About MC-Bauchemie Centrament GA

Centrament GA — properly Centrament Grouting Aid in MC-Bauchemie’s global catalogue — is a specialised powder admixture built around a naphthalene-sulphonate formaldehyde (SNF) superplasticiser base, carried in a mineral filler of quartz sand (30-60%) and a small proportion of talc (under 3%). It is not a bagged, ready-mixed grout the way a Conbextra-type product is; it is the active ingredient a grout designer doses into ordinary OPC or PPC cement and water to produce the grout used specifically for filling post-tensioning (PT) ducts around the high-tensile strand in prestressed concrete work — bridge girders, PT slabs, box-girder segments and cable-stay anchorages. MC-Bauchemie certifies it to EN 934-4:2009+A1:2012, “Admixtures for the production of grout for prestressing tendons,” under AVCP System 2+, with an independent notified body (Institut für Massivbau und Baustofftechnologie, Karlsruhe, ID 0754) auditing the declared performance — a level of third-party scrutiny that matters when the grout’s only job is protecting steel stressed to a large fraction of its breaking load for the full design life of a structure.

Within the wider Centrament range — which also covers the plasticiser series (Centrament N/P), the stabiliser series (Centrament Stabi/SRA), and its direct sibling Centrament Expanding Agent — Centrament GA occupies a narrow but critical niche: PT duct grouting, underpinning and penetration-sealing grouts, and factory dry-mix mortar manufacture. For Space Arc Engineering’s Delhi NCR and pan-India project base, that typically means supplying it to precast yards, grout-batching contractors and dry-mix mortar producers working on elevated corridors, metro viaducts, flyovers and box-girder bridges, where the gap between a compliant EN 934-4 grout and an improvised one shows up years later as strand corrosion, not on day one. Because dosage is mix-design specific and has to be trial-batched rather than read off a bag, we treat and supply Centrament GA as a specified, technically-supported admixture rather than a shelf product — MC-Bauchemie’s declared performance data backed by our own site technical team on the mix design.

The technical insight

The whole point of an EN 934-4 admixture is that a PT duct grout has almost no room for error: the strand inside is stressed to a large fraction of its breaking load, and any void, bleed-water pocket or contaminant next to it can turn into a corrosion-initiation site that isn’t discoverable again without opening up the structure. Centrament GA is engineered around that constraint rather than around general workability. Its expansion is deliberately bounded on both sides (-1% to +5% over 24h) — enough positive expansion to close the annulus around the strand as the grout sets, but capped so it can’t over-expand and crack the duct or sheathing. Its bleed limit (≤2% after 3h) exists for the same reason: free water that rises and sits against the top of an inclined or curved duct becomes exactly the kind of void a corrosion inspector dreads finding decades later. And the fluidity spec — funnel time held under 25 seconds a full 30 minutes after mixing — is a practical nod to how PT ducts actually get grouted: long runs, bends, and a pump crew that needs a real working window before the mix starts to stiffen, not five minutes. The thiocyanate and sulphide caps (0.10% each) matter for a chemistry reason specific to this application: naphthalene-sulphonate superplasticisers can carry trace sulphur-based residues from manufacture, and prestressing steel under sustained high stress is disproportionately vulnerable to the kind of localised corrosion those residues can trigger — which is why EN 934-4 tests for them specifically, where a general-purpose concrete admixture standard wouldn’t.

Where it is used

• Grouting of post-tensioning (PT) duct/cable ducts in prestressed concrete bridges and flyovers
• Segmental box-girder and precast PT beam grouting on metro-rail and highway viaduct projects
• Grouting of external post-tensioning tendons in bridge strengthening and retrofit works
• Anchor and duct grouting around cable-stay and similar high-tensile anchorage systems
• Underpinning and micro-pile grouting where controlled, non-shrink expansion is required
• Sealing of penetrations and backfilling of voids around embedded steel elements
• Base admixture for factory-produced dry-mix cementitious grout and mortar formulations
• Grout production for indirect-bond prestressed concrete with cladding-tube ducts

Key advantages

• EN 934-4:2009+A1:2012 certified performance, CE-marked under AVCP System 2+ with independent notified-body oversight (ID 0754, Karlsruhe)
• Chloride-free formulation, declared to contain only substances per EN 934-1:2008 Annex A.1/A.2 — corrosion-safe next to stressed high-tensile PT strand
• Self-limiting expansion band (-1% to +5% volume change in 24h) fills the duct annulus around the strand without risking duct-splitting over-expansion
• Low water secretion (bleeding capped at 2% of original volume after 3h) minimises the free-water lenses that leave voids and corrosion-initiation points around strand
• Retains pumpable fluidity (funnel method ≤25 seconds) a full 30 minutes after mixing — a real working margin for long or inclined ducts on box-girder and cable-stay work
• Declared compressive strength of ≥30 MPa at 28 days meets structural grout expectations, not just a flowable filler
• Thiocyanate and sulphide capped at 0.10% by mass each — guards against the accelerated corrosion risk that PT tendons are particularly sensitive to
• Works with standard OPC/PPC cement and conventional colloidal or paddle grout mixers — no exotic batching plant needed

Limitations & considerations

• It’s a raw-material admixture for grout designers, not a ready-to-pour bag product — needs a trial-batched mix design and QC, not a fixed water-ratio pour
• Contains 30-60% quartz sand and is classified H372 (STOT RE 1) — repeated dust inhalation risks lung damage, so dust control and RPE are mandatory during batching, not optional
• No single published dosage rate — the addition rate is project- and mix-specific and must be confirmed with MC-Bauchemie’s technical service or Space Arc’s technical team
• Publicly available documentation doesn’t list pack sizes or shelf life — confirm current pack format and batch shelf life at order time rather than assuming a figure
• A niche product: it has no real relevance outside PT duct grouting, underpinning grouts and factory dry-mix mortar production, so it isn’t a substitute for a general-purpose RMC plasticiser
• Declared corrosion behaviour follows EN 934-1’s standard clause; for very aggressive marine or de-icing-salt exposure, specifiers should still request project-specific corrosion data rather than rely on the standard declaration alone

Selection & best practice

Specifications

Industry use cases

How we position MC-Bauchemie Centrament GA

Centrament GA sits inside MC-Bauchemie’s Centrament admixture family alongside the Centrament N/P plasticiser series (general-purpose water reduction for RMC), the Centrament Stabi/SRA stabiliser series (bleed control and shrinkage reduction), and its closest sibling, Centrament Expanding Agent — the two are grouped together by MC-Bauchemie itself under “grouting aids and expanding agents” and are often specified together on the same PT or underpinning grout mix. For general shrinkage-compensated grouting work — machine base plates, bearing plinths, anchor bolt pockets — Space Arc’s Fosroc Conbextra GP1/GP2/GP3 range remains the standard bagged, ready-to-use alternative and is the right call whenever a finished grout (rather than a raw admixture) is what the job actually needs. But for cement grout formulated specifically to EN 934-4 for filling post-tensioning ducts, Centrament GA is the admixture MC-Bauchemie’s own system is built around, and Space Arc does not currently carry a direct raw-admixture equivalent from Fosroc’s India catalogue for that specific EN 934-4 use case.

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