JPH03183740A - Salt-resistant reinforcing bar for preventing deterioration of concrete - Google Patents

Abstract

PURPOSE:To maintain the durability of concrete structures exposed to salt damage by limiting the amounts of Si and S, reducing the amt. of Mn and adding specified amounts of Cu and W in a steel. CONSTITUTION:The compsn. of a reinforcing bar is formed of 0.001 to 1.0% C, 0.01 to 0.05% Si, 0.01 to <0.3% Mn, <0.025% P, <0.005% S, 0.01 to 0.5% Cu, 0.01 to 0.5% W, 0.001 to 0.10% Al, 0.0001 to 0.005% B and the balance Fe with inevitable impurities. If required, each 0.01 to 0.5% of one or 2 kinds among Nb, V, Ti and Mo are furthermore incorporated thereto. In the reinforcing bar having the compsn., corrosion hardly progresses even if free salt content in the neighborhood of the reinforcing bar reaches 0.25% expressed in terms of that in sand, so that the deterioration of concrete can mostly be stopped.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is applicable to reinforced concrete structures that are exposed to sea salt particles and seawater spray, such as concrete structures installed in seaside areas and concrete structures installed in the ocean. This article relates to salt-resistant reinforcing bars that are extremely effective in preventing deterioration of structures, concrete bridges, etc.

(Prior art) Recently, cracking and deterioration of reinforced concrete buildings using sea sand, concrete structures installed in coastal areas, and concrete bridges has become a problem in various fields, and various prevention methods have been proposed. It has been 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 sea sand and the salt from sea salt particles that permeate through concrete walls in beach areas, and the volume of the reinforcing steel increases. Since the expansion force increases by about 2.2 times, the concrete cannot withstand the expansion force and cracks occur along the buried reinforcing bars. If the crack is 0.2 mm or more, external corrosion factors such as oxygen, salt, and carbon dioxide in the air can more easily penetrate through the crack to the vicinity of the buried reinforcing steel inside, further promoting corrosion of the reinforcing steel. This will promote the carbonation of concrete and hasten 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 adding small amounts of special additive elements. The results of this research were firstly reinforced concrete reinforcing bars with excellent seawater resistance to which Cu and W were simultaneously added (Japanese Patent Publication No. 55-22546), concrete reinforcing bars with significantly improved salt resistance (Japanese Patent Application Laid-open No. 57-48054, JP-A No. 59-44457), the contents of which have already been published in other fields ( ``0
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19B1 year.

°°Cement Concrete” No. 434 (19B3
)P, 23/31゜“Corrosion of Re
1nforee+went in ConcreteC
construction P, 419+ 1983, “°Architectural Technical Construction” 1985 Kou 2291 January issue P155/164. Shokokusha).

The salt resistance mechanism of the steel components of reinforcing bars, which contributes to improving the salt resistance of the reinforcing bars themselves, 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 is based on the conventional development by the present inventors, and is aimed at solving CZ that is free from sea salt particles, sea water spray, etc. that penetrate concrete walls, which has recently become a particular problem. The objective is to almost completely stop the corrosion of reinforcing bars due to salt present in the - condition and the accompanying cracking of concrete.

Free salt near buried reinforcing bars in concrete structures that are more than 10 years old, which is currently a problem in various fields, is NaC.
It reaches 0.15 to 0.25% in terms of l, causing significant corrosion of reinforcing bars and accompanying crack initiation and growth in concrete. Therefore, it is desirable to be able to almost completely stop cracking in concrete with a free salt content of 0.25%.

(Means for Solving the Problem) The above-mentioned object of the present invention is to
t; 0.01-0.05%, Mn; 0.025
less than %, P; less than 0.025%, s; o, oos%
, W; 0.01~0.50%, W; 0.01~
0.50%, u; 0.001-0.10%, B;
A reinforcing bar for concrete characterized by containing 0.0001 to 0.005%, with the remainder consisting of iron and unavoidable impurities, further comprising Nb*v as a selected component in the above components.
, achieved by concrete reinforcing bars to which one or two types of TilMo are added.

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

The cause of this is that by lowering the amount of Si, the formation and growth of rust is suppressed, and at the same time, the amount of -04-inhibitor, an iron corrosion inhibitor that is produced as the reinforcing steel itself rusts, is dramatically increased. It is presumed that as the amount of S decreases significantly, the amount of MnS, which is a point where rust occurs, decreases significantly, resulting in a dramatic improvement in corrosion resistance.

Furthermore, the extreme decrease in Si and S is thought to be due to the reinforcement of the passive coating on the surface of the buried reinforcing bars in the alkaline atmosphere of concrete due to the addition of Cu.

The reason why each component is limited in the present invention will be explained below.

The reason why the C amount is limited to o, ooi ~ 1.0% is that the C amount o
If the C content is less than , ooi%, the required strength cannot be obtained, and the C content is 1.0%.
This is because excessively high temperatures cause embrittlement.

Also, the reason why the Mn amount was limited to less than 0.025% is that
．． This is because if it is less than 0.01%, the necessary strength cannot be obtained, and if it is less than 0.3%, mackerel formation is significantly reduced.

The reason why the amount of Si is set to 0.01 to 0.05% is that the lower the amount of Si, the more the amount of rust formed will be dramatically reduced, and the effective amount of -〇4- ions will be dramatically increased. is 0
．． This is because when the amount of Mn is less than 0.05% and the amount of Mn is less than 0.3%, rust formation is significantly reduced.

The reason why P is set to be 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, and the rust growth tends to be promoted.

The reason for limiting Cu to 0.01 to 0.5% is that CuO,
If it is less than 0.01%, it will not be effective in reinforcing the passive film on the surface of the reinforcing steel, and if it exceeds 0.5%, it will cause embrittlement of the steel.

Note that when a large amount of Cu is added, 0.03 to 0.3% of Ni may be added for the purpose of improving the releasability of hot-rolled scale.

The reason for limiting W to 0.01 to 0.5% is that if it is less than 0.01%, the amount of - ions produced is small and no corrosion resistance effect is observed, and if it exceeds 0.5%, it becomes expensive in terms of economic efficiency. Because it will be.

The reason why M is limited to 0.001 to 0.10% is that M is 0.
．． If N is less than 0.01%, the oxygen present in the steel cannot be fixed as a stable M oxide, and if N is more than 0.10%, large inclusions will grow and cause embrittlement of the steel, so the deoxidizing effect will not be effective. The ingredients were limited to the above range in terms of the required amount and strength.

The reason for limiting B to 0.0001 to 0.005% is that if B is less than 0.0001%, it will not be strong enough to compensate for the decrease in strength caused by the decrease in Mn content, and if it exceeds 0.005%, the steel will become brittle. In order to ensure strength, the components were limited to the above range.

The reason why the amount of S is limited to less than 0.005% is to reduce the amount of MnS, which is the source of rust. , Ca) S, etc. can also be expected to improve corrosion resistance. Furthermore, since it is common knowledge to carry out the above-mentioned operation in order to reduce the amount of S in steel, some amount of Ca is added.

Ce, etc. may be mixed in, but these elements do not have a negative effect on corrosion resistance, so Ca, C etc.
The amount is not specified.

In addition, Nb+V, Ti, and Mo are added as necessary, but they are added as elements to improve the strength and toughness of the reinforcing bars, and one or two of them are Nb, V, Ti, and Mo each in an amount of 0.01 to 0.01 or more. Add 0.5%. Nb, V, Ti,
If Mo is less than 0.01%, the specified strength and toughness cannot be obtained, and if it exceeds 0.5%, large inclusions will grow and cause scratches, so it was set at 0.01 to 0.5%. . The preferred range is 0.01 to 0.2%.

According to the present invention, the steel composed of the above-mentioned chemical components is melted in a converter, electric furnace, etc., and then undergoes an ingot-making step, or
Alternatively, after continuous casting and rolling, heat treatment such as patenting is performed as necessary, and wire is drawn to serve as a reinforcing bar. Further, the surface may be galvanized or coated with an organic coating, if necessary.

(Example) Steel having the composition range of the present invention is melted in a converter and made into ingots.

Table 1 shows the reinforcing bars drawn after blooming and the reinforcing steel components of the comparison steel, and Table 2 shows the deterioration status of the concrete in which these reinforcing bars were buried and the change over time in the corrosion status of the buried reinforcing bars.

The various reinforcing bars shown in the table are hot-rolled reinforcing bars with a diameter of 9ffi IDφ, 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 during crushing of 0.50% in terms of NaCl. A concrete specimen as shown in Fig. 1 was prepared, and after curing for 28 days, the concrete specimen was inserted into a constant temperature and humidity chamber, wet for 48 hours, dry for 24 hours, and wet for 48 hours.
The concrete was exposed to 56.70°, 100° for 138 days in a drying cycle of 48 hours for 1 week (2 cycles), and the occurrence of cracks in the concrete was observed. In Fig. 1, 1 indicates the concrete specimen, 2 indicates the buried reinforcing bar with 9 ribs, 3 indicates the mortar coating and epoxy seal, and l indicates the cover thickness.

The msn conditions were set as shown in Figure 2 to accelerate the corrosion of buried reinforcing bars under extremely harsh environmental conditions, such as repeated wet and dry cycles at a high temperature of 80°C, where maximum oxygen is dissolved in water vapor. It's for a reason.

At the same time, we investigated changes over time in the depth of carbonation of these concrete specimens due to carbon dioxide gas in the air, and changes over time in the amount of corrosion of buried reinforcing bars. The maximum width of cracks in concrete specimens was measured using a crack gauge.

The depth of neutralization by carbon dioxide gas was determined by spraying a phenolphthalein solution on the concrete and measuring the depth from the surface of the concrete specimen where the color changed from red to colorless.

The amount of corrosion of the buried reinforcing bars was determined by crushing the concrete, chemically removing rust from the reinforcing bars, weighing them, subtracting them from the weight before corrosion, and calculating the corrosion weight loss per 28 cm of reinforcing bar length.

For reference, reinforcing bar sample Nl11. N114.
Figure 3 shows the state of deterioration of the concrete specimens in which NIL5 was buried.

Also, reinforcing bar sample Nα1 in this table. Nα2. Nα3. N.L.
After exposing the concrete specimens in which IL4゜゜5 were buried in the above-mentioned constant temperature and humidity chamber for 100 days, the total salt content near the reinforcing bars and the free salt content extracted with cold water were chemically analyzed and calculated as NaCj in the crushed medium. ! When calculated as (%), the total salt content is approximately 0.50%, and the free salt content is approximately 0.50%.
It was 25%.

Therefore, it has been found that the reinforcing bars of the present invention hardly undergo corrosion even when the free salt content near the reinforcing bars reaches 0.25% in terms of crushing, and is effective in almost stopping the deterioration of concrete.

(Effects of the Invention) The present invention is useful as a concrete reinforcing bar that is extremely effective in maintaining the durability of concrete structures that are 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.

[Brief explanation of drawings]

Figures 1 (a) and (b) are explanatory diagrams showing the shape, dimensions, and reinforcement arrangement of a concrete specimen with embedded reinforcing bars, and Figure 2 shows test conditions for a rust acceleration test on a concrete specimen with embedded reinforcing bars. Figure 3 is a diagram showing the appearance of the concrete specimen. 1: Concrete specimen, 2: Buried reinforcing steel, 3: Mortar coated and epoxy seal. Figure ((2> (b) Scheming part 3° Epoto seal Figure 8-m

Claims (2)

[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; 0.005 %, Cu; 0.01 to 0.5%, W; 0.01 to 0.5%, M; 0.001 to 0.10%, B; 0.0001 to 0.005%, Salt-resistant reinforcing bars for preventing concrete deterioration, consisting of residual iron and unavoidable impurities. (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; 0.005 %, Cu; 0.01 to 0.5%, W; 0.01 to 0.5%, Al; 0.001 to 0.10%, B; 0.0001 to 0.005%, Further, any one or two of Nb, V, Ti, and Mo are added in an amount of 0.01 to 0.0, respectively.
A salt-resistant reinforcing bar for preventing concrete deterioration that contains 5%, with the remainder consisting of iron and unavoidable impurities.