Monitoring the curing process of mixtures produced by soil, fly ash and alkaline solution can be effectively performed by ultrasonic measurements of compression and shear wave velocities. These measurements detect the evolution of stiffness with time, as a result of alkali-activated ash reactions. Conventionally, ultrasonic testing relies on the use of a fixed input frequency, corresponding to the nominal frequency of the transducer, for which a maximum response is expected from the transducers. This procedure, however, has shown some limitations especially when applied to materials under curing, in which stiffness is changing with time. To overcome these limitations, a wide range of frequencies, from 24 to 200 kHz, was used at each of the selected curing periods for determining wave travel time, instead of a single frequency reading. The results show a clear increase in the optimum frequency with curing time, indicating that the ultrasound testing frequency should be adjusted to account for the stiffness increase due to curing. Additionally, the use of frequencies other than the nominal frequency of the ultrasonic transducers generated clearer signals, particularly at early curing periods.

中文翻译：

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碱活化土灰最佳超声检测频率的演变

通过压缩和剪切波速度的超声波测量可以有效地监测由土壤、粉煤灰和碱性溶液产生的混合物的固化过程。这些测量检测刚度随时间的演变，这是碱活化灰分反应的结果。传统上，超声波测试依赖于固定输入频率的使用，该频率对应于换能器的标称频率，对于该频率，期望换能器的最大响应。然而，该程序显示出一些局限性，尤其是在应用于固化材料时，其中刚度随时间变化。为了克服这些限制，在每个选定的固化周期使用 24 到 200 kHz 的宽频率范围来确定波传播时间，而不是单一频率读数。结果表明，最佳频率随固化时间明显增加，表明应调整超声检测频率以解决固化引起的刚度增加。此外，使用超声波换能器标称频率以外的频率会产生更清晰的信号，尤其是在早期固化阶段。