About Fosroc Conbextra BB80

Fosroc Conbextra BB80 is a single-component, non-shrink cementitious grout developed specifically for the demanding job of bedding bridge bearings and structural base plates. It is supplied as a ready-to-use dry powder in 25 kg moisture-resistant bags; only clean water is added on site, which removes the batching errors and quality variation that come with site-mixed sand-cement grouts. The “BB” in the name stands for bridge bearing, and the product sits at the high-strength end of the Fosroc Conbextra cementitious grout family, designed where the bearing transfers very large, often cyclic, loads into the substructure and a dense, void-free, durable bedding layer is critical.

In service, the grout has to do two things at once: completely fill the gap between the underside of a steel or elastomeric bearing and the concrete pedestal, and develop strength quickly so that erection props can be struck and traffic restored. Conbextra BB80 is engineered for exactly this. The freshly mixed grout flows readily, even in the cooler conditions encountered during night-time pours or in winter in North India, so it travels under the full bearing plate and around shims and anchor pockets without leaving honeycombing. As it sets, a controlled positive (gaseous/expansive) action compensates for plastic settlement and shrinkage, keeping the grout in firm contact with both the bearing and the concrete so the entire bearing area is supported.

For Indian infrastructure work, this product is most relevant to highway and railway bridges, metro viaducts, flyovers and ROBs, where bearing installation and replacement happen against tight traffic-block windows. It is suitable for section thicknesses from about 10 mm up to 100 mm; thicker pours are achieved by adding clean, graded 10 mm aggregate to extend the mix and reduce the heat and cost of deep lifts. Because it is a cementitious grout (not epoxy), it is compatible with damp substrates, tolerant of typical site temperatures, and far more economical than resin grouts for the large volumes a bridge programme consumes, while still meeting the structural performance demanded by bridge codes and ASTM C1107.

The technical insight

Conbextra BB80 is a blend of Portland cement, graded fillers/aggregate and chemical additives that deliver flow, controlled expansion and strength. Its defining feature is non-shrink behaviour: instead of the drying shrinkage that leaves a hollow under a bearing with ordinary mortar, BB80 produces a controlled positive expansion while plastic, so the hardened grout stays in full bearing contact. The expansion is engineered to occur before set, which is why the grout must be placed promptly and confined by formwork. The mix is designed for a low water:powder ratio (typically around 0.15-0.16 by mass), and keeping water to the published minimum is the single biggest factor in achieving the rated strength and durability; excess water raises permeability and bleed and lowers strength. The product is supplied in three flow regimes in practice (flowable, pourable and pumpable) by varying water within the permitted range, but BB80 itself is a high-strength formulation that reaches roughly 45 N/mm² at 24 hours and around 80-85 N/mm² at 28 days, with low chloride ion content (typically below 0.1%) so it is safe in contact with reinforcement and embedded steel.

Where it is used

• Bedding grout beneath steel and elastomeric bridge and flyover bearings
• Grouting parapet post and crash-barrier base plates on bridges and ROBs
• Base-plate grouting for flanged lighting columns and gantry/sign supports
• Heavy stanchion and column base plates in industrial structures
• Machine and reciprocating-equipment base plates needing high-strength bedding
• Filling pockets and gaps around holding-down bolts and anchor assemblies
• Bridge bearing replacement / remedial bedding during refurbishment
• Precast element seating where a dense, non-shrink bedding layer is required

Key advantages

• Non-shrink with controlled positive expansion, ensuring full, gap-free bearing contact
• High early strength (about 45 N/mm² at 24 hours) for fast prop removal and traffic reopening
• High ultimate strength (about 80-85 N/mm² at 28 days) for heavy, cyclic bearing loads
• Good flowability even at low temperatures, suiting night-time and winter pours
• Low permeability for long-term durability against water ingress and exposure
• Factory-blended powder; only clean water added, giving consistent, reliable site quality
• Low chloride content (typically <0.1%), safe around reinforcement and embedded steel
• Can be poured or pumped, and extended with 10 mm aggregate for sections up to and beyond 100 mm
• Meets ASTM C1107 Grade C, an internationally recognised non-shrink grout standard

Limitations & considerations

• Cementitious, not epoxy – not the first choice for aggressive chemical exposure or vibration-critical machine bases where an epoxy grout (e.g. Conbextra EP) is specified
• Strength and durability depend on strict water control; over-watering on site sharply reduces performance
• Section thickness governs the mix – below ~10 mm a different grout is needed, and above ~100 mm aggregate extension is required to manage heat and shrinkage
• Requires leak-tight formwork and continuous one-direction placement to avoid trapped air and honeycombing
• Substrate must be sound, clean and pre-saturated (saturated surface-dry); placing on a dry or dusty surface causes bond loss and rapid water loss
• Expansion is pre-set, so the grout has a limited working/placing time once mixed and must be poured promptly
• Needs proper curing; exposed surfaces left uncured in hot, dry Indian conditions can craze or lose strength
• Not designed as a flowing structural concrete or as a thin self-levelling topping

Selection & best practice

Specifications

Industry use cases

How we position Fosroc Conbextra BB80

Within the Fosroc range, Conbextra BB80 is the bridge-bearing specialist of the Conbextra cementitious grout family. Step up to the Conbextra GP / GP2 grades for general base-plate and equipment grouting where bridge-grade performance is not required, and move to an epoxy grout such as Conbextra EP where chemical attack, fuel/oil exposure or heavy dynamic vibration demands resin technology rather than a cementitious binder. For very deep or large-volume pours, BB80 is extended with aggregate, whereas Fosroc also offers free-flow high-strength grades for precision machine bases. Against the wider Indian market, BB80 competes with high-strength non-shrink grouts such as Sika SikaGrout and the MYK/MBCC (Master Builders Solutions) MasterFlow range; Dr. Fixit (Pidilite) and STP-branded products are more commonly associated with waterproofing and repair mortars than dedicated bridge-bearing grouts, so for bearing-specific work the realistic alternatives are Sika and Master Builders Solutions grout lines. Space Arc Engineering positions Conbextra BB80 as the dependable, code-compliant (ASTM C1107 Grade C) choice for highway, metro and rail bearing programmes where proven non-shrink performance, fast strength gain and Fosroc’s track record matter, and can advise on the right Conbextra or epoxy grade for each specific detail.

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