JP2745066B2 - Salt rebar for concrete deterioration prevention - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention relates to a concrete structure installed in a beach area,
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a salt-resistant rebar having a remarkably excellent effect of preventing deterioration of concrete structures installed in the ocean, such as reinforced concrete structures exposed to sea salt particles and seawater droplets, and concrete bridges.

(Prior art) Recently, reinforced concrete buildings using sea sand, concrete structures installed in beach areas, and cracks in concrete bridges have become a problem in various fields, and various prevention methods have been proposed. Have been put into practice.

The biggest cause of this concrete deterioration is the salt contained in sea sand and the salt of sea salt particles penetrating the concrete wall in the beach area corroding the reinforcing steel buried in concrete, and the volume of iron Since it becomes about 2.2 times, it cannot withstand the expansion force and cracks occur in the concrete along the buried rebar. When the crack becomes 0.2 mm or more, oxygen or salt, which is an external corrosion factor, and carbon dioxide gas in the air, penetrate through the crack more easily to the vicinity of the buried reinforcing steel inside, and further promote corrosion of the reinforcing steel, It promotes neutralization and hasten the deterioration of concrete.

The present inventors carried out research to control the chemical composition of the reinforcing bar itself and to improve the salt resistance of the reinforcing bar itself by adding a small amount of a special additive element in order to prevent such deterioration of concrete. As a result, a concrete reinforcing bar with excellent seawater resistance to which both Cu and W are added at the same time.
55-22546), and a reinforcing steel bar for concrete with significantly improved salt resistance (JP-A-57-48054 and JP-A-59-48054).
−44457), and these contents have already been published in other fields (“OFFSHORE GOTEBORG '81”).
Paper No.42 Goeteborg SWEDEN 1981, “Cement Concrete” No.434 (1983) P.23 / 31, “Corrosion of Re
inforcement in Concrete Construction "P.419,1983
Year, “Architectural Engineering Construction,” 1985 No.229 January, P155 / 164,
Shokokusha).

The published papers also describe in detail the mechanism of the salt resistance of the steel component of the reinforcing bar that contributes to the improvement of the salt resistance of the reinforcing bar itself, and its practical use is currently progressing.

(Problems to be Solved by the Invention) The present invention is based on the conventional development of the present inventors, and recently, free Cl such as sea salt particles and seawater droplets penetrating concrete walls, which has become a particular problem, has become a problem. ^The purpose is to almost completely stop the corrosion of the reinforcing steel by the salt existing in the state of-and the accompanying cracking of the concrete.

The free salt near buried reinforcing bars in concrete structures that have been a problem for more than 10 years now reaches 0.15% to 0.25% in NaCl conversion, causing significant corrosion of the reinforcing bars and accompanying cracking and growth of concrete. It's causing it.
Therefore, it is desirable that cracking of concrete can be almost completely stopped in the state of free salt content of 0.25%.

(Means for Solving the Problems) The object of the present invention is to provide C: 0.001 to 1.0%, Mn;
Less than 0.3%, Si: 0.01 to 0.05%, P: less than 0.025%, S: 0.005
%, Cu; 0.01 to 0.50%, W; 0.01 to 0.50%, Al; 0.001 to
0.10%, with the balance consisting of iron and unavoidable impurities, concrete reinforcing bars, and furthermore, concrete reinforcing bars in which Nb, V, Ti, and Mo are added to the above components as optional components. Achieved.

The greatest feature of the present invention is that the amount of Si and S in steel is extremely reduced, and the addition of Cu and W enhances the salt resistance effect and prevents the deterioration of concrete.

The reason for this is that by reducing the amount of Si, the formation and growth of rust are suppressed, and at the same time, the amount of WO ₄ ^- inhibitor, which is an iron corrosion inhibitor formed with the rusting of the reinforcing bar itself, is increased dramatically. In addition, it is presumed that the corrosion resistance is remarkably improved due to the remarkable decrease in the amount of MnS, which is a rust generation point, with the remarkable decrease in the S amount.

In addition, it is considered that the extreme decrease in Si and S is reinforced by Cu added to the passive film on the surface of buried reinforcing steel in an alkaline atmosphere of concrete.

 The reason for limiting each component in the present invention will be described below.

The reason for limiting the C content to 0.001 to 1.0% is that the C content is 0.001%
If the carbon content is less than 1.0%, the required strength cannot be obtained, and if the carbon content exceeds 1.0%, embrittlement is caused.

The reason for limiting the amount of Mn to 0.01 to less than 0.3% is that the amount of Mn is 0.0
If it is less than 1%, the required strength cannot be obtained, and if it is less than 0.3%, rust generation is significantly reduced.

The reason that the amount of Si is set to 0.01 to 0.05% is that the lower the amount of Si, the more drastically the amount of rust is reduced and the effective amount of WO ₄ ^- ions is drastically increased. Mn amount 0.
This is because when less than 3%, rust generation is significantly reduced.

The reason why P is set to less than 0.025% is that if P is 0.025% or more, there is no effect of suppressing rust growth in an alkaline atmosphere such as concrete, but rather it tends to promote.

The reason for limiting the Cu content to 0.01 to 0.5% is that if the Cu content is less than 0.01%, there is no effect on the reinforcement of the passive film on the rebar surface, and if it exceeds 0.5%, the steel becomes brittle. When a large amount of Cu is added, Ni is added in an amount of 0.03 to 0.03 in order to improve the peelability of the hot-rolled scale.
0.3% may be added.

The reason for limiting the 0.01~0.5% W WO ₄ is less than 0.01%
^- not observed production amount less corrosion resistant effect of the ions, 0.5
If it exceeds%, it is expensive in terms of economy.

The reason for limiting Al to 0.001% to 0.10% is that if Al is less than 0.001%, oxygen existing in steel cannot be fixed as a stable oxide of Al, and if Al exceeds 0.10%, large inclusions are formed and steel Since the material causes embrittlement, it is limited to the above component range in terms of the amount and strength required for the deoxidizing effect.

The reason why the amount of S is limited to less than 0.005% is to reduce the amount of MnS, which is a source of rust, due to the use of Ca compounds and rare earth elements used as desulfurizing agents to reduce the amount of S.
The effect of improving corrosion resistance by changing S to (Mn, Ca) S can also be expected. It is common practice to perform the above operations to reduce the amount of S in steel, so some Ca, Ce, etc. may be mixed in, but these elements may cause corrosion resistance and the like. Ca, Ce
The amount is not specified.

If necessary, Nb, V, Ti, and Mo are added, but are added as elements for improving the strength and toughness of the rebar, and one or two of them are added in a total amount of 0.01 to 0.5%. If it is less than 0.01%, the desired strength and toughness cannot be obtained, and if it exceeds 0.5%, large inclusions are formed, causing flaws.

According to the present invention, the steel composed of the above-mentioned chemical components is a converter,
It is melted in an electric furnace or the like and then passed through ingot making and lumping processes, or after continuous casting and rolling, is subjected to heat treatment such as patenting if necessary, and is drawn and used as a reinforcing bar. . Also, if necessary, galvanize the surface,
Organic coatings can also be applied.

(Example) The range of components and the steel of the present invention were melted in a converter, ingot-formed, lumped, and then drawn, the steel of the comparative steel, the components of the steel made of conventional electric furnace steel, and the components of these. The table below shows the deterioration of concrete with embedded reinforcement and the change over time of the corrosion of embedded reinforcement.

Various rebars in the table are 9mmφ hot rolled rebars, mechanically polished the surface, degreased, water / cement ratio 0.60, total salt content in sand NaC
The concrete specimen was buried in 0.50% concrete mortar in terms of l, and a concrete specimen as shown in Fig. 1 was prepared. After curing for 28 days, the concrete specimen was inserted into a thermo-hygrostat and wetted.
The concrete was exposed for 56, 70, 100, and 138 days with a cycle of 1 hour (2 cycles) for hr, dry 24 hr, wet 48 hr, and dry 48 hr. In FIG. 1, 1 is a concrete specimen, 2 is a buried reinforcing bar of 9 mmφ, 3 is a mortar-coated epoxy seal, and l is a cover thickness.

The exposure conditions were set as shown in Fig. 2 to promote the corrosion of buried rebar under extremely harsh environmental conditions of conducting dry and wet repetition at a high temperature of 80 ° C where oxygen is the largest solid solution in steam. That's why. At the same time, the temporal change of the neutralization depth of the concrete specimens due to the carbon dioxide gas in the air and the temporal change of the corrosion amount of the buried reinforcing steel were examined. The maximum value of the width of the crack of the concrete specimen was measured with a crack gauge.

The carbonation gas neutralization depth was measured by measuring the depth from the surface layer of the concrete specimen which turned from red to colorless in a concrete specimen in which a phenolphthalein solution was sprayed on concrete.

The amount of corrosion of the buried rebar was determined by chemically removing the rust of the rebar taken out by crushing the concrete, measuring the weight, subtracting it from the weight before corrosion, and obtaining the corrosion loss per 28 cm length of the rebar.

For reference, Fig. 3 shows the deterioration of the concrete specimens in which the reinforcing bar samples No. 1, No. 4, and No. 5 in this table were embedded.

In addition, after exposing the concrete specimens in which each of the reinforcing bar samples No. 1, No. 2, No. 3, No. 4, and No. 5 of this table were buried for 100 days in the constant temperature and humidity chamber, Chemical analysis of total salt content and free salt content extracted with cold water to convert NaCl in sand
(%), The total salt content was about 0.50
%, Free salt content was about 0.25%.

Therefore, it was found that the reinforcing bar of the present invention hardly corrodes even if the free salt content near the reinforcing bar reaches 0.25% in sand, and has the effect of almost stopping the deterioration of concrete.

(Effects of the Invention) The present invention is useful as a rebar for concrete which is dramatically effective in maintaining the durability of concrete structures exposed to salt damage, which will become an increasingly important problem in the future.

By using the rebar for concrete of the present invention,
It contributes to extending the life of concrete structures and improving stability, and can be used for various applications.

[Brief description of the drawings]

1 (a) and 1 (b) are explanatory diagrams showing the shape, dimensions and arrangement of reinforcing bars of a concrete specimen having a reinforcing bar embedded therein, and FIG. 2 is a test condition in a rust acceleration test of a concrete specimen having a reinforcing bar embedded therein. FIG. 3 is a view showing the appearance of a concrete specimen. 1: concrete specimen, 2: buried reinforcing bar, 3: epoxy seal over mortar.

Claims (2)

(57) [Claims] 1. C: 0.001 to 1.0%, Si: 0.01 to 0.05%, Mn: 0.01 to less than 0.3%, P: less than 0.025%, S: less than 0.005%, Cu; 0.01 to 0.5%, W: 0.01 to Salt-resistant steel bar containing 0.5%, Al; 0.001 to 0.10%, with the balance being iron and unavoidable impurities for preventing concrete deterioration. 2. C: 0.001 to 1.0%, Si: 0.01 to 0.05%, Mn: 0.01 to less than 0.3%, P: less than 0.025%, S: less than 0.005%, Cu; 0.01 to 0.5%, W: 0.01 to 0.5% Contain 0.5%, Al; 0.001 ~ 0.10%, and further contain any one or two of Nb, V, Ti, Mo in total of 0.01 ~ 0.5%, for concrete deterioration prevention consisting of iron and unavoidable impurities. Salt-resistant rebar.