Statistical analysis on the fracture behavior of rubberized steel fiber reinforced recycled aggregate concrete based on acoustic emission

Rubberized steel fiber reinforced recycled aggregate concrete (RSRAC) is an environmental-friendly building material produced from waste concrete and tires. However, the evolution of fracture behavior in RSRAC under flexural loads still remains unknown, and the individual as well as the coupling effects of recycled aggregate (RA), crumb rubber, and steel fiber are also unclear. In this paper, four groups of specimens with different contents of RA, crumb rubber, and steel fiber were prepared, and a series of four-point bending tests were conducted. The loading process was monitored by acoustic emission (AE) in real-time, and the fracture behavior was then analyzed through AE signals using multiple statistical methods including Ib-value method, cumulative energy analysis, intensity analysis, K-means clustering and RA-AF analysis. Scanning electron microscope (SEM) was also employed to give explanations in microscale. Results show that the fracture process of RSRAC can be divided into micro-crack stage, main collapse stage, and residual stage. A fluctuation greater than 0.06 in Ib-value could be regarded as a criterion for this division. AE counts, cumulative AE energy as well as cluster analysis are also effective in judging the sub-stages. The dominant failure mode in micro-crack stage and residual stage is tensile crack, and shear cracks mainly occur in the main collapse stage. SEM investigation has revealed that the shear cracks in the main collapse stage mainly come from the shear failure of acicular crystals or micro-chimeras at the interface. For effects of different materials, it is found that rubber can reduce the brittleness and improve the ductility of the concrete, but will lower the strength properties. Steel fiber can increase the brittleness of the fracture behavior and reduce the ductility, but is favorable to strength. While RA can increase the brittleness and is harmful to both ductility and strength. The coexistence of rubber and steel fiber can significantly shorten the residual stage. The work is expected to provide a deeper understanding on the properties of RSRAC.