Crack Evaluation of Concrete Using Mechanochromic Sensor.

In this study, the deformation of concrete materials was evaluated using a mechanochromic sensor that detects the discoloration reaction caused by deformation. This sensor was attached by applying the Loctite adhesive to both ends in the longitudinal direction. The process of applying tensile stress to the specimens was videotaped, and the deformation and discoloration were examined through image analysis. The mechanochromic sensor was not affected by the finished surface condition, and the discoloration reaction was detected for a concrete material deformation level of up to 0.01 mm. The detected level was caused by the elongation of the sensor, and the discoloration compared with the initial color was identified. In addition, the integration behavior of the mechanochromic sensor under the deterioration of concrete members in cold areas and winter environments, as well as the discoloration reaction of the sensor in a low-temperature environment, was examined. It was found that the discoloration ability of the mechanochromic sensor exposed to a low-temperature environment was restored in 2 h after the end of the freeze-thaw test, and it was judged that the deformation and discoloration levels will be properly measured when the surface temperature of the sensor is restored to a room temperature of approximately 15 °C. This appeared to be due to the room temperature recovery of the dielectric spacer of the sensor and the deformation structure of the resonance condition. The sensor was also attached when diagonal cracks occurred in the concrete beam members to evaluate the strain and discoloration rate according to the deformation and discoloration levels. Accordingly, the cracks and deformation of the concrete materials were monitored using measured values from the discoloration of the mechanochromic sensors, and the possibility of measuring the crack width was reviewed only by real-time monitoring and imaging with the naked eye.

Comparative Analyses of Four Complete Genomes in Pseudomonas amygdali Revealed Differential Adaptation to Hostile Environments and Secretion Systems.

Pseudomonas amygdali is a hemibiotrophic phytopathogen that causes disease in woody and herbaceous plants. Complete genomes of four P. amygdali pathovars were comparatively analyzed to decipher the impact of genomic diversity on host colonization. The pan-genome indicated that 3,928 core genes are conserved among pathovars, while 504-1,009 are unique to specific pathovars. The unique genome contained many mobile elements and exhibited a functional distribution different from the core genome. Genes involved in O-antigen biosynthesis and antimicrobial peptide resistance were significantly enriched for adaptation to hostile environments. While the type III secretion system was distributed in the core genome, unique genomes revealed a different organization of secretion systems as follows: type I in pv. tabaci, type II in pv. japonicus, type IV in pv. morsprunorum, and type VI in pv. lachrymans. These findings provide genetic insight into the dynamic interactions of the bacteria with plant hosts.

Electromagnetic Wave Shielding Properties of Amorphous Metallic Fiber-Reinforced High-Strength Concrete Using Waveguides.

In this study, high-strength concrete containing hooked-end steel or amorphous metallic fibers was fabricated, and the electrical conductivity and electromagnetic shielding effectiveness were evaluated after 28 and 208 days based on considerations of the influences of the moisture content. Amorphous metallic fibers, which have the same length and length/equivalent diameter ratio as hooked-end steel fibers, were favored for the formation of a conductive network because they can be added in large quantities owing to their low densities. These fibers have a large specific surface area as thin plates. The electromagnetic shielding effectiveness clearly improved as the electrical conductivity increased, and it can be expected that the shielding effectiveness will approach the saturation level when the fiber volume fraction of amorphous metallic fibers exceeds 0.5 vol.%. Meanwhile, it is necessary to reduce the amount of moisture to conservatively evaluate the electromagnetic shielding performance. In particular, when 0.5 vol.% of amorphous metallic fibers was added, a shielding effectiveness of >80 dB (based on a thickness of 300 mm) was achieved at a low moisture content after 208 days. Similar to the electrical conductivity, excellent shielding effectiveness can be expected from amorphous metallic fibers at low contents compared to that provided by hooked-end steel fibers.

Effect of Fiber Blending Ratio on the Tensile Properties of Steel Fiber Hybrid Reinforced Cementitious Composites under Different Strain Rates.

In this study, a high-performance hybrid fiber-reinforced cementitious composite (HP-HFRCC) was prepared, by mixing hooked steel fiber (HSF) and smooth steel fiber (SSF) at different blending ratios, to evaluate the synergistic effect of the blending ratio between HSF and SSF and the strain rate on the tensile properties of HP-HFRCC. The experimental results showed that the micro- and macrocrack control capacities of HP-HFRCC varied depending on the blending ratio and strain rate, and the requirement for deriving the appropriate blending ratio was confirmed. Among the HP-HFRCC specimens, the specimen mixed with HSF 1.0 vol.% and SSF 1.0 vol.% (H1.0S1.0) exhibited a significant increase in the synergistic effect on the tensile properties at the high strain rate, as SSF controlled the microcracks and HSF controlled the macrocracks. Consequently, it exhibited the highest strain rate sensitivities of tensile strength, strain capacity, and peak toughness among the specimens evaluated in this study.

Strain Behavior of Concrete Panels Subjected to Different Nose Shapes of Projectile Impact.

This study evaluates the fracture properties and rear-face strain distribution of nonreinforced and hooked steel fiber-reinforced concrete panels penetrated by projectiles of three different nose shapes: sharp, hemispherical, and flat. The sharp projectile nose resulted in a deeper penetration because of the concentration of the impact force. Conversely, the flat projectile nose resulted in shallower penetrations. The penetration based on different projectile nose shapes is directly related to the impact force transmitted to the rear face. Scabbing can be more accurately predicted by the tensile strain on the rear face of concrete due to the projectile nose shape. The tensile strain on the rear face of the concrete was reduced by the hooked steel fiber reinforcement because the hooked steel fiber absorbed some of the impact stress transmitted to the rear face of the concrete. Consequently, the strain behavior on the rear face of concrete according to the projectile nose shape was confirmed.

Effectiveness of Fiber Reinforcement on the Mechanical Properties and Shrinkage Cracking of Recycled Fine Aggregate Concrete.

This paper presents an experimental study conducted to investigate the effect of fiber reinforcement on the mechanical properties and shrinkage cracking of recycled fine aggregate concrete (RFAC) with two types of fiber-polyvinyl alcohol (PVA) and nylon. A small fiber volume fraction, such as 0.05% or 0.1%, in RFAC with polyvinyl alcohol or nylon fibers was used for optimum efficiency in minimum quantity. Additionally, to make a comparative evaluation of the mechanical properties and shrinkage cracking, we examined natural fine aggregate concrete as well. The test results revealed that the addition of fibers and fine aggregates plays an important role in improving the mechanical performance of the investigated concrete specimens as well as controlling their cracking behavior. The mechanical properties such as compressive strength, splitting tensile strength, and flexural strength of fiber-reinforced RFAC were slightly better than those of non-fiber-reinforced RFAC. The shrinkage cracking behavior was examined using plat-ring-type and slab-type tests. The fiber-reinforced RFAC showed a greater reduction in the surface cracks than non-fiber-reinforced concrete. The addition of fibers at a small volume fraction in RFAC is more effective for drying shrinkage cracks than for improving mechanical performance.