Damage Evolution Analysis in Cementitious Mixtures Using Acoustic Emission Techniques

Cracking is a typical defect of cement concrete pavements. This paper investigates the fracture behavior of cement mortar and concrete materials based on experimental observations using acoustic emission (AE) and embedded SmartRock sensor techniques. Examining the AE signals (e.g., AE counts, events, and energy), the bulk displacement responses using LVDT sensors, and the localized responses using the embedded SmartRock sensor during three-point bending (TPB) tests, the correlation between different types of intelligent sensing parameters and the evolution of macroscopic mechanical properties of cement mixtures was analyzed. In addition, a four-stage development process is proposed to describe the fracturing behaviors of the mortar and concrete, as well as the underlying mechanisms. The results show that the four-stage model proposed in this paper can describe the entire fracture process of concrete or mortar materials, especially the transition from Stage 3 to Stage 4. In addition, the SmartRock sensor can effectively monitor the mechanical degradation of the host matrix during the fracture process, and the AE energy and AE events can be used to predict efficiently the degree of material damage: the material stiffness decreases slowly in the early stages of loading and suddenly in the later stages of loading, which can be characterized by the change in AE energy. The rise time/AE amplitude values are an effective way to characterize the crack propagation of cement mixtures in different stages of fracture and help to conduct a comprehensive evaluation of the health of the material.