Fosroc Galvashield XPI
Embedded zinc galvanic anode that sacrifices itself to stop new corrosion forming at the edge of concrete patch repairs, without external power.
What is it?
A pre-manufactured embedded galvanic (sacrificial) anode: a zinc core in a high-alkalinity cementitious mortar, tied to rebar inside a concrete repair.
Where is it used?
Around the perimeter of concrete patch repairs and at joints between new and existing concrete on bridges, jetties, car parks, water tanks, RCC buildings and prestressed members.
Why use it?
It stops the ‘ring’ or incipient anode corrosion that typically restarts at the edge of a patch repair, extending the life of the repair by 10 to 20 years with no maintenance or power.
How is it applied?
Each anode is tied to clean reinforcing steel with its integral steel tie wires before the repair mortar (e.g. Renderoc) is placed, fully encapsulating the unit with at least 20 mm cover.
About Fosroc Galvashield XPI
Fosroc Galvashield XPI is an embedded galvanic anode unit used in reinforced concrete repair and rehabilitation to prevent the formation of new corrosion sites around a patch repair. Each unit consists of a specially designed zinc anode core (zinc complying with ASTM B418-95a Type I) cast around integral steel tie wires and surrounded by an enhanced, alkali-activated cementitious mortar with an internal pH of 14 or greater. The high pH keeps the zinc electrochemically active throughout the life of the anode while remaining non-corrosive to the reinforcing steel.\n\nThe product solves a problem that is well known to engineers across India but frequently ignored on site: the incipient or ‘ring’ anode effect. When a corroded section of a beam, slab, column or marine deck is broken out and repaired with fresh, chloride-free, high-alkalinity mortar, the patched steel becomes passive (cathodic). The older surrounding concrete, still carbonated or contaminated with chlorides from sea spray, de-icing salts or admixtures, now becomes anodic relative to the repair. Within months to a couple of years, new corrosion cracks appear in a halo right around the patch, and the repair fails. Galvashield XPI breaks this cycle. Because zinc is more electronegative than steel, the embedded zinc corrodes preferentially, throwing protective current onto the adjacent reinforcement and suppressing the new corrosion cell at the most vulnerable point: the interface between the repair and the old concrete.\n\nIn the Indian context this matters for coastal and marine structures along the entire seaboard (Mumbai, Chennai, Vizag, Kochi, the Gujarat and Konkan coasts), for sewage and effluent treatment works, for flyovers and metro viaducts exposed to humidity and pollution, and for water-retaining structures. Galvashield XPI is supplied by Fosroc Chemicals (India) Pvt. Ltd. and is a localised, low-cost, sacrificial measure that pairs naturally with the Renderoc repair range. Space Arc Engineering, as an authorised Fosroc distributor for Delhi NCR and Pan-India, supplies the anodes alongside the compatible repair mortars and protective coatings needed to deliver a complete, durable repair specification.
The technical insight
The XPI is a Type 1A-P alkali-activated anode (per Fosroc/Vector classification, ‘Type A’ meaning the activation comes from the high-pH mortar rather than from a halide humectant). Each unit carries a nominal 60 g of zinc in a 24 x 28 x 100 mm body. Performance hinges on two things being right on site: electrical continuity and mortar resistivity. The integral steel tie wires must be twist-tied tight to clean, electrically continuous reinforcement and the connection confirmed with a meter; if the steel is discontinuous, continuity must be re-established with tie wires. The surrounding repair mortar must be conductive, with resistivity below 50,000 ohm-cm, so the galvanic current can actually reach the steel. This is precisely why Fosroc specifies its own Renderoc repair systems as the encapsulating material, and why a high-resistance, polymer-rich or epoxy mortar must be bridged with a conductive Renderoc layer around the anode. Spacing is driven by steel density ratio (steel surface area divided by concrete surface area): the TDS gives 610 mm maximum spacing at a ratio below 0.6, 500 mm for 0.61 to 0.9, and 430 mm for 0.91 to 1.2, with closer spacing or higher-zinc anodes (XP2, XP4, XPX) recommended for aggressive marine or high-chloride exposure. The mortar contains no chlorides or other constituents detrimental to steel, in line with ACI 222R.
Where it is used
- Mitigating incipient (ring) anode corrosion around concrete patch repairs in all structural elements
- Preventing reinforcement corrosion in new construction at vulnerable interfaces
- Bridge widening, deck and slab extension projects
- Joints and interfaces between new and existing concrete
- Expansion joint repairs
- Prestressed and post-tensioned concrete members and anchorage zones
- Repair of epoxy-coated reinforcing bar
- Coastal and marine RCC: jetties, sea walls, splash-zone elements
- Water-retaining and effluent treatment structures
- Car park decks, flyovers and metro viaducts in carbonated or polluted environments
Key advantages
- Prevents new corrosion at the repair perimeter, the most common cause of patch repair failure
- Galvanic (sacrificial) action needs no external power source, wiring or rectifier
- Effective in both chloride-contaminated and carbonated concrete
- Suitable for conventionally reinforced as well as pre- and post-tensioned concrete
- Quick, simple installation by tying to rebar; no special equipment or operator training
- Low maintenance with no system monitoring required, though performance can be measured if needed
- Compact 24 x 28 x 100 mm unit fits within normal repair depths with only 20 mm cover
- 10 to 20 year service life reduces the frequency and cost of future repairs
- Chloride-free mortar that is non-corrosive to steel, compliant with ACI 222R
- Backed by independent test programmes and an established global track record (Vector technology)
Limitations & considerations
- Provides localised corrosion prevention only; not a substitute for cathodic protection over large or heavily corroding areas
- Does not repair structural damage; a structural engineer must be consulted where load capacity is affected
- Requires verified electrical continuity to the reinforcement to function; discontinuous steel must be bridged
- Repair mortar resistivity must be below 50,000 ohm-cm, so high-resistance epoxy or polymer mortars need a conductive Renderoc bridge
- Single zinc content (approx. 60 g); severe or high-chloride exposure may need closer spacing or higher-capacity anodes (XP2, XP4, XPX)
- Being sacrificial, the zinc is consumed over time and the anode has a finite design life
- Effectiveness depends on correct spacing relative to steel density ratio and on full encapsulation
- Minimum 20 mm cover over the unit must be maintained within the repair
Selection & best practice
Break out concrete from around and behind all corroding rebar to ICRI Guideline No. 03730, exposing clean, sound steel. Verify steel continuity across the patch with a meter and re-establish it with tie wires where bars are discontinuous. Position XPI units on the side of or beneath the exposed bar, as close as practical to the surrounding old concrete, leaving room for full encapsulation and at least 20 mm cover; for a second mat of steel, place units on a grid. Twist-tie the integral wires tight using a wire-twisting tool to eliminate movement and ensure a low-resistance connection, then confirm the connection with a meter. Set spacing from the steel density ratio per the TDS (610/500/430 mm), tightening it for marine, high-chloride or extended-life requirements, or stepping up to a higher-zinc anode. Encapsulate with a conductive Renderoc repair mortar (resistivity under 50,000 ohm-cm); if a high-resistance material is specified, pack Renderoc between the unit and the substrate first to create a conductive path. For broader-area control, combine perimeter XPI units with Galvashield CC units gridded through the remaining sound-but-contaminated concrete. Store boxes unopened in dry conditions away from temperature and humidity extremes and install within two years.
Specifications
| Product type | Embedded galvanic (sacrificial) anode unit for concrete repair |
| Anode core | Zinc complying with ASTM B418-95a Type I |
| Anode type / activation | Type 1A-P, alkali-activated (Type A), internal mortar pH 14 or greater |
| Encapsulating mortar | Enhanced cement-based mortar, chloride-free, non-corrosive to steel (per ACI 222R) |
| Nominal dimensions | 24 x 28 x 100 mm |
| Zinc mass | 60 g (nominal) per unit |
| Tie wires | Integral steel tie wires for tying to reinforcement |
| Maximum spacing (steel density ratio <0.6) | 610 mm between units |
| Maximum spacing (ratio 0.61–0.9) | 500 mm between units |
| Maximum spacing (ratio 0.91–1.2) | 430 mm between units |
| Minimum cover over unit | 20 mm |
| Required repair mortar resistivity | Less than 50,000 ohm-cm (use Renderoc systems) |
| Service life | 10 to 20 years (typical conditions) |
| Packaging | Boxes of 50 anodes, approx. 8.2 kg per box |
| Shelf life / storage | Install within 2 years; store dry, unopened, away from temperature/humidity extremes |
Industry use cases
Bridges and Highways
Embedded around patch repairs on bridge decks, soffits, piers and during deck widening or slab extension to stop ring-anode corrosion at the new-to-old concrete interface on flyovers and highway structures.
Marine and Coastal
Protects repairs on jetties, sea walls, splash-zone beams and columns along India’s coastline where chloride ingress from sea spray drives aggressive reinforcement corrosion.
Water and Wastewater
Used in repairs to water-retaining tanks, sewage and effluent treatment structures where carbonation and chemical exposure leave surrounding concrete contaminated.
Commercial and Infrastructure Buildings
Installed in spalled RCC beams, slabs, columns and car park decks in older buildings to prevent fresh corrosion cracks reappearing at the edge of cosmetic and structural patch repairs.
Metro and Rail Viaducts
Applied to repairs on prestressed and post-tensioned viaduct girders and anchorage zones where humidity and pollution accelerate corrosion of high-tensile steel.
Frequently asked questions
What does Fosroc Galvashield XPI actually do?
Why do patch repairs corrode at the edges, and how does XPI help?
How many anodes do I need and at what spacing?
What repair mortar should be used with Galvashield XPI?
How is Galvashield XPI different from Galvashield CC, XP2 or XP4?
Is Galvashield XPI available in India and from Space Arc Engineering?
How we position Fosroc Galvashield XPI
Galvashield XPI is Fosroc’s compact perimeter anode for preventing incipient (ring) anode corrosion around concrete patch repairs. Within the Fosroc galvanic range it is the entry-level localised option: step up to Galvashield XP2, XP4 or XPX where more zinc, higher current output and longer life are needed in aggressive marine or high-chloride exposure, and add Galvashield CC units gridded into the surrounding contaminated concrete where broader-area corrosion control is required. It is designed to be encapsulated in Fosroc’s Renderoc repair mortars, which provide the low-resistivity path the galvanic system depends on. Against competitor systems, the underlying technology is the same Vector Corrosion Technologies platform marketed by Sika as Sika Galvashield XP, so the products are directly comparable; the meaningful difference on an Indian project is specification compatibility (pairing the anode with Fosroc Renderoc repair mortars and protective coatings) and local supply. Embedded galvanic anodes are a specialist corrosion-prevention category and are not directly substituted by general waterproofing or admixture brands such as Dr. Fixit (Pidilite), STP or MBS, which address water ingress and concrete admixture needs rather than galvanic corrosion control; on a durable repair, those products complement the anode by reducing the moisture and chloride ingress that drive corrosion in the first place. Space Arc Engineering positions Galvashield XPI as part of a complete Fosroc concrete-repair-and-rehabilitation system rather than a stand-alone item, supplying it with the matched repair and protection materials and the technical support to specify spacing, continuity and encapsulation correctly.
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