Fosroc Conbextra BB92
An ultra-high-performance, non-shrink cementitious grout engineered for structural grouted connections under heavy static and dynamic loads, chiefly onshore wind turbine foundations and precast wind towers.
What is it?
A prepacked, single-component dry-powder precision grout blending Portland cement, graded fillers and chemical additives that deliver controlled positive expansion and ultra-high strength without added fibres.
Where is it used?
Grouted base-frame connections of steel wind turbine foundations, horizontal and vertical joints of precast/segmental concrete wind towers, and narrow voids requiring long-distance pumping.
Why use it?
It reaches >70 N/mm2 in 1 day and >100 N/mm2 at 28 days, resists fatigue from cyclic loads, and stays non-shrink, free-flowing and bleed-free where ordinary grouts would fail under dynamic service.
How is it applied?
Mixed at a 0.10-0.12 water/powder ratio with a high-shear mixer, then poured or pumped from one side into a pre-soaked, leakproof void in thicknesses up to 150 mm per pour, and wet-cured.
About Fosroc Conbextra BB92
Fosroc Conbextra BB92 sits at the very top of the Conbextra precision-grout family, formulated for the most demanding load case in modern infrastructure: the grouted connection between a steel tower and its concrete foundation, or between stacked segments of a precast concrete wind tower. Unlike a general-purpose bedding grout, BB92 is an ultra-high-performance (UHPC-class) material, supplied as a ready-to-use dry powder that is simply gauged with clean water on site. The blend of Portland cement, tightly graded aggregate fillers (granulometry 0-2 mm) and proprietary chemical additives produces a grout that is both extremely fluid and extremely strong, a combination that is otherwise difficult to achieve. For Space Arc Engineering’s customers across Delhi NCR and the rest of India, BB92 is the grout to reach for when a connection must carry millions of stress cycles over a 20-to-25-year design life without cracking, debonding or losing capacity. The product carries CE marking to EN 1504-6:2006 (anchoring products) and its mechanical performance has been benchmarked against the DNV-OS-C502 offshore guideline and CEB-FIP Model Code fatigue predictions, which is why it has become a default specification for turbine OEMs and EPC contractors. Because it is prepacked and factory-blended, BB92 removes the batching variability that plagues site-mixed grouts, giving a repeatable, certifiable result pour after pour, a critical advantage on a wind farm where dozens of identical foundations must each meet the same acceptance criteria.
The technical insight
The defining feature of Conbextra BB92 is its strength-to-flow ratio. At a pumpable 0.10 water/powder ratio it develops >70 N/mm2 at 1 day, >90 N/mm2 at 7 days and >100 N/mm2 at 28 days, yet still flows freely (slump flow >700 mm to EN 12350-8, flow trough >450 mm). This is achieved by minimising water demand through particle packing rather than by adding water, so the grout reaches a static modulus of elasticity of >=41 GPa and flexural strength rising from >7.5 N/mm2 at 1 day to >15 N/mm2 at 28 days, all without fibre reinforcement, which would otherwise impair pumpability. The controlled 0-1% positive expansion in the plastic state compensates for settlement and guarantees full contact under the base plate. Critically for wind loading, its fatigue resistance exceeds that predicted by CEB-FIP Model Code 1990 and the DNV-OS-C502 guideline for concrete of equal compressive strength, and it retains low-temperature reactivity, reaching >60 N/mm2 in 3 days even at 2 degrees C. Durability indicators are strong: chloride ion content <=0.05%, carbonation resistance dk <= reference concrete (MC0.45), capillary absorption <=0.5 kg.m-2.h-0.5, and retained bond strength >=2 MPa after 50 freeze-thaw cycles (EN 13687-1). The single-pour gap range of 10-150 mm is unusually wide for a UHPC grout, removing the need for aggregate extension.
Where it is used
- Grouting the base-frame connection of steel onshore wind turbine foundations under combined static and cyclic dynamic loads
- Filling horizontal and vertical joints between segments of precast/segmental concrete wind towers
- Long-distance pumped void filling in narrow gaps where high flow retention is required
- Non-structural offshore foundation connections
- Bedding beneath heavily loaded bridge bearings, parapet posts and flanged lighting/transmission columns
- High-fatigue machine and crane-rail base-plate grouting where conventional non-shrink grouts are inadequate
Key advantages
- Ultra-high early strength (>70 N/mm2 at 1 day) enables quick return to service and early removal of temporary supports, even at low temperatures
- Ultimate compressive strength >100 N/mm2 (0.10 w/p) and high flexural strength/modulus (>=41 GPa) without added fibres
- Proven fatigue resistance exceeding CEB-FIP Model Code 1990 and DNV-OS-C502 predictions, suiting cyclic wind/dynamic loads
- Non-shrink with controlled 0-1% positive expansion for full, gap-free contact under base plates
- Free-flowing and pumpable over long distances (slump flow >700 mm) with no segregation or bleeding, preventing pump blockages
- Prepacked single-component powder eliminates on-site batching variation and gives certifiable, repeatable results
- Wide single-pour gap range of 10-150 mm and CE marking to EN 1504-6:2006
Limitations & considerations
- Must not be applied at substrate/ambient temperatures below -5 degrees C or above 40 degrees C; substrate must be ice-free
- Should not be exposed to moving water or rainfall during placement and before final set
- A high-shear vane mixer (not a hand drill) is needed for larger quantities to achieve the rated flow and strength
- Premium UHPC-class pricing makes it over-specified for ordinary base-plate or pocket grouting, where standard Conbextra grades are more economical
- Requires foundation pre-soaking, leakproof formwork and disciplined single-side continuous pouring to avoid air entrapment
- In hot Indian summers, mixed grout must be shaded and gauged with cool water (<20 degrees C); in cold conditions hot water (30-40 degrees C) is advised
Selection & best practice
For wind farm work in India, treat BB92 as a system, not just a bag: clean the foundation to a sound base, blow bolt pockets free of debris, and flood the area with fresh water several hours before grouting, removing free water immediately before the pour. Use a mechanically powered high-shear mixer, gauge 2.5-3.0 litres of clean water per 25 kg bag (0.10-0.12 w/p), and mix a full 5 minutes; the mix looks dry for the first 2-3 minutes before flowing. Grout bolt pockets with mortar or resin first, then pour the main void from one side only, maintaining a continuous grout head and front to expel air. Stage batches so the next is ready before the last is exhausted. Cure exposed faces immediately with Fosroc Concure curing membrane or wet hessian. In NCR summers, shade the mixed grout and use cool water; in winter mornings use warm water to drive early strength.
Specifications
| Material type | Ultra-high-performance non-shrink cementitious precision grout (Portland cement, graded fillers, additives) |
| Compressive strength (0.10 w/p, pumpable) | >70 N/mm2 (1 day), >90 N/mm2 (7 days), >100 N/mm2 (28 days) per EN 12190 / EN 12390-3 |
| Compressive strength (0.12 w/p, flowable) | >60 N/mm2 (1 day), >80 N/mm2 (7 days), >90 N/mm2 (28 days) |
| Flexural strength (EN 196-1:2005) | >7.5 N/mm2 (1 day), >13 N/mm2 (7 days), >15 N/mm2 (28 days) |
| Static modulus of elasticity (EN 13412) | >=41 GPa |
| Water/powder ratio | 0.10-0.12 (2.5-3.0 litres per 25 kg) |
| Final set (EN 196-3:1996) | <5 hours at 20 degrees C |
| Plastic expansion | 0-1% |
| Slump flow (EN 12350-8) | >700 mm |
| Fresh wet density | 2.25-2.35 kg/litre |
| Single-pour gap depth | 10-150 mm (consult Fosroc for larger) |
| Granulometry | 0-2 mm |
| Standards / durability | CE to EN 1504-6:2006; chloride ion <=0.05%; reaction to fire Class A1; bond >=2 MPa after 50 freeze-thaw cycles |
| Yield | approx. 12 litres per 25 kg bag; approx. 475 litres per 1 tonne bag |
| Packaging | 25 kg bag and 1 tonne bulk bag |
| Shelf life | 12 months in unopened original packaging, dry storage |
Industry use cases
Renewable energy (wind)
Grouting steel base-frame connections of onshore turbine foundations and joints of precast concrete towers across India’s wind corridors (Tamil Nadu, Gujarat, Rajasthan, Karnataka), where cyclic loading demands certified fatigue performance.
Power transmission
Bedding flanged lighting columns, transmission-line tower base plates and substation equipment subject to wind-induced dynamic loads.
Bridges and highways
High-strength grouting beneath heavily loaded bridge bearings and parapet posts on national highway and metro viaduct projects requiring early return to service.
Heavy industry
Precision grouting of compressor, turbine, crane-rail and press base plates in cement, steel and petrochemical plants where impact and vibration cause grout fatigue.
Oil and gas
Non-structural offshore foundation connections and onshore installation grouting where high early strength and durability in aggressive environments are needed.
Frequently asked questions
What makes Conbextra BB92 different from standard Conbextra grouts like GP or HF?
What thickness can be grouted in a single pour?
How much water do I add per 25 kg bag?
Can Conbextra BB92 be used in cold Indian winters or high summer temperatures?
Is it suitable for offshore wind foundations?
What is the yield and shelf life?
How we position Fosroc Conbextra BB92
Conbextra BB92 is Fosroc’s specialist UHPC grout for fatigue-loaded grouted connections and is positioned well above the everyday grouts most contractors know. Within the Fosroc range, step down to Conbextra GP for general non-shrink base-plate and pocket grouting, Conbextra HF/HES for high-flow or high-early-strength static work, or Conbextra EP10/EP65 epoxy grouts for chemically aggressive or very high dynamic machine bases; pair the grouted connection with Nitobond/Nitoprime primers and Concure curing membranes from the same system. Against the wider market, BB92 competes with BASF/MBS MasterFlow 9500 and Master Builders Solutions high-performance turbine grouts, Sika SikaGrout/Sikadur structural grouts, STP/Krishna Constrochem precision grouts, and Dr. Fixit grouting solutions; Dr. Fixit and STP are typically chosen for general repair and waterproofing-adjacent grouting rather than certified turbine connections. Honestly, BB92 is over-specified and uneconomical for ordinary base-plate grouting, where a standard Conbextra grade wins on cost; its value is realised specifically where dynamic fatigue loading, high modulus and EN 1504-6 / DNV-benchmarked performance are genuine project requirements. As an authorised Fosroc distributor, Space Arc Engineering can advise on the correct grade and supply the full connection system across Delhi NCR and Pan-India.
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