The aim of this work was to provide further confirmation of the possible use of non-linear ultrasonic techniques for detecting the cracking due to corrosion of steel reinforcements in concrete. To this end accelerated steel corrosion tests have been conducted on model reinforced cement mortar specimens, while monitoring the appearance and width evolution of visible surface cracks, and performing non-linear ultrasonic measurements based on the phenomena of harmonic distortion and intermodulation. A new parameter, based on the difference between the amplitude of the fundamental frequency and the sum of the amplitudes of all the first-order and second-order intermodulation products, has been proposed in this work. The results confirm that the appearance of visible surface micro-cracks are preceded and accompanied by the observation of strong non-linear features in the received signal. Furthermore, the new parameter proposed in this work is as efficient as the relative non-linearity parameters, classically used in harmonic distortion non-linear ultrasonic studies, for detecting the non-linear features associated with the critical events of the cracking of cement mortar due to embedded steel corrosion. A hypothesis has been developed considering the possible effect of the filling of the void space by liquid containing rust products after the formation of new cracks or the enlargement of its width. This filling process, which might be particularly enhanced by net convective transport of liquid, would explain the evolution of the values of all the parameters used for putting in evidence the non-linear elastic features after the critical events of the cracking process.

中文翻译：

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使用超声波的高次谐波和互调产生来检测钢筋水泥砂浆中钢腐蚀引起的裂缝

这项工作的目的是进一步证实非线性超声技术可能用于检测混凝土中钢筋腐蚀引起的开裂。为此，对模型增强水泥砂浆试样进行了加速钢腐蚀试验，同时监测可见表面裂纹的外观和宽度演变，并根据谐波畸变和互调现象进行非线性超声测量。在这项工作中，基于基频幅度与所有一阶和二阶互调产物幅度之和的差值，提出了一个新参数。结果证实，在接收信号中观察到强烈的非线性特征之前并伴随着可见的表面微裂纹的出现。此外，这项工作中提出的新参数与谐波失真非线性超声研究中经典使用的相对非线性参数一样有效，用于检测与水泥砂浆开裂的关键事件相关的非线性特征。对嵌入式钢腐蚀。考虑到新裂缝形成或裂缝宽度扩大后含锈产物的液体填充空隙空间的可能影响，已经提出了一种假设。这种填充过程可能会因液体的净对流传输而特别增强，