Cornwall has already lived through one concrete scandal. The mundic crisis rooted in the use of sulphide-contaminated aggregates left thousands of properties blighted, ability to mortgage removed, and homeowners and buyers facing costly investigations and remediation.
Yet today, as recycled aggregates (often referred to as recycled inert aggregates) are increasingly promoted as a sustainable solution for construction, there is a growing risk that history is being overlooked. In a county with Cornwall’s unique geology, the use of recycled aggregates in cement and concrete products may quietly reintroduce the very conditions that caused mundic failures in the first place.
In short: recycled does not automatically mean safe nor sustainable.
Cornwall’s Geology: Not Neutral, Not Inert
Cornwall is not built on bland limestone or benign sand. It is a globally recognised metalliferous mining district. Tin, copper, arsenic and associated sulphide minerals such as pyrite are part of the natural geological fabric of the county and have been further redistributed by centuries of mining, processing, and waste disposal.
Soils, made ground, historic fill and demolition materials across Cornwall frequently contain trace metals and sulphide-bearing stone. When those materials are later crushed, screened and reborn as recycled aggregates, their geological history does not disappear. It is simply redistributed.
This matters enormously when recycled aggregates are proposed for use in cement based products.
Mundic, Sulphides and “Concrete Cancer”
Mundic is a term born in Cornwall, derived from “mundyk”, the local name for pyrite. It describes concrete deterioration caused by unstable mineral constituents within the aggregate, particularly sulphides.
As sulphide minerals oxidise in the presence of moisture and oxygen, they can:
- expand internally,
- generate sulphates,
- trigger internal sulphate attack within the cement matrix.
The result is cracking, expansion, loss of strength and, in severe cases, progressive structural degradation.
This process is sometimes referred to, informally but tellingly, as “concrete cancer”: a slow, internal chemical decay that may remain hidden for years before becoming visible, irreversible, and expensive to address. Like cancer, once it has taken hold, treatment options are limited and outcomes uncertain.
Why Recycled Aggregates Increase the Risk in Cornwall
Recycled aggregates are, by definition, variable. They may contain material sourced from:
- historic demolition rubble,
- old hardstandings,
- made ground,
- legacy fill influenced by mining activity.
In Cornwall, that variability intersects with a sulphide-rich geological background.
Even when recycled aggregates are washed, the risk is not eliminated. Washing can remove surface fines and loose contaminants, but it does not remove sulphide minerals locked within the stone itself. Those minerals remain dormant until time, moisture and micro-cracking allow oxidation to begin.
When such aggregates are blended into concrete or cement products, the concrete does not neutralise the problem, it provides an enclosed, moisture-retaining environment in which damaging reactions can continue unseen.
Recycled Aggregates and the False Comfort of Compliance
Standard grading, cleanliness checks and visual inspections are not designed to identify sulphide risk. A recycled aggregate can meet specification, look clean, and still contain the mineral seeds of future deterioration.
This is particularly relevant for recycled aggregates in Cornwall, where provenance and geology matter just as much as particle size and fines content.
The danger is not that every recycled aggregate will cause problems but that one bad stream, incorporated at scale into concrete products, can seed thousands of future defects before the issue is recognised.
Cornwall has already seen what happens when unsuitable aggregates are normalised before their long-term behaviour is understood.
Sustainability Without Selectivity Is Not Sustainability
Recycling is essential. Lower-carbon construction matters. But sustainability does not mean ignoring geology.
Which is precisely why responsible suppliers of recycled aggregates must be selective about end use. At Wheal Jane Waste & Recycling, recycled aggregates are supplied into applications where their performance characteristics are appropriate and well understood and deliberately kept out of structural concrete products, where even low-level sulphide contamination could pose long-term durability risks.
That distinction is not anti-recycling. It is pro-durability, pro-consumer, and pro-credibility.
Lessons Cornwall Cannot Afford to Forget
The mundic issue did not arise because standards were ignored. It arose because geology was underestimated.
Introducing recycled aggregates into cement and concrete products in Cornwall without rigorous sulphide-focused testing, provenance control, and conservative specification risks repeating that mistake under a greener banner.
The cost will not be immediate. It never is. But it will surface eventually, and when it does, responsibility will be hard to recycle.
Want to Know Where You Stand?
If you’re unsure whether a material, development site or property may be affected by mundic or sulphide-related concrete deterioration, specialist testing and assessment can remove uncertainty early before small questions become large liabilities.
Our sister company, Wheal Jane Consultancy has long experience working with Cornwall’s unique geology and mundic classification. Sometimes all that’s needed is reassurance. Sometimes it’s better to know exactly what you’re dealing with.
Either way, informed decisions today prevent expensive surprises tomorrow.
