Corrosion Propagation of Carbon Steel Rebar with Different Concrete Covers and Concrete/Mortar Compositions

The corrosion propagation of steel embedded in concrete is still not well understood. It is known that corrosion products build up and eventually cause cracks (when the metal loss reaches a critical penetration xcrit) by exceeding the tensile stress that concrete can support due to the larger volume that the corrosion products occupy. Moreover, it has been reported that the amount of corrosion products that could cause concrete to crack is dependent on the length of the anode (corroding site), rebar diameter, and the concrete cover thickness. In this project, three types of specimens were investigated. Specimen type 1 contained a #3 rebar with 0.8 or 1.2 cm cover and the rebar was embedded in mortar; a w/cm of 0.38 was used for most specimens and a few specimens were prepared with w/cm of 0.45. Specimen type 2 contained #5 rebar, a single rebar with a concrete cover of 5 cm, and two different concrete compositions with a w/cm of 0.41 (OPC and OPC+ 20% Fly Ash). These specimens have been within the corrosion propagation period for over three years. The third type of specimens are instrumented segments of reinforced concrete pipes, initially with no chlorides, but chlorides were transported via migration to initiate corrosion after a short period of time. The reinforced concrete pipes contained steel strands that range from 4.5 to 5.5 mm in diameter. The propagation period reported in here on all of the different type of specimens was at least 600 days. In just a few cases corrosion products were observed at the concrete/mortar surface and only some of the mortar specimens and one of the type 3 specimens showed cracks after corrosion was propagating for at least a year. Linear polarization, corrosion potential and electrochemical impedance spectroscopy tests were used to periodically monitor some of the specimens. Selected specimens were terminated and forensic examination was performed.