Investigation of the influence of the heterogeneous structure of concrete on its strength

Abstract

The structure heterogeneity and the strength of concrete was evaluated using multifractal analysis. The macrostructure of concrete with a predominance of crushed stone, sand and pores was studied. The relevance of the work lies in the possibility to carry out express-assessment of the quality of concrete products and structures using the developed algorithm with the use of portable equipment: photographing the structure of concrete; estimation of the range of colour range of the structure elements; calculation of the fractal dimensionality of the structure elements using the developed program; automatic strength prediction. Analysis results of the canonical spectrum f(α), statistical characteristics of structural components: uniformity, orderliness Δ=f(α)_q = 1−f(α)_q = 100, and regularity K=f(α)_q = -100−f(α)_q = 100 were calculated. The sensitivity between the indicators of breaking load during compression tests and statistical characteristics was recorded. This approach allowed screening out low-sensitivity structure features from the multifractal spectrum. Results of the analysis of complex and separate influence of statistical characteristics on the indicators of the breaking load of concrete are shown with regression linear models. Indicators of paired correlation R² were determined. A relation has been found between breaking load and repetitive structural elements of one phase. This method of investigating the strength properties of concrete can be considered as an express method with limited accuracy of the results, about 80 %. To simplify and facilitate the use of the method, the software can be placed in the form of a smartphone application, which will allow to take photos and process the data immediately. The proposed approach can be interpreted as an express method of predicting the strength of concrete mixture, which is implemented without the use of special equipment. It can be used to assess the residual life of concrete structures where full-scale testing is impossible due to damage to the integrity of the structure.