal curing was performed for 24 hours.

  The wetness and temperature of the water retaining material 2 are managed by a humidity sensor and a temperature sensor (not shown) provided between the water retaining material 2 and the flexible planar heater 3.

  It was confirmed by the above hydrothermal curing that the same improvement effect as in Example 1 was obtained by powder X-ray diffraction pattern of the core sample after the treatment.

  Example 3 is an example in which Example 2 is hydrothermally cured with hot water while hydrothermal curing is performed with water vapor.

  FIG. 14 shows a schematic cross-sectional view, 1 is a concrete wall column, 6 is a cover sheet, and the hem is fixed to the wall column 1, road surface, etc. so that a gap 7 is formed between the wall column 1 and the wall. Then, steam at 80 ° C. or higher was continuously supplied into the gap 7 through the steam supply pipe 8, and hydrothermal curing was performed for 24 hours. Both sides of the heat insulating cover sheet 6 may be left open.

  It was confirmed by the above-described hydrothermal curing with steam that the same improvement effect as in Example 1 was obtained from the powder X-ray diffraction pattern of the core sample after the treatment.

  Example 4 is an example of hydrothermal curing different from Example 2, FIG. 15 is a schematic perspective view thereof, and FIG. 16 is a longitudinal sectional view of FIG.

  In this embodiment, a stainless steel dish-shaped cover 9 having an open top is fixed to a concrete wall 1 'to form a water tank having a depth of 5 to 30 mm, and water 10 and a heater 11 (in the case of a waterproof heater, the structure is No matter), the temperature of the water 10 is maintained at 80 ° C. or higher, and the cracked portion generated in the concrete wall 1 ′ is hydrothermally cured.

  This embodiment is used to improve a cracked portion generated in a part of the concrete wall 1 ′. However, since a plate-like cover 9 corresponding to the area of the cracked portion must be prepared, it is convenient and economical. There's a problem.

  Although the four embodiments have been described above, it is needless to say that the present invention is not limited to these embodiments.

  It should be noted that the present invention is an improvement of a cracked concrete product or concrete structure, i.e., it stops the progress of the crack and does not eliminate the crack itself. After such improvement, the surface is made up by the method described in paragraph [0003].

DESCRIPTION OF SYMBOLS 1 Concrete wall slope 2 Water retention material 3 Flexible surface heater 4 Thermal insulation material 5 Current board 6 Thermal insulation cover sheet 7 Cavity 8 Water vapor supply pipe 9 Dish cover 10 Water 11 Heater

Claims (5)

A method for improving a cracked concrete, characterized in that the cracked part or the whole is hydrothermally cured with hot water or steam at 80 ° C. or higher. A water retaining material, a planar heater, and a heat insulating material are sequentially brought into contact with the surface of the cracked concrete structure, and water is moistened to the water retaining material, and the water temperature in the water retaining material is set to 80 ° C. or more with the planar heater. A method for improving cracked concrete, characterized by hydrothermal curing. 3. The method for improving cracked concrete according to claim 2, wherein the water retaining material is one having an upper edge inclined toward the concrete structure. A method for improving a cracked concrete, comprising covering a concrete structure with cracks with a heat insulating sheet, injecting steam at 80 ° C. or higher into the heat retaining sheet, and curing the concrete structure by heating with heat. . A cover for water tank formation is attached so as to cover the cracked part of the concrete structure where the crack has occurred, water and a heater are put in this cover, and the temperature of the water is raised to 80 ° C. or more and the water is heated and cured. How to improve the generated concrete.

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