Impressed Current Cathodic Protection System For Reinforced Concrete Structuers

Corrosion of the reinforcing steel is the major factor which deteriorates the durability of reinforced concrete (RC) structures. Currently, cathodic protection (CP) methods have been verified as the only effective approach to directly prevent the corrosion of steel RC structures. The key metrics to guarantee the accuracy and reliability of the impressed current cathodic protection (ICCP) system are the high-performace anodic matierlas and the numerical simulation of the electric field distribution. Based on the combination of the theoretical research, the numerical simulation and the experimental verification, the multi-scale carbon/cement anodic composites are prepared, and the electric field distributions are investigated deeply. The major contents are as follows:Firstly, the conductivity of the cement mateirlas mixed with carbon fiber (CF), carbon black (CB) and carbon nanotubes (CNT), respectively, is investigated. Considering the conductive mechanism, the economic cost and the constructability, the multi-scale carbon/cement anodic composites are prepared. Furthermore, the accelerated tests are employed to investigate the polarization behaviors of the anodic composites. Moreover, the polarization mechanism of anodic composites is furtherly elucided by SEM and EDX, etc.. The results indicate that the entire polarization process of the anodic materias exhibits three-stage characteristics. The first two stages where the conductivity increases solowly are resulted from the increasing of the water ratio and the establishment of the internal anti-electric field of cement matrics, respectively. However, the oxidation of CF leads to the extensive increased of the conductivity during the third stage. The first two stagtes can be defined as the normal serive-life of multi-scale carbon/cement anodic mateirials. Additionaly, it is found that the anodic composites are immune to Cl-in the acceleted polarization tests. Finally, the optimal proportion of multi-scale carbon/cement anodic composite is CF03CNT15CB2. The service-life of CF03CNT15CB2is more than200h under the extremely harsh circumstances, e.g.,1200mA/m2and PH=13.5.Secondly, three-dimensional simulation method is established based on the Laplace governing equations during the electric-field throwing process and the secondary-current distribution principle of COMSOL Multiphysics to achieve the numerical calculation of the electric field of ICCP system. Then the in-situ anodic and cathodic polarization curves under complex circumstances are used to characterize the reaction interfaces of RC structures; the geometric models had been split by the free triangular elements are adopted; and the stationary solver of COMSOL is used to finally establish the numerical simulation model of ICCP system. The electrical potential and current density on the surface of reinforcing steel and concrete are obtained by the afterprocessing program of COMSOL. The numerical results indicate that the electric field close to the anode and cathode zones is the strongest, and the current density in the steel-concrete interface is the higest. The effective cathodic protection can be achieved by paving the anodic composites on the outer-surface of the concrete adjacent to the reinforcing steel.Finally, the ICCP corrosion control prototypes for T-beams and hollow cylindrical pillars are built according to the3-D numerical simulation model and the multi-carbon/cement anodic materials. The half-cell potential of the reinforcing-steel surface is measured and compared with that of the simulation results. The results indicate that the relative error of the numerical results, except few points in T-beam, is within20%. The reliability of numerical simulation method is verified. Besides, the corrosion control effects of the ICCP sytems estalbished here are evaluated based on the protection potential standard and100mv-polarizaiton decay standard. The results show that the effective cathodic protection of the typical RC strcutes, e.g., T-beams and hollow cylindrical pillars, can be achieved by optimizating the ICCP system. Additionally, and the multi-scale carbon/cement anodic composites can be applied in the practical engineering.