Microcrack in concrete

Microcracks are very small cracks < 1 μm and not visible to the naked eye. They can form on the surface (craquelure), develop from the surface to the inside and the reversed direction, and be present only inside the concrete structure. Microcracks are caused by external influences (e.g. temperature differences, etc.) or internal influences (internal stress, pores, setting concrete/aggregates, etc.)