Repair and Service Life Extension of Grouted, Post-Tensioned Concrete Bridges

Abstract

Grouted, post-tensioned concrete systems are commonly used in the construction of segmental concrete bridges, with the aim of achieving a corrosion-free service life of 100+ years. Nevertheless, the utilization of inadequate grout materials and improper grouting techniques has resulted in the formation of voids in the anchorage regions, leading to premature corrosion of the strands within one or two decades. Furthermore, the re-grouting of these voids with repair grout has accelerated the corrosion of strands at the interface between the base grout (which is typically carbonated) and the repair grout. This accelerated corrosion is primarily attributed to the differences in the chemical properties of the grouts, raising concerns and creating hesitance regarding the re-grouting of voids in tendons. This study focused on the development of non-invasive chemical methods (such as re-alkalization) and electrochemical methods (such as galvanic cathodic protection), to repair the anchorages of grouted, post-tensioned concrete systems. Immersion experiments were conducted to assess the effectiveness of alkaline solutions in re-alkalizing carbonated grouts. The results indicated that 1 M Ca(OH)2 solution can restore the pH of carbonated grouts in approximately one day. Additionally, electrochemical impedance spectroscopy studies demonstrated that this solution can re-passivate the embedded strands within a week. However, achieving complete re-alkalization and re-grouting of voids can be challenging. Consequently, a redundant electrochemical system that operates externally to the anchorage was found necessary. Experiments were conducted to evaluate the viability of galvanic anodes in protecting the anchorages. The findings revealed that a thin layer of grout surrounding the strand is sufficient to provide ionic conductivity for the galvanic anode connected to the strand-end outside the anchorage, in effectively protecting the strand portions inside the anchorage. The study presents recommendations for repairing the anchorage regions using chemical and electrochemical methods. Additionally, a set of comprehensive and stringent performance specifications for grouts has been proposed to ensure complete filling of ducts during the grouting and re-grouting processes.