Question

________ are undesirable in water used in many industrial processes and the acid produced during their metabolism may be destructive to concrete and other structures.
1. Gelatin liquefying bacteria
2. Slime forming bacteria
3. Iron bacteria
4. Sulphur bacteria

Answer 1

Correct Answer - Option 4 : Sulphur bacteria

Concept:

The various water-soluble sulphate ions ( such as Calcium Sulphate, Magnesium Sulphate, Sodium Sulphate,  Potassium Sulphate) react with either hydrated calcium aluminates (C₃A) or the calcium hydroxide (Ca(OH)₂ )components of hardened cement paste leads to the formation of   Calcium Sulpho-Aluminate Hydrate (also called ettringite).

Due to this reaction, the volume of solid-phase increases up to 227%, causing gradual disintegration of concrete. This also leads to a reduction of the binding action of cement paste with aggregates.

Sources of Sulphur in Concrete:

The Sulphur may enter in concrete in various ways such as:

1. Concrete-making materials- hydraulic cement, fly ash, aggregate, and admixtures.

2. High-sulphate soils and ground waters.

3.  Industrial water polluted with sulphur.