RESUMO
Micro- and non-destructive methods of estimating compressive strength are useful for diagnosing the degradation of reinforced structures. The velocity of waves propagating through concrete can be measured using conventional non-destructive methods; however, the propagation path of waves varies depending on the distribution of coarse aggregate, resulting in variations in velocity at different measurement points. To address this issue, a method based on laser-induced breakdown spectroscopy (LIBS) and multivariate analysis was developed in this study for estimating the compressive strength of concrete non-destructively, ensuring the non-influence of the coarse aggregate spatial distribution. The method is based on the correlation between the emission intensity of the spectrum and the hardness of the object to be measured. Principal component analysis (PCA) and partial least squares regression (PLSR) were used to extract the mortar spectrum, which determines the compressive strength of concrete, from a mixture of aggregate and mortar spectra. The compressive strength estimated based on the proposed method was consistent with the values obtained from the compressive strength test, which indicates the possibility of using multi-variable analysis to estimate the compressive strength of concrete. Furthermore, the proposed method enabled on-site measurements through a simple experimental setup and insensitivity to spectral noise offered by partial least-squares regression.
RESUMO
This study developed a standoff detection system for Raman spectra in the deep-ultraviolet region to facilitate remote detection of various hazardous materials. Although Raman spectroscopy can distinguish various materials, the measurement of Raman spectra through standoff detection is challenging because of the low scattering cross-section of Raman scattering. The resonance Raman scattering effect in the deep-ultraviolet wavelength region is promising in terms of enhancing the spectral intensity of Raman scattering. A catoptric light receiver system was developed to effectively collect deep-ultraviolet light via a change in the distance from the primary to secondary mirror of the telescope. The experimental results for the standoff detection indicate that the system enables the measurement of the Raman spectrum of SO2 gas, which was locally present 20 m from the system with a wavelength resolution of 0.15 nm. The gas used in this remote measurement has a relatively simple molecular structure among chemical, biological, radiological, nuclear, and explosive gases. However, the high wavelength resolution of Raman spectroscopy will enable measurement of substances with complex molecular structures, such as bacteria and explosives, without losing the detailed structure of their spectra.
