Investigation On Embeded Monitoring Sensor For Reinforcement Corrosion

Nowadays, corrosion of reinforcement has become the main reason that leads to lack ofdurability and damage of reinforced concrete structures in its early service life. In orderto enlarge the service life of structure effectively, make sure the safety of it and reducethe cost of repair, it will have great meaning to develop a kind of monitoring system,which can monitor the corrosion situation inside the concrete immediately and exactly.By using this system, it will become more convenient to evaluate durability of concretestructures, to predict when corrosion will start, and to make a decision whether to repairit or not.In this paper,8kinds of embedded monitoring system at home and abroad werecompared from the following aspect: the design principle, the monitoring principle,advantage and disadvantage. Based on this, two kinds of sensors with specialmanufacture and design craft were designed. The first one is a kind of Macro BatterySensor which can predict the penetration depth of corrosion medium by recording thechange of macro current. At the same time, it can also be used as a concrete resistivityunit. The second one is Resistance Sensitive Sensor that can predict the penetrationdepth of corrosion medium through the change of resistance of gauge wire. Based onthe investigation above, a series of experiments were carried out:(1) Mortar with water to cement ratio of0.5was prepared. Anoder Ladder Systemof ETH and the two kinds of sensor designed by the author were put into the motat, thenNaCl solution was put onto the mortar. After that, compare the results obtained from thethree kinds of sensor. Results indicates that the corrosion time of four anodes of themacro battery sensor in different depths from the surface of mortar is almost the samewith that of the Anode Ladder System, which was10days,26days,46days and76days. So, we can draw a conclusion that the stability and sensitivity of the MacroBattery Sensor is very good. However, the result obtained from the Resistance SensitiveSensor was approximately4days later than that obtained from the other two sensors. So,the Resistance Sensitive Sensor is of less sensitive.(2) The relationship between the macro current and time in three kinds of mortarwith different water to cement ratio under chloride environment was studied by MacroBattery Sensor. Results indicate that when the anode began to corrosion, the macrocurrent would reach the peak value between10days and20days, then there would be a stable level which means the macro current was mainly controlled by the cathodereaction at this moment, but at a later stage it was influenced by corrosion products.Then the current began to reduce.(3) Change of macro current between the same anode and different cathodes of theETH Anode Ladder System was studied. Results indicated that the maximum value ofthe macro current was reduced by65%with the oxygen reduction around the cathodesand with the increasing of distance between anode and cathode.(4) Based on AC impedance technique, the dimention ratio value K of two bordercathodes of the Macro Battery Sensor was measured by using0.01mol/L KCl solution.The K value is0.1878cm. At the same time, the Macro Battery Sensor was used as aresistivity testing unit to get the change of the resistivity of mortar. Results showed thatthe resistivity reduced with the increase of humidity and concentration of chlorine ion.(5) The macro current of twenty-three Anode Ladder Systems made in Germanyused in Qingdao Jiaozhou bay subsea tunnel was determined. And its value was almostzero. It showed that all the anodes in different depth of the concrete have not rusted. Atthe same time, the macro batteries in concrete (the exposed under the marineatmosphere environment) were tested in site. Results showed that the Macro CurrentSensor had a very good reaction to the chloride ions under practical environment.