JP2636067B2 - Corrosion-resistant PC steel bar with excellent adhesion - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a prestressed concrete structure (hereinafter referred to as PC) in which durability is emphasized due to exposure to severe environmental conditions.
Used for marine structures and harbor structures, or as suspension materials for cable-stayed bridges that require rust prevention during erection and use, and as lock anchors, earth anchors, etc. The present invention relates to a deformed PC steel rod which has been subjected to corrosion resistance treatment.

[Conventional technology]

 Techniques for improving the corrosion resistance of PC steel bars include: (1) Galvanizing the surface of PC steel bars.

(2) Apply grease to the surface of the PC steel bar, and coat the outside of the bar with a plastic such as polyethylene.

(3) A 200 ± 50 μm epoxy coating is applied to the surface of the PC steel bar in the same manner as the rebar.

And so on.

[Problems to be solved by the invention]

In the above method (1), the temperature at the time of plating molten zinc rises to about 400 ° C., so that the yield point strength of the steel rod decreases. In use, mortar is often filled around the steel rod, but zinc plating reacts with alkaline mortar at this time to generate hydrogen gas. For this reason, there is a concern that the hydrogen gas is absorbed by the steel rod or the fixing tool of the steel rod and the like, thereby embrittlement and destruction thereof.

Further, the method (2) is excellent in corrosion resistance, but has difficulty in adhesion. That is, the plastic coating is
(A) A sheath having an inner diameter larger than the outer diameter of the rib attaching portion of the steel rod is covered. (B) Coating is performed in such a manner that the surface shape of the steel rod appears. However, in the former case, there is no adhesive force between the mortar. Also, in the latter case, the coating applied along the surface of the steel bar does not adhere to the vicinity of the root of the rib, so that the adhesion is greatly reduced, and the range of use is limited.

On the other hand, in the method (3), an epoxy having a high corrosion resistance is used for the same 200 μm as in the case of the rebar in order to combine the adhesion and the corrosion resistance.
m and coated. However, with this film thickness, pinholes in the film cannot be eliminated. 200 μm is the average film thickness, and the current manufacturing technology has to admit an error of ± 50 μm, so pinholes may occur when the film thickness is reduced in this range. If this pinhole is present, it is conceivable that a corrosive liquid may enter through this hole, leading to corrosion of the steel material. The corrosion progresses slowly in a simple form with rebar, but with PC steel rods,
Since a tensile stress is applied during use, a stress corrosion cracking phenomenon may be caused and the material itself may be broken.

Regarding the adhesion, the maximum adhesion stress does not decrease, but the initial slip stress decreases by about 20%, which is disadvantageous as compared with a bare steel rod as a design value in use.

[Means for solving the problem]

According to the present invention, in order to solve the above-mentioned problems, as shown in FIG. 1, a plastic film 4 is formed on the surface of a deformed PC steel rod 2 by powder coating. The film has an average thickness
300μm or more, 1/3 or less of the height of the rib 3 on the surface of the steel rod,
Further, sand particles 5 having a particle size of 200 μm or less are embedded in the film. Reference numeral 1 denotes a corrosion-resistant PC steel bar of the present invention obtained in this manner.

 The material for forming the film 4 is preferably an epoxy resin.

[Action]

Films coated by powder coating are superior to films coated by other methods in terms of adhesion to steel, uniformity, and the like, and have the highest reliability regarding corrosion resistance.

In the present invention, in addition to utilizing the powder coating,
Since the average film thickness is set to 300 μm or more, no pinholes exist even if the variation in film thickness that can be manufactured is considered ± 70 μm.

In addition, since the sand particles are embedded in the coating, the maximum adhesive stress and initial slip stress are equivalent to bare PC steel bars.

Here, the upper limit of the film thickness is set to 1/3 or less of the height of the rib of the steel rod, because the larger the film thickness, the higher the cost and the lower the adhesion. That is, when the film thickness is larger than the above-mentioned upper limit, even if sand particles are buried in the film, the maximum adhesion stress and initial slip stress cannot be maintained at the same level as the bare PC steel rod.

If the particle size of the sand particles is larger than the film thickness, the sand particles may penetrate through the plastic film and be embedded. In this case, there is no resin between the surface of the film and the surface of the steel rod at the particle penetrating portion, and the sealing effect of the film cannot be obtained. It is for this reason that the particle size of the sand particles used is limited to 200 μm or less. That is, assuming that the average thickness of the film is 300 μm, which is the minimum, and the variation of the film thickness is ± 70 μm, the minimum thickness of the film is 230 μm, which is larger than the maximum particle size of the sand particles of 200 μm, and penetration of the sand particles does not occur.

In addition, epoxy is preferred as a material for forming a film for the following reasons. In other words, powder coating resins include polyester and polyethylene in addition to epoxy. Polyethylene is excellent in corrosion resistance, but is inferior in adhesion, and polyester is inferior in corrosion resistance.

〔Example〕

A deformed PC steel rod having a diameter of 26 mmφ and a cross section shown in FIG. 2 was prepared. On the outer periphery of this PC steel rod 2, a height a = 1.7 mm, a root width b = 6.5 mm, a radius r = 21.0 mm of a root cut-up surface,
Trapezoidal ribs 3 having a side surface inclination angle of 45 ° (α = 90 °) are provided at a pitch c = 12.7 mm.

The thickness of this deformed PC steel rod is 300 μm by powder coating method.
Epoxy coatings of 00 μm, 500 μm, 600 μm and 700 μm were applied. The maximum particle size of the sand particles to be embedded in the epoxy film was 200 μm, and the resin coated on the steel rod was sprayed and embedded (before it hardened) while relatively soft. Some of the sand particles in the coating include those that come into contact with the PC steel rod and those that are exposed or protrude at partial points on the coating surface.

The adhesion characteristics of the five test materials thus obtained were tested. The results are shown in FIGS. 3 and 4. The figure shows the rate of decrease when the maximum adhesive stress level when bare and the initial slip stress level are set to 1.

From these figures, it can be seen that the film thickness is 600 μm (6
/ 17> 1/3) or more, it can be seen that the initial slip stress starts to decrease first, and that when the film thickness further increases, the maximum adhesive stress also decreases.

〔effect〕

As described above, according to the present invention, the average thickness of the plastic coating formed by powder coating is set to 300 μm or more, and further, the granules for increasing the frictional force between the PC steel rod and the member in contact with the outer surface of the coating are formed in the coating. Since sand particles with a diameter of 200μm or less are buried, reliable initial corrosion resistance and maximum adhesion stress equivalent to bare PC steel rods can be secured, and highly reliable corrosion resistance can be imparted. Expansion and the improvement of the reliability and durability of PC structures.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a corrosion-resistant PC steel rod according to the present invention;
FIG. 2 is a diagram showing the surface shape of a PC steel bar used as a test material, and FIGS. 3 and 4 are graphs showing test results on the maximum adhesive stress and initial slip stress. 1 ... Corrosion-resistant PC steel rod, 2 ... PC steel rod, 3 ... Rib, 4 ... Plastic film, 5 ... Sand particles.

Claims (1)

(57) [Claims] 1. A deformed PC steel rod having a rib on the outer periphery,
It has a plastic coating by powder coating on its surface,
The average thickness of this film is 300 μm or more, and the height of the rib is 1
Corrosion-resistant PC steel bar with excellent adhesion, characterized in that sand particles having a particle size of 200 μm or less are embedded in the coating.