Sulfates et concrete : cement résistant

Sulphates do not rust the steel: they attack the cement itself. Direct answer: sulphates from soils and waters react with the binder's hydrates to form expansive products (ettringite) — the concrete swells, cracks in a map pattern and degrades from within. Prevention starts with an environmental analysis, a tight concrete and, in severe exposure, a sulphate-resisting binder.

The attack, in two pictures

External attack: sulphates come from the environment — gypsum soils, sulphated groundwater, wastewater, tidal zones. They enter with the water and attack the paste. Internal attack: delayed ettringite formation, which develops in massive concrete that experienced excessive early-age temperature rise — a problem of thick pours, not of everyday sites.

The typical symptom

An external attack is recognised by whitish map cracking with measurable swelling, a softening surface (the concrete 'scratches' where it softens) and gypsum deposits in the cracks. The difference with shrinkage: here cracks open while swelling — the material pushes.

Prevention: the steps in order

• Analyse before founding in suspect zones: geotechnical survey, water and soil analysis — a trivial cost against a repair.
• Tight, impermeable concrete: low W/C, substantial dosage, careful compaction, serious curing — a sulphate that cannot enter cannot attack.
• Cut the water path: drainage, waterproofing, protective coatings on buried or immersed parts.
• Binder matched to aggressiveness: in severe attack, the code answer is a sulphate-resisting cement (SR type).

What DAM sells — and what we do not

Our range covers everyday and demanding uses: CPJ 45 and CPJ 55, compliant with NM 10.1.004 and EN 197-1, for structures, slabs, standard reinforced concrete and coastal works. We do not stock a sulphate-resisting (SR) cement: facing a confirmed attack or an aggressive soil identified by the geotechnical study, the answer is a specialised binder and a designed mix — consult a specialised firm, as for refractory work. We would rather tell you the limit than sell a solution outside our range.

For everything within everyday and coastal concrete, CPJ 45 and CPJ 55 remain the base — free personalized quote, delivered in Dakhla City.