Measurement of bitumen coverage of stones for road building, based on digital image analysis

The top layer of a road is made up of a mixture of stones and bitumen and the durability is dependent on how well the bitumen adheres to the stones. The standard way of determining the bitumen coverage in the industry is the so called rolling bottle method, where a number of stones covered with bitumen are put in a rolling bottle and the bitumen coverage is estimated after different times. This paper describes a novel method for measuring the bitumen coverage of the stones by using advanced segmentation methods instead of manual inspection. The stones are put on a table and a number of images with different exposure times are taken. The images are normalized and the stones are segmented from the background based on a threshold obtained from an optimality criterion. Then the bitumen covered parts of the stones are segmented based on a graph-cut method. The results are compared to manual inspection and are well in agreement with these.