Cement-Based Material Characterization Using Nonlinear Single-Impact Resonant Acoustic Spectroscopy (NSIRAS)

Abstract

The durability of infrastructure materials, such as concrete, has direct impact on society because the productivity of many industries and safety of human beings depend on infrastructure condition, and further because maintenance of the infrastructure can represent a significant portion of a government’s budget. Thus the enhancement of concrete durability and improvement of infrastructure condition monitoring are significant concerns to the scientific community. The resonant frequency method has been traditionally used to assess the mechanical condition of concrete. Resonance frequencies of a solid body depend on test sample mass and dimensions, elastic properties, and boundary conditions. Resonance frequencies have been used to determine engineering properties such as the elastic moduli and material damping. The method is useful to assess the performance of materials within accelerated degradation durability test procedures, and to inspect quality of the products during manufacturing processes (pass/fail tests). Different testing standards and recommendations prescribe test configurations, and specific tests are recommended for different materials. A basic resonant frequency test requires a forced vibration system to set up mechanical resonances, and some system to sense the frequency content from the resonant vibration signals. For concrete-like materials, these specifications are given by ASTM C215 [1], wherein an impulsive impact event is applied to the test sample to excite the resonant frequencies and a small sensor is mounted on the surface of the test sample. From the impulsive impact vibration signals thus obtained, two standard parameters are usually derived: (1) the dynamic modulus, which depends on sample dimensions, mass, and the resonant frequency peak (f), and (2) the attenuation or damping capacity of the material. Figure 12.1a, b illustrates typical signals obtained from a single-impact vibration test, where the spectral (frequency domain) signal is computed from the time signal using a Fourier transform algorithm. The continuous reduction of the vibration signal amplitude with time during the signal “ring-down” is seen in the time domain signal. The resonant frequency and damping characteristics are extracted from the spectral signal in the region around the resonant frequency peak. The damping capacity of the material is determined from the quality factor (Q) (or inverse attenuation), which is defined as the ratio between the resonant frequency peak (f) and the bandwidth frequencies corresponding to a 50% reduction of vibration energy in the power frequency spectrum for a given vibration mode [2]. Meaningful application of the ASTM C215 test is found within other standard durability test methods [3, 4].