Causes of Deterioration
The following are the causes of failure of structure:
Occurrences incidental to construction stage. This could be attributed to
- Local settlement of subgrade.
- Movement of formwork.
- Internal settlement of concrete suspension.
- Setting Shrinkage.
- Premature removal forms.
This may be due to-
- Difference in temperatures between the inside of the building with its environment.
- Variation in internal temperature of the building or structure.
Absorption of moisture by concrete
Corrosion of reinforcement
This could be caused by-
- The entry of moisture through cracks or pores.
- Electrolytic action
Aggressive action of chemical
Action of shock waves
Poor design details at-
- Re-entrant corners
- Changes in cross-section
- Rigid joints in precast elements
This led to-
- Leakage through joints
- Inadequate drainage
- Inefficient drainage slopes
- Unanticipated shear stresses in piers, columns and abutments etc
- Incompatibility of materials of sections
- Neglect in design
Errors in design
Errors in earlier repairs
External influences such as
- Cyclones etc.
Some of the major causes of deterioration of concrete structure are discussed in detail here.
Design and construction flows
Design of the concrete structures governs the performance of concrete structures. Well designed and detailed concrete structure will show less deterioration in comparison with poorly designed and detailed concrete, in the similar condition. The beam-column joints are particularly prone to defective concrete, if detailing and placing of reinforcement is not done properly. Inadequate concrete cover may lead to carbonation depth reaching up to the reinforcement, thus increasing the risk of corrosion of reinforcement.
Micro-cracks present in the concrete are the source of ingress of moisture and atmospheric carbon di-ozide into the concrete which attack reinforcement and react with various ingredients of concrete. In aggressive environment concrete structures will deteriorate faster and strength life of concrete structure will be severely reduced.
Poor Quality material used
Quality of material to be used in construction, should be ensured by means of various tests as specified by the IS codes. Alkali-aggregate reaction and sulphate attack results in early deterioration. Clayey materials in the fine aggregate may weaken the mortar aggregate bond and reduce the strength. Salinity causes corrosion of reinforcement bars as well as deterioration of concrete.
Quality of supervision
- Construction work should be carried out as per the l aid sown specification.
- Adherence to specified water/cement ratio controls strength, permeability and durability of concrete.
- Insufficient vibration may result in porous and honey combed concrete, whereas excess vibration may cause segregation.
Deterioration due to corrosion
- Spalling of concrete cover
- Cracks parallel to the reinforcement
- Spalling at edges
- Swelling of concrete
- Internal cracking and reduction in area of steel of reinforcement
Rehabilitation consists of restoring the structure to service level; it once had and now lost. Strengthening consists of endowing the structure with a service level higher than that initially planned by modifying the structure not necessarily damaged.
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