Top 5 Reasons Why Concrete Cracks

All structures will develop some cracks both structural and non structural. Most of them are just cosmetic and no need to worry about that. But some cracks may an indication of a larger problem underneath and can be corrected. There are two different categories of cracks such as structural & non structural.

Non-Structural Cracks

The non-structural cracks occurs due to many reasons and are classified depending on the width of the crack. Like, Thin(<1 mm), Medium (1-2 mm) and wide >2 mm. The main reasons for non structural cracks are

  • Settlement
  • Shrinkage
  • Thermal movement

Corrosion of Reinforcement

In most of the cases the damage of concrete is due to corrosion of reinforcement. Deterioration process in concrete begins with penetration of various aggressive agents, low permeability is the key to solve this problem. Concrete permeability depends upon water-cement ratio, curing and correct compaction. A well designed concrete is water tight and adequate cover gives good protection to reinforcements.

Reinforcement corrosion is very hard to repair and corrosion of reinforcement causes severe cracks with a brownish color. This leads to loss of strength and finally collapse.

Corrosion of reinforcement

Corrosion of reinforcement

Thermal Cracking of Concrete

Temperature difference leads to volume change which leads to cracks, this normally happens to mass concrete having thick sections. The temperature difference can be caused by either the center of concrete heating up more than the outside surface due to heat liberation at the time of setting. The more massive is the structure the more likely to have temperature differences.

 

Plastic Shrinkage Cracking

It occurs after a few hours of placing, it occurs due to rapid loss of moisture caused by humidity and wind velocity at the surface of concrete. When high rates of surface evaporation is caused the surface concrete shrinks and tensile stresses develop in the surface. This leads to shallow cracks formation of polygonal shape or parallel to one another. These are minor cracks and does not harm the structure.

Concrete Crazing

Crazing is the development of fine networks of  random cracks on the surface of concrete caused by shrinkage of  surface layer. Crazing of concrete develop at an early age and its very hard to detect unless wet and beginning to dry. They do not affect the structural integrity of the structure or the durability of the concrete. Crazing usually occurs due to poor workmanship like

  • Poor and inadequate curing
  • Intermittent wet curing and drying
  • Too much water bleed
  • Over vibration
Crazing of concrete surface

Crazing of concrete surface

Concrete Cracking due to Vegetation

When the soil under the building happens to be clay, cracking in walls and floors occurs either due to dehydrating action of growing roots. These roots on the soil  may shrink and cause foundation settlement due to an upward thrust on the soil that had been dehydrated by the roots, swells up on getting moisture from sources such as rain.

Large crack due to vegetation

Large crack due to vegetation

Structural Cracks

Concrete Cracking Due to Errors in Structural Design

Lack of adequate contraction joint and improper design of foundation resulting in differential movement within the structure. Corners provide a location for the concentration and therefore are the prime location for the initiation of cracks. That’s why we see cracks mainly on doors and window openings. Properly anchored diagonal reinforcement is required to prevent these type of cracks.

Structural crack in rcc slab

Structural crack in rcc slab

Settlement Due to Poor Bearing capacity of Soil

Soil sometimes cannot support the weight or bearing pressure of the building foundation. This results in sinking of the foundation, to avoid this foundation have to be designed according to the soil. Special types of footing are designed for weak soils. This kind of settlement is mostly found in residential buildings because footings are designed based on general guidelines rather than soil specific design.

A Settlement crack after repair

A Settlement crack after repair

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