A new image analysis technique for the quantitative assessment of microcracks in cement-based materials

The development of a new image analysis technique for the automatic detecti on and quantification of microcracking in cement-based materials is describ ed. An impregnation technique is used to highlight microcracks and other mi crodefects (porosity, air bubbles) present in the concrete matrix. Microcra ck observations of the: polished samples are carried out using an optical m icroscope. The first step of the image analysis process consists of extract ing the various defects from the observed image. The extraction process is essentially an automated thresholding operation carried out on the grey-lev el histogram. The second step consists of automatically sorting the various extracted defects on the basis of a certain number of shape factors. For t he third step, an innovative technique is used to reconnect several neighbo ring microscopic fields. Finally, the characteristics of the cracking patte rn are quantitatively determined using classical stereological techniques. The approximation of microcracks by straight lines enables researchers to d raw maps of the sample crack network over an area of a few tens of square c entimeters. Various tests were carried out to verify the accuracy and the r eproducibility of the results yielded by the method. Results obtained for u ndamaged and mechanically loaded samples are also presented. (C) 2000 Elsev ier Science Ltd. All rights reserved.