Concrete is known to be a very versatile and reliable material, but some construction errors and construction negligence can lead to the development of defects in a concrete structure. These defects in concrete structures can be due to poor construction practices, poor quality control, or poor structural design and detailing. Different types of defects in concrete structures can be cracking, crazing, blistering, delamination, dusting, curling, efflorescence, scaling, and spalling. Again, these defects can be due to various reasons or causes.
Causes of defects in concrete structures can be broadly categorized:
- Structural deficiency results from design errors, loading criteria, unexpected overloading, etc.
- Structural deficiency due to construction defects.
- Damage from fire, floods, earthquakes, cyclones, etc.
- Damage due to chemical attack.
- Damage due to marine environments.
- Damage due to abrasion of granular materials.
- Movement of concrete due to physical characteristics.
Structural Deficiency due to Design and Detailing
In such cases, the design must be reviewed in detail, and the design team must work out remedial measures. Once this is done, the methods of carrying out the corrective actions will be similar to those arising from other defects.
Structural Deficiency due to Construction Defects
Defective construction methods form the largest source of distress to the beams. Such defects can be broadly subdivided as follows:
- Defects due to the quality of raw materials.
- Non-adoption of designed concrete mix.
- Use a defective construction plant to produce, transport, and place the concrete.
- Defective workmanship.
- Inadequate quality detailing.
Choosing the correct type of cement for the concrete going into the structure is necessary. Ordinary Portland cement is the most common of all types of cement. Provided the quality of cement conforms to the relevant standard specifications at the time of use; usually, no problem is encountered in respect of ordinary Portland cement. However, where the concrete is exposed to an aggressive environment, it may be necessary to use particular types of cement, such as sulfate-resistant Portland cement, blast furnace slag cement, and low C3A cement.
The quality of aggregates, particularly regarding alkali-aggregate reactions, needs to be considered; fortunately, cases of defects/failures attributed to alkali-aggregate reactions in India are sporadic.
Using water containing salt for making concrete can also contribute to the deterioration of the concrete.
The concrete mix design can be satisfactorily carried out using various aggregates. However, reasonable continuity of grading of aggregates should be ensured.
Excessive use of water in the concrete mix is the largest single source of weakness.
The accuracy of weighing the various components depends on the quality of the available weigh batching system. Spring-loaded dials of the weigh batchers contribute toward excessive variability in the quality of weigh-batched concrete in India.
Other contributory factors that add to lousy workmanship include segregation, improper placement, inadequate or excessive vibration leakage of mortar through shuttering joints, insufficient concrete cover, sufficient curing, etc.
Proper reinforcement detailing, including adequate cover, is essential to ensure the successful placement of concrete. Inadequate detailing results in congestion of reinforcement to such an extent that concrete cannot be placed and compacted correctly, even if the concrete is workable. Detailing support should be based on adequately appreciating how the concrete placement and compaction will be carried out.
Other factors leading to poor design detailing are the following:
- Re-entrant comers.
- Abrupt changes in section.
- Inadequate joint detailing.
- Deflection limits.
- Poorly detailed drips and scuppers.
- Insufficient or improper drainage.
- Poor detailing of expansion joints.