Investigation Of Nonclassical Nonlinear Sound Propagation In Concrete

SPECIALIZATION:AcousticsPOSTGRADUATE:Master of ScienceMENTOR:Professor Xiaozhou LiuAbstract:When concrete is under sulfate erosion and the wet and dry cycles, the internal micro-damage occurs, the performance degradation occurs. Studies on structure concrete that is under sulfate erosion and the wet and dry cycles is not enough, the research at present is focused mainly on the mechanical properties of structure concrete. There are few works on the internal micro-damage and the performance degradation of structural concrete. Concrete nondestructive testing techniques are generally using linear ultrasonic method. The nonlinear acoustic method used to obtain the concrete damaging and deteriorating law has just started. Rock, concrete and other nonlinear mesoscopic elastic solids show the nonclassical nonlinear phenomena, including the amplitude of the odd harmonics higher than that of the even harmonics, nonlinear resonance frequency shift and the change of the nonlinear parameters, which are different from those in classical nonlinear. In this paper, the linear and nonlinear acoustic properties of the six samples of cement mortar prism concrete subjected to sulfate erosion and different extent of wet and dry cycles are experimental studied. Internal micro-damage and the performance degradation of structure concrete that is under sulfate erosion and the wet and dry cycles are analyzed in this paper. And we explore the possibility of using the nonclassical nonlinear parameters to characterize micro-damage of concrete at early age. The mix rate of concrete has great influence on the strength of concrete. At present, research method on different mix rate of concrete is always mechanical more than acoustic. Different mix rate has different porosity in concrete. The linear and nonlinear acoustic properties of concrete are also different. In this paper, the porosity, the linear and nonlinear acoustic properties such as sound velocity, harmonic, nonlinear frequency shift of the four samples are compared. And we explore the possibility of using the linear and nonlinear parameters to characterize the strength of concrete.