Frequently Asked Questions

What is the difference between using Cebex 200 in a site-batched grout and using a pre-bagged precision grout like Conbextra GP2 and when should each be preferred?

Both Cebex 200-dosed site-batched grout and Conbextra GP2 pre-bagged precision grout aim to achieve the same outcome — a non-shrink, high-strength grout that fills the void under machine base plates or around anchor bolts without settlement voids — but they differ in quality control, consistency, and the effort required to achieve reliable non-shrink performance. Conbextra GP2 pre-bagged precision grout is manufactured under factory quality control conditions with precisely formulated proportions of cement, graded aggregate, and expansive admixture — every bag produces a consistent, tested, certified non-shrink grout when mixed at the specified water:powder ratio. The factory-controlled proportions mean that the non-shrink performance is repeatable and predictable, and the performance data (compressive strength, non-shrink expansion, flow table value) is tested and certified per IS 9103 and IS 4031. Cebex 200 site-batched grout relies on accurate site measurement of the cement, sand, water, and Cebex 200 dosage to achieve the same result. Any variation in the sand grading (aggregate that is coarser or finer than tested), in the cement brand or grade, in the water dosage, or in the Cebex 200 dosage can result in either insufficient expansion (still shrinking grout) or over-expansion (grout that expands excessively, causing crack-inducing internal pressure in the set grout). Cebex 200 site-batched grout is preferred when: very large volumes of grout are required (entire power plant turbine grouting, for example) where the unit cost saving of site batching is significant; pre-bagged precision grout supply is unavailable or lead time is long; and when the grouting specification does not require a certified pre-bagged product. For critical precision machinery grouting (turbines, compressors, high-speed rotating equipment, CNC machining centres), the quality control assurance of Conbextra GP2 is generally preferred over site-batched Cebex 200 grout.

How is Cebex 200 dosed and mixed with cement and sand for a non-shrink grout and what is the correct mixing sequence?

The mixing procedure for Cebex 200-based non-shrink grout requires careful adherence to the correct mixing sequence to ensure uniform distribution of the Cebex 200 in the grout and consistent gas generation. The recommended mixing sequence is: weigh or measure the cement and clean washed fine sand (typically a cement:sand ratio of 1:1 to 1:1.5 for anchor bolt grouting, or 1:0 neat cement grout for very high strength requirements) into a clean drum or mechanical mixer; add the Cebex 200 powder at the specified dosage (typically 0.5 to 2.0 per cent by weight of cement — so for 50 kg of cement, the dosage is 250 to 1,000 grams of Cebex 200) and dry-mix the Cebex 200 into the cement and sand thoroughly before any water is added. Dry-mixing the Cebex 200 with the cement and sand before water is added is important — if Cebex 200 is added to a wet mix, the gas generation reaction starts immediately from the initial contact with moisture, and the gas is generated in an uncontrolled manner before the material is mixed into a homogeneous grout, resulting in non-uniform expansion and possible segregation of the Cebex 200 powder into gas-generating pockets rather than uniform distribution. After dry-mixing, add the gauging water and mix to a smooth, uniform grout consistency. For flow and pumpability requirements, Conplast SP superplasticizer can be added to the water before addition to reduce the water:cement ratio while maintaining workability. After mixing, the grout should be placed immediately — the gas generation is time-limited and begins as soon as water contacts the Cebex 200, so delays between mixing and pouring allow gas to escape from the mix before it is in the final position.

Does Cebex 200 affect the compressive strength of the grout and is the final strength the same as plain cement grout?

Cebex 200 has a minor effect on the final compressive strength of the cured grout compared to a plain cement-sand grout mixed at the same water-cement ratio. The gas generation from Cebex 200 introduces a small volume of fine voids within the grout matrix — these voids, although very fine and uniformly distributed, do reduce the solid volume fraction of the hardened grout and correspondingly reduce the compressive strength slightly compared to a void-free grout. The magnitude of this strength reduction depends on the Cebex 200 dosage (higher dosage produces more gas and more voids, with greater strength reduction) and the water-cement ratio of the grout (lower W/C ratio grout has higher base strength and can absorb a greater percentage strength reduction and still achieve the minimum required strength). At the recommended minimum effective dosage of Cebex 200 (0.5 per cent by weight of cement), the strength reduction is typically 5 to 10 per cent relative to the same mix without Cebex 200. At higher dosages (2 per cent), the reduction may be 10 to 20 per cent. For machine base grouting where a minimum compressive strength of 25 to 30 MPa is typically required (to develop adequate bearing area under dynamic machinery loads), a Cebex 200-modified cement grout at 0.45 to 0.50 water-cement ratio with minimal sand will achieve this strength comfortably even accounting for the strength reduction from air entrainment. If the minimum required grout strength is high (for example, 50 MPa or higher for high-load precision machinery), the water-cement ratio of the Cebex 200 grout must be reduced accordingly (with Conplast SP to maintain flow), and the strength should be verified by casting grout cubes from the actual site mix and testing at 28 days.