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Some road systems are unpaved due to limited governmental finance and fewer maintenance techniques. Such unpaved roads become vulnerable during heavy rainy seasons following restrained accessibility among cities and traffic accidents. Considering the circumstances, innovative and cost–effective approaches are required for unpaved roads. Microbially induced carbonate precipitation (MICP) is an emerging soil improvement technology using microbes to hydrolyze urea generating carbonate ions, and precipitates calcium carbonate in the presence of calcium ion. Induced calcium carbonate bonds soil particles enhancing stiffness and strength when the MICP reaction takes place within the soil system. This study introduces the use of microbes on unpaved road systems consisting of in situ lateritic soils. The MICP technology was implemented to improve soil strength through two approaches: surface spraying and mixing methods. A series of soil testing was performed with varying chemical concentrations to measure precipitation efficiency, strength, and quality for construction material and see the feasibility of the proposed methods. The laboratory test results indicated that the surface spraying method provided improved; however, it was highly affected by the infiltration characteristics of used soils. The mixing method showed promising results even under submerged conditions, but still required improvement. Overall, the proposed idea seems possible to apply to improving unpaved road systems in the lateritic region but requires further research and optimization.

This work was supported by the Korean Government (Defense Acquisition Program Administration, DAPA) through research institute (Agency for Defense Development, ADD).

Epoxy resin, which demonstrates a shape memory effect, is reinforced by chopped carbon fibers (CCFs) to improve the thermal and mechanical properties. The interfacial interactions between 2-mm-long CCFs and epoxy make an impact on not only molecular motion but also the physical behaviors of CCFs/epoxy composites. In particular, shape recovery ability of CCFs/epoxy composites is enhanced with an increase in thermal conductivity generated by crossing CCFs in the epoxy system, although CCFs/epoxy composites containing small amounts of CCFs, such as 1 or 3 phr (parts per hundred rubber), show slower recovery rates than those of raw epoxy specimens due to the difficulty of making heat bridges in composites. With these results, it is confirmed that for specific time-dependent purpose, the shape recovery vector of CCFs/epoxy can be controlled using the amount of CCFs.

In order to develop epoxy shape memory polymers (ESMPs) with high switching temperature and excellent toughness for deployable space structures, the crosslink density and chain flexibility of candidate ESMP samples were tunned by adding two flexible poly(oxypropylene) diamines, Jeffamine D-230 (D230) and Jeffamine D-400 (D400), as a secondary curing agent. The desired switching temperature of ESMPs for deployable space structures was set within the range of 120-135°C. By adding D230 and D400, the switching temperature of the ESMPs could be adjusted to within this range by increasing their crosslink density, and their impact strength could be significantly increased due to the stress relaxation properties of the diamines’ flexible molecular chains. The modulus and tensile strength of the ESMPs increased, but elongation at break decreased, in proportion to the diamine content. The ESMPs with a suitable switching temperature for deployable space structures had a high elongation at break greater than 22 % and good shape recovery and shape fixity ratios. The larger the value of shape recovery ratio, the faster the shape recovery speed.

We developed a continuous roll-to-roll redox-welding and embedding method for the fabrication of electrodes of silver nanowire (AgNWs) networks. The roll-to-roll welding method involved a sequence of oxidation and reduction reactions in an aqueous solution. The redox-welding significantly decreased the sheet resistance of the AgNW film owing to the strong fusion and interlocking at the nanowire junction, while the optical transmittance was maintained. The first oxidation step using HNO3 generated ionized silver (Ag+) which got re-deposited onto the nanowire junctions via an autocatalytic reaction. The oxide layers, which formed on the nanowire surface by both air exposure and the first step of oxidation, were removed by the second reduction step using NaBH4. The redox-welded AgNW electrodes exhibited a sheet resistance of 11.3 Ω sq-1 at the optical transmittance of 90.5% at 550 nm. Furthermore, redox-welding of the AgNWs significantly enhanced their mechanical robustness compared to that of the as-coated AgNWs. The redox-welded AgNWs embedded in a UV curable resin, using a roll-to-roll embedding process, were successfully applied as anode electrodes for large-area and flexible organic light emitting diodes (OLEDs). The device performance is superior to that of a device based on the as-coated AgNW electrode, and is also comparable to that of a device using commercial ITO as the electrode. The redox-welding and embedding processes provide a facile and reliable method for fabricating large-area transparent flexible electrodes for next-generation flexible optoelectronic devices.

Taking advantage of the superlative optoelectronic properties of single-layer MoS2, we developed a one-transistor–one-transistor (1T1T)-type MoS2 optoelectronic nonvolatile memory cell. The 1T1T memory cell consisted of a control transistor (CT) and a memory transistor (MT), in which the drain electrode of the MT was connected electrically to the gate electrode of the CT, whereas the source electrode of the CT was connected electrically to the gate electrode of the MT. Single-layer MoS2 films were utilized as the channel materials in both transistors, and gold nanoparticles acted as the floating gates in the MT. This 1T1T device architecture allowed for a nondestructive read-out operation in the memory because the writing (programming or erasing) and read-out processes were operated separately. The switching of the CT could be controlled by light illumination as well as the applied gate voltage due to the strong light absorption induced by the direct band gap of single-layer MoS2 (∼1.8 eV). The resulting ...

To develop epoxy-based shape memory polymers (ESMPs) with a high switching temperature and good mechanical and shape memory properties for deployable space structures, the crosslink density and chain flexibility of the conventional epoxy resin, diglycidyl ether of bisphenol-A, were controlled by adding a flexible epoxy resin, diglycidyl ether of ethoxylated bisphenol-A with six oxyethylene units (DGEEBA-6). With increasing DGEEBA-6 content, the crosslink density of the ESMPs increased, but their glass transition temperature (Tg) decreased. The ESMPs with suitable switching temperatures (120–135 °C) for deployable space structures showed enhanced toughness, modulus, tensile strength, elongation at break, and shape memory properties. The ESMPs had fast full recovery times of only 80 s at Tg + 20 °C. DGEEBA-6 was shown to be a good modifier of ESMPs for deployable space structures.

Currently, national highways are difficult to apply preventive maintenance method due to severe fluctuation of public performance depending on the pavement condition, climate (region) condition, and traffic condition. Asresult, the preventive maintenance method is applied from 2007 to present, and the road pavement condition evaluation is carried out every year. At the present, preventive maintenance method in the PMS (pavement management system) of the national highway is applied only to the section of less than 1,000 (number / day) of the dual lane road and the converted lane ESAL (Equivalent Single Axial Load), and the quality standard and the construction method are studying. In this paper, the slip resistance test was conducted to evaluate the performance of each section according to area and construction method.

We developed a method of chemically welding silver nanowires (AgNWs) using an aqueous solution containing sodium halide salts (NaF, NaCl, NaBr, or NaI). The halide welding was performed simply by immersing the as-coated AgNW film into the sodium halide solution, and the resulting material was compared with those obtained using two typical thermal and plasmonic welding techniques. The halide welding dramatically reduced the sheet resistance of the AgNW electrode because of the strong fusion among nanowires at each junction while preserving the optical transmittance. The dramatic decrease in the sheet resistance was attributed to the autocatalytic addition of dissolved silver ions to the nanowire junction. Unlike thermal and plasmonic welding methods, the halide welding could be applied to AgNW films with a variety of deposition densities because the halide ions uniformly contacted the surface or junction regions. The optimized AgNW electrodes exhibited a sheet resistance of 9.3 Ω/sq at an optical transmittance of 92%. The halide welding significantly enhanced the mechanical flexibility of the electrode compared with the as-coated AgNWs. The halide-welded AgNWs were successfully used as source-drain electrodes in a transparent and flexible organic field-effect transistor (OFET). This simple, low-cost, and low-power consumption halide welding technique provides an innovative approach to preparing transparent electrodes for use in next-generation flexible optoelectronic devices.

The three-dimensional (3D) deployment behavior of a shape memory polymer (SMP) was quantitatively characterized using 3D shape descriptors. 3D shape descriptor is a numerical value which represents and analyzes the shape information of a given 3D shape. A 3D deployable antenna was designed and fabricated using an epoxy-based SMP. First, the folding behavior of the antenna was observed during deployment in a device. At this time, its entire shape was scanned, processed, and converted into surface data. Two-dimensional (2D) (area and circularity) and 3D (compactness and cubeness) shape descriptors were calculated from the surface data and compared to determine if the 3D folding behavior of an SMP antenna could be adequately described by 3D compactness, which represents how compactly the SMP antenna was able to fold. In addition to 2D shape information, these data provide height information, resulting in a more accurate and sensitive characterization of the folding process. Finally, the 3D deployment behavior (folding-unfolding) of the SMP antenna was analyzed using a 3D descriptor. The shape fixation and recovery ratios of the SMP antenna according to the 3D descriptor were 100% and 99.5%, respectively, whereas those values evaluated with a one-dimensional descriptor, such as uniaxial strain, were 98.0% and 79.1%, respectively. These results demonstrate that a 3D descriptor (compactness) can adequately assess shape memory performance.