About Fosroc Cebex Cable Grout

Fosroc Cebex Cable Grout is a factory-blended powder admixture from the Fosroc Cebex range, designed specifically for the critical task of grouting the ducts that house post-tensioning and prestressing cables. In post-tensioned construction the high-tensile strand or tendon is stressed inside a duct after the concrete has gained strength; once locked off, that duct must be completely filled with a stable grout. The grout does two jobs at once. First, it bonds the strand to the surrounding concrete so the structure behaves as a single composite member. Second, and just as important, it forms a dense alkaline envelope around the steel that protects it from corrosion for the life of the structure. A duct that is poorly filled, that bleeds, or that shrinks back and leaves voids is one of the most common and most serious durability defects in prestressed structures, which is why a purpose-made product like Cebex Cable Grout exists rather than relying on a neat cement slurry. Cebex Cable Grout is supplied as a dry powder that requires only the addition of a controlled amount of clean water and Ordinary Portland Cement on site. It is an all-fines admixture containing expansive cement that imparts a controlled positive expansion in the plastic state while keeping the water demand low. The blend is engineered so that the grout mixes uniformly and resists the segregation and bleeding that would otherwise leave bleed-water channels and trapped voids along the high points of a duct. Space Arc Engineering supplies this product as an authorised Fosroc distributor and applicator across Delhi NCR and pan-India. Buyers should note the product family: the original Cebex Cable Grout and the current Cebex Cable Grout Plus share the same purpose and chemistry, with the Plus grade using an upgraded hydrogen-free expansion system. The verified performance figures quoted on this page are taken from the published Fosroc Cebex Cable Grout Plus data sheet; the older base grade performs in the same range. We always recommend confirming the exact grade, pack and current data sheet for your project specification before ordering.

The technical insight

The defining behaviour of this grout is controlled positive expansion in the plastic state. Ordinary cement grout settles and shrinks as it sets, and inside a sealed duct that shrinkage pulls the grout away from the strand and from the crown of the duct, leaving voids exactly where corrosion protection matters most. Cebex Cable Grout incorporates an expansive cement system that generates a positive volumetric expansion of up to 4% (measured to BS EN 445) while the grout is still fluid, counteracting settlement and pressing the grout into intimate contact with the strand and duct wall. The original Cebex Cable Grout used a gaseous expansion mechanism, while Cebex Cable Grout Plus uses a hydrogen-free expansion system, which removes the risk of hydrogen evolution inside the duct, an important consideration for highly stressed tendons. The second key property is rheology at a low water/cement ratio. The published properties are achieved at a 0.36 water/cement ratio, where the admixture still delivers a fluid grout with an efflux time of 10 to 20 seconds through the BS EN 445 flow cone, both initially and after 30 minutes, which means the grout stays pumpable long enough to fill a long duct in one continuous operation. That low w/c ratio is what gives the hardened grout its high strength and low permeability, while bleeding is held to under 1% after 3 hours so free water does not collect and freeze, corrode or leave voids. The system is entirely chloride-free (Nil to BS 5075), which is non-negotiable when the grout is in direct, permanent contact with high-tensile prestressing steel.

Where it is used

• Grouting post-tensioned bridge deck and box-girder cable ducts on flyovers, viaducts and elevated corridors
• Filling prestressed cable ducts in precast and cast-in-situ structural elements such as beams and girders
• Grouting slip-form silo wall tendon ducts in cement plants, grain and clinker storage
• Encapsulating and corrosion-protecting high-tensile strand in post-tensioned slabs and transfer structures
• Single-point continuous pumped grouting of long, profiled ducts in segmental construction
• Filling annular gaps of up to 60 mm thickness around tendons within a duct

Key advantages

• Controlled positive expansion of up to 4% in the plastic state compensates for settlement and shrinkage and eliminates voids around the strand
• Completely chloride-free (Nil to BS 5075), so it can safely contact high-tensile prestressing steel
• High early and ultimate strength without chlorides: about 25 N/mm2 at 1 day rising to 60 N/mm2 at 28 days (Plus grade, 0.36 w/c)
• Low bleeding of under 1% after 3 hours prevents bleed-water channels and trapped voids
• Stable, pumpable fluidity (10 to 20 seconds, BS EN 445 cone) held for at least 30 minutes for continuous single-point grouting of long ducts
• Low water/cement ratio gives low permeability and long-term durability of the hardened grout
• Pre-bagged and factory-blended for consistent, repeatable site mixing with only cement and water added
• Cebex Cable Grout Plus uses a hydrogen-free expansion system, removing the risk of hydrogen evolution in the duct

Limitations & considerations

• It is an admixture, not a ready-mix grout: it must be combined on site with the correct quantity of fresh OPC and accurately measured clean water to perform as specified
• Performance figures are tied to a 0.36 w/c ratio and good OPC; trials are recommended to confirm the best cement source, and over-watering will reduce strength and increase bleed
• The grout must be placed within 20 minutes of mixing to gain the full benefit of the expansion process
• Reactive expansion agents mean reliable strength sampling must be done in a temperature-controlled laboratory using 50 mm cube moulds under restraint, not by casual site sampling
• Ducts must be properly prepared: pre-soaked, drained of free water, cleaned and with anchorages sealed before grouting
• Low-temperature working (below 10 C) requires formwork left in place longer and, at 5 C or below, warm mixing water; high-temperature working above 35 C needs cool storage, shaded equipment and cool mixing water
• Not a free-flowing micro-concrete or general bedding grout: for baseplate and equipment grouting use a dedicated product such as Conbextra

Selection & best practice

Specifications

Industry use cases

How we position Fosroc Cebex Cable Grout

Cebex Cable Grout sits in Fosroc’s specialist post-tensioning grout family alongside the closely related Cebex Cable Grout Plus (the current hydrogen-free grade) and the plasticising expanding admixture Cebex 100, which is used for bed grouting, duct grouting and non-shrink infilling at a typical dosage of 225 g per 50 kg of cement. It should not be confused with Fosroc’s flowable cementitious grouts such as the Conbextra range, which are designed for baseplate, anchor and equipment grouting rather than cable ducts; for those applications Conbextra GP2 or HF is the correct choice. For full prestressing systems, Cebex Cable Grout is typically specified together with Fosroc duct, anchorage and curing products such as Concure. Among credible competitor systems available in India, specifiers may also evaluate Sika’s post-tensioning grouts (for example the SikaGrout PT range), BASF/Master Builders Solutions MasterFlow cable grouts, and grouts from STP. Dr. Fixit is strong in waterproofing and general repair but is less commonly specified for dedicated post-tensioning cable grouting. For most Indian post-tensioned bridge, metro and silo work, Cebex Cable Grout and Cebex Cable Grout Plus remain a well-proven, code-referenced choice, and Space Arc Engineering can help match the right grade and verify the current data sheet against your project specification.

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