What is the reason for micro-cracks in concrete? Why do they occur even before the structure is loaded?
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Micro crack we found in younger concrete
Reason of micro crack is
We can reduced that micro crack by adding some fibres to the concrete,
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.
Micro cracking in concrete is very important issue which is formed in microstruture. The reasons for micro cracks in concrete are ;
– Large variation in mechanical properties of constituents (specially hydrated cement paste and coarse aggregate)
– Thermal and shrinkage movement.
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 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.