Materials Performance

MAR 2018

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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37 MATERIALS PERFORMANCE: VOL. 57, NO. 3 MARCH 2018 tion and repair of the pipe may pre- clude the use of CP. Laboratory Phase This phase of the project was to determine the effect of CP on the perfor ma nce of passivated, cor- roded, and split prestressing wire im mersed i n a n environ ment to simulate sound mortar and mortar su r rou nd i ng s everely cor roded wire. The effect of low pH caused by corroding wire, the susceptibil- ity of prestressing wire to HE, and the approximate length of time and potentials to produce HE and even- tual wire failure were determined. The effect of discontinuing high levels of CP on the diffusion of hy- drogen from wire and the recovery of duct ilit y were evaluated. The maximum CP potential that high- st reng t h pre st re s si ng w i re c a n withstand without failure in those environments was determined. 10 Test Procedure ASTM A648, Class III prestress- i ng w i re spec i men s f rom t h ree manufacturers were subjected to no CP and to CP polarization poten- tials of –850 mV CSE and –1,000 mV CSE as well as cathodic overprotection values of –1,200 mV in a saturated calcium hydroxide (Ca[OH] 2 ) solu- tion for up to 86 months. Prior to exposure, most of the wire specimens were stressed and maintained at 60% of specified min- imum tensile strength, which is the approximate stressed value of the wire in PCCP. A coal tar epoxy coat- ing was applied to the wire speci- men surface 1 in. (2.5 cm) above and below the solution level to prevent failure at the air/solution interface. Specimens were immersed in so- lutions to simulate the high-alka- line, corrosion-inhibiting environ- ment provided by portland cement or in a hydrochloric acid (HCl) solu- tion (pH 2) to simulate the condition around a severely corroded wire in mortar. CP of Passive Wire in Simu- Cathodic Protection Criteria for Prestressed Concrete Pipe—An Update FIGURE 5 Time-to-failure of prestressing wire held at –1,200 mV CSE as a function of continuous torsion. lated Mortar at pH 12.45. At vary- i ng t i me per iods, f rom 3 to 80 months, two 6-gage stressed wire specimens at no CP, and at –850, –1,000, and –1,200 mV CSE , were re- move d f rom ex p o s u r e. Te n si le

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