Development On Corrosion Monitoring System Of Rebar Embedded In Concrete

Generally, rebar embedded in concrete should not be corroded due to high alkline. However, corrosion of rebar induced by and carbonation of conrete and chloride contamination is the major cause of damage of reinforced concrete structures. That will reduce the loading capacity of infrastructure, and even lead to collapse. Evaluation of coorsion for rebar in concrete can be really recognized as a basci indicator for remain loading capacity and wear of concrete. Therefore, detection/monitoring of corrosion for rebar should be significant both in sociology and economics.Prior to the CoulMonitor, corrosion monitoring in steel reinforced structures has been conducted either by taking concrete core samples from the structure, or by using linear polariztion method. The core sampling technique has the disadvantages of damaging the structure, temporarily disrupting traffic flow and other functions of the structure, as well as being labor intensive with some safety risk to the sampling technician. Although linear polarization method is one non-destructive evaluation (NDE) method, whose disadvantage mainly focus on the disturbation of testing result always due to high resistivity of concrete.CoulMonitor corrosion monitoring system is based on coulostatically-induced impulse perturbation method, which is also a NDE system. In this method, a known amount of small charge was instantaneously applied to the test electrode at equilibrium state and then the over-potential decay curve was recorded for analysis. The continuous monitoring is conducted by integrating microchip into coulostatic measurement. This method has some advantages in the determination of rebar corrosion processes because there is no current between the working and reference electrodes during recording over-potential decay curve and the influnence of high resistivity of concrete during measurement process can be elimination. The instruments communicate with an external datalogger using the SDI-12 industry standard protocol. The information stored in the datalogger can be downloaded to a portable PC on site or remotely using a wireless cellular connection. The whole sizes are compact and resultant weight are reasonable reduced. Also power unit is flexible and compatible for both alternative current and direct current solutions. Based on the above development and design, the whole system was built in a rugged portable box, therefore paved the way for the convenient corrosion monitoring based on the coulostatic method Therefore, CoulMonitor has many applications in the construction and maintenance of commercial and civil structures. Such structures can include, but are not limited to, high rise buildings, parking garages, bridges, dams, spillways, flood control channels, piers, pylons and erosion control structures. Once the Coulmonitor instrument is properly embedded in the completed structure, long term monitoring of corrosive conditions can proceed.In this thesis, measuremnts had been taken to make progress the hardware of CoulMonitor. Microcontroller based on C8051F020 centrally sequences polarization resistance and corrosion potential measurements with a cotinuous and time determination of corrosion rate of rebar. The main conclusions and characteristics of CoulMonitor are as follows:Using double amplifiers to boost the instantaneous polarization voltage into corrosion cell, which can reduce time-constant involved in the coulostatically-induced transients. Also, duration of charge transfer into cell will be shortened. That eliminate IR-drop influnence on measurement results and extend the applications of coulstatic technique.An analog circuit was designed to simultaneously follow corrosion potential of working electrode. That is relatively immune to interference between digital and analog circuit during the compensatation of corrosion potential at digital-to-analog (DAC) converter side.The data analysis package was also designed and realized based on the mix-programming idea. Using Visual C++ and MatLab to mix-program, adopting non-linear least-square functions of Matlab, this software can still own some advantages of VC programme such as high efficiency along with flexible operation style. Meanwhile, mix-program can sharply reduce complier larbour so that the CoulView analysis software can be rapidly developed by using dynamic link libraies technique. That also permit produce an integrated software package with advantage of installation and useage.