JP6460454B2 - Concrete production method - Google Patents

Description

  The present invention relates to a method for producing concrete having excellent long-term strength. However, long-term strength in the present invention refers to the compressive strength of concrete whose age is 91 days (about 3 months) or more.

In concrete production sites, it is necessary to increase the number of rotations (number of times of use) of the formwork in order to increase production efficiency. Therefore, it is generally possible to demold several hours after placing concrete on the formwork. Steam curing is carried out so as to develop a high strength. Incidentally, the steam curing process mainly includes a pre-curing process, a temperature raising process, a temperature maintaining process, and a temperature lowering process.
By the way, during the busy season, in order to further increase the number of rotations of the mold, shortening of the pre-curing process, omission or shortening of the temperature raising process and the temperature lowering process are performed. However, even if the strength of the concrete product becomes demoldable in a few hours, the steam curing that shortens the pre-curing process etc. does not increase the strength after the steam curing, and the concrete during storage and transportation Problems such as generation of defective products due to missing corners of products and insufficient strength at the time of shipment are likely to occur. In particular, as a bad influence of steam curing on concrete, as shown in Non-Patent Document 1 described later, there is a wide decrease in strength itself or a decrease in strength expression at a long age (for example, after 3 months of age). Are known.

Therefore, in Non-Patent Document 1, if the concrete strength decrease due to steam curing is quantitatively clarified, it is expected that the decrease in strength can be covered by the blending (mixing) of concrete. From the above, factors that affect the strength of concrete are extracted and a formula for estimating the strength is proposed. By the way, as shown in Table 11 on pages 34 to 35 of this document, in the concrete subjected to steam curing, the strength reaches a peak at the age of 13 weeks (about 3 months), and the strength is at least at the age of 1 year. There are many cases where it has decreased.
On the other hand, the method for producing a cement molded article described in Patent Document 1 is a method for curing at high temperature a cement blend to which a predetermined amount of one or more of lithium, aluminum, gallium, thallium sulfate and the like is added. However, in the method described in Patent Document 1, as shown in Table 8 on page 7, the compressive strength of the steam-cured specimens TR3S and TR3H reached a peak at the age of 28 days, and at least 3 months later. The strength decreases and the long-term strength cannot be improved.
In addition, in the method for producing a concrete product described in Patent Document 2, after molding concrete added with an ettringite component such as aluminum sulfate in a mold, the ambient temperature of the mold is raised to 75 ° C. or higher. In this method, the mold is removed while maintaining the atmospheric temperature for 1.5 hours at the longest. However, in the Example of patent document 2, only aluminum sulfate 18 hydrate (hydrate) is used, and there is no specific description about aluminum sulfate anhydride. In addition, in Table 2 on page 7 of Patent Document 2, the compressive strength of the material age 28 days after outdoor exposure is described, but the compressive strength of the material age in the long term is not described, In the manufacturing method, it is unknown whether there is an increase in long-term strength.
Furthermore, the manufacturing method of the concrete product described in Patent Document 3 is a first step at 35 to 60 ° C. after molding concrete to which one or more selected from aluminum sulfate, alum, and alum stone is added to a mold. In this method, heat curing is performed, and then the second stage heat curing is performed at a temperature exceeding 60 ° C. and not exceeding 100 ° C. However, also in the Example of patent document 3, only aluminum sulfate 18 hydrate (hydrate) is used, and there is no specific description about aluminum sulfate anhydride. In addition, Table 2 on page 6 of Patent Document 3 describes the compressive strength at 28 days of age of concrete kneaded and cured in a room at 20 ° C ± 3 ° C. Since it is not described, it is unclear whether or not the long-term strength is enhanced in the production method.

Masatoshi Nakanishi, 1 other person, “About the compressive strength of steam-cured concrete”, [online], Shimizu Corporation, [October 4, 2014 search], Internet <URL: https://www.shimz.co .jp / tw / sit / report / vol8 / pdf / 8_003.pdf>

JP 60-21839 A JP-A-10-101455 Japanese Patent Laid-Open No. 10-203881

  Therefore, an object of the present invention is to provide a concrete production method including steam curing in an essential process, and a concrete production method excellent in long-term strength development having an age of 91 days or more.

Therefore, the present inventors have studied a method for producing concrete having excellent long-term strength, and found that a concrete production method having the following configuration can achieve the above object, thereby completing the present invention. It was. That is, the present invention is as follows.
[1] When the total amount of aluminum sulfate anhydride and cement is 100% by mass, steam curing is performed after kneading and molding concrete added with 0.5 to 2.0% by mass of aluminum sulfate anhydride solid. To produce concrete.
[2] The method for producing concrete according to [1], wherein the time from molding the concrete to steam curing and demolding is less than 15 hours.
[3] The method for producing concrete according to [1] or [2], wherein the concrete is produced at an environmental temperature of 10 ° C. or lower.

  According to the concrete production method of the present invention, concrete excellent in long-term strength can be produced.

It is the figure which showed the temperature history of the steam curing used in the Example of this invention. It is the figure which showed ratio of the age of concrete, and the compressive strength of an Example / compressive strength of a comparative example.

Below, the manufacturing method of the concrete of this invention is demonstrated in detail.
As described above, the method for producing concrete according to the present invention kneads concrete added with 0.5 to 2.0 mass% of aluminum sulfate anhydride when the total amount of aluminum sulfate anhydride and cement is 100 mass%. Then, after molding, concrete is produced by steam curing. Next, the present invention will be described by dividing it into aluminum sulfate, concrete constituent materials and their blending, concrete kneading and forming methods, and concrete steam curing methods.

1. Aluminum sulfate Aluminum sulfate used in the present invention is anhydrous and solid. In addition to anhydrides, aluminum sulfate includes hexahydrate, 10 hydrate, 16 hydrate, 18 hydrate, and 27 hydrate. In these hydrates (water salts), The setting of cement starts early and it becomes difficult to knead the concrete. Here, the solid means a powder or a granule. The particle size of the solid is preferably 1 mm or less, more preferably 0.5 mm or less, and even more preferably 300 μm or less. Moreover, the average particle diameter of the solid is preferably 5 to 30 μm, more preferably 10 to 20 μm. When the particle diameter of the aluminum sulfate anhydride is 1 mm or less, the concrete can be easily kneaded and the long-term strength is highly expressed. In the measurement of the particle size and the average particle size, a laser diffraction particle size distribution measuring device is preferably used because of its high accuracy and ease of measurement.
The aluminum sulfate anhydride is used by adding a solid of aluminum sulfate anhydride to 0.5 to 2.0 mass% concrete when the total amount of aluminum sulfate anhydride and cement is 100 mass%. As shown in Table 3 below, when the added amount is out of the above range, the effect of improving the strength is lowered. The amount of aluminum sulfate anhydride added is preferably 1.0 to 1.8% by mass of aluminum sulfate anhydride when the total amount of aluminum sulfate anhydride and cement is 100% by mass.

2. Concrete Constituent Material and Its Mixing Concrete produced by the production method of the present invention includes at least cement, fine aggregate, coarse aggregate, water, and a water reducing agent as constituent materials. Hereinafter, cement, fine aggregate, coarse aggregate, water, water reducing agent, and the like will be described.

(1) Cement The above cements are ordinary Portland cement, early-strength Portland cement, ultra-early strong Portland cement, medium heat Portland cement, low heat Portland cement, sulfate-resistant Portland cement, blast furnace cement, fly ash cement, coal ash-containing cement, One or more selected from the group consisting of silica cement, white cement, and eco-cement can be used. Further, the unit amount of the cement (the mass of cement in 1 m ^{3 of} concrete) is not particularly limited.

(2) Fine Aggregate Examples of the fine aggregate include one or more selected from the group consisting of river sand, mountain sand, land sand, sea sand, crushed sand, dredged sand, slag fine aggregate, lightweight fine aggregate, and the like. . In addition to natural aggregate, recycled aggregate can be used as the fine aggregate. The unit amount of fine aggregate is not particularly limited.

(3) Coarse aggregate The coarse aggregate includes at least one selected from the group consisting of river gravel, mountain gravel, crushed stone, slag coarse aggregate, lightweight coarse aggregate, and the like. The coarse aggregate may be natural aggregate, artificial aggregate, or recycled aggregate. The unit amount of the coarse aggregate is not particularly limited.

(4) Water The water can be used as long as it does not adversely affect physical properties such as strength and fluidity of concrete. For example, from the group consisting of tap water, industrial water, and recovered water from ready-mixed concrete. One or more selected may be mentioned. The unit amount of water is not particularly limited.

(5) Water reducing agent Examples of the water reducing agent include one or more selected from the group consisting of a high performance AE water reducing agent, a high performance water reducing agent, an AE water reducing agent, and the like. Examples of the water reducing agent (compound) include at least one selected from the group consisting of polycarboxylic acid, naphthalenesulfonic acid formaldehyde condensate, melamine sulfonic acid formaldehyde condensate, lignin sulfonic acid, and the like, and salts thereof. . The water reducing agent is preferably used by dissolving it in concrete kneading water in advance.
The amount of the water reducing agent added is preferably 0.5 to 3.0 parts by mass with respect to 100 parts by mass of cement from the viewpoint of ensuring the fluidity of the concrete.

(6) Admixtures and admixtures as optional constituents Further, the concrete includes admixtures such as shrinkage reducing agents, AE agents, hydration heat inhibitors, whitening inhibitors, retarders, curing accelerators, Admixtures such as blast furnace slag, fly ash, coal ash, silica fume, limestone powder, siliceous powder, and expansion material may be included.

3. Concrete Kneading Method and Molding Method The concrete kneading method is not particularly limited. Further, the mixer to be used is not particularly limited, and a forced kneading mixer, a gravity mixer, or the like can be used. Also, the concrete molding method is not particularly limited.

4). Concrete Steam Curing Method A general method of concrete steam curing includes, for example, a pre-curing step, a temperature raising step, a temperature maintaining step, and a temperature lowering step as shown in pattern A of FIG. Demolding is performed after completion of the process. In a general steam curing method, one cycle from molding to demolding is approximately 15 to 18 hours.
In the concrete production method of the present invention, the above-described general steam curing can be performed, but the steam curing can be performed by shortening the time of one cycle from molding to demolding to less than 15 hours.
In order to increase the number of rotations of the mold in the present invention, the time for one cycle of steam curing is preferably less than 15 hours, more preferably 5 to 10 hours.

The steam curing method for shortening the time for one cycle is not particularly limited. For example, (1) a method for shortening the precuring time, (2) a method for shortening the temperature raising step by increasing the temperature rising rate, (3 ) A method of omitting the temperature raising step and placing the formwork containing the concrete immediately after the completion of the pre-curing in a curing device set at a predetermined temperature, (4) A method of increasing the temperature lowering rate and shortening the temperature lowering step (5) A method of omitting the temperature lowering step, removing the mold containing the concrete immediately after the temperature maintaining step from the curing device, and demolding, and a method of appropriately combining them.
An example of the steam curing method in which one cycle time is shortened is a pattern B in FIG.
In the present invention, the temperature maintaining step may be performed at two or more stages (for example, 40 ° C. and 70 ° C. as shown in pattern B in FIG. 1).

  The concrete production method of the present invention produces concrete at an environmental temperature of 10 ° C. or lower because, as shown in FIG. 2 to be described later, since the strength development is remarkable even in the concrete manufactured at an environmental temperature of 10 ° C. or lower. It can also be applied to cases. Here, the environmental temperature refers to the temperature around the formwork containing concrete.

EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to these Examples.
1. Materials used and formulation Table 1 shows the materials used in the test. Table 2 shows the concrete mix used in the test.

2. Compressive strength test (1) Test at an ambient temperature of 20 ° C. (Examples 1 and 2, Comparative Example 1)
When the total of cement and aluminum sulfate anhydride is set to 100 in the concrete shown in Table 2, the aluminum sulfate anhydride is 0.0% by mass (no addition), 0.5% by mass, and 1.0%, respectively. The mass% was added, and the concrete was kneaded in a room at 20 ° C. In addition, this concrete was adjusted using the high performance AE water reducing agent and the antifoaming agent so that it might become the target slump and target air amount which are shown in Table 2.
Next, the kneaded concrete was placed in a mold having an inner diameter of 100 mm and a height of 200 mm, steam-cured with a temperature history of pattern A shown in FIG. 1, demolded, and cured under water at 20 ° C. And the concrete test body was taken out from water with the age shown in Table 3, and the compressive strength was measured based on JIS A1108 "compressive strength test method of concrete". The results are shown in Table 3. The ratio of the compressive strength is shown in FIG.
Instead of aluminum sulfate anhydride, aluminum sulfate 14-18 hydrate is dissolved in kneaded water, and the total of cement and aluminum sulfate 14-18 hydrate is 100. Aluminum sulfate 14-18 hydrate When 1.0% by mass of K was added and the concrete was kneaded, the concrete was in a crumbly state and could not be kneaded.

(2) Test at an environmental temperature of 10 ° C. (Examples 3 and 4, Comparative Examples 2 and 3)
When the sum of cement and aluminum sulfate anhydride is 100, aluminum sulfate anhydride is 0.0 mass% (no additive), 1.0 mass%, 1.8 mass%, and 2.5 mass% concrete, respectively. 1 was added to the temperature history of pattern B shown in FIG. 1 (after the pre-curing was completed, the concrete was placed in a curing device set at 40 ° C. and cured at 70 ° C. The concrete temperature was 20 ° C. except that the concrete was taken out of the curing device and demolded immediately after finishing the process, and the concrete kneading and underwater curing were performed in an environment of 10 ° C. In the same manner as in the test, the compressive strength of the concrete specimen was measured. The results are shown in Table 3. The ratio of the compressive strength is shown in FIG.
Instead of aluminum sulfate anhydride, aluminum sulfate 14-18 hydrate is dissolved in kneaded water, and the total of cement and aluminum sulfate 14-18 hydrate is 100. Aluminum sulfate 14-18 hydrate When 1.0% by mass of K was added and the concrete was kneaded, the concrete was in a crumbly state and could not be kneaded.

3. Test results As shown in Table 3 and FIG. 2, the compressive strength of Examples 1 to 4 in which the addition amount of aluminum sulfate anhydride is in the range of 0.5 to 1.8% by mass is obtained by adding aluminum sulfate anhydride. Compared to the compressive strengths of Comparative Examples 1 and 2 that are not present, it is high at all ages.
In particular, even when pattern B steam curing in which the cycle time from molding to demolding is shortened to 5 hours is performed, as the age of the material increases, as the compression strength ratio in FIG. The strength development property of the concrete to which the material is added increases, and in particular, the elongation of compressive strength is remarkable after the age of 91 days. On the other hand, in Comparative Example 3 in which the amount of aluminum sulfate anhydride added was 2.5% by mass, as shown in Table 3, no increase in compressive strength was observed after the age of 28 days.
Moreover, about the fresh property of the concrete of Examples 1-4, since the substantially same slump is obtained with the addition amount of the water reducing agent substantially the same as Comparative Examples 1 and 2, without using a retarder, the formwork of concrete Can be easily placed and compacted.

Claims (2)

When the total amount of aluminum sulfate anhydride and cement 100 mass%, was added solid 0.5 to 2.0 mass% of aluminum sulfate anhydride (where gypsum is not added.) Concrete 10 ° C. or less A concrete production method in which after kneading and molding at an environmental temperature of 1, a pre-curing is performed at an environmental temperature of 10 ° C. or less, and after the pre-curing is completed, steam curing is performed to produce concrete. The method for producing concrete according to claim 1 , wherein the time from molding the concrete to steam curing and demolding is less than 15 hours.

Images