Principles and applications of ultrasonic-based nondestructive methods for self-healing in cementitious materials

Recently, self-healing technologies have emerged as a promising approach to extend the service life of social infrastructure in the field of concrete construction. However, current evaluations of the self-healing technologies developed for cementitious materials are mostly limited to lab-scale experiments to inspect changes in surface crack width (by optical microscopy) and permeability. Furthermore, there is a universal lack of unified test methods to assess the effectiveness of self-healing technologies. Particularly, with respect to the self-healing of concrete applied in actual construction, nondestructive test methods are required to avoid interrupting the use of the structures under evaluation. This paper presents a review of all existing research on the principles of ultrasonic test methods and case studies pertaining to self-healing concrete. The main objective of the study is to examine the applicability and limitation of various ultrasonic test methods in assessing the self-healing performance. Finally, future directions on the development of reliable assessment methods for self-healing cementitious materials are suggested.ope

Surface-Wave Based Model for Estimation of Discontinuity Depth in Concrete

In this paper, we propose an accurate and practical model for the estimation of surface-breaking discontinuity (i.e., crack) depth in concrete through quantitative characterization of surface-wave transmission across the discontinuity. The effects of three different mixture types (mortar, normal strength concrete, and high strength concrete) and four different simulated crack depths on surface-wave transmission were examined through experiments carried out on lab-scale concrete specimens. The crack depth estimation model is based on a surface-wave spectral energy approach that is capable of taking into account a wide range of wave frequencies. The accuracy of the proposed crack depth estimation model is validated by root mean square error analysis of data from repeated spectral energy transmission ratio measurements for each specimen

Performance assessment method for crack repair in concrete using PZT-based electromechanical impedance technique

Concrete cracks are considered as an important indicator for potential damage and durability and are generally monitored in structural maintenance. A typical repair method in practice for concrete cracks involving with durability issues is to use alternative materials to fill the cracks. As the recovery quality of the repair is difficult to determine, an effective assessment approach is necessary. The electromechanical impedance (EMI) technique is a widely favored method; however, the determination of the frequency range and corresponding damage indicator is a governing factor for practical applications. Furthermore, its application to the evaluation of the crack repair performance has not been reported in the literature to date. This study presents an applicability of the PZT-based EMI technique for the quality assessment of crack repair in concrete. To determine an optimal frequency range that strongly reflects the structural condition, the trends of four damage indicators are investigated with multiple damage severities in each sub-frequency range. Subsequently, the performance of the crack repair material is evaluated using the predefined optimal frequency range with the damage indicators. The proposed approach is shown to effectively assess the recovery quality of the crack repair material over time

Glucose measurement using Surface Enhanced Raman Scattering

Surface Enhanced Raman Scattering (SERS) has a great potential to serve as a monitoring technology for biomolecules, but sensing biomolecules for practical purposes have remained challenging for two reasons. One of the challenges is securing SERS substrates with uniform spatial enhancement that is crucial for quantitative measurements, and the other is finding proper linker molecules that will promote the surface enhancement. To address these challenges, we have been developing a new approach of using highly sensitive surface enhanced Raman scattering (SERS) platform for glucose sensing. In the presentation, I will discuss the fabrication of high performance 3D SERS substrate based on straightforward, two successive wet chemical processes, with experimentally proven strong enhancement and excellent spatial uniformity as well as the use of new linker molecules for making glucose-specific SERS substrates and their use in performing quantitative glucose measurements. Glucose sensing results from different development stages will be discussed

Star-shaped hole transporting materials with a triazine unit for efficient perovskite solar cells

Novel star-shaped hole transporting materials with a triazine unit have been synthesized. When the new Triazine-Th-OMeTPA was used as a hole transporting material in perovskite solar cells, the power conversion efficiency reached 12.51% under AM 1.5 G (100 mW cm(-2)) illumination, showing competitive photovoltaic performance with the widely used spiro-OMeTAD based solar cell (13.45%)

Glucose measurement using Surface Enhanced Raman Scattering

Surface Enhanced Raman Scattering (SERS) has a great potential to serve as a monitoring technology for biomolecules, but sensing biomolecules for practical purposes have remained challenging for two reasons. One of the challenges is securing SERS substrates with uniform spatial enhancement that is crucial for quantitative measurements, and the other is finding proper linker molecules that will promote the surface enhancement. To address these challenges, we have been developing a new approach of using highly sensitive surface enhanced Raman scattering (SERS) platform for glucose sensing. In the presentation, I will discuss the fabrication of high performance 3D SERS substrate based on straightforward, two successive wet chemical processes, with experimentally proven strong enhancement and excellent spatial uniformity as well as the use of new linker molecules for making glucose-specific SERS substrates and their use in performing quantitative glucose measurements. Glucose sensing results from different development stages will be discussed

Faecal microbiota changes associated with the moult fast in chinstrap and gentoo penguins.

In many seabirds, individuals abstain from eating during the moult period. Penguins have an intense moult that lasts for weeks, during which they are confined to land. Despite the importance for survival, it is still unclear how the faecal microbiota of Antarctic penguins changes in response to the moult fast. Here, we investigated the faecal microbiota of chinstrap (Pygoscelis antarcticus) and gentoo penguins (Pygoscelis papua) on King George Island, Antarctica. The bacterial community compositions during the feeding and moulting stages were compared for both species using bacterial 16S rRNA gene amplicon on an Illumina MiSeq platform. Our results showed that the moult fast altered the bacterial community structures in both penguin species. Interestingly, the bacterial community composition shifted in the same direction in response to the moult fast but formed two distinct clusters that were specific to each penguin species. A significant increase in bacterial diversity was observed in gentoo penguins, whereas no such change was observed for chinstrap penguins. By analysing the contribution of the ecological processes that determine bacterial community assembly, we observed that processes regulating community turnover were considerably different between the feeding and moulting stages for each penguin. At the phylum level, the relative abundances of Fusobacteria, Firmicutes and Proteobacteria were dominant in chinstrap penguins, and no significant changes were detected in these phyla between the feeding and moulting periods. Our results suggest that moult fast-induced changes in the faecal microbiota occur in both species