Monitoring fresh concrete by ultrasonic transmission measurements: Exploratory multi-way analysis of the spectral information

The setting of concrete can be monitored by measuring the characteristics of ultrasonic waves sent through a fresh sample at regular intervals. So far, the development of this ultrasonic method has mainly focussed on the wave velocity for technical reasons. However, the frequency spectrum might contain even more information since it takes the entire received signal into account. Therefore, the spectra measured on 34 concrete compositions during the first 48 h after mixing were collected in a three-way array (sample × frequency × concrete age) and analysed with multi-way techniques (PARAFAC and PARAFAC2) to quantify their mutual differences. C2 was able to model the data better than PARAFAC and distinguish between the different concrete mixtures. Moreover, the samples could be ordered by the model in agreement with the expected setting behaviour of the mixture. This exploratory data analysis proves the utility of the frequency spectra to monitor the setting of fresh concrete.