About Fosroc Galvashield DAS

Fosroc Galvashield DAS is a distributed galvanic anode system used for the long-term corrosion management of reinforced concrete. It belongs to the Galvashield family developed by Vector Corrosion Technologies and supplied through Fosroc’s global network, of which Space Arc Engineering is an authorised distributor for Delhi NCR and Pan-India. Unlike the discrete “puck” anodes (Galvashield XP, XPT, CC) that are placed locally around a patch repair to suppress the incipient-anode or “ring-anode” effect, DAS is a continuous strip system engineered to protect entire elements or large areas of slab, beam, column and wall.

Each anode consists of a high-purity zinc core cast within a proprietary alkali-activated cementitious mortar that holds an internal pH of 14 or greater. This high-alkalinity environment keeps the zinc electrochemically active throughout its life so that it continues to sacrifice itself in favour of the embedded steel. The strips are distributed across the concrete at a designed spacing, electrically connected to the rebar cage, and then buried within an overlay, a reinforced concrete jacket, a stay-in-place form or fresh structural concrete. Once the circuit is closed and the assembly is moist, the zinc dissolves preferentially and drives a galvanic current to the steel, shifting its potential in the negative direction and suppressing the corrosion reaction.

The system is offered in three forms to suit exposure. Type C (cast) anodes are mortar-encased and tolerate wetting before concrete placement, making them practical for site conditions where rain or dampness is likely. Type F (foil) anodes carry an external zinc foil wrap that delivers a high burst of initial current to rapidly polarise heavily corroding steel, and they are semi-flexible for shaped surfaces. Marine anodes are formulated for submerged, splash and tidal zones such as piles. Because anode size, zinc mass and spacing are all design variables, DAS can be specified across the full protection spectrum — from corrosion prevention in sound concrete, through corrosion control of actively corroding steel, up to a full cathodic-protection design meeting the recognised 100 mV polarisation-decay criterion.

The technical insight

The engineering logic of DAS rests on galvanic coupling: zinc (more electronegative) and steel form a cell in the concrete pore-solution electrolyte, so the zinc corrodes and the steel is cathodically polarised. The alkali-activated mortar carrier is the differentiator — most field zinc passivates and stops working as its corrosion products build up, but the pH-14-plus matrix keeps the zinc surface depassivated and the anode delivering current for the long term. Designers vary three levers — zinc mass per metre (roughly 0.25 to 1.2 lb/ft, i.e. 37 to 180 g/m on standard units), anode cross-section and on-centre spacing (150 mm to 750 mm) — to match the required current density to the steel area, chloride load and target life. A practical constraint often missed on Indian sites is electrolyte resistivity: for optimum output the encasement concrete should ideally be below 50,000 ohm-cm, so very dry or highly resistive overlays will throttle the current. Performance is verifiable in service by measuring the 100 mV potential decay (the NACE/ISO cathodic-protection criterion), which is why DAS installations can include reference electrodes and monitoring junction boxes rather than being purely “fit-and-forget”.

Where it is used

• Cathodic protection and corrosion control of bridge decks, piers, abutments and crash barriers exposed to de-icing salts or coastal chlorides
• Repair and life-extension of marine and coastal RCC — jetties, wharves, sea-facing columns, water-front retaining walls and pile caps
• Reinforced concrete jacketing / section enlargement of corroded columns and beams, with anodes embedded in the new jacket
• Embedding within bonded or unbonded concrete overlays on car-park decks and industrial floors
• New-construction durability provision for prestressed and post-tensioned elements in aggressive exposure zones
• Protection at new-to-old concrete interfaces during structural widening of bridges and decks
• Rehabilitation of cooling-tower bases, effluent channels and other industrial-plant concrete in chemically aggressive service

Key advantages

• Provides global, element-wide corrosion protection rather than only local patch protection, addressing chloride and carbonation-driven corrosion across the whole member
• Operates without any external power supply, transformer-rectifier or wiring infrastructure, unlike impressed-current cathodic protection (ICCP)
• High zinc capacity and high current output relative to discrete galvanic anodes, supporting a designed 10 to 40 year service life
• Alkali-activated mortar (pH >=14) keeps the zinc active over the long term, avoiding the early passivation that limits ordinary embedded zinc
• Fully customisable — anode type, zinc mass and spacing are tuned to the structure, so a single system spans corrosion prevention, control and full cathodic protection
• Embedded and tamper-proof, eliminating vandalism risk and giving more uniform performance than surface-mounted systems
• Low maintenance and optionally monitorable via the 100 mV criterion, suiting hard-to-access bridge and marine assets
• Three variants (Cast, Foil, Marine) cover dry decks, fast-polarisation needs and submerged/tidal zones

Limitations & considerations

• Galvanic output is self-limited by zinc potential, so on very high steel densities or extreme chloride loads an impressed-current system (ICCP) may be required instead for full protection
• Performance depends on a continuous moist, conductive electrolyte; output falls in very dry concrete or where encasement resistivity exceeds roughly 50,000 ohm-cm
• It is a corrosion-management system, not a structural repair — delaminated, spalled or carbonated cover concrete must first be cut out and reinstated
• Requires sound electrical continuity of the reinforcement cage; isolated or epoxy-coated bars and discontinuous steel can compromise the circuit
• Make-to-order / project-engineered product with design lead time — it needs a corrosion survey (half-cell potential, chloride profiling, resistivity) and an anode-spacing design, not an off-the-shelf purchase
• Service life is a function of site variables (steel density, chloride concentration, temperature, humidity, spacing), so the 10–40 year range is a design outcome, not a guaranteed figure
• Type F foil anodes must be kept dry before placement, demanding disciplined site storage and sequencing

Selection & best practice

Specifications

Industry use cases

How we position Fosroc Galvashield DAS

Within the Fosroc galvanic range, Galvashield DAS is the area/element-wide solution, sitting above the discrete-anode products: Galvashield XP, XPT and XP2 (embedded puck anodes for patch-repair perimeters), Galvashield CC (corrosion-control anodes) and the related Vector SM-DAS surface-mount strip. Where reinstatement and crack/spall repair are also needed, DAS pairs naturally with Fosroc Renderoc and Patchroc repair mortars and Nitobond bonding agents to deliver the cover concrete that encases the anode. For structures where galvanic current cannot deliver full protection — extreme chloride loads or very high steel density — an impressed-current cathodic protection (ICCP) design is the alternative, at the cost of external power and wiring. Among competitor galvanic/CP systems on the Indian market, the closest analogues are Sika’s FerroGard/galvanic anode and cathodic-protection offerings and specialist corrosion-engineering systems; general waterproofing-led brands such as Dr. Fixit (Pidilite), MBS and STP do not field a directly equivalent distributed galvanic anode, so DAS is best positioned against dedicated CP specialists rather than membrane/coating brands. Space Arc Engineering, as an authorised Fosroc distributor for Delhi NCR and Pan-India, supplies DAS with the upfront corrosion survey and anode-spacing design that the system requires.

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