Cement-based composites are generally non-conductors with high electrical resistivity, but they can be used as conductors by incorporating conductive materials. Recently, research has been actively conducted to develop high-conductive fiber-reinforced cement mortar (FRCM) due to increased interest in multifunctional cement mortar required by the market today. Thus, the present paper investigated the effect of the developed conductive FRCM containing carbon and steel fibers on the fresh and mechanical properties as well as electrical conductivity. The performance of conductivity FRCM was studied based on flow, unit weight, air content, three-point flexural, compression, and electrical resistance tests. In addition, their performance was also compared and reviewed with plain mortar (PM). Furthermore, the surface shape and element components of the developed conductive FRCM fracture surface were analyzed using a scanning electron microscopy (SEM) and an energy dispersive X-ray spectrometer (EDS). The results showed that the addition of steel fibers slightly decreased the relative flow value, whereas the incorporation of carbon fibers is very disadvantageous in terms of fluidity due to the fiber ball phenomenon. The unit weight of mixture containing carbon fibers was somewhat decreased, whereas the changes in the amount of air contents were relatively insignificant regardless of the fiber volume fractions. The flexural strength of conductive carbon fiber-reinforced cement mortar (CFRCM) and steel fiber-reinforced cement mortar (SFRCM) was significantly improved compared to that of PM. The compressive strength of CFRCM decreased significantly as the volume fraction of carbon fibers increased. Overall, even if the steel fibers were added up to 1.25%, the effect of improving the electrical conductivity of SFRCM was insignificant. In the case of the CFRCM used in this study, it was found that the percolation threshold existed between 0.3% and 0.4% fibers, and it was thus thought that the optimum dosage of carbon fiber should be secured by at least more than 0.4% in terms of electrical conductivity. Therefore, the most important factor for the electrical conductivity effect was found to be carbon fiber, whereas the effect of steel fiber was insignificant.

In this paper, a smart monitoring system for infra-structure is developed with an integrated management system using ubiquitous computing techniques. This system is designed to enable to use TCP/IP network protocol, communicating the data measure by a wireless sensing unit based on Bluetooth technology. In order to verify this system, a randomly excited self-anchored suspension bridge is tested for real time monitoring by remote network user. Dynamic characteristics are identified to construct an integrity structure using the acquired data from the monitoring test.

To improve the interfacial bond properties of the carbon fiber coated with a nano‐SiO₂ particle in a cement paste matrix, the present study proposed a method of coating nano‐SiO₂ particles on the surface of the carbon fiber by the chemical reaction of a silane coupling agent (glycidoxypropyltrimethoxysilane, GPTMS) and colloidal nano‐SiO₂ sol in an alkaline environment. To verify whether a nano‐SiO₂ particle was effectively modified on the surface of the carbon fiber, the surface morphology, chemical composition, and chemical structure were characterized and analyzed by several techniques such as the scanning electron microscope (SEM), energy‐dispersive spectrometer (EDS), and Fourier‐transform infrared spectroscopy (FT‐IR). Nano‐SiO₂ particles were entirely covered and uniformly distributed on the surface of the carbon fiber, resulting in the formation of a thin layer of nano‐SiO₂ particles. A thin layer of nano‐SiO₂ particles reacted with Ca(OH)₂ to form a calcium‐silicate‐hydrate (C‐S‐H) gel, which is most helpful to increase the form between the fiber and the matrix. In addition, a pull‐out test of the tow carbon fibers was performed to verify the effect of the new surface modification method on the interfacial bond properties of the carbon fiber embedded in the cement paste matrix. The experimental results showed that the frictional bond strength of the carbon fiber coated with a nano‐SiO₂ particle was significantly increased compared to the plain carbon fiber. These results were expected to improve the interfacial bonding force of hardened cement paste from the formation of the C‐S‐H gel produced through the chemical reaction of nano‐SiO₂ particles coated on the surface of the carbon fiber with Ca(OH)₂. In particular, it was confirmed that the carbon fiber‐reinforced cement paste (CFRCP) specimens coated with a nano‐SiO₂ particle and silica fume which replaced 10 wt.% of cement by mass showed the highest pull‐out resistance performance at 28 days of age. The new surface modification method developed in this study can be very beneficial and helpful in improving the interfacial bond properties of CFRCP.

The 8‐bit RGB image of a cracked concrete surface, obtained with a high‐resolution camera based on a close‐distance photographing and using an optical microscope, is used to estimate the geometrical parameters of the crack. The parameters such as the crack’s width, depth, and morphology can be determined by the pixel intensity distribution of the image. For the estimation, the image is transformed into 16‐bit gray scale to enhance the geometrical parameters of the crack and then a mathematical relationship relating the intensity distribution with the depth and width is derived based on the enhanced image. This relationship enables to estimate the width and depth with ±10% and ±15% accuracy, respectively, for the crack samples used for the experiments. It is expected that the accuracy can be further improved if the 8‐bit RGB image is synthesized by the images of the cracks obtained with different illumination directions.

Fiber-reinforced cement mortar (FRCM) has been widely used since it has many advantages compared to plain mortar (PM), and various fibers are highly applicable as repair and reinforcement materials for concrete. In the present paper, an experimental study was planned to investigate the properties, such as flexural performance (flexural strength and toughness), compressive strength, and impact resistance of mono fiber-reinforced cement mortar (MFRCM) containing only steel fiber (SF) or carbon fiber (CF), as well as hybrid fiber-reinforced cement mortar (HyFRCM) containing different combinations of SF and CF. The fiber content was used in five levels (0.0, 0.25, 0.5, 0.75, and 1.0%) at a total volume fraction of 1.0% by volume. The results show that HyFRCM containing 0.75% SF and 0.25% CF improved compressive strength, flexural strength, and impact resistance compared to MFRCM and other HyFRCM, resulting in a synergistic effect of hybrid reinforced fibers. It is noted that, in the case of HyFRCM containing 0.5% SF and 0.5% CF, the flexural strength was slightly lower, but the highest flexural toughness was obtained, which led us to judge that the result shown in this investigation can be the optimal fiber combination to improve toughness and energy absorption capacity.

Hyperspectral images in the spectral wavelength range of 500 nm to 650 nm are used to detect green mold pathogens, which are parasitic on the surface of lemons. The images reveal that the spectral range of 500 nm to 560 nm is appropriate for detecting the early stage of development of the pathogen in the lemon, because the spectral intensity is proportional to the infection degree. Within the range, it was found that the dominant spectral wavelengths of the fresh lemon and the green mold pathogen are 580 nm and 550 nm, respectively, with the 550 nm being the most sensitive in detecting the pathogen with spectral imaging. The spectral intensity ratio of the infected lemon to the fresh one in the spectral range of 500 nm to 560 nm increases with the increasing degree of the infection. Therefore, the ratio can be used to effectively estimate the degree of lemons infecting by the green mold pathogens. It also shows that the sudden decrease of the spectral intensity corresponding to the dominant spectral wavelength of the fresh lemon, together with the neighboring spectral wavelengths can be used to classify fresh and contaminated lemons. The spectral intensity ratio of discriminating the fresh lemon from the infected one is calculated as 1.15.