Monitoring the early strength formation process of cement is of great importance for structural construction management and safety. In this study, we investigated the relationship between the eigenfrequency and the early strength development of cement mortar. Embedded piezoceramic-based smart aggregates recorded the early strength of cement mortar. An eigenfrequency analysis model demonstrated the relationship between strength and frequency. Experiments were performed by using piezoelectric transducers to monitor the early strength formation process during the testing period. Three types of specimens with different strength grades were tested, and the early strength formation processes were recorded. The experimental results demonstrate that cement mortar strength has a good linear relationship with the resonance frequency, and the average square of the correlation coefficient is greater than 0.98. The results show that structural health monitoring technology is a feasible method of assessing structural safety conditions and has a broad market in the structural construction industry.
Damage detection is of great importance for structural construction management and safety. In this study, an ultra-sensitive flexible piezoelectret sensor for damage monitoring in structural health monitoring (SHM) is designed and fabricated, based on excellent electromechanical properties and piezoelectric response characteristics of electret films. The charge stability of the piezoelectret sensor was demonstrated by continuous potential measurement experiments. The experimentally measured piezoelectret coefficient is 6610 pC/N, which is about 10 times that of ordinary piezoelectric ceramics and proves the high sensitivity of piezoelectret. A series of comparative experiments on the piezoelectret sensor and piezoelectric ceramics demonstrate the high performance of the former. According to the damage detection test results, the damage index of cement mortar specimens was obtained. The linear relationship between the damage index and the crack widths proves the excellent performance of the piezoelectret sensor. A piezoelectret array is also used to detect cracks in cement mortar specimens, and can roughly estimate the depth of the fracture based on the damage index (DI) value of the sensing array.
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