Sulphate drift

Sulphate floating is a harmful reaction that destroys concrete . Attacking sulphate ions lead to the formation of voluminous reaction products in the cement stone, resulting in an explosive effect.

Crane runway console damaged by Ettringen drifts

Sulphate ions can be present in soils and water, but also in exhaust gases and thus cause an external attack on the concrete. In addition, an internal attack can occur if the concrete contains aggregates that can release sulfate ions.

During sulphate driving, the calcium aluminate and calcium aluminate hydrate contained in the cement stone react with sulphate ions. Other aluminum-containing phases can also react. Ettringite is formed as a reaction product .

High sulphate concentrations can also lead to the formation of gypsum. This arises from a reaction of the sulfate ions with the hydration product portlandite .

Since ettringite has a volume that is 8 times larger than its starting materials, a crystallization pressure builds up. The formation of gypsum is also associated with an increase in volume. The result is very high mechanical stresses which lead to cracks and flaking and can completely destroy the concrete structure. In the event of an external sulphate attack, the damage to the concrete is additionally accelerated by the formation of cracks, since the sulphate ions can more easily penetrate the cement stone due to the lower impermeability of the surface.

Network cracks are typical of concrete surfaces damaged by sulphate drift.

One way of preventing this damaging reaction is to use special cements with high sulphate resistance, which are marked with the addition SR.

literature

• J. Stark, B. Wicht: Durability of concrete. Springer Vieweg, Berlin 2013, ISBN 978-3-642-35277-5 .

Individual evidence

1. ↑ FW Locher: Chemical attack on concrete. Düsseldorf 1966. online (accessed on August 3, 2018)
2. ↑ K.-Ch. Thienel: Structural damage to concrete, reinforced concrete and prestressed concrete. Institute for Construction Materials. online (accessed August 3, 2018)
3. ^ Fritz Haase: Damage to concrete structures. S. 11. (accessed on August 3, 2018)
4. ↑ Jürgen Bokern: Concrete tests to assess an alkali-silica reaction, effect of climatic conditions on the transferability of test results. Approved dissertation at the Technical University Carolo-Wilhelmina, Braunschweig 2008, online (accessed on August 3, 2018)

Web links

• MECHANISMS OF SULPHATE ATTACK ON CONCRETE - NEW PHASE FORMATION AND EXPANSION PRESSURE IN MORTARS UNDER Na2SO4 LOAD (accessed on August 3, 2018)
• Building lime, gypsum and anhydrite (accessed on August 3, 2018)
• Ettringite drift in binder-treated, sulphate-containing soils (accessed on August 3, 2018)
• Structural damage caused by mineral driving phenomena (accessed on August 3, 2018)
• Demolition work and recycled concrete against the background of the sulfate problem (accessed on August 3, 2018)