Evaluation of steel fiber distribution in concreteby computer aided image analysis

Several methods for evaluation of uniformity of distribution of fibers in steel-fiber-reinforced concrete (SFRC) exist today. All of them are either ineffective, biased or their execution requires special expensive equipment. A promising new approach based on computer aided SFRC digital image analysis was developed and tested with excellent results. The process of taking and adjusting the pictures of SFRC samples is described in the paper. ASEF (Automatic Specimen Evaluation of Fibers) program was prepared in MATLAB environment for quick and accurate detection of fibers in the photographs. Basically, the detection algorithm exploits different reflectance of steel fibers and concrete matrix. No unusual devices are needed for employment of the method. The whole procedure is very simple and can be used successfully in both laboratory and construction site. Examples of application of the method are presented in the paper. Several mixtures of high-performance concrete containing 120 kg of steel fibers per cubic meter of concrete were compared with respect to the uniformity of dispersion of fibers, optimal mix composition was selected. Large scale specimens made of normal strength SFRC for tunnel linings were examined, the analysis led to a conclusion that sufficient uniformity of dispersion of the fibers in the mix was reached.