Causes of Cracks in concrete structures

There are many Causes of Cracks in concrete structures, they are

Thermal movement
The permeability of concrete.
Corrosion of Reinforcement
Creep
Moisture Movement
Structural design and specifications
Poor Construction practices.
Improper maintenance

1.Thermal movement

All materials expand on heating and contract on cooling. The thermal movement depends on temperature variations, dimensions, a coefficient of thermal expansion and physical properties of materials. The external exposed to direct solar radiation and the roof subject to thermal variation is liable to cracking.

Remedial Measures:

Thermal joints avoid by expansion joints, control joints and slip joints.

2.The Permeability of concrete

Concrete permeability controls by factors like water-cement ratio, water hydration, curing, air voids, micro-cracks and continues exposure to thermal variations.

3.Corrosion of Reinforcement

Concrete provides protection to reinforcing steel. Steel will not corrode as concrete around it is impervious. And does not allow moisture or chlorides to penetrate within the coverage area. A properly designed and constructed concrete is initially water-tight. The reinforcement steel protects by a physical barrier of the concrete cover having low permeability and high density.

Remedial Measures:

Increase the concrete cover with proper materials like plastic, concrete, readymade cover blocks, etc., instead of using stones and wood pieces. Increased concrete cover over the reinforcing bar reduces corrosion.

use concrete with low permeability.

4.Creep

Concrete subjected to loading exhibits a slow time-dependent deformation known as creep. Creep increases with increase in water and cement content, water-cement ratio and temperature. It decreases with increase in humidity of surrounding atmosphere and age of material at the time of loading. Use of admixtures and pozzolanas in concrete increases creep. Amount of creep in steel increases with rising in temperature.

5.Moisture Movement

Shrinkage occurs in all building materials that are cement/lime based. Heavy aggregate concrete shows less shrinkage than lightweight aggregate concrete.

Materials with pores in the structure in the form of intermolecular space expand on absorbing moisture and shrink on drying. These movements are cyclic in nature and causes by increase or decrease in inter pore pressure with moisture changes.

Remedial Measures:

Shrinkage cracks in masonry minimize by avoiding the use of rich cement mortar in masonry.

Plastering of masonry after proper curing.

6.Structural design and specifications

Cracks in concrete forms due to poor structural design and specifications. At the starting of design first, consider the environmental conditions existing around the building site. It is important to determine the type of foundations, the type of concrete materials use in concrete. And the grade of concrete depending on chemicals present in groundwater and subsoil. Closely spaced of reinforcement steel bars due to inadequate detailing causes segregation.

precautions while designing

specification for concrete materials and concrete.

Proper quality and thickness of concrete cover around the reinforcement steel.

proper reinforcement layout and detailing

7.Poor Construction practices

Construction should design and supervise only by civil engineers or persons having proper knowledge and experience in construction practices. People without construction knowledge are engaging nowadays to supervise construction works and to carry out construction works.

Lack of good construction practices due to ignorance, carelessness, greed or negligence.

For a healthy building, it is necessary to ensure good quality materials selection and good construction practices.

Some of the main causes for poor construction practices

Using poor quality materials
improper selection of materials
cheap and nonstandard materials
improper concrete mix
Inadequate control on various steps of concrete products such as batching, mixing, transporting, placing, finishing and curing
Inadequate quality control and supervision causing large voids(honeycomb)
Improper construction joints between
Addition of excess water in concrete and mortar mixes.
Poor quality of plumbing and sanitation materials and practices.

8.improper Maintenance

Buildings should maintain at regular interval of time properly to avoid damages. Attend Leakages as earliest as possible before corrosion of steel inside concrete starts. The external painting of the building helps in protecting the building against moisture and other chemical attacks. Necessary water-proofing and protective coating on reinforcement steel or concrete.