High precision measurement of surface cracks using an optical system

In this contribution an advanced technique to measure the width of surface cracks in concrete is presented. The goal is to provide a system for laboratory applications with a high resolution in order to be able to estimate the stabilization of surface cracks in the range of 0–250 μm during laboratory loading tests. Using digital imaging and suitable image processing algorithms, an automated system for the determination of crack widths was developed. A 4 megapixel monochrome digital camera was used in combination with a special telecentric lens, in order to achieve a resolution of 1 μm per pixel. The main challenge in this work was to develop a robust image processing algorithm, which determines the surface crack width under changing environmental conditions, especially in terms of ambient light.