Syifaul Huzni

Simulation of the Ill-Posed Problem of Reinforced Concrete Corrosion Detection Using Boundary Element Method

Many studies have suggested that the corrosion detection of reinforced concrete (RC) based on electrical potential on concrete surface was an ill-posed problem, and thus it may present an inaccurate interpretation of corrosion. However, it is difficult to prove the ill-posed problem of the RC corrosion detection by experiment. One promising technique is using a numerical method. The objective of this study is to simulate the ill-posed problem of RC corrosion detection based on electrical potential on a concrete surface using the Boundary Element Method (BEM). BEM simulates electrical potential within a concrete domain. In order to simulate the electrical potential, the domain is assumed to be governed by Laplace’s equation. The boundary conditions for the corrosion area and the noncorrosion area of rebar were selected from its polarization curve. A rectangular reinforced concrete model with a single rebar was chosen to be simulated using BEM. The numerical simulation results using BEM showed that the same electrical potential distribution on the concrete surface could be generated from different combinations of parameters. Corresponding to such a phenomenon, this problem can be categorized as an ill-posed problem since it has many solutions. Therefore, BEM successfully simulates the ill-posed problem of reinforced concrete corrosion detection.

CORROSION RISK ASSESSMENT OF PUBLIC BUILDINGS AFFECTED BY THE 2004 TSUNAMI IN BANDA ACEH

Banda Aceh region has a coastal environment and frequent earthquakes. The 2004 Sumatra tsunami caused many buildings to collapse and became submerged by seawater in the region. Thus, the buildings might become susceptible to corrosion, which will reduce their strength. Consequently, sudden failure might happen when even a small earthquake occurs. This study reports a corrosion risk assessment for some reinforced concrete (RC) public buildings in Banda Aceh region in order to understand how the tsunami has influenced the corrosion risk level. The assessment was performed by using half-cell potential mapping technique. Six buildings were chosen: three existing buildings, two newly constructed buildings in the tsunami-affected area and one building located outside that area. The assessments were carried out from 2009 until mid of 2010. The assessment results indicated that the corrosion risk to the existing buildings were at intermediate to severe level. In addition, newly developed buildings were at intermediate level, while outside building was still at low levels. Those findings showed that the RC buildings around the tsunami-affected area, either existing or new buildings, had become corrosive. Therefore, it is important to conduct regular corrosion assessments to prevent early failure due to the coexistence of rebar corrosion and earthquake.

Comparison of GA and PSO in boundary element inverse analysis for rebar corrosion detection

This paper presents the comparison of the two optimization methods, particle swarm optimization (PSO) and genetic algorithm (GA) in boundary element inverse analysis that applied to detect the corrosion location of rebar in the concrete. This comparison focuses at analyzing the performance of both methods in reaching the global optimum, considering that both heuristics are based on population search techniques. The model of 2-dimension rectangular reinforced concrete was used as a case example to compare both methods in boundary element inverse analysis. The boundary element inverse analysis was developed by combining Boundary Element Method (BEM) and PSO or GA. The inverse analysis is carried out by means of minimizing a cost function. The cost function is a residual between the calculated and measured potentials on the concrete surface. The calculated potentials are obtained by solving the Laplaces equation using BEM. The GA or PSO is used to minimize the cost function. Thus, the corrosion location of reinforcing steel in concrete can be detected. The numerical simulation results showed that one of PSO or GA can be used for the inverse analysis for detecting rebar corrosion by combining with BEM. However, it shows that PSO seem numerically superior compared to GA in term of consistency and accuracy in finding global optimum solution for such a problem.

The Influence of Inertia Weight on Particle Swarm Optimization in Boundary Element Inverse Analysis for Rebar Corrosion Detection

Particle Swarm Optimization (PSO) has been applied as optimization tool in various engineering problems. Inverse analysis is one of the potential application fields for PSO. In this research, the behavior of PSO, related to its inertia weight, in boundary element inverse analysis for detecting corrosion of rebar in concrete is studied. Boundary element inverse analysis was developed by combining BEM and PSO. The inverse analysis is carried out by means of minimizing a cost function. The cost function is a residual between the calculated and measured potentials on the concrete surface. The calculated potentials are obtained by solving the Laplace’s equation using BEM. PSO is used to minimize the cost function. Thus, the corrosion profile of concrete steel, such as location and size, can be detected. Variation in its inertia weight was applied to analyze the behavior of PSO for inverse analysis. The numerical simulation results show that PSO can be used for the inverse analysis for detecting rebar corrosion by combining with BEM. Also, it shows different behavior in minimizing cost function depending on inertia weight.

Application of BEM for Improving Corrosion Assessment of Public Building Stricken by Tsunami Aceh 2004

The earthquake and tsunami that struck Aceh region on December 2004 caused many public buildings submerged by seawater. In long periods, it will promote the premature failure of the existing buildings constructed by reinforced concrete structure due to corrosion. Early detection of the corrosion is urgent. The corrosion assessment using haft-cell potential mapping has been conducted to understand the current status of public buildings after five years tsunami Aceh 2004. The results for four existing public buildings in the region show that the corrosion level of steel in concrete of the buildings was already at intermediate risk. However, these results show only the corrosion risk instead of the actual corrosion of the steel. To improve the corrosion assessment, BEM was employed by simulating some factors that might affect the measured potential on the concrete surface. Laplace equation is used to model the potential in concrete structure. The steel surfaces were represented by using polarization curves. BEM is employed to solve the Laplace equation; hence the potential and current density in the whole domain can be obtained. The simulation results show that the potential corrosion on concrete surface was significantly affected by corrosion of steel, concrete conductivity and concrete cover. Accordingly, by employing BEM, more precise corrosion of steel in concrete can be identified from the measured potential on the concrete surface. Moreover, further study is needed to apply the proposed method in the field.

Pre and Post Processing for Boundary Element Method (BEM) 3D Reinforced Concrete Corrosion Simulation

Corrosion simulation of rebar in concrete structures using BEM 3D have been developed. However, pre processing procedure such as geometry development and meshing is still performed manually. In addition, the visualization of BEM simulation results is still illustrated using the simple chart and graph. Nowadays, many softwares have been developed under open source platform that can be used freely. There is open source softwares for CAE purposes such as Salome and VisIt. The aim of this study is to implement the open source software as pre- and post-processing for the developed BEM 3D code in order to simulate corrosion of reinforced concrete. Salome 2.3.9 is used for developing geometry and meshing the model. The visualization of the simulation results are conducted using VisIt 1.8. The study shows that the open source software i.e. Salome and VisIt, perform well as pre and post processing of developed code for simulating the corrosion of reinforced concrete. It shows that the meshing procedure and the interpretation of results become simpler and easier.

The Evaluation of Cathodic Protection System Design by Using Boundary Element Method

Cathodic protection system is one of corrosion protection systems that well acknowledged protecting infrastructure such as pipeline and storage tank. Early damage of the infrastructure can be caused by improper design of the protection system. Currently, many cathodic protection systems are designed only based on the previous experiences. It is urgently needed the tool that can be used to simulate the effectiveness of any design of cathodic protection system before the system is applied to any structure. In this study, the three-dimensional boundary element method was developed to simulate the effectiveness of sacrificial anode cathodic protection system. The potential in the domain was modeled using Laplace equation. The equation was solved by applying boundary element method, hence the potential and current density on the metal surface and at any location in the domain can be obtained. The boundary conditions on the protected structures and sacrificial anode were represented by their polarization curves. A cathodic protection system for liquid storage tank and submersible pump were evaluated in this study. The effect of placement of sacrificial anode were examined to optimize the protection system. The result shows that the proposed method can be used as a tool to simulate the effectiveness of the sacrificial anode cathodic protection system.

Boundary element inverse analysis by using particle swarm optimization for reinforced concrete corrosion identification

Boundary element inverse analysis (BEIA) by using genetic algorithm (GA) to identify corrosion location has been introduced by many researchers. However, the BEIA using GA is more complex to be programmed since it involved with genetic operators such as crossover and mutation. Recently, Particle Swarm Optimization (PSO) already takes researcher’s attention because of its simplicity to be programmed and comparable accuracy. This study is conducted to develop BEIA by combining Boundary Element Method (BEM) and PSO to identify the corrosion location of the steels in concrete structure from some potential data on concrete surface. The potential in the concrete domain was modeled by Laplace’s equation. The anode and cathode are represented by each polarization curve. The inverse problem is carried out by means of minimizing a cost function i.e. a difference between the calculated and measured potentials on the concrete surface. The calculated values of potential are obtained by solving the Laplace’s equation using boundary element method (BEM). Numerical simulation results show that the developed BEIA has proven that it can identify the corrosion location on the surface of reinforcement steel precisely.

Effect soil resistivity in mapping potential corrosion in underground pipelines area

The research has been conducted to map potential corrosion in underground pipeline using Kriging interpolation method. The project area is located in North Aceh, Indonesia between latitudes 5°11’N and 5°15’N, and longitude 96°48’E and 97°03’E. The measuring of corrosion potential for underground piping installation lines has been done with Wenner method. The result of this measurement is interpolated by Kriging method to obtain the mapping. The results show the distribution of various resistivity values with varying contours based on depth measurement. From the inversion data onto res2dinv software, images that have different colors are obtained. Each color represents different resistivity values that make up some irregular layers. In conclusion, the site of the study was potentially mildly corrosive, corrosive and highly corrosive.The research has been conducted to map potential corrosion in underground pipeline using Kriging interpolation method. The project area is located in North Aceh, Indonesia between latitudes 5°11’N and 5°15’N, and longitude 96°48’E and 97°03’E. The measuring of corrosion potential for underground piping installation lines has been done with Wenner method. The result of this measurement is interpolated by Kriging method to obtain the mapping. The results show the distribution of various resistivity values with varying contours based on depth measurement. From the inversion data onto res2dinv software, images that have different colors are obtained. Each color represents different resistivity values that make up some irregular layers. In conclusion, the site of the study was potentially mildly corrosive, corrosive and highly corrosive.

Corrosion of Reinforced Concrete Structures Submerged by the 2004 Tsunami in West Aceh, Indonesia

The earthquake and tsunami of 26 December 2004 caused the infrastructure in Aceh’s West Coast region to be submerged by seawater and to require the rehabilitation and reconstruction. The infrastructure that was submerged in the tsunami might experience a decrease in strength due to corrosion attack and would unexpectedly collapse if an earthquake occurs even on a small scale. This study was conducted to examine the corrosion risk level of the infrastructures in Aceh’s West Coast region, Indonesia, which submerged by the 2004 tsunami. Three locations were chosen for the study, i.e., Suak Ribee, Ujong Kalak, and Padang Seurahet. The assessments were carried out in 2014 and 2015. Three to four columns in each of the buildings were selected for the assessment. The half-cell potential technique method which refers to ASTM C876 was used to obtain and analyze the assessment data. The results of the assessment show that the electrical potentials on the surface of concrete for the buildings which submerged by the tsunami were range between -100 and -450 mV (vs. Cu/CuSO4) and categorized into low to high corrosion risk level. Meanwhile, the electrical potentials for new buildings range between (-100) and (-350) mV which indicated low to medium corrosion risk. Hence, the corrosion actively occurred in the areas having medium to high corrosion risk. Also, it was found that the corrosion risk level for the building tends to increase by increasing time. Therefore, the prevention and/or rehabilitation is necessary for stopping the corrosion, and so the premature failure of the building might be avoided.