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Experimental study on the change of magnetic field in the process of concrete failure under load

Many building structures in our life are mainly composed of concrete. Thus, monitoring of the failure of concrete structures is of great significance. We built an experimental system to monitor the magnetic field change upon concrete damage, based on which the magnetic field signal of the concrete failure process was tested. And then the relationships between magnetic induction intensity and load, acoustic emission (AE) were analyzed. The results show that the magnetic field can be produced in the process of concrete failure under load, and the change of magnetic induction intensity is consistent with the load. In the compaction stage, the magnetic induction intensity fluctuates and decreases. In the linear elastic stage, the magnetic induction intensity tends to increase steadily. In the plastic stage, the magnetic induction intensity has a tendency of increasing obviously. In the accelerated failure stage, the magnetic induction intensity increases rapidly. In the postpeak stage, the increase of magnetic induction intensity gradually decreases. There is a good correspondence between magnetic induction intensity and AE. When the magnetic induction intensity increases rapidly, the corresponding AE energy grows suddenly. The average coefficient of the correlation between the magnetic induction intensity and cumulative AE energy is above 0.9, showing a high correlation. This further proves that magnetic field can reflect the deformation and failure state of concrete. In conclusion, using magnetic field signal to evaluate the stability of concrete structure is expected to become a new nondestructive and noncontact monitoring method, which is convenient, fast, and continuous as well.