JPS6310228B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is applicable to concrete structures installed in seaside areas, concrete structures installed in the ocean, etc.
This invention relates to salt-resistant reinforcing bars that are extremely effective in preventing deterioration of reinforced concrete structures, concrete bridges, etc. that are exposed to sea salt particles and seawater spray. (Prior art) Recently, reinforced concrete buildings using sea sand, concrete buildings installed in seaside areas,
Cracking and deterioration of concrete bridges has become a problem in various fields, and various prevention methods have been proposed and put into practice. The biggest cause of this concrete deterioration is that the reinforcing bars embedded in the concrete corrode due to the salt contained in the sea sand and the salt from the sea salt particles that permeate through the concrete walls in beach areas, causing the volume to decrease. about
Since the expansion force increases by 2.2 times, the concrete along the buried reinforcing bars can no longer withstand the expansion force and cracks occur. If the crack is 0.2 mm or more, external corrosion factors such as oxygen, salt, and carbon dioxide 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 damaging the concrete. This will promote carbonation and accelerate the deterioration of concrete. In order to prevent such concrete deterioration, the present inventors controlled the chemical composition of the reinforcing bars themselves,
Research was conducted to improve the salt resistance of reinforcing bars themselves by adding 1 to 5.5% Ni, and the result was a reinforcing bar for concrete that had significantly improved salt resistance (Japanese Patent Application Laid-Open No. 57-48054, JP-A-59 -44457), and these 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 Rein forcement in Concrete
Construction” P. 419, 1983, “Architectural Technology and Construction” 1985 No. 229, January issue, P. 155/164, Shokokusha). Also, in the early stages of the steel composition of reinforcing bars, which contributes to improving the salt resistance of the reinforcing bars themselves. The salt resistance mechanism of the present invention is also described in detail in these published papers, and is currently being put into practical use. (Problems to be solved by the invention) The present invention Recently, with the development of chloride, corrosion of reinforcing bars due to salt existing in a free Cl state such as sea salt particles and sea water spray that permeate concrete walls and cracks in concrete have become a particular problem. The goal is to almost completely stop the generation of salt.The free salt content near the buried reinforcing bars in concrete structures that are more than 10 years old, which is currently a problem in various fields, reaches 0.15 to 0.25% in terms of NaCl. This causes severe corrosion of reinforcing bars and the accompanying cracking and growth of concrete.In addition, free salt content is 0.25% in terms of NaCl in concrete that has been used for nearly 30 years.
There are extreme cases in which the amount exceeds . Therefore, cracking in concrete can be almost completely stopped with a free salt content of 0.25%;
It is desirable to significantly retard cracking in concrete even at high concentrations of salt exceeding %. (Means for Solving the Problems) The above-mentioned object of the present invention is to provide C: 0.01 to 0.01 in weight%.
1.0%, Mn: 0.05-1.0%, Si: 0.05% or less, P:
Less than 0.015%, S: less than 0.005%, Ni: 1.0 to 4.5%,
This is achieved by a concrete reinforcing bar characterized by having W: 0.001% to less than 0.2%, Al: 0.01% to 0.07%, and the balance being iron and unavoidable impurities. The greatest feature of the present invention is that it lowers the amount of Si and S in the steel, and improves the salt resistance effect by adding Ni and W.
This prevents the deterioration of concrete exposed to high concentrations of salt. The reason for this is that by lowering the amount of Si,
At the same time, it suppresses the formation and growth of rust, and even after rust has progressed considerably on the surface of reinforcing bars buried in concrete exposed to high concentrations of free salt, Si is hardly concentrated in the rust layer and Ni is concentrated. Since W transferred from the reinforcing bars themselves is evenly present in the rust layer, it is presumed that even a small amount of W effectively suppresses rust growth. In addition, the significant decrease in the amount of S is due to the decrease in the amount of MnS, which is the point where rust occurs.
It is thought that corrosion resistance will be dramatically improved. The reason why each component is limited in the present invention will be explained below. The reason for limiting the amount of C to 0.01 to 1.0% is that the amount of C
If the C content is less than 0.01%, the required strength cannot be obtained, and the C content is 1.0%.
This is because excessively high temperatures cause embrittlement. Further, the reason why the Mn content is limited to 0.05 to 1.0% is that if the Mn content is less than 0.05%, the necessary strength cannot be obtained, and if it exceeds 1.0%, embrittlement will occur. The reason why the amount of Si is set to 0.05% or less is that the lower the amount of Si, the more the amount of rust generated will be dramatically reduced, and the more evenly distributed W in the rust layer,
This is to bring about the effect of reducing Fe ³⁺ in the rust layer consisting of Fe ₂ O ₃ and Fe ₃ O ₄ to Fe ²⁺ and suppress the formation of the rust layer. Ni is an important element that holds the key to the present invention. In particular, when rusting of reinforcing bars progresses due to high concentrations of salt, Ni concentrates in the rust layer and significantly suppresses the growth of the rust layer. This effect cannot be expected when the Ni content is less than 1.0%, and there is no change in the effect when the Ni content exceeds 4.5%.
Therefore, the lower limit was set at 1.0% and the upper limit was set at 4.5%. W is also an important element in the present invention. The uniform presence of W originating from the reinforcing steel itself in the rust layer retards the growth of the rust layer by changing Fe ³⁺ of Fe ₂ O ₃ and Fe ₃ O ₄ in the rust layer to Fe ²⁺ . This effect is W
It is noticeable even in minute amounts exceeding 0.001%, and its coexistence with Ni has the effect of significantly suppressing the growth of the rust layer. This effect cannot be expected when the W content is less than 0.001%, and the effect remains unchanged when the W content is 0.2% or more. Therefore, the range was set to 0.001% to less than 0.2%. The reason why P is set to be less than 0.015% is that P of 0.015% or more has no effect of suppressing rust growth in an alkaline atmosphere such as concrete, but rather tends to promote it. The reason for limiting Al to 0.01 to 0.07% is that if Al is less than 0.01%, the oxygen present in the steel cannot be fixed as a stable Al oxide.
If the content is too high, large inclusions will form and cause embrittlement of the steel, so the composition was limited to the above range in terms of the amount and strength necessary for the deoxidizing effect. The reason for limiting the amount of S to less than 0.005% is to reduce the amount of MnS, which is the source of rust.
MnS becomes (Mn, Ca)S due to compounds and rare earth elements.
It is also possible to expect the effect of improving corrosion resistance by changing to In addition, it is common knowledge to carry out the operations described above in order to reduce the amount of S in steel.
Ca may be mixed in at an amount of 0.0002% or less, but these elements do not have a negative effect on corrosion resistance, so Ca is not specified. In addition, Nb and V are added as necessary, but they are added as well-known elements to improve the strength and toughness of reinforcing bars, and they are added at 0.01 to 0.2% as a single type, but they are already commonly used for the above purposes. It is known. Further, if necessary, 0.01 to 0.3% Cu is added to improve weather resistance before being buried in concrete, but this purpose is already well known. According to the present invention, the steel composed of the above chemical components is melted in a converter, electric furnace, etc., and then passed through the steps of ingot making and blooming, or after continuous casting and rolling, if necessary, it is patented. It is subjected to heat treatments such as, etc., and then drawn into wire and used as reinforcing bars. Further, the surface may be galvanized or coated with an organic coating, if necessary. (Example) Steel having the composition range of the present invention was melted in a converter, and ingots were formed.
After blooming, the composition of drawn reinforcing bars, comparative steel reinforcing bars, and conventional electric furnace steel reinforcing bars, the deterioration status of the concrete in which these reinforcing bars are buried, and the changes over time in the corrosion status of the buried reinforcing bars are shown in the table. . The various reinforcing bars in the table are hot-rolled reinforcing bars with a diameter of 9 mm, the surface of which is mechanically polished, degreased, and buried in concrete mortar with a water-cement ratio of 0.60 and a total salt content in the sand of 1.0% in terms of NaCl, as shown in Figure 1. After curing for 28 days, the concrete specimen was placed in a constant temperature and humidity chamber, and was heated for 56 days in a cycle of 48 hrs wet, 24 hrs dry, 48 hrs wet, 48 hrs dry for 1 week (2 cycles). The occurrence of cracks in the concrete was observed after 70 days of exposure. The exposure conditions shown in Figure 2 were set to prevent corrosion of buried reinforcing bars under extremely harsh environmental conditions, including repeated wet and dry cycles at a high temperature of 80°C, where maximum oxygen is dissolved in water vapor. This is to promote At the same time, we investigated the changes over time in the depth of carbonation of these concrete specimens due to carbon dioxide gas in the air, and the changes over time in the amount of corrosion of the buried reinforcing bars. The maximum width of cracks in the concrete specimen was measured using a crack gauge. The depth of neutralization by carbon dioxide gas was determined by spraying a phenolphthalein solution on concrete and measuring the depth from the surface of the concrete specimen, which changed from red to colorless. The amount of corrosion of buried reinforcing bars can be determined by crushing the concrete, chemically removing rust from the reinforcing bars, weighing them, and subtracting the weight from the weight before corrosion to determine the length of the reinforcing bars.
It was calculated as corrosion loss per 28 cm. Also, reinforcing bar samples No. 1, No. 2, No. 3, and No. in this table.
4. After exposing the concrete specimens in which No. 5 was buried in the above-mentioned constant temperature and humidity chamber for 56 days and 70 days,
When the total salt content near the reinforcing bars and the free salt content extracted by cold water were chemically analyzed and calculated as NaCl (%) in sand, the total salt content was approximately 1.0%.
The free salt content was approximately 0.6%. Therefore, it was found that the reinforcing bars of the present invention have a significantly lower corrosion rate than conventional reinforcing bars, and significantly retard the deterioration of concrete, even if the free salt near the reinforcing bars reaches 0.6% in terms of sand. Therefore, it is estimated that even in a harsh environment where free salt content ultimately accumulates to 0.6% in sand, it is effective in inhibiting the deterioration of concrete. (Effects of the Invention) The present invention is useful as a groundbreakingly effective reinforcing bar for concrete in maintaining the durability of concrete structures exposed to salt damage, which will become an increasingly problematic problem in the future. By using the reinforcing bars for concrete of the present invention, it contributes to extending the lifespan and improving the stability of concrete structures, and can be used for various purposes. 【table】

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the shape, dimensions, and reinforcement arrangement of a concrete specimen in which reinforcing bars are embedded. Second
The figure shows the test conditions for a rust acceleration test on concrete specimens with embedded reinforcing bars.

Claims (1)

[Claims] 1% by weight: C: 0.01 to 1.0%, Si: 0.05% or less, Mn: 0.05 to 1.0%, P: less than 0.015%, S: less than 0.005%, Ni: 1.0 to 4.5%, W A reinforcing steel bar for preventing concrete deterioration, containing: 0.001% to less than 0.2%, Al: 0.01% to 0.07%, and the remainder consisting of iron and unavoidable impurities. 2 C: 0.01 to 1.0% by weight, Si: 0.05% or less, Mn: 0.05 to 1.0%, P: less than 0.015%, S: less than 0.005%, Ni: 1.0 to 4.5%, W: 0.001 to less than 0.2%. , Al: 0.01 to 0.07%, and further contains one of Nb and V at 0.01 to 0.2%, with the balance being iron and inevitable impurities, for preventing concrete deterioration. 3 C: 0.01 to 1.0% by weight, Si: 0.05% or less, Mn: 0.05 to 1.0%, P: less than 0.015%, S: less than 0.005%, Ni: 1.0 to 4.5%, W: 0.001 to less than 0.2%. , Al: 0.01 to 0.07%, and one of Nb and V 0.01 to 0.2%,
A reinforcing steel bar for preventing concrete deterioration that further contains 0.01 to 0.3% Cu, with the balance consisting of iron and unavoidable impurities.