On the Role of the Pore Water Chemistry of Deficient Post-Tension Grout to Promote Steel Corrosion

Corrosion failure of post-tension tendons with pre-packaged thixotropic grout was documented in Florida Bridges in less than 10 years of service. Analysis of deficient grout in Florida post-tensioned (PT) bridges where severe corrosion developed indicated enhanced sulfate ion concentration, high pore water pH, enhanced moisture and low chloride content. The corrosion wasn’t consistent with the conventional causes of steel corrosion such as bleed water accumulation in grout void spaces, chloride contamination and pore water carbonation. Corrosion development was associated with deficient grout with enhanced sulfate levels. However, limited information is available on the corrosion behavior of PT strand in grout materials with enhanced sulfate content. Review of the technical literature has not shown consistent evidence of the role of sulfate ions in the corrosion of steel in solution and in hydrated cementitious material. In this research, the role of sulfates in cementitous materials was examined including identifying practical limits for sulfates in grout materials. Laboratory samples were created with 15% and 20% excess water to enhance deficient grout materials and included enhanced sodium and chloride content. Enhanced sulfate and chloride ion presence was thought to provide aggressive corrosion condition of steel in segregated grout. Testing was intended to differentiate the corrosion of steel in pore water condition of deficient grout