JPH0320441A - Salt-resistant reinforcing bar for preventing deterioration of concrete - Google Patents

Abstract

PURPOSE:To obtain the salt-resistant reinforcing bar for preventing the deterioration of concrete exposed to salt damage by specifying the compsn. constituted of C, Si, Mn, P, S, Cu, W, Al and Fe. CONSTITUTION:The salt-resistant reinforcing bar for preventing the deterioration of concrete contains 0.001 to 0.1% 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 and 0.001 to 0.10% Al, furthermore contains, at need, total 0.01 to 0.5% of one or two kinds among Nb, V, Ti and Mo and the balance Fe with inevitable impurities, which almost perfectly prevents the corrosion of a reinforcing bar caused by the salinity in the state of free Cl<-> such as sea salt grains and sea water splashes penetrating into a concrete wall and the generation of cracks in concrete following the above. By using the reinforcing bar, the service life of concrete structures exposed to salt damage can be prolonged and its stability can be improved.

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 buildings installed in coastal areas, and concrete bridges has become a problem in various fields, and various prevention methods have been proposed. The measures are being 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 approximately 2.2 times, the concrete along the buried reinforcing bars can no longer withstand the expansion force and cracks occur. The crack is 0. When the temperature exceeds 2 am, external corrosion factors such as oxygen, salt, and carbon dioxide in the air can more easily penetrate through these cracks to the vicinity of the buried reinforcing bars, further promoting corrosion of the reinforcing bars and causing carbonation of the concrete. This will 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 adding small amounts of special additive elements. As a result of this, first of all, there is the reinforcing steel for concrete with excellent seawater resistance by adding Cu and W at the same time (Japanese Patent Publication No. 55-22546), and the reinforcing steel for concrete with significantly improved salt resistance (Japanese Patent Publication No. 57-48054). Publication, Japanese Unexamined Patent Publication No. 59-44457), the contents of which have already been published in other fields ("OF
FSHORE GOTEBORG '8 1' Pap
er Na4 2 Goeteborg SWEDEN
19B1, “'Cement Concrete” k 4
34 (1983) P. 23/31 “Corrosio”
of Reinforcement in Co
ncreteConstruction” P. 41
9 +1983, “Architectural Technology and Construction” 1985
N2291 January issue P155/164, Shokokusha). In addition, the salt-resistant mechanism of the 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 aims to solve the problem of free CI, such as sea salt particles and sea water spray, which have recently become a problem, especially when penetrating through concrete walls. The goal is to almost completely stop the corrosion of reinforcing bars and the accompanying cracking of concrete caused by the salt present in - conditions. 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 1%, 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 Problems) The above object of the present invention is to provide C; 0.001 to 1.0%,
Mn; 0.01-0. Less than 3%, Si; 0.
01-0.05%lP; less than 025%. S ;00
Less than 5%, Cu; 0.01-0.50%, W
;0.01~0.50%, A#: 0.001~
Concrete reinforcing bar containing 0.10%, the balance consisting of iron and unavoidable impurities;
This is accomplished by adding one or two types of reinforcing steel for concrete.

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

The reason for this is that lowering the amount of Si reduces the growth of mackerel. At the same time as suppressing the tc length, it is possible to dramatically increase the amount of -04-inhibitor, a corrosion inhibitor for iron that is generated as the reinforcing bar itself turns into a mackerel. It is presumed that corrosion resistance is dramatically improved due to a significant decrease in li.

Also, Si. The extreme decrease in S is due to the C added to the passive film on the surface of the buried reinforcing bars in the alkaline atmosphere of concrete.
This is thought to be reinforced by u. The reasons for limiting each precept in the present invention will be explained below.

The reason for limiting the amount of C to 0.001 to 1.0% is that Cfo
．． If it is less than oot%, the required strength cannot be obtained, and the C amount is 1.0%.
This is because it causes people to kneel.

Further, the reason why the amount of F4+1 was limited to less than 0.01% to less than 0.3% is that if the Mn content is less than 10.01%, the required strength cannot be obtained.

This is because if it is less than 3%, the rust growth will be significantly reduced.

The reason why the amount of Si was set to 0.01 to 0.05% is that the lower the amount of Si is, the more the strength of the regeneration will be dramatically lowered, and WO.
--The effective amount of ions is dramatically increased, but Si is 0
．． The old amount is 0.05% or less. This is because rust formation is significantly reduced when the content is less than 3%.

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.

Cu is O. The reason why it was limited to 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 reinforcing bar surface. This is because if it exceeds 5%, the rope becomes brittle.

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 why W is limited to 0.01 to 0.5% is that if it is less than 0.01%, the raw tc amount of -04- ions will be small and no corrosion resistance effect will be observed. This is because if it exceeds 5%, it becomes expensive in terms of economy.

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

The reason for limiting the S amount to less than 0.005% is to reduce MnS il, which is the source of rust. +Ca) It can also be expected to improve corrosion resistance by changing to S and the like. Also, S in steel
It is common knowledge to carry out the above-mentioned operations to reduce the amount of corrosion, so a small amount of Ca, Ce, etc. may be mixed in, but these elements do not have a negative effect on corrosion resistance. Therefore, the amounts of Ca and Ce are not specified.

Also, Nb + V and Tit Mo are added as necessary, but depending on the strength of the reinforcing bars. It is added as an element to improve toughness, and one or both of them are added in a total of 0.01 to 0.5%. o. If the oi% is less than the specified strength, ! 71 characteristics were not obtained, and 0. If it exceeds 5%, large inclusions will grow and cause scratches, so the content was set at 0.01-0.5%.

The steel constructed with the above chemical composition according to the invention can be used in a converter. It is melted in an electric furnace, etc., and then goes through the steps of ingot making and blooming, 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 can be galvanized or coated with an organic coating, if necessary.

(Example) A steel having the composition range of the present invention was melted in a converter, and after ingot formation and blooming,
The table shows the classification of drawn reinforcing bars, comparison steel reinforcing bars, and conventional electric furnace steel reinforcing bars, as well as 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.

The various reinforcing bars shown in the table are hot-rolled reinforcing bars of 9 mlφ, whose surfaces are 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 0.50% in terms of NalJ. 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 tank, and the humidity was 48 hours, drying was 24 hours, and humidity was 48 hours.
The concrete was exposed for 56,70, 100, and 138 days in a cycle of 48 hours of drying and 1 week of fgt (2 cycles), and the occurrence of cracks in the concrete was observed. In Figure 1, 1 is a concrete specimen, and 2 is a buried reinforcing bar of 9Mφ. 3 is epoxy seal over mortar coating, j! Shows ridiculous thickness.

The exposure conditions were set as shown in Figure 2 because the extremely harsh environmental conditions of repeatedly drying and moistening at a high temperature of 80°C, where the maximum amount of oxygen is dissolved in water vapor, promotes corrosion of buried reinforcing bars. This is to do so. 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 the mackerel from the reinforcing bars, measuring the weight, subtracting it from the weight before corrosion, and determining the corrosion weight loss per 280 reinforcing bar length.

For reference, reinforcing bar sample Nα1 in this table. Nt14, N
α5. Figure 3 shows the deterioration status of the concrete specimens buried in each case. Also, reinforcing bar sample N (Ll, NO.2. NO.
3. No. After exposing the concrete specimens embedded with 4 and Nt15 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 by cold water were chemically analyzed and calculated as sand equivalent NaCf (χ). The total salt content was approximately 0.50% in both cases, and the free salt content was approximately 0. It was .25%.

Therefore, it was found that the reinforcing bars of the present invention hardly undergo corrosion even if the free salt near the reinforcing bars reaches 0.25% in terms of sand, 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 the drawing]

Figure 1(a). (b) is an explanatory diagram showing the shape, dimensions, and reinforcement arrangement of a concrete specimen with embedded reinforcing bars, Figure 2 is a diagram showing the test conditions for a promotion test for concrete specimens with embedded reinforcing bars, and Figure 3 is a diagram showing the appearance of a concrete specimen. 1: Concrete specimen, 2: Buried reinforcing bars, 3: Epoxy seal over mortar coating. Figure 1 (d) (b) Measuring part 3: Epo-o-shishiru of Kerugal lacquering Figure 2 Kazuichi Uma →

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%, with the balance consisting of iron and inevitable impurities to prevent concrete deterioration. Salt-resistant reinforcing bars for use. (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%, and further contains any of Nb, V, Ti, and Mo. Salt-resistant reinforcing bars for preventing concrete deterioration, containing 0.01 to 0.5% of one or two types in total, with the balance consisting of iron and unavoidable impurities.