||Effectiveness of Sacrificial Anodes in High-resistivity Shotcrete Repairs
Michael M. Sprinkel
Associate Director for Structures
VDOT employs shotcrete to repair overhead and vertical surfaces of reinforced concrete that have deteriorated, primarily due to chloride-induced corrosion. A phenomena that affects the durability of such repairs is the "halo effect", wherein, the steel within the freshly repaired area serves as a cathode to drive accelerated corrosion of reinforcement in the surrounding unrepaired concrete.
To mitigate corrosion of the surrounding reinforcement, sacrificial galvanic anodes have been introduced into repair areas. The anode, usually zinc, is a less noble metal and sacrificially corrodes to protect the surrounding reinforcement. Manufacturers of the anodes claim that the anodes are ineffective if the resistivity of the concrete in the repair, surrounding the anodes, is greater than 30,000 ohm-cm, a value not uncommon for quality shotcrete material.
The proposed evaluation concerns shotcrete repairs to concrete bridge substructure and superstructure components. The subject structures are being repaired under a term contract administered by the Culpeper District.