About MC-Bauchemie MC-Crete 500

MC-Crete 500 is MC-Bauchemie’s calcium nitrite corrosion inhibitor, supplied as an aqueous solution that goes into the concrete at the mixing stage rather than onto the finished surface. It is a preventive admixture, chosen at the design stage for structures where chlorides are a known threat over the decades of service life ahead. The active chemistry, calcium nitrite, is entirely chloride-free, so nothing in the product itself works against the reinforcement it is meant to protect.

The way engineers should think about it is as insurance built into the mix. Ordinary reinforced concrete tolerates only a small amount of chloride at the steel before the passive oxide film breaks down and corrosion begins. MC-Crete 500 pushes that tolerance level considerably higher, so it takes far more chloride ingress, and far more time, before the reinforcement is at risk. For a jetty, a coastal slab or a car park deck salted every winter, that margin is the difference between a structure that lasts its full design life and one that starts spalling within a decade.

The technical insight

The mechanism is electrochemical, not a barrier. Steel in sound concrete is protected by a thin passive oxide layer held in place by the high alkalinity of the pore solution. Chloride ions that diffuse in eventually depassivate that film at discrete anodic sites, and once an anode forms, pitting corrosion runs. Nitrite ions from MC-Crete 500 compete for those same anodic sites: they oxidise the exposed iron and repair the passive film faster than chloride can break it down, effectively re-stabilising the steel. Because it acts at the anode, it is classed as an anodic inhibitor. The practical result is a shift in the critical chloride threshold, from roughly 0.2 to 0.4 percent chloride by weight of cement in an uninhibited mix up to about 0.6 to 1.2 percent when dosed. The nitrite does not stop chloride entering the concrete; it changes how much chloride the steel can sit in before corrosion initiates, which is why correct dosage relative to the expected chloride load matters so much.

Where it is used

• Reinforced concrete for marine and coastal structures in EN 1504 exposure classes XS1, XS2 and XS3
• Bridge decks and parapets subject to de-icing salt run-off
• Multi-storey car park decks and ramps exposed to salt carried in on vehicles
• Reinforced concrete piles cast into chloride-contaminated or aggressive ground
• Jetties, sea walls and other splash-zone RCC where chloride ingress is continuous
• Precast and ready-mix concrete specified for extended design service life in aggressive exposure
• Water-retaining and coastal infrastructure where early rebar corrosion would be costly to repair
• New-build RCC where corrosion protection is designed in at the mix stage rather than retrofitted

Key advantages

• Raises the critical chloride threshold at the steel, giving a quantifiable, design-usable durability gain
• Calcium nitrite chemistry is chloride-free, so it adds no aggressive ions of its own
• Backed by decades of international field performance data on nitrite inhibitors
• Dual action: alongside corrosion protection it gives a mild early-strength gain, useful for faster form turnaround
• Compatible with supplementary cementitious materials such as fly ash and GGBS, and with superplasticisers
• Dosed at the batching plant, so protection is uniform through the full concrete section, not just at a surface
• Dosage can be tuned to the expected chloride exposure rather than a one-size-fits-all rate
• Suits both ready-mix and precast production without special equipment

Limitations & considerations

• It inhibits corrosion at the steel but does not reduce chloride ingress; concrete cover, low w/c ratio and good compaction still do the primary work
• As an accelerator it mildly speeds initial and final set, which can be a problem in hot weather placements
• Retarder dosage often needs adjusting to keep workability retention when both admixtures are used together
• Dosage must be matched to the anticipated chloride load; under-dosing leaves the threshold too low for the exposure
• It is a design-stage, in-mix solution and cannot be applied to hardened or existing concrete
• Trial mixes are needed to confirm setting, strength and workability with the specific cement and SCMs in use

Selection & best practice

Specifications

Industry use cases

How we position MC-Bauchemie MC-Crete 500

MC-Crete 500 sits in MC-Bauchemie’s admixture range as the corrosion-protection specialist, and pairs naturally with the rest of a durability-focused mix design: MC-Bauchemie’s Centrament and MC-PowerFlow superplasticiser families for water reduction and workability, alongside their waterproofing admixtures where reducing chloride ingress in the first place is part of the strategy. For chloride-exposed structures we often specify it together with a low-permeability concrete and protective coatings rather than in isolation. Where a project standardises on Fosroc, we supply the directly equivalent calcium nitrite inhibitor, and for surface protection over completed marine RCC we can bring in protective anti-carbonation and anti-chloride coatings from our Fosroc and Dr. Fixit ranges. Talk to Space Arc for the full corrosion-protection scheme rather than a single product.

Related Concrete Admixtures products

View all Concrete Admixtures products →