KR19990015976A - Repair method of concrete crack by steel reinforcement - Google Patents

Abstract

It is made by mixing cement, sand and polymer, and using a mortar containing 10 to 20% by weight of the amount of polymer in the polymer mortar.

When repairing the cracks caused by the rebar rusting, remove the lifting part, remove the rust of the reinforcing bar, then wash off the foreign substance on the surface of the reinforcing bar and apply a permeable hardener. When the permeable hardener dries, apply a reducing agent to the rebar and concrete surface, apply antirust paste, apply polymer mortar several times, and finish by applying surface treatment and antirust paste.

Description

[Name of invention]

Repair method of concrete crack by steel reinforcement

Detailed description of the invention

[Field of Invention]

The present invention relates to a repair method for repairing cracks caused by rusting of steel in reinforced concrete structures. In addition, the present invention relates to a repair method for repairing cracks using the mortar by properly mixing the mortar used for repairing the crack due to the rebar rust.

[Background of invention]

The causes of cracking in reinforced concrete structures are the deterioration of concrete structures due to dry shrinkage, overload, and steel bar rusting. The deterioration of concrete can be caused by the neutralization of concrete, alkali aggregate reaction, salting, east sea, erosion, corrosion, transfer, etc.

Repairing method when cracking occurs in reinforced concrete includes injection, suture, weaving, grouting, dry packing, and coating and surface treatment.

When the steel is rusted, the volume around the reinforcing bar increases, causing expansion pressure. Therefore, when the coating thickness is thin, cracks are generated on the surface, and when the coating thickness is thick, the cracks often extend along the reinforcing bar surface.

Conventionally, when rust is formed in a steel bar and a crack occurs in a concrete structure, epoxy resin is mainly injected into a crack gap to fill a gap or to cut a cracked part and to finish by applying a repair mortar. These repair methods were forcibly processed without removing the root cause of the crack, and still had the problem of cracking again over time.

In order to solve this problem, a repair mortar and a repair method using the same have been developed for repairing a part where cracking occurs due to the reinforcing bar.

[Purpose of invention]

The present invention is to provide a repair method for repairing the crack site caused by the reinforcing bar.

Another object of the present invention is to provide a repairing method for repairing cracks by developing a repair mortar for repairing cracks due to the rebar rust.

Still another object of the present invention is to provide a repair method in which a cracked reinforced concrete structure can maintain durability after repair.

[Summary of invention]

In the polymer mortar prepared by mixing cement, sand and polymer, a mortar containing 10 to 20% by weight of the amount of polymer is used.

When repairing the cracks caused by the rebar rusting, remove the lifting part, remove the rust of the reinforcing bar, then wash off the foreign substance on the surface of the reinforcing bar and apply a permeable hardener. When the permeable hardener dries, apply a reducing agent to the rebar and concrete surface, apply antirust paste, apply polymer mortar several times, and finish by applying surface treatment and antirust paste.

[Detailed Description by Specific Example of the Invention]

Repair mortar

Mortar, which is widely used as a construction material, has the disadvantage that the binder is cement hydrate, which has a low curing time, a weak tensile strength, a large dry shrinkage, and a weak durability against chemicals. In order to be used as a material for repairing cracks caused by deterioration of reinforced concrete structures, these defects must be compensated for, and a polymer mortar is proposed as a complementary method. The polymer mortar has good workability due to the ball bearing action of the polymer particles and the entrained air and the dispersing action of the surfactant contained in the polymer, and has high resistance to bleeding and material separation. In general, the mortar incorporating the polymer has a generally increased bending strength, tensile strength, and shear strength compared to the mortar, and the amount of dry shrinkage decreases because the unit quantity required to obtain the same workability due to the surfactant effect of the polymer is small. Its melting and weathering properties are known to improve.

The properties of the polymer mortar are governed by the polymer cement (P / C) rather than the water cement (W / C), where the polymer cement ratio is expressed as the weight ratio of solid components in the polymer dispersion to cement.

Example of a repair mortar

In order to find the most suitable formulation for repair in the mortar test in which the polymer was mixed, the performance evaluation test was performed according to the amount of the polymer incorporation amount into 10%, 20%, and 30% by weight of the cement. The cement used in this formulation is usually Portland cement, and sand is a silicic acid, with a maximum particle diameter of 5 mm. The cement admixture used in the experiment is an aqueous polymer dispersion, SBR latex, a synthetic rubber product, whose physical properties are 47 ± 1 (%) solids, pH 11 ± 0.5, density 1.014g / cm ³ , surface tension of about 45mN / min, viscosity Maximum 200mPa, average particle size 160μm, the lowest film formation temperature is about 0 ℃. A compounding example is as follows.

Table: Polymer Mortar Mixing Examples

The specimen was prepared in accordance with KSF 2403. The sand was sealed by adjusting the amount of cement and surface, and the sand was mixed with a trowel, mixed with a predetermined polymer dispersion and water, and mixed for about 3 minutes. It was manufactured using a soft mold and cured in an atmosphere of 1 day, and then cured underwater.

The specimens were tested for flexural strength and compressive strength in accordance with KSF 2405 at the curing time (7 days, 14 days and 28 days). The test results are as follows.

Table: Test specimen test results of the compounding example

The mortar incorporating the polymer has a lower compressive strength as compared with the comparative example, and the more the polymer is mixed, the greater the decrease in strength. When used as a repair mortar, the compressive strength is not considered to be a determinant.

The flexural strength was better in mortar specimens containing polymer than in general mortar. Incorporation of the polymer increased the flexural strength.

Considering the decrease in compressive strength, the increase in flexural strength, and the price of the polymer, the amount of polymer to be used for the repair mortar is considered to be appropriate if it is in the range of 10% to 20% by weight of the cement. Considering convenience, P / C = 20% would be desirable.

Conservative method

When a crack occurs in a reinforced concrete structure, an injection method of injecting epoxy resins while applying pressure to cracks is usually used. However, even if the crack is generated due to expansion pressure due to rust in the reinforcing bar, if the injection method is adopted, the root cause could not be removed. Filling method of the present invention is a method for removing the rust generated in the reinforcing bar and no longer rust is generated to maintain durability even after repair.

Embodiment of the repair method

Repair method of the present invention was constructed in the following steps.

1) Step of lifting up

The concrete was removed to the rear of the rebar to make it easier to remove the rust.

2) rust removal step

Completely remove the rust of the exposed rebar using a wire brush or electric wire brush. If the rust is not completely removed, it is to prevent the corrosion from developing again after the repair.

3) washing and cleaning steps

After removing rust completely, use a high pressure water washer (discharge pressure 100 ~ 150kg / m ³ ) to remove foreign substances remaining on the surface. If water is not available, compressed air or a vacuum cleaner can be used. The order of cleaning was from top to bottom, so that the contaminated water did not get on the bottom side, and the oily parts were washed with solvent or detergent.

4) Application step of penetration hardener

Penetration hardener was applied to reinforce the weakness of the surface when removing the lift after the surface was dried after cleaning. The solidifying agent used had a viscosity of 10 cps or more, specific gravity of 1.1 ± 0.02, pH of 11 ± 0.5, condensation point of 0 ° C. at 20 ° C., and an application amount of 400 g / m ² . Apply the stock solution as it is using a brush, but wait twice until the application and then apply twice.

5) Alkali reducing agent application step

After the penetration solidifying agent dried, an alkali reducing agent was applied to the exposed steel bars and concrete surfaces using a brush.

6) Antirust Paste Coating Step

After the alkali reducing agent was dried, a rust preventive paste was applied. The rust preventive paste is mixed with 20 kg of rust preventive cement to 6 kg of admixture, and then emptied by electric stirrer. At this time, the mixed material used was a solid content of 24 ± 1%, pH 7.5 ± 1.0, viscosity of 10 cps or less, specific gravity of 1.0 ± 0.05. Antirust paste is applied with a brush and once applied thickness is 1 ~ 2mm and applied within 40 minutes after emptying.

7) Repair mortar filling step in section defect

As the repair mortar, the polymer mortar described above was used, and the polymer incorporation amount was 20% by weight of cement. One coat thickness did not exceed 6 mm.

8) Neutralization prevention layer finishing step

The anti-rust paste was applied on the entire surface to prevent the neutralization from being processed in the future.

Comparative Example 1

The crack site was repaired by the usual injection method. The order is to remove impurities such as corrosives on the surface of the test object, apply a caulking material mixed 1: 1 with the main material and the hardening material on the crack line, install a nipple for injecting epoxy into the crack area, and inject the water into the tap. After the instrument was inserted, epoxy was injected into the cylinder. Epoxy resin was injected at a strong pressure so as to fully penetrate into the crack to confirm that the injection was sufficient and cured. Next, the caulking material which covered the surface after the epoxy resin had hardened was removed.

The above test was performed by artificially cracking the specimens produced in the laboratory, and performed the post-repair performance test on the healthy test specimens (Comparative Example 2) and the repaired specimens without cracking.

The performance tests were conducted for compressive strength, split tear strength, adhesion strength, neutralization acceleration test, and permeability test. The test results are as follows.

Table: Test Results

Compressive strength was measured by taking a 10cm diameter core from each specimen. The test specimen showed 274kg / cm ² , 267kg / cm ^{2 for the} injection method, and 239kg / cm ² for the repair method. This is about 87% stronger than sound test specimens and is not considered dangerous in terms of repair. In the injection method, 97% of the test specimens are considered to be the result of the epoxy resin not being filled to the minute cracks.

Halyeol tensile strength of test samples sound 28.7kg / cm ^2, injection 33.6kg / cm ^2, this Maintenance gongbeopin charging method is shown to 31.0kg / cm ² had an excellent strength than healthy specimens. This is considered to be due to the characteristics of the polymer.

Bonding strength was performed by attaching 5cm × 5cm attachment pieces to the repaired surface, and both the injection and filling methods showed lower adhesion strength than the healthy test specimens, which caused cracks due to artificial deterioration and the repaired surface was not smooth. Think of it as a result.

The neutralization promotion test shows the results measured after 28 days of neutralization promotion. Integrity test body 26.5mm, injection method 11.5m, charging method was 3.5mm was very excellent.

Neutralization depth is a factor that has a close relationship with the durability of concrete.

The peculiarity of the core specimen was filled with 200 ml of water in a funnel having a diameter of 9 cm at the bottom of the core specimen, and the water permeability was measured every 24 hours for 7 days. The measurement results are shown in the following table.

Table: Permeability Test Results (Unit: ml)

In the case of healthy test specimens, 81ml absorbed about 40.5%, the injection method was 10.5ml, 5.3%, and the filling method was only 0.4ml, which was less than 1%. This is considered to be excellent in waterproofing ability because the filling method is applied to the surface of the test specimen using a tight material.

In the embodiment of this repair method, a polymer mortar blended for this purpose was used, but it is judged that repairing using a repair mortar that is commercially available will produce similar results.

Claims (4)

A concrete mortar for repairing concrete, characterized in that the polymer mortar prepared by mixing cement, sand, and polymer contains 10 to 20% by weight based on the amount of cement. According to claim 1, wherein the amount of polymer is concrete crack repair mortar, characterized in that 20% by weight based on the amount of cement. Lifting site removal step of removing the concrete to the back of the rebar to easily remove the rebar rust; A rust removal step of completely removing the rust of the exposed rebar using a wire brush, an electric wire brush, or the like; A washing and cleaning step of removing foreign matter remaining on the surface by using a high pressure water cleaner, compressed air, or a vacuum cleaner; Applying a penetration solidifying agent to reinforce the weakened surface; Applying an alkali reducing agent to the rebar and concrete surfaces; Coating the anti-rust paste within 40 minutes after the alkali reducing agent is dried and once applied with a thickness of 1 to 2 mm; Filling the maintenance mortar so that the one-time thickness does not exceed 6 mm; And Forming an anti-neutralization layer by coating the anti-rust paste to prevent neutralization, and then finishing; Repair method of the concrete crack by rebar rust characterized in that consisting of. 4. The method of claim 3, wherein the repair mortar of claim 1 is used in the repair mortar filling step. 5.