How ripped

Micro cracks are present even in mechanically unloaded concrete due to the deviating deformational behavior of the individual constituents. A method was developed at the Institute for Construction Materials to visualize micro cracks in concrete. High strength concrete specimens were selected in order to investigate the effects of specimen preparation, concrete composition as well as curing condition and applied load upon the formation of micro cracks. Autogenous shrinkage turned out to be the main impact for micro crack formation in high strength concrete. Starting point for micro cracks in the matrix are either air voids or the interfacial transition zone around the aggregates. There was no clear evidence of any impact of micro cracks on any mechanical or durability property of high strength concrete.

Figure: Colored micro crack running through a concrete matrix