Types of cracks
- Structural cracks.
- Non Structural Cracks.
Structural cracks are those which result from incorrect design, faulty construction or overloading and these may endanger the safety of a building and their inmates.
Non Structural Cracks.
Non Structural cracks occur mostly due to internally induced stresses in building materials. These cracks normally do not endanger the safety but may look unsightly, create an impression of faulty work or give a feeling of instability.
Cracks reappear over repaired surface as rust scales were not removed
Defects in Concrete:
Concrete defects can be broadly classified into two categories :
1. Macro Defects:
If these defects are present, concrete has low strength and will rapidly deteriorate due to easy ingress of water and other chemicals. Invariably, structure will require repairs within a few years of its construction. Causes will have to be analysed and defects removed before doing any additional protective treatment. Often, waterproofing of concrete slabs is carried out superficially and it fails to give the desired benefit because the defective concrete below this waterproofing layer has not been treated to seal the macro/micro defects which existed within the concrete slab. The main causes of these defects are generally due to inadequacies in design and / or construction practices.
2 Micro Defects:
These defects are not visible to the naked eye. They are usually very fine voids caused by large capillary pores resulting from the use of low grades (strength) of concrete with high water to cement ratio.
They could also occur due to addition of excess water or high water to cement ratio of concrete mix. Fine cracks are generally present in concrete and can occur due to various reasons. They do not pose a serious threat to concrete deterioration initially as they are generally not deep and are discontinuous. With lapse of time due to variations in temperatures, changes in weather conditions, changes in loading conditions they increase in depth, length and width and combine with other fine cracks to create continuous passage for moisture, chlorides, sulphates and other chemicals from the environment to enter and start corrosion of steel in concrete and other deleterious reactions.
Corrosion of steel and spalling of concrete due to ingress of moisture
To conclude, macro defects and micro defects in concrete are both harmful to the health of buildings and can cause deterioration of concrete depending on the extent of their presence, environmental conditions around the building and maintenance done during its life cycle. However macro defects by virtue of being larger can cause faster deterioration and more damage to the structure than the micro defects.