Sulphate Attack
Summary
Sulphate Attack - is a very harmful mode of chemical deterioration in concrete.
Technical Information
Sulphate attack in concrete slabs can cause extensive cracking, expansion and loss of bond between cement and aggregate.
There are two types of sulphate attack:
External sulphate attack
An external sulphate attack is by far the most common type. It is caused by sulphates introduced from the exterior of the concrete, into the pores.
Internal sulphate attack
This is caused by sulphates present in the concrete mix prior to pouring. Also know as delayed ettringite formation.
Sulphates can originate from the following external sources:
- Seawater.
- Oxidisation of sulphide minerals in clay.
- Bacterial action in sewers.
Sulphates can originate from the following internal sources:
- Sulphate rich aggregate.
- Excess gypsum in the cement.
- Contamination in the mix.
In ground supported floors, sulphate attack can cause heave, due to the expansion from the reaction, when the underlying soil contains sulphates or sulphides. Therefore, it is common practice to isolate the floor slab from the sub-base by a suitable membrane.
Related Definitions
Air Entrainment , Steel Fibre Reinforcement , Freeze-Thaw , Porosity , GypsumResources
J. Marchand, I. Odler, J.P. Skalny: Sulphate Attack in Concrete.The Concrete Society: Technical Report 34; Appendix B.
http://www.understanding-cement.com/sulfate.html
Please share this definition:
