Electronic Theses and Dissertation

Korosi tulangan baja merupakan salah satu penyebab utama kemerosotan struktur beton bertulang, khususnya pada lingkungan marin yang kaya ion klorida. Metode Potensial Setengah Sel (Half-Cell Potential, HCP) digunakan secara luas untuk penilaian korosi tanpa merusak, namun masih bersifat kualitatif dan tidak dapat menentukan lokasi, ukuran, geometri, maupun keterpisahan zona korosi secara langsung. Keterbatasan ini timbul karena sinyal potensial pada permukaan baja beton mengalami susut ohmik dan pelebaran ruang saat merambat melalui selimut beton, sehingga bacaan potensial di permukaan tidak selalu mewakili kondisi elektrokimia sebenarnya pada tulangan. Penelitian ini bertujuan mengembangkan kerangka kuantitatif untuk pendeteksian korosi tulangan yang mampu mengatasi keterbatasan metode HCP konvensional, dengan mengintegrasikan elektroda referensi keadaan padat Cu/CuSO₄ tertanam, simulasi Metode Elemen Hingga (Finite Element Method, FEM), dan analisis invers berbasis Optimisasi Topologi Inversi (Inverse Topology Optimization, ITO). Elektroda referensi Cu/CuSO₄ difabrikasi dalam ukuran ringkas untuk aplikasi tertanam dan dikarakterisasi melalui pengukuran Potensial Sirkuit Terbuka (Open Circuit Potential, OCP), perbandingan dengan elektroda Ag/AgCl, uji korosi terinduksi melalui perendaman dalam larutan NaCl 3,5%, serta analisis kurva polarisasi. Hasil eksperimen menunjukkan elektroda memiliki kestabilan baik, dengan deviasi standar OCP kurang dari 2 mV dan nilai rata-rata sekitar 0,94 mV. Setelah perendaman, OCP bergeser dari −0,198 V menjadi −0,396 V terhadap Cu/CuSO₄, menandakan peralihan dari keadaan relatif pasif ke korosi aktif. Parameter kinetika dari kurva polarisasi, meliputi Ecorr sekitar −0,39 V dan icorr sekitar 4,54 A/m², digunakan sebagai syarat batas simulasi. Model FEM berbasis persamaan Laplace divalidasi melalui uji analitik dengan galat nol dan studi independensi mesh. Hasil simulasi menunjukkan potensial tulangan −0,396 V hanya terdeteksi sebagai −0,249 V di permukaan beton, setara dengan kehilangan amplitudo sekitar 146,9 mV atau 74,2% dari rentang sinyal anoda–katoda. Selanjutnya, analisis ITO berhasil
memprediksi dan merekonstruksi lokasi serta ukuran zona korosi berdasarkan data potensial permukaan. Pada kasus zona tunggal, galat rekonstruksi sangat kecil dengan sisa akar rerata kuadrat mendekati tingkat derau pengukuran. Pada kasus multi-lokasi, ITO mampu memulihkan lebih dari satu zona korosi tanpa asumsi awal terhadap jumlah maupun bentuknya, meskipun keterpisahan zona masih dipengaruhi oleh ketebalan selimut beton, kualitas data pengukuran, dan parameter regularisasi. Secara keseluruhan, penelitian ini menghasilkan kerangka terpadu yang menghubungkan data eksperimen, model fisik berbasis FEM, dan analisis invers berbasis ITO, sehingga mampu memajukan penilaian korosi beton bertulang dari pendekatan kualitatif berbasis ambang potensial menuju pendekatan kuantitatif berbasis model.

Kata kunci: korosi beton bertulang; elektroda referensi Cu/CuSO₄ tertanam; potensial setengah sel (HCP); metode elemen hingga (FEM); optimisasi topologi inversi (ITO)

The corrosion of steel reinforcement is one of the principal causes of deterioration in reinforced concrete structures, particularly in chloride-rich marine environments. The Half-Cell Potential (HCP) method is widely used for non-destructive corrosionassessment; however, it remains qualitative and cannot directly determine the location, size, geometry, or separability of corrosion zones. This limitation arises because the potential signal at the steel–concrete interface undergoes ohmic drop and spatial spreading as it propagates through the concrete cover, so that surface potential readings do not necessarily represent the true electrochemical condition at the reinforcement. This study therefore aims to develop a quantitative framework for detecting reinforcement corrosion that overcomes the limitations of the conventional HCP method, by integrating an embedded solid-state Cu/CuSO₄ reference electrode, Finite Element Method (FEM) simulation, and inverse analysis based on Inverse Topology Optimization (ITO). The Cu/CuSO₄ reference electrode was fabricated in a compact form for embedded applications and characterized through Open Circuit Potential (OCP) measurement, comparison with an Ag/AgCl electrode, an induced-corrosion test via immersion in a 3.5% NaCl solution, and polarization curve analysis. The experimental results show that the electrode exhibits good stability, with an OCP standard deviation below 2 mV and a mean value of approximately 0.94 mV. After immersion, the OCP shifted from −0.198 V to −0.396 V versus Cu/CuSO₄, indicating a transition from a relatively passive state to active corrosion. The kinetic parameters obtained from the polarization curves, comprising Ecorr of approximately −0.39 V and icorr of approximately 4.54 A/m², were used as boundary conditions in the simulation. The FEM model, based on the Laplace equation, was validated through an analytical test with zero error and a meshindependence study. The simulation reveals that a reinforcement potential of −0.396 V was detected as only −0.249 V at the concrete surface, corresponding to an amplitude loss of approximately 146.9 mV, or 74.2% of the anodic–cathodic signal range. Subsequently, the ITO analysis successfully predicted and reconstructed the location and size of the corrosion zones from the surface potential data. For the single-zone case, the reconstruction error was very small, with the root-mean-square residual approaching the measurement noise level. For the multiple-location case, the ITO method recovered more than one corrosion zone without any prior assumption regarding their number or shape, although zone separability remained influenced by the concrete cover thickness, the quality of the measurement data, and the regularization parameters. Overall, this study delivers an integrated framework that links experimental data, an FEM-based physical model, and ITO-based inverse analysis, thereby advancing the assessment of reinforced concrete corrosion from a qualitative, potential-threshold approach toward a quantitative, model-based approach. Keywords: reinforced concrete corrosion; embedded Cu/CuSO₄ reference electrode; half-cell potential (HCP); finite element method (FEM); inverse topology optimization (ITO)