Fractal express methods evaluation of a breaking stress of concrete

We have offered the methods of the operative evaluation of a breaking stress in testing strength on compression of heavy concrete of grade 400 with the use of fractal formalism. The methods are based on the setting of the relations of the values of a breaking stress and fractal measurement of concrete: 1. Areas with crushed stone prevailing (R² = 0.7224); 2. Areas with sand prevailing (R² = 0.6102); 3. Pin holes (R² = 0.6874). During fractal experimenting the indexes of breaking were increased from 391.63 to 515.13 kH in reducing fractal dimension of areas 1 from 1.866 to 1.588; areas 3 from 1.826 to 1.684 and internal quality (boundary of its elements) from 1.617 to 1.353. Increase of fractal dimension was fixed only for areas containing sand (areas 2) from 1.755 to 1.944. These results make possible to apply fractal dimension as the indicator of structural changes of concrete in the prediction of its properties. In fractal modelling the accuracy of the results depends on the option of the task way for space metric that is proved by the obtained linear model (R² = 0.9254), which describes the connection between the elements of macrostructure and strength criterion of concrete.

Such methods provide a satisfactory in practical purposes operative prediction for the values of breaking stress of concrete of grade 400 with significant reduction of time and money expenditures on full-scale testing and the application of microscopy.