Description of the Prior Art In general, it is known that concrete structure has a semi-permanent life, however, it is deteriorated by various factors such as the influence of the environment, materials, and weather conditions, and reduced rapidly in its life by corrosion of reinforcing steel embedded therein.

If a reinforced concrete or prestressed concrete structure is exposed to the salty atmosphere of sea water for a long period of time, the concrete will be chemically corroded by the functions of chlorine ions, sulfate ions, or the likes of the seawater elements, and the reinforcing steel or the prestress steel materials embedded in the concrete are corroded, thus accelerating the deterioration of the concrete.

Additionally, as traffic volume is rapidly increased, carbon dioxide gas of a considerably large amount is discharged from automobiles and promotes the carbonation of the concrete at a high rate. If the concrete is carbonated, the passive film for protecting the reinforcing steel is broken down and the reinforcing steel is corroded. The corroded reinforcing steel causes the expansion of the volume thereof, and thereby cracking and exfoliation of the concrete occur, and more severely, the

concrete structure can be destroyed.

To solve the problems outlined above, it is necessary to prevent the corrosion of the reinforcing steel embedded in the concrete. For this purpose, various methods such as water-repellent coating and painting have been used in the prior arts.

However, the water-repellent coating method is impossible to apply in places where water pressure exists or water is in direct contact with the concrete structure.

The water repellent coating method provides an excellent waterproofing effect initially to prevent the intrusion of water and salt which are factors in the corrosion of the reinforcing steel, but as time passes the main constituents of the water repellent are lost, thereby reducing its waterproofing effect. Therefore, there is the continued problem of periodically re-coating the concrete surface.

In the meantime, the painting method utilizes painting materials for improving the durability of the concrete structure, for example, epoxy resin ester, fluorine resin, and acrylic rubber. Those, organic coating materials, have excellent adhesive strength to the concrete initially, but as time passes the painting materials are separated from the interface of the concrete, because they differ from the concrete in the strain intensity to the coefficient of thermal expansion or the dry shrinkage, thereby reducing the adhesive strength.

It is, therefore, highly required to improve the resistance to chloride and to prevent the intrusion of chloride, water and oxygen, which are factors in the corrosion of the reinforcing steel, so that the deterioration of the concrete can be suppressed.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a concrete structure with long-term durability by preventing the deterioration of concrete due to intrusion of chloride, water and oxygen and the corrosion of reinforcing steel.

It is another object of the present invention to provide the reinforcing steel

with a rust-preventive effect and the concrete structure with long-term durability by preventing the intrusion of carbon dioxide and the resulting carbonization of the concrete.

It is a further object of the present invention to provide a concrete structure, which is easily preserved and repaired and to provide an economical method whereby the construction fee and construction period are considerably reduced.

To achieve the above objects, according to the present invention, there is provided a concrete structure surface coating of aluminum oxide film. The aluminum oxide film coated on the concrete surface can efficiently prevent the corrosion of the reinforcing steel embedded in the concrete, thereby preventing deterioration of the concrete.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will become more fully understood from the detailed description given hereinafter and the accompanying drawing which is given by way of illustration only, and thus is not a limitation of the present invention, and wherein: Fig. 1 illustrates a diffusion cell for testing the resistance to the intrusion of chloride into a concrete structure according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, a method for preventing deterioration of concrete using aluminium oxide film comprises the steps of: mixing aluminium flakes or aluminum powder with a polyurethane co-polymer or epoxy resin which has an excellent adhesive strength and elasticity; mixing xylene in the ratio of 10% by weight so as to make the mixture in liquid state applicable to concrete surface; and adhering the liquid mixture to concrete surface.

The aluminium oxide film formed by the above process prevents the

deterioration of the concrete covering and internal reinforcing steel.

It is preferable that the content of aluminium flakes is about 10% and that of polyurethane co-polymer or epoxy resin is about 30%, but it will be appreciated that the viscosity can be regulated according to usage. At this time, polyurethane co- polymer or epoxy resin are highly adhesive resins which are over 40kg/cu in adhesive strength.

In this invention, aluminium serves as a reductant by virtue of its good electron releasing properties. The following reaction shows the electron releasing property of aluminium: Al-Al"+ 3e' Aluminium which is more in reactivity than steel is oxidized faster than steel, so that aluminium exhibits faster process of rusting than concrete where aluminium is coated, thereby oxide film is formed on the concrete surface.

The aluminium oxide film formed by the above manner prevents air from permeating through the concrete surface, and the inner aluminum oxide layer from further rusting, thereby providing a remarkable rust preventing effect. Furthermore, the aluminium oxide film provides a very excellent corrosion resistance and waterproofing capability on the concrete surface so as to prevent the reinforcing steel embedded in the concrete from rusting.

Additionally, the aluminium oxide increases the surface hardness of the coating to improve abrasion resistance and impact resistance. The aluminium particles, which are arranged on the concrete surface, reflect ultraviolet rays so as to prevent the deterioration of coating and to improve the durability of the concrete structure. What is more, the aluminium oxide serves as a good sacrificial anode agent, so that it provides an electrical anticorrosion effect on defective portions of the concrete structure.

Therefore, contrary to the concrete structures constructed by the prior art

methods, the concrete structure constructed according to the present invention keeps its durability for a long time without problems such as exfoliation, discoloration, cracking and excitation.

In the meanwhile, polyurethane co-polymer and epoxy resin with high adhesive strength are adhered strongly to the concrete, and have a cracking follow-up ability to adapt well to any deformation of the concrete. Additionally, they can prevent the intrusion of materials, which cause the reinforcing steel bars to be corroded, for example, chloride ions, carbon dioxide, water and oxygen, thereby protecting the reinforcing steel embedded in the concrete structure from the corrosion.

Titanium, which has high strength and corrosion resistance and a lower density, can be added in the mixed aluminium liquid to improve the abrasion resistance of the concrete structure.

The mixed aluminium liquid manufactured by the above method is coated on the concrete surface in accordance with the following steps: (1) Removing impurities or foreign matters from the concrete surface; (2) Coating the mixed aluminium liquid on the concrete surface by using brush, roller, sprayer or the likes. At this time, the coating must be performed as thinly as possible so that the aluminum flakes and adhesive resin to permeate into the concrete smoothly. The mixed aluminium liquid is coated repeatedly within the range that one coating is not less than là; and (3) Naturally hardening at room and air temperature after coating.

The following examples explain the present invention in more detail. They are made by way of example for preferred embodiments of the present invention and not for purposes of limitation.

Example 1

Aluminium flakes in the amount of 10% by weight was taken and mixed with polyurethane co-polymer in the amount of 30% by weight, the adhesive strength of which was not less than 40kg/cu£. In the mixture, xylene in the amount of 10% by weight was added to ensure a liquid state. The mixed aluminium oxide liquid was coated on the concrete surface by a sprayer five or six times, within the range that one coating was not less than l 001l. The coated layer was naturally hardened at room temperature.

Example 2 Aluminium powder in the amount of 12% by weight was taken and mixed with epoxy resin in the amount of 30% by weight. In the mixture, xylene in the amount of 10% by weight was added to ensure a liquid state, and then titanium in the amount of 20% by weight was added to the aluminum oxide liquid. The mixed aluminium oxide liquid was coated on the concrete surface by a sprayer five or six times, within the range that one coating was not above I 00t. The coated layer was naturally hardened at room temperature.

Comparison Example To prevent the deterioration of the concrete structure, a water repellent was coated onto the concrete surface, and then the coated layer was hardened naturally.

In order to evaluate the quality of the concrete structures applying examples 1 and 2 and the comparison example respectively, the following tests were performed: Test on resistance to chloride intrusion To take test specimens, concrete structures to which examples 1,2 and the comparison example were applied respectively, and a non-coated concrete structure,

were cut to a thickness of 5 cm by a cutting machine. A diffusion cell was made as shown in Figure 1, NaCI liquid in the amount of 3.0% as an electrolyte filled a negative electrode, and NaOH of 0.3N filled a positive electrode. The diffusion cell was connected to a DC power supply of 60V for 6 hours in order to pass an electric current through the diffusion cell. To calculate the total electric charge which passed through the circuit, the electric current value was measured every 30 minutes. The result is shown in Table 1 as follows: Table 1 Test Specimen Electric Charge Example 1 Example 2 Comparison 2,210 Example Non-coated 3,400 Concrete Referring to the table l, the specimens coated with the aluminum oxide made by examples 1 and 2 of the present invention were scarcely intruded by chloride, while the specimen coated with the water repellent had the passed electric charge of about 2210 Coulomb. Compared to the present invention, the specimen coated with the water repellent had a still lower inhibition effect, but it was a little more effective in protection than the concrete from the chloride intrusion than the non-coated concrete.

Therefore, it will be appreciated that the concrete structure in accordance with the present invention has a high resistance to the intrusion of chloride.

Test on protection from carbonation The concrete structures to which examples 1,2 and the comparison example

were applied respectively, and a non-coated concrete structure were cut to make test specimens as a test on their resistance to chloride intrusion. The specimens were put into an acceleration tester respectively, with a temperature of 40 °C, a relative humidity of 50%, and a density of C02 of 10%. After accelerated testing, the carbonated thickness (mm) was measured after the fourth week, eighth week and thirteenth week from the start of the test. The result is shown in Table 2 as follows: Table 2 Accelerated Period Test Specimen Fourth Week Eighth Week Thirteenth Week Example 1 0 0 0 Example 2 0 0 0 Comparison 4 8 13 Example Non-coated 8 17 Above 25 Concrete Referring to Table 2, it will be appreciated that the concrete structure coated with the aluminum oxide film in accordance with the present invention has an excellent protective effect to carbonization, when compared to the concrete structure coated with the water repellent, or to the non-coated concrete structure.

Test on anticorrosion of the reinforcing steel The specimen made by example 1 and the specimen from the non-coated concrete were immersed in NaCl liquid in the amount of 3% and connected to a direct current of 5V for 630 hours to measure for any occurring potential difference. The potential difference induced electrolytic corrosion of the reinforcing steels. The corrosion area ratio was measured after the corroded reinforcing steel had been taken out from the specimens respectively. The result is shown in Table 3 as follows: Table 3 Specimen Corrosion Area Rate (%) Example 1 0.5 Non-coated Concrete 14.3

As shown in Table 3, the reinforcing steel embedded in the non-coated structure showed a corrosion rate of 14.3%, while the reinforcing steel embedded in the concrete structure coated with the aluminum oxide film exhibited an extremely small rate of corrosion to the extent that corrosion was not seen with unaided eyes.

Therefore, the reinforcing steel in accordance with the present invention ensures a high durability of the concrete structure.

Those skilled in the art will readily recognize that these and various other modifications and changes may be made to the present invention without strictly following the exemplary application illustrated and described herein, and without departing from the true spirit and scope of the present invention, which is set forth in the following claims.