Study on failure characteristics of baking-free bricks with wrap-shell aggregate

Using sediment at the bottom of rivers and lakes as raw materials to prepare non-fired wrap shell aggregate (WSLAs) and using wrap shell aggregates to replace natural crushed stones to prepare baking-free bricks is a means of resource utilization. In this paper, using harmless treated sludge and other cementitious material mix as the core and cement as the shell, the wrap shell aggregate baking-free bricks were prepared and its damage characteristics were studied. By means of physical test and image processing, the mechanical properties of the baking-free brick under different aggregate substitution rate and grading conditions were analyzed. At the same time, the existing image analysis method is compared to select the most suitable method to study the damage characteristics of the baking-free brick, and further explore the meso-mechanism of the baking-free brick and the development and evolution of the crack under different substitution rates. The main research contents and conclusions are as follows: (1) Based on image processing technology, Multifractal spectroscopy and Grey Level Co-occurrence Matrix are faster, lower cost, and more accurate image analysis methods. These two methods make the development and evolution of cracks more convincing through quantitative analysis when exploring the damage characteristics of the wrap shell aggregate baking-free brick. (2) The fracture width Delta a, maximum peak value and Delta f are linear with the substitution rate, indicating that with the increase of the substitution rate, the fracture diversity is higher, the fracture complexity is higher, and the fracture propagation is wider and richer. (3) When GLCM analysis is used, the correlation between fracture characteristic values and the substitution rate is also linear, and the results show that the energy and correlation decrease with the increase of WSLAs substitution rate. Entropy and contrast increase with the increase of WSLAs substitution rate. (4) Both multifractal spectrum and gray level co-occurrence matrix can well reflect the fracture characteristics under different CAWS substitution rates. From the perspective of fracture complexity, the entropy linear correlation degree of gray level co-occurrence matrix is better than that of multifractal spectrum, which can simply and intuitively reflect the fracture expansion degree. The grayscale level co-existence matrix divides the crack expansion form into four different levels for more detailed research. For crack propagation, the two methods can be compared and verified at the same time to provide reference value for further engineering applications.