The technology of piezoceramic based smart aggregates (SAs) has demonstrated its potential in the comprehensive monitoring of concrete structures. However, its usage in the moisture monitoring of concrete structures has not yet been explored. In this research, SA transducers are used to detect the degree of water infiltration in concrete components and an active sensing method is proposed for moisture monitoring. For experimental study and verification, two short plain concrete columns, with embedded SAs, were fabricated, and an apparatus was developed to perform moisture monitoring of these two columns under different moisture conditions. Data were analyzed to study the relationship between the depth of water seepage and the sensing indicators of receiving signals. Experimental results show that the sensing indicators are very sensitive to the degree of water infiltration inside the column. These sensing indicators show a decreasing trend with increasing depth of water seepage, and this leads to the promising conclusion that these parameters can be used as evaluation indices for the water seepage monitoring of concrete structures.

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Piezoceramic-based smart aggregate has been widely used to evaluate early-age concrete strength and to detect damage in concrete structures. In these structural health monitoring systems, they are generally verified and calibrated through experiments under load-free condition. However, the stress levels of actual concrete members are different. The microstructures of concrete will change with the variation of external load, and the high-frequency waves used in the monitoring system may be highly sensitive to these changes. In this study, the effects of axial compressive loading on the monitoring results are investigated. Specifically, three loading cases, that is, single cycle load, cyclic load, and step-by-step load, are employed to stress the concrete specimens embedded with smart aggregates. The amplitude and velocity of monitoring signals were measured before, during, and after each loading case. The test results show that the axial load lower than 30% of failure load still have a significant impact on the received signals. The amplitude attenuation is dependent on both frequency and load history, while the velocity is highly stress-dependent. The results indicate that the baselines of monitoring signals obtained from the same concrete structure in its healthy state can vary under different stress levels. The axial load variation should be carefully considered during the monitoring process. This study also provides a potential method to assess stress state in concrete structures using smart aggregates