Method for demolishing ultrafast-hardening concrete bodies and method for repairing ultrafast-hardening concrete structures

Abstract

This invention provides a method for demolishing ultrafast-hardening concrete that facilitates the demolition of the ultrafast-hardening concrete structure. [Solution] A method for demolishing an ultrafast hardening concrete body, comprising a heating step of heating the area to be demolished in the ultrafast hardening concrete body, a water contact holding step of bringing water into contact with the area to be demolished after the heating step and maintaining that state, and a demolition step of demolishing the area to be demolished after the water contact holding step.

Description

Technical Field

[0001] The present invention relates to a method for disassembling a high-early-strength concrete hardened body and a method for repairing a high-early-strength concrete structure.

Background Art

[0002] Concrete structures need to be repaired or replaced at an appropriate time depending on the degree of deterioration. For example, when replacing or repairing an expansion joint installed in a road (especially a highway) or a bridge, the concrete hardened body for fixing the expansion joint is disassembled once, and after replacing or repairing the expansion joint, new fixing concrete is placed. In this case, since repair work is carried out on a road or bridge in use, traffic control and the like are taken to carry out the repair work. In order to minimize the impact on traffic such as congestion, high-early-strength concrete that exhibits a compressive strength of 24 N / mm or more about 3 hours after placement is generally used as a repair material. 2 High-early-strength concrete reaches the required strength in a short time and exhibits a high strength of 50 N / mm or more after 7 days of curing. Since it also has high durability, it is used in disaster recovery and emergency repair of facilities. On the other hand, when disassembling a high-strength concrete structure, noise is generated due to the cutting sound during crushing and the operating sound of a generator or compressor, so there is concern about complaints from neighboring residents. Therefore, there is a demand for a method of disassembling work with time restrictions such as shortening the working time and making it difficult to generate noise.

[0003] High-early-strength concrete reaches the required strength in a short time and exhibits a high strength of 50 N / mm or more after 7 days of curing. 2 Since it also has high durability, it is used in disaster recovery and emergency repair of facilities. On the other hand, when disassembling a high-strength concrete structure, noise is generated due to the cutting sound during crushing and the operating sound of a generator or compressor, so there is concern about complaints from neighboring residents. Therefore, there is a demand for a method of disassembling work with time restrictions such as shortening the working time and making it difficult to generate noise.

[0004] Most of the methods for disassembling concrete structures are methods that apply physical impact to the concrete structures. As general disassembling methods, methods using the impact force of a crusher or a rock drill (breaker) or a water jet are known. When using these methods, environmental loads such as dust and vibration can be relatively suppressed. However, when the strength of the concrete structure to be disassembled is high, the cutting sound during crushing becomes large, and time constraints such as shortening the working time and restricting the working time are imposed. To solve problems such as noise from cutting and the time required for the work, it is necessary to reduce the strength of the concrete structure. Methods include using static destructive agents such as chemical expansives and expansive mortar to create cracks in the concrete structure, and heating the surface temperature of the concrete structure to 300°C, which causes the water in the concrete to turn into steam and expand, thus creating cracks.

[0005] Furthermore, as a method for demolishing (crushing) ultrafast-hardening concrete, Patent Document 1 proposes a concrete crushing method comprising a heating step of heating the area to be removed from the ultrafast-hardening concrete, and a crushing step of crushing the hardened material within the area to be removed, wherein the heating step is characterized by heating for 50 minutes or more using a heating means of 200°C or more and less than 250°C. Furthermore, Patent Document 2 proposes a concrete crushing method comprising a cutting step of forming grooves in the ultrafast-hardening concrete, a heating step of inserting a plate-shaped heating means into the grooves to heat the hardened material, and a crushing step of crushing the hardened material. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2017-186854 [Patent Document 2] Japanese Patent Publication No. 2019-90287 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The methods described in Patent Documents 1 and 2 can reduce the strength of the ultrafast-hardening concrete by decomposing ettringite through heating, thus facilitating the crushing of the ultrafast-hardening concrete. However, the effect of this method in facilitating the crushing of the ultrafast-hardening concrete is still insufficient, and therefore it cannot be said that the problems of noise and working time during the demolition of the ultrafast-hardening concrete have been solved.

[0008] The present invention was made to solve the above-mentioned problems and aims to provide a method for dismantling a rapidly hardening concrete structure that facilitates its demolition. Furthermore, the present invention aims to provide a method for repairing a rapidly hardening concrete structure that facilitates the demolition and repair of the rapidly hardening concrete structure. [Means for solving the problem]

[0009] The inventors of this invention conducted diligent research to solve the above problems and discovered that by heating the area to be demolished in a super-fast hardening concrete body and then bringing it into contact with water and holding it, the area to be demolished can be over-expanded, causing cracks to form, thereby facilitating the demolition of the area to be demolished. This led to the completion of the present invention. In other words, the present invention is illustrated as follows.

[0010] [1] A heating step to heat the area to be demolished of the ultrafast-hardening concrete body, A water contact holding step involves bringing water into contact with the area to be dismantled after the heating step and maintaining that state, A dismantling step to dismantle the area to be dismantled after the water contact holding step, A method for demolishing a super-fast hardening concrete body, comprising the following features. [2] The method for demolishing an ultrafast-hardening concrete body according to [1], wherein the heating of the area to be demolished is performed by a non-contact heating method. [3] The method for demolishing an ultrafast hardened concrete body according to [2], wherein the non-contact heating method is high-frequency dielectric heating, microwave heating and / or induction heating. [4] The method for demolishing an ultrafast hardening concrete body according to any one of [1] to [3], wherein the heating step involves heating the area to be demolished to a temperature of over 105°C for 3 hours or more. [5] The method for demolishing an ultrafast hardening concrete body according to any one of [1] to [4], wherein the water contact holding step involves contact with and holding time with the water of the area to be demolished for 3 hours or more. [6] A method for demolishing an ultrafast hardening concrete body according to any one of [1] to [5], wherein the ultrafast hardening concrete body is mainly composed of calcium sulfoaluminate. [7] A method for dismantling a superfast hardening concrete body described in any one of [1] to [6], used for repairing or replacing a superfast hardening concrete body that fixes expansion joints of bridges or roads. A method for repairing an ultrafast hardening concrete structure, comprising a filling step of filling the area demolished and removed by the demolition method of an ultrafast hardening concrete structure described in any one of [1] to [7]. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a method for dismantling a rapidly hardening concrete body that facilitates its demolition. Furthermore, according to the present invention, it is possible to provide a method for repairing a rapidly hardening concrete structure that facilitates the demolition and repair of the rapidly hardening concrete body. [Brief explanation of the drawing]

[0012] [Figure 1] This is the temperature program pattern for the heating test of the test specimen in the example. [Figure 2] This is a photograph of the specimen after 7 days of immersion in water after being heated at 120°C. [Modes for carrying out the invention]

[0013] The embodiments of the present invention will be described in detail below. The present invention is not limited to the embodiments described below, and it should be understood that modifications, improvements, etc., made to the embodiments described below, based on the ordinary knowledge of those skilled in the art, without departing from the spirit of the invention, also fall within the scope of the present invention.

[0014] A method for dismantling an ultrafast-hardening concrete body according to an embodiment of the present invention comprises a heating step, a water contact holding step, and a dismantling step. Herein, in this specification, "ultrafast hardening concrete" refers to a hardened ultrafast hardening concrete in which a calcium aluminate component is mixed with Portland cement as a rapid hardening component, and in the initial stages of hydration, the calcium aluminate component and Portland cement react to produce ettringite (3CaO·Al2O3·3CaSO4·32H2O), thereby exhibiting strength. More specifically, the ultrafast hardening concrete hardened material has a hardness of 24 N / mm² three hours after placement. 2 This refers to a hardened body of ultrafast-setting concrete that exhibits the above compressive strength. The ultrafast-setting concrete is not particularly limited, and known materials can be used. For example, ultrafast-setting concrete contains ultrafast-setting cement, fine aggregate, and water, and may optionally include coarse aggregate, fibers, setting retarders, water-reducing agents, concrete admixtures, etc. Ultra-fast hardening cement contains C 12 A7(12CaO・7Al2O3), C3A(3CaO・Al2O3), C 11A7·CaF2 (11CaO·7Al2O3·CaF2), NC8A3 (Na2O·8CaO·3Al2O3), CSA (calcium sulfoaluminate; 3CaO·3Al2O3·CaSO4), CA (CaO·Al2O3), CA2 (CaO·2Al2O3), etc. can be used. These can be used alone or in combination of two or more. Among them, the ultra-rapid hardening cement preferably contains calcium sulfoaluminate, and more preferably has calcium sulfoaluminate as the main component. In this specification, the "main component" means that the proportion in the whole is 50% by mass or more. When there is gypsum and no calcium hydroxide, the reaction of the following formula (1) proceeds rapidly in calcium sulfoaluminate, and a large amount of ettringite (3CaO·Al2O3·3CaSO4·32H2O) is generated to exhibit early strength. 3CaO·3Al2O3·CaSO4 + 2CaSO4 + 38H2O → 3CaO·Al2O3·3CaSO4·32H2O + 2Al2O3·3H2O ···(1)

[0015] The heating step is a step of heating the disassembly target region of the ultra-rapid hardening concrete hardened body. For heating the disassembly target region of the ultra-rapid hardening concrete hardened body, known heating methods can be used, which may be a contact heating method or a non-contact heating method. Among them, heating the disassembly target region of the ultra-rapid hardening concrete hardened body is preferably performed by a non-contact heating method. By using a non-contact heating method, it becomes easier to uniformly heat the disassembly target region of the ultra-rapid hardening concrete hardened body, leading to reduction of energy loss and improvement of heating efficiency, and ensuring safety during work. Furthermore, since it is not necessary to form grooves in the ultra-rapid hardening concrete hardened body and insert heating means to facilitate heating of the ultra-rapid hardening concrete hardened body, the heating work can also be efficiently performed.

[0016] The non-contact heating method is not particularly limited, but high-frequency dielectric heating, microwave heating, or induction heating can be used, and these heating methods may be used in combination. By using these heating methods, the area of ​​the ultrafast-hardening concrete body to be demolished can be heated efficiently and uniformly. High-frequency dielectric heating, microwave heating, and induction heating can be performed using commercially available heating equipment capable of performing such heating.

[0017] The heating process preferably involves heating the area of ​​the ultrafast-hardening concrete body to be demolished to a temperature above 105°C for 3 hours or more. Heating the area of ​​the ultrafast-hardening concrete body to be demolished under these conditions causes the area to over-expand, which can lead to cracking in the area during the water contact holding process. If the heating temperature is 105°C or lower and the heating time is less than 3 hours, the expansion of the area will be smaller, making it less likely for cracks to occur in the area during the water contact holding process. From the viewpoint of stably ensuring the above effects, the heating temperature of the area to be demolished in the ultrafast-hardening concrete body is more preferably 110°C or higher, even more preferably 115°C or higher, and particularly preferably 120°C or higher. Furthermore, the heating time of the area to be demolished in the ultrafast-hardening concrete body is more preferably 3.5 hours or longer, even more preferably 4 hours or longer, and particularly preferably 4.5 hours or longer. The upper limit of the heating temperature is not particularly limited, but for example, it could be 300°C, 250°C, 200°C, or 180°C. Similarly, the upper limit of the heating time is not particularly limited, but for example, it could be 12 hours, 11 hours, or 10 hours.

[0018] The water contact holding process involves bringing water into contact with the area of ​​the ultrafast-hardening concrete body to be demolished after the heating process, and maintaining that state. Performing the water contact holding process after the heating process allows for the generation of cracks in the area of ​​the ultrafast-hardening concrete body to be demolished, making it easier to demolish that area during the demolition process. The water contact holding process may be performed immediately after the heating process, or after a certain period of time has passed since the heating process. For example, when working on roads or bridges, the heating process can be performed during times of low traffic (e.g., at night), work can be interrupted and traffic restrictions lifted during times of high traffic, and the water contact holding process can be performed during subsequent times of low traffic (e.g., the following night). Alternatively, the heating process and the water contact holding process may be performed consecutively during times of low traffic. Furthermore, when the water contact holding process is performed immediately after the heating process, it may be performed while the temperature of the area to be demolished in the ultrafast-hardening concrete is high, or it may be performed after the temperature of the area to be demolished in the ultrafast-hardening concrete has decreased.

[0019] There are no particular limitations on the method of maintaining water contact with the area to be demolished of the ultrafast-hardening concrete, but examples include continuously spraying water on the area to be demolished, spraying water on the area to be demolished and covering the surface with a sheet, or placing a water-soaked sheet on the surface of the area to be demolished. Depending on the weather, the water contact maintenance process can also be carried out by exposing the area to be demolished of the ultrafast-hardening concrete to rain.

[0020] In the water contact holding process, it is preferable that the contact and holding time with water in the area of ​​the ultrafast-hardening concrete body to be demolished is 3 hours or more. By performing the water contact holding process under these conditions, cracks can be stably generated in the area of ​​the ultrafast-hardening concrete body to be demolished. From the viewpoint of stably ensuring this effect, the above time is more preferably 3.5 hours or more, even more preferably 4 hours or more, and particularly preferably 4.5 hours or more. The upper limit of the above time is not particularly limited, but for example, it could be 48 hours or 24 hours.

[0021] The demolition process involves demolishing the target area of ​​the ultrafast-hardening concrete body after the water contact holding process. Since the strength of the target area of ​​the ultrafast-hardening concrete body after the water contact holding process has significantly decreased and cracks have formed, it can be demolished (crushed) more easily than with conventional methods. Therefore, it is possible to reduce noise during the demolition of the ultrafast-hardening concrete body while shortening the working time. The demolition method is not particularly limited, and known methods can be used. For example, crushers, rock drills (breakers), or water jets can be used. Since the strength of the area of ​​the ultrafast-hardening concrete body to be demolished after the water contact holding process is reduced, it is preferable to carry out the demolition process as soon as possible after the water contact holding process (at least on the same day).

[0022] The method for dismantling a rapidly hardening concrete body according to the embodiment of the present invention can be used for various concrete structures having a rapidly hardening concrete body. In particular, the method for dismantling a rapidly hardening concrete body according to the embodiment of the present invention is suitable for use in repairing or replacing rapidly hardening concrete bodies that fix expansion joints of bridges or roads. Here, bridge or road expansion joints are devices that fill gaps in bridges or roads, and are installed, for example, between bridge girders and abutments or between bridge girders. Bridges and roads deform due to temperature changes, earthquakes, and vibrations caused by passing vehicles, and expansion joints play a role in absorbing this deformation.

[0023] A repair method for an ultrafast-hardening concrete structure according to an embodiment of the present invention includes a filling step of filling the area demolished and removed by the above-described method for demolishing the ultrafast-hardening concrete structure with a repair material. Since this repair method uses the above-described method for demolishing the ultrafast-hardening concrete structure, the demolition and repair of the ultrafast-hardening concrete structure become easier. While not particularly limited, ultrafast-setting concrete can be used as a repair material. The repair material can be used to repair ultra-fast-setting concrete structures by filling the demolition and removal areas with the repair material and then curing it until the desired strength is achieved. [Examples]

[0024] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0025] [Raw materials used] Ultra-fast setting cement: Ultra-fast setting cement with calcium sulfoaluminate as the main component. Fine aggregate: Mountain sand from Shizuoka Prefecture (surface dry density 2.58 g / cm³) 3 , water absorption rate 2.29%) Water-reducing agent: Naphthalene sulfonic acid-based high-performance water-reducing agent Coagulation retarder

[0026] [Preparation of ultra-fast-setting concrete] Ultra-fast hardening concrete was prepared by mixing ultra-fast hardening cement, fine aggregate, water-reducing agent, setting retarder, and water using a Hobart mixer. The water-cement ratio was 40%, the S / C ratio was 2.0, the water-reducing agent was added at a rate of C × 0.4 mass%, and the setting retarder was added at a rate of C × 0.6 mass. C represents the added mass (kg) of ultra-fast hardening cement, and S represents the added mass (kg) of fine aggregate.

[0027] [Preparation of test specimens] Three 4cm x 4cm x 16cm specimens were prepared using ultrafast-setting concrete. The specimens were prepared by pouring ultrafast-setting concrete into designated formwork, removing the formwork the following day, and then curing them in the air for 7 days.

[0028] [Heating and immersion tests of the test specimens] The heating test conditions involved varying the maximum temperature in five stages: 65°C, 80°C, 90°C, 105°C, and 120°C, and maintaining each temperature for 6 hours. The heating test was conducted using a dryer at temperatures above 100°C and a curing tank at temperatures below 100°C, under programmed operation. The heating rate was 20°C / h, and the cooling rate was 5-6°C / h. The temperature program patterns are shown in Figure 1. After heating was complete, the specimen was moved to a 20°C constant temperature chamber after confirming that its temperature had cooled to approximately room temperature. Once the specimen's temperature stabilized, its length was measured, and then immersion in water was started in the constant temperature chamber.

[0029] [Expansion rate measurement and visual inspection] The length of the specimens was measured before and after heating, and then, at a predetermined age, the specimens were removed from the water and the change in length was measured. At the same time, the presence or absence of cracks was visually confirmed. The length was measured by the distance between the gauge plugs at both ends, referring to JIS A1146:2017 "Test method for alkali-silica reactivity of aggregates (mortar bar method)". The expansion rate was calculated according to the method for calculating the rate of length change specified in JIS A1146:2017 or JIS A6202:2017 Annex A, using the measurement value before heating as the reference. Measurements were carried out until the length change converged, which occurred at an age of approximately 70 days. Figure 2 shows a photograph of the specimen heated at 120°C after 7 days of immersion. The specimen heated at 120°C developed cracks in both the longitudinal and transverse directions after just one day of immersion, suggesting that excessive expansion occurred in a very short period of time. On the other hand, specimens heated between 65 and 105°C tended to show a higher final expansion rate with increasing heating temperature. Of these, specimens heated at 65°C and 80°C did not develop cracks throughout the test period, and the final expansion rate at 80°C was only about 0.2%. Furthermore, specimens heated at 90°C and 105°C did not develop large cracks in the longitudinal or transverse directions, but their final expansion rates reached about 0.5%.

[0030] As can be seen from the above results, the present invention provides a method for dismantling a rapidly hardening concrete body that facilitates its demolition. Furthermore, the present invention provides a method for repairing a rapidly hardening concrete structure that facilitates the demolition and repair of the rapidly hardening concrete body.

Claims

1. A heating process to heat the area to be demolished in the ultra-fast hardening concrete body, A water contact holding step involves bringing water into contact with the area to be dismantled after the heating step and maintaining that state, A dismantling step to dismantle the area to be dismantled after the water contact holding step, A method for demolishing a super-fast hardening concrete body, comprising the following features.

2. The method for demolishing an ultrafast-hardening concrete body according to claim 1, wherein the heating of the area to be demolished is performed by a non-contact heating method.

3. The method for demolishing an ultrafast-hardening concrete body according to claim 2, wherein the non-contact heating method is high-frequency dielectric heating, microwave heating and / or induction heating.

4. The method for demolishing an ultrafast-hardening concrete body according to any one of claims 1 to 3, wherein the heating step involves heating the area to be demolished to a temperature of over 105°C for 3 hours or more.

5. The method for demolishing an ultrafast-hardening concrete body according to any one of claims 1 to 3, wherein the water contact and holding step involves contact with the water and holding time of the area to be demolished for 3 hours or more.

6. The method for demolishing an ultrafast-hardening concrete body according to any one of claims 1 to 3, wherein the ultrafast-hardening concrete body mainly consists of calcium sulfoaluminate.

7. A method for dismantling an ultrafast-hardening concrete body according to any one of claims 1 to 3, used for repairing or replacing an ultrafast-hardening concrete body that fixes an expansion joint of a bridge or road.

8. A method for repairing an ultrafast-hardening concrete structure, comprising a filling step of filling the area demolished and removed by the ultrafast-hardening concrete structure demolition method described in any one of claims 1 to 3 with a repair material.

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