Quantitative study of meso-damage process on concrete by CT technology and improved differential box counting method

• Published in: Measurement : journal of the International Measurement Confederation 2020-08, Vol.160, p.107832, Article 107832
• Main Authors: Zhang, Le, Dang, Faning, Ding, Weihua, Zhu, Lin
• Format: Article
• Language: English
• Subjects: Computed tomography; Concrete; Concrete CT image; Damage; Damage variable; Differential box counting method; Dynamic loads; Fractal analysis; Fractal dimension; Fractal geometry; Fractals; Image compression; Improved differential box counting method; Mathematical analysis; Portable equipment; Quantitative analysis; Tomography
• ISSN: 0263-2241; 1873-412X
• DOI: 10.1016/j.measurement.2020.107832

[Display omitted] •X-ray CT analysis of concrete was carried out.•An improved differential box counting (IDBC) method was proposed.•The concrete damage process was described using the fractal theory.•The relationship between fractal dimension, damage variable and stress were studied.•The correlations between area of cracks region and the stress was explored. To study the change of concrete internal structure before and after stress, the meso-mechanical experiment of concrete was conducted using CT technology and a portable dynamic loading device. And CT images of the concrete internal structure change under uniaxial compression condition were obtained. For establishing the relationship between the micro-structure and macro-mechanics of concrete, an improved differential box counting (IDBC) method was proposed to calculate the fractal dimension of the CT images, which could describe the entire damage process of concrete. By comparing the fractal dimension calculated by the two methods, it can be seen that the fitting error of the fractal dimension obtained by the IDBC method is reduced by nearly 50% compared with that obtained by the DBC method. Afterward, the damage variable expression was established on the basis of the fractal dimension. The research results indicated that the damage variable established in this research can describe the damage process of concrete well. That is, the damage variable equaled to 0 during the first scan, and before reaching the peak stress, the damage variable showed a trend of increasing first and then decreasing. After the concrete specimen has completely fractured, the damage variable reached a maximum of one. Furthermore, through extracting the area of CT image cracks region at different stress stages, the relationship between the area of cracks region and the stress was studied. It appeared that the CT technology and fractal theory are promising methods to analyze the evolution of the concrete damage process under static uniaxial compression.