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Causes of Microcracking in Concrete

Microcracking in concrete is very important issue which is formed in microstructure. The causes of microcracking are manifolds; in simple word, the main causes are:

• Large variation in mechanical properties of constituents (specially hydrated cement paste and coarse aggregate)

• Thermal and shrinkage movement

The first one is the main cause; as this cracking is formed at interface between mortar and embedded aggregate.When failure is initiated the cracking pattern follows this interface. This zone is known as interface zone, sometimes also called transition zone.

Behavior of transition zone has to be realized to find cause of microcracking. You should keep in mind that microstructure of bulk cement paste is quite different form hydrated cement paste around coarse aggregate.

The main cause behind this is that dry particles of cement, during mixing, cannot be reached to comparatively large aggregate particles i.e. cannot be packed closely. Thus less cement particles are available to be hydrated and filled the actual voids present due to improper packing which yields a zone of higher porosity

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