Research On Water Seepage Monitoring Method Of Concrete Based On Piezoelectric Smart Aggregates

In recent years, with the rapid development of smart materials and smartsensors, structural health monitoring technology has been further developed, thestudy of smart materials in civil engineering has stepped into a new stage both athome and abroad. Among them, the piezoelectric ceramic materials have bothpiezoelectric effect and inverse piezoelectric effect, so it can be used as actuatorand sensor. Besides, the piezoelectric ceramic materials has the advantage ofhigh frequency response, low cost, good repeatability and is suitable forreal-time monitoring, etc, making it widely used in the field of st ructural healthmonitoring. Presently, embedded piezoelectric smart aggregate sensors havebeen mainly researched and applied in the health monitoring of the crack in theconcrete structure, early hydration, concrete-filled steel tube debonding and pilefoundation. However, they are rarely used to monitor the water seepage in theconcrete structure. In this paper, the water seepage monitoring system whichbased on smart aggregates was established, to research on the performance ofsensor working in water, temperature effect, wave velocity characterization,numerical simulation and related aspects. The following several aspects wasincluded:An SA was immersed in tap water, describing the process of water infusedthe internal of SA by soaking time. Experimental research was done on theperformance of SA (signal amplitude) with the change of soaking time,considering the influence of frequency of the excitation signal. The results showthat the influence of water on SA's performance is vital, the amplitude of sensingsignals increases greatly for the early hours in water, and tends to be stable forsubsequent time.By active monitoring the concrete specimen which was under varioustemperature environment, the amplitude of the monitoring signal was taken asevaluation index. Experimental research was done on the influence oftemperature variation on a SA-based concrete structure health monitoring systemfunction unit. The results show that the amplitude of P-wave has strongsensitivity to temperature. The amplitude of the monitoring signal decreases withtemperature decreases and vice versa. Besides, with the increase of themonitoring signal frequency, the influence on the amplitude of P-wave decreases. Based on water seepage depth monitoring system of concrete, differentfrequency excitation signal was adopted to monitor water seepage of two plaincolumns actively, which was under different water infiltrating depths and samewater infiltrating depth respectively. The change law of the monitoring signalamplitude and wave velocity with the concrete water infiltrating depth wasstudied. The influence of peak to peak method, cross correlation method andcross power spectrum phase method on the P-wave total travel time werediscussed comparatively, and the water seepage of concrete was qualitativelyevaluated based on the equivalent P-wave velocity. The results show that underthe same water infiltrating depth, the amplitude response signal falls rapidlyfirstly and then stays stable; Under different water infiltrating depth, theamplitude response signal shows a decrease tendency with the increase of waterseepage depth, but when the water saturated to the specimen, amplitude responsesignal increases slightly. Besides, with the increase of water seepage depth,equivalent P-wave velocity increases nonlinearly. At the same time, the testshows that it has a lot of advantages to use cross-correlation method to determinethe total travel time.The finite element software ANSYS was used to establish the finite elementmodel of short concrete column based on SA and to simulate the water seepageof concrete. The resaons of differences between experimental results andsimulation results were discussed by the changes of P-wave amplitude andvelocity.Research shows that the P-wave amplitude and velocity have a goodsimilarity between the experiment and simulation results on the change tendency.The main factor causing the difference on both results is that nu mericalsimulations ignore the influence of material inhomogeneity and the porestructure,showing that the influence of pore structure of concrete materials on theP wave amplitude values and P wave velocity is obvious.