JPH0430464B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention is applicable to concrete structures installed in coastal areas, concrete structures installed in the ocean, reinforced concrete structures exposed to sea salt particles and seawater spray, and concrete bridges. This article relates to seawater-resistant reinforcing bars that are used in such applications and have dramatically superior anti-deterioration properties. (Prior art) Recently, cracking and deterioration of reinforced concrete buildings using sea sand, concrete buildings installed in coastal areas, and concrete bridges has become a problem in various fields, and various prevention methods have been proposed. , has been put into practice. The biggest cause of this concrete deterioration is that the reinforcing bars embedded in the concrete corrode due to salt contained in sea sand and sea salt particles that permeate concrete walls in seashore areas and the ocean. ,
As its volume increases by approximately 2.2 times, it becomes unable to withstand the expansion force and cracks occur in the concrete along the buried reinforcing bars. If the crack is 0.2 mm or more, external corrosion factors such as oxygen, salt, and carbon dioxide gas in the air will more easily penetrate through the crack to the area around the buried reinforcing steel, further promoting corrosion of the reinforcing steel and causing concrete damage. This will accelerate the carbonation of concrete and accelerate the deterioration of concrete. In order to prevent such deterioration of concrete, the present inventors conducted research to improve the salt resistance of the reinforcing bars themselves by controlling the chemical composition of the reinforcing bars themselves, and as a result of their research, they developed reinforcing bars for concrete with significantly improved salt resistance. (Unexamined Japanese Patent Publication No. 57-48054, Unexamined Japanese Patent Publication No. 59-44457
The contents have already been published in various other areas. (“OFFSHORE GOTEBORG'81“Paper No.
42Goteborg SWEDEN 1981, “Cement Concrete” No.434 (1983) P.23/31, “Corrosion of Reinforcement
Reinforcement in Concrete Construction)”
P.419 1983, “Architectural Technology and Construction” 1985 No.229 January issue P155/164, Shokokusha). In addition, the salt resistance mechanism of the steel components of reinforcing bars at an early stage, which contributes to improving the salt resistance of reinforcing bars themselves, is also described in detail in these published papers. (Problems to be Solved by the Invention) The present invention focuses on the development of conventional salt-resistant concrete reinforcing bars, and aims to eliminate free chlorine from sea salt particles and seawater splashes that penetrate concrete walls, which has recently become a particular problem. The purpose is to prevent the corrosion of reinforcing bars due to salt present in ^- conditions, and the accompanying cracking and deterioration of concrete. Free salt near the buried reinforcing bars of concrete structures that are more than 10 years old, which is currently a problem in various fields, can reach up to 1.0% in terms of NaCl in the harsh marine environment, leading to severe corrosion of the reinforcing bars and the resulting cracks in the concrete. It is causing growth. Therefore, it is desirable to completely stop the corrosion of buried reinforcing steel bars even with such high concentrations of salt, and to stop the occurrence of cracks in concrete. (Means for Solving the Problems) The above object of the present invention is achieved by providing a reinforcing steel bar having the following configuration. (1) C: 1.0% or less, Si: 0.25% or less, Mn: 2.0%
Below, Al: 7.0 to 20.0%, P: 0.015% or less,
Contains S: 0.005% or less, Cr: more than 0.5 to 5.5%,
Seawater-resistant reinforcing steel bar consisting of residual iron and unavoidable impurities. (2) C: 1.0% or less, Si: 0.25% or less, Mn: 2.0%
Below, Al: 7.0 to 20.0%, P: 0.015% or less,
S; 0.005% or less, Cr; more than 0.5 to 5.5%, and
A seawater-resistant reinforcing steel bar containing 0.01 to 0.5% of Ti and Nb, either alone or in combination, with the remainder being iron and unavoidable impurities. The biggest feature of the present invention is that the steel contains 7.0 to 20.0% Al.
The purpose is to contain a large amount of salt to form a strong passive film on the buried reinforcing bars in concrete that are exposed to high concentrations of salt, almost eliminating rusting and completely preventing concrete deterioration. . That is, unlike conventional inventions, the idea is not to suppress the growth of rust, but rather to eliminate or suppress the generation of rust even in the presence of high concentrations of salt as described above. The cause of this is currently under investigation and is not clear, but it is believed that Al ³⁺ dissolved from the alloy of the present invention reacts with Cl ^- and is generated.
It is presumed that AlCl ₃ reacts with OH ^- in water and immediately changes to extremely stable Al(OH) ₃ , which grows and blocks corrosion factors. This thing is
This is also evidenced by the fact that the surface potential of reinforcing steel in an aqueous solution of Ca(OH) ₂ at PH12 containing 3.6% NaCl rapidly shifts toward you as days pass. The reasons for limiting each component in the present invention will be explained below. The reason for limiting the C content to 1.0% or less is that the C content is 1.0%.
This is because exceeding this value causes embrittlement. The lower the C content, the better, and preferably 0.1% or less. The reason why the Mn content is limited to 2.0% or less is that exceeding 2.0% causes embrittlement, so the preferred range is
It is 0.8% or less. More preferably, it is 0.3% or less. The reason why the amount of Si is set to 0.25% or less is that if the amount of Si exceeds 0.25%, graphitization of cementite in the steel is significantly promoted and workability is deteriorated. In general, the lower the amount of Si, the less rust will occur, so a lower amount of Si is desirable. The most desirable range is a Si content of less than 0.05%. Al is an important element that holds the key to the present invention, and is particularly effective in suppressing rust formation even at extremely high concentrations of salt. This effect cannot be expected when the Al content is less than 7.0%, and when it exceeds 20.0%, it is not only economically disadvantageous but also may generate intermetallic compounds and become brittle. The most preferable range is an Al content of 8.0% or more and 18% or less. The reason why P is set to be 0.015% or less is that P exceeding 0.015% has no effect of suppressing rust formation in an alkaline atmosphere such as concrete, but rather tends to accelerate it. The reason why the Cr content is set to exceed 0.5% is that hot rolling performance improves when the Al content is 7.0% or more.
If it exceeded 5.5%, embrittlement was observed in some cases, so the Cr content was set at more than 0.5% to 5.5%. The most preferred range is 0.7-2.0%. The reason for limiting the amount of S to 0.005% or less is to reduce the amount of MnS, which is the source of rust. The effect of improving corrosion resistance by changing to Ca)S, etc. can also be expected. In addition, it is common knowledge to carry out the operations described above to reduce the amount of S in steel, so a small amount of Ca, Ce, etc. may be mixed in, but these elements have no effect on corrosion resistance. Since it does not have any adverse effects, there is no problem in mixing it in the same amount as added for desulfurization. In the present invention, in addition to the above basic components, Ti and Nb are used alone or in combination to
By containing it in the range of ~0.5%, properties such as strength of reinforcing bars can be improved. In particular, when a large amount of Al is contained as in the present invention, it is advantageous to convert C, whose solid solubility decreases, into carbide. In addition, the corrosion resistance of the steel of the present invention against salt and the performance of preventing cracking and deterioration of concrete are as follows:
Since V, W, Co, and Mo added as trace components are well maintained by the basic component system mentioned above,
does not have any negative effects, so its presence at 0.5% or less is acceptable. According to the present invention, the steel composed of the above chemical components is melted in a converter, electric furnace, etc., and then undergoes the steps of ingot making and blooming, or after continuous casting and rolling, if necessary. It is subjected to heat treatment such as patenting and used as drawn reinforcing steel. Further, galvanizing and organic coating can be applied as necessary. (Examples) Example 1 Steel with the components listed in Table 1 was melted in a vacuum melting furnace, and the components and corrosion test results of reinforcing bars made of ingots, bloomed and drawn, and reinforcing bars made of conventional steel are shown. Width 25mm x length 60mm x from the center of the prepared reinforcing bar
A specimen with a thickness of 2 mm was taken, and the surface was polished by mechanical grinding. On the other hand, CaO, the main component of concrete, is 3.6
% Ca(OH) ₂ + dissolved in NaCl aqueous solution with pH 12
A NaCl aqueous solution was prepared. Thereafter, the surface of the sample was ground as described above, and the side and back surfaces were coated with silicone resin. The sample was degreased, dried, and immediately immersed in the above Ca(OH) ₂ +NaCl aqueous solution. During the test, the surface of the liquid was sealed with liquid paraffin, the liquid was replaced every 3 days, and the samples were immersed continuously for 20 days to observe the occurrence of rust. (A) in the table shows the area where rust occurs (%), and (B) in the table shows the depth of local corrosion in mm. Example 2 Hot-rolled reinforcing bars (9 mmφ) made of the ingredients shown in Table 1 were embedded in a concrete mortar made of sand containing 1.0% NaCl, Portland cement, water, and gravel, and after curing at room temperature for 28 days, they were exposed to a seashore area for 1 year. did. The water-cement ratio of the concrete was 0.60, and the fog thickness was 2 cm. After one year of exposure, the concrete was crushed and the rusting status of the reinforcing bars was investigated. The results are shown in (C) in Table 1. From (A), (B), and (C) in Table 1, the reinforcing bars of the present invention have a high concentration of salt in the concrete of 1.0% in terms of NaCl in sand.
It was clearly observed that no rust occurred even in water at a high concentration of 3.6% NaCl, and it was found that the deterioration of concrete caused by rust occurrence and rust growth could be completely stopped. Therefore, it is presumed that deterioration of concrete is completely suppressed even in extremely harsh marine environments. Example 3 Tensile test pieces were prepared from hot-rolled steel sheets having the components shown in Table 2, and a tensile test was conducted according to the method specified in JIS Z 2241. The results are shown in Table 2.

【table】

【table】

[Table] (Effects of the invention) The present invention is useful as a groundbreakingly effective concrete reinforcing bar to maintain the durability of concrete structures exposed to salt damage and seawater spray, which will become increasingly problematic in the future. be. By using the seawater-resistant reinforcing steel bar of the present invention, it is possible to extend the lifespan and improve the stability of concrete structures, and it can be used for various purposes.

Claims (1)

[Claims] 1 C: 1.0% or less, Si: 0.25% or less, Mn: 2.0%
Below, Al; 7.0 to 20.0%, P; 0.015% or less, S;
A seawater-resistant reinforcing steel bar containing 0.005% or less, Cr; more than 0.5 to 5.5%, and the balance consisting of iron and inevitable impurities. 2 C: 1.0% or less, Si: 0.25% or less, Mn: 2.0%
Below, Al; 7.0 to 20.0%, P; 0.015% or less, S;
0.005% or less, Cr; more than 0.5 to 5.5%, plus Ti, Nb
A seawater-resistant reinforcing steel bar containing 0.01 to 0.5% of either alone or in combination, with the balance consisting of iron and unavoidable impurities.