Preliminary Study On Cathodic Protection Effect Of Discrete Sacrificial Anodes On Rebars In Concrete

The effectiveness of zinc-based sacrificial discrete anodes in several conditions is studied, which include 3% sodium chloride solution, 3% sodium chloride alkaline solution and different types of concrete specimens. The concrete specimens were cast with and without chloride which was added 1% by cement weight; Both Galvashield XP anodes and domestic anodes were used to protect the common hot-rolled bars with 10mm diameter. To judge the effectiveness of cathodic protection system, in the solution enviroment"-850mV(CSE) potential"specification is suitable and in concrete situation"-100mV"polariztation standard is adopted. Results show that: (1) In 3% NaCl solution, cathodic protection of one steel bar by single sacrificial anode satisfies with"-850mV(CSE) potential"requirement, while the protection system of three steel bars does not.;(2) In 3% NaCl-saturated Ca(OH)2 solution, discrete anode also display good performance in protection and meets the requirement of"-850mV(CSE) potential";(3) the potentials of steel bars in concrete containing chloride are lower than those in concrete without chloride at the same conditions; (4) the polarization of steel bars meets the"-100mV polarization"specification when the concrete specimens are immersed in chloride solution or water with the concrete covers thickness less than 20mm。Sacrificial anode cathodic protection technology was applied to pavement layer and guardrail of Yong Ding River super large bridge, in which concrete strength was C50 and concrete cover thickness was 50mm. The system covers approximately 100 meters from pier No.9 to pier No.13. Self-maded anodes, domestic anodes and imported anodes were used for comparision and three anodes were installed every square meter. Data were collected and transferred with special apparatus. Results show that :(1)Variation of temperature and humidity in the air shows no obvious influence on the potential values of steel bar. (2)Sacrificail anode cathodic protection system can hardly meet the requirement of"-100mV"specification in dry newly built concrete structures, and further observation is needed to evaluate the effectiveness of the protection system when confronting corrosion environment.