# What is Candlot Salt?
**Candlot salt, also known as ettringite, is a crystalline mineral that forms as a by-product during the hydration of Portland cement.** It is named after the French chemist Candlot, who described the phenomenon in the 19th century. In normal quantities it is harmless, but excessive formation can cause severe concrete damage.
## How Does Candlot Salt Form?
Candlot salt forms when calcium aluminate in cement reacts with sulphate (gite) and water. This process is part of normal cement hardening and helps regulate the setting rate. Problems arise when:
– **External sulphates** (from groundwater or soil) penetrate hardened concrete
– The **temperature during curing** was too high (above 70°C)
– There is **too much sulphate** in the cement composition
## Damage Mechanism
When ettringite forms in already hardened concrete, the crystals occupy considerably more volume than the original constituents. This leads to:
– Internal stresses in the concrete
– Cracking and spalling of the concrete surface
– Loss of strength and durability
– In severe cases: complete degradation of the concrete element
## Prevention
– Use **sulphate-resistant cement** (blast furnace cement) where contact with sulphate-bearing groundwater is expected
– Limit the **curing temperature** when pouring mass concrete
– Ensure adequate **concrete cover** and a dense concrete mix
– Carry out a **ground investigation** to determine sulphate concentrations in the soil
## Related Terms
– Cement
– Concrete
– Hydration
– Sulphate-resistant cement
– Concrete deterioration
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