Fosroc Galvashield XP
Fosroc Galvashield XP is a discrete sacrificial galvanic anode for the cathodic protection of steel reinforcement in concrete patch repair applications. The anode consists of a high-purity zinc core encapsulated in a proprietary alkaline mortar matrix, supplied as a finished cylindrical unit with embedded tie wires for connection to the host reinforcement. Galvashield XP is installed at the perimeter of a concrete patch repair by tying the anode tie wires to the exposed reinforcement before the repair mortar is placed, encapsulating the anode in the placed mortar. In service, the zinc anode corrodes preferentially to the steel reinforcement (sacrificial galvanic action), providing cathodic protection current to the surrounding reinforcement and preventing the formation of an 'incipient anode' or 'halo' corrosion at the boundary between the patch repair and the surrounding chloride-contaminated concrete. The published anode service life is 10-20 years depending on the substrate chloride content and the protected reinforcement area per anode. TRSC specifies Galvashield XP on chloride-contaminated concrete repair projects where the substrate surrounding the patches carries chloride content above the corrosion threshold and the engineering intent is to prevent incipient-anode corrosion at the patch boundaries.
Fosroc Galvashield XP (and the equivalent Vector Corrosion Technologies Galvashield product line, marketed in Australia under both Fosroc and direct distribution) is TRSC's default sacrificial galvanic anode specification for chloride-contaminated concrete repair where the engineering intent is to prevent incipient-anode (halo) corrosion at the patch boundaries. The engineering basis for the specification is well-established: in chloride-contaminated concrete, patch repair removes the most-deteriorated concrete and replaces it with new alkaline mortar, but the surrounding substrate remains chloride-contaminated; the new mortar is alkaline and the surrounding substrate is less alkaline, which creates an electrochemical potential difference that drives a corrosion cell at the patch boundary — the incipient anode mechanism. Sacrificial galvanic anodes installed at the patch boundary supply protective current to the surrounding reinforcement, suppressing the corrosion cell and extending the corrosion-protection service life of the patch. The most common specification pitfalls TRSC encounters in the field are: (1) anode spacing — the published protection radius of Galvashield XP is approximately 300-450 mm depending on the substrate condition; field installations that space anodes too widely produce gaps in the protection coverage, leaving sections of reinforcement unprotected and producing visible halo corrosion within 2-5 years of the original repair; the spacing must be designed per the substrate chloride profile and the reinforcement layout; (2) tie wire connection — the anode tie wires must be securely tied to the host reinforcement to provide the electrical connection that drives the galvanic action; field installations with loose or rusted tie connections do not provide the protective current and the anodes are functionally dead; the contractor must demonstrate the connection technique on the first installation as a witness hold point; (3) mortar encapsulation — the anode must be fully encapsulated in the placed repair mortar to maintain the alkaline environment around the zinc core; field installations that leave anodes partially exposed or in air voids produce anodes with shortened service life. TRSC remediation specifications that nominate Galvashield XP include the anode spacing per chloride profile, the connection inspection requirement, and the encapsulation verification at the end of each repair phase. The product was specified on the Marina Mirage marine concrete repair where the substrate chloride profiles indicated severe contamination and the engineering intent was to prevent incipient-anode corrosion at the patch boundaries.