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Soham Ortiz
Field Engineer
Asked a question 2 years ago

What is the reason for micro cracks in concrete?

What is the reason for micro-cracks in concrete? Why do they occur even before the structure is loaded?

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The term micro cracking refers to very small cracks that form in concrete but are not visible to the naked eye. Some microcracking occurs as a natural part of the cement hydration process, but it also occurs as compressive loads are applied. Bond cracks form where the coarse aggregate and the cement meet.

Probably the single most common reason for early cracks in concrete is plastic shrinkage. When the concrete is still in its plastic state (before hardening), it is full of water. This water takes up space and makes the slab a certain size. As the slab loses moisture while curing it gets a bit smaller.

The reason why micro-cracks occur in concrete even before loading is because of the Interfacial Transition Zone.

The interfacial transition zone is the weakest link in the concrete. It is caused by the formation of a water film around the aggregate surface. When concrete is mixed, the water forms a film around the aggregate, and as a result, the water-cement ratio near that aggregate increases. A high water-cement ratio means less strength.

This water film hinders the hydration reaction and results in a porous network of hydrated products. This porous network is much weaker than the bulk mortar. Therefore, even small changes in temperature cause differential movement of the material in the concrete. Differential movement occurs due to the difference in the porosity of the hydrated products.

As a result, the micro-cracks are formed. They are formed even without the application of loads.


Timmothy Ferguson
Assistant Project Manager

Micro cracking in concrete is very important issue which is formed in microstruture. The reasons for micro cracks in concrete are ;

– Manifolds.
– Large variation in mechanical properties of constituents (specially hydrated cement paste and coarse aggregate)
– Thermal and shrinkage movement.

Terry Collins
Sustainability consultant

Micro crack we found in younger concrete

Reason of micro crack is

  • Due to plastic shrinkage
  • Due to higher temperature at site
  • Due to improper curing
  • Due to higher water cement ratio
  • Due to improper cement used at particular site (like we cannot use rapid hardening cement in mass concreting)
  • Due to premature drying
  • Due to improper concrete mixing

We can reduced that micro crack by adding some fibres to the concrete,