The procedure of state estimation of concrete structure of a high voltage pylon footing before and after its repair by polyurethane grouting is presented in the paper. Analysis of the grouting effectiveness was realised on samples taken from inspection core drilling to the structure. The analysis consisted of rough determination of compressive strength of drill core sample, description of deformation behaviour of the specimen under the load, and structural-textural analysis of created geocomposite using method of fluorescence microscopy combined with image analysis