Abstract: Concrete specimens with different water contents were obtained by means of drying method, and nonlinear ultrasonic characteristic test of concrete was carried out. And the influence of moisture content on the harmonic amplitude and ultrasonic nonlinear coefficient in nonlinear ultrasonic testing of concrete was studied. The results show that with the increase of water content, the first and second order amplitudes of concrete ultrasonic spectrum increases; meanwhile, the ultrasonic nonlinear coefficient of the material decreases. When the concrete is filled with free water, the internal micro-crack deformation is inhibited by free water in the pores, and the reduction of deformation can be equivalent to the reduction of concrete damage, resulting in a reduction of the measured ultrasonic nonlinear coefficient. The research results can provide a reference for nondestructive testing of concrete structures in water environment.

Key words: hydraulic engineering, concrete, water content, nonlinear ultrasonic, micro-crack

摘要： 采用烘干法获得了不同含水量下的混凝土试件，并进行了混凝土非线性超声特性试验。研究了含水量对混凝土非线性超声检测中谐波幅值和超声非线性系数的影响规律。试验结果表明：随着含水量的增加，混凝土超声频谱的一阶和二阶幅值增加，材料的超声非线性系数减小；当混凝土填充自由水分后，内部的微裂纹变形受到孔隙间自由水分的抑制，变形减小可以等效于混凝土损伤减小，造成测量得到的超声非线性系数减小。研究结果可为水环境工作中的混凝土结构的无损检测提供参考。

关键词: 水利工程, 混凝土, 含水量, 非线性超声, 微裂纹