Fosroc Conbextra Cable Grout Plus
Pre-bagged, shrinkage-compensated cementitious grout engineered for post-tensioned cable ducts — high flow, negligible bleed, non-metallic dual expansion, EN 447 / MORTH-IRC compliant.
What is it?
A single-component, pre-bagged cementitious grout based on Portland cement and additives, with a non-metallic dual (gaseous) expansion system, designed specifically to fill post-tensioned (PT) cable ducts around stressed strands.
Where is it used?
Post-tensioned bridge girders, box girders, flyovers, metro viaducts, anchorage zones, and ground-anchor ducts on infrastructure and building projects across India.
Why use it?
It delivers controlled plastic-state expansion, negligible bleed and high fluidity so ducts fill completely, leaving no voids and forming a high-alkalinity passive layer that protects the tendon from corrosion.
How is it applied?
Mixed with a measured quantity of clean water in a high-shear colloidal grout plant, then pumped through the duct from the lowest vent until clean grout emerges at the outlet.
About Fosroc Conbextra Cable Grout Plus
Fosroc Conbextra Cable Grout Plus is the upgraded member of Fosroc’s Conbextra cable-duct grout family, formulated for grouting post-tensioned (PT) cable ducts in prestressed concrete structures. Like the rest of the range it is supplied as a ready-to-use dry powder — a blend of Portland cements and chemical additives — that requires only the addition of a controlled amount of clean water on site to produce a free-flowing, non-shrink grout. The “Plus” designation reflects Fosroc’s non-metallic dual expansion system: a hydrogen-free gaseous expansion mechanism combined with a plastic-state shrinkage-compensating action, with no metallic iron in the mix. This matters because traditional aluminium-powder or iron-based expansion agents can generate hydrogen or stain/corrode at the strand interface, whereas Conbextra Cable Grout Plus achieves controlled expansion without those risks while still developing high early and ultimate strength without chlorides. In a PT duct, the grout has two jobs that pull in opposite directions: it must be fluid enough to travel the full length of a long, congested duct and surround every strand, yet it must resist bleed and segregation so that water does not collect at high points and crests where it would leave a void or a corrosion-prone water lens. Conbextra Cable Grout Plus is engineered around exactly this balance — high flow with negligible bleed and controlled volume change — so the hardened grout forms a dense, low-permeability, highly alkaline matrix that passivates and physically protects the prestressing steel for the design life of the structure. For Indian projects this is squarely a bridge-and-viaduct product: it is the material a PT specialist reaches for when a method statement calls for a pre-packaged, all-fines cementitious duct grout that satisfies EN 447 and MORTH/IRC fluidity, bleed and strength requirements. Space Arc Engineering supplies and supports the product as an authorised Fosroc distributor and applicator across Delhi NCR and Pan-India.
The technical insight
Conbextra Cable Grout Plus is an “all-fines” cementitious system — there is no coarse sand fraction — so the entire mix can flow through the narrow annular gaps between strands and the duct wall. The verified Conbextra Cable Grout family data (Fosroc India TDS) shows a water/powder ratio of 0.33-0.35 (maximum 0.35), a fresh wet density around 2.05 g/cc, a cone efflux (fluidity) time under 25 seconds and wick-induced bleed below 0.3% when tested to EN 445, with controlled plastic expansion up to +2%. Compressive strength reaches over 27 MPa at 7 days and over 30 MPa at 28 days (ASTM C109, 50 mm cubes), with initial set beyond 3 hours and final set within 24 hours — enough working time to grout a long duct in one continuous pour. The “Plus” upgrade sits on top of this performance baseline: its non-metallic, hydrogen-free dual expansion replaces the older expansion chemistry, eliminating any free hydrogen evolution (a concern for stress-corrosion of high-tensile strand) and any metallic iron that could rust-stain. Because the reactive expansion agents are temperature-sensitive, Fosroc specifies temperature-controlled laboratory sampling rather than site cube casting, and a high-shear colloidal mixer or a paddle mixer at 1500 rpm minimum mixed for about 5 minutes to fully wet and activate the powder. The combination of high alkalinity, low permeability and negligible bleed is what converts a simple void-filling operation into genuine long-term corrosion protection for the tendon.
Where it is used
- Grouting of post-tensioned (PT) cable ducts in prestressed concrete bridge and viaduct girders
- Box-girder and I-girder tendon ducts on flyovers, ROBs and elevated metro corridors
- Anchorage-zone and coupler-zone filling on post-tensioned members
- Vertical, inclined and looped tendon ducts where bleed control is critical at high points
- Grouting of ground anchors and rock/soil anchors with small annular gaps
- Re-grouting and remedial grouting of partially filled or void-affected ducts identified during inspection
Key advantages
- Pre-bagged, factory-blended powder — only clean water is added on site, removing batching variation and the risk of wrong proportioning
- Non-metallic dual expansion system: hydrogen-free gaseous expansion with no metallic iron, avoiding hydrogen evolution and rust staining at the strand
- High flow / low efflux time fills small gaps around congested strand bundles over long duct runs
- Negligible bleed (< 0.3%) prevents water lenses and voids at duct crests and high points
- Shrinkage-compensated with controlled plastic expansion (up to +2%) for full, intimate contact with strand and duct
- Develops high early and ultimate strength without chloride, giving a dense, low-permeability, highly alkaline passivating matrix
- Complies with EN 447 (tested to EN 445) and MORTH/IRC requirements for fluidity, bleed and strength — accepted on government infrastructure projects
- Pumpable or pourable across a useful range of consistencies and ambient temperatures
Limitations & considerations
- Single-purpose product — formulated for cable-duct and small-gap anchor grouting, not for general structural gap grouting or baseplate bedding (use Conbextra GP/EP or HF Plus for those)
- Requires a high-shear colloidal grout plant or a paddle mixer at ≥1500 rpm; hand-mixing or low-shear drills will not properly activate the mix
- Strict water control needed — exceeding the maximum W/P ratio (~0.35, up to ~8.75 L per standard bag) raises bleed and lowers strength
- Reactive expansion agents are temperature-sensitive: Fosroc mandates temperature-controlled laboratory sampling rather than casting site cubes for QC
- Low-temperature work (below 10°C) needs extended formwork/retention time and, below ~5°C, warm mixing water to develop strength
- Best grouted in a single continuous operation from the lowest vent; interrupted or multi-stage grouting risks cold joints and trapped air
- Exposed grout faces must be cured (e.g. with a Fosroc Concure membrane) to avoid surface drying
Selection & best practice
Treat the grout as a system, not just a powder. Before grouting, flush each duct with lime water and plug any leaks; confirm vents and outlets at all high and low points. Mix in a colloidal grout plant (or ≥1500 rpm paddle), adding the full bag slowly to accurately measured clean water and mixing for about 5 minutes to a smooth, lump-free consistency — never exceed the maximum water/powder ratio. Carry out a flow-cone (efflux) check and, where the spec demands, a wick-induced bleed test to confirm EN 445 compliance before pumping. Grout continuously from the lowest vent, advancing strand-by-strand and crest-by-crest, and keep pumping at each outlet until grout of the same consistency emerges, then seal the vent under slight pressure. In hot weather use chilled mixing water to hold grout temperature near 25°C; in cold weather extend formwork retention and use warm water below ~5°C ambient. Cure exposed faces with Concure and clean tools with water immediately, or Fosroc Acid Etch once cured.
Specifications
| Chemical type / system | Single-component cementitious grout — Portland cements + chemical additives with non-metallic dual (gaseous) expansion system |
| Form | Pre-bagged dry powder; add clean water on site |
| Water / powder ratio | 0.33 – 0.35 (max 0.35); approx. max 8.75 L water per bag |
| Fresh wet density | approx. 2.05 g/cc |
| Fluidity (cone efflux time) | < 25 seconds (EN 445) |
| Bleed | < 0.3% (EN 445 wick-induced bleed test) |
| Volume change / expansion | up to +2% (EN 445) |
| Setting time | Initial > 3 hrs; Final < 24 hrs (EN 445) |
| Compressive strength (7 days) | > 27 MPa (ASTM C109, 50 mm cube) |
| Compressive strength (28 days) | > 30 MPa (ASTM C109, 50 mm cube) |
| Standards compliance | EN 447 (tested to EN 445); MORTH / IRC guidelines for fluidity, bleed & strength |
| Mixing equipment | High-shear colloidal mixer or paddle mixer ≥ 1500 rpm; mix ~5 min |
| Pack size | Typically supplied in 25 kg bags — confirm against current regional Fosroc datasheet |
| Curing | Cure exposed faces with Fosroc Concure membrane |
Industry use cases
Highway & expressway bridges
Grouting PT tendon ducts in box and I-girders on NHAI/MORTH bridge and flyover projects, where EN 447 and MORTH/IRC fluidity, bleed and strength compliance is a tender requirement.
Metro & elevated rail
Filling cable ducts in segmental box-girder viaducts and long-span continuous spans on urban metro corridors, where long, looped ducts make bleed control and continuous grouting essential.
Railway ROBs & bridges
Post-tensioned road-over-bridges and railway bridge girders requiring a pre-packaged, single-component duct grout for consistent, audit-ready quality.
Industrial & power infrastructure
Grouting of prestressing ducts in heavy industrial structures, beams and rock/ground anchors with small annular gaps where corrosion protection of high-tensile steel is critical.
Remedial & inspection works
Re-grouting ducts found partially filled or void-affected during NDT/borescope inspection of existing post-tensioned structures.
Frequently asked questions
Is Conbextra Cable Grout Plus cementitious or epoxy?
How is it different from standard Conbextra Cable Grout and Cable Grout HS?
What standards does it comply with for Indian projects?
How much water do I add and what mixer should I use?
Why is bleed control so important in cable-duct grouting?
Does Space Arc supply it in Delhi NCR and Pan-India?
How we position Fosroc Conbextra Cable Grout Plus
Within the Fosroc range, Conbextra Cable Grout Plus is the duct-grouting specialist and sits beside standard Conbextra Cable Grout and Conbextra Cable Grout HS — all three are pre-bagged PT duct grouts, differing in strength and expansion chemistry, with “Plus” using the upgraded non-metallic dual expansion system. It should not be confused with Fosroc’s general grouting products: Conbextra GP and Conbextra HF / HF Plus are flowable structural grouts for machine bases, baseplates and structural gaps, while Conbextra EP epoxy grouts handle dynamic and chemically aggressive duty — those are different jobs and use a different chemistry. For tendon protection it is also paired with duct, anchorage and corrosion-protection systems on a typical PT package. Among credible alternatives an Indian specifier may evaluate, Sika offers SikaGrout / Sika cable-duct grout systems, MBS (MYK / BASF Master Builders Solutions, MasterFlow) offers comparable PT duct grouts, and STP and Dr. Fixit cover parts of the broader grout and waterproofing range — though Dr. Fixit is more strongly associated with waterproofing than with EN 447 PT duct grouting. The honest position: for post-tensioned cable ducts on MORTH/IRC and EN 447 governed bridge and metro work, Conbextra Cable Grout Plus is a well-proven, specification-ready choice, and the deciding factor on most projects is matching the exact variant (standard / HS / Plus) to the strength and expansion clauses in the approved method statement.
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