본 연구에서는 PVA(Poly Vinyl Alcohol)섬유와 GO(Graphene Oxide)를 혼입한 섬유보강 콘크리트(FRC)의 역학적 특성 을 평가하고자 하였다. GO와 PVA 섬유를 동시에 혼입한 FRC 각각의 재료를 단일로 사용하였을 때보다 기대효과가 다소 미흡 하였지만, 각 재료의 하이브리드화로 인장강도가 개선되면서 PVA 섬유 혼입률 0.1∼0.3%과 GO 혼입률 0.025%에서 우수한 효 과를 얻을 수 있었다. 특히 PVA 섬유는 0.3%로 혼합하였을 때 부작용을 최소화하면서 최대의 효과를 보였지만, 적절한 GO 배 합비를 조절할 필요가 있으며 FRC내 GO와 PVA 섬유의 최적배합을 구하기 위한 추가적인 연구가 필요할 것으로 사료된다.

PURPOSES : The purpose of this study is to experimentally analyze the flexural strength characteristics of cement mortar mixtures simultaneously incorporated with graphene oxide (GO) and polyvinyl alcohol (PVA) fibers, and to understand the composite effect of those on enhancing resistance against the initiation and progression of micro-cracks, as well as the control of macro-cracks in flexural behavior. METHODS : Cement mortar(w/c=0.5) specimens for flexural strength test, mixing 6 mm and 12 mm PVA fibers at 1% and 2% volume ratios, were fabricated. Additionally, specimens incorporating GO at a cement weight ratio of 0.05% were prepared for each mixture to analyze the effect of GO. Therefore total eight types of mixture were prepared. The fabricated specimens were subjected to flexural strength tests after curing in waterbath for 7 and 28 days. Concurrently, digital images for analyzing deformation in accordance with loading history were obtained at a rate of 20 Hz using the DIC technique. Through displacement and strain calculation via DIC, the flexural behavior characteristics of the mixtures combined with GO and PVA fibers were precisely analyzed. Furthermore, the composite effect on flexural behavior characteristics when GO and PVA fibers are incorporated was discussed. RESULTS : For the PVA fiber-reinforced cement mortar mixture, the incorporation of 0.05% GO increased the crack initiation load by up to 23%, and the maximum resistive load after cracking by up to 24%. Moreover, introducing GO into the PVA fiber-reinforced mixture increased the flexural strain just before cracking by approximately 30 to 50%, while the maximum resistive load after cracking exhibited similar strain levels with or without GO incorporation. Therefore, under flexural behavior, the integration of GO might delay crack initiation by increasing the strain concurrent with the rise in flexural stress before crack occurrence. It also seems to contribute to reducing crack expansion by synergistically interacting with PVA fibers after crack occurrence. CONCLUSIONS : It was experimentally examined that the flexural strength of PVA fiber reinforced cement mortar is improved by incorporating GO. Moreover, GO enhances resistance of crack occurrance and reduces crack propagation in combination with PVA fibers. This study suggests that simultaneous incorporation of GO and PVA fibers can synergistically improve the performance of cement composites.

Graphene fiber is considered as a potential material for wearable applications owing to its lightness, flexibility, and high electrical conductivity. After the graphene oxide (GO) solution in the liquid crystal state is assembled into GO fiber through wet spinning, the reduced graphene oxide (rGO) fiber is obtained through a reduction process. In order to further improve the electrical conductivity, herein, we report N, P, and S doped rGO fibers through a facile vacuum diffusion process. The precursors of heteroatoms such as melamine, red phosphorus, and sulfur powders were used through a vacuum diffusion process. The resulting N, P, and S doped rGO fibers with atomic% of 6.52, 4.43 and 2.06% achieved the higher electrical conductivities compared to that of rGO fiber while preserving the fibrious morphology. In particular, N doped rGO fiber achieved the highest conductivity of 1.11 × 104 S m−1, which is 2.44 times greater than that of pristine rGO fiber. The heteroatom doping of rGO fiber through a vacuum diffusion process is facile to improve the electrical conductivity while maintaining the original structure.

In this research, carbon nanotubes(CNT) and graphene nanoplates(GnP) are deposited on the surface of carbon fibers(CF) at once. Investigating the effect between CNT and GnP on increasing the interfacial and mechanical properties of carbon fiber reinforced epoxy composites(CFRP). The cross section of the CFRP composites indicates that the GnPs/CNTs hybrid coating exhibits significantly higher mechanical performance in all coating samples. The interlayer shear strength of the GnPs/CNT hybrid coated CFRP composite was 90% higher than that of the uncoated CF composite. The flexural and tensile strength of CFRP composites using GnPs /CNT hybrid coatings were improved by 52% and 70%, respectively, compared to uncoated CF.

GNPs have several excellent mechanical properties including high strength, a good young’s modulus, thermal conductivity, corrosion resistance, electronic shielding, etc. In this study, CF/GNP/Epoxy composites were manufactured using GNP weight ratios of 0.15 wt%, 0.3 wt%, 0.5 wt%, 0.7 wt% and 1 wt%. The composites were manufactured with a mechanical method (3-roll-mill). Tensile, impact and wear tests were performed according to ASTM standards D3039, D256 and D3181, respectively. The results show that the CF/GNP0.3wt%/Epoxy composites have good mechanical properties, e.g., tensile strength and impact and wear resistance. In this study, both carbon fabric and GNPs were used as reinforcements in the composites. The mechanical properties increased and weight loss decreased as the GNP content in the resin films was increased.