Particular situations will require a special concrete mix to fulfil the circumstances. The concrete mix may contain additives, admixtures, cements and aggregates not used in the normal range of concretes.
For example, underwater concrete has an anti-washout additive to prevent the cement fines from being lost when the concrete is placed through water, thereby maintaining the materials integrity and durability. Refractory concretes are able to withstand constant high temperatures when used as linings to chimneys etc.
The flexibility of concrete as a material enables it to be used in many situations where other materials are inadequate or expensive.