Novel methodology on direct extraction of the strength information from cementitious materials using piezo-sensor based electromechanical impedance (EMI) method

Abstract

It is critical to develop an accurate non-destructive testing (NDT) methods to evaluate the real-time concrete strength gain due to the fast pace of construction. Among the NDTs for concrete strength monitoring, piezoelectric materials based electromechanical impedance (EMI) method has attracted much attention recently. Some statistical approaches are proposed for impedance signal processing, such as root mean square deviation (RMSD) and mean absolute percentage deviation (MAPD). However, these methods require the baseline value for calculation, which is not convenient, particularly for the very early strength gain monitoring. In this study, three features extracted directly from phase angle spectrum, including resonant frequency of the first local phase angle peak (PARF), local phase angle peak value (PA), and the corresponding width of half-prominence (HPW) are employed as indicators to monitor the strength gain process. Among these three indicators, the first peak of phase angle resonant frequency (PARF) is found the most reliable. The PARF index can directly be obtained from the impedance spectrum without baseline calculation. Five types of different cement mortar with various water-to-cement ratios from 0.38 to 0.46 were prepared. The EMI test and conventional cubic testing (ASTM 109) were conducted concurrently at a very early age (4th to 8th hour) and an early age (1st, 3rd, and 7th day). To examine the correlation between the compressive strength obtained and the EMI-PARF indices, a linear least-squares regression analysis was performed. Furthermore, the finite element analysis (FEA) was conducted to discuss the relationship between the features obtained from the phase angle spectrum and the stiffness of the host structure. The PARF index exhibits a high correlation with the mechanical properties of cementitious materials. Both experiments and FEA results ascertain that piezoelectric-based EMI coupled with the PARF index is a reliable method for in-place strength gain evaluation of cementitious materials.