About Fosroc Galvashield DAS Jacket Type M

Fosroc Galvashield DAS Jacket Type M is part of the Galvashield DAS (Distributed Anode System) family, a galvanic corrosion-protection technology developed by Vector Corrosion Technologies and supplied in India through Fosroc and its authorised distribution network, including Space Arc Engineering. The “Jacket” products take the Galvashield DAS anode and package it for the most demanding situation a corrosion engineer faces in Indian conditions: piles and columns where chloride-driven reinforcement corrosion has already cracked and spalled the cover concrete, particularly through the splash and tidal zone of coastal and marine structures. The “Type M” designation refers to the mortar-filled modular jacket configuration, where the annular gap between the host member and a stay-in-place PVC or FRP jacket is filled with portland cement concrete or repair mortar that simultaneously reinstates lost section and embeds the anodes. At the heart of the system are the alkali-activated zinc DAS anodes — high-purity zinc cast around steel tie wires within an enhanced cement-based mortar held at an internal pH of 14 or greater. That high-alkalinity environment keeps the zinc anodically active for the life of the system without depending on saltwater contact, which is the key reason a single jacket product can work in the wet tidal zone, the damp splash zone, the dry upper pile and even in non-marine columns. Once the rebar is made electrically continuous and connected to the anodes, the zinc preferentially corrodes in place of the steel, supplying protective galvanic current that the system self-regulates according to the corrosion rate and environment. The result is a self-powered, near-zero-maintenance protection layer that does not need rectifiers, wiring runs to a power supply, or the ongoing monitoring burden of an impressed-current cathodic protection (ICCP) installation. For Indian asset owners — port trusts, bridge authorities, coastal industrial plants and infrastructure operators — this combines two jobs that are usually separate (structural patch repair and corrosion mitigation) into one specialist operation, which is why the DAS Jacket sits firmly in the protective coatings and corrosion-control segment rather than being a plain repair mortar.

The technical insight

The defining engineering feature is the alkali-activated anode mortar (internal pH 14 or greater) cast around the zinc. In ordinary galvanic anodes, the zinc passivates as its surrounding environment loses alkalinity and the current output collapses; the enhanced high-pH mortar in the DAS anode keeps the zinc surface depassivated and electrochemically active across wet, damp and dry exposure zones — this is what lets one jacket protect submerged, tidal, splash and dry pile sections without relying on chloride/saltwater activation. The DAS anode itself is supplied in two distributed sizes — DAS at 28 x 38 mm carrying 890 g/m of zinc (0.6 lb/ft) and the higher-output DAS-X at 32 x 50 mm carrying 2,450 g/m of zinc (1.65 lb/ft) — so the designer scales zinc mass (and therefore total current capacity and service life) to the steel density and chloride load of the specific member. Because output is governed by the corrosion cell, the system self-regulates: current rises where steel is actively corroding and tapers where it is passive, which independent test programmes have shown can meet the NACE/AMPP cathodic protection criterion of a minimum 100 mV potential shift. For deep marine piles, the jacket is typically paired with a bulk zinc anode (around 48 lb / ~22 kg) installed below mean low tide and wired up into the jacket junction box to cover the permanently submerged section that the jacket above cannot reach.

Where it is used

• Galvanic cathodic protection of chloride-contaminated, corroding RCC piles in marine and coastal structures
• Repair and protection of bridge piers and columns showing spalling and rebar corrosion
• Splash- and tidal-zone protection of jetty, wharf and port piles above the permanently submerged section
• Protection of prestressed concrete piling and steel H-piles in aggressive exposure
• Single-step concrete reinstatement plus corrosion mitigation on coastal industrial and infrastructure columns
• Non-marine RCC columns affected by carbonation- or chloride-induced corrosion where impressed-current CP is not justified
• Combined use with other Galvashield embedded anodes as part of a whole-structure corrosion management strategy

Key advantages

• Two operations in one: reinstates spalled/lost concrete section and delivers ongoing galvanic protection in a single installation
• Self-powered and self-regulating — no external power, no rectifiers, no transformer/rectifier housing, near-zero maintenance
• Alkali-activated zinc anodes (internal pH 14+) stay active in wet, damp and dry zones without relying on saltwater contact
• Works across marine, brackish, freshwater and non-marine exposures, making it versatile for varied Indian coastal and inland assets
• Long service life — 10 to 40 years depending on zinc mass, steel density, chloride level and humidity
• Meets the NACE/AMPP 100 mV potential-shift cathodic-protection criterion in independent test programmes
• Modular stay-in-place PVC/FRP jacket gives a clean, durable finished appearance and can be round or square in custom lengths
• Most work can be done with the structure in service, minimising operational downtime
• Anode performance can be monitored if required, but monitoring is optional unlike most ICCP systems

Limitations & considerations

• A galvanic (sacrificial) system — total current output is finite and lower than impressed-current CP, so it is sized for the design life and cannot be ‘turned up’ later
• Service life is project-specific and falls with higher reinforcement density, higher chloride concentration, very high conductivity concrete and high humidity
• Performance depends on the rebar being electrically continuous; discontinuous steel must be bonded before the system will work correctly
• Permanently submerged pile sections below mean low tide generally need a supplementary bulk zinc anode — the jacket alone does not cover them
• Not a structural strengthening product; where structural damage exists a structural engineer must assess load capacity separately
• Requires correct surface preparation (breaking out unsound concrete, grit/hydro-blasting steel) and trained installation for the anodes to function as designed
• Higher first cost than a plain repair mortar; the value is realised over the extended maintenance-free service life, not on day one

Selection & best practice

Specifications

Industry use cases

How we position Fosroc Galvashield DAS Jacket Type M

Galvashield DAS Jacket Type M occupies the specialist niche where structural patch repair and corrosion mitigation must happen together on piles and columns — typically chloride-attacked marine and coastal RCC. Within the Fosroc/Vector galvanic range it complements the embedded discrete anodes (Galvashield XP, CC, R, and the broader Galvashield DAS embedded forms) and the distributed Galvashield DAS used in patch and deck repairs; the Jacket is the format you reach for when the member is already spalling and needs section reinstated. Against impressed-current cathodic protection (ICCP) it positions as the lower-maintenance, no-power alternative for assets where running a rectified system is not justified, accepting a finite galvanic current budget in exchange. Compared with competitor galvanic and CP systems — Sika (FerroGard embedded anodes and Sika galvanic/CP ranges), MBS, and STP/cathodic-protection specialists — its differentiator is the alkali-activated anode that stays active across wet-to-dry exposure plus the integrated jacket-and-fill delivery. It should not be confused with plain polymer-modified repair mortars (Fosroc Renderoc, Sika MonoTop, Dr. Fixit repair systems), which reinstate concrete but provide no ongoing cathodic protection; the honest framing for a client is that the DAS Jacket costs more upfront and is justified by extended, near-maintenance-free service life on high-value corroding pile and column assets.

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