For decades, concrete in Bermuda has been mixed with seawater, which introduced high chloride concentrations into the concrete. To protect steel reinforcement from corrosion, hot-dipped galvanized (HDG) rebar has been used since the 1950’s, including in the Longbird Bridge, which was built in 1954 by the US Navy and demolished in 2020 by Bermuda’s Ministry of Works & Engineering, after being closed due to hurricane damage. Over the nearly seven decades the Longbird Bridge stood, several inspections and corings were conducted to evaluate the galvanized rebar. Following the bridge’s recent demolition, samples of the rebar and concrete were collected and sent for testing.
In “Synthesis of Studies: Hot-Dip Galvanized Reinforcing Steel Performance on the Longbird Bridge in,” Francis P. Gerace P.E. and Peter M. Melewski P.E. describe findings of the recent metallurgical examination and past analyses. Their September 2020 report found that:
Despite the bridge being subjected to nearly seven decades of heavy chloride concentrations from initial construction and its location just a few feet above the ocean in tidal and splash zones, “the galvanized coating on the rebar was in exceptionally good condition” at the time of demolition. “In almost all cases the rebar still had a coating thickness which exceeded ASTM A767 – Class 1 minimum requirements of 150µm (6 mils) for new rebar.”
“The HDG reinforcement performed as expected, with no resultant spalling or cracking pressure on the concrete. In other words, if it were not for hurricanes, the rebar would have easily served for over 100 years.”
Photo credit: Akil Simmons