M4 Malpas Viaduct, UK – structural rehabilitation of half-joints.

Malpas Viaduct is a 860m long reinforced concrete structure, located near Newport, Wales carrying the M4 motorway. The structure forms a vital regional link together with the adjacent Brynglas tunnel and River Usk Bridge. A particular feature of the structure is the inclusion of half-joints which are hidden critical elements. The structure was suffering from early signs of structural deterioration as a result of chloride contamination. This paper offers an overall review of the rehabilitation programme, from condition inspection, to structural assessment and finally concrete repairs and corrosion protection. The structural assessment utilised non-linear finite element methods and aimed at firstly assessing the current load carrying capacity of the viaduct and secondly develop a detailed concrete repair sequence which negated the requirement of extensive temporary supports while maintaining full traffic and load carrying capacity on the M4. The rehabilitation strategy incorporated the design and installation of an innovative hybrid corrosion protection electrochemical system to extend the service life of the hidden critical elements by 30 years. The system is the first of its kind in half-joints and offers targeted corrosion protection that passivates the reinforcement from residual chloride contamination and the simplicity and low maintenance of galvanic anodes. [ABSTRACT FROM AUTHOR]