JP6375326B2 - Manufacturing method of concrete products - Google Patents

Description

  The present invention relates to a method for producing a concrete product that prevents drying of concrete during steam curing.

  Conventionally, precast concrete products do not require on-site concrete curing, and the production time of the products is shortened. Therefore, after the concrete is placed in a mold, steam curing is performed by heating in a curing tank. Is adopted. In general, the concrete subjected to steam curing is often stored in the air as a secondary curing, but it is known that the concrete is dried from the concrete surface layer in the air storage (for example, Non-Patent Document 1). .

Asami Terakawa, 3 others, “Effects of curing conditions on pore structure of precast concrete products”, Annual Report of Concrete Engineering, 2012, Volume 34, No.2, pages 469-474

  The present inventor has focused on drying concrete during steam curing rather than drying during secondary curing, and has reached the present invention. An object of this invention is to provide the manufacturing method of the concrete product which can prevent the drying of the concrete during steam curing.

[Application Example 1]
The method for producing a concrete product according to this application example is as follows:
A first step of placing concrete in the formwork;
A second step of steam curing the placed concrete in a curing tank;
Including
The second step includes a temperature raising step for raising the atmospheric temperature in the curing tank to a first temperature, a temperature lowering step for lowering the atmospheric temperature in the curing tank from the first temperature, and the temperature raising step. the look containing a step maintained to keep the ambient temperature of the curing tank at the first temperature, a water supply step of supplying a liquid water relative to pouring the concrete, the between the cooling step,
The water supply process is started at the same time as the temperature of the atmosphere in the curing tank rises and reaches the first temperature .

  According to this application example, drying of concrete during steam curing can be prevented.

[Application Example 2 ]
In the method for manufacturing a concrete product according to this application example,
In the water supply step, liquid water can be supplied from above the placed concrete to the upper surface of the concrete.

  According to this application example, by supplying liquid water directly to the top surface of the concrete, the temperature of the top surface of the concrete can be lowered and drying of the top surface of the concrete can be prevented.

  The method for producing a concrete product according to the present invention can prevent drying of concrete during steam curing.

It is a graph which shows the relationship between time and temperature in the manufacturing method of the concrete which concerns on one Embodiment. It is a longitudinal cross-sectional view which shows typically the water supply process in the manufacturing method of the concrete which concerns on one Embodiment. It is a graph which shows the compressive strength test result of Example 1 and Comparative Examples 1-3. 4 is a graph showing the amount of pores in Example 1 and Comparative Example 1. 4 is a graph showing the amount of pores in Example 1 and Comparative Example 1. 4 is a graph showing the water absorption rate of Example 1 and Comparative Example 1. 4 is a graph showing the water absorption rate of Example 1 and Comparative Example 1. It is a graph which shows the neutralization rate coefficient of Example 1 and Comparative Examples 1-3.

DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. The embodiments described below do not unduly limit the contents of the present invention described in the claims. In addition, not all of the configurations described below are essential constituent requirements of the present invention.

1. Concrete Manufacturing Method A concrete manufacturing method according to this embodiment will be described with reference to FIG. FIG. 1 is a graph showing the relationship between time and temperature in the method for producing concrete according to the present embodiment, where the horizontal axis represents time and the vertical axis represents temperature, and the ambient temperature in the curing tank and the surface temperature of the concrete. The temperature transition in each process is shown.

  As shown in FIG. 1, the concrete product manufacturing method according to the present embodiment includes a first step of placing concrete in a mold, and a second step of steam curing the placed concrete in a curing tank. The second step includes a water supply step of supplying liquid water to the placed concrete. According to this manufacturing method, drying of concrete during steam curing can be prevented.

1-1. 1st process 1st process places concrete in a formwork. The formwork is prepared in advance prior to the first step. The formwork is usually constructed by assembling a plurality of iron parts. The mold has an opening at the top, and the upper surface of the placed concrete is exposed to the opening.

  The concrete in the first step is a mixture in which an aggregate such as sand or gravel and water are mixed with cement at an appropriate ratio. A known aggregate can be appropriately selected in accordance with the product. In the first step, concrete is poured into a mold assembled in a predetermined shape and placed. Surface finishing can also be performed on the top surface of the concrete in the formwork. Although a 1st process is performed in a curing tank, you may place in a different place from a curing tank and may arrange | position in a curing tank.

  In the first step, the atmospheric temperature in the curing tank is, for example, substantially the same as the outside air temperature. You may set the atmospheric temperature in a curing tank to appropriate room temperature.

  The pre-time in the first step can be set to 0.5 to 3 hours, for example.

1-2. Second Step In the second step, the concrete placed in the mold in the first step is steam-cured in a curing tank. The second step is performed with the concrete placed in the mold. The atmospheric temperature in the curing tank is controlled to a predetermined temperature by high-temperature steam controlled to a predetermined temperature. The inside of the curing tank is set to, for example, a temperature range of 100 ° C. or lower, preferably 65 ° C. or lower, in saturated steam at atmospheric pressure. The relative humidity at the ambient temperature in the curing tank is maintained at 100%.

  As shown in FIG. 1, the second step includes a temperature raising step, a maintaining step, and a temperature lowering step, and the atmospheric temperature in the curing tank is set to a predetermined set temperature for each step. The second step preferably includes a maintenance step in terms of product quality, but may include, for example, a temperature raising step and a temperature lowering step.

1-2-1. Temperature raising step The second step includes a temperature raising step of raising the ambient temperature in the curing tank to the first temperature. 1st temperature is the highest temperature of the atmospheric temperature in a curing tank in a 2nd process. The first temperature can be set to, for example, a temperature range of 100 ° C. or lower, and is preferably a temperature range of 45 ° C. to 65 ° C. If the first temperature is 45 ° C. or higher, it is preferable from the viewpoint of productivity in industrialization, and if it is 100 ° C. or lower, steam curing at normal pressure is possible.

  In the temperature raising step, the rate of temperature rise when raising the temperature from the initial temperature, for example from room temperature to the first temperature, can be set to 10 ° C / hour to 30 ° C / hour, preferably 10 ° C / hour to 20 ° C / Can be set to time. A temperature increase rate of 10 ° C./hour or more is preferable from the viewpoint of productivity, and a temperature increase rate of 30 ° C./hour or less is preferable because there is little adverse effect on product quality. If the initial temperature is the same as the outside air temperature, it may be adjusted by the temperature raising time.

  During this temperature raising step, the concrete hardens while generating heat due to the hydration reaction. Since concrete has a large heat capacity, it starts to be heated later than the temperature rise in the curing tank, but eventually rises above the temperature in the curing tank due to heat generated by the hydration reaction. And the temperature difference between the ambient temperature in the curing tank and the concrete at the end of the heating process or the initial of the maintenance process described below is maintained in the maintenance process because of the large heat capacity of the concrete, and gradually in the cooling process. It is kept small.

1-2-2. Maintenance Step The second step may include a maintenance step of maintaining the atmospheric temperature in the curing tank at the first temperature between the temperature raising step and the temperature lowering step. The maintenance process is controlled so that the atmospheric temperature in the curing tank is maintained at the first temperature, but allows a slight temperature variation as the atmospheric temperature.

  A maintenance process can be maintained at the 1st temperature for 0.5 hours-10 hours, for example. If the maintenance step is 0.5 hours or more, the strength of the product can be improved, and if it is 10 hours or less, it is preferable from the viewpoint of productivity. In the maintenance process, even if the atmospheric temperature is maintained at the first temperature, the temperature of the concrete continues to generate heat due to the hydration reaction and rises above the first temperature. Although it depends on the conditions of the concrete used, the temperature of the concrete rises to a temperature that is 5 ° C. to 10 ° C. higher than the first temperature. When the temperature rise of the concrete is finished, the temperature is maintained for the same time as the maintenance process, or the temperature is gradually lowered.

1-2-3. Temperature decreasing step The second step includes a temperature decreasing step of lowering the atmospheric temperature in the curing tank from the first temperature. In the temperature lowering step, the temperature is gradually lowered from the first temperature to the temperature of the first step (room temperature). The atmospheric temperature in the temperature lowering process is also lowered by introducing water vapor controlled to a predetermined temperature. The temperature lowering rate in the temperature lowering step can be set to, for example, -5 ° C / hour to -30 ° C / hour. A temperature drop rate of −5 ° C./hour or more is preferred from the viewpoint of productivity, and a temperature drop rate of −30 ° C./hour or less is preferred because there is little adverse effect on product quality. When the ambient temperature decreases in the temperature lowering process, the concrete temperature decreases slightly later. This is because concrete has a large heat capacity. In the temperature lowering step, for example, the ambient temperature is lowered to the outside temperature.

  The concrete product obtained by completing the temperature lowering step is obtained by curing the mixture in the first step by a hydration reaction.

1-2-4. Water Supply Process The water supply process is performed in the second process and supplies liquid water to the concrete placed in the first process. Unlike water vapor during curing because liquid water is supplied to the concrete in the water supply process, it continues to be in direct contact with the concrete surface, so that drying of the concrete during steam curing can be prevented.

  The water supply process can be performed during the temperature lowering process. By performing the water supply process at least during the temperature lowering process, it is possible to prevent drying of the concrete due to the difference between the atmospheric temperature in the curing tank and the concrete temperature during the temperature lowering process.

The concrete drying will be described. The concrete placed in the first step is heated as the atmospheric temperature in the curing tank rises in the second step. Since concrete has a large heat capacity, it is difficult to warm, and the temperature rises slightly later than the increase in the ambient temperature in the curing tank. Moreover, when concrete hardens by hydration reaction between cement and water, the reaction heat is generated. Therefore, even if the atmosphere temperature of the curing tank reaches the first temperature and transitions to the maintenance process, the concrete is heated to a temperature higher than the first temperature by the reaction heat. Here, even if the relative humidity in the curing tank is maintained at 100%, the relative humidity of the concrete having a higher temperature than the atmosphere in the curing tank is, for example, less than 80%. Although a relative humidity of 80% or more is required for the hydration reaction of concrete, the hydration reaction in the concrete is stopped or delayed when it falls below 80%. This is the drying of concrete during steam curing. In other words, the water in the concrete evaporates and shifts to the curing tank atmosphere.

  In the temperature lowering step, the temperature of the atmosphere in the curing tank is decreased, so that the difference between the ambient temperature and the concrete temperature is further increased. This is because concrete has a large heat capacity, so even if the ambient temperature in the curing tank starts to decrease, it is difficult to decrease. Therefore, in the temperature lowering step, the difference between the concrete temperature and the ambient temperature in the curing tank is not easily reduced, and therefore it is preferable to prevent drying in the temperature lowering step. In addition, since the concrete surface has already hardened to some extent in the temperature lowering step, even if liquid water is supplied, the surface is not adversely affected.

  The drying of concrete during steam curing appears as a decrease in the volume of the concrete (drying shrinkage), but the decrease in the volume of the concrete can be suppressed by the water supply process. In addition, drying of concrete during steam curing also appears as a decrease in durability of the concrete product, but the durability (neutralization, etc.) of the concrete can be improved by the water supply process. The durability of concrete is manifested in the denseness of the concrete structure.

  In the water supply process, liquid water is supplied to the concrete under steam curing, so that it is not easily lost by evaporation from the surface of the concrete, and drying can be prevented. The water supply process also has an effect of cooling the concrete.

  The water supply process can be started after the concrete surface temperature in the temperature lowering process exceeds the first temperature and before the concrete surface temperature starts to decrease. By doing in this way, drying of concrete during a temperature-fall process can be prevented. In particular, since the drying of concrete occurs when the temperature is higher than the atmospheric temperature in the curing tank, it is preferable that the surface temperature of the concrete exceeds the first temperature. Moreover, since the surface temperature of concrete begins to fall after the atmospheric temperature in a curing tank begins to fall, it is preferable that it is before the concrete surface temperature begins to fall at the latest.

  A water supply process can be started simultaneously with switching from a maintenance process to a temperature fall process, for example. By doing in this way, drying of the concrete in a temperature-falling process can be prevented from the time when the difference of the atmospheric temperature in a curing tank and the temperature of concrete becomes the largest.

  Moreover, a water supply process can be performed after the surface temperature of concrete exceeds 1st temperature. By doing in this way, the drying of the concrete by the difference of the atmospheric temperature in a curing tank and the surface temperature of concrete can be prevented. For example, the water supply process may be started from a temperature raising process or a maintenance process.

2. Concrete Manufacturing Apparatus A manufacturing apparatus used in the concrete manufacturing method according to the present embodiment will be described with reference to FIG. FIG. 2 is a longitudinal sectional view of a manufacturing apparatus schematically showing a water supply step in the concrete manufacturing method according to the present embodiment.

  As shown in FIG. 2, the concrete 30 placed in the mold 20 in the first step is disposed in the curing tank 10.

  The water supply process is performed by supplying liquid water 14 to the upper surface 32 of the concrete 30 from above the placed concrete 30. By supplying the liquid water 14 directly to the upper surface 32 of the concrete 30, the temperature of the upper surface 32 of the concrete 30 can be lowered and drying of the upper surface 32 of the concrete 30 can be prevented.

  The mold 20 is a metal, synthetic resin, or wooden mold that forms the outer shape of a desired product, and can be filled with concrete 30 inside.

  The reason why water is supplied from above the concrete 30 is that the upper surface 32 of the concrete 30 filled in the mold 20 is usually exposed to the opening of the mold 20. If water is supplied from above the concrete 30, the water can be efficiently supplied to the upper surface 32.

  The water supply device 12 supplies water to the upper surface 32 from above the concrete 30 in a liquid state. The water supply device 12 in FIG. 2 is a watering device (sprinkler). By using the water supply device 12 as a watering device, it is possible to prevent the upper surface 32 from being roughened by the collision of water droplets, and to supply mist-like water evenly to the entire upper surface 32.

3. In the water supply process in FIG. 2, although mist-like water is sprinkled on the upper surface 32 of the concrete 30 exposed to the opening of the mold 20, the position where the upper surface 32 of the concrete 30 is lower than the upper end of the mold 20. The concrete 30 may be filled so that the liquid water is accumulated between the upper surface 32 and the upper end of the mold 20. By doing in this way, it will be in the state which covers the upper surface 32 of the concrete 30 with water, and can prevent drying reliably.

(1) Materials used Concrete was prepared using the materials shown in Table 1.

(2) Preparation of concrete and curing conditions According to the formulation shown in Table 2, specimens of Example 1 and Comparative Examples 1 to 3 (columns having a diameter of 100 mm and a height of 200 mm) were prepared. The water-cement ratio (w / c: percentage of w / c with water amount w, cement amount c) of the specimen of Example 1 and Comparative Example 1 was set to 40% in accordance with the actual precast concrete product, and the comparison was made. The water-cement ratio of the specimens of Example 2 and Comparative Example 3 was 50% in accordance with the on-site simulated concrete.

The curing conditions of the specimens of Example 1 and Comparative Example 1 are as follows: the kneading temperature in the first step is 25 ° C., the concrete is placed in the mold and the pre-heating time until the start of temperature rise is 2 hours, In the temperature raising step in the second step, the temperature raising rate is raised to 20 ° C./hour to the first temperature (atmosphere temperature in the curing tank) of 65 ° C., the maintaining step is set to 65 ° C. for 3 hours, and the temperature lowering step is to lower the temperature. The temperature was lowered to 25 ° C. at a rate of 5 ° C./hour. The specimen of Example 1 started the water supply process at the same time as the atmospheric temperature in the curing tank reached 65 ° C., and continued to supply water until the end of the temperature lowering process. In the water supply step, as shown in FIG. 2 , water was sprinkled from above the specimen with a sprinkler, and liquid water was sufficiently supplied to the surface of the specimen. The specimens of Example 1 and Comparative Example 1 were stored in the air after steam curing, and the following tests were performed on materials having a material age of 1 day and a material age of 14 days.

  Comparative Example 2 was a specimen in which cast-in-place concrete was sealed and cured for 5 days, and Comparative Example 3 was a specimen in which cast-in-place concrete was cured in water for 28 days.

(3) Compressive strength test Specimens 1 day and 14 days old of Example 1, Specimens 1 day and 14 days of Comparative Example 1, and 5 days of Comparative Example 2 And the specimen of 14 days of age and the specimen of 28 days of age of Comparative Example 3 were subjected to a compressive strength test according to the compression test method of JIS A 1108 concrete. The results of the compressive strength test are shown in FIG.

As shown in FIG. 3, the specimen 1 day old of Example 1 had a compressive strength of 29 (N / mm ² ), and the compressive strength was lower than that of the specimen 1 day old of Comparative Example 1. However, when the material age was 14 days, it was reversed, and the specimen of 14 days of age in Example 1 showed a higher value than the specimen of 14 days of age of Comparative Example 1.

(4) Pore size distribution test Slice concrete to 5 mm in depth with a concrete cutter from the specimen of the first day of the age of Example 1 and Comparative Example 1 and the specimen of the same age of 14 to 30 mm. After subdividing with nippers and stopping hydration, the pore diameter and pore volume were measured by mercury porosimetry using a mercury porosimeter. FIG. 4 shows the measurement results of the specimens with the age of 1 day, and FIG. 5 shows the measurement results of the specimens with the age of 14 days. In FIG. 4 and FIG. 5, “5 nm-50 nm”, “50 nm-100 nm”, “100 nm-1 μm”, and “> 1 μm” indicate the measured pore diameters divided into four sections.

  As shown in FIGS. 4 and 5, it can be seen that the specimen of Example 1 has a smaller amount of pores (ml / g) than the specimen of Comparative Example 1, and the concrete structure is denser, It was found that the amount of pores having a diameter of 50 nm or more that affects the progress of neutralization is small.

(5) Water absorption test The specimens of the first day of the age of Example 1 and Comparative Example 1 and the specimens of the same age of 14 days are kept at 20 ° C. in a temperature-controlled room with a relative humidity of 60% for 1 day, and then 100 ° C. The water absorption (100 × (BA) / A (%) from the mass after drying (A) and the mass after removal from the water (B) ) The water absorption rate (%) is shown in FIGS.

  As shown in FIGS. 6 and 7, it was found that the water absorption rate of Example 1 was lower than that of Comparative Example 1, and the concrete structure was dense.

(6) Neutralization rate test About the test body of Example 1 and Comparative Examples 1-3, the neutralization rate test was done according to the measuring method of the neutralization depth of JIS A1153 concrete. Neutralization rate coefficient (C (mm / √week) = neutralization depth X (mm) / √t (t = material age (week)) from concrete surface) at the 4th week of promoting material . The neutralization rate coefficient is shown in FIGS.

  As shown in FIGS. 8 and 9, the specimen of Example 1 had a smaller neutralization rate coefficient than the specimens of Comparative Examples 1 to 3.

  The present invention is not limited to the above-described embodiments, and various modifications can be made. For example, the present invention includes configurations that are substantially the same as the configurations described in the embodiments (for example, configurations that have the same functions, methods, and results, or configurations that have the same objects and effects). In addition, the invention includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. In addition, the present invention includes a configuration that exhibits the same operational effects as the configuration described in the embodiment or a configuration that can achieve the same object. In addition, the invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

  DESCRIPTION OF SYMBOLS 10 ... Curing tank, 12 ... Water supply apparatus, 14 ... Liquid water, 20 ... Formwork, 30 ... Concrete, 32 ... Top surface

Claims (2)

A first step of placing concrete in the formwork;
A second step of steam curing the placed concrete in a curing tank;
Including
The second step includes a temperature raising step for raising the atmospheric temperature in the curing tank to a first temperature, a temperature lowering step for lowering the atmospheric temperature in the curing tank from the first temperature, and the temperature raising step. the look containing a step maintained to keep the ambient temperature of the curing tank at the first temperature, a water supply step of supplying a liquid water relative to pouring the concrete, the between the cooling step,
The said water supply process starts simultaneously with the atmospheric temperature in the said curing tank rising and reaching | attaining said 1st temperature, The manufacturing method of the concrete product characterized by the above-mentioned . In claim 1 ,
In the method for producing a concrete product, the water supply step supplies liquid water to the upper surface of the concrete from above the placed concrete.

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