51315-5838-Corrosion Propagation of Carbon Steel with Multiple Concrete Covers and Concrete Compositions

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Product Number: 51315-5838-SG

ISBN: 5838 2015 CP

Author: Francisco Presuel-Moreno

Publication Date: 2015

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The corrosion propagation of steel in concrete is still not well understood. It is known that corrosion products build up and eventually cause cracks 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) and the concrete cover thickness. In here three type of specimens were investigated. Specimen set 1 contained #5 rebar single rebar with 50 mm of concrete cover 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 ponding solution was 15% NaCl and was placed in the center 5 cm of a 30 cm long rebar. Specimen set 2 contained a #3 rebar with 10 mm cover and embedded in mortar; a w/cm of 0.45 for mortar with type I cement and 0.38 for mortar with 20% fly ash and cement type I these specimens were exposed to 15% NaCl and were exposed for > 800 days. Corrosion initiated after 400 days of exposure on specimens with Fly Ash. The third type of specimens are instrumented segments of reinforced concrete pipes with no chlorides initially but chlorides transported via migration to initiate corrosion. The reinforced concrete pipes contained steel strands that range from 5 to 7 mm in diameter. The propagation period reported in here on all of these specimens was at least 600 days (in several cases even longer). Just in a few cases were corrosion products observed at the concrete/mortar surface and only the mortar specimens with type I cement suffered cracks after approximately one year of corrosion having initiated. Linear polarization corrosion potential and on some electrochemical impedance spectroscopy was used to monitor the specimens.