High Sophisticated Full Field Interferometry on Concentrated Loaded Concrete

A new non-destructive testing method with the Speckle Pattern Interferometry (ESPI) allows to measure with accuracy strains, and therefore deformations and cracks. For concentrated loadings or for fastening elements, the initiation of cracks starts already at a low load level, where the maximum load is accompanied by already visible cracks. Hence the detection of micro cracks and their influence on the failure model, as well as the deformed state are researched by using a non-contact measuring method.

Electronic Speckle Pattern Interferometry (ESPI) is used to analyse superficial deformation, crack initiation and the distribution of strain. Superficial micro cracks can be made visible directly after their initiation and their crack width can be quantified in the range of micrometers. Difficulties and possibilities for a two-dimensional application are shown. Due to the low deformation, various outer influences can degrade the results. A satisfactory output can only be guaranteed with the knowledge of the behaviour of concrete surface, impact of vibration and outer light etc. Primarily the crack width is important for serviceability limit state, so design loads can be defined using test results having in regard to safety factors.