About MC-Bauchemie MC-Crete 720

MC-Crete 720 solves a problem that has frustrated concrete producers for years: getting silica fume evenly into a mix. Densified microsilica powder is notoriously light, dusty and prone to balling, and poor dispersion leaves reactive particles clumped and inert. MC-Bauchemie sidesteps all of that by supplying the silica fume already dispersed in water as a stable, pourable slurry at around 50% solids. The reactive amorphous silicon dioxide is held in suspension and delivered straight into the batch, so every cubic metre gets a uniform dose without the handling losses, health hazards and mixing headaches of a bagged powder.

Once in the mix, MC-Crete 720 works on two fronts. Physically, its sub-micron particles, roughly a hundred times finer than cement grains, slot into the voids between cement particles and pack the paste tighter. Chemically, that same amorphous silica reacts with the free calcium hydroxide left over from cement hydration, converting a weak, soluble by-product into additional binding calcium silicate hydrate gel. The combined effect is a denser, less permeable matrix that resists the chloride ingress, sulphate attack and carbonation that drive reinforcement corrosion. For Indian projects facing coastal air, de-icing salts, aggressive groundwater or industrial effluent, that translates into structures engineered to last decades longer than plain OPC concrete would allow.

The technical insight

The durability gain comes down to pore refinement plus pozzolanic conversion working together. Ordinary Portland cement hydration produces C-S-H gel, the material that gives concrete its strength, but it also leaves behind calcium hydroxide, a comparatively weak and readily leached phase that occupies space without contributing much. MC-Crete 720’s amorphous SiO2 is a highly reactive pozzolan: it consumes that calcium hydroxide and reprecipitates it as secondary C-S-H, so a liability becomes load-bearing gel. At the same time the extreme fineness, a median particle size in the 0.10 to 0.15 micron range with a specific surface area of roughly 15,000 to 25,000 m2/kg, lets the particles fill the capillary pores that would otherwise form continuous pathways for water and dissolved salts. Break those pathways and the chloride diffusion coefficient can fall by several times over an equivalent plain-OPC mix at the same water-cement ratio, which is precisely why microsilica concrete is specified where reinforcement must survive decades of chloride exposure. Because the reaction is genuinely pozzolanic rather than just a filler effect, the strength contribution keeps building past 28 days as the calcium hydroxide is progressively consumed.

Where it is used

• Marine and coastal structures such as jetties, sea walls and splash-zone elements exposed to chloride-laden air and water
• Bridge decks and piers in de-icing salt environments where chloride-driven rebar corrosion is the main durability threat
• Parking structures and elevated decks subject to salt tracking and repeated wetting
• Chemical plant foundations, bunds and containment slabs exposed to aggressive process spillage
• High-rise columns and transfer elements in high-strength C60 to C80 grade concrete
• Sewage and effluent treatment tanks and channels facing biogenic sulphuric acid and sulphate attack
• High-performance and self-compacting mixes where a denser paste and improved cohesion are required
• Precast and infrastructure elements specified for extended design service life under severe exposure

Key advantages

• Supplied pre-dispersed as a slurry, eliminating the dust, balling and dispersion problems of densified microsilica powder
• Delivers uniform silica fume distribution through the batch water or a liquid dispenser for consistent, repeatable dosing
• Markedly reduces permeability and chloride diffusion, extending the service life of reinforced concrete in severe exposure
• Contributes measurable later-age compressive strength gain versus a comparable control mix
• Improves resistance to sulphate attack, carbonation and chemical aggression through a denser, refined pore structure
• Enhances paste cohesion and reduces bleed and segregation, aiding pumpability and finish in high-performance mixes
• Compatible with common PCE and SNF superplasticisers, retarders and accelerators, giving mix-design flexibility
• Backed by MC-Bauchemie technical support and supplied with authorised-distributor documentation through Space Arc

Limitations & considerations

• Silica fume increases the water demand and stickiness of the mix, so an effective superplasticiser is essentially mandatory to keep it workable
• Dosage must be established by trial mix for the specific materials; overdosing raises cost and can make placing and finishing difficult
• The slurry can settle on standing and must be re-agitated before use to keep the solids in uniform suspension
• Denser, low-bleed microsilica concrete is prone to plastic shrinkage cracking, so disciplined early curing and evaporation control are critical
• It reduces permeability and reinforcement corrosion risk but is not a waterproofing membrane; positive water pressure still needs a dedicated waterproofing system
• Full pozzolanic and strength benefit depends on adequate moist curing, without which the reaction stalls

Selection & best practice

Specifications

Industry use cases

How we position MC-Bauchemie MC-Crete 720

MC-Crete 720 sits at the durability end of the concrete admixture range, so it is usually specified alongside rather than instead of a superplasticiser. On MC-Bauchemie mixes it pairs naturally with the MC-PowerFlow and Muraplast PCE-based high-range water reducers to restore workability, and with MC-Bauchemie’s set-control admixtures where placing times or heat need managing. Where a client is standardised on Fosroc, the equivalent workhorse water reducers are the Conplast SP and Auramix families, which are documented for use with microsilica-bearing concrete. For the wider durability package we can also supply crystalline and membrane waterproofing, surface protective and anti-carbonation coatings, and concrete repair mortars from our Fosroc, Sika and Dr. Fixit lines, so a single specification can cover the mix, the surface protection and any future repair. Talk to Space Arc for a trial-mix-backed recommendation matched to your exposure class and existing admixture regime.

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