Advances in nanotechnology have provided approaches for the fabrication of new composite materials for sensing. Flexible sensors can make up for the shortcomings of traditional strain sensors in monitoring the surface strain and cracks of concrete structures. Using reduced graphene oxide (RGO) as a conductive filler, cellulose nanofiber (CNF) as a dispersant and structural skeleton, and waterborne epoxy (WEP) as a polymer matrix, a flexible composite material with piezoresistive effect was prepared by the solution blending and solvent evaporation method. The mechanical, electrical, and electromechanical properties of the composite were investigated. The results show that CNF can significantly improve the dispersion of RGO in the WEP matrix and help to form stable reinforcing and conductive networks, leading to great changes in the mechanical properties and resistivity of the composite. The composite film can withstand large deformations (>55% strain), and the resistance change rate demonstrates a high sensitivity to mechanical strain with a gauge factor of 34–71. Within a 4% strain range, the piezoresistive property of the composite is stable with good linearity and repeatability. The performance of the flexible film sensor made of the composite is tested and it can monitor the strain and crack of the concrete surface well.
The culture broth of the cyanobacterium-symbiotic fungus Simplicillium lanosoniveum var. Tianjinienss Q. L. Dong exhibited unanticipated antibacterial activities against the Gram-positive bacteria, particularly the pathogenic bacterium Staphylococcus aureus, indicating the secretion of antibiotic-like metabolite, for which the modified Sabouraud medium was the suitable medium. The antibiotic-like metabolite was separated with macroporous resins CT-12 (absorption) and 95% ethanol (desorption), purified by ion-exchange resins D301T and displayed a characteristic absorption peak at 228 nm, suggesting the presence of nitrogen. The negative biuret and ninhydrin tests confirmed the absence of -NH and -COOH groups. Further, HPLC and mass spectrometry analyses showed that the retention time and molecular weight of the antibiotic-like metabolite were 4.1031 min and 163.0182 (Δ ± 2.3 ppm), respectively. Taking together, we speculated that the antibiotic-like metabolite was a new antibiotic structurally similar to alkaloid, which was the first one isolated from the species of Simplicillium genus.
To study the evolution of the performance of prestressed concrete beams under the combined effect of corrosion and fatigue, static and fatigue loading experiments of seven partially prestressed reinforced-concrete T-beams are carried out. The results show that brittle failure, marked by longitudinal steel bar fracture at the main crack, occurred under fatigue loading. With an increase in the maximum applied fatigue load and the corrosion degree of the longitudinal steel bar, the fatigue life of the test beam is abruptly shortened, the mid-span deflection growth rate is gradually reduced and the brittleness is more significant. A calculation method for the stiffness and deflection of the corroded partially prestressed concrete that considers the stress redistribution between the prestressing strand and steel bars during fatigue, the fatigue damage of concrete, the corrosion and fatigue damage of steel bars, and the contribution of the tensile force to the stiffness of concrete is proposed. The error between the calculated and experimental results is less than 10%. The research results of this paper can be applied to predict the deflection of an actual bridge structure under fatigue loading in a chloride corrosion environment.
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