Fosroc Conbextra BB72 IN
Free-flow, non-shrink cementitious precision grout with 75 N/mm² ultimate strength — built for precast wind turbine tower joints and heavily loaded foundations.
What is it?
A ready-to-use powder grout blending Portland cement, graded fillers and chemical additives that expand the mix in its plastic stage while keeping water demand low. Mixed with measured water, it becomes a free-flowing, non-shrink grout with high early and ultimate strength, compliant with ASTM C 1107 Type C.
Where is it used?
Precision grouting of heavily loaded foundations — most notably the joints between precast concrete segments of wind turbine towers — plus machinery base plates, column bases and anchor pockets with gaps from 10 mm to 100 mm.
Why use it?
Plastic-stage expansion keeps the hardened grout in full contact with the base plate or joint face, so design loads transfer without hard spots or voids. The 75 N/mm² ultimate strength and pumpable rheology suit both static and dynamic loading.
How is it applied?
Mix the full 25 kg bag with clean water at a 0.16 water:powder ratio (about 4 litres per bag) using a forced-action mixer, then pour or pump continuously from one side of the prepared, pre-soaked gap until grout emerges at the vents.
About Fosroc Conbextra BB72 IN
Conbextra BB72 IN is Fosroc’s precision grout for foundations that carry serious load. It arrives on site as a single pre-weighed 25 kg bag — a factory blend of Portland cement, graded fillers and chemical additives — so there is no site batching of sand or cement and no variation between mixes. Add a controlled quantity of clean water and the powder turns into a free-flowing grout that fills gaps between 10 mm and 100 mm thick under its own head, reaching every corner of a base plate or joint without rodding.
Where BB72 IN earns its keep is the wind sector. Precast concrete tower segments must be joined with a grout that flows completely through the joint, gains strength quickly so erection crews can keep climbing, and never pulls away from the mating faces. Fosroc formulated this grade specifically for that duty, and the same properties make it a dependable choice for turbine and generator plinths, compressor bases and structural column grouting across Indian power, cement and process plants. Space Arc Engineering stocks it in Delhi NCR and supplies pan-India, with applicator support where the pour is critical.
The technical insight
Ordinary cement grout bleeds and settles before it sets, leaving a thin void under the plate — exactly where bearing contact matters most. BB72 IN counters this with additives that generate a controlled expansion while the grout is still plastic, offsetting settlement and plastic shrinkage so the hardened grout stays locked against the underside of the plate or joint face. The same chemistry suppresses water demand: at a water:powder ratio of just 0.16 the mix still flows freely, and that low ratio is what delivers the dense matrix behind the 75 N/mm² ultimate compressive strength and the high early strengths that let wind-tower erection proceed on schedule. The system is classified Type C under ASTM C 1107.
Where it is used
- Grouting joints between precast concrete wind turbine tower segments
- Precision grouting of heavily loaded machinery foundations and bedplates
- Base plate and sole plate grouting for structural steel columns
- Anchor bolt pockets and holding-down bolt grouting
- Turbine, generator and compressor plinths in power and process plants
- Free-flow filling of gaps from 10 mm to 100 mm under equipment bases
- Pumped grouting where access prevents pouring from one side
Key advantages
- High ultimate compressive strength of 75 N/mm² for heavy static and dynamic loads
- High early strength supports fast erection cycles on wind tower projects
- Controlled plastic-stage expansion — no shrinkage voids under plates or in joints
- Free-flowing rheology fills 10-100 mm gaps fully; suitable for pumping
- Low water demand (0.16 w/p) produces a dense, durable hardened grout
- Single pre-bagged 25 kg component removes on-site batching variation
- Complies with ASTM C 1107 Type C for non-shrink hydraulic cement grout
Limitations & considerations
- Strength and expansion depend on the exact 0.16 water:powder ratio — water must be measured, never judged by eye
- Suitable for gap thicknesses of 10-100 mm only; thinner or deeper pours need a different grade or Fosroc guidance
- Expansion only benefits confined pours — unrestrained faces should be shuttered
- Cementitious base is not suited to aggressive chemical exposure; an epoxy grout such as Conbextra EP is the right call there
- Working time shortens in hot Indian summer conditions, so mixing and placing must be continuous and planned
- Where 90 N/mm² windmill-grade performance is specified, Conbextra BB92 IN is the correct grade, not BB72 IN
Selection & best practice
Preparation decides the result. Scabble the foundation concrete to remove laitance and expose sound aggregate, degrease steel undersides, and soak the substrate for several hours before removing standing water — a saturated, surface-dry base stops the concrete robbing mix water from the grout. Shutter all sides with a head box on the pouring side and provide vents at high points. Charge a forced-action mixer with the measured water — 0.16 water:powder, roughly 4 litres per 25 kg bag, from a graduated container — then add the full bag and mix to a uniform, lump-free consistency. Pour or pump continuously from one side only so air escapes ahead of the grout, and keep placing until it flows out of the far side and vents. Cure exposed shoulders with wet hessian or curing compound, and cast cubes with each pour so loading is authorised on measured strength, not the calendar.
Specifications
| Form | Ready-to-use powder — Portland cement, graded fillers, chemical additives |
| Type | Non-shrink, high-flow, high early and ultimate strength cement grout |
| Ultimate compressive strength | 75 N/mm² |
| Water:powder ratio | 0.16 (approx. 4 litres per 25 kg bag) |
| Gap thickness range | 10 mm – 100 mm |
| Standards compliance | ASTM C 1107, Type C |
| Expansion system | Controlled expansion in the plastic stage |
| Pack size | 25 kg bag |
Industry use cases
Wind Energy
Joint grouting between precast concrete tower segments, where full-section flow and rapid early strength keep turbine erection on programme.
Power Generation
Turbine, generator and auxiliary equipment foundations in thermal and hydel stations that demand permanent full-contact bearing.
Heavy Manufacturing
Compressor bases, mill stands and machine bedplates in steel, cement and process plants carrying sustained heavy loads.
Industrial Construction
Structural steel column base plates and holding-down bolt pockets grouted to design bearing across PEB and plant structures.
Infrastructure
Precision grouting of heavily loaded plinths and equipment supports on utility and infrastructure projects pan-India.
Frequently asked questions
How much water does one 25 kg bag of Conbextra BB72 IN need?
What gap thickness can it be used for?
What is the difference between Conbextra BB72 IN and BB92 IN?
Does it meet any recognised standard?
Can Conbextra BB72 IN be pumped?
When can the foundation be loaded after grouting?
How we position Fosroc Conbextra BB72 IN
Within the Fosroc grout family, BB72 IN sits between the general-purpose grades and the top windmill specification: choose Conbextra GP2 for routine base plate and pocket grouting at standard strengths, and step up to Conbextra BB92 IN when the specification calls for 90 N/mm² with dynamic load resistance on wind projects. Where machinery sees chemical exposure or severe dynamic loading, the epoxy-based Conbextra EP grades are the better system, and Cebex 100 admixture covers site-batched cement grouts. Space Arc also stocks equivalent precision grouts from Sika and MC-Bauchemie when a project specification names another manufacturer.
Related Grouts & Anchors products
Source Fosroc Conbextra BB72 IN for your project
Authorised distribution, technical advice & professional application across Delhi NCR and Pan-India.