Review of Electrochemical Testing to Assess Corrosion of Post-Tensioned Tendons with Segregated Grout

Abstract

Post-tensioned (PT) construction incorporating bonded tendons with cementitious grouts has been used for highway bridges. The tendon duct and the encapsulating grout materials provide barrier corrosion protection for the embedded high-strength steel strand. Although generally used in good engineering practice, cases of PT tendon corrosion have been documented relating to inadequate detailing for joints and development of grout bleed water. Recently, in the past several years, unexpected severe localized strand corrosion has related to the segregation of thixotropic grouts. In the latter case, thixotropic grouts (that have been developed to mitigate grout bleeding) formed physical and chemical deficiencies that have been characterized to have high moisture content and elevated sulfate ion concentrations. The early presence of elevated sulfate ion concentrations in the deficient grout hinders stable steel passivation. The corrosion mechanism can be complicated due to the compounding effects of physical grout deficiency, moisture content, pore water pH, and the presence of sulfate ions. There remains interest to reliably assess corrosion of PT tendons with deficient grout. A review of electrochemical techniques and test methods used in earlier research by the authors to identify the role of sulfates on localized steel corrosion in alkaline solutions is presented. It was evident that different testing methods can reveal various aspects of the corrosion of strands in the deficient PT grout. The open-circuit potential and linear polarization method could differentiate corrosion activity between hardened and deficient grout environments but did not reveal the development of localized corrosion. Electrochemical impedance spectroscopy was useful to identify grout deficiencies by the differentiation of its bulk electrical properties. Potentiodynamic polarization and electrochemical noise technique were used to identify metastable and pitting in alkaline sulfate solutions representative of the deficient grout pore water.