Fosroc Cebex CP
Plasticising and expanding admixture for non-shrink cementitious grouts used to fill post-tensioning ducts and protect prestressing cables.
What is it?
A powder admixture for site-batched cementitious grouts that plasticises the mix so it flows at a low water/cement ratio, while a controlled expansion system compensates for plastic settlement and shrinkage inside post-tensioning ducts.
Where is it used?
Grouting of post-tensioned cable ducts in bridges, flyovers, elevated metro viaducts, silos, water-retaining structures and other prestressed-concrete elements where complete duct filling and corrosion protection of the strand are critical.
Why use it?
It lets contractors achieve a fully fluid, pumpable grout at a reduced water/cement ratio, so the hardened grout has low permeability and high strength, fully encapsulating the tendons without segregation, bleed voids or chloride-induced corrosion risk.
How is it applied?
Dosed by weight of cement (guideline 1.0-2.0%), blended with OPC and clean water in a high-shear colloidal grout mixer, then pumped continuously into the duct from the lowest vent until clean grout flows from the high points.
About Fosroc Cebex CP
Fosroc Cebex CP is a cementitious grouting additive engineered specifically for the grouting of prestressing cables inside post-tensioning ducts. It belongs to Fosroc’s long-established Cebex family of plasticising and expanding grout admixtures, and is positioned as the cable-duct specialist of that range. The product is supplied as a dry powder that is added to a site-batched mix of Ordinary Portland Cement and clean water to produce a free-flowing, non-shrink cementitious slurry.
The job Cebex CP does is deceptively important. In a post-tensioned bridge deck, viaduct or silo, high-tensile steel strand is stressed and then permanently protected by filling the surrounding duct with cement grout. If that grout bleeds, segregates or leaves voids at high points, the exposed strand becomes a long-term corrosion risk and a durability liability for the whole structure. Cebex CP addresses this on two fronts at once: a plasticising component that keeps the grout highly fluid even at a low water/cement ratio, and an expansion system that gently expands the grout in its plastic state to counter natural settlement and ensure the duct is completely filled around the cable.
Because the grout can be made fluid without flooding it with water, the hardened grout retains high strength and low permeability, which translates directly into durable, well-protected tendons. The composition is formulated to develop high early strength without the use of chlorides, and it contains no metallic iron that could later corrode and stain. Fosroc states that Cebex CP does not noticeably affect the setting time of the grout, and that a typical mix can still be pumped for up to around two hours after mixing depending on cement type and ambient temperature – a practical window for the long pumping runs common on Indian bridge and metro projects. As an authorised Fosroc distributor and applicator serving Delhi NCR and pan-India, Space Arc Engineering supplies Cebex CP alongside the wider Fosroc grouting system and provides on-site technical support to contractors and PT specialists.
The technical insight
The technical value of Cebex CP lies in decoupling fluidity from water content. In an unadmixed cement grout, the only way to get the slurry fluid enough to pump through a congested duct is to add water – but high water/cement ratios cause bleed channels, segregation and a weak, porous hardened grout that exposes the strand. Cebex CP’s plasticising fraction breaks this trade-off, dispersing the cement so the grout flows freely at a markedly reduced water/cement ratio. Lower water means lower permeability, higher strength and far better long-term corrosion protection for the tendon.
The second mechanism is controlled plastic-state expansion. As cement grout sets it naturally settles and shrinks, which in a horizontal or inclined duct tends to leave a void along the crown – precisely where water and chlorides later collect against the strand. Cebex CP introduces a measured expansion while the grout is still plastic, lifting the grout to maintain interfacial contact and fill the duct cross-section. Across the Cebex family this expansion is gaseous and is characterised to ASTM C827 (settlement/change in height of cementitious mixtures); the related Cebex 100 datasheet quotes a typical unrestrained expansion of up to 4%. The system is deliberately chloride-free and iron-free, since chlorides accelerate strand corrosion and free iron particles can rust and stain. The net result is a grout that pumps like a high-water mix but cures like a low-water one.
Where it is used
- Grouting of post-tensioned cable ducts in bridge and flyover decks
- Grouting of tendon ducts in elevated metro and rail viaducts
- Cable-duct grouting in prestressed silos, water tanks and reservoirs
- Filling of ducts in post-tensioned floor slabs and transfer beams
- Protective grouting of vertical and inclined prestressing tendons in tall structures
- General cementitious slurries requiring high fluidity at a low water/cement ratio without segregation
Key advantages
- Keeps the grout highly fluid at a low water/cement ratio, easing pumping and injection
- Plastic-state expansion compensates for settlement and shrinkage, helping fully fill the duct around the cable
- Low water/cement ratio gives a hardened grout with low permeability and good durability
- Develops high early strength without the use of chlorides
- Contains no metallic iron, so there is no rust staining or corrosion from the admixture itself
- Resists segregation and bleed, giving uniform encapsulation and protection of the prestressing strand
- Does not noticeably affect grout setting time, preserving a practical pumping window of up to about 2 hours
- Supplied as a pre-formulated powder for simple, repeatable site batching with OPC and water
Limitations & considerations
- It is an admixture, not a ready grout – performance depends on correct cement, clean water and an accurately controlled water/cement ratio
- Requires high-shear or colloidal mechanical mixing and continuous pumping; hand mixing will not give a sound cable grout
- Pumping window (about 2 hours) and expansion are affected by cement type and ambient temperature, which matters on hot Indian sites
- Overdosing can cause excessive expansion or frothing, so dosage must be measured by weight of cement
- Intended for cementitious cable-duct and slurry grouting; it is not an epoxy grout, a free-flow machine-base grout, or a waterproofing admixture
- Verify the current project-specific datasheet and any client/IRC or NHAI specification limits before finalising the mix design
Selection & best practice
Establish the mix by trial: fix the lowest water/cement ratio that still gives the required efflux/fluidity, then dose Cebex CP by weight of cement (guideline 1.0-2.0%) and verify fluidity, expansion and strength against the project specification. Use clean potable water and fresh OPC, and batch in a high-shear colloidal grout mixer feeding a holding tank with gentle agitation. Pump continuously from the lowest injection point, venting air at every high point and crown until clean, consistent grout flows out, then cap each vent under slight pressure. Grout in cooler parts of the day in hot weather to preserve the pumping window, never re-temper with extra water, and flush all lines and equipment with clean water immediately after the run.
Specifications
| Product type | Plasticising and expanding admixture for cementitious cable/duct grouts (Cebex family) |
| Form | Dry powder admixture (added to OPC + clean water on site) |
| Primary use | Grouting of prestressing cables in post-tensioning ducts |
| Guideline dosage | Approx. 1.0-2.0% by weight of cement (confirm by trial mix) |
| Chloride content | Chloride-free (no chlorides used) |
| Iron content | No metallic iron |
| Expansion | Controlled plastic-state expansion to counter settlement/shrinkage; Cebex family characterised to ASTM C827 |
| Effect on setting time | No noticeable effect on grout setting times |
| Pumping window | Grout typically pumpable up to ~2 hours after mixing (varies with cement type and temperature) |
| Water/cement ratio | Designed to perform at a reduced (low) water/cement ratio |
| Mixing | Mechanical high-shear / colloidal grout mixer; continuous pumping |
| Related Fosroc products | Cebex 100, Cebex 200, Cebex Cable Grout, Conbextra duct grouts |
Industry use cases
Bridges & Flyovers
Grouting post-tensioned box-girder and deck tendon ducts so strand is fully encapsulated, with no crown voids or bleed channels that would invite corrosion.
Metro & Rail Viaducts
Filling cable ducts in precast and cast-in-situ post-tensioned viaduct segments, where long continuous pumping runs and reliable duct filling are essential.
Industrial & Storage
Cable-duct grouting in prestressed concrete silos, water-retaining tanks and reservoirs where low-permeability grout protects vertical and inclined tendons.
Buildings & Infrastructure
Grouting ducts in post-tensioned floor slabs, transfer beams and bridge cross-heads, ensuring durable bond and corrosion protection of the prestressing system.
Frequently asked questions
What exactly is Fosroc Cebex CP used for?
How does Cebex CP protect the prestressing cable?
What is the dosage of Cebex CP?
Does Cebex CP change the grout’s setting time?
How is Cebex CP different from Cebex 100 or Cebex Cable Grout?
Can Space Arc supply Cebex CP across India?
What should I check before specifying Cebex CP on a project?
How we position Fosroc Cebex CP
Within Fosroc’s grouting line-up, Cebex CP sits in the Cebex family of plasticising, expanding grout admixtures and is the variant aimed at prestressing-cable duct grouting. It overlaps with Cebex 100 (the general-purpose site grout admixture for bed grouting, duct grouting and non-shrink infill) and Cebex Cable Grout (a pre-bagged all-fines cable-grout product), while the Conbextra range covers free-flow and high-strength structural grouts for base plates and ducts – choose by whether you need a site-batched admixture (Cebex CP/100) or a pre-bagged grout. Against competitors, credible alternatives for post-tensioning duct grouting in India include Sika (Sika Intraplast / SikaGrout PT cable-grout systems), MBS (Master Builders Solutions, formerly BASF, with MasterFlow and MasterInject PT grouts), STP and, for broader admixture/repair ranges, Dr. Fixit (Pidilite). For most contractors the deciding factors are specification compliance for PT grouting, proven duct-filling and anti-bleed performance, and reliable local supply and technical backup – which is where Space Arc Engineering’s role as an authorised Fosroc distributor and applicator in Delhi NCR and pan-India adds value alongside the product itself.
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