Anaerobic corrosion of steel reinforcement is rarely reported and limited literature is available on the subject. Corrosion of steel is an electrochemical process requiring a supply of oxygen in the presence of moisture. Steel corrosion product usually occupies a much larger volume than the un-corroded steel resulting in cracked or spalled concrete. If the supply of oxygen is restricted, black rust may be formed by the process of anaerobic corrosion. Black rust is not expansive, which makes it particularly difficult to detect in reinforced concrete. This paper presents a case study of anaerobic corrosion in the Mizen Bridge, together with an in-depth review of anaerobic corrosion of reinforcement in concrete, outlining black rust formation, characteristics and detection methods.

Mizen Head Footbridge in County Cork, Ireland, is a reinforced concrete through-arch structure spanning 50 m. The original structure was completed in 1909. After 100 years of service the bridge was demolished and reconstructed in 2009/10. This paper describes the design and construction challenges of safely demolishing and reconstructing the bridge in a difficult site location. The bridge provided access to a lighthouse on a tiny island, Cloghá n, at the tip of Mizen Head in southwest Cork. The original structure was commissioned by the Commissioners of Irish Lights (CIL). The structural form was chosen from a design competition held in the early 1900s. The entries to this competition are held in the CIL archives and are on display in the Visitors' Centre at Mizen Head.