Method for preventing micro-exfoliation of precast concrete products, device for preventing micro-exfoliation of precast concrete products, and method for manufacturing precast concrete products

Abstract

To provide a method to suppress micro-delamination of precast concrete products that can suppress micro-delamination on the surface of precast concrete products, a device using this method to suppress micro-delamination of precast concrete products, and a manufacturing method of the precast concrete products.SOLUTION: In a method to suppress micro-delamination of precast concrete products according to the present invention, after casting concrete materials in a formwork, the integrated temperature at the time of exposure until de-molding and exposing outdoors is controlled so as to satisfy the following conditions (1) - (3) according to the exposure environment temperature.(1) When the exposure environment temperature is 20°C or less, the integrated temperature during exposure is 480°C.h or more.(2) When the exposure environment temperature exceeds 20°C and is 40°C or less, the integrated temperature during exposure is 840°C.h or more. (3) When the exposure environment temperature exceeds 40°C and is 60°C or less, the integrated temperature during exposure is 1180°C.h or more.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for suppressing minor spalling of a precast concrete product, an apparatus for suppressing minor spalling of a precast concrete product using said method, and a method for manufacturing said precast concrete product. [Background technology]

[0002] In recent years, there has been a growing interest in the appearance of precast concrete products from the viewpoint of aesthetics and scenery. In particular, micro-peeling on the surface of precast concrete products, which is not a problem for cast-in-place concrete, is considered to be a problem.

[0003] Precast concrete products are cured after they are formed to ensure a specified strength. Curing is divided into curing from when the product is formed until it is stripped from the form (hereinafter referred to as "primary curing"), and curing after stripping (hereinafter referred to as "secondary curing"). Primary curing is carried out to ensure the necessary strength so that the precast concrete product does not chip or peel when the formwork is stripped. Meanwhile, secondary curing is carried out to ensure the design strength of the precast concrete product after stripping.

[0004] In precast concrete products, secondary curing is usually performed by exposing the product to outdoor storage immediately after demolding (after primary curing) due to restrictions on indoor storage space. Precast concrete products that have completed the secondary curing period can be shipped immediately, but if they are not shipped immediately, they are kept in outdoor storage until they are shipped, separated from precast concrete products undergoing secondary curing. However, particularly in cold regions, precast concrete products that are manufactured from spring to autumn and stored outdoors are subject to repeated freezing and thawing in winter, which causes micro-peeling on the product surface, which is a problem.

[0005] In order to prevent such micro-flaking, it is necessary to block the supply of moisture to the precast concrete product from rain or snow. To prevent this, conventional measures include storing the product indoors until it is shipped, installing a roof over the outdoor storage area, or covering the precast concrete product with a sheet. Summary of the Invention [Problem to be solved by the invention]

[0006] However, these measures have difficulty in sufficiently blocking the supply of moisture to precast concrete products due to problems such as restrictions on indoor storage space, the cost of installing a roof, and the labor required for work, and the current situation is that micro-peeling occurs on the surface of many products. Conventionally, a release agent is applied to the formwork in order to facilitate demolding. It is believed that micro-peeling occurs on the product surface when a large amount of this release agent adheres to the product surface after demolding. However, since it is difficult to strictly control the amount of release agent applied to the formwork, it is difficult to control the amount of release agent attached to the product surface. Therefore, there is a demand for suppressing micro-peeling on the product surface regardless of the storage environment or the amount of release agent applied to the formwork.

[0007] The present invention has been made in consideration of the above circumstances, and has an objective of providing a method for suppressing micro-peeling of precast concrete products that is capable of suppressing micro-peeling on the product surface, an apparatus for suppressing micro-peeling of precast concrete products using said method, and a method for manufacturing said precast concrete product. [Means for solving the problem]

[0008] The method for suppressing micro-peeling of precast concrete products according to the present invention is a method for suppressing micro-peeling of precast concrete products, in which the accumulated temperature during exposure from when the concrete material is poured into a formwork to when it is removed from the formwork and exposed to the outdoors is controlled so as to satisfy the following conditions (1) to (3) according to the exposure environmental temperature. (1) When the exposure environment temperature is 20°C or less, the cumulative exposure temperature is 480°C·h or more. (2) When the exposure environment temperature is more than 20°C and less than 40°C, the cumulative exposure temperature is 840°C·h or more. (3) When the exposure environment temperature is more than 40°C and less than 60°C, the cumulative exposure temperature is 1180°C·h or more.

[0009] With this configuration, the method for suppressing micro-peeling of a precast concrete product can suppress micro-peeling on the surface of the product.

[0010] The device for suppressing micro-exfoliation of precast concrete products according to the present invention is a device for suppressing micro-exfoliation of precast concrete products, and is equipped with a control means for controlling the accumulated temperature during exposure from when the concrete material is poured into a formwork to when it is removed from the formwork and exposed to the outdoors, so as to satisfy the following conditions (1) to (3) in accordance with the exposure environmental temperature. (1) When the exposure environment temperature is 20°C or less, the cumulative exposure temperature is 480°C·h or more. (2) When the exposure environment temperature is more than 20°C and less than 40°C, the cumulative exposure temperature is 840°C·h or more. (3) When the exposure environment temperature is more than 40°C and less than 60°C, the cumulative exposure temperature is 1180°C·h or more.

[0011] With the above-described configuration of the device for suppressing micro-exfoliation of a precast concrete product, a precast concrete product can be obtained in which micro-exfoliation on the surface of the product is suppressed.

[0012] The manufacturing method of a precast concrete product according to the present invention is a method for manufacturing a precast concrete product, and includes the steps of pouring concrete material into a formwork and, after pouring, removing the concrete material from the formwork and exposing the concrete material to the outdoors, wherein the accumulated temperature during exposure from pouring to removing the concrete material from the formwork and exposing the concrete material to the outdoors satisfies the following conditions (1) to (3) depending on the exposure environment temperature. (1) When the exposure environment temperature is 20°C or less, the cumulative exposure temperature is 480°C·h or more. (2) When the exposure environment temperature is more than 20°C and less than 40°C, the cumulative exposure temperature is 840°C·h or more. (3) When the exposure environment temperature is more than 40°C and less than 60°C, the cumulative exposure temperature is 1180°C·h or more.

[0013] With this configuration, the manufacturing method for a precast concrete product can obtain a precast concrete product in which micro-peeling on the surface of the product is suppressed. Effect of the Invention

[0014] According to the present invention, it is possible to provide a method for suppressing micro-peeling of precast concrete products, which is capable of suppressing micro-peeling on the surface of a precast concrete product, an apparatus for suppressing micro-peeling of precast concrete products using said method, and a method for manufacturing said precast concrete product. [Brief description of the drawings]

[0015] [Figure 1] 1 is a graph showing a part of the temperature history inside the tank and on the surface of the test specimen in the examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, a method for suppressing minor spalling of a precast concrete product, an apparatus for suppressing minor spalling of a precast concrete product, and a method for manufacturing a precast concrete product according to this embodiment will be described.

[0017] <Method for preventing micro-peeling of precast concrete products> The method for suppressing micro-peelling of precast concrete products according to this embodiment controls the accumulated temperature during exposure from when the concrete material is poured into a formwork until it is removed from the formwork and exposed to the outdoors so as to satisfy the following conditions (1) to (3) according to the exposure environmental temperature. (1) When the exposure environment temperature is 20°C or less, the cumulative exposure temperature is 480°C·h or more. (2) When the exposure environment temperature is more than 20°C and less than 40°C, the cumulative exposure temperature is 840°C·h or more. (3) When the exposure environment temperature is more than 40°C and less than 60°C, the cumulative exposure temperature is 1180°C·h or more.

[0018] Here, the accumulated temperature during exposure refers to the accumulated temperature from when the concrete material is poured into a formwork to when it is removed from the formwork and exposed to the outdoors, and is the accumulated value of the product of the surface temperature of the poured concrete and time, as shown in the following formula (i).

[0019] M = Σ(θ T) (i) M: Cumulative temperature (°C h) θ: Surface temperature of poured concrete (℃) T: Time (h)

[0020] The surface temperature θ of the poured concrete can be measured, for example, by a thermocouple attached to the inner surface of the formwork.

[0021] Moreover, the time T is preferably 1 / 12h (i.e., 5 min) or more, and is preferably 1h or less. For example, if the time T is 1h, the surface temperature θ is measured every 1h after pouring. Then, the product of the measured surface temperature θ and the time T (1h) is integrated to calculate the integrated temperature.

[0022] The exposure environment temperature is the surface temperature of a precast concrete product when the concrete material is poured into a formwork, removed from the formwork, and exposed to the outdoors. The exposure environment temperature is measured by measuring the surface temperature of precast concrete products of the same composition that have been placed in an exposure environment in advance. If the surface temperature of a precast concrete product is not uniform, the maximum value of the surface temperatures is taken as the exposure environment temperature. The surface temperature of a precast concrete product can be measured, for example, with a thermocouple thermometer, an infrared radiation thermometer, etc.

[0023] The concrete material used in the method for suppressing micro-peel off of a precast concrete product according to the present embodiment includes cement, coarse aggregate, fine aggregate, and water. The concrete material may be a mortar material that does not include coarse aggregate.

[0024] The cement (C) is not particularly limited, and examples of the cement that can be used include Portland cements such as ordinary Portland cement, high-early-strength Portland cement, ultra-high-early-strength Portland cement, moderate-heat Portland cement, and low-heat Portland cement, as specified in JIS R 5210, and mixed cements obtained by mixing Portland cement with fly ash, blast furnace slag, etc. One type of cement may be used alone, or two or more types may be used in combination.

[0025] The amount of cement to be mixed is not particularly limited, and may be, for example, 250 kg / m 3 More than 450kg / m 3 When two or more types of cement are contained, the above blending amount is the total blending amount of the cements.

[0026] The water-cement ratio (W / C) is preferably 0.35 or more and 0.55 or less, and more preferably 0.45 or more and 0.55 or less, from the viewpoint of ensuring workability and durability.

[0027] The coarse aggregate (G) is not particularly limited, and examples thereof include natural aggregates such as river gravel, mountain gravel, and sea gravel, artificial aggregates such as crushed stone such as sandstone, hard limestone, basalt, andesite, and recycled aggregates, etc. One type of coarse aggregate may be used alone, or two or more types may be used in combination.

[0028] The amount of coarse aggregate to be mixed is not particularly limited, and may be, for example, 700 kg / m 3 More than 1200kg / m 3 When two or more types of coarse aggregate are contained, the above blending amount is the total blending amount of the coarse aggregate.

[0029] The fine aggregate (S) is not particularly limited, and examples thereof include natural fine aggregates such as river sand, mountain sand, sea sand, land sand, and natural lightweight fine aggregates (perlite, vermiculite, etc.), artificial fine aggregates such as crushed sand, artificial lightweight fine aggregate, and blast furnace slag fine aggregate, by-product lightweight fine aggregate, etc. One type of fine aggregate may be used alone, or two or more types may be used in combination.

[0030] The amount of fine aggregate to be mixed is not particularly limited, and may be, for example, 500 kg / m 3 More than 900kg / m 3 When two or more types of fine aggregate are contained, the above blending amount is the total blending amount of the fine aggregate.

[0031] The water (W) is not particularly limited, and may be, for example, tap water, industrial water, recycled water, groundwater, river water, rainwater, etc. The amount of water to be added is not particularly limited, and may be, for example, 140 kg / m 3 More than 190kg / m 3 It can be as follows:

[0032] The concrete material may further include an admixture. Examples of the admixture include inorganic fine powders such as fly ash, silica fume, cement kiln dust, blast furnace fume, ground granulated blast furnace slag, ground cooled blast furnace slag, ground converter slag, hemihydrate gypsum, expanding agent, ground limestone, ground quicklime, and ground dolomite, and inorganic fillers such as sodium bentonite, calcium bentonite, attapulgite, sepiolite, activated clay, acid clay, allophane, imogolite, shirasu (volcanic ash), shirasu balloon, kaolinite, metakaolin (calcined clay), synthetic zeolite, artificial zeolite, artificial zeolite, mordenite, and clinoptilolite. The admixture may be used alone or in combination of two or more.

[0033] When a concrete material contains fly ash (FA) as an admixture, the fly ash replacement ratio (FA / (FA+C)) is preferably 0.1 or more and 0.3 or less, and more preferably 0.15 or more and 0.25 or less, from the viewpoint of ensuring workability and durability.

[0034] The concrete material may further contain a chemical admixture. Examples of the chemical admixture include an air-entraining agent, an air-entraining water-reducing agent, a fluidizing agent, a separation reducing agent, a shrinkage reducing agent, etc. The chemical admixture may be used alone or in combination of two or more kinds.

[0035] The method for suppressing micro-peelling of precast concrete products according to this embodiment is not particularly limited, but can be used, for example, for precast concrete products such as L-shaped retaining walls, flumes, and flat plates that are typically manufactured using a vibration compaction method.

[0036] The method for suppressing micro-peeling of precast concrete products according to this embodiment can suppress micro-peeling on the surface of the product by controlling the accumulated temperature during exposure from when the concrete material is poured into a formwork until it is removed from the formwork and exposed to the outdoors so as to satisfy the above conditions (1) to (3) according to the exposure environmental temperature.

[0037] <Device for preventing micro-peeling of precast concrete products> The micro-peel prevention device for precast concrete products in this embodiment is equipped with a control means that controls the accumulated temperature during exposure from when the above-mentioned concrete material is poured into a formwork to when it is removed from the formwork and exposed to the outdoors, so that the following conditions (1) to (3) are satisfied in accordance with the exposure environmental temperature. (1) When the exposure environment temperature is 20°C or less, the cumulative exposure temperature is 480°C·h or more. (2) When the exposure environment temperature is more than 20°C and less than 40°C, the cumulative exposure temperature is 840°C·h or more. (3) When the exposure environment temperature is more than 40°C and less than 60°C, the cumulative exposure temperature is 1180°C·h or more.

[0038] The control means includes an accumulated temperature calculation means for measuring the surface temperature θ of the poured concrete and calculating the accumulated temperature during exposure, and an exposure environment temperature measurement means for measuring the exposure environment temperature, and controls the accumulated temperature during exposure measured by the accumulated temperature calculation means in accordance with the exposure environment temperature measured by the exposure environment temperature measurement means.

[0039] The integrated temperature calculation means can measure the surface temperature θ of the poured cement, for example, by a thermocouple attached to the inner surface of the formwork.

[0040] The exposure environment temperature measuring means can obtain the exposure environment temperature by measuring the surface temperature of a precast concrete product of the same composition that has been placed in advance in an exposure environment. The exposure environment temperature can be measured, for example, by a thermocouple thermometer, an infrared radiation thermometer, or the like.

[0041] The device for suppressing micro-peeling of precast concrete products in this embodiment is equipped with a control means for controlling the accumulated temperature during exposure from when the concrete material is poured into a formwork until it is removed from the formwork and exposed to the outdoors, so that the above conditions (1) to (3) are satisfied in accordance with the exposure environmental temperature, thereby suppressing micro-peeling on the surface of the product.

[0042] <Manufacturing method of precast concrete products> The manufacturing method of a precast concrete product according to this embodiment includes a step of pouring concrete material into a formwork, and a step of, after pouring, removing the concrete from the formwork and exposing the concrete to the outdoors, and the accumulated temperature during exposure from pouring to removing the concrete from the formwork and exposing the concrete to the outdoors satisfies the following conditions (1) to (3) according to the exposure environment temperature. (1) When the exposure environment temperature is 20°C or less, the cumulative exposure temperature is 480°C·h or more. (2) When the exposure environment temperature is more than 20°C and less than 40°C, the cumulative exposure temperature is 840°C·h or more. (3) When the exposure environment temperature is more than 40°C and less than 60°C, the cumulative exposure temperature is 1180°C·h or more.

[0043] In the process of pouring the concrete material into the formwork, the concrete material is mixed and then poured into the formwork for vibration molding. The mixing temperature is not particularly limited, and can be, for example, 5°C to 35°C. The vibration molding method is not particularly limited, and any conventionally known method can be used.

[0044] In order to make it easier to remove the mold, 30g / m 3 More than 127g / m 3 The following release agents may be applied. As the release agent, for example, a conventionally known release agent such as an oil-based or water-based release agent may be used.

[0045] After casting, the precast concrete product is cured in the process of removing the formwork and exposing it to the outdoors. The curing method is not particularly limited, and any conventionally known method can be used.

[0046] The manufacturing method of a precast concrete product according to this embodiment includes the steps of pouring concrete material into a formwork and, after pouring, removing the concrete from the formwork and exposing the concrete to the outdoors. The accumulated temperature during exposure from pouring to removing the concrete from the formwork and exposing the concrete to the outdoors satisfies the above conditions (1) to (3) according to the exposure environment temperature, thereby making it possible to obtain a precast concrete product in which micro-peeling on the product surface is suppressed. EXAMPLES

[0047] Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[0048] The surface of the precast concrete product where micro-flaking occurs is thought to be composed of mortar components, and therefore, in this example, a test was carried out using a mortar material.

[0049] The mortar materials with the composition shown in Table 1 were mixed using a Hobart mixer (manufactured by HOBART). After applying a release agent to a formwork with a diameter of 100 mm and a height of 200 mm, the mixed mortar materials were poured to a height of approximately 50 mm, and after curing under the curing temperature conditions in Table 2, the specimens were demolded. During the curing period, the surface temperature of the specimens was measured every 5 minutes using a thermocouple. The accumulated temperature during exposure was calculated based on the above formula (i). After demolding, each specimen was dried for 3 days in a temperature-controllable dryer. The temperature inside the dryer was set to the exposure environment temperature shown in Table 1.

[0050] [Table 1]

[0051] Details of the components shown in Table 1 are given below. Water (W): Tap water Cement (C): Ordinary Portland cement (manufactured by Sumitomo Osaka Cement Co., Ltd.) Fine aggregate (S): Mountain sand (Kakegawa, Shizuoka Prefecture) Fly ash (FA): Type II produced at Hokuriku Electric Power Company's Nanao-Ota Thermal Power Plant High-performance water reducing agent (SP): Mighty 21LV-S (Kao Corporation) Release agent: Panelol MDW-2 (manufactured by Daiseki Co., Ltd.)

[0052] [Table 2]

[0053] Next, a peel test was performed using each dried specimen. Specifically, each specimen was placed in a PVC pipe with an inner diameter of 107 mm with the surface with the release agent facing upward, and the gap between the specimen and the PVC pipe was filled with epoxy resin to prepare a specimen for the peel test. Then, tap water was poured onto the upper surface of the specimen for the peel test. The depth of the poured tap water was 5 mm. Furthermore, each specimen for the peel test was placed in a temperature-controllable test tank, and the temperature in the tank was kept at -10°C for 6 hours, and then at 20°C for 2 hours, and this cycle was repeated 50 times. Figure 1 shows a part of the temperature history inside the tank and on the surface of the specimen with the release agent attached.

[0054] The amount of peeling from the surface of each peel test specimen was determined by taking a peeled sample, drying it in a dryer, and then measuring its mass. 2 The amount of peeling and the evaluation results are shown in Table 1.

[0055] As can be seen from the results in Table 1, when the exposure environment temperature is 20°C or less, if the accumulated exposure temperature is 480°C·h or more, micro-peeling on the surface of the test specimen can be suppressed regardless of the amount of release agent applied. Also, when the exposure environment temperature is more than 20°C and less than 40°C, if the accumulated exposure temperature is 840°C·h or more, micro-peeling on the surface of the test specimen can be suppressed regardless of the amount of release agent applied. Furthermore, when the exposure environment temperature is more than 40°C and less than 60°C, if the accumulated exposure temperature is 1180°C·h or more, micro-peeling on the surface of the test specimen can be suppressed regardless of the amount of release agent applied.

Claims

1. 1. A method for inhibiting micro-sparging of a precast concrete product, comprising: After pouring a concrete material having a water-cement ratio of 0.35 or more and 0.55 or less into a formwork, the accumulated temperature during exposure until the concrete material is demolded is controlled so as to satisfy the following conditions (1) to (3) according to the exposure environment temperature, The method for suppressing micro-exfoliation of a precast concrete product, wherein the concrete material contains cement, and the cement is ordinary Portland cement as defined in JIS R 5210. (1) When the exposure environment temperature is 20°C or less, the cumulative exposure temperature is 480°C / h or more. (2) When the exposure environment temperature is more than 20°C and less than 40°C, the cumulative exposure temperature is 840°C / h or more. (3) When the exposure environment temperature is more than 40°C and less than 60°C, the cumulative exposure temperature is 1180°C / h or more.

2. A device for suppressing micro-peel off of precast concrete products, comprising: A control means is provided for controlling an accumulated temperature during exposure from pouring a concrete material having a water-cement ratio of 0.35 or more to 0.55 or less into a formwork until removal from the formwork so as to satisfy the following conditions (1) to (3) according to an exposure environment temperature: The device for suppressing micro-exfoliation of a precast concrete product, wherein the concrete material contains cement, and the cement is ordinary Portland cement as defined in JIS R 5210. (1) When the exposure environment temperature is 20°C or less, the cumulative exposure temperature is 480°C / h or more. (2) When the exposure environment temperature is more than 20°C and less than 40°C, the cumulative exposure temperature is 840°C / h or more. (3) When the exposure environment temperature is more than 40°C and less than 60°C, the cumulative exposure temperature is 1180°C / h or more.

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