Nowadays, Sulphate resisting cement is one of the best selling cement in the construction industry. The other types of cement like ordinary portland cement is very susceptible to the attack of sulphates.
The attack of sulphates on cement can cause the chemical breakdown of hardened concrete, which finally leads to cracking and durability loss. The compounds which are responsible for the attack of sulphates on concrete are salts of water-soluble sulphates.
The sulphate attack is mostly seen in marine or coastal structures, where sulphate salt content is very high. In these areas, the attack of sulphate is faster than that of other places due to the alternate wetting and drying.
You know that the aluminates and calcium are the two elements majorly seen in the cement composition. When sulphate attacks, the calcium turns into calcium sulphates and aluminates turn into calcium aluminate. These elements can expand and causes cracking.
Researchers say that calcium aluminates can again convert in the form of calcium sulpho aluminates. The volume of sulpho aluminate will be 220 percent greater than the original aluminates.
Solids sulphates cannot attack with concrete, they are attacked in the form of solution like seawater etc..You know that you cannot do anything with movement or direction of seawater. The only thing that you can do is to change the composition of cement or add some ingredients.
To overcome sulphate attack, the use of cement with low C3A content found to be effective.
The sulphate resisting cement is the cement which has the capability to resist against sulphate attack by introducing low C3A and relatively low C4AF content in the cement.
The specification for sulphate cement content should not allow C3A content more than 5 percent. Because of this, you can say that sulphate resisting cement contains more silica. The below pictures shows the attack of sulphate on concrete.
What are the uses of Sulphate resisting cement?
- The uses are they can be used in marine or coastal areas.
- Underground Structures
- They can be used for laying foundation to reduce the attack of sulphate from the soil.
- Construction of sewage treatment works
- Fabrication of pipes
- They can be used where the presence of natural sulphates in aggregate
- Retaining walls