JPH0455350A - Reinforced concrete - Google Patents

Abstract

PURPOSE:To enhance the adhesive strength of reinforcing bars to concrete and the strength of reinforced concrete by embedding the reinforcing bars in fresh concrete contg. cement, fine aggregate and fly ash of a specified particle size. CONSTITUTION:Fly ash discharged at the time of burning coal is classified without crushing to obtain fly ash of <=20mum particle size. This fly ash, cement and fine aggregate are kneaded with water and reinforcing bars are embedded in the resulting fresh concrete.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention embeds reinforcing bars inside. Regarding so-called reinforced concrete.

(Prior Art) In order to improve the strength of reinforced concrete, it is necessary to increase the strength of the concrete itself and at the same time to increase the adhesion between the concrete and the reinforcing bars.

From this point of view, as a technique to increase the adhesion between reinforcing bars and concrete, ribs and uneven shapes are formed on the surface of reinforcing bars. By using so-called imitation steel bars as reinforcing bars, it is possible to improve adhesion by increasing the contact area between the reinforcing bars and concrete.

(Problem to be Solved by the Invention) By the way, even when such a deformed steel bar is used as a reinforcing bar, if you look at the surface of the reinforcing bar microscopically, there are extremely small surface irregularities, and the reinforcing bar is A gap exists between the surface of the recess formed on the surface of the concrete and the concrete, and it is thought that the adhesive force between the reinforcing bars and the concrete is caused by the limited contact area between the two.

This invention was made based on this point of view, and by increasing the contact area between the reinforcing bars and concrete while maintaining the conventional adhesion between the cement and the reinforcing bar surface, the bond between the reinforcing bars and the concrete is improved. The purpose is to provide reinforced concrete with high strength by increasing the overall adhesion of the concrete.

(Means for Solving the Problem) In order to achieve this object, the invention according to claim 1 provides concrete containing cement and fine aggregate, in which reinforcing bars are buried in the concrete, The fly ash emitted during combustion is processed without being crushed.
The concrete is classified as it is to have a particle size of 20 μm or less, and the fine particles obtained by this classification are added to the concrete.

(Function) According to the invention described in claim 1, the fly ash added to the concrete fits into the microscopic recesses formed on the surface of the reinforcing bar, thereby reducing the contact area between the reinforcing bar surface and concrete. Since it is possible to enlarge
The adhesion between the two can be improved.

This fly ash is made from fly ash discharged during coal combustion, without being crushed.
The fine particles obtained through this classification are classified by particle size of μm or less, so they do not prevent contact between the cement particles and the reinforcing steel surface.
, and because it is spherical, it easily fits into the gap between the surface of the reinforcing bar and the cement grains, effectively increasing the contact area between the two.

Furthermore, since this fly ash is pozzolan,
As it hardens, it adheres to the surface of the reinforcing bars, ensuring reliable adhesion between the surface of the reinforcing bars and concrete.

In this way, the conventional adhesion between cement grains and the reinforcing bar surface between reinforcing bars and concrete is not hindered, and at the same time, the contact area is expanded to ensure reliable adhesion, which improves the overall relationship between the two. Adhesion can be increased.

(Example) Examples will be described below.

First, a steel material (hereinafter referred to as reinforcing bar 1) used as a reinforcing bar in this example had ribs 2a and 2b integrally formed on its circumferential surface as shown in FIG.

It is a so-called deformed steel bar, which conforms to JIS G3112, is made of 5D35, and is called 016.

On the surface of this reinforcing bar 1, the aforementioned ribs 2a and 2b are formed at appropriate intervals from a macroscopic perspective, but from a microscopic perspective, for example, on the order of several tens of itm, there are countless unevenness vertically and horizontally. is formed.

Among these innumerable irregularities, it is the recesses formed on the surface of the reinforcing bar 1 that are considered problematic in this application.

These minute recesses are usually recognized as grooves with a triangular cross section (hereinafter referred to as ■groove 3), and the angles formed by both side surfaces in the cross section (hereinafter referred to as included angles) have various values. There is.

The concrete 4 in which the reinforcing bars 1 are buried is constructed as follows.

In other words, the mixing conditions for concrete 4 are as shown in the table below:
As per 1.

Table, 1 Ice binding material ratio 50% Fly ash mixing rate 15% Slump 12cm Air volume 4% The composition of this concrete 4 is the same as the above-mentioned coating.

Under the conditions of 1, the compositions shown in Table 2 below were obtained.

Table 2 (hereinafter referred to as margin) Table 2 shows FA20. as an example of the present application. F.A.
The compositions of three types of concrete, IO and FA5, are shown, and at the same time, the compositions of two types of concrete, no FA and unclassified FA, are shown as comparative examples.

The above table also applies to these comparative examples.

The formulation conditions of 1 are complied with.

The cement shown in Table 2 is ordinary Portland cement, and the average particle size of the cement is approximately 2.
It is about 5 μm.

Sand (average particle size 2.7+am) is used as the fine aggregate, and gravel (average particle size 6.8 mm) is used as the coarse aggregate.

As the AE water reducing agent, for example, "Hozolith No70 (trade name)" manufactured by Nisso Master Builders Co., Ltd. is used, and an AE agent (for example, trade name AE-775 manufactured by Nisso Master Builders Co., Ltd.) is used. Used as appropriate to adjust conditions.

Fly ash is collected from the flue gas of coal boilers, etc. using means such as an electrostatic precipitator, and in these Examples and Comparative Examples, the fly ash obtained in this way was used without being crushed. ing.

In the case of non-classified FA as a comparative example, the primordium collected in this way was added as is, and the particle size distribution of the primordium was as shown in Figure 5, and The average particle size is approximately 20 μm.

As is clear from FIG. 5, the original particle size distribution of fly ash (shown by the white bars in FIG. 5) is also shown by the black bars. The particle size distribution is almost the same as that of the cement.

Furthermore, FA20. as an example of the present application. FAIO,F
In the case of A5, the primordial material collected with the electrostatic precipitator as described above is classified into predetermined particle sizes using a classifier, and only the fine particles (hereinafter referred to as classified fly ash) are added.

Each classified fly ash is basically spherical particles having a predetermined particle size or less.

In the case of FA20, the fly ash to be added is the fine-grained fly ash that is classified with a particle size of 20 μm, and is added as a compounding component of concrete, and in the case of FAIO, the fly ash is classified with a particle size of 10 μm. In the case of FA5, classified fly ash classified to have a particle size of 5 μm is added as a compounding component of concrete.

The average particle size of each classified fly ash is FA2
0 is approximately 7 μm, FAIO is approximately 3.5 μm, FA5 is approximately 2 μm,
Their particle size distributions are shown in FIGS. 4(a) to (C).

In these graphs, the particle size distribution of cement is also shown as a black bar graph for convenience of comparison with cement.

In addition, in Tables 2 and 2 above and the following, concrete materials to which the above-mentioned classified ply ash has been added are FA20. It is written as FAIO or FA5.

When concrete 4 having such a composition is mixed and reinforcing bars 1 are buried, the result is as shown in FIG. 1.

This Il! FIG. 1 shows a boundary tissue model with the surface of the reinforcing bar 1 in the case of FA20.

In the case of FAIO or FA5, the boundary structure between the reinforcing bar 1 and the surface is basically the same, but as the particle size of the classified fly ash added becomes smaller,
Since the space formed between the concrete 4 and the surface of the reinforcing bars 1 becomes geometrically smaller, the adhesion between the concrete 4 and the surface of the reinforcing bars 1 is further improved as described later (see Table 3). ).

Figure 141 shows the microscopic ■ formed on the surface of reinforcing bar 1.
This shows a case where the included angle of the groove 3 is relatively large, and fine aggregate or coarse aggregate whose grain size is geometrically larger than that of the groove 3 cannot be located in the groove 3, and as a result, Only the cement grains 5 and the classified ply ash grains 6, which are smaller than the grooves 3, are filled in the grooves 3.

゛That is, in the case of FA20 as an example of the present application, (1) cement grains 5 are sparsely arranged in the groove 3 as in the past, and at the same time, cement grains 5 are formed between the cement grains 5 and the V-groove 3. The gap is filled with classified fly ash 6 having a spherical shape and a diameter smaller than that of the cement grains 5, and furthermore, the gap formed between the classified fly ash 6 and the groove 3 is filled with classified fly ash 6 having a smaller diameter. Since the cement particles 4 and classified fly ash 6 are filled, there is a large contact surface between the concrete 4 formed by hardening and the V-groove 3 on the surface of the reinforcing bar 1.

As described above, these classified fly ash 6 have a smaller particle size than the cement particles 5, so they prevent the cement particles 5 from coming into contact with the surface of the reinforcing bars 1. The adhesion takes place between the surface of the

Further, since these classified fly ash 6 are also pozzolan, the concrete 4 reliably adheres to the surface within the grooves 3 of the reinforcing bars 1, and the adhesion between the concrete 4 and the reinforcing bars 1 is improved.

In contrast, in the conventional case, only the cement grains 4 in FIG.
Cement grains 4 with large grain sizes are only sparsely arranged and adhered inside, and the concrete 4 on the surface of the reinforcing bars 1.
It is clear that the adhesion force is smaller than that of the present invention.

Moreover, when the included angle of the groove 3 is small, it is as shown in FIG.

In other words, conventionally, in this case, as shown in FIG. 3(a), cement grains 4 with an average grain size of 25 μm are
A large gap is formed between the groove bottom and the groove bottom, resulting in a large portion that does not contribute to the adhesion force to the reinforcing bar 1.

Since there are many such grooves 3 on the surface of the reinforcing bar 1, in the conventional case, the contact surface is small and the adhesion force is considered to be limited from this point of view.

On the other hand, in the case of this embodiment, as shown in FIG. 3(b),
Classified fly ash 6 with a smaller diameter than cement grains 5 is added, and also contains fine particles due to classification, so these classified fly ash 6 can enter into the V-groove 3, which was not possible in the past. Even in these V-grooves 3 which could not generate adhesive force, the classified fly ash 6 makes it possible to generate adhesive force.

Recognizing the mechanism of strengthening the adhesion of the classified ply ash 6 to the reinforcing bars 1, the reinforcing bars 1 were buried in each of the concretes 4 listed in Table 2 and hardened, and the pull-out force was measured. The adhesion force of No. 4 to reinforcing bar No. 1 was measured.

Note that fly ash is a pozzolan and requires a long period of time to completely harden, so for convenience of the test, it was decided to measure it at the stage of 28 days after concrete was placed.

In this respect, for example, "New System of Civil Engineering 28 Concrete Materials" published by Gihodo Publishing Co., Ltd. and edited by Japan Society of Civil Engineers
It is considered to be appropriate for measurement as specified in Figure 6 and shown in Figure 6.

In other words, Figure 6 shows the general relationship between the replacement rate of the cement content of concrete with fly ash and the compressive strength of concrete. is expressed as 100.

Graphs A, B, C, and D in FIG. 6 each show the change in compressive strength depending on the replacement rate at a predetermined age, where A is for age 28EI, and B is for age 91E.

C indicates the compressive strength at the age of 6 months, and D indicates the compressive strength at the age of 1 year.

From the development of compressive strength shown in Fig. 6, in the case of the above-mentioned example, the replacement rate of cement with fly ash is 15% (position of the broken line in Fig. 6), so the material age is 28%. The strength in 1 day is 95% of the strength of concrete using only cement and no replacement with fly ash.
%, it can be predicted that the compressive strength at one year of age will be approximately 20% higher than that without replacement.

Therefore, from this point of view, it is considered that there is no problem in determining that the final adhesion strength will be significantly increased if the materials are approximately the same at the age of 28 days.

(Hereafter, blank space) Table 3 As is clear from the measurement results shown in Table 3, FA20. In the case of FAIO and FA5, the adhesion to reinforcing bars is almost the same or better than that obtained without adding fly ash to cement (no FA).

Therefore, considering the increase in adhesion due to pozzolan, it can be judged that the adhesion to reinforcing bars is significantly improved compared to the case without FA.

In addition, in the case of concrete with unclassified fly ash added (unclassified FA), the material age is 28 compared to FA20.
The adhesion force with the reinforcing steel is significantly inferior.

This is because the particle size distribution of the fly ash is almost the same as that of the cement grains 5 as shown in Fig. 5, and the fly ash grains added for 1,000 yen prevent the cement grains 5 from adhering to the reinforcing bars as before. Moreover, since the particle size of fly ash is large, it is considered that the above-mentioned adhesion mechanism with the reinforcing bars according to the present application cannot be expected.

In the embodiments described above, the reinforcing bar is explained using a different diameter steel bar, but the present invention is not limited to this, and the present invention can be similarly implemented using other reinforcing bars such as round steel.

In addition, even if the mixing conditions and composition of the concrete or the use of additives such as admixtures are appropriate, the adhesion of the concrete to the reinforcing bars can be improved by carrying out the same procedure as in the above example. Needless to say, it can be improved.

(Effects of the Invention) As explained above, according to the invention as set forth in claim 1, the fly ash added to the concrete fits into the microscopic recesses formed on the surface of the reinforcing bars. Since the contact area between the reinforcing steel surface and the concrete can be expanded, the adhesion between the two can be improved.

This fly ash is made from fly ash discharged during coal combustion, without being crushed.
The fine particles obtained through this classification are classified by particle size of μm or less, so they do not prevent contact between the cement particles and the reinforcing steel surface.
, and because it is spherical, it easily fits into the gap between the surface of the reinforcing bar and the cement grains, effectively increasing the contact area between the two.

Furthermore, since this fly ash is pozzolan,
As it hardens, it adheres to the surface of the reinforcing bars, ensuring reliable adhesion between the surface of the reinforcing bars and concrete.

In this way, the conventional adhesion between cement grains and the reinforcing bar surface between reinforcing bars and concrete is not hindered, and at the same time, the contact area is expanded to ensure reliable adhesion, which improves the overall relationship between the two. Adhesion can be increased.

[Brief explanation of drawings]

An explanatory diagram of the adhesion structure between the reinforcing steel surface and concrete,
Figure 2 is a perspective view of the reinforcing bars used in the example, and Figure 3 is an illustration of the micro recesses on the surface of the reinforcing bars. The explanatory diagram, FIG. 4, is a particle size distribution diagram of the classified fly ash used in this invention, and (a) is for FA20;
(b) shows the case of FAIO, (C) shows the case of FA5, Figure 5 is a particle size distribution diagram of fly ash collected without classification, and Figure 6 shows the cement in concrete using fly ash. FIG. 3 is an explanatory diagram of how strength develops when replaced. Reinforcing bars, 3; ■Grooves, concrete, cement grains, fly ash grains.

Claims (3)

[Claims] (1) In concrete containing cement and fine aggregate, in which reinforcing bars are buried in the concrete, fly ash discharged during coal combustion is classified into particles with a particle size of 20 μm or less without being crushed. A reinforced concrete characterized in that the fine particles obtained by this classification are added to the concrete. (2) The reinforced concrete according to claim 1, wherein the fly ash to be added is classified according to a particle size of 10 μm or less. (3) The reinforced concrete according to claim 1, wherein the fly ash to be added is classified according to a particle size of 5 μm or less.