콘크리트내로의 방청제 압력주입에 의한 철근 콘크리트 구조물의 방식공법 개발에 관한 연구

Abstract

This research investigated the water movement and penetration in concrete through some tests in order to perform the pressure injection of corrosion inhibitor to reinforced concrete structures and calculated the concentration of corrosion inhibitor (nitrate lithium) according to the penetration depth based on a penetration test using the nitrate lithium (LiNO2), which has been used as a practical repair material, and that can be used to calculate the effective corrosion inhibitor. In addition, based on an FEM analysis, this research performed a basic research for the estimation of the penetration depth of corrosion inhibitor that applies water pressure and pressuring time according to the strength of concrete as its variables and that leads to develop a penetration method of corrosion inhibitor as an effective level for the concrete structures degraded by salt and carbonation damages. This research is organized by seven chapters as follows; Chapter 1 describes the background and need for this research, the objective of this research, and the organization of this research. Chapter 2 introduces the corrosion mechanism of rebars in reinforced concrete structures and the diagnosis and corrosion protection methods for rebars in reinforced concrete structures. Also, Chapter 2 investigates some corrosion protection methods in rebars and applies a method that uses corrosion inhibitor in this research. Chapter 3 investigates the theory on the water penetration and diffusion in the concrete under pressure and applies it to this research. Chapter 4 carries out the pressure injection of the nitrate corrosion inhibitor (LiNO2) to an actual concrete structure for calculating the penetration depth of such corrosion inhibitor. In addition, Chapter 4 estimates the pressure and pressuring time by calculating the penetration concentration of corrosion inhibitor as a quantitative manner according to the calculated penetration depth. Chapter 5 verifies the estimation of the penetration depth of corrosion inhibitor using an FEM analysis based on the results obtained in Chapter 4. Also, Chapter 5 verifies the penetration depth of corrosion inhibitor using the strength of concrete, pressuring pressure, and pressuring time as its variables using an ADINA FSI module in performing the FEM analysis. Chapter 6 develops a device for introducing a pressure injection method of corrosion inhibitor based on the previously performed experiments and analyses and implements a Mock-Up test in order to perform site and practical applications. Chapter 7 represents the results of this research and future study.

In this research, the water penetration and diffusion mechanism in concrete was verified through literature references and experiments in order to develop a method that penetrates the highly concentrated components of corrosion inhibitor to the location of the rebars in concrete by installing injection holes on the surface of concrete. Also, the effective concentration of corrosion inhibitor was determined by measuring the concentration of nitrate ions (a type of corrosion inhibitor) according to the penetration depth using a colorimeter. In addition, the penetration depth was predicted by applying an FEM analysis using the strength, water pressure, and pressuring time as its variables in order to evaluate the penetration of corrosion inhibitor as a quantitative manner. The results of this test can be summarized as follows; 1) In the results of the pressured penetration test of corrosion inhibitor into the concrete, it shows a similar tendency to that of the water penetration, and the penetration depth was increased according to the high water-cement ratio, high pressure, and long pressuring time. Here, it was evident that the penetration is largely affected by the water-cement ratio.

2) Based on the penetrative diffusion current equation, Eq. (3.11), using the diffusion coefficient, , according to the water-cement ratio and the variables of pressure P and pressuring time h, a prediction equation, Eq. (4.5), for the penetration of corrosion inhibitor into the concrete was proposed. In addition, in the results of the comparison between the values predicted by the prediction equation and the values obtained from the experiment showed that the difference in the penetration depth is average 1.65mm, and the average error is 11.6% and that agrees with its results.

3) In the results of the calculation of the amount of nitrate ions that represents the mole ratio of the chloride ions and nitrate ions ([NO2-]/[Cl-]), which is determined by 0.6 and shows an excellent corrosion protection effect as the chloride ions approach to the amount of critical corrosion, using Eq. (4.6) and Eq. (4.7), it showed 77.7㎎/ℓ and that represents 0.932kg/m3 as a converted unit. In addition, in the specimen with the water-cement ratio of 65%, the nitrate ions were detected by more than 0.932kg/m3 at a deeper location than the regular cover thickness of 4cm in most architectural structures.

4) In the results of the FEM analysis performed by using the diffusion coefficients obtained by the experiment, it was recognized that the penetration can be performed by the maximum 80mm as the water pressure of 2.5MPa is applied at W/C 65% for more than 200 hours and by the maximum 40mm as it is applied at W/C 55% based on the results of the analysis.

5) Based on the analysis, it was possible to analyze some variables, which are difficult to investigate through experiments, related to the penetration possibility and pressuring time under a high pressure condition. Thus, it was considered that the results provide enough basic data for penetrating the corrosion inhibitor into the concrete under a high pressure condition.

6) The effectiveness of the pressured injection method of corrosion inhibitor developed in this research was verified through a Mock-Up test for an actual structure.