An exploratory experimental and 3D numerical investigation on the effect of porosity on wave propagation in cement paste

Piezoelectric transducers have been widely employed in the field of structural health monitoring (SHM). Currently, most piezoelectric transducers based non-destructive monitoring method lays basis on wave-based method. The change of wave after propagating in the target medium can reflect the internal state of the structure, such as damage and porosity. Owing to that concrete is a severely heterogeneous material at micro scale, the relationship between stress wave parameters and microstructure of concrete such as pores and preexisting cracks in concrete is still unclear, which limits the generalization of monitoring system in different concrete structures. This paper presents an experimental study by setting up a kind of monitoring platform with piezoelectric transducers to investigate the relationship between porosity in cement paste and stress wave parameters. Meanwhile, 3D models of cement paste specimens were built with X-ray computed tomography (CT) scanning method, and the actual pore structure and distribution inside the specimens were obtained. The test and numerical results share similar decreasing trend of amplitude and velocity with an increment of porosity. It indicates that the proposed 3D model building method provides a vivid way to investigate the influence of micro-structure on stress wave transferring in cement based materials. Additionally, it also provides a promising approach to assess the porosity in cementitious materials using smart aggregate (SA)-based non-destructive monitoring method.