Fosroc Conplast MS Densified
A densified microsilica (silica fume) powder admixture that cuts permeability, lifts strength and protects concrete against chlorides, sulphates and ASR in demanding structures.
What is it?
Fosroc Conplast MS is a high-quality densified microsilica (silica fume) supplied as a fine grey powder. It is a pozzolanic mineral admixture, not a liquid chemical admixture, conforming to ASTM C1240-95a with a minimum SiO2 content of 85%.
Where is it used?
High-performance and high-durability concrete: marine and coastal RCC, bridges, jetties, effluent and water-retaining structures, high-strength columns, silos, tunnel linings and any element exposed to chlorides, sulphates, abrasion or alkali-silica reaction.
Why use it?
Its sub-micron amorphous silica reacts with free lime to densify the cement paste and choke capillary pores, sharply lowering permeability and chloride-ion penetration while raising compressive and flexural strength and long-term durability.
How is it applied?
Dosed at 4-10% by weight of cement and added early in the mix – dry-blended with aggregate and cement, batched with cement in wet plants, or as a slurry – paired with a high-range water reducer such as Conplast SP430 to keep the water-cement ratio low.
About Fosroc Conplast MS Densified
Fosroc Conplast MS is the silica-fume (microsilica) line within the Conplast admixture family, supplied in densified powder form to Indian sites by Fosroc Chemicals (India) Pvt. Ltd. Unlike the liquid Conplast superplasticisers and water reducers, Conplast MS is a supplementary cementitious material: an ultra-fine, amorphous silicon-dioxide pozzolan recovered from the production of silicon and ferro-silicon alloys. Its particles are roughly a hundred times finer than ordinary Portland cement, which lets it work on two fronts at once. Physically, the microscopic spheres pack into the voids between cement grains, refining the pore structure of the paste and the interfacial transition zone around aggregate. Chemically, the highly reactive silica consumes the weak, soluble calcium hydroxide (free lime) left over from cement hydration and converts it into additional strong, stable calcium-silicate-hydrate (C-S-H) gel. The combined effect is a far denser, more impermeable and more chemically resistant concrete. The word \”densified\” refers to the supplied form: raw silica fume is extremely light and dusty, so Fosroc supplies Conplast MS as a densified powder with a bulk density of approximately 610 kg/m3, which is easier to store, transport, weigh-batch and disperse on site than fluffy undensified fume. For Indian contractors, consultants and ready-mix producers, Conplast MS is the route to M50-and-above grades, very-low-permeability decks and structures, and long design-life infrastructure where ordinary OPC or fly-ash mixes alone cannot meet durability requirements. Space Arc Engineering supplies genuine Fosroc Conplast MS, along with the complementary Conplast superplasticisers it is normally used with, across Delhi NCR and on a Pan-India basis with technical guidance on dosage and mix trials.
The technical insight
The performance of Conplast MS rests on the pozzolanic reaction and pore-refinement, not on water reduction – so it is almost always used together with a high-range water reducer rather than on its own. Microsilica is so fine that adding it actually increases water demand; if you simply add it to a fixed water content the mix stiffens and bleeds less but can become unworkable. The correct practice is to add Conplast MS and simultaneously use a superplasticiser such as Conplast SP430 or the workability-retaining Conplast SP423 to drive the water-cement ratio down (often below 0.40) while keeping the mix placeable. That combination is what delivers the headline gains: dramatically reduced chloride-ion penetration (a key input to service-life models and DRCM/RCPT acceptance), higher 28-day and ultimate strengths, and resistance to sulphate and alkali-silica attack. Because microsilica makes concrete more cohesive and \”sticky\”, Fosroc advises targeting a slump 25-35 mm higher than the normal requirement so the mix still flows and compacts properly. Curing discipline is critical: microsilica concrete has very low bleed water, so the surface can dry and plastic-crack within minutes if left exposed – early, continuous moist curing is non-negotiable. The chemistry is governed by the reactive amorphous silica content (SiO2 minimum 85%, alkalies as Na2O maximum 1%, loss on ignition maximum 5%), which is why the material is specified to ASTM C1240 rather than to a liquid-admixture standard such as IS 9103 or ASTM C494.
Where it is used
- High-strength concrete (M50, M60 and above) for columns, transfer girders and heavily loaded elements
- Marine and coastal RCC – jetties, sea walls, piers and splash-zone structures exposed to chlorides
- Bridge decks, piers and crash barriers requiring very low permeability and long service life
- Water-retaining and water-treatment structures: tanks, reservoirs, effluent and sewage works needing sulphate resistance
- Industrial floors and pavements subject to abrasion, impact and chemical spillage
- Tunnel linings, basements and below-ground structures where watertightness is critical
- Underwater and tremie concrete where high cohesion and anti-washout behaviour are required
- Concrete in aggressive soils or groundwater where sulphate and alkali-silica reaction must be controlled
- Repair micro-concretes and high-durability overlays where a dense, low-shrinkage matrix is specified
Key advantages
- Sharply reduces permeability by blocking the capillary pore network against moisture and aggressive ions
- Cuts chloride-ion penetration, extending the corrosion-initiation life of embedded reinforcement
- Raises compressive and flexural strength, enabling high-grade and high-performance mixes
- Improves resistance to sulphate attack, abrasion, frost and alkali-silica reaction (ASR) in one product
- Densified powder form (approx. 610 kg/m3 bulk density) is easier to store, weigh-batch and disperse than undensified fume
- Increases mix cohesion, reducing segregation and bleeding and improving anti-washout behaviour for underwater work
- Conforms to the international ASTM C1240 standard for silica fume, giving specifiers a recognised basis for approval
- Flexible dosing into dry-batch, wet-batch or slurry operations, compatible with OPC and Conplast liquid admixtures
Limitations & considerations
- Not a water reducer – it raises water demand, so it must be paired with a superplasticiser such as Conplast SP430 or SP423 to stay workable
- Very low bleed makes the surface prone to rapid plastic-shrinkage cracking; immediate, continuous moist curing is essential
- It is a fine dust – handling requires dust masks, gloves and goggles, and it can cause respiratory and eye irritation
- Overdosing or poor dispersion can make concrete excessively sticky and hard to finish; optimum dosage must be set by site trials
- Higher material cost per cubic metre than plain OPC or fly-ash mixes, justified only where durability or strength demands it
- Conforms to ASTM C1240 for silica fume rather than to liquid-admixture codes (IS 9103 / ASTM C494), so it is specified differently
- Performance depends on adequate mixing energy and time; under-mixing leaves agglomerated densified particles undispersed
- 12-month shelf life and must be kept dry in unopened bags – it absorbs moisture and is sensitive to damp storage
Selection & best practice
Always run laboratory and site trials with your own cement and aggregates before fixing the dosage – start within the 4-10% by weight of cement range and pair Conplast MS with a high-range water reducer (e.g. Conplast SP430) to reach the target water-cement ratio. Add the microsilica early in the batching cycle: dry-blend it with aggregate and cement in dry-batch plants, charge it with the cement in wet-batch plants, or introduce it as a slurry, and allow extra mixing time for full dispersion. Design for a slump 25-35 mm above the normal requirement to absorb the added cohesion, and begin moist curing immediately after finishing – microsilica concrete bleeds very little and will crack if the surface is allowed to dry. Store bags in a dry, covered location, use within 12 months, and protect operatives with dust masks, gloves and goggles.
Specifications
| Product type | Densified microsilica (silica fume) – pozzolanic mineral admixture |
| Form / appearance | Fine grey powder (densified) |
| Standard compliance | Conforms to ASTM C1240-95a |
| Silica content (SiO2) | Minimum 85% |
| Alkalies (as Na2O) | Maximum 1% |
| Loss on ignition | Maximum 5% |
| Bulk density | Approx. 610 kg/m3 |
| Dosage | 4 to 10% by weight of cement (set by trial) |
| Recommended use with | High-range water reducer, e.g. Conplast SP430 / SP423 |
| Target slump adjustment | 25-35 mm above normal slump requirement |
| Packaging | 15 kg bags |
| Shelf life | Minimum 12 months, dry storage in unopened packs |
| Health & safety | Non-flammable; dust hazard – use mask, gloves and goggles |
Industry use cases
Marine & Coastal Infrastructure
Jetties, sea walls and splash-zone RCC where Conplast MS slashes chloride-ion ingress to protect reinforcement and extend service life in the harsh coastal environment of Indian ports.
Bridges & Highways
Bridge decks, piers and crash barriers cast with microsilica concrete for very low permeability, abrasion resistance and the long design lives demanded by NHAI and MoRTH durability specifications.
Water & Wastewater
Reservoirs, water-treatment tanks and effluent structures where the sulphate resistance and watertightness of Conplast MS concrete prevent leakage and chemical degradation.
High-Rise & Commercial Construction
M50-M70 columns and transfer structures in tall buildings, where microsilica lets RMC producers hit high grades with manageable section sizes.
Industrial & Power
Abrasion-resistant industrial floors, chimney and silo concrete, and structures in aggressive soils where frost, abrasion and ASR resistance are required in a single mix.
Tunnels & Underground
Tunnel linings, basements and underwater/tremie pours that benefit from the high cohesion, anti-washout behaviour and low permeability of densified-microsilica concrete.
Frequently asked questions
Is Fosroc Conplast MS a superplasticiser?
What dosage of Conplast MS should I use?
What standard does Conplast MS comply with?
How is Conplast MS added to the concrete mix?
Why does microsilica concrete crack and how do I prevent it?
How is Conplast MS packaged and stored, and is it available in Delhi NCR?
How we position Fosroc Conplast MS Densified
Within the Fosroc range, Conplast MS occupies a different role from the liquid Conplast admixtures and is normally specified alongside them rather than instead of them. It is the densified-microsilica mineral addition, while products such as Conplast SP430 (chloride-free superplasticiser) and Conplast SP423 (workability-retention admixture) are the chemical water reducers that make a low water-cement ratio achievable; in practice the two are combined to produce high-performance concrete. Where integral waterproofing rather than silica-fume densification is the goal, Fosroc Conplast WL, Conplast WP200/X421 or the crystalline Conplast Crystalline are the relevant siblings. Fosroc also offers Conplast SF1000, a closely related densified silica-fume admixture, so specifiers should confirm the exact grade against the current Fosroc India catalogue. Against the wider market, the most credible alternatives a consultant might cross-evaluate are Sika’s silica-fume / SikaFume products and Sika ViscoCrete superplasticisers, BASF/Master Builders Solutions (MBS) MasterLife and MasterGlenium ranges, and locally Elkem Microsilica grade 920D and Corniche/other densified silica-fume suppliers; for purely waterproofing duties (a different need) Dr. Fixit and STP (Pidilite/STP) products compete, though they are not microsilica pozzolans. For Indian projects, Space Arc Engineering positions Conplast MS as the dependable, ASTM C1240-compliant choice for low-permeability, high-durability concrete, supplied genuine with the matching Conplast superplasticisers and on-site technical support across Delhi NCR and Pan-India.
Related Concrete Admixtures products
Source Fosroc Conplast MS Densified for your project
Authorised distribution, technical advice & professional application across Delhi NCR and Pan-India.