Frequently Asked Questions

Does adding Cebex 100 reduce the compressive strength of the concrete and how should the concrete mix design be adjusted to account for any strength reduction?

Yes — Cebex 100 introduces controlled air entrainment into the concrete mix, and increased air content in concrete has a well-established effect on compressive strength: each 1 per cent increase in air content typically reduces compressive strength by approximately 5 to 6 per cent at a given water-cement ratio. This means that if Cebex 100 at the recommended dosage increases the air content of the concrete from a base of 1.5 per cent to 3.5 per cent (a 2 per cent increase), the compressive strength reduction is approximately 10 to 12 per cent relative to the non-air-entrained mix at the same water-cement ratio. For structural concrete where a minimum characteristic compressive strength (say M30 or M35 grade per IS 456:2000) is specified, this strength reduction must be accounted for in the mix design by: adjusting the mix to a slightly lower water-cement ratio (adding more cement or using a higher dosage of Conplast SP superplasticizer to compensate for workability reduction at the lower W/C ratio); targeting a higher mean compressive strength in the mix design (if the target mean strength for M30 grade is 38 MPa based on the standard deviation of the mix, increase the target to 42 MPa to account for the 10 to 12 per cent strength reduction from air entrainment); or using Cebex 100 at the minimum effective dosage to minimise the air content increase while still achieving the required pumpability improvement. Concrete cube testing of trial mixes with the proposed Cebex 100 dosage is the definitive way to quantify the strength reduction for a specific mix before use on a structural pour. For non-structural applications where strength is not the critical parameter, the air entrainment strength effect is generally unimportant.

Can Fosroc Cebex 100 be used for all types of concrete pumping applications or are there specific cases where it is not suitable?

Fosroc Cebex 100 is a general-purpose pumping aid suitable for most standard reinforced concrete pumping applications — slabs, columns, beams, walls, and raft foundations where the concrete design strength is M20 to M40 grade and the pumpability of the mix is the primary concern. There are however specific applications where Cebex 100 is either not suitable or requires additional care in the mix design. Very high strength concrete (M50 and above): the air entrainment introduced by Cebex 100 reduces compressive strength, and this reduction becomes increasingly problematic at high target strength mixes where the strength margin between target mean and minimum characteristic is narrow. At M50 and above, the mix design typically already uses high cement content and low W/C ratio to achieve strength — any air content reduction in strength works against the design intent, and Cebex 100 is generally not recommended at these strengths. If pumpability of a high-strength mix is a concern, the solution is typically to increase the superplasticizer dosage (Conplast SP430 or equivalent) rather than to add an air-entraining agent. Water-retaining structures (IS 3370): concrete mixes for water-retaining structures (tanks, reservoirs, swimming pools) designed to IS 3370 with a maximum water-cement ratio of 0.45 must have low permeability — the air voids introduced by Cebex 100, even though small and uniformly distributed, create a pathway for water permeation through the concrete matrix that increases permeability. Cebex 100 should not be used in concrete for water-retaining structure walls and slabs where IS 3370 watertightness requirements apply.

How should Cebex 100 be dosed and added to the concrete mix at a ready-mix concrete plant in India and are there special handling requirements?

Cebex 100 is a liquid admixture supplied in canisters or drums and added to the concrete mix during batching at the ready-mix concrete (RMC) plant, or alternatively at the truck mixer drum before the mix is dispatched to site. The dosage is measured by volume (millilitres per 100 kilograms of cementitious content) and must be accurately measured — Cebex 100 is a powerful air-entraining agent and over-dosing (adding too much) causes excessive air entrainment (above 5 to 6 per cent air content) that significantly reduces strength and can cause the concrete mix to become spongy and unworkable. Under-dosing provides insufficient air entrainment and does not improve pumpability adequately. At a modern RMC plant in India, Cebex 100 is typically dispensed through the plant admixture dosing system (a pump connected to the admixture storage tank, controlled by the batching computer) alongside the other admixtures (superplasticizer, retarder) — the batching computer doses the correct volume based on the batch size. For plants without automated admixture dosing or for on-site batching, Cebex 100 must be measured manually in a graduated measuring cylinder and added to the mixing water before introduction to the mixer drum. Handling precautions: Cebex 100 is a surfactant-based liquid that should be handled with basic precautions (avoid eye contact, wear gloves); it is not classified as a hazardous material but should be stored in a cool area away from direct sunlight and extreme temperature. The product should be used within the shelf life period specified on the packaging (typically 12 months from manufacture date). Addition of Cebex 100 directly to a dry aggregate/cement mixture without water is not recommended — it should always be diluted into the mixing water or gauging water first.