Cracks that run directly over reinforcing bars in such a position that they could not have been caused by shrinkage, plastic settlement, or thermal contraction, must have been caused by build up of rust forming on the reinforcement.

These cracks are a symptom of deterioration which will eventually lead to spalling and complete loss of cover.

Horizontal surface repair is common on slabs either elevated or on grade. Deterioration may be caused by corrosion of embedded reinforcement resulting in determination and spalling.

Other common causes include deterioration due to carbonation and chloride ion ingress and chemical attack.

After an evaluation of the deterioration by an engineer, a plan should be developed including objectives and specifications for the repair.