JPS5812222B2 - Corrosion-resistant reinforced concrete - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to reinforced concrete with enhanced corrosion protection.

Reinforced concrete is widely used as an economical structural material, and its use as a material for port facilities and general construction will continue to expand steadily.

However, in recent years, as the air, rivers, and oceans have become increasingly polluted, concrete, which was previously thought to have a semi-permanent lifespan, is now being observed to be destroyed in a much shorter period of time than expected.

Destruction of concrete, which occupies an important position in structures and is highly reliable, may cause serious disasters, and countermeasures must be established immediately.

The causes of concrete failure are thought to be as follows, and the main cause is thought to be the infiltration of corrosive substances through the pores.

(1) Alkalinity of concrete (initial alkalinity is p
H12-13) are washed away by rainwater or react with acidic gases such as sulfur oxides, nitrogen oxides, or carbon dioxide gas in the atmosphere, and gradually become neutralized.

(2) Along with carbonation, on the other hand, cracks occur in concrete.

(3) The phenomenon of (1) is further promoted through the cracks.

(4) Reinforcing bars in neutralized or acidified concrete develop rust and corrosion progresses.

(5) As corrosion progresses, the volume expands and cracks in the concrete develop.

(6) The progress of corrosion and the development of cracks overlap, leading to concrete destruction.

(7) Recently, there has been a shortage of good quality river sand as a sand material for concrete, so sea sand is often used.
In this case, corrosion of the reinforcing bars will progress even if the phenomenon described in item (1) does not occur.

Adding corrosion inhibitors such as sodium nitrite and sodium benzoate to concrete has been proposed as a method to prevent concrete from corroding, but even if these types of agents are simply added to concrete, it will harden. Even after it has previously flowed out or solidified, there is a lot of runoff due to rainwater, which poses problems not only from an economic point of view but also from the safety and health of the runoff.

As a result of various efforts to improve the above-mentioned problems, we found that a porous object such as solidified metal powder or pumice was pre-impregnated with a corrosion inhibitor, and a low melting point wax was applied on top of this. The inventors have discovered that the above object can be achieved by using a coated material as an aggregate for concrete by mixing it with a portion of sand or gravel, and have thus arrived at the present invention.

As the porous object, a sintered metal, an oxide such as alumina or pumice, or a porous natural stone is used, and as the corrosion inhibitor, the aforementioned sodium nitrite or sodium benzoate is used.

To impregnate a porous object with a corrosion inhibitor, the porous object is immersed in an aqueous solution of a corrosion inhibitor such as sodium nitrite or sodium benzoate, and the corrosion inhibitor is sufficiently penetrated into the pores of the porous object. After drying, the porous object is generally removed and dried.

A common method for coating this with wax is to immerse the porous object impregnated with the corrosion inhibitor in the molten wax as described above and then take it out.

The amount of corrosion inhibitor impregnated into the porous object is sufficiently effective even if it is less than 11% of the concrete volume, and the higher the impregnated amount, the better the corrosion protection, but if the amount is too large, it will lead to an increase in cost, and The upper limit of the amount should be determined by experiment, as this will cause a decrease in the strength of the concrete.

Further, the thickness of the wax coating layer is not particularly limited, but should be determined as appropriate for the application site.

The concrete of the present invention has the following effects.

(1) The corrosion inhibitor sealed in the porous object gradually dissolves when cement and water are mixed, so the effect lasts.

(2) Corrosion inhibitors encapsulated in wax do not come into contact with water during concrete mixing, so they do not elute.

The initial environment when this concrete was poured had a pH of 12~
13, the reinforcing bars do not corrode in this state, so no corrosion inhibitor is required.

(3) Water use reaction that occurs when concrete hardens (
When wax is melted by heat generated by the reaction between cement and water, or by sunlight during use as concrete, the corrosion inhibitor sealed inside begins to melt due to the presence of moisture, causing iron rust to occur. To prevent.

It should be noted that if there is no infiltration of moisture, it will not melt, but if there is no intrusion of moisture, the reinforcing steel will not corrode.

(4) Since the eluted wax fills the fine pores of the concrete, it physically prevents rainwater and acid gases that accelerate the corrosion of reinforcing bars from entering through the pores, thereby improving the anticorrosion effect.

(5) The melting point of the wax used can be appropriately selected depending on the degree of water use reaction and the weather conditions of the region where the concrete is used.

(6) In places where the temperature-raising effect of direct sunlight cannot be expected, wax elution can be promoted by lightly heating the outside of the concrete with a burner or the like.

(7) A porous object in which a corrosion inhibitor is sealed with wax is sanitary because the inhibitor inside does not flow out even if it is exposed to rainwater under normal storage conditions.

(8) Wax is chemically stable and does not react with any corrosion inhibitor.

Sample concrete for comparison of examples was made by adding Tsuki1 sand or river sand and salt (simulating sea sand) to commercially available Portland cement. After adding water and mixing well, mild steel with a diameter of 15 mm was used. A buried test block was prepared.

The block size is 25 mm on one side and 100 mm in length, with a 15 wng x 60 mm mild steel rod sealed in the center.

In addition, sodium nitrite (
4) and sodium benzoate N (B) in a common amount, and further coated with paraffin having a melting point of 55°C.
The product of the present invention was prepared by adding each of these components to prepare a test block.

After the cement has set for the above test block, approximately 4
The specimens were left indoors for a week and were placed under the following conditions.

(1) Soaked in seawater for 1 year (2) Leaving for 6 months in a glass tank at 60°C containing 802 100 ppm and humidity of 80-100% (3) Leaving the concrete in the atmosphere for more than 1 year after testing The effectiveness of the present invention was determined by destroying the mild steel and measuring the amount of corrosion on the mild steel (those with rust were washed with hydrochloric acid and the difference in weight before and after the test was taken as the amount of corrosion).

The results are shown in Table 1. (Note) The ratio of corrosion amount under each condition is shown as 100 for mild steel when concrete with the composition shown in (1) is left in the atmosphere for one year.

As can be seen from Table 1, in a slow corrosive environment such as the atmosphere, there is almost no corrosion of mild steel, not only with the present invention but also with the conventional concrete method, but when immersed in seawater for 1 year, there is almost no corrosion of mild steel. Corrosion of mild steel begins to progress, and corrosion of mild steel is severe in environments containing acidic corrosive gases such as SO2.

Also, these corrosion tendencies are lower than when river sand is used.
This is even more remarkable in the case of sand to which ail has been added.

On the other hand, a sintered iron body with a corrosion inhibitor sealed in it is
With or without wax coating? It provides concrete with excellent corrosion resistance, and almost no corrosion is observed even in environments containing SO.

However, in the case where wax was not coated, only slight corrosion occurred in the 802 environment.

Claims (1)

[Claims] 1. Formed by adding aggregate made of cement with at least one of gravel and sand, and a porous substance that has a corrosion inhibitor in its pores and whose outer periphery is covered with wax. Reinforced concrete is characterized by: