Extending the Service Life of a Reinforced Concrete Railroad Bridge with Galvanic Encasements
Reinforced concrete structures can be designed and maintained to achieve long service lives, even in aggressive chloride environments. Unfortunately, many structures, such as bridges, piers, and wharves, show signs of active corrosion (e.g. rust staining, concrete spalling, etc.) in as little as 5 to 10 years. If left unchecked, chloride induced corrosion can lead to major structural problems.
Many severely corroded structures have been replaced at great expense and with significant disruption to the public. When compared to replacing structures, Galvanic Encasements can make effective long-term use of existing columns, abutments, piers & beams by extending their life with cathodic protection. There are many benefits to this approach including economic, environmental and disruption.
Two railroad bridges in the Midwest US were showing signs of chloride-included corrosion and becoming a local eye-sore and a safety concern.
The columns were heavily chloride-contaminated from years of de-icing chemical exposure and suffering from extensive concrete cracking, spalling and delamination. In addition to shotcrete repairs and epoxy injection crack repairs of the abutments, the columns were repaired and protected by Vector Construction’s Cedar Rapids, Iowa office using Galvanic Encasements.
As part of the concrete preservation process, an evaluation consisting of a combination of non-destructive and destructive testing was conducted to determine the condition of the structures including corrosion potentials, chloride profile and cover depth as determined by ground penetrating radar. Together this information revealed that significant chloride concentrations existed at the level of the reinforcing steel and that corrosion was active throughout the columns.
To thwart the ongoing process of corrosion and effectively restore the structure to its former grandeur, the existing columns and abutments were repaired with a galvanic encasement system that included a distributed galvanic anode system (Galvashield® DAS) inside a modular stay-in-place PVC jacket filled with concrete.
The deteriorated concrete was first removed and the rebar is cleaned of corrosion byproducts (below, left). Then, galvanic anode strips were distributed around the column and connected to the existing reinforcing steel (mid-left). Once the anodes are secured to the existing concrete structure, the PVC forms are fitted around the columns and filled with concrete (mid-right). The end result is shown in the picture below (right).
Aside from the dramatic aesthetic improvement, the rehabilitated structure will have decades of galvanic protection to allow the bridges to remain in service for decades to come, a significant improvement over regular concrete repairs that do not address the fundamental problem, corrosion.
Galvanic encasements utilizing distributed galvanic anodes provide a one-step repair and protection solution galvanic protection to preserve and extend the service life of corroded concrete elements such as columns, piles and bridge abutments.